Network Working Group C. Feather Request for Comments: 3977 THUS plc Obsoletes: 977 October 2006 Updates: 2980 Category: Standards Track Network News Transfer Protocol (NNTP) Status of This Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2006). Abstract The Network News Transfer Protocol (NNTP) has been in use in the Internet for a decade, and remains one of the most popular protocols (by volume) in use today. This document is a replacement for RFC 977, and officially updates the protocol specification. It clarifies some vagueness in RFC 977, includes some new base functionality, and provides a specific mechanism to add standardized extensions to NNTP. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Author's Note . . . . . . . . . . . . . . . . . . . . . . 4 2. Notation . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Basic Concepts . . . . . . . . . . . . . . . . . . . . . . . 6 3.1. Commands and Responses . . . . . . . . . . . . . . . . . 6 3.1.1. Multi-line Data Blocks . . . . . . . . . . . . . . . . 8 3.2. Response Codes . . . . . . . . . . . . . . . . . . . . . 9 3.2.1. Generic Response Codes . . . . . . . . . . . . . . . 10 3.2.1.1. Examples . . . . . . . . . . . . . . . . . . . . 12 3.3. Capabilities and Extensions . . . . . . . . . . . . . . . 14 3.3.1. Capability Descriptions . . . . . . . . . . . . . . . 14 3.3.2. Standard Capabilities . . . . . . . . . . . . . . . . 15 3.3.3. Extensions . . . . . . . . . . . . . . . . . . . . . 16 3.3.4. Initial IANA Register . . . . . . . . . . . . . . . . 18 3.4. Mandatory and Optional Commands . . . . . . . . . . . . . 20 Feather Standards Track [Page 1] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 3.4.1. Reading and Transit Servers . . . . . . . . . . . . . 21 3.4.2. Mode Switching . . . . . . . . . . . . . . . . . . . 21 3.5. Pipelining . . . . . . . . . . . . . . . . . . . . . . . 22 3.5.1. Examples . . . . . . . . . . . . . . . . . . . . . . 23 3.6. Articles . . . . . . . . . . . . . . . . . . . . . . . . 24 4. The WILDMAT Format . . . . . . . . . . . . . . . . . . . . . 25 4.1. Wildmat Syntax . . . . . . . . . . . . . . . . . . . . . 26 4.2. Wildmat Semantics . . . . . . . . . . . . . . . . . . . . 26 4.3. Extensions . . . . . . . . . . . . . . . . . . . . . . . 27 4.4. Examples . . . . . . . . . . . . . . . . . . . . . . . . 27 5. Session Administration Commands . . . . . . . . . . . . . . . 28 5.1. Initial Connection . . . . . . . . . . . . . . . . . . . 28 5.2. CAPABILITIES . . . . . . . . . . . . . . . . . . . . . . 29 5.3. MODE READER . . . . . . . . . . . . . . . . . . . . . . . 32 5.4. QUIT . . . . . . . . . . . . . . . . . . . . . . . . . . 34 6. Article Posting and Retrieval . . . . . . . . . . . . . . . . 35 6.1. Group and Article Selection . . . . . . . . . . . . . . . 36 6.1.1. GROUP . . . . . . . . . . . . . . . . . . . . . . . . 36 6.1.2. LISTGROUP . . . . . . . . . . . . . . . . . . . . . . 39 6.1.3. LAST . . . . . . . . . . . . . . . . . . . . . . . . 42 6.1.4. NEXT . . . . . . . . . . . . . . . . . . . . . . . . 44 6.2. Retrieval of Articles and Article Sections . . . . . . . 45 6.2.1. ARTICLE . . . . . . . . . . . . . . . . . . . . . . . 46 6.2.2. HEAD . . . . . . . . . . . . . . . . . . . . . . . . 49 6.2.3. BODY . . . . . . . . . . . . . . . . . . . . . . . . 51 6.2.4. STAT . . . . . . . . . . . . . . . . . . . . . . . . 53 6.3. Article Posting . . . . . . . . . . . . . . . . . . . . . 56 6.3.1. POST . . . . . . . . . . . . . . . . . . . . . . . . 56 6.3.2. IHAVE . . . . . . . . . . . . . . . . . . . . . . . . 58 7. Information Commands . . . . . . . . . . . . . . . . . . . . 61 7.1. DATE . . . . . . . . . . . . . . . . . . . . . . . . . . 61 7.2. HELP . . . . . . . . . . . . . . . . . . . . . . . . . . 62 7.3. NEWGROUPS . . . . . . . . . . . . . . . . . . . . . . . . 63 7.4. NEWNEWS . . . . . . . . . . . . . . . . . . . . . . . . . 64 7.5. Time . . . . . . . . . . . . . . . . . . . . . . . . . . 65 7.5.1. Examples . . . . . . . . . . . . . . . . . . . . . . 66 7.6. The LIST Commands . . . . . . . . . . . . . . . . . . . . 66 7.6.1. LIST . . . . . . . . . . . . . . . . . . . . . . . . 67 7.6.2. Standard LIST Keywords . . . . . . . . . . . . . . . 69 7.6.3. LIST ACTIVE . . . . . . . . . . . . . . . . . . . . . 70 7.6.4. LIST ACTIVE.TIMES . . . . . . . . . . . . . . . . . . 71 7.6.5. LIST DISTRIB.PATS . . . . . . . . . . . . . . . . . . 72 7.6.6. LIST NEWSGROUPS . . . . . . . . . . . . . . . . . . . 73 8. Article Field Access Commands . . . . . . . . . . . . . . . . 73 8.1. Article Metadata . . . . . . . . . . . . . . . . . . . . 74 8.1.1. The :bytes Metadata Item . . . . . . . . . . . . . . 74 8.1.2. The :lines Metadata Item . . . . . . . . . . . . . . 75 8.2. Database Consistency . . . . . . . . . . . . . . . . . . 75 Feather Standards Track [Page 2] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 8.3. OVER . . . . . . . . . . . . . . . . . . . . . . . . . . 76 8.4. LIST OVERVIEW.FMT . . . . . . . . . . . . . . . . . . . . 81 8.5. HDR . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 8.6. LIST HEADERS . . . . . . . . . . . . . . . . . . . . . . 87 9. Augmented BNF Syntax for NNTP . . . . . . . . . . . . . . . . 90 9.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 90 9.2. Commands . . . . . . . . . . . . . . . . . . . . . . . . 92 9.3. Command Continuation . . . . . . . . . . . . . . . . . . 93 9.4. Responses . . . . . . . . . . . . . . . . . . . . . . . . 93 9.4.1. Generic Responses . . . . . . . . . . . . . . . . . . 93 9.4.2. Initial Response Line Contents . . . . . . . . . . . 94 9.4.3. Multi-line Response Contents . . . . . . . . . . . . 94 9.5. Capability Lines . . . . . . . . . . . . . . . . . . . . 95 9.6. LIST Variants . . . . . . . . . . . . . . . . . . . . . . 96 9.7. Articles . . . . . . . . . . . . . . . . . . . . . . . . 97 9.8. General Non-terminals . . . . . . . . . . . . . . . . . . 97 9.9. Extensions and Validation . . . . . . . . . . . . . . . . 99 10. Internationalisation Considerations . . . . . . . . . . . . .100 10.1. Introduction and Historical Situation . . . . . . . . . .100 10.2. This Specification . . . . . . . . . . . . . . . . . . .101 10.3. Outstanding Issues . . . . . . . . . . . . . . . . . . .102 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .103 12. Security Considerations . . . . . . . . . . . . . . . . . . .103 12.1. Personal and Proprietary Information . . . . . . . . . .104 12.2. Abuse of Server Log Information . . . . . . . . . . . . .104 12.3. Weak Authentication and Access Control . . . . . . . . .104 12.4. DNS Spoofing . . . . . . . . . . . . . . . . . . . . . .104 12.5. UTF-8 Issues . . . . . . . . . . . . . . . . . . . . . .105 12.6. Caching of Capability Lists . . . . . . . . . . . . . . .106 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . .107 14. References . . . . . . . . . . . . . . . . . . . . . . . . .110 14.1. Normative References . . . . . . . . . . . . . . . . . .110 14.2. Informative References . . . . . . . . . . . . . . . . .110 A. Interaction with Other Specifications . . . . . . . . . . . .112 A.1. Header Folding . . . . . . . . . . . . . . . . . . . . .112 A.2. Message-IDs . . . . . . . . . . . . . . . . . . . . . . .112 A.3. Article Posting . . . . . . . . . . . . . . . . . . . . .114 B. Summary of Commands . . . . . . . . . . . . . . . . . . . . .115 C. Summary of Response Codes . . . . . . . . . . . . . . . . . .117 D. Changes from RFC 977 . . . . . . . . . . . . . . . . . . . .121 1. Introduction This document specifies the Network News Transfer Protocol (NNTP), which is used for the distribution, inquiry, retrieval, and posting of Netnews articles using a reliable stream-based mechanism. For news-reading clients, NNTP enables retrieval of news articles that Feather Standards Track [Page 3] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 are stored in a central database, giving subscribers the ability to select only those articles they wish to read. The Netnews model provides for indexing, cross-referencing, and expiration of aged messages. NNTP is designed for efficient transmission of Netnews articles over a reliable full duplex communication channel. Although the protocol specification in this document is largely compatible with the version specified in RFC 977 [RFC977], a number of changes are summarised in Appendix D. In particular: o the default character set is changed from US-ASCII [ANSI1986] to UTF-8 [RFC3629] (note that US-ASCII is a subset of UTF-8); o a number of commands that were optional in RFC 977 or that have been taken from RFC 2980 [RFC2980] are now mandatory; and o a CAPABILITIES command has been added to allow clients to determine what functionality is available from a server. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. An implementation is not compliant if it fails to satisfy one or more of the MUST requirements for this protocol. An implementation that satisfies all the MUST and all the SHOULD requirements for its protocols is said to be "unconditionally compliant"; one that satisfies all the MUST requirements but not all the SHOULD requirements for NNTP is said to be "conditionally compliant". For the remainder of this document, the terms "client" and "client host" refer to a host making use of the NNTP service, while the terms "server" and "server host" refer to a host that offers the NNTP service. 1.1. Author's Note This document is written in XML using an NNTP-specific DTD. Custom software is used to convert this to RFC 2629 [RFC2629] format, and then the public "xml2rfc" package to further reduce this to text, nroff source, and HTML. No perl was used in producing this document. Feather Standards Track [Page 4] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 2. Notation The following notational conventions are used in this document. UPPERCASE indicates literal text to be included in the command. lowercase indicates a token described elsewhere. [brackets] indicate that the enclosed material is optional. elliptical indicates that the argument may be repeated any ... marks number of times (it must occur at least once). vertical|bar indicates a choice of two mutually exclusive arguments (exactly one must be provided). The name "message-id" for a command or response argument indicates that it is the message-id of an article as described in Section 3.6, including the angle brackets. The name "wildmat" for an argument indicates that it is a wildmat as defined in Section 4. If the argument does not meet the requirements of that section (for example, if it does not fit the grammar of Section 4.1), the NNTP server MAY place some interpretation on it (not specified by this document) or otherwise MUST treat it as a syntax error. Responses for each command will be described in tables listing the required format of a response followed by the meaning that should be ascribed to that response. The terms "NUL", "TAB", "LF", "CR, and "space" refer to the octets %x00, %x09, %x0A, %x0D, and %x20, respectively (that is, the octets with those codes in US-ASCII [ANSI1986] and thus in UTF-8 [RFC3629]). The term "CRLF" or "CRLF pair" means the sequence CR immediately followed by LF (that is, %x0D.0A). A "printable US-ASCII character" is an octet in the range %x21-7E. Quoted characters refer to the octets with those codes in US-ASCII (so "." and "<" refer to %x2E and %x3C) and will always be printable US-ASCII characters; similarly, "digit" refers to the octets %x30-39. A "keyword" MUST consist only of US-ASCII letters, digits, and the characters dot (".") and dash ("-") and MUST begin with a letter. Keywords MUST be at least three characters in length. Feather Standards Track [Page 5] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 Examples in this document are not normative but serve to illustrate usages, arguments, and responses. In the examples, a "[C]" will be used to represent the client host and an "[S]" will be used to represent the server host. Most of the examples do not rely on a particular server state. In some cases, however, they do assume that the currently selected newsgroup (see the GROUP command, Section 6.1.1) is invalid; when so, this is indicated at the start of the example. Examples may use commands or other keywords not defined in this specification (such as an XENCRYPT command). These will be used to illustrate some point and do not imply that any such command is defined elsewhere or needs to exist in any particular implementation. Terms that might be read as specifying details of a client or server implementation, such as "database", are used simply to ease description. Provided that implementations conform to the protocol and format specifications in this document, no specific technique is mandated. 