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Transport QUIC The QUIC transport protocol has several features that are desirable in a transport for HTTP, such as stream multiplexing, per-stream flow control, and low-latency connection establishment. This document describes a mapping of HTTP semantics over QUIC. This document also identifies HTTP/2 features that are subsumed by QUIC, and describes how HTTP/2 extensions can be ported to QUIC. Discussion of this draft takes place on the QUIC working group mailing list (quic@ietf.org), which is archived at https://mailarchive.ietf.org/arch/search/?email_list=quic. Working Group information can be found at https://github.com/quicwg; source code and issues list for this draft can be found at https://github.com/quicwg/base-drafts/labels/-http.

The QUIC transport protocol has several features that are desirable in a transport for HTTP, such as stream multiplexing, per-stream flow control, and low-latency connection establishment. This document describes a mapping of HTTP semantics over QUIC, drawing heavily on the existing TCP mapping, HTTP/2. Specifically, this document identifies HTTP/2 features that are subsumed by QUIC, and describes how the other features can be implemented atop QUIC. QUIC is described in . For a full description of HTTP/2, see .

The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “NOT RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here. Field definitions are given in Augmented Backus-Naur Form (ABNF), as defined in . This document uses the variable-length integer encoding from . Protocol elements called “frames” exist in both this document and . Where frames from are referenced, the frame name will be prefaced with “QUIC.” For example, “QUIC APPLICATION_CLOSE frames.” References without this preface refer to frames defined in .

An HTTP origin advertises the availability of an equivalent HTTP/QUIC endpoint via the Alt-Svc HTTP response header or the HTTP/2 ALTSVC frame (), using the ALPN token defined in . For example, an origin could indicate in an HTTP/1.1 or HTTP/2 response that HTTP/QUIC was available on UDP port 50781 at the same hostname by including the following header in any response:

On receipt of an Alt-Svc header indicating HTTP/QUIC support, a client MAY attempt to establish a QUIC connection to the indicated host and port and, if successful, send HTTP requests using the mapping described in this document. Connectivity problems (e.g. firewall blocking UDP) can result in QUIC connection establishment failure, in which case the client SHOULD continue using the existing connection or try another alternative endpoint offered by the origin. Servers MAY serve HTTP/QUIC on any UDP port. Servers MUST use the same port across all IP addresses that serve a single domain, and SHOULD NOT change this port.

This document defines the “quic” parameter for Alt-Svc, which MAY be used to provide version-negotiation hints to HTTP/QUIC clients. QUIC versions are four-octet sequences with no additional constraints on format. Syntax:

Leading zeros SHOULD be omitted for brevity. When multiple versions are supported, the “quic” parameter MAY be repeated multiple times in a single Alt-Svc entry. For example, if a server supported both version 0x00000001 and the version rendered in ASCII as “Q034”, it could specify the following header:

Where multiple versions are listed, the order of the values reflects the server’s preference (with the first value being the most preferred version). Origins SHOULD list only versions which are supported by the alternative, but MAY omit supported versions for any reason.

HTTP/QUIC relies on QUIC as the underlying transport. The QUIC version being used MUST use TLS version 1.3 or greater as its handshake protocol. The Server Name Indication (SNI) extension MUST be included in the TLS handshake. QUIC connections are established as described in . During connection establishment, HTTP/QUIC support is indicated by selecting the ALPN token “hq” in the TLS handshake. Support for other application-layer protocols MAY be offered in the same handshake. While connection-level options pertaining to the core QUIC protocol are set in the initial crypto handshake, HTTP-specific settings are conveyed in the SETTINGS frame. After the QUIC connection is established, a SETTINGS frame () MUST be sent by each endpoint as the initial frame of their respective HTTP control stream (Stream ID 2 or 3, see ). The server MUST NOT send data on any other stream until the client’s SETTINGS frame has been received.

RFC Editor’s Note: Please remove this section prior to publication of a final version of this document. Only implementations of the final, published RFC can identify themselves as “hq”. Until such an RFC exists, implementations MUST NOT identify themselves using this string. Implementations of draft versions of the protocol MUST add the string “-“ and the corresponding draft number to the identifier. For example, draft-ietf-quic-http-01 is identified using the string “hq-01”. Non-compatible experiments that are based on these draft versions MUST append the string “-“ and an experiment name to the identifier. For example, an experimental implementation based on draft-ietf-quic-http-09 which reserves an extra stream for unsolicited transmission of 1980s pop music might identify itself as “hq-09-rickroll”. Note that any label MUST conform to the “token” syntax defined in Section 3.2.6 of . Experimenters are encouraged to coordinate their experiments on the quic@ietf.org mailing list.

Once a connection exists to a server endpoint, this connection MAY be reused for requests with multiple different URI authority components. The client MAY send any requests for which the client considers the server authoritative. An authoritative HTTP/QUIC endpoint is typically discovered because the client has received an Alt-Svc record from the request’s origin which nominates the endpoint as a valid HTTP Alternative Service for that origin. As required by , clients MUST check that the nominated server can present a valid certificate for the origin before considering it authoritative. Clients MUST NOT assume that an HTTP/QUIC endpoint is authoritative for other origins without an explicit signal. A server that does not wish clients to reuse connections for a particular origin can indicate that it is not authoritative for a request by sending a 421 (Misdirected Request) status code in response to the request (see Section 9.1.2 of ).

