Network Working Group R. Stewart Internet-Draft Huawei Intended status: Informational K. Poon Expires: January 13, 2011 Oracle Corporation M. Tuexen Muenster Univ. of Applied Sciences V. Yasevich HP P. Lei Cisco Systems, Inc. July 12, 2010 Sockets API Extensions for Stream Control Transmission Protocol (SCTP) draft-ietf-tsvwg-sctpsocket-23.txt Abstract This document describes a mapping of the Stream Control Transmission Protocol SCTP into a sockets API. The benefits of this mapping include compatibility for TCP applications, access to new SCTP features and a consolidated error and event notification scheme. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on January 13, 2011. Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of Stewart, et al. Expires January 13, 2011 [Page 1] Internet-Draft SCTP sockets API July 2010 publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. Stewart, et al. Expires January 13, 2011 [Page 2] Internet-Draft SCTP sockets API July 2010 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 7 2. Data Types . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3. One-to-Many Style Interface . . . . . . . . . . . . . . . . . 8 3.1. Basic Operation . . . . . . . . . . . . . . . . . . . . . 8 3.1.1. socket() . . . . . . . . . . . . . . . . . . . . . . . 9 3.1.2. bind() . . . . . . . . . . . . . . . . . . . . . . . . 10 3.1.3. listen() . . . . . . . . . . . . . . . . . . . . . . . 11 3.1.4. sendmsg() and recvmsg() . . . . . . . . . . . . . . . 11 3.1.5. close() . . . . . . . . . . . . . . . . . . . . . . . 13 3.1.6. connect() . . . . . . . . . . . . . . . . . . . . . . 14 3.2. Non-blocking mode . . . . . . . . . . . . . . . . . . . . 14 3.3. Special considerations . . . . . . . . . . . . . . . . . . 15 4. One-to-One Style Interface . . . . . . . . . . . . . . . . . . 16 4.1. Basic Operation . . . . . . . . . . . . . . . . . . . . . 17 4.1.1. socket() . . . . . . . . . . . . . . . . . . . . . . . 17 4.1.2. bind() . . . . . . . . . . . . . . . . . . . . . . . . 18 4.1.3. listen() . . . . . . . . . . . . . . . . . . . . . . . 19 4.1.4. accept() . . . . . . . . . . . . . . . . . . . . . . . 19 4.1.5. connect() . . . . . . . . . . . . . . . . . . . . . . 20 4.1.6. close() . . . . . . . . . . . . . . . . . . . . . . . 21 4.1.7. shutdown() . . . . . . . . . . . . . . . . . . . . . . 21 4.1.8. sendmsg() and recvmsg() . . . . . . . . . . . . . . . 22 4.1.9. getpeername() . . . . . . . . . . . . . . . . . . . . 22 5. Data Structures . . . . . . . . . . . . . . . . . . . . . . . 23 5.1. The msghdr and cmsghdr Structures . . . . . . . . . . . . 23 5.2. SCTP msg_control Structures . . . . . . . . . . . . . . . 24 5.2.1. SCTP Initiation Structure (SCTP_INIT) . . . . . . . . 25 5.2.2. SCTP Header Information Structure (SCTP_SNDRCV) . . . 26 5.2.3. Extended SCTP Header Information Structure (SCTP_EXTRCV) . . . . . . . . . . . . . . . . . . . . 28 5.2.4. SCTP Send Information Structure (SCTP_SNDINFO) . . . . 29 5.2.5. SCTP Receive Information Structure (SCTP_RCVINFO) . . 31 5.2.6. SCTP Next Receive Information Structure (SCTP_NXTINFO) . . . . . . . . . . . . . . . . . . . . 32 5.2.7. SCTP PR-SCTP Information Structure (SCTP_PRINFO) . . . 32 5.2.8. SCTP AUTH Information Structure (SCTP_AUTHINFO) . . . 33 5.2.9. SCTP Destination Address Structure (IPv4) (SCTP_DSTADDRV4) . . . . . . . . . . . . . . . . . . . 33 5.2.10. SCTP Destination Address Structure (IPv6) (SCTP_DSTADDRV6) . . . . . . . . . . . . . . . . . . . 34 5.3. SCTP Events and Notifications . . . . . . . . . . . . . . 34 5.3.1. SCTP Notification Structure . . . . . . . . . . . . . 35 5.3.2. SCTP_ASSOC_CHANGE . . . . . . . . . . . . . . . . . . 36 5.3.3. SCTP_PEER_ADDR_CHANGE . . . . . . . . . . . . . . . . 37 5.3.4. SCTP_REMOTE_ERROR . . . . . . . . . . . . . . . . . . 38 5.3.5. SCTP_SEND_FAILED . . . . . . . . . . . . . . . . . . . 39 Stewart, et al. Expires January 13, 2011 [Page 3] Internet-Draft SCTP sockets API July 2010 5.3.6. SCTP_SHUTDOWN_EVENT . . . . . . . . . . . . . . . . . 40 5.3.7. SCTP_ADAPTATION_INDICATION . . . . . . . . . . . . . . 41 5.3.8. SCTP_PARTIAL_DELIVERY_EVENT . . . . . . . . . . . . . 42 5.3.9. SCTP_AUTHENTICATION_EVENT . . . . . . . . . . . . . . 42 5.3.10. SCTP_SENDER_DRY_EVENT . . . . . . . . . . . . . . . . 43 5.3.11. SCTP_NOTIFICATIONS_STOPPED_EVENT . . . . . . . . . . . 44 5.3.12. SCTP_SEND_FAILED_EVENT . . . . . . . . . . . . . . . . 44 5.4. Ancillary Data Considerations and Semantics . . . . . . . 45 5.4.1. Multiple Items and Ordering . . . . . . . . . . . . . 45 5.4.2. Accessing and Manipulating Ancillary Data . . . . . . 46 5.4.3. Control Message Buffer Sizing . . . . . . . . . . . . 46 6. Common Operations for Both Styles . . . . . . . . . . . . . . 47 6.1. send(), recv(), sendto(), and recvfrom() . . . . . . . . . 47 6.2. setsockopt() and getsockopt() . . . . . . . . . . . . . . 49 6.3. read() and write() . . . . . . . . . . . . . . . . . . . . 50 6.4. getsockname() . . . . . . . . . . . . . . . . . . . . . . 50 6.5. Implicit Association Setup . . . . . . . . . . . . . . . . 51 7. Socket Options . . . . . . . . . . . . . . . . . . . . . . . . 52 7.1. Read / Write Options . . . . . . . . . . . . . . . . . . . 54 7.1.1. Retransmission Timeout Parameters (SCTP_RTOINFO) . . . 54 7.1.2. Association Parameters (SCTP_ASSOCINFO) . . . . . . . 54 7.1.3. Initialization Parameters (SCTP_INITMSG) . . . . . . . 56 7.1.4. SO_LINGER . . . . . . . . . . . . . . . . . . . . . . 56 7.1.5. SCTP_NODELAY . . . . . . . . . . . . . . . . . . . . . 57 7.1.6. SO_RCVBUF . . . . . . . . . . . . . . . . . . . . . . 57 7.1.7. SO_SNDBUF . . . . . . . . . . . . . . . . . . . . . . 57 7.1.8. Automatic Close of Associations (SCTP_AUTOCLOSE) . . . 57 7.1.9. Set Primary Address (SCTP_PRIMARY_ADDR) . . . . . . . 58 7.1.10. Set Adaptation Layer Indicator (SCTP_ADAPTATION_LAYER) . . . . . . . . . . . . . . . 58 7.1.11. Enable/Disable Message Fragmentation (SCTP_DISABLE_FRAGMENTS) . . . . . . . . . . . . . . . 58 7.1.12. Peer Address Parameters (SCTP_PEER_ADDR_PARAMS) . . . 58 7.1.13. Set Default Send Parameters (SCTP_DEFAULT_SEND_PARAM) . . . . . . . . . . . . . . 61 7.1.14. Set Notification and Ancillary Events (SCTP_EVENTS) . 61 7.1.15. Set/Clear IPv4 Mapped Addresses (SCTP_I_WANT_MAPPED_V4_ADDR) . . . . . . . . . . . . . 61 7.1.16. Get or Set the Maximum Fragmentation Size (SCTP_MAXSEG) . . . . . . . . . . . . . . . . . . . . 61 7.1.17. Get or Set the List of Supported HMAC Identifiers (SCTP_HMAC_IDENT) . . . . . . . . . . . . . . . . . . 62 7.1.18. Get or Set the Active Shared Key (SCTP_AUTH_ACTIVE_KEY) . . . . . . . . . . . . . . . . 63 7.1.19. Get or Set Delayed SACK Timer (SCTP_DELAYED_SACK) . . 63 7.1.20. Get or Set Fragmented Interleave (SCTP_FRAGMENT_INTERLEAVE) . . . . . . . . . . . . . . 64 7.1.21. Set or Get the SCTP Partial Delivery Point Stewart, et al. Expires January 13, 2011 [Page 4] Internet-Draft SCTP sockets API July 2010 (SCTP_PARTIAL_DELIVERY_POINT) . . . . . . . . . . . . 65 7.1.22. Set or Get the Use of Extended Receive Info (SCTP_USE_EXT_RCVINFO) . . . . . . . . . . . . . . . . 66 7.1.23. Set or Get the Auto ASCONF Flag (SCTP_AUTO_ASCONF) . . 66 7.1.24. Set or Get the Maximum Burst (SCTP_MAX_BURST) . . . . 66 7.1.25. Set or Get the Default Context (SCTP_CONTEXT) . . . . 67 7.1.26. Enable or Disable Explicit EOR Marking (SCTP_EXPLICIT_EOR) . . . . . . . . . . . . . . . . . 67 7.1.27. Enable SCTP Port Reusage (SCTP_REUSE_PORT) . . . . . . 67 7.1.28. Set Notification Event (SCTP_EVENT) . . . . . . . . . 68 7.1.29. Enable or Disable the Delivery of SCTP_RCVINFO as Ancillary Data (SCTP_RECVRCVINFO) . . . . . . . . . . 68 7.1.30. Enable or Disable the Delivery of SCTP_NXTINFO as Ancillary Data (SCTP_RECVNXTINFO) . . . . . . . . . . 68 7.1.31. Set Default Send Parameters (SCTP_DEFAULT_SNDINFO) . . 68 7.2. Read-Only Options . . . . . . . . . . . . . . . . . . . . 68 7.2.1. Association Status (SCTP_STATUS) . . . . . . . . . . . 69 7.2.2. Peer Address Information (SCTP_GET_PEER_ADDR_INFO) . . 70 7.2.3. Get the List of Chunks the Peer Requires to be Authenticated (SCTP_PEER_AUTH_CHUNKS) . . . . . . . . 71 7.2.4. Get the List of Chunks the Local Endpoint Requires to be Authenticated (SCTP_LOCAL_AUTH_CHUNKS) . . . . . 71 7.2.5. Get the Current Number of Associations (SCTP_GET_ASSOC_NUMBER) . . . . . . . . . . . . . . . 72 7.2.6. Get the Current Identifiers of Associations (SCTP_GET_ASSOC_ID_LIST) . . . . . . . . . . . . . . . 72 7.3. Write-Only Options . . . . . . . . . . . . . . . . . . . . 72 7.3.1. Set Peer Primary Address (SCTP_SET_PEER_PRIMARY_ADDR) . . . . . . . . . . . . . 72 7.3.2. Add a Chunk That Must Be Authenticated (SCTP_AUTH_CHUNK) . . . . . . . . . . . . . . . . . . 73 7.3.3. Set a Shared Key (SCTP_AUTH_KEY) . . . . . . . . . . . 73 7.3.4. Deactivate a Shared Key (SCTP_AUTH_DEACTIVATE_KEY) . . 74 7.3.5. Delete a Shared Key (SCTP_AUTH_DELETE_KEY) . . . . . . 74 7.4. Ancillary Data and Notification Interest Options . . . . . 75 8. New Functions . . . . . . . . . . . . . . . . . . . . . . . . 78 8.1. sctp_bindx() . . . . . . . . . . . . . . . . . . . . . . . 78 8.2. sctp_peeloff() . . . . . . . . . . . . . . . . . . . . . . 80 8.3. sctp_getpaddrs() . . . . . . . . . . . . . . . . . . . . . 80 8.4. sctp_freepaddrs() . . . . . . . . . . . . . . . . . . . . 81 8.5. sctp_getladdrs() . . . . . . . . . . . . . . . . . . . . . 81 8.6. sctp_freeladdrs() . . . . . . . . . . . . . . . . . . . . 82 8.7. sctp_sendmsg() . . . . . . . . . . . . . . . . . . . . . . 82 8.8. sctp_recvmsg() . . . . . . . . . . . . . . . . . . . . . . 83 8.9. sctp_connectx() . . . . . . . . . . . . . . . . . . . . . 84 8.10. sctp_send() . . . . . . . . . . . . . . . . . . . . . . . 85 8.11. sctp_sendx() . . . . . . . . . . . . . . . . . . . . . . . 86 8.12. sctp_recvxxx() . . . . . . . . . . . . . . . . . . . . . . 87 Stewart, et al. Expires January 13, 2011 [Page 5] Internet-Draft SCTP sockets API July 2010 8.13. sctp_sendxxx() . . . . . . . . . . . . . . . . . . . . . . 88 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 89 10. Security Considerations . . . . . . . . . . . . . . . . . . . 89 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 89 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 90 12.1. Normative References . . . . . . . . . . . . . . . . . . . 90 12.2. Informative References . . . . . . . . . . . . . . . . . . 90 Appendix A. One-to-One Style Code Example . . . . . . . . . . . . 90 Appendix B. One-to-Many Style Code Example . . . . . . . . . . . 96 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 97 Stewart, et al. Expires January 13, 2011 [Page 6] Internet-Draft SCTP sockets API July 2010 1. Introduction The sockets API has provided a standard mapping of the Internet Protocol suite to many operating systems. Both TCP [RFC0793] and UDP [RFC0768] have benefited from this standard representation and access method across many diverse platforms. SCTP is a new protocol that provides many of the characteristics of TCP but also incorporates semantics more akin to UDP. This document defines a method to map the existing sockets API for use with SCTP, providing both a base for access to new features and compatibility so that most existing TCP applications can be migrated to SCTP with few (if any) changes. There are three basic design objectives: 1. Maintain consistency with existing sockets APIs: We define a sockets mapping for SCTP that is consistent with other sockets API protocol mappings (for instance UDP, TCP, IPv4, and IPv6). 2. Support a one-to-many style interface: This set of semantics is similar to that defined for connection-less protocols, such as UDP. A one-to-many style SCTP socket should be able to control multiple SCTP associations. This is similar to a UDP socket, which can communicate with many peer endpoints. Each of these associations is assigned an association ID so that an application can use the ID to differentiate them. Note that SCTP is connection-oriented in nature, and it does not support broadcast or multicast communications, as UDP does. 3. Support a one-to-one style interface: This interface supports a similar semantics as sockets for connection-oriented protocols, such as TCP. A one-to-one style SCTP socket should only control one SCTP association. One purpose of defining this interface is to allow existing applications built on other connection-oriented protocols be ported to use SCTP with very little effort. Developers familiar with these semantics can easily adapt to SCTP. Another purpose is to make sure that existing mechanisms in most operating systems that support sockets, such as select(), should continue to work with this style of socket. Extensions are added to this mapping to provide mechanisms to exploit new features of SCTP. Goals 2 and 3 are not compatible, so this document defines two modes of mapping, namely the one-to-many style mapping and the one-to-one style mapping. These two modes share some common data structures and operations, but will require the use of two different application programming styles. Note that all new SCTP features can be used with both styles of socket. The decision on which one to use depends mainly on the nature of applications. A mechanism is defined to extract a one-to-many style SCTP association into a one-to-one style socket. Stewart, et al. Expires January 13, 2011 [Page 7] Internet-Draft SCTP sockets API July 2010 Some of the SCTP mechanisms cannot be adequately mapped to an existing socket interface. In some cases, it is more desirable to have a new interface instead of using existing socket calls. Section 8 of this document describes these new interfaces. 2. Data Types Whenever possible, data types from Draft 6.6 (March 1997) of POSIX 1003.1g are used: uintN_t means an unsigned integer of exactly N bits (e.g. uint16_t). This document also assumes the argument data types from 1003.1g when possible (e.g. the final argument to setsockopt() is a size_t value). Whenever buffer sizes are specified, the POSIX 1003.1 size_t data type is used. 3. One-to-Many Style Interface The one-to-many style interface has the following characteristics: o Outbound association setup is implicit. o Messages are delivered in complete messages (with one notable exception). o There is a 1 to many relationship between socket and association. 3.1. Basic Operation A typical server in this style uses the following socket calls in sequence to prepare an endpoint for servicing requests: o socket() o bind() o listen() o recvmsg() o sendmsg() o close() A typical client uses the following calls in sequence to setup an association with a server to request services: o socket() o sendmsg() o recvmsg() o close() In this style, by default, all the associations connected to the endpoint are represented with a single socket. Each association is assigned an association ID (type is sctp_assoc_t) so that an application can use it to differentiate between them. In some implementations, the peer endpoints' addresses can also be used for this purpose. But this is not required for performance reasons. If Stewart, et al. Expires January 13, 2011 [Page 8] Internet-Draft SCTP sockets API July 2010 an implementation does not support using addresses to differentiate between different associations, the sendto() call can only be used to setup an association implicitly. It cannot be used to send data to an established association as the association ID cannot be specified. Once as association ID is assigned to an SCTP association, that ID will not be reused until the application explicitly terminates the association. The resources belonging to that association will not be freed until that happens. This is similar to the close() operation on a normal socket. The only exception is when the SCTP_AUTOCLOSE option (section 7.1.8) is set. In this case, after the association is terminated gracefully and automatically, the association ID assigned to it can be reused. All applications using this option should be aware of this to avoid the possible problem of sending data to an incorrect peer endpoint. If the server or client wishes to branch an existing association off to a separate socket, it is required to call sctp_peeloff() and to specify the association identifier. The sctp_peeloff() call will return a new socket which can then be used with recv() and send() functions for message passing. See Section 8.2 for more on branched- off associations. The returned socket is a one-to-one style socket. Once an association is branched off to a separate socket, it becomes completely separated from the original socket. All subsequent control and data operations to that association must be done through the new socket. For example, the close operation on the original socket will not terminate any associations that have been branched off to a different socket. One-to-many style socket calls are discussed in more detail in the following subsections. 3.1.1. socket() Applications use socket() to create a socket descriptor to represent an SCTP endpoint. The function prototype is int socket(int domain, int type, int protocol); and one uses PF_INET or PF_INET6 as the domain, SOCK_SEQPACKET as the type and IPPROTO_SCTP as the protocol. Here, SOCK_SEQPACKET indicates the creation of a one-to-many style Stewart, et al. Expires January 13, 2011 [Page 9] Internet-Draft SCTP sockets API July 2010 socket. Using the PF_INET domain indicates the creation of an endpoint which can use only IPv4 addresses, while PF_INET6 creates an endpoint which can use both IPv6 and IPv4 addresses. 3.1.2. bind() Applications use bind() to specify which local address and port the SCTP endpoint should associate itself with. An SCTP endpoint can be associated with multiple addresses. To do this, sctp_bindx() is introduced in Section 8.1 to help applications do the job of associating multiple addresses. But note that an endpoint can only be associated with one local port. These addresses associated with a socket are the eligible transport addresses for the endpoint to send and receive data. The endpoint will also present these addresses to its peers during the association initialization process, see [RFC4960]. After calling bind(), if the endpoint wishes to accept new associations on the socket, it must call listen() (see Section 3.1.3). The function prototype of bind() is int bind(int sd, struct sockaddr *addr, socklen_t addrlen); and the arguments are sd: The socket descriptor returned by socket(). addr: The address structure (struct sockaddr_in for an IPv4 address or struct sockaddr_in6 for an IPv6 address, see [RFC3493]). addrlen: The size of the address structure. If sd is an IPv4 socket, the address passed must be an IPv4 address. If the sd is an IPv6 socket, the address passed can either be an IPv4 or an IPv6 address. Applications cannot call bind() multiple times to associate multiple addresses to an endpoint. After the first call to bind(), all subsequent calls will return an error. If the IP address part of addr is specified as a wildcard (INADDR_ANY for an IPv4 address, or as IN6ADDR_ANY_INIT or in6addr_any for an IPv6 address), the operating system will associate the endpoint with Stewart, et al. Expires January 13, 2011 [Page 10] Internet-Draft SCTP sockets API July 2010 an optimal address set of the available interfaces. If the IPv4 sin_port or IPv6 sin6_port is set to 0, the operating system will choose an ephemeral port for the endpoint. If a bind() is not called prior to a sendmsg() call that initiates a new association, the system picks an ephemeral port and will choose an address set equivalent to binding with a wildcard address. One of those addresses will be the primary address for the association. This automatically enables the multi-homing capability of SCTP. 3.1.3. listen() By default, a one-to-many style socket does not accept new association requests. An application uses listen() to mark a socket as being able to accept new associations. The function prototype is int listen(int sd, int backlog); and the arguments are sd: The socket descriptor of the endpoint. backlog: If backlog is non-zero, enable listening else disable listening. Note that one-to-many style socket consumers do not need to call accept to retrieve new associations. Calling accept() on a one-to- many style socket should return EOPNOTSUPP. Rather, new associations are accepted automatically, and notifications of the new associations are delivered via recvmsg() with the SCTP_ASSOC_CHANGE event (if these notifications are enabled). Clients will typically not call listen(), so that they can be assured that only actively initiated associations are on the socket. Server or peer-to-peer sockets, on the other hand, will always accept new associations, so a well- written application using server one-to-many style sockets must be prepared to handle new associations from unwanted peers. Also note that the SCTP_ASSOC_CHANGE event provides the association ID for a new association, so if applications wish to use the association ID as input to other socket calls, they should ensure that the SCTP_ASSOC_CHANGE event is enabled. 