3. Basic Concepts 3.1. Commands and Responses NNTP operates over any reliable bi-directional 8-bit-wide data stream channel. When the connection is established, the NNTP server host MUST send a greeting. The client host and server host then exchange commands and responses (respectively) until the connection is closed or aborted. If the connection used is TCP, then the server host starts the NNTP service by listening on a TCP port. When a client host wishes to make use of the service, it MUST establish a TCP connection with the server host by connecting to that host on the same port on which the server is listening. The character set for all NNTP commands is UTF-8 [RFC3629]. Commands in NNTP MUST consist of a keyword, which MAY be followed by one or more arguments. A CRLF pair MUST terminate all commands. Multiple commands MUST NOT be on the same line. Unless otherwise noted elsewhere in this document, arguments SHOULD consist of printable US- ASCII characters. Keywords and arguments MUST each be separated by one or more space or TAB characters. Command lines MUST NOT exceed 512 octets, which includes the terminating CRLF pair. The arguments MUST NOT exceed 497 octets. A server MAY relax these limits for commands defined in an extension. Where this specification permits UTF-8 characters outside the range of U+0000 to U+007F, implementations MUST NOT use the Byte Order Mark (U+FEFF, encoding %xEF.BB.BF) and MUST use the Word Joiner (U+2060, encoding %xE2.91.A0) for the meaning Zero Width No-Break Space in Feather Standards Track [Page 6] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 command lines and the initial lines of responses. Implementations SHOULD apply these same principles throughout. The term "character" means a single Unicode code point. Implementations are not required to carry out Unicode normalisation. Thus, U+0084 (A-dieresis) is one character, while U+0041 U+0308 (A composed with dieresis) is two; the two need not be treated as equivalent. Commands may have variants; if so, they use a second keyword immediately after the first to indicate which variant is required. The only such commands in this specification are LIST and MODE. Note that such variants are sometimes referred to as if they were commands in their own right: "the LIST ACTIVE" command should be read as shorthand for "the ACTIVE variant of the LIST command". Keywords are case insensitive; the case of keywords for commands MUST be ignored by the server. Command and response arguments are case or language specific only when stated, either in this document or in other relevant specifications. In some cases, a command involves more data than just a single line. The further data may be sent either immediately after the command line (there are no instances of this in this specification, but there are in extensions such as [NNTP-STREAM]) or following a request from the server (indicated by a 3xx response). Each response MUST start with a three-digit response code that is sufficient to distinguish all responses. Certain valid responses are defined to be multi-line; for all others, the response is contained in a single line. The initial line of the response MUST NOT exceed 512 octets, which includes the response code and the terminating CRLF pair; an extension MAY specify a greater maximum for commands that it defines, but not for any other command. Single-line responses consist of an initial line only. Multi-line responses consist of an initial line followed by a multi-line data block. An NNTP server MAY have an inactivity autologout timer. Such a timer SHOULD be of at least three minutes' duration, with the exception that there MAY be a shorter limit on how long the server is willing to wait for the first command from the client. The receipt of any command from the client during the timer interval SHOULD suffice to reset the autologout timer. Similarly, the receipt of any significant amount of data from a client that is sending a multi-line data block (such as during a POST or IHAVE command) SHOULD suffice to reset the autologout timer. When the timer expires, the server SHOULD close the connection without sending any response to the client. Feather Standards Track [Page 7] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 3.1.1. Multi-line Data Blocks A multi-line data block is used in certain commands and responses. It MUST adhere to the following rules: 1. The block consists of a sequence of zero or more "lines", each being a stream of octets ending with a CRLF pair. Apart from those line endings, the stream MUST NOT include the octets NUL, LF, or CR. 2. In a multi-line response, the block immediately follows the CRLF at the end of the initial line of the response. When used in any other context, the specific command will define when the block is sent. 3. If any line of the data block begins with the "termination octet" ("." or %x2E), that line MUST be "dot-stuffed" by prepending an additional termination octet to that line of the block. 4. The lines of the block MUST be followed by a terminating line consisting of a single termination octet followed by a CRLF pair in the normal way. Thus, unless it is empty, a multi-line block is always terminated with the five octets CRLF "." CRLF (%x0D.0A.2E.0D.0A). 5. When a multi-line block is interpreted, the "dot-stuffing" MUST be undone; i.e., the recipient MUST ensure that, in any line beginning with the termination octet followed by octets other than a CRLF pair, that initial termination octet is disregarded. 6. Likewise, the terminating line ("." CRLF or %x2E.0D.0A) MUST NOT be considered part of the multi-line block; i.e., the recipient MUST ensure that any line beginning with the termination octet followed immediately by a CRLF pair is disregarded. (The first CRLF pair of the terminating CRLF "." CRLF of a non-empty block is, of course, part of the last line of the block.) Note that texts using an encoding (such as UTF-16 or UTF-32) that may contain the octets NUL, LF, or CR other than a CRLF pair cannot be reliably conveyed in the above format (that is, they violate the MUST requirement above). However, except when stated otherwise, this specification does not require the content to be UTF-8, and therefore (subject to that same requirement) it MAY include octets above and below 128 mixed arbitrarily. This document does not place any limit on the length of a line in a multi-line block. However, the standards that define the format of articles may do so. Feather Standards Track [Page 8] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 3.2. Response Codes Each response MUST begin with a three-digit status indicator. These are status reports from the server and indicate the response to the last command received from the client. The first digit of the response broadly indicates the success, failure, or progress of the previous command: 1xx - Informative message 2xx - Command completed OK 3xx - Command OK so far; send the rest of it 4xx - Command was syntactically correct but failed for some reason 5xx - Command unknown, unsupported, unavailable, or syntax error The next digit in the code indicates the function response category: x0x - Connection, setup, and miscellaneous messages x1x - Newsgroup selection x2x - Article selection x3x - Distribution functions x4x - Posting x8x - Reserved for authentication and privacy extensions x9x - Reserved for private use (non-standard extensions) Certain responses contain arguments such as numbers and names in addition to the status indicator. In those cases, to simplify interpretation by the client, the number and type of such arguments is fixed for each response code, as is whether the code is single-line or multi-line. Any extension MUST follow this principle as well. Note that, for historical reasons, the 211 response code is an exception to this in that the response may be single-line or multi-line depending on the command (GROUP or LISTGROUP) that generated it. In all other cases, the client MUST only use the status indicator itself to determine the nature of the response. The exact response codes that can be returned by any given command are detailed in the description of that command. Arguments MUST be separated from the numeric status indicator and from each other by a single space. All numeric arguments MUST be in base 10 (decimal) format and MAY have leading zeros. String arguments MUST contain at least one character and MUST NOT contain TAB, LF, CR, or space. The server MAY add any text after the response code or last argument, as appropriate, and the client MUST NOT make decisions based on this text. Such text MUST be separated from the numeric status indicator or the last argument by at least one space. Feather Standards Track [Page 9] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 The server MUST respond to any command with the appropriate generic response (given in Section 3.2.1) if it represents the situation. Otherwise, each recognized command MUST return one of the response codes specifically listed in its description or in an extension. A server MAY provide extensions to this specification, including new commands, new variants or features of existing commands, and other ways of changing the internal state of the server. However, the server MUST NOT produce any other responses to a client that does not invoke any of the additional features. (Therefore, a client that restricts itself to this specification will only receive the responses that are listed.) If a client receives an unexpected response, it SHOULD use the first digit of the response to determine the result. For example, an unexpected 2xx should be taken as success, and an unexpected 4xx or 5xx as failure. Response codes not specified in this document MAY be used for any installation-specific additional commands also not specified. These SHOULD be chosen to fit the pattern of x9x specified above. Neither this document nor any registered extension (see Section 3.3.3) will specify any response codes of the x9x pattern. (Implementers of extensions are accordingly cautioned not to use such responses for extensions that may subsequently be submitted for registration.) 3.2.1. Generic Response Codes The server MUST respond to any command with the appropriate one of the following generic responses if it represents the situation. If the command is not recognized, or if it is an optional command that is not implemented by the server, the response code 500 MUST be returned. If there is a syntax error in the arguments of a recognized command, including the case where more arguments are provided than the command specifies or the command line is longer than the server accepts, the response code 501 MUST be returned. The line MUST NOT be truncated or split and then interpreted. Note that where a command has variants depending on a second keyword (e.g., LIST ACTIVE and LIST NEWSGROUPS), 501 MUST be used when the base command is implemented but the requested variant is not, and 500 MUST be used only when the base command itself is not implemented. If an argument is required to be a base64-encoded string [RFC4648] (there are no such arguments in this specification, but there may be Feather Standards Track [Page 10] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 in extensions) and is not validly encoded, the response code 504 MUST be returned. If the server experiences an internal fault or problem that means it is unable to carry out the command (for example, a necessary file is missing or a necessary service could not be contacted), the response code 403 MUST be returned. If the server recognizes the command but does not provide an optional feature (for example, because it does not store the required information), or if it only handles a subset of legitimate cases (see the HDR command, Section 8.5, for an example), the response code 503 MUST be returned. If the client is not authorized to use the specified facility when the server is in its current state, then the appropriate one of the following response codes MUST be used. 502: It is necessary to terminate the connection and to start a new one with the appropriate authority before the command can be used. Historically, some mode-switching servers (see Section 3.4.1) used this response to indicate that this command will become available after the MODE READER command (Section 5.3) is used, but this usage does not conform to this specification and MUST NOT be used. Note that the server MUST NOT close the connection immediately after a 502 response except at the initial connection (Section 5.1) and with the MODE READER command. 480: The client must authenticate itself to the server (that is, it must provide information as to the identity of the client) before the facility can be used on this connection. This will involve the use of an authentication extension such as [NNTP-AUTH]. 483: The client must negotiate appropriate privacy protection on the connection. This will involve the use of a privacy extension such as [NNTP-TLS]. 401: The client must change the state of the connection in some other manner. The first argument of the response MUST be the capability label (see Section 5.2) of the facility that provides the necessary mechanism (usually an extension, which may be a private extension). The server MUST NOT use this response code except as specified by the definition of the capability in question. If the server has to terminate the connection for some reason, it MUST give a 400 response code to the next command and then immediately close the connection. Following a 400 response, clients SHOULD NOT simply reconnect immediately and retry the same actions. Rather, a client SHOULD either use an exponentially increasing delay between retries (e.g., double the waiting time after each 400 Feather Standards Track [Page 11] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 response) or present any associated text to the user for them to decide whether and when to retry. The client MUST be prepared to receive any of these responses for any command (except, of course, that the server MUST NOT generate a 500 response code for mandatory commands). 3.2.1.1. Examples Example of an unknown command: [C] MAIL [S] 500 Unknown command Example of an unsupported command: [C] CAPABILITIES [S] 101 Capability list: [S] VERSION 2 [S] READER [S] NEWNEWS [S] LIST ACTIVE NEWSGROUPS [S] . [C] OVER [S] 500 Unknown command Example of an unsupported variant: [C] MODE POSTER [S] 501 Unknown MODE option Example of a syntax error: [C] ARTICLE a.message.id@no.angle.brackets [S] 501 Syntax error Example of an overlong command line: [C] HEAD 53 54 55 [S] 501 Too many arguments Example of a bad wildmat: [C] LIST ACTIVE u[ks].* [S] 501 Syntax error Feather Standards Track [Page 12] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 Example of a base64-encoding error (the second argument is meant to be base64 encoded): [C] XENCRYPT RSA abcd=efg [S] 504 Base64 encoding error Example of an attempt to access a facility not available to this connection: [C] MODE READER [S] 200 Reader mode, posting permitted [C] IHAVE [S] 500 Permission denied Example of an attempt to access a facility requiring authentication: [C] GROUP secret.group [S] 480 Permission denied Example of a successful attempt following such authentication: [C] XSECRET fred flintstone [S] 290 Password for fred accepted [C] GROUP secret.group [S] 211 5 1 20 secret.group selected Example of an attempt to access a facility requiring privacy: [C] GROUP secret.group [S] 483 Secure connection required [C] XENCRYPT [Client and server negotiate encryption on the link] [S] 283 Encrypted link established [C] GROUP secret.group [S] 211 5 1 20 secret.group selected Example of a need to change mode before a facility is used: [C] GROUP binary.group [S] 401 XHOST Not on this virtual host [C] XHOST binary.news.example.org [S] 290 binary.news.example.org virtual host selected [C] GROUP binary.group [S] 211 5 1 77 binary.group selected Feather Standards Track [Page 13] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 Example of a temporary failure: [C] GROUP archive.local [S] 403 Archive server temporarily offline Example of the server needing to close down immediately: [C] ARTICLE 123 [S] 400 Power supply failed, running on UPS [Server closes connection.] 3.3. Capabilities and Extensions Not all NNTP servers provide exactly the same facilities, both because this specification allows variation and because servers may provide extensions. A set of facilities that are related are called a "capability". This specification provides a way to determine what capabilities are available, includes a list of standard capabilities, and includes a mechanism (the extension mechanism) for defining new capabilities. 3.3.1. Capability Descriptions A client can determine the available capabilities of the server by using the CAPABILITIES command (Section 5.2). This returns a capability list, which is a list of capability lines. Each line describes one available capability. Each capability line consists of one or more tokens, which MUST be separated by one or more space or TAB characters. A token is a string of 1 or more printable UTF-8 characters (that is, either printable US-ASCII characters or any UTF-8 sequence outside the US- ASCII range, but not space or TAB). Unless stated otherwise, tokens are case insensitive. Each capability line consists of the following: o The capability label, which is a keyword indicating the capability. A capability label may be defined by this specification or a successor, or by an extension. o The label is then followed by zero or more tokens, which are arguments of the capability. The form and meaning of these tokens is specific to each capability. The server MUST ensure that the capability list accurately reflects the capabilities (including extensions) currently available. If a capability is only available with the server in a certain state (for example, only after authentication), the list MUST only include the Feather Standards Track [Page 14] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 capability label when the server is in that state. Similarly, if only some of the commands in an extension will be available, or if the behaviour of the extension will change in some other manner, according to the state of the server, this MUST be indicated by different arguments in the capability line. Note that a capability line can only begin with a letter. Lines beginning with other characters are reserved for future versions of this specification. In order to interoperate with such versions, clients MUST be prepared to receive lines beginning with other characters and MUST ignore any they do not understand. 3.3.2. Standard Capabilities The following capabilities are defined by this specification. VERSION This capability MUST be advertised by all servers and MUST be the first capability in the capability list; it indicates the version(s) of NNTP that the server supports. There must be at least one argument; each argument is a decimal number and MUST NOT have a leading zero. Version numbers are assigned only in RFCs that update or replace this specification; servers MUST NOT create their own version numbers. The version number of this specification is 2. READER This capability indicates that the server implements the various commands useful for reading clients. IHAVE This capability indicates that the server implements the IHAVE command. POST This capability indicates that the server implements the POST command. NEWNEWS This capability indicates that the server implements the NEWNEWS command. HDR This capability indicates that the server implements the header access commands (HDR and LIST HEADERS). Feather Standards Track [Page 15] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 OVER This capability indicates that the server implements the overview access commands (OVER and LIST OVERVIEW.FMT). If and only if the server supports the message-id form of the OVER command, there must be a single argument MSGID. LIST This capability indicates that the server implements at least one variant of the LIST command. There MUST be one argument for each variant of the LIST command supported by the server, giving the keyword for that variant. IMPLEMENTATION This capability MAY be provided by a server. If so, the arguments SHOULD be used to provide information such as the server software name and version number. The client MUST NOT use this line to determine capabilities of the server. (While servers often provide this information in the initial greeting, clients need to guess whether this is the case; this capability makes it clear what the information is.) MODE-READER This capability indicates that the server is mode-switching (Section 3.4.2) and that the MODE READER command needs to be used to enable the READER capability. 3.3.3. Extensions Although NNTP is widely and robustly deployed, some parts of the Internet community might wish to extend the NNTP service. It must be emphasized that any extension to NNTP should not be considered lightly. NNTP's strength comes primarily from its simplicity. Experience with many protocols has shown that: Protocols with few options tend towards ubiquity, whilst protocols with many options tend towards obscurity. This means that each and every extension, regardless of its benefits, must be carefully scrutinized with respect to its implementation, deployment, and interoperability costs. In many cases, the cost of extending the NNTP service will likely outweigh the benefit. An extension is a package of associated facilities, often but not always including one or more new commands. Each extension MUST define at least one new capability label (this will often, but need not, be the name of one of these new commands). While any additional capability information can normally be specified using arguments to Feather Standards Track [Page 16] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 that label, an extension MAY define more than one capability label. However, this SHOULD be limited to exceptional circumstances. An extension is either a private extension, or its capabilities are included in the IANA registry of capabilities (see Section 3.3.4) and it is defined in an RFC (in which case it is a "registered extension"). Such RFCs either must be on the standards track or must define an IESG-approved experimental protocol. The definition of an extension must include the following: o a descriptive name for the extension. o the capability label or labels defined by the extension (the capability label of a registered extension MUST NOT begin with "X"). o The syntax, values, and meanings of any arguments for each capability label defined by the extension. o Any new NNTP commands associated with the extension (the names of commands associated with registered extensions MUST NOT begin with "X"). o The syntax and possible values of arguments associated with the new NNTP commands. o The response codes and possible values of arguments for the responses of the new NNTP commands. o Any new arguments the extension associates with any other pre-existing NNTP commands. o Any increase in the maximum length of commands and initial response lines over the value specified in this document. o A specific statement about the effect on pipelining that this extension may have (if any). o A specific statement about the circumstances when use of this extension can alter the contents of the capabilities list (other than the new capability labels it defines). o A specific statement about the circumstances under which the extension can cause any pre-existing command to produce a 401, 480, or 483 response. Feather Standards Track [Page 17] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 o A description of how the use of MODE READER on a mode-switching server interacts with the extension. o A description of how support for the extension affects the behaviour of a server and NNTP client in any other manner not outlined above. o Formal syntax as described in Section 9.9. A private extension MAY or MAY NOT be included in the capabilities list. If it is, the capability label MUST begin with "X". A server MAY provide additional keywords (for new commands and also for new variants of existing commands) as part of a private extension. To avoid the risk of a clash with a future registered extension, these keywords SHOULD begin with "X". If the server advertises a capability defined by a registered extension, it MUST implement the extension so as to fully conform with the specification (for example, it MUST implement all the commands that the extension describes as mandatory). If it does not implement the extension as specified, it MUST NOT list the extension in the capabilities list under its registered name. In that case, it MAY, but SHOULD NOT, provide a private extension (not listed, or listed with a different name) that implements part of the extension or implements the commands of the extension with a different meaning. A server MUST NOT send different response codes to basic NNTP commands documented here or to commands documented in registered extensions in response to the availability or use of a private extension. 3.3.4. Initial IANA Register IANA will maintain a registry of NNTP capability labels. All capability labels in the registry MUST be keywords and MUST NOT begin with X. Feather Standards Track [Page 18] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 The initial content of the registry consists of these entries: +-------------------+--------------------------+--------------------+ | Label | Meaning | Definition | +-------------------+--------------------------+--------------------+ | AUTHINFO | Authentication | [NNTP-AUTH] | | | | | | HDR | Batched header retrieval | Section 3.3.2, | | | | Section 8.5, and | | | | Section 8.6 | | | | | | IHAVE | IHAVE command available | Section 3.3.2 and | | | | Section 6.3.2 | | | | | | IMPLEMENTATION | Server | Section 3.3.2 | | | implementation-specific | | | | information | | | | | | | LIST | LIST command variants | Section 3.3.2 and | | | | Section 7.6.1 | | | | | | MODE-READER | Mode-switching server | Section 3.4.2 | | | and MODE READER command | | | | available | | | | | | | NEWNEWS | NEWNEWS command | Section 3.3.2 and | | | available | Section 7.4 | | | | | | OVER | Overview support | Section 3.3.2, | | | | Section 8.3, and | | | | Section 8.4 | | | | | | POST | POST command available | Section 3.3.2 and | | | | Section 6.3.1 | | | | | | READER | Reader commands | Section 3.3.2 | | | available | | | | | | | SASL | Supported SASL | [NNTP-AUTH] | | | mechanisms | | | | | | | STARTTLS | Transport layer security | [NNTP-TLS] | | | | | | STREAMING | Streaming feeds | [NNTP-STREAM] | | | | | | VERSION | Supported NNTP versions | Section 3.3.2 | +-------------------+--------------------------+--------------------+ Feather Standards Track [Page 19] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 3.4. Mandatory and Optional Commands For a number of reasons, not all the commands in this specification are mandatory. However, it is equally undesirable for every command to be optional, since this means that a client will have no idea what facilities are available. Therefore, as a compromise, some of the commands in this specification are mandatory (they must be supported by all servers) while the remainder are not. The latter are then subdivided into bundles, each indicated by a single capability label. o If the label is included in the capability list returned by the server, the server MUST support all commands in that bundle. o If the label is not included, the server MAY support none or some of the commands but SHOULD NOT support all of them. In general, there will be no way for a client to determine which commands are supported without trying them. The bundles have been chosen to provide useful functionality, and therefore server authors are discouraged from implementing only part of a bundle. The description of each command will either indicate that it is mandatory, or will give, using the term "indicating capability", the capability label indicating whether the bundle including this command is available. Where a server does not implement a command, it MUST always generate a 500 generic response code (or a 501 generic response code in the case of a variant of a command depending on a second keyword where the base command is recognised). Otherwise, the command MUST be fully implemented as specified; a server MUST NOT only partially implement any of the commands in this specification. (Client authors should note that some servers not conforming to this specification will return a 502 generic response code to some commands that are not implemented.) Note: some commands have cases that require other commands to be used first. If the former command is implemented but the latter is not, the former MUST still generate the relevant specific response code. For example, if ARTICLE (Section 6.2.1) is implemented but GROUP (Section 6.1.1) is not, the correct response to "ARTICLE 1234" remains 412. Feather Standards Track [Page 20] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 3.4.1. Reading and Transit Servers NNTP is traditionally used in two different ways. The first use is "reading", where the client fetches articles from a large store maintained by the server for immediate or later presentation to a user and sends articles created by that user back to the server (an action called "posting") to be stored and distributed to other stores and users. The second use is for the bulk transfer of articles from one store to another. Since the hosts making this transfer tend to be peers in a network that transmit articles among one another, and not end-user systems, this process is called "peering" or "transit". (Even so, one host is still the client and the other is the server). In practice, these two uses are so different that some server implementations are optimised for reading or for transit and, as a result, do not offer the other facility or only offer limited features. Other implementations are more general and offer both. This specification allows for this by bundling the relevant commands accordingly: the IHAVE command is designed for transit, while the commands indicated by the READER capability are designed for reading clients. Except as an effect of the MODE READER command (Section 5.3) on a mode-switching server, once a server advertises either or both of the IHAVE or READER capabilities, it MUST continue to advertise them for the entire session. A server MAY provide different modes of behaviour (transit, reader, or a combination) to different client connections and MAY use external information, such as the IP address of the client, to determine which mode to provide to any given connection. The official TCP port for the NNTP service is 119. However, if a host wishes to offer separate servers for transit and reading clients, port 433 SHOULD be used for the transit server and 119 for the reading server. 