3.1.4. sendmsg() and recvmsg() An application uses the sendmsg() and recvmsg() call to transmit data to and receive data from its peer. Stewart, et al. Expires January 13, 2011 [Page 11] Internet-Draft SCTP sockets API July 2010 The function prototypes are ssize_t sendmsg(int sd, const struct msghdr *message, int flags); and ssize_t recvmsg(int sd, struct msghdr *message, int flags); using the arguments: sd: The socket descriptor of the endpoint. message: Pointer to the msghdr structure which contains a single user message and possibly some ancillary data. See Section 5 for complete description of the data structures. flags: No new flags are defined for SCTP at this level. See Section 5 for SCTP specific flags used in the msghdr structure. As described in Section 5, different types of ancillary data can be sent and received along with user data. When sending, the ancillary data is used to specify the sent behavior, such as the SCTP stream number to use. When receiving, the ancillary data is used to describe the received data, such as the SCTP stream sequence number of the message. When sending user data with sendmsg(), the msg_name field in the msghdr structure will be filled with one of the transport addresses of the intended receiver. If there is no existing association between the sender and the intended receiver, the sender's SCTP stack will set up a new association and then send the user data (see Section 6.5 for more on implicit association setup). If sendmsg() is called with no data and there is no existing association, a new one will be established. The SCTP_INIT type ancillary data can be used to change some of the parameters used to set up a new association. If sendmsg() is called with NULL data, and there is no existing association but the SCTP_ABORT or SCTP_EOF flags are set, then -1 is retured and errno is set to EINVAL. Sending a message using sendmsg() is atomic unless explicit EOR marking is enabled on the socket specified by sd (see Section 7.1.26). If a peer sends a SHUTDOWN, an SCTP_SHUTDOWN_EVENT notification will be delivered if that notification has been enabled, and no more data can be sent to that association. Any attempt to send more data will cause sendmsg() to return with an ESHUTDOWN error. Note that the socket is still open for reading at this point so it is possible to retrieve notifications. Stewart, et al. Expires January 13, 2011 [Page 12] Internet-Draft SCTP sockets API July 2010 When receiving a user message with recvmsg(), the msg_name field in the msghdr structure will be populated with the source transport address of the user data. The caller of recvmsg() can use this address information to determine to which association the received user message belongs. Note that if SCTP_ASSOC_CHANGE events are disabled, applications must use the peer transport address provided in the msg_name field by recvmsg() to perform correlation to an association, since they will not have the association ID. If all data in a single message has been delivered, MSG_EOR will be set in the msg_flags field of the msghdr structure (see section Section 5.1). If the application does not provide enough buffer space to completely receive a data message, MSG_EOR will not be set in msg_flags. Successive reads will consume more of the same message until the entire message has been delivered, and MSG_EOR will be set. If the SCTP stack is running low on buffers, it may partially deliver a message. In this case, MSG_EOR will not be set, and more calls to recvmsg() will be necessary to completely consume the message. Only one message at a time can be partially delivered in any stream. The socket option SCTP_FRAGMENT_INTERLEAVE controls various aspects of what interlacing of messages occurs for both the one-to-one and the one-to-many model sockets. Please consult Section 7.1.20 for further details on message delivery options. Note, if the socket is a branched-off socket that only represents one association (see Section 3.1), the msg_name field can be used to override the primary address when sending data. 3.1.5. close() Applications use close() to perform graceful shutdown (as described in Section 10.1 of [RFC4960]) on all the associations currently represented by a one-to-many style socket. The function prototype is int close(int sd); and the argument is sd: The socket descriptor of the associations to be closed. To gracefully shutdown a specific association represented by the one- to-many style socket, an application should use the sendmsg() call, and include the SCTP_EOF flag. A user may optionally terminate an association non-gracefully by sending with the SCTP_ABORT flag and Stewart, et al. Expires January 13, 2011 [Page 13] Internet-Draft SCTP sockets API July 2010 possibly passing a user specified abort code in the data field. Both flags SCTP_EOF and SCTP_ABORT are passed with ancillary data (see Section 5.2.2) in the sendmsg() call. If sd in the close() call is a branched-off socket representing only one association, the shutdown is performed on that association only. 3.1.6. connect() An application may use the connect() call in the one-to-many style to initiate an association without sending data. The function prototype is int connect(int sd, const struct sockaddr *nam, socklen_t len); and the arguments are sd: The socket descriptor to have a new association added to. nam: The address structure (struct sockaddr_in for an IPv4 address or struct sockaddr_in6 for an IPv6 address, see [RFC3493]). len: The size of the address. Multiple connect() calls can be made on the same socket to create multiple associations. This is different from the semantics of connect() on a UDP socket. 3.2. Non-blocking mode Some SCTP application may wish to avoid being blocked when calling a socket interface function. Once a bind() and/or subsequent sctp_bindx() calls are complete on a one-to-many style socket, an application may set the non-blocking option by a fcntl() (such as O_NONBLOCK). After setting the socket to non-blocking mode, the sendmsg() function returns immediately. The success or failure of sending the data message (with possible SCTP_INITMSG ancillary data) will be signaled by the SCTP_ASSOC_CHANGE event with SCTP_COMM_UP or CANT_START_ASSOC. If user data could not be sent (due to a CANT_START_ASSOC), the sender will also receive an SCTP_SEND_FAILED event. Events can be received by the user calling recvmsg(). A server (having called listen()) is also notified of an association up event by the reception of an SCTP_ASSOC_CHANGE with SCTP_COMM_UP via the calling of recvmsg() and possibly the reception of the first data message. To shutdown the association gracefully, the user must call sendmsg() Stewart, et al. Expires January 13, 2011 [Page 14] Internet-Draft SCTP sockets API July 2010 with no data and with the SCTP_EOF flag set. The function returns immediately, and completion of the graceful shutdown is indicated by an SCTP_ASSOC_CHANGE notification of type SHUTDOWN_COMPLETE (see Section 5.3.2). Note that this can also be done using the sctp_send() call described in Section 8.10. An application is recommended to use caution when using select() (or poll()) for writing on a one-to-many style socket. The reason being that the interpretation of select on write is implementation specific. Generally a positive return on a select on write would only indicate that one of the associations represented by the one-to- many socket is writable. An application that writes after the select() returns may still block since the association that was writeable is not the destination association of the write call. Likewise select() (or poll()) for reading from a one-to-many socket will only return an indication that one of the associations represented by the socket has data to be read. An application that wishes to know that a particular association is ready for reading or writing should either use the one-to-one style or use the sctp_peeloff() (see Section 8.2) function to separate the association of interest from the one-to-many socket. 3.3. Special considerations The fact that a one-to-many style socket can provide access to many SCTP associations through a single socket descriptor has important implications for both application programmers and system programmers implementing this API. A key issue is how buffer space inside the sockets layer is managed. Because this implementation detail directly affects how application programmers must write their code to ensure correct operation and portability, this section provides some guidance to both implementers and application programmers. An important feature that SCTP shares with TCP is flow control. Specifically, a sender may not send data faster than the receiver can consume it. For TCP, flow control is typically provided for in the sockets API as follows. If the reader stops reading, the sender queues messages in the socket layer until it uses all of its socket buffer space allocation creating a "stalled connection". Further attempts to write to the socket will block or return the error EAGAIN or EWOULDBLOCK for a non-blocking socket. At some point, either the connection is closed, or the receiver begins to read again freeing space in the output queue. For one-to-one style SCTP sockets (this includes sockets descriptors Stewart, et al. Expires January 13, 2011 [Page 15] Internet-Draft SCTP sockets API July 2010 that were separated from a one-to-many style socket with sctp_peeloff()) the behavior is identical. For one-to-many style SCTP sockets there are multiple associations for a single socket, which makes the situation more complicated. If the implementation uses a single buffer space allocation shared by all associations, a single stalled association can prevent the further sending of data on all associations active on a particular one-to-many style socket. For a blocking socket, it should be clear that a single stalled association can block the entire socket. For this reason, application programmers may want to use non-blocking one-to-many style sockets. The application should at least be able to send messages to the non-stalled associations. But a non-blocking socket is not sufficient if the API implementer has chosen a single shared buffer allocation for the socket. A single stalled association would eventually cause the shared allocation to fill, and it would become impossible to send even to non-stalled associations. The API implementer can solve this problem by providing each association with its own allocation of outbound buffer space. Each association should conceptually have as much buffer space as it would have if it had its own socket. As a bonus, this simplifies the implementation of sctp_peeloff(). To ensure that a given stalled association will not prevent other non-stalled associations from being writable, application programmers should either: o demand that the underlying implementation dedicates independent buffer space reservation to each association (as suggested above), or o verify that their application layer protocol does not permit large amounts of unread data at the receiver (this is true of some request-response protocols, for example), or o use one-to-one style sockets for association which may potentially stall (either from the beginning, or by using sctp_peeloff before sending large amounts of data that may cause a stalled condition). 4. One-to-One Style Interface The goal of this style is to follow as closely as possible the current practice of using the sockets interface for a connection oriented protocol, such as TCP. This style enables existing applications using connection oriented protocols to be ported to SCTP with very little effort. Stewart, et al. Expires January 13, 2011 [Page 16] Internet-Draft SCTP sockets API July 2010 One-to-one style sockets can be connected (explicitly or implicitly) at most once, simular to TCP sockets. Note that some new SCTP features and some new SCTP socket options can only be utilized through the use of sendmsg() and recvmsg() calls, see Section 4.1.8. 4.1. Basic Operation A typical server in one-to-one style uses the following system call sequence to prepare an SCTP endpoint for servicing requests: o socket() o bind() o listen() o accept() The accept() call blocks until a new association is set up. It returns with a new socket descriptor. The server then uses the new socket descriptor to communicate with the client, using recv() and send() calls to get requests and send back responses. Then it calls o close() to terminate the association. A typical client uses the following system call sequence to setup an association with a server to request services: o socket() o connect() After returning from connect(), the client uses send()/sendmsg() and recv()/recvmsg() calls to send out requests and receive responses from the server. The client calls o close() to terminate this association when done. 4.1.1. socket() Applications call socket() to create a socket descriptor to represent an SCTP endpoint. The function prototype is int socket(int domain, int type, int protocol); Stewart, et al. Expires January 13, 2011 [Page 17] Internet-Draft SCTP sockets API July 2010 and one uses PF_INET or PF_INET6 as the domain, SOCK_STREAM as the type and IPPROTO_SCTP as the protocol. Here, SOCK_STREAM indicates the creation of a one-to-one style socket. Using the PF_INET domain indicates the creation of an endpoint which can use only IPv4 addresses, while PF_INET6 creates an endpoint which can use both IPv6 and IPv4 addresses. 4.1.2. bind() Applications use bind() to specify which local address and port the SCTP endpoint should associate itself with. An SCTP endpoint can be associated with multiple addresses. To do this, sctp_bindx() is introduced in Section 8.1 to help applications do the job of associating multiple addresses. But note that an endpoint can only be associated with one local port. These addresses associated with a socket are the eligible transport addresses for the endpoint to send and receive data. The endpoint will also present these addresses to its peers during the association initialization process, see [RFC4960]. The function prototype of bind() is int bind(int sd, struct sockaddr *addr, socklen_t addrlen); and the arguments are sd: The socket descriptor returned by socket(). addr: The address structure (struct sockaddr_in for an IPv4 address or struct sockaddr_in6 for an IPv6 address, see [RFC3493]). addrlen: The size of the address structure. If sd is an IPv4 socket, the address passed must be an IPv4 address. If the sd is an IPv6 socket, the address passed can either be an IPv4 or an IPv6 address. Applications cannot call bind() multiple times to associate multiple addresses to the endpoint. After the first call to bind(), all subsequent calls will return an error. If the IP address part of addr is specified as a wildcard (INADDR_ANY for an IPv4 address, or as IN6ADDR_ANY_INIT or in6addr_any for an IPv6 address), the operating system will associate the endpoint with Stewart, et al. Expires January 13, 2011 [Page 18] Internet-Draft SCTP sockets API July 2010 an optimal address set of the available interfaces. If the IPv4 sin_port or IPv6 sin6_port is set to 0, the operating system will choose an ephemeral port for the endpoint. If a bind() is not called prior to the connect() call, the system picks an ephemeral port and will choose an address set equivalent to binding with a wildcard address. One of these addresses will be the primary address for the association. This automatically enables the multi-homing capability of SCTP. The completion of this bind() process does not ready the SCTP endpoint to accept inbound SCTP association requests. Until a listen() system call, described below, is performed on the socket, the SCTP endpoint will promptly reject an inbound SCTP INIT request with an SCTP ABORT. 4.1.3. listen() Applications use listen() to ready the SCTP endpoint for accepting inbound associations. The function prototype is int listen(int sd, int backlog); and the arguments are sd: the socket descriptor of the SCTP endpoint. backlog: this specifies the max number of outstanding associations allowed in the socket's accept queue. These are the associations that have finished the four-way initiation handshake (see Section 5 of [RFC4960]) and are in the ESTABLISHED state. Note, a backlog of '0' indicates that the caller no longer wishes to receive new associations. 4.1.4. accept() Applications use the accept() call to remove an established SCTP association from the accept queue of the endpoint. A new socket descriptor will be returned from accept() to represent the newly formed association. The function prototype is int accept(int sd, struct sockaddr *addr, socklen_t *addrlen); Stewart, et al. Expires January 13, 2011 [Page 19] Internet-Draft SCTP sockets API July 2010 and the arguments are sd: The listening socket descriptor. addr: On return, addr (struct sockaddr_in for an IPv4 address or struct sockaddr_in6 for an IPv6 address, see [RFC3493]) will contain the primary address of the peer endpoint. addrlen: On return, addrlen will contain the size of addr. The functions returns the socket descriptor for the newly formed association. 4.1.5. connect() Applications use connect() to initiate an association to a peer. The function prototype is int connect(int sd, const struct sockaddr *addr, socklen_t addrlen); and the arguments are sd: The socket descriptor of the endpoint. addr: The peer's (struct sockaddr_in for an IPv4 address or struct sockaddr_in6 for an IPv6 address, see [RFC3493]) address. addrlen: The size of the address. This operation corresponds to the ASSOCIATE primitive described in section 10.1 of [RFC4960]. The number of outbound streams the new association has is stack dependent. Applications can use the SCTP_INITMSG option described in Section 7.1.3 should be used before connecting to change the number of outbound streams. If a bind() is not called prior to the connect() call, the system picks an ephemeral port and will choose an address set equivalent to binding with INADDR_ANY and IN6ADDR_ANY_INIT for IPv4 and IPv6 socket respectively. One of the addresses will be the primary address for the association. This automatically enables the multi-homing capability of SCTP. Note that SCTP allows data exchange, similar to T/TCP [RFC1644], during the association set up phase. If an application wants to do this, it cannot use the connect() call. Instead, it should use sendto() or sendmsg() to initiate an association. If it uses sendto() and it wants to change the initialization behavior, it needs to use the SCTP_INITMSG socket option before calling sendto(). Or it can use sendmsg() with SCTP_INIT type ancillary data to initiate an association without doing the setsockopt(). Note that the implicit Stewart, et al. Expires January 13, 2011 [Page 20] Internet-Draft SCTP sockets API July 2010 setup is supported for the one-to-many style sockets. SCTP does not support half close semantics. This means that unlike T/TCP, MSG_EOF should not be set in the flags parameter when calling sendto() or sendmsg() when the call is used to initiate a connection. MSG_EOF is not an acceptable flag with an SCTP socket. 4.1.6. close() Applications use close() to gracefully close down an association. The function prototype is int close(int sd); and the argument is sd: The socket descriptor of the association to be closed. After an application calls close() on a socket descriptor, no further socket operations will succeed on that descriptor. 4.1.7. shutdown() SCTP differs from TCP in that it does not have half closed semantics. Hence the shutdown() call for SCTP is an approximation of the TCP shutdown() call, and solves some different problems. Full TCP- compatibility is not provided, so developers porting TCP applications to SCTP may need to recode sections that use shutdown(). (Note that it is possible to achieve the same results as half close in SCTP using SCTP streams.) The function prototype is int shutdown(int sd, int how); and the arguments are sd: The socket descriptor of the association to be closed. how: Specifies the type of shutdown. The values are as follows: SHUT_RD: Disables further receive operations. No SCTP protocol action is taken. SHUT_WR: Disables further send operations, and initiates the SCTP shutdown sequence. SHUT_RDWR: Disables further send and receive operations and initiates the SCTP shutdown sequence. The major difference between SCTP and TCP shutdown() is that SCTP SHUT_WR initiates immediate and full protocol shutdown, whereas TCP Stewart, et al. Expires January 13, 2011 [Page 21] Internet-Draft SCTP sockets API July 2010 SHUT_WR causes TCP to go into the half closed state. SHUT_RD behaves the same for SCTP as TCP. The purpose of SCTP SHUT_WR is to close the SCTP association while still leaving the socket descriptor open. This allows the caller to receive back any data which SCTP is unable to deliver (see Section 5.3.5 for more information) and receive event notifications. To perform the ABORT operation described in [RFC4960] section 10.1, an application can use the socket option SO_LINGER. It is described in Section 7.1.4. 4.1.8. sendmsg() and recvmsg() With a one-to-one style socket, the application can also use sendmsg() and recvmsg() to transmit data to and receive data from its peer. The semantics is similar to those used in the one-to-many style (section Section 3.1.3), with the following differences: 1. When sending, the msg_name field in the msghdr is not used to specify the intended receiver, rather it is used to indicate a preferred peer address if the sender wishes to discourage the stack from sending the message to the primary address of the receiver. If the socket is connected and the transport address given is not part of the current association, the data will not be sent and an SCTP_SEND_FAILED event will be delivered to the application if send failure events are enabled. 2. Using sendmsg() on a non-connected one-to-one style socket for implicit connection setup may or may not work depending on the SCTP implementation. 4.1.9. getpeername() Applications use getpeername() to retrieve the primary socket address of the peer. This call is for TCP compatibility, and is not multi- homed. It does not work with one-to-many style sockets. See Section 8.3 for a multi-homed/one-to-many style version of the call. The function prototype is int getpeername(int sd, struct sockaddr *address, socklen_t *len); and the arguments are: sd: The socket descriptor to be queried. Stewart, et al. Expires January 13, 2011 [Page 22] Internet-Draft SCTP sockets API July 2010 address: On return, the peer primary address is stored in this buffer. If the socket is an IPv4 socket, the address will be IPv4. If the socket is an IPv6 socket, the address will be either an IPv6 or IPv4 address. len: The caller should set the length of address here. On return, this is set to the length of the returned address. If the actual length of the address is greater than the length of the supplied sockaddr structure, the stored address will be truncated. 5. Data Structures This section discusses important data structures which are specific to SCTP and are used with sendmsg() and recvmsg() calls to control SCTP endpoint operations and to access ancillary information and notifications. 5.1. The msghdr and cmsghdr Structures The msghdr structure used in the sendmsg() and recvmsg() calls, as well as the ancillary data carried in the structure, is the key for the application to set and get various control information from the SCTP endpoint. The msghdr and the related cmsghdr structures are defined and discussed in detail in [RFC3542]. They are defined as: struct msghdr { void *msg_name; /* ptr to socket address structure */ socklen_t msg_namelen; /* size of socket address structure */ struct iovec *msg_iov; /* scatter/gather array */ size_t msg_iovlen; /* # elements in msg_iov */ void *msg_control; /* ancillary data */ socklen_t msg_controllen; /* ancillary data buffer length */ int msg_flags; /* flags on received message */ }; struct cmsghdr { socklen_t cmsg_len; /* #bytes, including this header */ int cmsg_level; /* originating protocol */ int cmsg_type; /* protocol-specific type */ /* followed by unsigned char cmsg_data[]; */ }; In the msghdr structure, the usage of msg_name has been discussed in previous sections (see Section 3.1.3 and Section 4.1.8). Stewart, et al. Expires January 13, 2011 [Page 23] Internet-Draft SCTP sockets API July 2010 The scatter/gather buffers, or I/O vectors (pointed to by the msg_iov field) are treated as a single SCTP data chunk, rather than multiple chunks, for both sendmsg() and recvmsg(). The msg_flags are not used when sending a message with sendmsg(). If a notification has arrived, recvmsg() will return the notification with the MSG_NOTIFICATION flag set in msg_flags. If the MSG_NOTIFICATION flag is not set, recvmsg() will return data. See Section 5.3 for more information about notifications. If all portions of a data frame or notification have been read, recvmsg() will return with MSG_EOR set in msg_flags. 