3.4.2. Mode Switching An implementation MAY, but SHOULD NOT, provide both transit and reader facilities on the same server but require the client to select which it wishes to use. Such an arrangement is called a "mode-switching" server. Feather Standards Track [Page 21] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 A mode-switching server has two modes: o Transit mode, which applies after the initial connection. * It MUST advertise the MODE-READER capability. * It MUST NOT advertise the READER capability. However, the server MAY cease to advertise the MODE-READER capability after the client uses any command except CAPABILITIES. o Reading mode, after a successful MODE READER command (see Section 5.3). * It MUST NOT advertise the MODE-READER capability. * It MUST advertise the READER capability. * It MAY NOT advertise the IHAVE capability, even if it was advertising it in transit mode. A client SHOULD only issue a MODE READER command to a server if it is advertising the MODE-READER capability. If the server does not support CAPABILITIES (and therefore does not conform to this specification), the client MAY use the following heuristic: o If the client wishes to use any "reader" commands, it SHOULD use the MODE READER command immediately after the initial connection. o Otherwise, it SHOULD NOT use the MODE READER command. In each case, it should be prepared for some commands to be unavailable that would have been available if it had made the other choice. 3.5. Pipelining NNTP is designed to operate over a reliable bi-directional connection, such as TCP. Therefore, if a command does not depend on the response to the previous one, it should not matter if it is sent before that response is received. Doing this is called "pipelining". However, certain server implementations throw away all text received from the client following certain commands before sending their response. If this happens, pipelining will be affected because one or more commands will have been ignored or misinterpreted, and the client will be matching the wrong responses to each command. Since there are significant benefits to pipelining, but also circumstances where it is reasonable or common for servers to behave in the above Feather Standards Track [Page 22] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 manner, this document puts certain requirements on both clients and servers. Except where stated otherwise, a client MAY use pipelining. That is, it may send a command before receiving the response for the previous command. The server MUST allow pipelining and MUST NOT throw away any text received after a command. Irrespective of whether pipelining is used, the server MUST process commands in the order they are sent. If the specific description of a command says it "MUST NOT be pipelined", that command MUST end any pipeline of commands. That is, the client MUST NOT send any following command until it receives the CRLF at the end of the response from the command. The server MAY ignore any data received after the command and before the CRLF at the end of the response is sent to the client. The initial connection must not be part of a pipeline; that is, the client MUST NOT send any command until it receives the CRLF at the end of the greeting. If the client uses blocking system calls to send commands, it MUST ensure that the amount of text sent in pipelining does not cause a deadlock between transmission and reception. The amount of text involved will depend on window sizes in the transmission layer; typically, it is 4k octets for TCP. (Since the server only sends data in response to commands from the client, the converse problem does not occur.) 3.5.1. Examples Example of correct use of pipelining: [C] GROUP misc.test [C] STAT [C] NEXT [S] 211 1234 3000234 3002322 misc.test [S] 223 3000234 <45223423@example.com> retrieved [S] 223 3000237 <668929@example.org> retrieved Example of incorrect use of pipelining (the MODE READER command may not be pipelined): [C] MODE READER [C] DATE [C] NEXT [S] 200 Server ready, posting allowed [S] 223 3000237 <668929@example.org> retrieved Feather Standards Track [Page 23] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 The DATE command has been thrown away by the server, so there is no 111 response to match it. 3.6. Articles NNTP is intended to transfer articles between clients and servers. For the purposes of this specification, articles are required to conform to the rules in this section, and clients and servers MUST correctly process any article received from the other that does so. Note that this requirement applies only to the contents of communications over NNTP; it does not prevent the client or server from subsequently rejecting an article for reasons of local policy. Also see Appendix A for further restrictions on the format of articles in some uses of NNTP. An article consists of two parts: the headers and the body. They are separated by a single empty line, or in other words by two consecutive CRLF pairs (if there is more than one empty line, the second and subsequent ones are part of the body). In order to meet the general requirements of NNTP, an article MUST NOT include the octet NUL, MUST NOT contain the octets LF and CR other than as part of a CRLF pair, and MUST end with a CRLF pair. This specification puts no further restrictions on the body; in particular, it MAY be empty. The headers of an article consist of one or more header lines. Each header line consists of a header name, a colon, a space, the header content, and a CRLF, in that order. The name consists of one or more printable US-ASCII characters other than colon and, for the purposes of this specification, is not case sensitive. There MAY be more than one header line with the same name. The content MUST NOT contain CRLF; it MAY be empty. A header may be "folded"; that is, a CRLF pair may be placed before any TAB or space in the line. There MUST still be some other octet between any two CRLF pairs in a header line. (Note that folding means that the header line occupies more than one line when displayed or transmitted; nevertheless, it is still referred to as "a" header line.) The presence or absence of folding does not affect the meaning of the header line; that is, the CRLF pairs introduced by folding are not considered part of the header content. Header lines SHOULD NOT be folded before the space after the colon that follows the header name and SHOULD include at least one octet other than %x09 or %x20 between CRLF pairs. However, if an article that fails to satisfy this requirement has been received from elsewhere, clients and servers MAY transfer it to each other without re-folding it. Feather Standards Track [Page 24] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 The content of a header SHOULD be in UTF-8. However, if an implementation receives an article from elsewhere that uses octets in the range 128 to 255 in some other manner, it MAY pass it to a client or server without modification. Therefore, implementations MUST be prepared to receive such headers, and data derived from them (e.g., in the responses from the OVER command, Section 8.3), and MUST NOT assume that they are always UTF-8. Any external processing of those headers, including identifying the encoding used, is outside the scope of this document. Each article MUST have a unique message-id; two articles offered by an NNTP server MUST NOT have the same message-id. For the purposes of this specification, message-ids are opaque strings that MUST meet the following requirements: o A message-id MUST begin with "<", end with ">", and MUST NOT contain the latter except at the end. o A message-id MUST be between 3 and 250 octets in length. o A message-id MUST NOT contain octets other than printable US-ASCII characters. Two message-ids are the same if and only if they consist of the same sequence of octets. This specification does not describe how the message-id of an article is determined. If the server does not have any way to determine a message-id from the article itself, it MUST synthesize one (this specification does not require that the article be changed as a result). See also Appendix A.2. 4. The WILDMAT Format The WILDMAT format described here is based on the version first developed by Rich Salz [SALZ1992], which was in turn derived from the format used in the UNIX "find" command to articulate file names. It was developed to provide a uniform mechanism for matching patterns in the same manner that the UNIX shell matches filenames. Feather Standards Track [Page 25] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 4.1. Wildmat Syntax A wildmat is described by the following ABNF [RFC4234] syntax, which is an extract of that in Section 9.8. wildmat = wildmat-pattern *("," ["!"] wildmat-pattern) wildmat-pattern = 1*wildmat-item wildmat-item = wildmat-exact / wildmat-wild wildmat-exact = %x22-29 / %x2B / %x2D-3E / %x40-5A / %x5E-7E / UTF8-non-ascii ; exclude ! * , ? [ \ ] wildmat-wild = "*" / "?" Note: the characters ",", "\", "[", and "]" are not allowed in wildmats, while * and ? are always wildcards. This should not be a problem, since these characters cannot occur in newsgroup names, which is the only current use of wildmats. Backslash is commonly used to suppress the special meaning of characters, whereas brackets are used to introduce sets. However, these usages are not universal, and interpretation of these characters in the context of UTF-8 strings is potentially complex and differs from existing practice, so they were omitted from this specification. A future extension to this specification may provide semantics for these characters. 4.2. Wildmat Semantics A wildmat is tested against a string and either matches or does not match. To do this, each constituent is matched against the string, and the rightmost pattern that matches is identified. If that is not preceded with "!", the whole wildmat matches. If it is preceded by "!", or if no matches, the whole wildmat does not match. For example, consider the wildmat "a*,!*b,*c*": o The string "aaa" matches because the rightmost match is with "a*". o The string "abb" does not match because the rightmost match is with "*b". o The string "ccb" matches because the rightmost match is with "*c*". o The string "xxx" does not match because no matches. A matches a string if the string can be broken into components, each of which matches the corresponding in the pattern. The matches must be in the same order, and the whole Feather Standards Track [Page 26] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 string must be used in the match. The pattern is "anchored"; that is, the first and last characters in the string must match the first and last item, respectively (unless that item is an asterisk matching zero characters). A matches the same character (which may be more than one octet in UTF-8). "?" matches exactly one character (which may be more than one octet). "*" matches zero or more characters. It can match an empty string, but it cannot match a subsequence of a UTF-8 sequence that is not aligned to the character boundaries. 4.3. Extensions An NNTP server or extension MAY extend the syntax or semantics of wildmats provided that all wildmats that meet the requirements of Section 4.1 have the meaning ascribed to them by Section 4.2. Future editions of this document may also extend wildmats. 4.4. Examples In these examples, $ and @ are used to represent the two octets %xC2 and %xA3, respectively; $@ is thus the UTF-8 encoding for the pound sterling symbol, shown as # in the descriptions. Wildmat Description of strings that match abc The one string "abc" abc,def The two strings "abc" and "def" $@ The one character string "#" a* Any string that begins with "a" a*b Any string that begins with "a" and ends with "b" a*,*b Any string that begins with "a" or ends with "b" a*,!*b Any string that begins with "a" and does not end with "b" a*,!*b,c* Any string that begins with "a" and does not end with "b", and any string that begins with "c" no matter what it ends with a*,c*,!*b Any string that begins with "a" or "c" and does not end with "b" ?a* Any string with "a" as its second character ??a* Any string with "a" as its third character *a? Any string with "a" as its penultimate character *a?? Any string with "a" as its antepenultimate character Feather Standards Track [Page 27] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 5. Session Administration Commands 5.1. Initial Connection 5.1.1. Usage This command MUST NOT be pipelined. Responses [1] 200 Service available, posting allowed 201 Service available, posting prohibited 400 Service temporarily unavailable [2] 502 Service permanently unavailable [2] [1] These are the only valid response codes for the initial greeting; the server MUST not return any other generic response code. [2] Following a 400 or 502 response, the server MUST immediately close the connection. 5.1.2. Description There is no command presented by the client upon initial connection to the server. The server MUST present an appropriate response code as a greeting to the client. This response informs the client whether service is available and whether the client is permitted to post. If the server will accept further commands from the client including POST, the server MUST present a 200 greeting code. If the server will accept further commands from the client, but the client is not authorized to post articles using the POST command, the server MUST present a 201 greeting code. Otherwise, the server MUST present a 400 or 502 greeting code and then immediately close the connection. 400 SHOULD be used if the issue is only temporary (for example, because of load) and the client can expect to be able to connect successfully at some point in the future without making any changes. 502 MUST be used if the client is not permitted under any circumstances to interact with the server, and MAY be used if the server has insufficient information to determine whether the issue is temporary or permanent. Note: the distinction between the 200 and 201 response codes has turned out in practice to be insufficient; for example, some servers do not allow posting until the client has authenticated, while other clients assume that a 201 response means that posting will never be possible even after authentication. Therefore, clients SHOULD use Feather Standards Track [Page 28] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 the CAPABILITIES command (Section 5.2) rather than rely on this response. 5.1.3. Examples Example of a normal connection from an authorized client that then terminates the session (see Section 5.4): [Initial connection set-up completed.] [S] 200 NNTP Service Ready, posting permitted [C] QUIT [S] 205 NNTP Service exits normally [Server closes connection.] Example of a normal connection from an authorized client that is not permitted to post, which also immediately terminates the session: [Initial connection set-up completed.] [S] 201 NNTP Service Ready, posting prohibited [C] QUIT [S] 205 NNTP Service exits normally [Server closes connection.] Example of a normal connection from an unauthorized client: [Initial connection set-up completed.] [S] 502 NNTP Service permanently unavailable [Server closes connection.] Example of a connection from a client if the server is unable to provide service: [Initial connection set-up completed.] [S] 400 NNTP Service temporarily unavailable [Server closes connection.] 5.2. CAPABILITIES 5.2.1. Usage This command is mandatory. Syntax CAPABILITIES [keyword] Responses 101 Capability list follows (multi-line) Feather Standards Track [Page 29] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 Parameters keyword additional feature, see description 5.2.2. Description The CAPABILITIES command allows a client to determine the capabilities of the server at any given time. This command MAY be issued at any time; the server MUST NOT require it to be issued in order to make use of any capability. The response generated by this command MAY change during a session because of other state information (which, in turn, may be changed by the effects of other commands or by external events). An NNTP client is only able to get the current and correct information concerning available capabilities at any point during a session by issuing a CAPABILITIES command at that point of that session and processing the response. The capability list is returned as a multi-line data block following the 101 response code. Each capability is described by a separate capability line. The server MUST NOT list the same capability twice in the response, even with different arguments. Except that the VERSION capability MUST be the first line, the order in which the capability lines appears is not significant; the server need not even consistently return the same order. While some capabilities are likely to be always available or never available, others (notably extensions) will appear and disappear depending on server state changes within the session or on external events between sessions. An NNTP client MAY cache the results of this command, but MUST NOT rely on the correctness of any cached results, whether from earlier in this session or from a previous session, MUST cope gracefully with the cached status being out of date, and SHOULD (if caching results) provide a way to force the cached information to be refreshed. Furthermore, a client MUST NOT use cached results in relation to security, privacy, and authentication extensions. See Section 12.6 for further discussion of this topic. The keyword argument is not used by this specification. It is provided so that extensions or revisions to this specification can include extra features for this command without requiring the CAPABILITIES command to be used twice (once to determine if the extra features are available, and a second time to make use of them). If the server does not recognise the argument (and it is a keyword), it MUST respond with the 101 response code as if the argument had been omitted. If an argument is provided that the server does recognise, it MAY use the 101 response code or MAY use some other response code Feather Standards Track [Page 30] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 (which will be defined in the specification of that feature). If the argument is not a keyword, the 501 generic response code MUST be returned. The server MUST NOT generate any other response code to the CAPABILITIES command. 5.2.3. Examples Example of a minimal response (a read-only server): [C] CAPABILITIES [S] 101 Capability list: [S] VERSION 2 [S] READER [S] LIST ACTIVE NEWSGROUPS [S] . Example of a response from a server that has a range of facilities and that also describes itself: [C] CAPABILITIES [S] 101 Capability list: [S] VERSION 2 [S] READER [S] IHAVE [S] POST [S] NEWNEWS [S] LIST ACTIVE NEWSGROUPS ACTIVE.TIMES OVERVIEW.FMT [S] IMPLEMENTATION INN 4.2 2004-12-25 [S] OVER MSGID [S] STREAMING [S] XSECRET [S] . Example of a server that supports more than one version of NNTP: [C] CAPABILITIES [S] 101 Capability list: [S] VERSION 2 3 [S] READER [S] LIST ACTIVE NEWSGROUPS [S] . Feather Standards Track [Page 31] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 Example of a client attempting to use a feature of the CAPABILITIES command that the server does not support: [C] CAPABILITIES AUTOUPDATE [S] 101 Capability list: [S] VERSION 2 [S] READER [S] IHAVE [S] LIST ACTIVE NEWSGROUPS OVERVIEW.FMT HEADERS [S] OVER MSGID [S] HDR [S] NEWNEWS [S] . 5.3. MODE READER 5.3.1. Usage Indicating capability: MODE-READER This command MUST NOT be pipelined. Syntax MODE READER Responses 200 Posting allowed 201 Posting prohibited 502 Reading service permanently unavailable [1] [1] Following a 502 response the server MUST immediately close the connection. 5.3.2. Description The MODE READER command instructs a mode-switching server to switch modes, as described in Section 3.4.2. If the server is mode-switching, it switches from its transit mode to its reader mode, indicating this by changing the capability list accordingly. It MUST then return a 200 or 201 response with the same meaning as for the initial greeting (as described in Section 5.1.1). Note that the response need not be the same as that presented during the initial greeting. The client MUST NOT issue MODE READER more than once in a session or after any security or privacy commands are issued. When the MODE READER command is issued, the server MAY reset its state to that immediately after the initial connection before switching mode. Feather Standards Track [Page 32] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 If the server is not mode-switching, then the following apply: o If it advertises the READER capability, it MUST return a 200 or 201 response with the same meaning as for the initial greeting; in this case, the command MUST NOT affect the server state in any way. o If it does not advertise the READER capability, it MUST return a 502 response and then immediately close the connection. 5.3.3. Examples Example of use of the MODE READER command on a transit-only server (which therefore does not providing reading facilities): [C] CAPABILITIES [S] 101 Capability list: [S] VERSION 2 [S] IHAVE [S] . [C] MODE READER [S] 502 Transit service only [Server closes connection.] Example of use of the MODE READER command on a server that provides reading facilities: [C] CAPABILITIES [S] 101 Capability list: [S] VERSION 2 [S] READER [S] LIST ACTIVE NEWSGROUPS [S] . [C] MODE READER [S] 200 Reader mode, posting permitted [C] IHAVE [S] 500 Permission denied [C] GROUP misc.test [S] 211 1234 3000234 3002322 misc.test Note that in both of these situations, the client SHOULD NOT use MODE READER. Feather Standards Track [Page 33] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 Example of use of the MODE READER command on a mode-switching server: [C] CAPABILITIES [S] 101 Capability list: [S] VERSION 2 [S] IHAVE [S] MODE-READER [S] . [C] MODE READER [S] 200 Reader mode, posting permitted [C] CAPABILITIES [S] 101 Capability list: [S] VERSION 2 [S] READER [S] NEWNEWS [S] LIST ACTIVE NEWSGROUPS [S] STARTTLS [S] . In this case, the server offers (but does not require) TLS privacy in its reading mode but not in its transit mode. Example of use of the MODE READER command where the client is not permitted to post: [C] MODE READER [S] 201 NNTP Service Ready, posting prohibited 5.4. QUIT 5.4.1. Usage This command is mandatory. Syntax QUIT Responses 205 Connection closing 5.4.2. Description The client uses the QUIT command to terminate the session. The server MUST acknowledge the QUIT command and then close the connection to the client. This is the preferred method for a client to indicate that it has finished all of its transactions with the NNTP server. Feather Standards Track [Page 34] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 If a client simply disconnects (or if the connection times out or some other fault occurs), the server MUST gracefully cease its attempts to service the client, disconnecting from its end if necessary. The server MUST NOT generate any response code to the QUIT command other than 205 or, if any arguments are provided, 501. 5.4.3. Examples [C] QUIT [S] 205 closing connection [Server closes connection.] 6. Article Posting and Retrieval News-reading clients have available a variety of mechanisms to retrieve articles via NNTP. The news articles are stored and indexed using three types of keys. The first type of key is the message-id of an article and is globally unique. The second type of key is composed of a newsgroup name and an article number within that newsgroup. On a particular server, there MUST only be one article with a given number within any newsgroup, and an article MUST NOT have two different numbers in the same newsgroup. An article can be cross-posted to multiple newsgroups, so there may be multiple keys that point to the same article on the same server; these MAY have different numbers in each newsgroup. However, this type of key is not required to be globally unique, so the same key MAY refer to different articles on different servers. (Note that the terms "group" and "newsgroup" are equivalent.) The final type of key is the arrival timestamp, giving the time that the article arrived at the server. The server MUST ensure that article numbers are issued in order of arrival timestamp; that is, articles arriving later MUST have higher numbers than those that arrive earlier. The server SHOULD allocate the next sequential unused number to each new article. Article numbers MUST lie between 1 and 2,147,483,647, inclusive. The client and server MAY use leading zeroes in specifying article numbers but MUST NOT use more than 16 digits. In some situations, the value zero replaces an article number to show some special situation. Note that it is likely that the article number limit of 2,147,483,647 will be increased by a future revision or extension to this specification. While servers MUST NOT send article numbers greater than this current limit, client and server developers are advised to Feather Standards Track [Page 35] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 use internal structures and datatypes capable of handling larger values in anticipation of such a change. 6.1. Group and Article Selection The following commands are used to set the "currently selected newsgroup" and the "current article number", which are used by various commands. At the start of an NNTP session, both of these values are set to the special value "invalid". 