5.2. SCTP msg_control Structures A key element of all SCTP specific socket extensions is the use of ancillary data to specify and access SCTP specific data via the struct msghdr's msg_control member used in sendmsg() and recvmsg(). Fine-grained control over initialization and sending parameters are handled with ancillary data. Each ancillary data item is proceeded by a struct cmsghdr (see Section 5.1), which defines the function and purpose of the data contained in the cmsg_data[] member. By default on either style socket, SCTP will pass no ancillary data; Specific ancillary data items can be enabled with socket options defined for SCTP; see Section 7.4. Note that all ancillary types are fixed length; see Section 5.4 for further discussion on this. These data structures use struct sockaddr_storage (defined in [RFC3493]) as a portable, fixed length address format. Other protocols may also provide ancillary data to the socket layer consumer. These ancillary data items from other protocols may intermingle with SCTP data. For example, the IPv6 socket API definitions ([RFC3542] and [RFC3493]) define a number of ancillary data items. If a socket API consumer enables delivery of both SCTP and IPv6 ancillary data, they both may appear in the same msg_control buffer in any order. An application may thus need to handle other types of ancillary data besides those passed by SCTP. The sockets application must provide a buffer large enough to accommodate all ancillary data provided via recvmsg(). If the buffer is not large enough, the ancillary data will be truncated and the msghdr's msg_flags will include MSG_CTRUNC. Stewart, et al. Expires January 13, 2011 [Page 24] Internet-Draft SCTP sockets API July 2010 5.2.1. SCTP Initiation Structure (SCTP_INIT) This cmsghdr structure provides information for initializing new SCTP associations with sendmsg(). The SCTP_INITMSG socket option uses this same data structure. This structure is not used for recvmsg(). +--------------+-----------+---------------------+ | cmsg_level | cmsg_type | cmsg_data[] | +--------------+-----------+---------------------+ | IPPROTO_SCTP | SCTP_INIT | struct sctp_initmsg | +--------------+-----------+---------------------+ The sctp_initmsg structure is defined below: struct sctp_initmsg { uint16_t sinit_num_ostreams; uint16_t sinit_max_instreams; uint16_t sinit_max_attempts; uint16_t sinit_max_init_timeo; }; sinit_num_ostreams: This is an integer number representing the number of streams that the application wishes to be able to send to. This number is confirmed in the SCTP_COMM_UP notification and must be verified since it is a negotiated number with the remote endpoint. The default value of 0 indicates to use the endpoint default value. sinit_max_instreams: This value represents the maximum number of inbound streams the application is prepared to support. This value is bounded by the actual implementation. In other words the user may be able to support more streams than the Operating System. In such a case, the Operating System limit overrides the value requested by the user. The default value of 0 indicates to use the endpoints default value. sinit_max_attempts: This integer specifies how many attempts the SCTP endpoint should make at resending the INIT. This value overrides the system SCTP 'Max.Init.Retransmits' value. The default value of 0 indicates to use the endpoints default value. This is normally set to the system's default 'Max.Init.Retransmit' value. sinit_max_init_timeo: This value represents the largest Time-Out or RTO value (in milliseconds) to use in attempting an INIT. Normally the 'RTO.Max' is used to limit the doubling of the RTO upon timeout. For the INIT message this value may override 'RTO.Max'. This value must not influence 'RTO.Max' during data transmission and is only used to bound the initial setup time. A default value of 0 indicates to use the endpoints default value. This is normally set to the system's 'RTO.Max' value (60 seconds). Stewart, et al. Expires January 13, 2011 [Page 25] Internet-Draft SCTP sockets API July 2010 5.2.2. SCTP Header Information Structure (SCTP_SNDRCV) This cmsghdr structure specifies SCTP options for sendmsg() and describes SCTP header information about a received message through recvmsg(). This structure mixes the send and receive path. SCTP_SNDINFO described in Section 5.2.4 and SCTP_RCVINFO described in Section 5.2.5 split this information. These structures should be used, when possible, since SCTP_SNDRCV is deprecated. +--------------+-------------+------------------------+ | cmsg_level | cmsg_type | cmsg_data[] | +--------------+-------------+------------------------+ | IPPROTO_SCTP | SCTP_SNDRCV | struct sctp_sndrcvinfo | +--------------+-------------+------------------------+ The sctp_sndrcvinfo structure is defined below: struct sctp_sndrcvinfo { uint16_t sinfo_stream; uint16_t sinfo_ssn; uint16_t sinfo_flags; uint32_t sinfo_ppid; uint32_t sinfo_context; uint32_t sinfo_pr_value; uint32_t sinfo_tsn; uint32_t sinfo_cumtsn; sctp_assoc_t sinfo_assoc_id; }; sinfo_stream: For recvmsg() the SCTP stack places the message's stream number in this value. For sendmsg() this value holds the stream number that the application wishes to send this message to. If a sender specifies an invalid stream number an error indication is returned and the call fails. sinfo_ssn: For recvmsg() this value contains the stream sequence number that the remote endpoint placed in the DATA chunk. For fragmented messages this is the same number for all deliveries of the message (if more than one recvmsg() is needed to read the message). The sendmsg() call will ignore this parameter. sinfo_flags: This field may contain any of the following flags and is composed of a bitwise OR of these values. recvmsg() flags: SCTP_UNORDERED: This flag is present when the message was sent non-ordered. Stewart, et al. Expires January 13, 2011 [Page 26] Internet-Draft SCTP sockets API July 2010 sendmsg() flags: SCTP_UNORDERED: This flag requests the un-ordered delivery of the message. If this flag is clear the datagram is considered an ordered send. SCTP_ADDR_OVER: This flag, in the one-to-many style, requests the SCTP stack to override the primary destination address with the address found with the sendto/sendmsg call. SCTP_ABORT: Setting this flag causes the specified association to abort by sending an ABORT message to the peer (one-to- many style only). The ABORT chunk will contain an error cause 'User Initiated Abort' with cause code 12. The cause specific information of this error cause is provided in msg_iov. SCTP_EOF: Setting this flag invokes the SCTP graceful shutdown procedure on the specified association. Graceful shutdown assures that all data queued by both endpoints is successfully transmitted before closing the association (one-to-many style only). SCTP_SENDALL: This flag, if set, will cause a one-to-many model socket to send the message to all associations that are currently established on this socket. For the one-to- one socket, this flag has no effect. sinfo_ppid: This value in sendmsg() is an unsigned integer that is passed to the remote end in each user message. In recvmsg() this value is the same information that was passed by the upper layer in the peer application. Please note that the SCTP stack performs no byte order modification of this field. For example, if the DATA chunk has to contain a given value in network byte order, the SCTP user has to perform the htonl() computation. sinfo_context: This value is an opaque 32 bit context datum that is used in the sendmsg() function. This value is passed back to the upper layer if an error occurs on the send of a message and is retrieved with each undelivered message (Note: if an endpoint has done multiple sends, all of which fail, multiple different sinfo_context values will be returned. One with each user data message). sinfo_pr_value: The meaning of this field depends on the PR-SCTP policy specified by the sinfo_pr_policy field. It is ignored when SCTP_PR_SCTP_NONE is specified. In case of SCTP_PR_SCTP_TTL the lifetime is specified. sinfo_tsn: For the receiving side, this field holds a TSN that was assigned to one of the SCTP Data Chunks. sinfo_cumtsn: This field will hold the current cumulative TSN as known by the underlying SCTP layer. Note this field is ignored when sending. Stewart, et al. Expires January 13, 2011 [Page 27] Internet-Draft SCTP sockets API July 2010 sinfo_assoc_id: The association handle field, sinfo_assoc_id, holds the identifier for the association announced in the SCTP_COMM_UP notification. All notifications for a given association have the same identifier. Ignored for one-to-one style sockets. An sctp_sndrcvinfo item always corresponds to the data in msg_iov. 5.2.3. Extended SCTP Header Information Structure (SCTP_EXTRCV) This cmsghdr structure specifies SCTP options for SCTP header information about a received message via recvmsg(). Note that this structure is an extended version of SCTP_SNDRCV (see Section 5.2.2) and will only be received if the user has set the socket option SCTP_USE_EXT_RCVINFO to true in addition to any event subscription needed to receive ancillary data. See Section 7.1.22 on this socket option. Note that next message data is not valid unless the current message is completely read, i.e. the MSG_EOR is set, in other words if the application has more data to read from the current message then no next message information will be available. SCTP_NXTINFO described in Section 5.2.6 should be used when possible, since SCTP_EXTRCV is considered deprecated. +--------------+-------------+------------------------+ | cmsg_level | cmsg_type | cmsg_data[] | +--------------+-------------+------------------------+ | IPPROTO_SCTP | SCTP_EXTRCV | struct sctp_extrcvinfo | +--------------+-------------+------------------------+ The sctp_extrcvinfo structure is defined below: struct sctp_extrcvinfo { uint16_t sinfo_stream; uint16_t sinfo_ssn; uint16_t sinfo_flags; uint32_t sinfo_ppid; uint32_t sinfo_context; uint32_t sinfo_pr_value; uint32_t sinfo_tsn; uint32_t sinfo_cumtsn; uint16_t serinfo_next_flags; uint16_t serinfo_next_stream; uint32_t serinfo_next_aid; uint32_t serinfo_next_length; uint32_t serinfo_next_ppid; sctp_assoc_t sinfo_assoc_id; }; Stewart, et al. Expires January 13, 2011 [Page 28] Internet-Draft SCTP sockets API July 2010 sinfo_*: Please see Section 5.2.2 for the details for these fields. serinfo_next_flags: This bitmask will hold one or more of the following values: SCTP_NEXT_MSG_AVAIL: This bit, when set to 1, indicates that next message information is available i.e.: next_stream, next_asocid, next_length and next_ppid fields all have valid values. If this bit is set to 0, then these fields are not valid and should be ignored. SCTP_NEXT_MSG_ISCOMPLETE: This bit, when set, indicates that the next message is completely in the receive buffer. The next_length field thus contains the entire message size. If this flag is set to 0, then the next_length field only contains part of the message size since the message is still being received (it is being partially delivered). SCTP_NEXT_MSG_IS_UNORDERED: This bit, when set, indicates that the next message to be received was sent by the peer as unordered. If this bit is not set (i.e the bit is 0) the next message to be read is an ordered message in the stream specified. SCTP_NEXT_MSG_IS_NOTIFICATION: This bit, when set, indicates that the next message to be received is not a message from the peer, but instead is a MSG_NOTIFICATION from the local SCTP stack. serinfo_next_stream: This value, when valid (see serinfo_next_flags), contains the next stream number that will be received on a subsequent call to one of the receive message functions. serinfo_next_aid: This value, when valid (see serinfo_next_flags), contains the next association identification that will be received on a subsequent call to one of the receive message functions. serinfo_next_length: This value, when valid (see serinfo_next_flags), contains the length of the next message that will be received on a subsequent call to one of the receive message functions. Note that this length may be a partial length depending on the settings of next_flags. serinfo_next_ppid: This value, when valid (see serinfo_next_flags), contains the ppid of the next message that will be received on a subsequent call to one of the receive message functions. 5.2.4. SCTP Send Information Structure (SCTP_SNDINFO) This cmsghdr structure specifies SCTP options for sendmsg(). +--------------+--------------+---------------------+ | cmsg_level | cmsg_type | cmsg_data[] | +--------------+--------------+---------------------+ | IPPROTO_SCTP | SCTP_SNDINFO | struct sctp_sndinfo | +--------------+--------------+---------------------+ Stewart, et al. Expires January 13, 2011 [Page 29] Internet-Draft SCTP sockets API July 2010 The sctp_sndinfo structure is defined below: struct sctp_sndinfo { uint16_t snd_sid; uint16_t snd_flags; uint32_t snd_ppid; uint32_t snd_context; sctp_assoc_t snd_assoc_id; }; snd_sid: This value holds the stream number that the application wishes to send this message to. If a sender specifies an invalid stream number an error indication is returned and the call fails. snd_flags: This field may contain any of the following flags and is composed of a bitwise OR of these values. SCTP_UNORDERED: This flag requests the un-ordered delivery of the message. If this flag is clear the datagram is considered an ordered send. SCTP_ADDR_OVER: This flag, in the one-to-many style, requests the SCTP stack to override the primary destination address with the address found with the sendto()/sendmsg call. SCTP_ABORT: Setting this flag causes the specified association to abort by sending an ABORT message to the peer (one-to-many style only). The ABORT chunk will contain an error cause 'User Initiated Abort' with cause code 12. The cause specific information of this error cause is provided in msg_iov. SCTP_EOF: Setting this flag invokes the SCTP graceful shutdown procedures on the specified association. Graceful shutdown assures that all data queued by both endpoints is successfully transmitted before closing the association (one-to-many style only). SCTP_SENDALL: This flag, if set, will cause a one-to-many model socket to send the message to all associations that are currently established on this socket. For the one-to-one socket, this flag has no effect. snd_ppid: This value in sendmsg() is an unsigned integer that is passed to the remote end in each user message. Please note that the SCTP stack performs no byte order modification of this field. For example, if the DATA chunk has to contain a given value in network byte order, the SCTP user has to perform the htonl() computation. snd_context: This value is an opaque 32 bit context datum that is used in the sendmsg() function. This value is passed back to the upper layer if an error occurs on the send of a message and is retrieved with each undelivered message (Note: if an endpoint has done multiple sends, all of which fail, multiple different sinfo_context values will be returned. One with each user data Stewart, et al. Expires January 13, 2011 [Page 30] Internet-Draft SCTP sockets API July 2010 message). snd_assoc_id: The association handle field, sinfo_assoc_id, holds the identifier for the association announced in the SCTP_COMM_UP notification. All notifications for a given association have the same identifier. Ignored for one-to-one style sockets. An sctp_sndinfo item always corresponds to the data in msg_iov. 5.2.5. SCTP Receive Information Structure (SCTP_RCVINFO) This cmsghdr structure describes SCTP receive information about a received message through recvmsg(). To enable the delivery of this information an application must use the SCTP_RECVRCVINFO socket option (see Section 7.1.29). +--------------+--------------+---------------------+ | cmsg_level | cmsg_type | cmsg_data[] | +--------------+--------------+---------------------+ | IPPROTO_SCTP | SCTP_RCVINFO | struct sctp_rcvinfo | +--------------+--------------+---------------------+ The sctp_rcvinfo structure is defined below: struct sctp_rcvinfo { uint16_t rcv_sid; uint16_t rcv_ssn; uint16_t rcv_flags; uint32_t rcv_ppid; uint32_t rcv_tsn; uint32_t rcv_cumtsn; sctp_assoc_t rcv_assoc_id; }; rcv_sid: The SCTP stack places the message's stream number in this value. rcv_ssn: This value contains the stream sequence number that the remote endpoint placed in the DATA chunk. For fragmented messages this is the same number for all deliveries of the message (if more than one recvmsg() is needed to read the message). rcv_flags: This field may contain any of the following flags and is composed of a bitwise OR of these values. SCTP_UNORDERED: This flag is present when the message was sent non-ordered. Stewart, et al. Expires January 13, 2011 [Page 31] Internet-Draft SCTP sockets API July 2010 rcv_ppid: This value is the same information that was passed by the upper layer in the peer application. Please note that the SCTP stack performs no byte order modification of this field. For example, if the DATA chunk has to contain a given value in network byte order, the SCTP user has to perform the htonl() computation. rcv_tsn: This field holds a TSN that was assigned to one of the SCTP Data Chunks. rcv_cumtsn: This field will hold the current cumulative TSN as known by the underlying SCTP layer. rcv_assoc_id: The association handle field, sinfo_assoc_id, holds the identifier for the association announced in the SCTP_COMM_UP notification. All notifications for a given association have the same identifier. Ignored for one-to-one style sockets. A sctp_rcvinfo item always corresponds to the data in msg_iov. 5.2.6. SCTP Next Receive Information Structure (SCTP_NXTINFO) This cmsghdr structure describes SCTP receive information of the next message which will be delivered through recvmsg() if this information is already available when delivering the current message. It uses the same structure as the SCTP Receive Information Structure. To enable the delivery of this information an application must use the SCTP_RECVNXTINFO socket option (see Section 7.1.30). +--------------+--------------+---------------------+ | cmsg_level | cmsg_type | cmsg_data[] | +--------------+--------------+---------------------+ | IPPROTO_SCTP | SCTP_NXTINFO | struct sctp_rcvinfo | +--------------+--------------+---------------------+ 5.2.7. SCTP PR-SCTP Information Structure (SCTP_PRINFO) This cmsghdr structure specifies SCTP options for sendmsg(). +--------------+-------------+--------------------+ | cmsg_level | cmsg_type | cmsg_data[] | +--------------+-------------+--------------------+ | IPPROTO_SCTP | SCTP_PRINFO | struct sctp_prinfo | +--------------+-------------+--------------------+ The sctp_prinfo structure is defined below: struct sctp_prinfo { uint16_t pr_policy; uint32_t pr_value; Stewart, et al. Expires January 13, 2011 [Page 32] Internet-Draft SCTP sockets API July 2010 }; pr_policy: This specifies which PR-SCTP policy is used. Using SCTP_PR_SCTP_NONE results in a reliable transmission. When SCTP_PR_SCTP_TTL is used, the PR-SCTP policy "timed reliability" defined in [RFC3758] is used. In this case, the lifetime is provided in pr_value. pr_value: The meaning of this field depends on the PR-SCTP policy specified by the pr_policy field. It is ignored when SCTP_PR_SCTP_NONE is specified. In case of SCTP_PR_SCTP_TTL the lifetime in milliseconds is specified. An sctp_prinfo item always corresponds to the data in msg_iov. 5.2.8. SCTP AUTH Information Structure (SCTP_AUTHINFO) This cmsghdr structure specifies SCTP options for sendmsg(). +--------------+---------------+----------------------+ | cmsg_level | cmsg_type | cmsg_data[] | +--------------+---------------+----------------------+ | IPPROTO_SCTP | SCTP_AUTHINFO | struct sctp_authinfo | +--------------+---------------+----------------------+ The sctp_authinfo structure is defined below: struct sctp_authinfo { uint16_t auth_keyid; }; auth_keyid: This specifies the shared key identifier used for sending the user message. An sctp_authinfo item always corresponds to the data in msg_iov. Please note that the SCTP implementation must not bundle user messages that needs to be authenticated using different shared key identifiers. 5.2.9. SCTP Destination Address Structure (IPv4) (SCTP_DSTADDRV4) This cmsghdr structure specifies SCTP options for sendmsg(). +--------------+----------------+----------------+ | cmsg_level | cmsg_type | cmsg_data[] | +--------------+----------------+----------------+ | IPPROTO_SCTP | SCTP_DSTADDRV4 | struct in_addr | +--------------+----------------+----------------+ Stewart, et al. Expires January 13, 2011 [Page 33] Internet-Draft SCTP sockets API July 2010 This ancillary data can be used to provide more than one destination address to sendmsg(). It can be used to implement sctp_sendxxx() using send_msg(). 5.2.10. SCTP Destination Address Structure (IPv6) (SCTP_DSTADDRV6) This cmsghdr structure specifies SCTP options for sendmsg(). +--------------+----------------+-----------------+ | cmsg_level | cmsg_type | cmsg_data[] | +--------------+----------------+-----------------+ | IPPROTO_SCTP | SCTP_DSTADDRV6 | struct in6_addr | +--------------+----------------+-----------------+ This ancillary data can be used to provide more than one destination address to sendmsg(). It can be used to implement sctp_sendxxx() using send_msg(). 