6.1.1. GROUP 6.1.1.1. Usage Indicating capability: READER Syntax GROUP group Responses 211 number low high group Group successfully selected 411 No such newsgroup Parameters group Name of newsgroup number Estimated number of articles in the group low Reported low water mark high Reported high water mark 6.1.1.2. Description The GROUP command selects a newsgroup as the currently selected newsgroup and returns summary information about it. The required argument is the name of the newsgroup to be selected (e.g., "news.software.nntp"). A list of valid newsgroups may be obtained by using the LIST ACTIVE command (see Section 7.6.3). The successful selection response will return the article numbers of the first and last articles in the group at the moment of selection (these numbers are referred to as the "reported low water mark" and the "reported high water mark") and an estimate of the number of articles in the group currently available. If the group is not empty, the estimate MUST be at least the actual number of articles available and MUST be no greater than one more than the difference between the reported low and high water marks. (Some implementations will actually count the number of articles Feather Standards Track [Page 36] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 currently stored. Others will just subtract the low water mark from the high water mark and add one to get an estimate.) If the group is empty, one of the following three situations will occur. Clients MUST accept all three cases; servers MUST NOT represent an empty group in any other way. o The high water mark will be one less than the low water mark, and the estimated article count will be zero. Servers SHOULD use this method to show an empty group. This is the only time that the high water mark can be less than the low water mark. o All three numbers will be zero. o The high water mark is greater than or equal to the low water mark. The estimated article count might be zero or non-zero; if it is non-zero, the same requirements apply as for a non-empty group. The set of articles in a group may change after the GROUP command is carried out: o Articles may be removed from the group. o Articles may be reinstated in the group with the same article number, but those articles MUST have numbers no less than the reported low water mark (note that this is a reinstatement of the previous article, not a new article reusing the number). o New articles may be added with article numbers greater than the reported high water mark. (If an article that was the one with the highest number has been removed and the high water mark has been adjusted accordingly, the next new article will not have the number one greater than the reported high water mark.) Except when the group is empty and all three numbers are zero, whenever a subsequent GROUP command for the same newsgroup is issued, either by the same client or a different client, the reported low water mark in the response MUST be no less than that in any previous response for that newsgroup in this session, and it SHOULD be no less than that in any previous response for that newsgroup ever sent to any client. Any failure to meet the latter condition SHOULD be transient only. The client may make use of the low water mark to remove all remembered information about articles with lower numbers, as these will never recur. This includes the situation when the high water mark is one less than the low water mark. No similar assumption can be made about the high water mark, as this can Feather Standards Track [Page 37] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 decrease if an article is removed and then increase again if it is reinstated or if new articles arrive. When a valid group is selected by means of this command, the currently selected newsgroup MUST be set to that group, and the current article number MUST be set to the first article in the group (this applies even if the group is already the currently selected newsgroup). If an empty newsgroup is selected, the current article number is made invalid. If an invalid group is specified, the currently selected newsgroup and current article number MUST NOT be changed. The GROUP or LISTGROUP command (see Section 6.1.2) MUST be used by a client, and a successful response received, before any other command is used that depends on the value of the currently selected newsgroup or current article number. If the group specified is not available on the server, a 411 response MUST be returned. 6.1.1.3. Examples Example for a group known to the server: [C] GROUP misc.test [S] 211 1234 3000234 3002322 misc.test Example for a group unknown to the server: [C] GROUP example.is.sob.bradner.or.barber [S] 411 example.is.sob.bradner.or.barber is unknown Example of an empty group using the preferred response: [C] GROUP example.currently.empty.newsgroup [S] 211 0 4000 3999 example.currently.empty.newsgroup Example of an empty group using an alternative response: [C] GROUP example.currently.empty.newsgroup [S] 211 0 0 0 example.currently.empty.newsgroup Example of an empty group using a different alternative response: [C] GROUP example.currently.empty.newsgroup [S] 211 0 4000 4321 example.currently.empty.newsgroup Feather Standards Track [Page 38] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 Example reselecting the currently selected newsgroup: [C] GROUP misc.test [S] 211 1234 234 567 misc.test [C] STAT 444 [S] 223 444 <123456@example.net> retrieved [C] GROUP misc.test [S] 211 1234 234 567 misc.test [C] STAT [S] 223 234 retrieved 6.1.2. LISTGROUP 6.1.2.1. Usage Indicating capability: READER Syntax LISTGROUP [group [range]] Responses 211 number low high group Article numbers follow (multi-line) 411 No such newsgroup 412 No newsgroup selected [1] Parameters group Name of newsgroup range Range of articles to report number Estimated number of articles in the group low Reported low water mark high Reported high water mark [1] The 412 response can only occur if no group has been specified. 6.1.2.2. Description The LISTGROUP command selects a newsgroup in the same manner as the GROUP command (see Section 6.1.1) but also provides a list of article numbers in the newsgroup. If no group is specified, the currently selected newsgroup is used. On success, a list of article numbers is returned as a multi-line data block following the 211 response code (the arguments on the initial response line are the same as for the GROUP command). The list contains one number per line and is in numerical order. It lists precisely those articles that exist in the group at the moment of selection (therefore, an empty group produces an empty list). If the optional range argument is specified, only articles within the Feather Standards Track [Page 39] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 range are included in the list (therefore, the list MAY be empty even if the group is not). The range argument may be any of the following: o An article number. o An article number followed by a dash to indicate all following. o An article number followed by a dash followed by another article number. In the last case, if the second number is less than the first number, then the range contains no articles. Omitting the range is equivalent to the range 1- being specified. If the group specified is not available on the server, a 411 response MUST be returned. If no group is specified and the currently selected newsgroup is invalid, a 412 response MUST be returned. Except that the group argument is optional, that a range argument can be specified, and that a multi-line data block follows the 211 response code, the LISTGROUP command is identical to the GROUP command. In particular, when successful, the command sets the current article number to the first article in the group, if any, even if this is not within the range specified by the second argument. Note that the range argument is a new feature in this specification and servers that do not support CAPABILITIES (and therefore do not conform to this specification) are unlikely to support it. 6.1.2.3. Examples Example of LISTGROUP being used to select a group: [C] LISTGROUP misc.test [S] 211 2000 3000234 3002322 misc.test list follows [S] 3000234 [S] 3000237 [S] 3000238 [S] 3000239 [S] 3002322 [S] . Feather Standards Track [Page 40] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 Example of LISTGROUP on an empty group: [C] LISTGROUP example.empty.newsgroup [S] 211 0 0 0 example.empty.newsgroup list follows [S] . Example of LISTGROUP on a valid, currently selected newsgroup: [C] GROUP misc.test [S] 211 2000 3000234 3002322 misc.test [C] LISTGROUP [S] 211 2000 3000234 3002322 misc.test list follows [S] 3000234 [S] 3000237 [S] 3000238 [S] 3000239 [S] 3002322 [S] . Example of LISTGROUP with a range: [C] LISTGROUP misc.test 3000238-3000248 [S] 211 2000 3000234 3002322 misc.test list follows [S] 3000238 [S] 3000239 [S] . Example of LISTGROUP with an empty range: [C] LISTGROUP misc.test 12345678- [S] 211 2000 3000234 3002322 misc.test list follows [S] . Example of LISTGROUP with an invalid range: [C] LISTGROUP misc.test 9999-111 [S] 211 2000 3000234 3002322 misc.test list follows [S] . Feather Standards Track [Page 41] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 6.1.3. LAST 6.1.3.1. Usage Indicating capability: READER Syntax LAST Responses 223 n message-id Article found 412 No newsgroup selected 420 Current article number is invalid 422 No previous article in this group Parameters n Article number message-id Article message-id 6.1.3.2. Description If the currently selected newsgroup is valid, the current article number MUST be set to the previous article in that newsgroup (that is, the highest existing article number less than the current article number). If successful, a response indicating the new current article number and the message-id of that article MUST be returned. No article text is sent in response to this command. There MAY be no previous article in the group, although the current article number is not the reported low water mark. There MUST NOT be a previous article when the current article number is the reported low water mark. Because articles can be removed and added, the results of multiple LAST and NEXT commands MAY not be consistent over the life of a particular NNTP session. If the current article number is already the first article of the newsgroup, a 422 response MUST be returned. If the current article number is invalid, a 420 response MUST be returned. If the currently selected newsgroup is invalid, a 412 response MUST be returned. In all three cases, the currently selected newsgroup and current article number MUST NOT be altered. Feather Standards Track [Page 42] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 6.1.3.3. Examples Example of a successful article retrieval using LAST: [C] GROUP misc.test [S] 211 1234 3000234 3002322 misc.test [C] NEXT [S] 223 3000237 <668929@example.org> retrieved [C] LAST [S] 223 3000234 <45223423@example.com> retrieved Example of an attempt to retrieve an article without having selected a group (via the GROUP command) first: [Assumes currently selected newsgroup is invalid.] [C] LAST [S] 412 no newsgroup selected Example of an attempt to retrieve an article using the LAST command when the current article number is that of the first article in the group: [C] GROUP misc.test [S] 211 1234 3000234 3002322 misc.test [C] LAST [S] 422 No previous article to retrieve Example of an attempt to retrieve an article using the LAST command when the currently selected newsgroup is empty: [C] GROUP example.empty.newsgroup [S] 211 0 0 0 example.empty.newsgroup [C] LAST [S] 420 No current article selected Feather Standards Track [Page 43] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 6.1.4. NEXT 6.1.4.1. Usage Indicating capability: READER Syntax NEXT Responses 223 n message-id Article found 412 No newsgroup selected 420 Current article number is invalid 421 No next article in this group Parameters n Article number message-id Article message-id 6.1.4.2. Description If the currently selected newsgroup is valid, the current article number MUST be set to the next article in that newsgroup (that is, the lowest existing article number greater than the current article number). If successful, a response indicating the new current article number and the message-id of that article MUST be returned. No article text is sent in response to this command. If the current article number is already the last article of the newsgroup, a 421 response MUST be returned. In all other aspects (apart, of course, from the lack of 422 response), this command is identical to the LAST command (Section 6.1.3). 6.1.4.3. Examples Example of a successful article retrieval using NEXT: [C] GROUP misc.test [S] 211 1234 3000234 3002322 misc.test [C] NEXT [S] 223 3000237 <668929@example.org> retrieved Feather Standards Track [Page 44] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 Example of an attempt to retrieve an article without having selected a group (via the GROUP command) first: [Assumes currently selected newsgroup is invalid.] [C] NEXT [S] 412 no newsgroup selected Example of an attempt to retrieve an article using the NEXT command when the current article number is that of the last article in the group: [C] GROUP misc.test [S] 211 1234 3000234 3002322 misc.test [C] STAT 3002322 [S] 223 3002322 <411@example.net> retrieved [C] NEXT [S] 421 No next article to retrieve Example of an attempt to retrieve an article using the NEXT command when the currently selected newsgroup is empty: [C] GROUP example.empty.newsgroup [S] 211 0 0 0 example.empty.newsgroup [C] NEXT [S] 420 No current article selected 6.2. Retrieval of Articles and Article Sections The ARTICLE, BODY, HEAD, and STAT commands are very similar. They differ only in the parts of the article that are presented to the client and in the successful response code. The ARTICLE command is described here in full, while the other three commands are described in terms of the differences. As specified in Section 3.6, an article consists of two parts: the article headers and the article body. When responding to one of these commands, the server MUST present the entire article or appropriate part and MUST NOT attempt to alter or translate it in any way. Feather Standards Track [Page 45] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 6.2.1. ARTICLE 6.2.1.1. Usage Indicating capability: READER Syntax ARTICLE message-id ARTICLE number ARTICLE Responses First form (message-id specified) 220 0|n message-id Article follows (multi-line) 430 No article with that message-id Second form (article number specified) 220 n message-id Article follows (multi-line) 412 No newsgroup selected 423 No article with that number Third form (current article number used) 220 n message-id Article follows (multi-line) 412 No newsgroup selected 420 Current article number is invalid Parameters number Requested article number n Returned article number message-id Article message-id 6.2.1.2. Description The ARTICLE command selects an article according to the arguments and presents the entire article (that is, the headers, an empty line, and the body, in that order) to the client. The command has three forms. In the first form, a message-id is specified, and the server presents the article with that message-id. In this case, the server MUST NOT alter the currently selected newsgroup or current article number. This is both to facilitate the presentation of articles that may be referenced within another article being read, and because of the semantic difficulties of determining the proper sequence and membership of an article that may have been cross-posted to more than one newsgroup. Feather Standards Track [Page 46] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 In the response, the article number MUST be replaced with zero, unless there is a currently selected newsgroup and the article is present in that group, in which case the server MAY use the article's number in that group. (The server is not required to determine whether the article is in the currently selected newsgroup or, if so, what article number it has; the client MUST always be prepared for zero to be specified.) The server MUST NOT provide an article number unless use of that number in a second ARTICLE command immediately following this one would return the same article. Even if the server chooses to return article numbers in these circumstances, it need not do so consistently; it MAY return zero to any such command (also see the STAT examples, Section 6.2.4.3). In the second form, an article number is specified. If there is an article with that number in the currently selected newsgroup, the server MUST set the current article number to that number. In the third form, the article indicated by the current article number in the currently selected newsgroup is used. Note that a previously valid article number MAY become invalid if the article has been removed. A previously invalid article number MAY become valid if the article has been reinstated, but this article number MUST be no less than the reported low water mark for that group. The server MUST NOT change the currently selected newsgroup as a result of this command. The server MUST NOT change the current article number except when an article number argument was provided and the article exists; in particular, it MUST NOT change it following an unsuccessful response. Since the message-id is unique for each article, it may be used by a client to skip duplicate displays of articles that have been posted more than once, or to more than one newsgroup. The article is returned as a multi-line data block following the 220 response code. If the argument is a message-id and no such article exists, a 430 response MUST be returned. If the argument is a number or is omitted and the currently selected newsgroup is invalid, a 412 response MUST be returned. If the argument is a number and that article does not exist in the currently selected newsgroup, a 423 response MUST be returned. If the argument is omitted and the current article number is invalid, a 420 response MUST be returned. Feather Standards Track [Page 47] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 6.2.1.3. Examples Example of a successful retrieval of an article (explicitly not using an article number): [C] GROUP misc.test [S] 211 1234 3000234 3002322 misc.test [C] ARTICLE [S] 220 3000234 <45223423@example.com> [S] Path: pathost!demo!whitehouse!not-for-mail [S] From: "Demo User" [S] Newsgroups: misc.test [S] Subject: I am just a test article [S] Date: 6 Oct 1998 04:38:40 -0500 [S] Organization: An Example Net, Uncertain, Texas [S] Message-ID: <45223423@example.com> [S] [S] This is just a test article. [S] . Example of a successful retrieval of an article by message-id: [C] ARTICLE <45223423@example.com> [S] 220 0 <45223423@example.com> [S] Path: pathost!demo!whitehouse!not-for-mail [S] From: "Demo User" [S] Newsgroups: misc.test [S] Subject: I am just a test article [S] Date: 6 Oct 1998 04:38:40 -0500 [S] Organization: An Example Net, Uncertain, Texas [S] Message-ID: <45223423@example.com> [S] [S] This is just a test article. [S] . Example of an unsuccessful retrieval of an article by message-id: [C] ARTICLE [S] 430 No Such Article Found Example of an unsuccessful retrieval of an article by number: [C] GROUP misc.test [S] 211 1234 3000234 3002322 news.groups [C] ARTICLE 300256 [S] 423 No article with that number Feather Standards Track [Page 48] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 Example of an unsuccessful retrieval of an article by number because no newsgroup was selected first: [Assumes currently selected newsgroup is invalid.] [C] ARTICLE 300256 [S] 412 No newsgroup selected Example of an attempt to retrieve an article when the currently selected newsgroup is empty: [C] GROUP example.empty.newsgroup [S] 211 0 0 0 example.empty.newsgroup [C] ARTICLE [S] 420 No current article selected 6.2.2. HEAD 6.2.2.1. Usage This command is mandatory. Syntax HEAD message-id HEAD number HEAD Responses First form (message-id specified) 221 0|n message-id Headers follow (multi-line) 430 No article with that message-id Second form (article number specified) 221 n message-id Headers follow (multi-line) 412 No newsgroup selected 423 No article with that number Third form (current article number used) 221 n message-id Headers follow (multi-line) 412 No newsgroup selected 420 Current article number is invalid Parameters number Requested article number n Returned article number message-id Article message-id Feather Standards Track [Page 49] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 6.2.2.2. Description The HEAD command behaves identically to the ARTICLE command except that, if the article exists, the response code is 221 instead of 220 and only the headers are presented (the empty line separating the headers and body MUST NOT be included). 6.2.2.3. Examples Example of a successful retrieval of the headers of an article (explicitly not using an article number): [C] GROUP misc.test [S] 211 1234 3000234 3002322 misc.test [C] HEAD [S] 221 3000234 <45223423@example.com> [S] Path: pathost!demo!whitehouse!not-for-mail [S] From: "Demo User" [S] Newsgroups: misc.test [S] Subject: I am just a test article [S] Date: 6 Oct 1998 04:38:40 -0500 [S] Organization: An Example Net, Uncertain, Texas [S] Message-ID: <45223423@example.com> [S] . Example of a successful retrieval of the headers of an article by message-id: [C] HEAD <45223423@example.com> [S] 221 0 <45223423@example.com> [S] Path: pathost!demo!whitehouse!not-for-mail [S] From: "Demo User" [S] Newsgroups: misc.test [S] Subject: I am just a test article [S] Date: 6 Oct 1998 04:38:40 -0500 [S] Organization: An Example Net, Uncertain, Texas [S] Message-ID: <45223423@example.com> [S] . Example of an unsuccessful retrieval of the headers of an article by message-id: [C] HEAD [S] 430 No Such Article Found Feather Standards Track [Page 50] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 Example of an unsuccessful retrieval of the headers of an article by number: [C] GROUP misc.test [S] 211 1234 3000234 3002322 misc.test [C] HEAD 300256 [S] 423 No article with that number Example of an unsuccessful retrieval of the headers of an article by number because no newsgroup was selected first: [Assumes currently selected newsgroup is invalid.] [C] HEAD 300256 [S] 412 No newsgroup selected Example of an attempt to retrieve the headers of an article when the currently selected newsgroup is empty: [C] GROUP example.empty.newsgroup [S] 211 0 0 0 example.empty.newsgroup [C] HEAD [S] 420 No current article selected 6.2.3. BODY 6.2.3.1. Usage Indicating capability: READER Syntax BODY message-id BODY number BODY Responses First form (message-id specified) 222 0|n message-id Body follows (multi-line) 430 No article with that message-id Second form (article number specified) 222 n message-id Body follows (multi-line) 412 No newsgroup selected 423 No article with that number Feather Standards Track [Page 51] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 Third form (current article number used) 222 n message-id Body follows (multi-line) 412 No newsgroup selected 420 Current article number is invalid Parameters number Requested article number n Returned article number message-id Article message-id 6.2.3.2. Description The BODY command behaves identically to the ARTICLE command except that, if the article exists, the response code is 222 instead of 220 and only the body is presented (the empty line separating the headers and body MUST NOT be included). 6.2.3.3. Examples Example of a successful retrieval of the body of an article (explicitly not using an article number): [C] GROUP misc.test [S] 211 1234 3000234 3002322 misc.test [C] BODY [S] 222 3000234 <45223423@example.com> [S] This is just a test article. [S] . Example of a successful retrieval of the body of an article by message-id: [C] BODY <45223423@example.com> [S] 222 0 <45223423@example.com> [S] This is just a test article. [S] . Example of an unsuccessful retrieval of the body of an article by message-id: [C] BODY [S] 430 No Such Article Found Feather Standards Track [Page 52] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 Example of an unsuccessful retrieval of the body of an article by number: [C] GROUP misc.test [S] 211 1234 3000234 3002322 misc.test [C] BODY 300256 [S] 423 No article with that number Example of an unsuccessful retrieval of the body of an article by number because no newsgroup was selected first: [Assumes currently selected newsgroup is invalid.] [C] BODY 300256 [S] 412 No newsgroup selected Example of an attempt to retrieve the body of an article when the currently selected newsgroup is empty: [C] GROUP example.empty.newsgroup [S] 211 0 0 0 example.empty.newsgroup [C] BODY [S] 420 No current article selected 6.2.4. STAT 6.2.4.1. Usage This command is mandatory. Syntax STAT message-id STAT number STAT Responses First form (message-id specified) 223 0|n message-id Article exists 430 No article with that message-id Second form (article number specified) 223 n message-id Article exists 412 No newsgroup selected 423 No article with that number Feather Standards Track [Page 53] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 Third form (current article number used) 223 n message-id Article exists 412 No newsgroup selected 420 Current article number is invalid Parameters number Requested article number n Returned article number message-id Article message-id 6.2.4.2. Description The STAT command behaves identically to the ARTICLE command except that, if the article exists, it is NOT presented to the client and the response code is 223 instead of 220. Note that the response is NOT multi-line. This command allows the client to determine whether an article exists and, in the second and third forms, what its message-id is, without having to process an arbitrary amount of text. 6.2.4.3. Examples Example of STAT on an existing article (explicitly not using an article number): [C] GROUP misc.test [S] 211 1234 3000234 3002322 misc.test [C] STAT [S] 223 3000234 <45223423@example.com> Example of STAT on an existing article by message-id: [C] STAT <45223423@example.com> [S] 223 0 <45223423@example.com> Example of STAT on an article not on the server by message-id: [C] STAT [S] 430 No Such Article Found Example of STAT on an article not in the server by number: [C] GROUP misc.test [S] 211 1234 3000234 3002322 misc.test [C] STAT 300256 [S] 423 No article with that number Feather Standards Track [Page 54] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 Example of STAT on an article by number when no newsgroup was selected first: [Assumes currently selected newsgroup is invalid.] [C] STAT 300256 [S] 412 No newsgroup selected Example of STAT on an article when the currently selected newsgroup is empty: [C] GROUP example.empty.newsgroup [S] 211 0 0 0 example.empty.newsgroup [C] STAT [S] 420 No current article selected Example of STAT by message-id on a server that sometimes reports the actual article number: [C] GROUP misc.test [S] 211 1234 3000234 3002322 misc.test [C] STAT [S] 223 3000234 <45223423@example.com> [C] STAT <45223423@example.com> [S] 223 0 <45223423@example.com> [C] STAT <45223423@example.com> [S] 223 3000234 <45223423@example.com> [C] GROUP example.empty.newsgroup [S] 211 0 0 0 example.empty.newsgroup [C] STAT <45223423@example.com> [S] 223 0 <45223423@example.com> [C] GROUP alt.crossposts [S] 211 9999 111111 222222 alt.crossposts [C] STAT <45223423@example.com> [S] 223 123456 <45223423@example.com> [C] STAT [S] 223 111111 <23894720@example.com> The first STAT command establishes the identity of an article in the group. The second and third show that the server may, but need not, give the article number when the message-id is specified. The fourth STAT command shows that zero must be specified if the article isn't in the currently selected newsgroup. The fifth shows that the number, if provided, must be that relating to the currently selected newsgroup. The last one shows that the current article number is still not changed by the use of STAT with a message-id even if it returns an article number. Feather Standards Track [Page 55] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 6.3. Article Posting Article posting is done in one of two ways: individual article posting from news-reading clients using POST, and article transfer from other news servers using IHAVE. 