5.3. SCTP Events and Notifications An SCTP application may need to understand and process events and errors that happen on the SCTP stack. These events include network status changes, association startups, remote operational errors and undeliverable messages. All of these can be essential for the application. When an SCTP application layer does a recvmsg() the message read is normally a data message from a peer endpoint. If the application wishes to have the SCTP stack deliver notifications of non-data events, it sets the appropriate socket option for the notifications it wants. See Section 7.4 for these socket options. When a notification arrives, recvmsg() returns the notification in the application-supplied data buffer via msg_iov, and sets MSG_NOTIFICATION in msg_flags. This section details the notification structures. Every notification structure carries some common fields which provide general information. A recvmsg() call will return only one notification at a time. Just as when reading normal data, it may return part of a notification if the msg_iov buffer is not large enough. If a single read is not sufficient, msg_flags will have MSG_EOR clear. The user must finish reading the notification before subsequent data can arrive. Stewart, et al. Expires January 13, 2011 [Page 34] Internet-Draft SCTP sockets API July 2010 5.3.1. SCTP Notification Structure The notification structure is defined as the union of all notification types. union sctp_notification { struct sctp_tlv { uint16_t sn_type; /* Notification type. */ uint16_t sn_flags; uint32_t sn_length; } sn_header; struct sctp_assoc_change sn_assoc_change; struct sctp_paddr_change sn_paddr_change; struct sctp_remote_error sn_remote_error; struct sctp_send_failed sn_send_failed; struct sctp_shutdown_event sn_shutdown_event; struct sctp_adaptation_event sn_adaptation_event; struct sctp_pdapi_event sn_pdapi_event; struct sctp_authkey_event sn_auth_event; struct sctp_sender_dry_event sn_sender_dry_event; }; sn_type: The following list describes the SCTP notification and event types for the field sn_type. SCTP_ASSOC_CHANGE: This tag indicates that an association has either been opened or closed. Refer to Section 5.3.2 for details. SCTP_PEER_ADDR_CHANGE: This tag indicates that an address that is part of an existing association has experienced a change of state (e.g. a failure or return to service of the reachability of an endpoint via a specific transport address). Please see Section 5.3.3 for data structure details. SCTP_REMOTE_ERROR: The attached error message is an Operational Error received from the remote peer. It includes the complete TLV sent by the remote endpoint. See Section 5.3.4 for the detailed format. SCTP_SEND_FAILED: The attached datagram could not be sent to the remote endpoint. This structure includes the original SCTP_SNDRCVINFO that was used in sending this message i.e. this structure uses the sctp_sndrcvinfo per Section 5.3.5. SCTP_SHUTDOWN_EVENT: The peer has sent a SHUTDOWN. No further data should be sent on this socket. SCTP_ADAPTATION_INDICATION: This notification holds the peer's indicated adaptation layer. Please see Section 5.3.7. Stewart, et al. Expires January 13, 2011 [Page 35] Internet-Draft SCTP sockets API July 2010 SCTP_PARTIAL_DELIVERY_EVENT: This notification is used to tell a receiver that the partial delivery has been aborted. This may indicate the association is about to be aborted. Please see Section 5.3.8. SCTP_AUTHENTICATION_EVENT: This notification is used to tell a receiver that either an error occurred on authentication, or a new key was made active. See Section 5.3.9. SCTP_SENDER_DRY_EVENT: This notification is used to inform the application that the sender has no user data queued anymore, neither for transmission nor retransmission. See Section 5.3.10. sn_flags: These are notification-specific flags. sn_length: This is the length of the whole sctp_notification structure including the sn_type, sn_flags, and sn_length fields. 5.3.2. SCTP_ASSOC_CHANGE Communication notifications inform the ULP that an SCTP association has either begun or ended. The identifier for a new association is provided by this notification. The notification information has the following format: struct sctp_assoc_change { uint16_t sac_type; uint16_t sac_flags; uint32_t sac_length; uint16_t sac_state; uint16_t sac_error; uint16_t sac_outbound_streams; uint16_t sac_inbound_streams; sctp_assoc_t sac_assoc_id; uint8_t sac_info[]; }; sac_type: It should be SCTP_ASSOC_CHANGE. sac_flags: Currently unused. sac_length: This field is the total length of the notification data, including the notification header. sac_state: This field holds one of a number of values that communicate the event that happened to the association. They include: SCTP_COMM_UP: A new association is now ready and data may be exchanged with this peer. When an association has been established successfully, this notification should be the first one. Stewart, et al. Expires January 13, 2011 [Page 36] Internet-Draft SCTP sockets API July 2010 SCTP_COMM_LOST: The association has failed. The association is now in the closed state. If SEND FAILED notifications are turned on, a SCTP_COMM_LOST is accompanied by a series of SCTP_SEND_FAILED events, one for each outstanding message. SCTP_RESTART: SCTP has detected that the peer has restarted. SCTP_SHUTDOWN_COMP: The association has gracefully closed. SCTP_CANT_STR_ASSOC: The association failed to setup. If non blocking mode is set and data was sent (on a one-to-many style socket), a SCTP_CANT_STR_ASSOC is accompanied by a series of SCTP_SEND_FAILED events, one for each outstanding message. sac_error: If the state was reached due to an error condition (e.g. SCTP_COMM_LOST) any relevant error information is available in this field. This corresponds to the protocol error codes defined in [RFC4960]. sac_outbound_streams: sac_inbound_streams: The maximum number of streams allowed in each direction are available in sac_outbound_streams and sac_inbound streams. sac_assoc_id: The association id field holds the identifier for the association. All notifications for a given association have the same association identifier. For a one-to-one style socket, this field is ignored. sac_info: If the sac_state is SCTP_COMM_LOST and an ABORT chunk was received for this association, sac_info[] contains the complete ABORT chunk as defined in the SCTP specification [RFC4960] section 3.3.7. If the sac_state is SCTP_COMM_UP or SCTP_RESTART, sac_info may contain an array of uint8_t describing the features that the current association supports. Features may include SCTP_ASSOC_SUPPORTS_PR: Both endpoints support the protocol extension described in [RFC3758]. SCTP_ASSOC_SUPPORTS_AUTH: Both endpoints support the protocol extension described in [RFC4895]. SCTP_ASSOC_SUPPORTS_ASCONF: Both endpoints support the protocol extension described in [RFC5061]. SCTP_ASSOC_SUPPORTS_MULTIBUF: For a one-to-many style socket, the local endpoints use separate send and/or receive buffers for each SCTP association. 5.3.3. SCTP_PEER_ADDR_CHANGE When a destination address of a multi-homed peer encounters a state change a peer address change event is sent. The notification has the following format: Stewart, et al. Expires January 13, 2011 [Page 37] Internet-Draft SCTP sockets API July 2010 struct sctp_paddr_change { uint16_t spc_type; uint16_t spc_flags; uint32_t spc_length; struct sockaddr_storage spc_aaddr; uint32_t spc_state; uint32_t spc_error; sctp_assoc_t spc_assoc_id; } spc_type: It should be SCTP_PEER_ADDR_CHANGE. spc_flags: Currently unused. spc_length: This field is the total length of the notification data, including the notification header. spc_aaddr: The affected address field holds the remote peer's address that is encountering the change of state. spc_state: This field holds one of a number of values that communicate the event that happened to the address. They include: SCTP_ADDR_AVAILABLE: This address is now reachable. This notification is provided whenever an address becomes reachable and was unreachable. SCTP_ADDR_UNREACHABLE: The address specified can no longer be reached. Any data sent to this address is rerouted to an alternate until this address becomes reachable. This notification is provided whenever an address becomes unreachable and was reachable. SCTP_ADDR_REMOVED: The address is no longer part of the association. SCTP_ADDR_ADDED: The address is now part of the association. SCTP_ADDR_MADE_PRIM: This address has now been made to be the primary destination address. SCTP_ADDR_CONFIRMED: This address has now been confirmed as a valid address. This notification is provided once for each address as soon as the address is confirmed. spc_error: If the state was reached due to any error condition (e.g. SCTP_ADDR_UNREACHABLE) any relevant error information is available in this field. spc_assoc_id: The association id field holds the identifier for the association. All notifications for a given association have the same association identifier. For a one-to-one style socket, this field is ignored. 5.3.4. SCTP_REMOTE_ERROR A remote peer may send an Operational Error message to its peer. This message indicates a variety of error conditions on an association. The entire ERROR chunk as it appears on the wire is included in an SCTP_REMOTE_ERROR event. Please refer to the SCTP Stewart, et al. Expires January 13, 2011 [Page 38] Internet-Draft SCTP sockets API July 2010 specification [RFC4960] and any extensions for a list of possible error formats. An SCTP error notification has the following format: struct sctp_remote_error { uint16_t sre_type; uint16_t sre_flags; uint32_t sre_length; uint16_t sre_error; sctp_assoc_t sre_assoc_id; uint8_t sre_data[]; }; sre_type: It should be SCTP_REMOTE_ERROR. sre_flags: Currently unused. sre_length: This field is the total length of the notification data, including the notification header and the contents of sre_data. sre_error: This value represents one of the Operational Error causes defined in the SCTP specification, in network byte order. sre_assoc_id: The association id field holds the identifier for the association. All notifications for a given association have the same association identifier. For a one-to-one style socket, this field is ignored. sre_data: This contains the ERROR chunk as defined in the SCTP specification [RFC4960] section 3.3.10. 5.3.5. SCTP_SEND_FAILED Please note that this notification is deprecated. If SCTP cannot deliver a message, it can return back the message as a notification if the SCTP_SEND_FAILED event is enabled. The notification has the following format: struct sctp_send_failed { uint16_t ssf_type; uint16_t ssf_flags; uint32_t ssf_length; uint32_t ssf_error; struct sctp_sndrcvinfo ssf_info; sctp_assoc_t ssf_assoc_id; uint8_t ssf_data[]; }; ssf_type: It should be SCTP_SEND_FAILED. Stewart, et al. Expires January 13, 2011 [Page 39] Internet-Draft SCTP sockets API July 2010 ssf_flags: The flag value will take one of the following values: SCTP_DATA_UNSENT: Indicates that the data was never put on the wire. SCTP_DATA_SENT: Indicates that the data was put on the wire. Note that this does not necessarily mean that the data was (or was not) successfully delivered. ssf_length: This field is the total length of the notification data, including the notification header and the payload in ssf_data. ssf_error: This value represents the reason why the send failed, and if set, will be an SCTP protocol error code as defined in [RFC4960] section 3.3.10. ssf_info: The send information associated with the undelivered message. The ssf_info.sinfo_flags field will also contain an indication if the beginning of the message and/or end of the message is present. In cases where no data has been sent on the wire, this field will have or'ed in the value SCTP_DATA_NOT_FRAG, which is a composition of both a "BEGIN" and "END" fragmentation bit. In cases where only part of the data has been sent, this field will have or'ed in the value SCTP_DATA_LAST_FRAG, which corresponds to the "END" bit. Note that the message itself may be more than one chunk. If the ssf_info.sinfo_flags field holds neither of these two values then a piece that has been fragmented and sent but not acknowledged is present. This piece is from an unspecified position in the message and the application can make no assumptions about the data itself. Applications wanting to examine a recovered message should look for the SCTP_DATA_NOT_FRAG. Without this flag the application should assume part of the message arrived and take appropriate steps to audit and recover any lost or missing data. ssf_assoc_id: The association id field, ssf_assoc_id, holds the identifier for the association. All notifications for a given association have the same association identifier. For a one-to- one style socket, this field is ignored. ssf_data: The undelivered message or part of the undelivered message will be present in the ssf_data field. Note that the ssf_info.sinfo_flags field as noted above should be used to determine if a complete message is present or just a piece of the message. Note that only user data is present in this field, any chunk headers or SCTP common headers must be removed by the SCTP stack. 5.3.6. SCTP_SHUTDOWN_EVENT When a peer sends a SHUTDOWN, SCTP delivers this notification to inform the application that it should cease sending data. Stewart, et al. Expires January 13, 2011 [Page 40] Internet-Draft SCTP sockets API July 2010 struct sctp_shutdown_event { uint16_t sse_type; uint16_t sse_flags; uint32_t sse_length; sctp_assoc_t sse_assoc_id; }; sse_type: It should be SCTP_SHUTDOWN_EVENT. sse_flags: Currently unused. sse_length: This field is the total length of the notification data, including the notification header. It will generally be sizeof (struct sctp_shutdown_event). sse_flags: Currently unused. sse_assoc_id: The association id field holds the identifier for the association. All notifications for a given association have the same association identifier. For a one-to-one style socket, this field is ignored. 5.3.7. SCTP_ADAPTATION_INDICATION When a peer sends an Adaptation Layer Indication parameter as described in [RFC5061], SCTP delivers this notification to inform the application about the peer's adaptation layer indication. struct sctp_adaptation_event { uint16_t sai_type; uint16_t sai_flags; uint32_t sai_length; uint32_t sai_adaptation_ind; sctp_assoc_t sai_assoc_id; }; sai_type: It should be SCTP_ADAPTATION_INDICATION. sai_flags: Currently unused. sai_length: This field is the total length of the notification data, including the notification header. It will generally be sizeof (struct sctp_adaptation_event). sai_adaptation_ind: This field holds the bit array sent by the peer in the adaptation layer indication parameter. The bits are in network byte order. sai_assoc_id: The association id field holds the identifier for the association. All notifications for a given association have the same association identifier. For a one-to-one style socket, this field is ignored. Stewart, et al. Expires January 13, 2011 [Page 41] Internet-Draft SCTP sockets API July 2010 5.3.8. SCTP_PARTIAL_DELIVERY_EVENT When a receiver is engaged in a partial delivery of a message this notification will be used to indicate various events. struct sctp_pdapi_event { uint16_t pdapi_type; uint16_t pdapi_flags; uint32_t pdapi_length; uint32_t pdapi_indication; uint32_t pdapi_stream; uint32_t pdapi_seq; sctp_assoc_t pdapi_assoc_id; }; pdapi_type: It should be SCTP_PARTIAL_DELIVERY_EVENT. pdapi_flags: Currently unused. pdapi_length: This field is the total length of the notification data, including the notification header. It will generally be sizeof(struct sctp_pdapi_event). pdapi_indication: This field holds the indication being sent to the application. Currently there is only one defined value: SCTP_PARTIAL_DELIVERY_ABORTED: This indicates that the partial delivery of a user message has been aborted. This happens, for example, if an association is aborted while a partial delivery is going on or the user message gets abandoned using PR-SCTP while the partial delivery of this message is going on. pdapi_stream: This field holds the stream on which the partial delivery event happened. pdapi_seq: This field holds the stream sequence number which was being partially delivered. pdapi_assoc_id: The association id field holds the identifier for the association. All notifications for a given association have the same association identifier. For a one-to-one style socket this field is ignored. 5.3.9. SCTP_AUTHENTICATION_EVENT [RFC4895] defines an extension to authenticate SCTP messages. The following notification is used to report different events relating to the use of this extension. Stewart, et al. Expires January 13, 2011 [Page 42] Internet-Draft SCTP sockets API July 2010 struct sctp_authkey_event { uint16_t auth_type; uint16_t auth_flags; uint32_t auth_length; uint16_t auth_keynumber; uint32_t auth_indication; sctp_assoc_t auth_assoc_id; }; auth_type: It should be SCTP_AUTHENTICATION_EVENT. auth_flags: Currently unused. auth_length: This field is the total length of the notification data, including the notification header. It will generally be sizeof (struct sctp_authkey_event). auth_keynumber: This field holds the keynumber for the affected key indicated in the event (depends on auth_indication). auth_indication: This field holds the error or indication being reported. The following values are currently defined: SCTP_AUTH_NEW_KEY: This report indicates that a new key has been made active (used for the first time by the peer) and is now the active key. The auth_keynumber field holds the user specified key number. SCTP_AUTH_NO_AUTH: This report indicates that the peer does not support SCTP AUTH as defined in [RFC4895]. SCTP_AUTH_FREE_KEY: This report indicates that the SCTP implementation will not use the key identifier specified in auth_keynumber anymore. auth_assoc_id: The association id field holds the identifier for the association. All notifications for a given association have the same association identifier. For a one-to-one style socket this field is ignored. 5.3.10. SCTP_SENDER_DRY_EVENT When the SCTP implementation has no user data anymore to send or retransmit, this notification is given to the user. If the user subscribes to this event and SCTP has at this point of time no user data to send or retransmit, this notification is also given to the user. struct sctp_sender_dry_event { uint16_t sender_dry_type; uint16_t sender_dry_flags; uint32_t sender_dry_length; sctp_assoc_t sender_dry_assoc_id; }; Stewart, et al. Expires January 13, 2011 [Page 43] Internet-Draft SCTP sockets API July 2010 sender_dry_type: It should be SCTP_SENDER_DRY_EVENT. sender_dry_flags: Currently unused. sender_dry_length: This field is the total length of the notification data, including the notification header. It will generally be sizeof(struct sctp_sender_dry_event). 5.3.11. SCTP_NOTIFICATIONS_STOPPED_EVENT Notifications, when subscribed to, are reliable. They are always delivered as long as there is space in the socket receive buffer. However, if an implementation experiences a notification storm, it may run out of socket buffer space. When this occurs it may wish to disable notifications. If the implementation chooses to do this, it will append a final notification SCTP_NOTIFICATIONS_STOPPED_EVENT. This notification is an union sctp_notification, where only the struct sctp_tlv (see the union above) is used. That merely has this type in the sn_type field, the sn_length field set to the sizeof an sctp_tlv structure and the sn_flags set to 0. If an application receives this notification, it will need to resubscribe to any notifications of interest to it, except for the data io event. An endpoint is automatically subscribed to this event as soon as it is subscribed to any event other than data io events. 5.3.12. SCTP_SEND_FAILED_EVENT If SCTP cannot deliver a message, it can return back the message as a notification if the SCTP_SEND_FAILED_EVENT event is enabled. The notification has the following format: struct sctp_send_failed { uint16_t ssf_type; uint16_t ssf_flags; uint32_t ssf_length; uint32_t ssf_error; struct sctp_sndinfo ssf_info; sctp_assoc_t ssf_assoc_id; uint8_t ssf_data[]; }; ssf_type: It should be SCTP_SEND_FAILED_EVENT. ssf_flags: The flag value will take one of the following values: SCTP_DATA_UNSENT: Indicates that the data was never put on the wire. Stewart, et al. Expires January 13, 2011 [Page 44] Internet-Draft SCTP sockets API July 2010 SCTP_DATA_SENT: Indicates that the data was put on the wire. Note that this does not necessarily mean that the data was (or was not) successfully delivered. ssf_length: This field is the total length of the notification data, including the notification header and the payload in ssf_data. ssf_error: This value represents the reason why the send failed, and if set, will be an SCTP protocol error code as defined in [RFC4960] section 3.3.10. ssf_info: The send information associated with the undelivered message. The ssf_info.snd_flags field will also contain an indication if the beginning of the message and/or end of the message is present. In cases where no data has been sent on the wire, this field will have or'ed in the value SCTP_DATA_NOT_FRAG, which is a composition of both a "BEGIN" and "END" fragmentation bit. In cases where only part of the data has been sent, this field will have or'ed in the value SCTP_DATA_LAST_FRAG, which corresponds to the "END" bit. Note that the message itself may be more than one chunk. If the ssf_info.snd_flags field holds neither of these two values then a piece that has been fragmented and sent but not acknowledged is present. This piece is from an unspecified position in the message and the application can make no assumptions about the data itself. Applications wanting to examine a recovered message should look for the SCTP_DATA_NOT_FRAG. Without this flag the application should assume part of the message arrived and take appropriate steps to audit and recover any lost or missing data. ssf_assoc_id: The association id field, ssf_assoc_id, holds the identifier for the association. All notifications for a given association have the same association identifier. For a one-to- one style socket, this field is ignored. ssf_data: The undelivered message or part of the undelivered message will be present in the ssf_data field. Note that the ssf_info.sinfo_flags field as noted above should be used to determine if a complete message is present or just a piece of the message. Note that only user data is present in this field, any chunk headers or SCTP common headers must be removed by the SCTP stack. 5.4. Ancillary Data Considerations and Semantics Programming with ancillary socket data contains some subtleties and pitfalls, which are discussed below. 5.4.1. Multiple Items and Ordering Multiple ancillary data items may be included in any call to sendmsg() or recvmsg(); these may include multiple SCTP or non-SCTP items, or both. Stewart, et al. Expires January 13, 2011 [Page 45] Internet-Draft SCTP sockets API July 2010 The ordering of ancillary data items (either by SCTP or another protocol) is not significant and is implementation-dependent, so applications must not depend on any ordering. SCTP_SNDRCV/SCTP_SNDINFO/SCTP_RCVINFO type ancillary data always correspond to the data in the msghdr's msg_iov member. There can be only one single such type ancillary data for each sendmsg() or recvmsg() call. 5.4.2. Accessing and Manipulating Ancillary Data Applications can infer the presence of data or ancillary data by examining the msg_iovlen and msg_controllen msghdr members, respectively. Implementations may have different padding requirements for ancillary data, so portable applications should make use of the macros CMSG_FIRSTHDR, CMSG_NXTHDR, CMSG_DATA, CMSG_SPACE, and CMSG_LEN. See [RFC3542] and the SCTP implementation's documentation for more information. The following is an example, from [RFC3542], demonstrating the use of these macros to access ancillary data: struct msghdr msg; struct cmsghdr *cmsgptr; /* fill in msg */ /* call recvmsg() */ for (cmsgptr = CMSG_FIRSTHDR(&msg); cmsgptr != NULL; cmsgptr = CMSG_NXTHDR(&msg, cmsgptr)) { if (cmsgptr->cmsg_level == ... && cmsgptr->cmsg_type == ... ) { u_char *ptr; ptr = CMSG_DATA(cmsgptr); /* process data pointed to by ptr */ } } 5.4.3. Control Message Buffer Sizing The information conveyed via SCTP_SNDRCV/SCTP_SNDINFO/SCTP_RCVINFO ancillary data will often be fundamental to the correct and sane operation of the sockets application. This is particularly true of the one-to-many semantics, but also of the one-to-one semantics. For example, if an application needs to send and receive data on different SCTP streams, SCTP_SNDRCV/SCTP_SNDINFO/SCTP_RCVINFO ancillary data is indispensable. Stewart, et al. Expires January 13, 2011 [Page 46] Internet-Draft SCTP sockets API July 2010 Given that some ancillary data is critical, and that multiple ancillary data items may appear in any order, applications should be carefully written to always provide a large enough buffer to contain all possible ancillary data that can be presented by recvmsg(). If the buffer is too small, and crucial data is truncated, it may pose a fatal error condition. Thus, it is essential that applications be able to deterministically calculate the maximum required buffer size to pass to recvmsg(). One constraint imposed on this specification that makes this possible is that all ancillary data definitions are of a fixed length. One way to calculate the maximum required buffer size might be to take the sum the sizes of all enabled ancillary data item structures, as calculated by CMSG_SPACE. For example, if we enabled SCTP_SNDRCV_INFO and IPV6_RECVPKTINFO [RFC3542], we would calculate and allocate the buffer size as follows: size_t total; void *buf; total = CMSG_SPACE(sizeof (struct sctp_sndrcvinfo)) + CMSG_SPACE(sizeof (struct in6_pktinfo)); buf = malloc(total); We could then use this buffer (buf) for msg_control on each call to recvmsg() and be assured that we would not lose any ancillary data to truncation. 6. Common Operations for Both Styles 6.1. send(), recv(), sendto(), and recvfrom() Applications can use send() and sendto() to transmit data to the peer of an SCTP endpoint. recv() and recvfrom() can be used to receive data from the peer. The function prototypes are ssize_t send(int sd, const void *msg, size_t len, int flags); Stewart, et al. Expires January 13, 2011 [Page 47] Internet-Draft SCTP sockets API July 2010 ssize_t sendto(int sd, const void *msg, size_t len, int flags, const struct sockaddr *to, socklen_t tolen); ssize_t recv(int sd, void *buf, size_t len, int flags); ssize_t recvfrom(int sd, void *buf, size_t len, int flags, struct sockaddr *from, socklen_t *fromlen); and the arguments are sd: The socket descriptor of an SCTP endpoint. msg: The message to be sent. len: the size of the message or the size of the buffer. to: one of the peer addresses of the association to be used to send the message. tolen: The size of the address. buf: The buffer to store a received message. from: The buffer to store the peer address used to send the received message. fromlen: The size of the from address. flags: (described below). These calls give access to only basic SCTP protocol features. If either peer in the association uses multiple streams, or sends unordered data, these calls will usually be inadequate, and may deliver the data in unpredictable ways. SCTP has the concept of multiple streams in one association. The above calls do not allow the caller to specify on which stream a message should be sent. The system uses stream 0 as the default stream for send() and sendto(). recv() and recvfrom() return data from any stream, but the caller can not distinguish the different streams. This may result in data seeming to arrive out of order. Similarly, if a data chunk is sent unordered, recv() and recvfrom() provide no indication. Stewart, et al. Expires January 13, 2011 [Page 48] Internet-Draft SCTP sockets API July 2010 SCTP is message based. The msg buffer above in send() and sendto() is considered to be a single message. This means that if the caller wants to send a message that is composed by several buffers, the caller needs to combine them before calling send() or sendto(). Alternately, the caller can use sendmsg() to do that without combining them. Sending a message using send() or sendto() is atomic unless explicit EOR marking is enabled on the socket specified by sd. Using sendto() on a non-connected one-to-one style socket for implicit connection setup may or may not work depending on the SCTP implementation. recv() and recvfrom() cannot distinguish message boundaries. In receiving, if the buffer supplied is not large enough to hold a complete message, the receive call acts like a stream socket and returns as much data as will fit in the buffer. Note, the send() and recv() calls may not be used for a one-to-many style socket. Note, if an application calls a send function with no user data and no ancillary data the SCTP implementation should reject the request with an appropriate error message. An implementation is not allowed to send a DATA chunk with no user data [RFC4960]. 6.2. setsockopt() and getsockopt() Applications use setsockopt() and getsockopt() to set or retrieve socket options. Socket options are used to change the default behavior of socket calls. They are described in Section 7. The function prototypes are int getsockopt(int sd, int level, int optname, void *optval, socklen_t *optlen); and int setsockopt(int sd, int level, int optname, const void *optval, socklen_t optlen); and the arguments are Stewart, et al. Expires January 13, 2011 [Page 49] Internet-Draft SCTP sockets API July 2010 sd: The socket descriptor. level: Set to IPPROTO_SCTP for all SCTP options. optname: The option name. optval: The buffer to store the value of the option. optlen: The size of the buffer (or the length of the option returned). All socket options set on a one-to-one style listening socket also apply to all accepted sockets. For one-to-many style sockets often a socket option will pass a structure that includes an assoc_id field. This field can be filled with the association id of a particular association and unless otherwise specified can be filled with one of the following constants: SCTP_FUTURE_ASSOC: Specifies that only future associations created after this socket option will be affected by this call. SCTP_CURRENT_ASSOC: Specifies that only currently existing associations will be affected by this call, future associations will still receive the previous default value. SCTP_ALL_ASSOC: Specifies that all current and future associations will be affected by this call. 6.3. read() and write() Applications can use read() and write() to send and receive data to and from a peer. They have the same semantics as send() and recv() except that the flags parameter cannot be used. Note, these calls, when used in the one-to-many style, should only be used with branched off socket descriptors (see Section 8.2). 6.4. getsockname() Applications use getsockname() to retrieve the locally-bound socket address of the specified socket. This is especially useful if the caller let SCTP choose a local port. This call is for single homed endpoints. It does not work well with multi-homed endpoints. See Section 8.5 for a multi-homed version of the call. The function prototype is int getsockname(int sd, struct sockaddr *address, socklen_t *len); and the arguments are Stewart, et al. Expires January 13, 2011 [Page 50] Internet-Draft SCTP sockets API July 2010 sd: The socket descriptor to be queried. address: On return, one locally bound address (chosen by the SCTP stack) is stored in this buffer. If the socket is an IPv4 socket, the address will be IPv4. If the socket is an IPv6 socket, the address will be either an IPv6 or IPv4 address. len: The caller should set the length of the address here. On return, this is set to the length of the returned address. If the actual length of the address is greater than the length of the supplied sockaddr structure, the stored address will be truncated. If the socket has not been bound to a local name, the value stored in the object pointed to by address is unspecified. 6.5. Implicit Association Setup Once the bind() call is complete, the application can begin sending and receiving data using the sendmsg()/recvmsg() or sendto()/ recvfrom() calls, without going through any explicit association setup procedures (i.e., no connect() calls required). Whenever sendmsg() or sendto() is called and the SCTP stack at the sender finds that no association exists between the sender and the intended receiver (identified by the address passed either in the msg_name field of msghdr structure in the sendmsg() call or the dest_addr field in the sendto() call), the SCTP stack will automatically setup an association to the intended receiver. Upon the successful association setup an SCTP_COMM_UP notification will be dispatched to the socket at both the sender and receiver side. This notification can be read by the recvmsg() system call (see Section 3.1.3). Note, if the SCTP stack at the sender side supports bundling, the first user message may be bundled with the COOKIE ECHO message [RFC4960]. When the SCTP stack sets up a new association implicitly, the SCTP_INIT type ancillary data may also be passed along (see Section 5.2.1 for details of the data structures) to change some parameters used in setting up new association. If this information is not present in the sendmsg() call, or if the implicit association setup is triggered by a sendto() call, the default association initialization parameters will be used. These default association parameters may be set with respective setsockopt() calls or be left to the system defaults. Stewart, et al. Expires January 13, 2011 [Page 51] Internet-Draft SCTP sockets API July 2010 Implicit association setup cannot be initiated by send() calls. 7. Socket Options The following sub-section describes various SCTP level socket options that are common to both styles. SCTP associations can be multi- homed. Therefore, certain option parameters include a sockaddr_storage structure to select which peer address the option should be applied to. For the one-to-many style sockets, an sctp_assoc_t (association ID) parameter is used to identify the association instance that the operation affects. So it must be set when using this style. For the one-to-one style sockets and branched off one-to-many style sockets (see Section 8.2) this association ID parameter is ignored. Note that socket or IP level options are set or retrieved per socket. This means that for one-to-many style sockets, the options will be applied to all associations (similar to using SCTP_ALL_ASSOC as the association ID) belonging to the socket. For one-to-one style, these options will be applied to all peer addresses of the association controlled by the socket. Applications should be careful in setting those options. For some IP stacks getsockopt() is read-only; so a new interface will be needed when information must be passed both into and out of the SCTP stack. The syntax for sctp_opt_info() is int sctp_opt_info(int sd, sctp_assoc_t id, int opt, void *arg, socklen_t *size); The sctp_opt_info() call is a replacement for getsockopt() only and will not set any options associated with the specified socket. A setsockopt() must be used to set any writeable option. For one-to-many style sockets, id specifies the association to query. For one-to-one style sockets, id is ignored. For one-to-many sockets, any association identifier in the structure provided as arg is ignored and id takes precedence. Note that SCTP_CURRENT_ASSOC and SCTP_ALL_ASSOC cannot be used here. Using them will result in an error (returning -1 and errno set to EINVAL). SCTP_FUTURE_ASSOC can be used to query information for Stewart, et al. Expires January 13, 2011 [Page 52] Internet-Draft SCTP sockets API July 2010 future associations. The field opt specifies which SCTP socket option to get. It can get any socket option currently supported that requests information (either read/write options or read only) such as: SCTP_RTOINFO SCTP_ASSOCINFO SCTP_DEFAULT_SEND_PARAM SCTP_GET_PEER_ADDR_INFO SCTP_PRIMARY_ADDR SCTP_PEER_ADDR_PARAMS SCTP_STATUS SCTP_CONTEXT SCTP_AUTH_ACTIVE_KEY SCTP_PEER_AUTH_CHUNKS SCTP_LOCAL_AUTH_CHUNKS The arg field is an option-specific structure buffer provided by the caller. See Section 8.5 subsections for more information on these options and option-specific structures. sctp_opt_info() returns 0 on success, or on failure returns -1 and sets errno to the appropriate error code. All options that support specific settings on an association by filling in either an association id variable or a sockaddr_storage should also support the setting of the same value for the entire endpoint (i.e. future associations). To accomplish this the following logic is used when setting one of these options: o If an address is specified via a sockaddr_storage that is included in the structure, the address is used to lookup the association and the settings are applied to the specific address (if appropriate) or to the entire association. o If an association identification is filled in but not a sockaddr_storage (if present), the association is found using the association identification and the settings should be applied to the specified association (since a specific address is not specified). Note this also applies to options that hold an association identification in their structure but do not have a sockaddr_storage field. o If neither the sockaddr_storage nor association identification is set, i.e. the sockaddr_storage is set to all 0 (INADDR_ANY) and the association identification is SCTP_FUTURE_ASSOC, the settings are a default and to be applied to the endpoint. Stewart, et al. Expires January 13, 2011 [Page 53] Internet-Draft SCTP sockets API July 2010 7.1. Read / Write Options 7.1.1. Retransmission Timeout Parameters (SCTP_RTOINFO) The protocol parameters used to initialize and limit the retransmission timeout (RTO) are tunable. See [RFC4960] for more information on how these parameters are used in RTO calculation. The following structure is used to access and modify these parameters: struct sctp_rtoinfo { sctp_assoc_t srto_assoc_id; uint32_t srto_initial; uint32_t srto_max; uint32_t srto_min; }; srto_initial: This contains the initial RTO value. srto_max and srto_min: These contain the maximum and minimum bounds for all RTOs. srto_assoc_id: This parameter is ignored for one-to-one style sockets. For one-to-many style sockets the application may fill in an association identification or SCTP_FUTURE_ASSOC. It is an error to use SCTP_{CURRENT|ALL}_ASSOC in srto_asssoc_id. All times are given in milliseconds. A value of 0, when modifying the parameters, indicates that the current value should not be changed. To access or modify these parameters, the application should call getsockopt() or setsockopt() respectively with the option name SCTP_RTOINFO. 7.1.2. Association Parameters (SCTP_ASSOCINFO) This option is used to both examine and set various association and endpoint parameters. See [RFC4960] for more information on how this parameter is used. The following structure is used to access and modify these parameters: Stewart, et al. Expires January 13, 2011 [Page 54] Internet-Draft SCTP sockets API July 2010 struct sctp_assocparams { sctp_assoc_t sasoc_assoc_id; uint16_t sasoc_asocmaxrxt; uint16_t sasoc_number_peer_destinations; uint32_t sasoc_peer_rwnd; uint32_t sasoc_local_rwnd; uint32_t sasoc_cookie_life; }; sasoc_assoc_id: This parameter is ignored for one-to-one style sockets. For one-to-many style sockets the application may fill in an association identification or SCTP_FUTURE_ASSOC. It is an error to use SCTP_{CURRENT|ALL}_ASSOC in sasoc_asssoc_id. sasoc_asocmaxrxt: This contains the maximum retransmission attempts to make for the association. sasoc_number_peer_destinations: This is the number of destination addresses that the peer has. sasoc_peer_rwnd: This holds the current value of the peers rwnd (reported in the last SACK) minus any outstanding data (i.e. data in flight). sasoc_local_rwnd: This holds the last reported rwnd that was sent to the peer. sasoc_cookie_life: This is the association's cookie life value used when issuing cookies. The values of the sasoc_peer_rwnd is meaningless when examining endpoint information. All time values are given in milliseconds. A value of 0, when modifying the parameters, indicates that the current value should not be changed. The values of the sasoc_asocmaxrxt and sasoc_cookie_life may be set on either an endpoint or association basis. The rwnd and destination counts (sasoc_number_peer_destinations, sasoc_peer_rwnd, sasoc_local_rwnd) are not settable and any value placed in these is ignored. To access or modify these parameters, the application should call getsockopt() or setsockopt() respectively with the option name SCTP_ASSOCINFO. The maximum number of retransmissions before an address is considered unreachable is also tunable, but is address-specific, so it is covered in a separate option. If an application attempts to set the value of the association maximum retransmission parameter to more than the sum of all maximum retransmission parameters, setsockopt() may return an error. The reason for this, from [RFC4960] section Stewart, et al. Expires January 13, 2011 [Page 55] Internet-Draft SCTP sockets API July 2010 8.2: Note: When configuring the SCTP endpoint, the user should avoid having the value of 'Association.Max.Retrans' (sasoc_maxrt in this option) larger than the summation of the 'Path.Max.Retrans' (see Section 7.1.2 on spp_pathmaxrxt) of all the destination addresses for the remote endpoint. Otherwise, all the destination addresses may become inactive while the endpoint still considers the peer endpoint reachable. 7.1.3. Initialization Parameters (SCTP_INITMSG) Applications can specify protocol parameters for the default association initialization. The structure used to access and modify these parameters is defined in Section 5.2.1. The option name argument to setsockopt() and getsockopt() is SCTP_INITMSG. Setting initialization parameters is effective only on an unconnected socket (for one-to-many style sockets only future associations are affected by the change). With one-to-one style sockets, this option is inherited by sockets derived from a listening socket. 7.1.4. SO_LINGER An application can use this option to perform the SCTP ABORT primitive. This option affects all associations related to the socket. The linger option structure is: struct linger { int l_onoff; /* option on/off */ int l_linger; /* linger time */ }; To enable the option, set l_onoff to 1. If the l_linger value is set to 0, calling close() is the same as the ABORT primitive. If the value is set to a negative value, the setsockopt() call will return an error. If the value is set to a positive value linger_time, the close() can be blocked for at most linger_time ms. If the graceful shutdown phase does not finish during this period, close() will return but the graceful shutdown phase will continue in the system. Note, this is a socket level option not an SCTP level option. So when setting SO_LINGER an application must specify a level of SOL_SOCKET in the setsockopt() call. Stewart, et al. Expires January 13, 2011 [Page 56] Internet-Draft SCTP sockets API July 2010 7.1.5. SCTP_NODELAY Turn on/off any Nagle-like algorithm. This means that packets are generally sent as soon as possible and no unnecessary delays are introduced, at the cost of more packets in the network. Expects an integer boolean flag. Turning this option on disables any Nagle-like algorithm. 7.1.6. SO_RCVBUF Sets the receive buffer size in octets. For SCTP one-to-one style sockets, this controls the receiver window size. For one-to-many style sockets the meaning is implementation dependent. It might control the receive buffer for each association bound to the socket descriptor or it might control the receive buffer for the whole socket. The call expects an integer. 7.1.7. SO_SNDBUF Sets the send buffer size. For SCTP one-to-one style sockets, this controls the amount of data SCTP may have waiting in internal buffers to be sent. This option therefore bounds the maximum size of data that can be sent in a single send call. For one-to-many style sockets, the effect is the same, except that it applies to one or all associations (see Section 3.3) bound to the socket descriptor used in the setsockopt() or getsockopt() call. The option applies to each association's window size separately. The call expects an integer. 7.1.8. Automatic Close of Associations (SCTP_AUTOCLOSE) This socket option is applicable to the one-to-many style socket only. When set it will cause associations that are idle for more than the specified number of seconds to automatically close using the graceful shutdown procedure. An association being idle is defined as an association that has not sent or received user data. The special value of '0' indicates that no automatic close of any association should be performed, this is the default value. The option expects an integer defining the number of seconds of idle time before an association is closed. An application using this option should enable receiving the association change notification. This is the only mechanism an application is informed about the closing of an association. After an association is closed, the association ID assigned to it can be reused. An application should be aware of this to avoid the possible problem of sending data to an incorrect peer endpoint. Stewart, et al. Expires January 13, 2011 [Page 57] Internet-Draft SCTP sockets API July 2010 7.1.9. Set Primary Address (SCTP_PRIMARY_ADDR) Requests that the local SCTP stack uses the enclosed peer address as the association's primary. The enclosed address must be one of the association peer's addresses. The following structure is used to make a set peer primary request: struct sctp_setprim { sctp_assoc_t ssp_assoc_id; struct sockaddr_storage ssp_addr; }; ssp_addr: The address to set as primary. ssp_assoc_id: This parameter is ignored for one-to-one style sockets. For one-to-many style sockets it identifies the association for this request. Note that the special sctp_assoc_t SCTP_{FUTURE|ALL|CURRENT}_ASSOC are not allowed. 7.1.10. Set Adaptation Layer Indicator (SCTP_ADAPTATION_LAYER) Requests that the local endpoint set the specified Adaptation Layer Indication parameter for all future INIT and INIT-ACK exchanges. The following structure is used to access and modify this parameter: struct sctp_setadaptation { uint32_t ssb_adaptation_ind; }; ssb_adaptation_ind: The adaptation layer indicator that will be included in any outgoing Adaptation Layer Indication parameter. 