6.3.1. POST 6.3.1.1. Usage Indicating capability: POST This command MUST NOT be pipelined. Syntax POST Responses Initial responses 340 Send article to be posted 440 Posting not permitted Subsequent responses 240 Article received OK 441 Posting failed 6.3.1.2. Description If posting is allowed, a 340 response MUST be returned to indicate that the article to be posted should be sent. If posting is prohibited for some installation-dependent reason, a 440 response MUST be returned. If posting is permitted, the article MUST be in the format specified in Section 3.6 and MUST be sent by the client to the server as a multi-line data block (see Section 3.1.1). Thus a single dot (".") on a line indicates the end of the text, and lines starting with a dot in the original text have that dot doubled during transmission. Following the presentation of the termination sequence by the client, the server MUST return a response indicating success or failure of the article transfer. Note that response codes 340 and 440 are used in direct response to the POST command while 240 and 441 are returned after the article is sent. Feather Standards Track [Page 56] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 A response of 240 SHOULD indicate that, barring unforeseen server errors, the posted article will be made available on the server and/or transferred to other servers, as appropriate, possibly following further processing. In other words, articles not wanted by the server SHOULD be rejected with a 441 response, rather than being accepted and then discarded silently. However, the client SHOULD NOT assume that the article has been successfully transferred unless it receives an affirmative response from the server and SHOULD NOT assume that it is being made available to other clients without explicitly checking (for example, using the STAT command). If the session is interrupted before the response is received, it is possible that an affirmative response was sent but has been lost. Therefore, in any subsequent session, the client SHOULD either check whether the article was successfully posted before resending or ensure that the server will allocate the same message-id to the new attempt (see Appendix A.2). The latter approach is preferred since the article might not have been made available for reading yet (for example, it may have to go through a moderation process). 6.3.1.3. Examples Example of a successful posting: [C] POST [S] 340 Input article; end with . [C] From: "Demo User" [C] Newsgroups: misc.test [C] Subject: I am just a test article [C] Organization: An Example Net [C] [C] This is just a test article. [C] . [S] 240 Article received OK Example of an unsuccessful posting: [C] POST [S] 340 Input article; end with . [C] From: "Demo User" [C] Newsgroups: misc.test [C] Subject: I am just a test article [C] Organization: An Example Net [C] [C] This is just a test article. [C] . [S] 441 Posting failed Feather Standards Track [Page 57] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 Example of an attempt to post when posting is not allowed: [Initial connection set-up completed.] [S] 201 NNTP Service Ready, posting prohibited [C] POST [S] 440 Posting not permitted 6.3.2. IHAVE 6.3.2.1. Usage Indicating capability: IHAVE This command MUST NOT be pipelined. Syntax IHAVE message-id Responses Initial responses 335 Send article to be transferred 435 Article not wanted 436 Transfer not possible; try again later Subsequent responses 235 Article transferred OK 436 Transfer failed; try again later 437 Transfer rejected; do not retry Parameters message-id Article message-id 6.3.2.2. Description The IHAVE command informs the server that the client has an article with the specified message-id. If the server desires a copy of that article, a 335 response MUST be returned, instructing the client to send the entire article. If the server does not want the article (if, for example, the server already has a copy of it), a 435 response MUST be returned, indicating that the article is not wanted. Finally, if the article isn't wanted immediately but the client should retry later if possible (if, for example, another client is in the process of sending the same article to the server), a 436 response MUST be returned. Feather Standards Track [Page 58] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 If transmission of the article is requested, the client MUST send the entire article, including headers and body, to the server as a multi-line data block (see Section 3.1.1). Thus, a single dot (".") on a line indicates the end of the text, and lines starting with a dot in the original text have that dot doubled during transmission. The server MUST return a 235 response, indicating that the article was successfully transferred; a 436 response, indicating that the transfer failed but should be tried again later; or a 437 response, indicating that the article was rejected. This function differs from the POST command in that it is intended for use in transferring already-posted articles between hosts. It SHOULD NOT be used when the client is a personal news-reading program, since use of this command indicates that the article has already been posted at another site and is simply being forwarded from another host. However, despite this, the server MAY elect not to post or forward the article if, after further examination of the article, it deems it inappropriate to do so. Reasons for such subsequent rejection of an article may include problems such as inappropriate newsgroups or distributions, disc space limitations, article lengths, garbled headers, and the like. These are typically restrictions enforced by the server host's news software and not necessarily by the NNTP server itself. The client SHOULD NOT assume that the article has been successfully transferred unless it receives an affirmative response from the server. A lack of response (such as a dropped network connection or a network timeout) SHOULD be treated the same as a 436 response. Because some news server software may not immediately be able to determine whether an article is suitable for posting or forwarding, an NNTP server MAY acknowledge the successful transfer of the article (with a 235 response) but later silently discard it. Feather Standards Track [Page 59] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 6.3.2.3. Examples Example of successfully sending an article to another site: [C] IHAVE [S] 335 Send it; end with . [C] Path: pathost!demo!somewhere!not-for-mail [C] From: "Demo User" [C] Newsgroups: misc.test [C] Subject: I am just a test article [C] Date: 6 Oct 1998 04:38:40 -0500 [C] Organization: An Example Com, San Jose, CA [C] Message-ID: [C] [C] This is just a test article. [C] . [S] 235 Article transferred OK Example of sending an article to another site that rejects it. Note that the message-id in the IHAVE command is not the same as the one in the article headers; while this is bad practice and SHOULD NOT be done, it is not forbidden. [C] IHAVE [S] 335 Send it; end with . [C] Path: pathost!demo!somewhere!not-for-mail [C] From: "Demo User" [C] Newsgroups: misc.test [C] Subject: I am just a test article [C] Date: 6 Oct 1998 04:38:40 -0500 [C] Organization: An Example Com, San Jose, CA [C] Message-ID: [C] [C] This is just a test article. [C] . [S] 437 Article rejected; don't send again Feather Standards Track [Page 60] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 Example of sending an article to another site where the transfer fails: [C] IHAVE [S] 335 Send it; end with . [C] Path: pathost!demo!somewhere!not-for-mail [C] From: "Demo User" [C] Newsgroups: misc.test [C] Subject: I am just a test article [C] Date: 6 Oct 1998 04:38:40 -0500 [C] Organization: An Example Com, San Jose, CA [C] Message-ID: [C] [C] This is just a test article. [C] . [S] 436 Transfer failed Example of sending an article to a site that already has it: [C] IHAVE [S] 435 Duplicate Example of sending an article to a site that requests that the article be tried again later: [C] IHAVE [S] 436 Retry later 7. Information Commands This section lists other commands that may be used at any time between the beginning of a session and its termination. Using these commands does not alter any state information, but the response generated from their use may provide useful information to clients. 7.1. DATE 7.1.1. Usage Indicating capability: READER Syntax DATE Responses 111 yyyymmddhhmmss Server date and time Feather Standards Track [Page 61] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 Parameters yyyymmddhhmmss Current UTC date and time on server 7.1.2. Description This command exists to help clients find out the current Coordinated Universal Time [TF.686-1] from the server's perspective. This command SHOULD NOT be used as a substitute for NTP [RFC1305] but to provide information that might be useful when using the NEWNEWS command (see Section 7.4). The DATE command MUST return a timestamp from the same clock as is used for determining article arrival and group creation times (see Section 6). This clock SHOULD be monotonic, and adjustments SHOULD be made by running it fast or slow compared to "real" time rather than by making sudden jumps. A system providing NNTP service SHOULD keep the system clock as accurate as possible, either with NTP or by some other method. The server MUST return a 111 response specifying the date and time on the server in the form yyyymmddhhmmss. This date and time is in Coordinated Universal Time. 7.1.3. Examples [C] DATE [S] 111 19990623135624 7.2. HELP 7.2.1. Usage This command is mandatory. Syntax HELP Responses 100 Help text follows (multi-line) 7.2.2. Description This command provides a short summary of the commands that are understood by this implementation of the server. The help text will be presented as a multi-line data block following the 100 response code. Feather Standards Track [Page 62] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 This text is not guaranteed to be in any particular format (but must be UTF-8) and MUST NOT be used by clients as a replacement for the CAPABILITIES command described in Section 5.2. 7.2.3. Examples [C] HELP [S] 100 Help text follows [S] This is some help text. There is no specific [S] formatting requirement for this test, though [S] it is customary for it to list the valid commands [S] and give a brief definition of what they do. [S] . 7.3. NEWGROUPS 7.3.1. Usage Indicating capability: READER Syntax NEWGROUPS date time [GMT] Responses 231 List of new newsgroups follows (multi-line) Parameters date Date in yymmdd or yyyymmdd format time Time in hhmmss format 7.3.2. Description This command returns a list of newsgroups created on the server since the specified date and time. The results are in the same format as the LIST ACTIVE command (see Section 7.6.3). However, they MAY include groups not available on the server (and so not returned by LIST ACTIVE) and MAY omit groups for which the creation date is not available. The date is specified as 6 or 8 digits in the format [xx]yymmdd, where xx is the first two digits of the year (19-99), yy is the last two digits of the year (00-99), mm is the month (01-12), and dd is the day of the month (01-31). Clients SHOULD specify all four digits of the year. If the first two digits of the year are not specified (this is supported only for backward compatibility), the year is to be taken from the current century if yy is smaller than or equal to the current year, and the previous century otherwise. Feather Standards Track [Page 63] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 The time is specified as 6 digits in the format hhmmss, where hh is the hours in the 24-hour clock (00-23), mm is the minutes (00-59), and ss is the seconds (00-60, to allow for leap seconds). The token "GMT" specifies that the date and time are given in Coordinated Universal Time [TF.686-1]; if it is omitted, then the date and time are specified in the server's local timezone. Note that there is no way of using the protocol specified in this document to establish the server's local timezone. Note that an empty list is a possible valid response and indicates that there are no new newsgroups since that date-time. Clients SHOULD make all queries using Coordinated Universal Time (i.e., by including the "GMT" argument) when possible. 7.3.3. Examples Example where there are new groups: [C] NEWGROUPS 19990624 000000 GMT [S] 231 list of new newsgroups follows [S] alt.rfc-writers.recovery 4 1 y [S] tx.natives.recovery 89 56 y [S] . Example where there are no new groups: [C] NEWGROUPS 19990624 000000 GMT [S] 231 list of new newsgroups follows [S] . 7.4. NEWNEWS 7.4.1. Usage Indicating capability: NEWNEWS Syntax NEWNEWS wildmat date time [GMT] Responses 230 List of new articles follows (multi-line) Parameters wildmat Newsgroups of interest date Date in yymmdd or yyyymmdd format time Time in hhmmss format Feather Standards Track [Page 64] RFC 3977 Network News Transfer Protocol (NNTP) October 2006 7.4.2. Description This command returns a list of message-ids of articles posted or received on the server, in the newsgroups whose names match the wildmat, since the specified date and time. One message-id is sent on each line; the order of the response has no specific significance and may vary from response to response in the same session. A message-id MAY appear mor