7.1.11. Enable/Disable Message Fragmentation (SCTP_DISABLE_FRAGMENTS) This option is a on/off flag and is passed as an integer where a non- zero is on and a zero is off. If enabled no SCTP message fragmentation will be performed. Instead, if a message being sent exceeds the current PMTU size, the message will not be sent and instead an error will be indicated to the user. 7.1.12. Peer Address Parameters (SCTP_PEER_ADDR_PARAMS) Applications can enable or disable heartbeats for any peer address of an association, modify an address's heartbeat interval, force a heartbeat to be sent immediately, and adjust the address's maximum number of retransmissions sent before an address is considered unreachable. Stewart, et al. Expires January 13, 2011 [Page 58] Internet-Draft SCTP sockets API July 2010 The following structure is used to access and modify an address's parameters: struct sctp_paddrparams { sctp_assoc_t spp_assoc_id; struct sockaddr_storage spp_address; uint32_t spp_hbinterval; uint16_t spp_pathmaxrxt; uint32_t spp_pathmtu; uint32_t spp_flags; uint32_t spp_ipv6_flowlabel; uint8_t spp_ipv4_tos; }; spp_assoc_id: This parameter is ignored for one-to-one style sockets. For one-to-many style sockets it identifies the association for this query. Note that the predefined constants are not allowed. spp_address: This specifies which address is of interest. If a wildcard address is provided it applies to all current and future paths. spp_hbinterval: This contains the value of the heartbeat interval, in milliseconds (HB.Interval in [RFC4960]). Note that unless the spp_flag is set to SPP_HB_ENABLE the value of this field is ignored. Note also that a value of zero indicates the current setting should be left unchanged. To set an actual value of zero the use of the flag SPP_HB_TIME_IS_ZERO should be used. Even when it is set to 0, it does not mean that SCTP will continuously send out heartbeat since the actual interval also includes a the current RTO and jitter (see Section 8.3 in [RFC4960]). spp_pathmaxrxt: This contains the maximum number of retransmissions before this address shall be considered unreachable. Note that a value of zero indicates the current setting should be left unchanged. spp_ipv6_flowlabel: This field is used in conjunction with the SPP_IPV6_FLOWLABEL flag. This setting has precedence over any IPv6 layer setting. spp_ipv4_tos: This field is used in conjunction with the SPP_IPV4_TOS flag. This setting has precedence over any IPv4 layer setting. spp_flags: These flags are used to control various features on an association. The flag field is a bit mask which may contain zero or more of the following options: SPP_HB_ENABLE: Enable heartbeats on the specified address. Stewart, et al. Expires January 13, 2011 [Page 59] Internet-Draft SCTP sockets API July 2010 SPP_HB_DISABLE: Disable heartbeats on the specified address. Note that SPP_HB_ENABLE and SPP_HB_DISABLE are mutually exclusive, only one of these two should be specified. Enabling both fields will have undetermined results. SPP_HB_DEMAND: Request a user initiated heartbeat to be made immediately. This must not be used in conjunction with a wildcard address. SPP_HB_TIME_IS_ZERO: Specifies that the time for heartbeat delay is to be set to the value of 0 milliseconds. SPP_PMTUD_ENABLE: This field will enable PMTU discovery upon the specified address. SPP_PMTUD_DISABLE: This field will disable PMTU discovery upon the specified address. Note that if the address field is empty then all addresses on the association are affected. Note also that SPP_PMTUD_ENABLE and SPP_PMTUD_DISABLE are mutually exclusive. Enabling both will have undetermined results. SPP_IPV6_FLOWLABEL: Setting this flag enables the setting of the IPV6 flowlabel value. The value is obtained in the spp_ipv6_flowlabel field. Upon retrieval, this flag will be set to indicate that the spp_ipv6_flowlabel field has a valid value returned. If a specific destination address is set (in the spp_address field), then the value returned is that of the address. If just an association is specified (and no address), then the association's default flowlabel is returned. If neither an association nor a destination is specified, then the socket's default flowlabel is returned. For non IPv6 sockets, this flag will be left cleared. SPP_IPV4_TOS: Setting this flag enables the setting of the IPV4 TOS value associated with either the association or a specific address. The value is obtained in the spp_ipv4_tos field. Upon retrieval, this flag will be set to indicate that the spp_ipv4_tos field has a valid value returned. If a specific destination address is set when called (in the spp_address field) then that specific destination address' TOS value is returned. If just an association is specified then the association default TOS is returned. If neither an association nor an destination is specified, then the sockets default TOS is returned. To read or modify these parameters, the application should call sctp_opt_info() with the SCTP_PEER_ADDR_PARAMS option. Stewart, et al. Expires January 13, 2011 [Page 60] Internet-Draft SCTP sockets API July 2010 7.1.13. Set Default Send Parameters (SCTP_DEFAULT_SEND_PARAM) Please note that this options is deprecated. Section 7.1.31 should be used instead. Applications that wish to use the sendto() system call may wish to specify a default set of parameters that would normally be supplied through the inclusion of ancillary data. This socket option allows such an application to set the default sctp_sndrcvinfo structure. The application that wishes to use this socket option simply passes the sctp_sndrcvinfo structure defined in Section 5.2.2 to this call. The input parameters accepted by this call include sinfo_stream, sinfo_flags, sinfo_ppid, sinfo_context, sinfo_pr_policy and sinfo_pr_value. The sinfo_flags is composed of a bitwise OR of SCTP_UNORDERED, SCTP_EOF, and SCTP_SENDALL. The sinfo_assoc_id field specifies the association to apply the parameters to. In a one-to- many style sockets any of the predefined constants are also allowed in this field. The field is ignored on the one-to-one style. 7.1.14. Set Notification and Ancillary Events (SCTP_EVENTS) This socket option is used to specify various notifications and ancillary data the user wishes to receive. Please see Section 7.4 for a full description of this option and its usage. Note that this option is considered deprecated and present for backward compatibility. New applications should use the SCTP_SET_EVENT option. See Section 7.4 for a full description of that option as well. 7.1.15. Set/Clear IPv4 Mapped Addresses (SCTP_I_WANT_MAPPED_V4_ADDR) This socket option is a boolean flag which turns on or off the mapping of IPv4 addresses. If this option is turned on and the socket is type PF_INET6, then IPv4 addresses will be mapped to V6 representation. If this option is turned off, then no mapping will be done of V4 addresses and a user will receive both PF_INET6 and PF_INET type addresses on the socket. See [RFC3542] for more details on mapped V6 addresses. By default this option is turned off and expects an integer to be passed where non-zero turns on the option and zero turns off the option. 7.1.16. Get or Set the Maximum Fragmentation Size (SCTP_MAXSEG) This option will get or set the maximum size to put in any outgoing SCTP DATA chunk. If a message is larger than this size it will be fragmented by SCTP into the specified size. Note that the underlying Stewart, et al. Expires January 13, 2011 [Page 61] Internet-Draft SCTP sockets API July 2010 SCTP implementation may fragment into smaller sized chunks when the PMTU of the underlying association is smaller than the value set by the user. The default value for this option is '0' which indicates the user is not limiting fragmentation and only the PMTU will affect SCTP's choice of DATA chunk size. Note also that values set larger than the maximum size of an IP datagram will effectively let SCTP control fragmentation (i.e. the same as setting this option to 0). The following structure is used to access and modify this parameter: struct sctp_assoc_value { sctp_assoc_t assoc_id; uint32_t assoc_value; }; assoc_id: This parameter is ignored for one-to-one style sockets. For one-to-many style sockets this parameter indicates which association the user is performing an action upon. It is an error to use SCTP_{CURRENT|ALL}_ASSOC in sasoc_asssoc_id. assoc_value: This parameter specifies the maximum size in bytes. 7.1.17. Get or Set the List of Supported HMAC Identifiers (SCTP_HMAC_IDENT) This option gets or sets the list of HMAC algorithms that the local endpoint requires the peer to use. The following structure is used to get or set these identifiers: struct sctp_hmacalgo { uint32_t shmac_number_of_idents; uint16_t shmac_idents[]; }; shmac_number_of_idents: This field gives the number of elements present in the array shmac_idents. shmac_idents: This parameter contains an array of HMAC identifiers that the local endpoint is requesting the peer to use, in priority order. The following identifiers are valid: * SCTP_AUTH_HMAC_ID_SHA1 * SCTP_AUTH_HMAC_ID_SHA256 Note that the list supplied must include SCTP_AUTH_HMAC_ID_SHA1 and may include any of the other values in its preferred order (lowest list position has the highest preference in algorithm selection). Note also that the lack of SCTP_AUTH_HMAC_ID_SHA1, or the inclusion of an unknown HMAC identifier (including optional identifiers unknown to the implementation) will cause the set option to fail and return Stewart, et al. Expires January 13, 2011 [Page 62] Internet-Draft SCTP sockets API July 2010 an error. 7.1.18. Get or Set the Active Shared Key (SCTP_AUTH_ACTIVE_KEY) This option will get or set the active shared key to be used to build the association shared key. The following structure is used to access and modify these parameters: struct sctp_authkeyid { sctp_assoc_t scact_assoc_id; uint16_t scact_keynumber; }; scact_assoc_id: This parameter sets the active key of the specified association. The special SCTP_{FUTURE|CURRENT|ALL}_ASSOC can be used. For one-to-one sockets, this parameter is ignored. Note, however, that this option will set the active key on the association if the socket is connected, otherwise this will set the default active key for the endpoint. scact_keynumber: This parameter is the shared key identifier which the application is requesting to become the active shared key to be used for sending authenticated chunks. The key identifier must correspond to an existing shared key. Note that shared key identifier '0' defaults to a null key. When used with setsockopt() the SCTP implementation must use the indicated shared key identifier for all messages being given to an SCTP implementation via a send call after the setsockopt() call until changed again. Therefore, the SCTP implementation must not bundle user messages which should be authenticated using different shared key identifiers. Initially the key with key identifier 0 is the active key. 7.1.19. Get or Set Delayed SACK Timer (SCTP_DELAYED_SACK) This option will affect the way delayed acks are performed. This option allows the application to get or set the delayed ack time, in milliseconds. It also allows changing the delayed ack frequency. Changing the frequency to 1 disables the delayed sack algorithm. Note that if sack_delay or sack_freq are 0 when setting this option, the current values will remain unchanged. The following structure is used to access and modify these parameters: Stewart, et al. Expires January 13, 2011 [Page 63] Internet-Draft SCTP sockets API July 2010 struct sctp_sack_info { sctp_assoc_t sack_assoc_id; uint32_t sack_delay; uint32_t sack_freq; }; sack_assoc_id: This parameter is ignored for one-to-one style sockets. For one-to-many style sockets this parameter indicates which association the user is performing an action upon. The special SCTP_{FUTURE|CURRENT|ALL}_ASSOC can also be used. sack_delay: This parameter contains the number of milliseconds that the user is requesting the delayed ACK timer to be set to. Note that this value is defined in the standard to be between 200 and 500 milliseconds. sack_freq: This parameter contains the number of packets that must be received before a sack is sent without waiting for the delay timer to expire. The default value is 2, setting this value to 1 will disable the delayed sack algorithm. 7.1.20. Get or Set Fragmented Interleave (SCTP_FRAGMENT_INTERLEAVE) Fragmented interleave controls how the presentation of messages occurs for the message receiver. There are three levels of fragment interleave defined. Two of the levels affect the one-to-one model, while the one-to-many model is affected by all three levels. This option takes an integer value. It can be set to a value of 0, 1 or 2. Attempting to set this level to other values will return an error. Setting the three levels provides the following receiver interactions: level 0: Prevents the interleaving of any messages. This means that when a partial delivery begins, no other messages will be received except the message being partially delivered. If another message arrives on a different stream (or association) that could be delivered, it will be blocked waiting for the user to read all of the partially delivered message. level 1: Allows interleaving of messages that are from different associations. For the one-to-one model, level 0 and level 1 thus have the same meaning since a one-to-one socket always receives messages from the same association. Note that setting the one-to- many model to this level may cause multiple partial deliveries from different associations but for any given association, only one message will be delivered until all parts of a message have been delivered. This means that one large message, being read with an association identification of "X", will block other Stewart, et al. Expires January 13, 2011 [Page 64] Internet-Draft SCTP sockets API July 2010 messages from association "X" from being delivered. level 2: Allows complete interleaving of messages. This level requires that the sender carefully observes not only the peer association identification (or address) but must also pay careful attention to the stream number. With this option enabled a partially delivered message may begin being delivered for association "X" stream "Y" and the next subsequent receive may return a message from association "X" stream "Z". Note that no other messages would be delivered for association "X" stream "Y" until all of stream "Y"'s partially delivered message was read. Note that this option also affects the one-to-one model. Also note that for the one-to-many model not only may another streams message from the same association be delivered from the next receive, some other associations message may be delivered upon the next receive. An implementation should default the one-to-many model to level 1. The reason for this is that otherwise it is possible that a peer could begin sending a partial message and thus block all other peers from sending data. However a setting of level 2 requires the application to not only be aware of the association (via the association id or peer's address) but also the stream number. The stream number is not present unless the user has subscribed to the sctp_data_io_events (see Section 7.4). This is also why we recommend that the one-to-one model be defaulted to level 0 (level 1 for the one-to-one model has no effect). Note that an implementation should return an error if an application attempts to set the level to 2 and has not subscribed to the sctp_data_io_events. For applications that have subscribed to events those events appear in the normal socket buffer data stream. This means that unless the user has set the fragmentation interleave level to 0, notifications may also be interleaved with partially delivered messages. 7.1.21. Set or Get the SCTP Partial Delivery Point (SCTP_PARTIAL_DELIVERY_POINT) This option will set or get the SCTP partial delivery point. This point is the size of a message where the partial delivery API will be invoked to help free up rwnd space for the peer. Setting this to a lower value will cause partial deliveries to happen more often. The call's argument is an integer that sets or gets the partial delivery point in bytes. Note also that the call will fail if the user attempts to set this value larger than the socket receive buffer size. Note that any single message having a length smaller than or equal to the SCTP partial delivery point will be delivered in one single read Stewart, et al. Expires January 13, 2011 [Page 65] Internet-Draft SCTP sockets API July 2010 call as long as the user provided buffer is large enough to hold the message. 7.1.22. Set or Get the Use of Extended Receive Info (SCTP_USE_EXT_RCVINFO) This option will enable or disable the use of the extended version of the sctp_sndrcvinfo structure. If this option is disabled, then the normal sctp_sndrcvinfo structure is returned in all receive message calls. If this option is enabled then the sctp_extrcvinfo structure is returned in all receive message calls. This option is present for compatibility with older applications and is deprecated. Future applications should use SCTP_NXTINFO to retrieve this same information via ancillary data. Note that the sctp_extrcvinfo structure is never used in any send call. 7.1.23. Set or Get the Auto ASCONF Flag (SCTP_AUTO_ASCONF) This option will enable or disable the use of the automatic generation of ASCONF chunks to add and delete addresses to an existing association. Note that this option has two caveats namely: a) it only affects sockets that are bound to all addresses on the machine, and b) the system administrator may have an overriding control that turns the ASCONF feature off no matter what setting the socket option may have. 7.1.24. Set or Get the Maximum Burst (SCTP_MAX_BURST) This option will allow a user to change the maximum burst of packets that can be emitted by this association. Note that the default value is 4, and some implementations may restrict this setting so that it can only be lowered. To set or get this option the user fills in the following structure: struct sctp_assoc_value { sctp_assoc_t assoc_id; uint32_t assoc_value; }; assoc_id: This parameter is ignored for one-to-one style sockets. For one-to-many style sockets this parameter indicates which association the user is performing an action upon. The special SCTP_{FUTURE|CURRENT|ALL}_ASSOC can also be used. Stewart, et al. Expires January 13, 2011 [Page 66] Internet-Draft SCTP sockets API July 2010 assoc_value: This parameter contains the maximum burst. 7.1.25. Set or Get the Default Context (SCTP_CONTEXT) The context field in the sctp_sndrcvinfo structure is normally only used when a failed message is retrieved holding the value that was sent down on the actual send call. This option allows the setting of a default context on an association basis that will be received on reading messages from the peer. This is especially helpful in the one-to-many model for an application to keep some reference to an internal state machine that is processing messages on the association. Note that the setting of this value only affects received messages from the peer and does not affect the value that is saved with outbound messages. To set or get this option the user fills in the following structure: struct sctp_assoc_value { sctp_assoc_t assoc_id; uint32_t assoc_value; }; assoc_id: This parameter is ignored for one-to-one style sockets. For one-to-many style sockets this parameter indicates which association the user is performing an action upon. The special SCTP_{FUTURE|CURRENT|ALL}_ASSOC can also be used. assoc_value: This parameter contains the context. 7.1.26. Enable or Disable Explicit EOR Marking (SCTP_EXPLICIT_EOR) This boolean flag is used to enable or disable explicit end of record (EOR) marking. When this option is enabled, a user may make multiple send system calls to send a record and must indicate that they are finished sending a particular record by including the SCTP_EOR flag. If this boolean flag is disabled then each individual send system call is considered to have an SCTP_EOR indicator set on it implicitly without the user having to explicitly add this flag. 7.1.27. Enable SCTP Port Reusage (SCTP_REUSE_PORT) This option only supports one-to-one style SCTP sockets. If used on a one-to-many style SCTP socket an error is indicated. This setsockopt() call must not be used after calling bind() or sctp_bindx() for a one-to-one style SCTP socket. If using bind() or sctp_bindx() on a socket with the SCTP_REUSE_PORT option, all other SCTP sockets bound to the same port must have set the SCTP_REUSE_PORT. Calling bind() or sctp_bindx() for a socket without Stewart, et al. Expires January 13, 2011 [Page 67] Internet-Draft SCTP sockets API July 2010 having set the SCTP_REUSE_PORT option will fail if there are other sockets bound to the same port. At most one socket being bound to the same port may be listening. It should be noted that the behavior of the socket level socket option to reuse ports and/or addresses for SCTP sockets is unspecified. 7.1.28. Set Notification Event (SCTP_EVENT) This socket option is used to set a specific notification option. Please see Section 7.4 for a full description of this option and its usage. 7.1.29. Enable or Disable the Delivery of SCTP_RCVINFO as Ancillary Data (SCTP_RECVRCVINFO) Setting this option specifies that SCTP_RCVINFO defined in Section 5.2.5 is returned as ancillary data by recvmsg(). The call expects an integer. 7.1.30. Enable or Disable the Delivery of SCTP_NXTINFO as Ancillary Data (SCTP_RECVNXTINFO) Setting this option specifies that SCTP_NXTINFO defined in Section 5.2.6 is returned as ancillary data by recvmsg(). The call expects an integer. 7.1.31. Set Default Send Parameters (SCTP_DEFAULT_SNDINFO) Applications that wish to use the sendto() system call may wish to specify a default set of parameters that would normally be supplied through the inclusion of ancillary data. This socket option allows such an application to set the default sctp_sndrcvinfo structure. The application that wishes to use this socket option simply passes the sctp_sndinfo structure defined in Section 5.2.4 to this call. The input parameters accepted by this call include snd_sid, snd_flags, snd_ppid, snd_context. The snd_flags is composed of a bitwise OR of SCTP_UNORDERED, SCTP_EOF, and SCTP_SENDALL. The snd_assoc_id field specifies the association to apply the parameters to. In a one-to-many style sockets any of the predefined constants are also allowed in this field. The field is ignored on the one-to- one style. 7.2. Read-Only Options The options defined in this subsection are read-only. Using this option in a setsockopt() call will result in an error indicating Stewart, et al. Expires January 13, 2011 [Page 68] Internet-Draft SCTP sockets API July 2010 EOPNOTSUPP. 7.2.1. Association Status (SCTP_STATUS) Applications can retrieve current status information about an association, including association state, peer receiver window size, number of unacked data chunks, and number of data chunks pending receipt. This information is read-only. The following structure is used to access this information: struct sctp_status { sctp_assoc_t sstat_assoc_id; int32_t sstat_state; uint32_t sstat_rwnd; uint16_t sstat_unackdata; uint16_t sstat_penddata; uint16_t sstat_instrms; uint16_t sstat_outstrms; uint32_t sstat_fragmentation_point; struct sctp_paddrinfo sstat_primary; }; sstat_assoc_id: This parameter is ignored for one-to-one style sockets. For one-to-many style sockets it holds the identifier for the association. All notifications for a given association have the same association identifier. The special SCTP_{FUTURE| CURRENT|ALL}_ASSOC cannot be used. sstat_state: This contains the association's current state one of the following values: * SCTP_CLOSED * SCTP_BOUND * SCTP_LISTEN * SCTP_COOKIE_WAIT * SCTP_COOKIE_ECHOED * SCTP_ESTABLISHED * SCTP_SHUTDOWN_PENDING * SCTP_SHUTDOWN_SENT * SCTP_SHUTDOWN_RECEIVED * SCTP_SHUTDOWN_ACK_SENT sstat_rwnd: This contains the association peer's current receiver window size. sstat_unackdata: This is the number of unacked data chunks. sstat_penddata: This is the number of data chunks pending receipt. Stewart, et al. Expires January 13, 2011 [Page 69] Internet-Draft SCTP sockets API July 2010 sstat_instrms: The number of streams that the peer will be using outbound. sstat_outstrms: The number of streams that the endpoint is allowed to use outbound. sstat_fragmentation_point: The size at which SCTP fragmentation will occur. sstat_primary: This is information on the current primary peer address. To access these status values, the application calls getsockopt() with the option name SCTP_STATUS. 7.2.2. Peer Address Information (SCTP_GET_PEER_ADDR_INFO) Applications can retrieve information about a specific peer address of an association, including its reachability state, congestion window, and retransmission timer values. This information is read- only. The following structure is used to access this information: struct sctp_paddrinfo { sctp_assoc_t spinfo_assoc_id; struct sockaddr_storage spinfo_address; int32_t spinfo_state; uint32_t spinfo_cwnd; uint32_t spinfo_srtt; uint32_t spinfo_rto; uint32_t spinfo_mtu; }; spinfo_assoc_id: This parameter is ignored for one-to-one style sockets. For one-to-many style sockets the following applies: This field may be filled by the application, if so, this field will have priority in looking up the association using the address specified in spinfo_address. Note that if the address does not belong to the association specified then this call will fail. If the application does not fill in the spinfo_assoc_id, then the address will be used to lookup the association and on return this field will have the valid association id. In other words, this call can be used to translate an address into an association id. Note that the predefined constants are not allowed on this option. spinfo_address: This is filled by the application, and contains the peer address of interest. Stewart, et al. Expires January 13, 2011 [Page 70] Internet-Draft SCTP sockets API July 2010 spinfo_state: This contains the peer address' state (either SCTP_ACTIVE or SCTP_INACTIVE and possibly the modifier SCTP_UNCONFIRMED). spinfo_cwnd: This contains the peer address' current congestion window. spinfo_srtt: This contains the peer address' current smoothed round- trip time calculation in milliseconds. spinfo_rto: This contains the peer address' current retransmission timeout value in milliseconds. spinfo_mtu: The current P-MTU of this address. 7.2.3. Get the List of Chunks the Peer Requires to be Authenticated (SCTP_PEER_AUTH_CHUNKS) This option gets a list of chunk types (see [RFC4960] for a specified association that the peer requires to be received authenticated only. The following structure is used to access these parameters: struct sctp_authchunks { sctp_assoc_t gauth_assoc_id; uint32_t gauth_number_of_chunks uint8_t gauth_chunks[]; }; gauth_assoc_id: This parameter indicates for which association the user is requesting the list of peer authenticated chunks. For one-to-one sockets, this parameter is ignored. Note that the predefined constants are not allowed with this option. gauth_number_of_chunks: This parameter gives the number of elements in the array gauth_chunks. gauth_chunks: This parameter contains an array of chunk types that the peer is requesting to be authenticated. 7.2.4. Get the List of Chunks the Local Endpoint Requires to be Authenticated (SCTP_LOCAL_AUTH_CHUNKS) This option gets a list of chunk types (see [RFC4960]) for a specified association that the local endpoint requires to be received authenticated only. The following structure is used to access these parameters: struct sctp_authchunks { sctp_assoc_t gauth_assoc_id; uint32_t gauth_number_of_chunks; uint8_t gauth_chunks[]; }; Stewart, et al. Expires January 13, 2011 [Page 71] Internet-Draft SCTP sockets API July 2010 gauth_assoc_id: This parameter indicates for which association the user is requesting the list of local authenticated chunks. For one-to-one sockets, this parameter is ignored. gauth_number_of_chunks: This parameter gives the number of elements in the array gauth_chunks. gauth_chunks: This parameter contains an array of chunk types that the local endpoint is requesting to be authenticated. 7.2.5. Get the Current Number of Associations (SCTP_GET_ASSOC_NUMBER) This option gets the current number of associations that are attached to a one-to-many style socket. The option value is an uint32_t. Note that this number is only a snap shot. This means that the number of associations may have changed when the caller gets back the option result. 7.2.6. Get the Current Identifiers of Associations (SCTP_GET_ASSOC_ID_LIST) This option gets the current list of SCTP association identifiers of the SCTP associations handled by a one-to-many style socket. The option value has the structure struct sctp_assoc_ids { uint32_t gaids_number_of_ids; sctp_assoc_t gaids_assoc_id[]; }; The caller must provide a large enough buffer to hold all association identifiers. If the buffer is too small, an error must be returned. The user can use the SCTP_GET_ASSOC_NUMBER socket option to get an idea how large the buffer has to be. gaids_number_of_ids gives the number of elements in the array gaids_assoc_id. Note also that the some or all of sctp_assoc_t returned in the array may become invalid by the time the caller gets back the result. 7.3. Write-Only Options The options defined in this subsection are write-only. Using this option in a getsockopt() or sctp_opt_info() call will result in an error indicating EOPNOTSUPP. 7.3.1. Set Peer Primary Address (SCTP_SET_PEER_PRIMARY_ADDR) Requests that the peer marks the enclosed address as the association primary (see [RFC5061]). The enclosed address must be one of the association's locally bound addresses. Stewart, et al. Expires January 13, 2011 [Page 72] Internet-Draft SCTP sockets API July 2010 The following structure is used to make a set peer primary request: struct sctp_setpeerprim { sctp_assoc_t sspp_assoc_id; struct sockaddr_storage sspp_addr; }; sspp_addr: The address to set as primary. sspp_assoc_id: This parameter is ignored for one-to-one style sockets. For one-to-many style sockets it identifies the association for this request. Note that the predefined constants are not allowed on this option. 7.3.2. Add a Chunk That Must Be Authenticated (SCTP_AUTH_CHUNK) This set option adds a chunk type that the user is requesting to be received only in an authenticated way. Changes to the list of chunks will only affect future associations on the socket. The following structure is used to add a chunk: struct sctp_authchunk { uint8_t sauth_chunk; }; sauth_chunk: This parameter contains a chunk type that the user is requesting to be authenticated. The chunk types for INIT, INIT-ACK, SHUTDOWN-COMPLETE, and AUTH chunks must not be used. If they are used, an error must be returned. The usage of this option enables SCTP AUTH in cases where it is not required by other means (for example the use of dynamic address reconfiguration). 7.3.3. Set a Shared Key (SCTP_AUTH_KEY) This option will set a shared secret key that is used to build an association shared key. The following structure is used to access and modify these parameters: struct sctp_authkey { sctp_assoc_t sca_assoc_id; uint16_t sca_keynumber; uint16_t sca_keylength; uint8_t sca_key[]; }; Stewart, et al. Expires January 13, 2011 [Page 73] Internet-Draft SCTP sockets API July 2010 sca_assoc_id: This parameter indicates what association the shared key is being set upon. The special SCTP_{FUTURE|CURRENT| ALL}_ASSOC can be used. For one-to-one sockets, this parameter is ignored. Note, however, that this option will set a key on the association if the socket is connected, otherwise this will set a key on the endpoint. sca_keynumber: This parameter is the shared key identifier by which the application will refer to this shared key. If a key of the specified index already exists, then this new key will replace the old existing key. Note that shared key identifier '0' defaults to a null key. sca_keylength: This parameter is the length of the array sca_key. sca_key: This parameter contains an array of bytes that is to be used by the endpoint (or association) as the shared secret key. Note, if the length of this field is zero, a null key is set. 7.3.4. Deactivate a Shared Key (SCTP_AUTH_DEACTIVATE_KEY) This set option indicates that the application will not send user messages anymore using the indicated key identifier. struct sctp_authkeyid { sctp_assoc_t scact_assoc_id; uint16_t scact_keynumber; }; scact_assoc_id: This parameter indicates which association the shared key identifier is being deleted from. The special SCTP_{FUTURE|CURRENT|ALL}_ASSOC can be used. For one-to-one sockets, this parameter is ignored. Note, however, that this option will deactivate the key from the association if the socket is connected, otherwise this will deactivate the key from the endpoint. scact_keynumber: This parameter is the shared key identifier which the application is requesting to be deactivated. The key identifier must correspond to an existing shared key. Note if this parameter is zero, use of the null key identifier '0' is deactivated on the endpoint and/or association. The currently active key cannot be deactivated. 7.3.5. Delete a Shared Key (SCTP_AUTH_DELETE_KEY) This set option will delete a shared secret key which has been deactivated of an SCTP association. Stewart, et al. Expires January 13, 2011 [Page 74] Internet-Draft SCTP sockets API July 2010 struct sctp_authkeyid { sctp_assoc_t scact_assoc_id; uint16_t scact_keynumber; }; scact_assoc_id: This parameter indicates which association the shared key identifier is being deleted from. The special SCTP_{FUTURE|CURRENT|ALL}_ASSOC can be used. For one-to-one sockets, this parameter is ignored. Note, however, that this option will delete the key from the association if the socket is connected, otherwise this will delete the key from the endpoint. scact_keynumber: This parameter is the shared key identifier which the application is requesting to be deleted. The key identifier must correspond to an existing shared key and must not be in use for any packet being sent by the SCTP implementation. This means in particular, that it must be deactivated first. Note if this parameter is zero, use of the null key identifier '0' is deleted from the endpoint and/or association. Only deactivated keys that are no longer used by the association can be deleted. 7.4. Ancillary Data and Notification Interest Options Applications can receive per-message ancillary information and notifications of certain SCTP events with recvmsg(). The following optional information is available to the application: SCTP_SNDRCV (sctp_data_io_event): Per-message information (i.e. stream number, TSN, SSN, etc. described in Section 5.2.2) SCTP_ASSOC_CHANGE (sctp_association_event): described in Section 5.3.2 SCTP_PEER_ADDR_CHANGE (sctp_address_event): described in Section 5.3.3 SCTP_SEND_FAILED (sctp_send_failure_event): described in Section 5.3.5 SCTP_REMOTE_ERROR (sctp_peer_error_event): described in Section 5.3.4 SCTP_SHUTDOWN_EVENT (sctp_shutdown_event): described in Section 5.3.6 SCTP_PARTIAL_DELIVERY_EVENT (sctp_partial_delivery_event): described in Section 5.3.8 SCTP_ADAPTATION_INDICATION (sctp_adaptation_layer_event): described in Section 5.3.7 Stewart, et al. Expires January 13, 2011 [Page 75] Internet-Draft SCTP sockets API July 2010 SCTP_AUTHENTICATION_EVENT (sctp_authentication_event): described in Section 5.3.9) SCTP_SENDER_DRY_EVENT (sctp_sender_dry_event): described in Section 5.3.10 SCTP_NOTIFICATIONS_STOPPED_EVENT (): described in Section 5.3.11 To receive any ancillary data or notifications, first the application registers its interest by calling the SCTP_EVENTS (deprecated, see below) setsockopt() with the following structure: struct sctp_event_subscribe{ uint8_t sctp_data_io_event; uint8_t sctp_association_event; uint8_t sctp_address_event; uint8_t sctp_send_failure_event; uint8_t sctp_peer_error_event; uint8_t sctp_shutdown_event; uint8_t sctp_partial_delivery_event; uint8_t sctp_adaptation_layer_event; uint8_t sctp_authentication_event; uint8_t sctp_sender_dry_event; }; sctp_data_io_event: Setting this flag to 1 will cause the reception of SCTP_SNDRCV information on a per message basis. The application will need to use the recvmsg() interface so that it can receive the event information contained in the msg_control field. Setting the flag to 0 will disable the reception of the message control information. sctp_association_event: Setting this flag to 1 will enable the reception of association event notifications. Setting the flag to 0 will disable association event notifications. sctp_address_event: Setting this flag to 1 will enable the reception of address event notifications. Setting the flag to 0 will disable address event notifications. sctp_send_failure_event: Setting this flag to 1 will enable the reception of send failure event notifications. Setting the flag to 0 will disable send failure event notifications. sctp_peer_error_event: Setting this flag to 1 will enable the reception of peer error event notifications. Setting the flag to 0 will disable peer error event notifications. sctp_shutdown_event: Setting this flag to 1 will enable the reception of shutdown event notifications. Setting the flag to 0 will disable shutdown event notifications. Stewart, et al. Expires January 13, 2011 [Page 76] Internet-Draft SCTP sockets API July 2010 sctp_partial_delivery_event: Setting this flag to 1 will enable the reception of partial delivery notifications. Setting the flag to 0 will disable partial delivery event notifications. sctp_adaptation_layer_event: Setting this flag to 1 will enable the reception of adaptation layer notifications. Setting the flag to 0 will disable adaptation layer event notifications. sctp_authentication_event: Setting this flag to 1 will enable the reception of authentication layer notifications. Setting the flag to 0 will disable authentication layer event notifications. sctp_sender_dry_event: Setting this flag to 1 will enable the reception of sender dry notifications. Setting the flag to 0 will disable sender dry event notifications. An example where an application would like to receive data io events and association events but no others would be as follows: { struct sctp_event_subscribe events; memset(&events,0,sizeof(events)); events.sctp_data_io_event = 1; events.sctp_association_event = 1; setsockopt(fd, IPPROTO_SCTP, SCTP_EVENTS, &events, sizeof(events)); } Note that for one-to-many style SCTP sockets, the caller of recvmsg() receives ancillary data and notifications for all associations bound to the file descriptor. For one-to-one style SCTP sockets, the caller receives ancillary data and notifications only for the single association bound to the file descriptor. The SCTP_EVENTS socket option has one issue for future compatibility. As new features are added the structure (sctp_event_subscribe) must be expanded. This can cause an application binary interface (ABI) issue unless an implementation has added padding at the end of the structure. To avoid this problem, SCTP_EVENTS has been deprecated and a new option SCTP_EVENT socket option has taken its place. The option is used with the following structure: struct sctp_event { sctp_assoc_t se_assoc_id; uint16_t se_type; uint8_t se_on; }; Stewart, et al. Expires January 13, 2011 [Page 77] Internet-Draft SCTP sockets API July 2010 se_assoc_id: The se_assoc_id field is ignored for one-to-one style sockets. For one-to-many style sockets any this field can be a particular association id or SCTP_{FUTURE|CURRENT|ALL}_ASSOC. se_type: The se_type field can be filled with any value that would show up in the respective sn_type field (in the sctp_tlv structure of the notification). se_on: The se_on field is set to 1 to turn on an event and set to 0 to turn off an event. To use this option the user fills in this structure and then calls the setsockopt to turn on or off an individual event. The following is an example use of this option: { struct sctp_event event; memset(&event, 0, sizeof(event)); event.se_assoc_id = SCTP_FUTURE_ASSOC; event.se_type = SCTP_SENDER_DRY_EVENT; event.se_on = 1; setsockopt(fd, IPPROTO_SCTP, SCTP_EVENT, &event, sizeof(event)); } By default both the one-to-one style and the one-to-many style socket has all options off. 8. New Functions Depending on the system, the following interface can be implemented as a system call or library function. 8.1. sctp_bindx() This function allows the user to bind a specific subset of addresses or, if the SCTP extension described in [RFC5061] is supported, add or delete specific addresses. The function prototype is int sctp_bindx(int sd, struct sockaddr *addrs, int addrcnt, int flags); If sd is an IPv4 socket, the addresses passed must be IPv4 addresses. If the sd is an IPv6 socket, the addresses passed can either be IPv4 Stewart, et al. Expires January 13, 2011 [Page 78] Internet-Draft SCTP sockets API July 2010 or IPv6 addresses. A single address may be specified as INADDR_ANY or IN6ADDR_ANY, see Section 3.1.2 for this usage. addrs is a pointer to an array of one or more socket addresses. Each address is contained in its appropriate structure. For an IPv6 socket, an array of sockaddr_in6 is used. For a IPv4 socket, an array of sockaddr_in is used. The caller specifies the number of addresses in the array with addrcnt. Note that the wildcard addresses cannot be used in combination with non wildcard addresses on a socket with this function, doing so will result in an error. On success, sctp_bindx() returns 0. On failure, sctp_bindx() returns -1 and sets errno to the appropriate error code. For SCTP, the port given in each socket address must be the same, or sctp_bindx() will fail, setting errno to EINVAL. The flags parameter is formed from the bitwise OR of zero or more of the following currently defined flags: o SCTP_BINDX_ADD_ADDR o SCTP_BINDX_REM_ADDR SCTP_BINDX_ADD_ADDR directs SCTP to add the given addresses to the association, and SCTP_BINDX_REM_ADDR directs SCTP to remove the given addresses from the association. The two flags are mutually exclusive; if both are given, sctp_bindx() will fail with EINVAL. A caller may not remove all addresses from an association; sctp_bindx() will reject such an attempt with EINVAL. An application can use sctp_bindx(SCTP_BINDX_ADD_ADDR) to associate additional addresses with an endpoint after calling bind(). Or use sctp_bindx(SCTP_BINDX_REM_ADDR) to remove some addresses a listening socket is associated with, so that no new association accepted will be associated with these addresses. If the endpoint supports dynamic address reconfiguration an SCTP_BINDX_REM_ADDR or SCTP_BINDX_ADD_ADDR may cause an endpoint to send the appropriate message to the peer to change the peer's address lists. Adding and removing addresses from a connected association is an optional functionality. Implementations that do not support this functionality should return EOPNOTSUPP. sctp_bindx() can be called on an already bound socket or on an unbound socket. If the socket is unbound and the first port number in the addrs is zero, the kernel will choose a port number. All port numbers after the first one being 0 must also be zero. If the first port number is not zero, the following port numbers must be zero or Stewart, et al. Expires January 13, 2011 [Page 79] Internet-Draft SCTP sockets API July 2010 have the same value as the first one. For an already bound socket, all port numbers provided must be the bound one or 0. sctp_bindx() is an atomic operation. Therefore, the binding will be either successful on all addresses or fail on all addresses. If multiple addresses are provided and the sctp_bindx() call fails there is no indication which address is responsible for the failure. The only way to get a specific error indication is to call sctp_bindx() with only one address sequentially. 8.2. sctp_peeloff() After an association is established on a one-to-many style socket, the application may wish to branch off the association into a separate socket/file descriptor. This is particularly desirable when, for instance, the application wishes to have a number of sporadic message senders/receivers remain under the original one-to-many style socket, but branch off these associations carrying high volume data traffic into their own separate socket descriptors. The application uses the sctp_peeloff() call to branch off an association into a separate socket (Note the semantics are somewhat changed from the traditional one-to-one style accept() call). Note that the new socket is a one-to-one style socket. Thus it will be confined to operations allowed for a one-to-one style socket. The function prototype is int sctp_peeloff(int sd, sctp_assoc_t assoc_id); and the arguments are sd: The original one-to-many style socket descriptor returned from the socket() system call (see Section 3.1.1). assoc_id: the specified identifier of the association that is to be branched off to a separate file descriptor (Note, in a traditional one-to-one style accept() call, this would be an out parameter, but for the one-to-many style call, this is an in parameter). The function returns a non-negative file descriptor representing the branched-off association, or -1 if an error occurred. The variable errno is then set appropriately. 8.3. sctp_getpaddrs() sctp_getpaddrs() returns all peer addresses in an association. Stewart, et al. Expires January 13, 2011 [Page 80] Internet-Draft SCTP sockets API July 2010 The function protoype is: int sctp_getpaddrs(int sd, sctp_assoc_t id, struct sockaddr **addrs); On return, addrs will point to an array dynamically allocated sockaddr structures of the appropriate type for the socket type. The caller should use sctp_freepaddrs() to free the memory. Note that the in/out parameter addrs must not be NULL. If sd is an IPv4 socket, the addresses returned will be all IPv4 addresses. If sd is an IPv6 socket, the addresses returned can be a mix of IPv4 or IPv6 addresses. For one-to-many style sockets, id specifies the association to query. For one-to-one style sockets, id is ignored. On success, sctp_getpaddrs() returns the number of peer addresses in the association. If there is no association on this socket, sctp_getpaddrs() returns 0, and the value of *addrs is undefined. If an error occurs, sctp_getpaddrs() returns -1, and the value of *addrs is undefined. 8.4. sctp_freepaddrs() sctp_freepaddrs() frees all resources allocated by sctp_getpaddrs(). The function prototype is void sctp_freepaddrs(struct sockaddr *addrs); and addrs is the array of peer addresses returned by sctp_getpaddrs(). 8.5. sctp_getladdrs() sctp_getladdrs() returns all locally bound address(es) on a socket. The function prototype is int sctp_getladdrs(int sd, sctp_assoc_t id, struct sockaddr **addrs); On return, addrs will point to a dynamically allocated array of sockaddr structures of the appropriate type for the socket type. The caller should use sctp_freeladdrs() to free the memory. Note that Stewart, et al. Expires January 13, 2011 [Page 81] Internet-Draft SCTP sockets API July 2010 the in/out parameter addrs must not be NULL. If sd is an IPv4 socket, the addresses returned will be all IPv4 addresses. If sd is an IPv6 socket, the addresses returned can be a mix of IPv4 or IPv6 addresses. For one-to-many style sockets, id specifies the association to query. For one-to-one style sockets, id is ignored. If the id field is set to the value '0' then the locally bound addresses are returned without regard to any particular association. On success, sctp_getladdrs() returns the number of local addresses bound to the socket. If the socket is unbound, sctp_getladdrs() returns 0, and the value of *addrs is undefined. If an error occurs, sctp_getladdrs() returns -1, and the value of *addrs is undefined. 8.6. sctp_freeladdrs() sctp_freeladdrs() frees all resources allocated by sctp_getladdrs(). The function prototype is void sctp_freeladdrs(struct sockaddr *addrs); and addrs is the array of peer addresses returned by sctp_getladdrs(). 8.7. sctp_sendmsg() An implementation may provide a library function (or possibly system call) to assist the user with the advanced features of SCTP. The function prototype is ssize_t sctp_sendmsg(int sd, const void *msg, size_t len, const struct sockaddr *to, socklen_t tolen, uint32_t ppid, uint32_t flags, uint16_t stream_no, uint32_t pr_value, uint32_t context); and the arguments are: Stewart, et al. Expires January 13, 2011 [Page 82] Internet-Draft SCTP sockets API July 2010 sd: The socket descriptor. msg: The message to be sent. len: The length of the message. to: The destination address of the message. tolen: The length of the destination address. ppid: The same as sinfo_ppid (see Section 5.2.2). flags: The same as sinfo_flags (see Section 5.2.2). stream_no: The same as sinfo_stream (see Section 5.2.2). pr_value: The same as sinfo_pr_value (see Section 5.2.2). context: The same as sinfo_context (see Section 5.2.2). The call returns the number of characters sent, or -1 if an error occurred. The variable errno is then set appropriately. Sending a message using sctp_sendmsg() is atomic (unless explicit EOR marking is enabled on the socket specified by sd). Using sctp_sendmsg() on a non-connected one-to-one style socket for implicit connection setup may or may not work depending on the SCTP implementation. 8.8. sctp_recvmsg() This function is deprecated. An implementation may provide a library function (or possibly system call) to assist the user with the advanced features of SCTP. Note that in order for the sctp_sndrcvinfo structure to be filled in by sctp_recvmsg() the caller must enable the sctp_data_io_events with the SCTP_EVENTS option. Note that the setting of the SCTP_USE_EXT_RCVINFO will affect this function as well, causing the sctp_sndrcvinfo information to be extended. The function prototype is ssize_t sctp_recvmsg(int sd, void *msg, size_t len, struct sockaddr *from, socklen_t *fromlen struct sctp_sndrcvinfo *sinfo int *msg_flags); and the arguments are sd: The socket descriptor. Stewart, et al. Expires January 13, 2011 [Page 83] Internet-Draft SCTP sockets API July 2010 msg: The message buffer to be filled. len: The length of the message buffer. from: A pointer to an address to be filled with the sender of this messages address. fromlen: An in/out parameter describing the from length. sinfo: A pointer to an sctp_sndrcvinfo structure to be filled upon receipt of the message. msg_flags: A pointer to an integer to be filled with any message flags (e.g. MSG_NOTIFICATION). Note that this field is an in-out field. Options for the receive may also be passed into the value (e.g. MSG_PEEK). On return from the call, the msg_flags value will be different than what was sent in to the call. If implemented via a recvmsg() call, the msg_flags should only contain the value of the flags from the recvmsg() call. The call returns the number of bytes received, or -1 if an error occurred. The variable errno is then set appropriately. 8.9. sctp_connectx() An implementation may provide a library function (or possibly system call) to assist the user with associating to an endpoint that is multi-homed. Much like sctp_bindx() this call allows a caller to specify multiple addresses at which a peer can be reached. The way the SCTP stack uses the list of addresses to set up the association is implementation dependent. This function only specifies that the stack will try to make use of all the addresses in the list when needed. Note that the list of addresses passed in is only used for setting up the association. It does not necessarily equal the set of addresses the peer uses for the resulting association. If the caller wants to find out the set of peer addresses, it must use sctp_getpaddrs() to retrieve them after the association has been set up. The function prototype is int sctp_connectx(int sd, struct sockaddr *addrs, int addrcnt, sctp_assoc_t *id); and the arguments are: sd: The socket descriptor. addrs: An (packed) array of addresses. Stewart, et al. Expires January 13, 2011 [Page 84] Internet-Draft SCTP sockets API July 2010 addrcnt: The number of addresses in the array. id: An output parameter that if passed in as a non-NULL will return the association identification for the newly created association (if successful). The call returns 0 on success or -1 if an error occurred. The variable errno is then set appropriately. 8.10. sctp_send() This function is deprecated. An implementation may provide another alternative function or system call to assist an application with the sending of data without the use of the CMSG header structures. The function prototype is ssize_t sctp_send(int sd, const void *msg, size_t len, const struct sctp_sndrcvinfo *sinfo, int flags); and the arguments are sd: The socket descriptor. msg: The message to be sent. len: The length of the message. sinfo: A pointer to an sctp_sndrcvinfo structure used as described in Section 5.2.2 for a sendmsg call. flags: The same flags as used by the sendmsg() call flags (e.g. MSG_DONTROUTE). The call returns the number of bytes sent, or -1 if an error occurred. The variable errno is then set appropriately. This function call may also be used to terminate an association using an association identification by setting the sinfo.sinfo_flags to SCTP_EOF and the sinfo.sinfo_assoc_id to the association that needs to be terminated. In such a case the len of the message would be zero. Using sctp_send() on a non-connected one-to-one style socket for implicit connection setup may or may not work depending on the SCTP implementation. Sending a message using sctp_send() is atomic unless explicit EOR marking is enabled on the socket specified by sd. Stewart, et al. Expires January 13, 2011 [Page 85] Internet-Draft SCTP sockets API July 2010 8.11. sctp_sendx() This function is deprecated. An implementation may provide another alternative function or system call to assist an application with the sending of data without the use of the CMSG header structures that also gives a list of addresses. The list of addresses is provided for implicit association setup. In such a case the list of addresses serves the same purpose as the addresses given in sctp_connectx() (see Section 8.9). The function prototype is ssize_t sctp_sendx(int sd, const void *msg, size_t len, struct sockaddr *addrs, int addrcnt, struct sctp_sndrcvinfo *sinfo, int flags); and the arguments are: sd: The socket descriptor. msg: The message to be sent. len: The length of the message. addrs: is an array of addresses. addrcnt: The number of addresses in the array. sinfo: A pointer to a sctp_sndrcvinfo structure used as described in Section 5.2.2 for a sendmsg() call. flags: The same flags as used by the sendmsg() call flags (e.g. MSG_DONTROUTE). The call returns the number of bytes sent, or -1 if an error occurred. The variable errno is then set appropriately. Note that on return from this call the sinfo structure will have changed in that the sinfo_assoc_id will be filled in with the new association id. This function call may also be used to terminate an association using an association identification by setting the sinfo.sinfo_flags to SCTP_EOF and the sinfo.sinfo_assoc_id to the association that needs to be terminated. In such a case the len of the message would be zero. Sending a message using sctp_send() is atomic unless explicit EOR marking is enabled on the socket specified by sd. Stewart, et al. Expires January 13, 2011 [Page 86] Internet-Draft SCTP sockets API July 2010 Using sctp_sendx() on a non-connected one-to-one style socket for implicit connection setup may or may not work depending on the SCTP implementation. 8.12. sctp_recvxxx() An implementation may provide a library function (or possibly system call) to assist the user with the advanced features of SCTP. Note that in order for the sctp_recvinfo structure to be filled in by sctp_recvxxx() the caller must set the SCTP_RECVRCVINFO and SCTP_RECVNXTINFO socket option. The function prototype is struct sctp_recvinfo { uint16_t recv_version; uint16_t recv_length; struct sctp_rcvinfo recv_rcvinfo; struct sctp_rcvinfo recv_nxtinfo; }; ssize_t sctp_recvxxx(int sd, void *msg, size_t len, struct sockaddr *from, socklen_t *fromlen struct sctp_recvinfo *info int *msg_flags); and the arguments are sd: The socket descriptor. msg: The message buffer to be filled. len: The length of the message buffer. from: A pointer to an address to be filled with the sender of this messages address. fromlen: An in/out parameter describing the from length. info: A pointer to an sctp_recvinfo structure to be filled upon receipt of the message. msg_flags: A pointer to an integer to be filled with any message flags (e.g. MSG_NOTIFICATION). Note that this field is an in-out field. Options for the receive may also be passed into the value (e.g. MSG_PEEK). On return from the call, the msg_flags value will be different than what was sent in to the call. If implemented via a recvmsg() call, the msg_flags should only contain the value of the flags from the recvmsg() call. The call returns the number of bytes received, or -1 if an error occurred. The variable errno is then set appropriately. Stewart, et al. Expires January 13, 2011 [Page 87] Internet-Draft SCTP sockets API July 2010 8.13. sctp_sendxxx() An implementation may provide another alternative function or system call to assist an application with the sending of data without the use of the CMSG header structures that also gives a list of addresses. The list of addresses is provided for implicit association setup. In such a case the list of addresses serves the same purpose as the addresses given in sctp_connectx() (see Section 8.9). The function prototype is struct sctp_sendinfo { uint16_t send_version; uint16_t send_length; struct sctp_sndinfo send_sndinfo; struct sctp_prinfo send_prinfo; struct sctp_authinfo send_authinfo; }; ssize_t sctp_sendxxx(int sd, const void *msg, size_t len, struct sockaddr *addrs, int addrcnt, struct sctp_sendinfo *info, int flags); and the arguments are: sd: The socket descriptor. msg: The message to be sent. len: The length of the message. addrs: is an array of addresses. addrcnt: The number of addresses in the array. sinfo: A pointer to a sctp_sendinfo structure. flags: The same flags as used by the sendmsg() call flags (e.g. MSG_DONTROUTE). The call returns the number of bytes sent, or -1 if an error occurred. The variable errno is then set appropriately. Note that on return from this call the sinfo structure will have changed in that the send_sndinfo.snd_sid will be filled in with the new association id. This function call may also be used to terminate an association using an association identification by setting the send_sndinfo.snd_flags to SCTP_EOF and the send_sndinfo.snd_sid to the association that needs to be terminated. In such a case the len of the message would Stewart, et al. Expires January 13, 2011 [Page 88] Internet-Draft SCTP sockets API July 2010 be zero. Sending a message using sctp_sendxxx() is atomic unless explicit EOR marking is enabled on the socket specified by sd. Using sctp_sendxxx() on a non-connected one-to-one style socket for implicit connection setup may or may not work depending on the SCTP implementation. 9. IANA Considerations This document requires no actions from IANA. 10. Security Considerations Many TCP and UDP implementations reserve port numbers below 1024 for privileged users. If the target platform supports privileged users, the SCTP implementation should restrict the ability to call bind() or sctp_bindx() on these port numbers to privileged users. Similarly unprivileged users should not be able to set protocol parameters that could result in the congestion control algorithm being more aggressive than permitted on the public Internet. These parameters are: o struct sctp_rtoinfo If an unprivileged user inherits a one-to-many style socket with open associations on a privileged port, it may be permitted to accept new associations, but it should not be permitted to open new associations. This could be relevant for the r* family of protocols. Applications using the one-to-many style sockets and using the interleave level if 0 are subject to denial of service attacks as described in Section 7.1.20. 11. Acknowledgments Special acknowledgment is given to Ken Fujita, Jonathan Woods, Qiaobing Xie, and La Monte Yarroll, who helped extensively in the early formation of this document. The authors also wish to thank Kavitha Baratakke, Mike Bartlett, Jon Berger, Mark Butler, Scott Kimble, Renee Revis, Andreas Fink, Jonathan Leighton, Irene Ruengeler, and many others on the TSVWG mailing list for contributing valuable comments. Stewart, et al. Expires January 13, 2011 [Page 89] Internet-Draft SCTP sockets API July 2010 A special thanks to Phillip Conrad, for his suggested text, quick and constructive insights, and most of all his persistent fighting to keep the interface to SCTP usable for the application programmer. 12. References 12.1. Normative References [RFC3493] Gilligan, R., Thomson, S., Bound, J., McCann, J., and W. Stevens, "Basic Socket Interface Extensions for IPv6", RFC 3493, February 2003. [RFC3542] Stevens, W., Thomas, M., Nordmark, E., and T. Jinmei, "Advanced Sockets Application Program Interface (API) for IPv6", RFC 3542, May 2003. [RFC3758] Stewart, R., Ramalho, M., Xie, Q., Tuexen, M., and P. Conrad, "Stream Control Transmission Protocol (SCTP) Partial Reliability Extension", RFC 3758, May 2004. [RFC4895] Tuexen, M., Stewart, R., Lei, P., and E. Rescorla, "Authenticated Chunks for the Stream Control Transmission Protocol (SCTP)", RFC 4895, August 2007. [RFC4960] Stewart, R., "Stream Control Transmission Protocol", RFC 4960, September 2007. [RFC5061] Stewart, R., Xie, Q., Tuexen, M., Maruyama, S., and M. Kozuka, "Stream Control Transmission Protocol (SCTP) Dynamic Address Reconfiguration", RFC 5061, September 2007. 12.2. Informative References [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, September 1981. [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, August 1980. [RFC1644] Braden, B., "T/TCP -- TCP Extensions for Transactions Functional Specification", RFC 1644, July 1994. Appendix A. One-to-One Style Code Example The following code is a simple implementation of an echo server over Stewart, et al. Expires January 13, 2011 [Page 90] Internet-Draft SCTP sockets API July 2010 SCTP. The example shows how to use some features of one-to-one style IPv4 SCTP sockets, including: o Opening, binding, and listening for new associations on a socket o Enabling ancillary data o Enabling notifications o Using ancillary data with sendmsg() and recvmsg() o Using MSG_EOR to determine if an entire message has been read o Handling notifications #include #include #include #include #include #include #include #include #include #define BUFLEN 100 static void handle_event(void *buf) { struct sctp_assoc_change *sac; struct sctp_send_failed *ssf; struct sctp_paddr_change *spc; struct sctp_remote_error *sre; union sctp_notification *snp; char addrbuf[INET6_ADDRSTRLEN]; const char *ap; struct sockaddr_in *sin; struct sockaddr_in6 *sin6; snp = buf; switch (snp->sn_header.sn_type) { case SCTP_ASSOC_CHANGE: sac = &snp->sn_assoc_change; printf("^^^ assoc_change: state=%hu, error=%hu, instr=%hu " "outstr=%hu\n", sac->sac_state, sac->sac_error, sac->sac_inbound_streams, sac->sac_outbound_streams); break; case SCTP_SEND_FAILED: ssf = &snp->sn_send_failed; printf("^^^ sendfailed: len=%hu err=%d\n", ssf->ssf_length, ssf->ssf_error); break; Stewart, et al. Expires January 13, 2011 [Page 91] Internet-Draft SCTP sockets API July 2010 case SCTP_PEER_ADDR_CHANGE: spc = &snp->sn_paddr_change; if (spc->spc_aaddr.ss_family == AF_INET) { sin = (struct sockaddr_in *)&spc->spc_aaddr; ap = inet_ntop(AF_INET, &sin->sin_addr, addrbuf, INET6_ADDRSTRLEN); } else { sin6 = (struct sockaddr_in6 *)&spc->spc_aaddr; ap = inet_ntop(AF_INET6, &sin6->sin6_addr, addrbuf, INET6_ADDRSTRLEN); } printf("^^^ intf_change: %s state=%d, error=%d\n", ap, spc->spc_state, spc->spc_error); break; case SCTP_REMOTE_ERROR: sre = &snp->sn_remote_error; printf("^^^ remote_error: err=%hu len=%hu\n", ntohs(sre->sre_error), ntohs(sre->sre_length)); break; case SCTP_SHUTDOWN_EVENT: printf("^^^ shutdown event\n"); break; default: printf("unknown type: %hu\n", snp->sn_header.sn_type); break; }; } static void * mysctp_recvmsg(int fd, struct msghdr *msg, void *buf, size_t *buflen, ssize_t *nrp, size_t cmsglen) { ssize_t nr = 0, nnr = 0; struct iovec iov; *nrp = 0; iov.iov_base = buf; iov.iov_len = *buflen; msg->msg_iov = &iov; msg->msg_iovlen = 1; for (;;) { #ifndef MSG_XPG4_2 #define MSG_XPG4_2 0 #endif msg->msg_flags = MSG_XPG4_2; msg->msg_controllen = cmsglen; Stewart, et al. Expires January 13, 2011 [Page 92] Internet-Draft SCTP sockets API July 2010 nnr = recvmsg(fd, msg, 0); if (nnr <= 0) { /* EOF or error */ *nrp = nr; return (NULL); } nr += nnr; if ((msg->msg_flags & MSG_EOR) != 0) { *nrp = nr; return (buf); } /* Realloc the buffer? */ if (*buflen == (size_t)nr) { buf = realloc(buf, *buflen * 2); if (buf == 0) { fprintf(stderr, "out of memory\n"); exit(1); } *buflen *= 2; } /* Set the next read offset */ iov.iov_base = (char *)buf + nr; iov.iov_len = *buflen - nr; } } static void echo(int fd, int socketModeone_to_many) { ssize_t nr; struct sctp_sndrcvinfo *sri; struct msghdr msg; struct cmsghdr *cmsg; char cbuf[sizeof (*cmsg) + sizeof (*sri)]; char *buf; size_t buflen; struct iovec iov; size_t cmsglen = sizeof (*cmsg) + sizeof (*sri); /* Allocate the initial data buffer */ buflen = BUFLEN; if (!(buf = malloc(BUFLEN))) { fprintf(stderr, "out of memory\n"); exit(1); } /* Set up the msghdr structure for receiving */ Stewart, et al. Expires January 13, 2011 [Page 93] Internet-Draft SCTP sockets API July 2010 memset(&msg, 0, sizeof (msg)); msg.msg_control = cbuf; msg.msg_controllen = cmsglen; msg.msg_flags = 0; cmsg = (struct cmsghdr *)cbuf; sri = (struct sctp_sndrcvinfo *)(cmsg + 1); /* Wait for something to echo */ while (buf = mysctp_recvmsg(fd, &msg, buf, &buflen, &nr, cmsglen)) { /* Intercept notifications here */ if (msg.msg_flags & MSG_NOTIFICATION) { handle_event(buf); continue; } iov.iov_base = buf; iov.iov_len = nr; msg.msg_iov = &iov; msg.msg_iovlen = 1; printf("got %u bytes on stream %hu:\n", nr, sri->sinfo_stream); write(0, buf, nr); /* Echo it back */ msg.msg_flags = MSG_XPG4_2; if (sendmsg(fd, &msg, 0) < 0) { perror("sendmsg"); exit(1); } } if (nr < 0) { perror("recvmsg"); } if(socketModeone_to_many == 0) close(fd); } int main() { struct sctp_event_subscribe event; int lfd, cfd; int onoff = 1; struct sockaddr_in sin; if ((lfd = socket(AF_INET, SOCK_STREAM, IPPROTO_SCTP)) == -1) { Stewart, et al. Expires January 13, 2011 [Page 94] Internet-Draft SCTP sockets API July 2010 perror("socket"); exit(1); } sin.sin_family = AF_INET; sin.sin_port = htons(7); sin.sin_addr.s_addr = INADDR_ANY; if (bind(lfd, (struct sockaddr *)&sin, sizeof (sin)) == -1) { perror("bind"); exit(1); } if (listen(lfd, 1) == -1) { perror("listen"); exit(1); } /* Wait for new associations */ for (;;) { if ((cfd = accept(lfd, NULL, 0)) == -1) { perror("accept"); exit(1); } /* Enable all events */ event.sctp_data_io_event = 1; event.sctp_association_event = 1; event.sctp_address_event = 1; event.sctp_send_failure_event = 1; event.sctp_peer_error_event = 1; event.sctp_shutdown_event = 1; event.sctp_partial_delivery_event = 1; event.sctp_adaptation_layer_event = 1; if (setsockopt(cfd, IPPROTO_SCTP, SCTP_EVENTS, &event, sizeof(event)) != 0) { perror("setevent failed"); exit(1); } /* Echo back any and all data */ echo(cfd,0); } } Stewart, et al. Expires January 13, 2011 [Page 95] Internet-Draft SCTP sockets API July 2010 Appendix B. One-to-Many Style Code Example The following code is a simple implementation of an echo server over SCTP. The example shows how to use some features of one-to-many style IPv4 SCTP sockets, including: o Opening and binding of a socket o Enabling ancillary data o Enabling notifications o Using ancillary data with sendmsg() and recvmsg() o Using MSG_EOR to determine if an entire message has been read o Handling notifications Note most functions defined in Appendix A are reused in this example. int main() { int fd; int idleTime = 2; struct sockaddr_in sin; struct sctp_event_subscribe event; if ((fd = socket(AF_INET, SOCK_SEQPACKET, IPPROTO_SCTP)) == -1) { perror("socket"); exit(1); } sin.sin_family = AF_INET; sin.sin_port = htons(7); sin.sin_addr.s_addr = INADDR_ANY; if (bind(fd, (struct sockaddr *)&sin, sizeof (sin)) == -1) { perror("bind"); exit(1); } /* Enable all notifications and events */ event.sctp_data_io_event = 1; event.sctp_association_event = 1; event.sctp_address_event = 1; event.sctp_send_failure_event = 1; event.sctp_peer_error_event = 1; event.sctp_shutdown_event = 1; event.sctp_partial_delivery_event = 1; event.sctp_adaptation_layer_event = 1; if (setsockopt(fd, IPPROTO_SCTP, SCTP_EVENTS, &event, sizeof(event)) != 0) { perror("setevent failed"); exit(1); Stewart, et al. Expires January 13, 2011 [Page 96] Internet-Draft SCTP sockets API July 2010 } /* Set associations to auto-close in 2 seconds of * inactivity */ if (setsockopt(fd, IPPROTO_SCTP, SCTP_AUTOCLOSE, &idleTime, 4) < 0) { perror("setsockopt SCTP_AUTOCLOSE"); exit(1); } /* Allow new associations to be accepted */ if (listen(fd, 1) < 0) { perror("listen"); exit(1); } /* Wait for new associations */ while(1){ /* Echo back any and all data */ echo(fd,1); /* from appendix a */ } } Authors' Addresses Randall R. Stewart Huawei Chapin, SC 29036 USA Email: rstewart@huawei.com Kacheong Poon Oracle Corporation Email: ka-cheong.poon@oracle.com Michael Tuexen Muenster University of Applied Sciences Stegerwaldstr. 39 48565 Steinfurt Germany Email: tuexen@fh-muenster.de Stewart, et al. Expires January 13, 2011 [Page 97] Internet-Draft SCTP sockets API July 2010 Vladislav Yasevich HP 110 Spitrook Rd Nashua, NH 03062 USA Email: vladislav.yasevich@hp.com Peter Lei Cisco Systems, Inc. 8735 West Higgins Road Suite 300 Chicago, IL 60631 USA Email: peterlei@cisco.com Stewart, et al. Expires January 13, 2011 [Page 98]