A QUIC stream provides reliable in-order delivery of bytes, but makes no guarantees about order of delivery with regard to bytes on other streams. On the wire, data is framed into QUIC STREAM frames, but this framing is invisible to the HTTP framing layer. A QUIC receiver buffers and orders received STREAM frames, exposing the data contained within as a reliable byte stream to the application. QUIC reserves the first client-initiated, bidirectional stream (Stream 0) for cryptographic operations. HTTP over QUIC reserves the first unidirectional stream sent by either peer (Streams 2 and 3) for sending and receiving HTTP control frames. This pair of unidirectional streams is analogous to HTTP/2’s Stream 0. The data sent on these streams is critical to the HTTP connection. If either control stream is closed for any reason, this MUST be treated as a connection error of type QUIC_CLOSED_CRITICAL_STREAM. When HTTP headers and data are sent over QUIC, the QUIC layer handles most of the stream management. An HTTP request/response consumes a single client-initiated, bidirectional stream. A bidirectional stream ensures that the response can be readily correlated with the request. This means that the client’s first request occurs on QUIC stream 4, with subsequent requests on stream 8, 12, and so on. Server push uses server-initiated, unidirectional streams. Thus, the server’s first push consumes stream 7 and subsequent pushes use stream 11, 15, and so on. These streams carry frames related to the request/response (see ). When a stream terminates cleanly, if the last frame on the stream was truncated, this MUST be treated as a connection error (see HTTP_MALFORMED_FRAME in ). Streams which terminate abruptly may be reset at any point in the frame. Streams SHOULD be used sequentially, with no gaps. HTTP does not need to do any separate multiplexing when using QUIC - data sent over a QUIC stream always maps to a particular HTTP transaction. Requests and responses are considered complete when the corresponding QUIC stream is closed in the appropriate direction.

Since most connection-level concerns will be managed by QUIC, the primary use of Streams 2 and 3 will be for the SETTINGS frame when the connection opens and for PRIORITY frames subsequently. A pair of unidirectional streams is used rather than a single bidirectional stream. This allows either peer to send data as soon they are able. Depending on whether 0-RTT is enabled on the connection, either client or server might be able to send stream data first after the cryptographic handshake completes.

A client sends an HTTP request on a client-initiated, bidirectional QUIC stream. A server sends an HTTP response on the same stream as the request. An HTTP message (request or response) consists of: one header block (see ) containing the message headers (see , Section 3.2), the payload body (see , Section 3.3), sent as a series of DATA frames (see ), optionally, one header block containing the trailer-part, if present (see , Section 4.1.2). In addition, prior to sending the message header block indicated above, a response may contain zero or more header blocks containing the message headers of informational (1xx) HTTP responses (see , Section 3.2 and , Section 6.2). PUSH_PROMISE frames MAY be interleaved with the frames of a response message indicating a pushed resource related to the response. These PUSH_PROMISE frames are not part of the response, but carry the headers of a separate HTTP request message. See for more details. The “chunked” transfer encoding defined in Section 4.1 of MUST NOT be used. Trailing header fields are carried in an additional header block following the body. Such a header block is a sequence of HEADERS frames with End Header Block set on the last frame. Senders MUST send only one header block in the trailers section; receivers MUST discard any subsequent header blocks. An HTTP request/response exchange fully consumes a QUIC stream. After sending a request, a client closes the stream for sending; after sending a response, the server closes the stream for sending and the QUIC stream is fully closed. A server can send a complete response prior to the client sending an entire request if the response does not depend on any portion of the request that has not been sent and received. When this is true, a server MAY request that the client abort transmission of a request without error by triggering a QUIC STOP_SENDING with error code HTTP_EARLY_RESPONSE, sending a complete response, and cleanly closing its streams. Clients MUST NOT discard complete responses as a result of having their request terminated abruptly, though clients can always discard responses at their discretion for other reasons. Servers MUST NOT abort a response in progress as a result of receiving a solicited RST_STREAM.

HTTP/QUIC uses HPACK header compression as described in . HPACK was designed for HTTP/2 with the assumption of in-order delivery such as that provided by TCP. A sequence of encoded header blocks must arrive (and be decoded) at an endpoint in the same order in which they were encoded. This ensures that the dynamic state at the two endpoints remains in sync. QUIC streams provide in-order delivery of data sent on those streams, but there are no guarantees about order of delivery between streams. QUIC anticipates moving to a modified version of HPACK without this assumption. In the meantime, by fixing the size of the dynamic table at zero, HPACK can be used in an unordered environment.

The pseudo-method CONNECT (, Section 4.3.6) is primarily used with HTTP proxies to establish a TLS session with an origin server for the purposes of interacting with “https” resources. In HTTP/1.x, CONNECT is used to convert an entire HTTP connection into a tunnel to a remote host. In HTTP/2, the CONNECT method is used to establish a tunnel over a single HTTP/2 stream to a remote host for similar purposes. A CONNECT request in HTTP/QUIC functions in the same manner as in HTTP/2. The request MUST be formatted as described in , Section 8.3. A CONNECT request that does not conform to these restrictions is malformed. The request stream MUST NOT be half-closed at the end of the request. A proxy that supports CONNECT establishes a TCP connection () to the server identified in the “:authority” pseudo-header field. Once this connection is successfully established, the proxy sends a HEADERS frame containing a 2xx series status code to the client, as defined in , Section 4.3.6. All DATA frames on the request stream correspond to data sent on the TCP connection. Any DATA frame sent by the client is transmitted by the proxy to the TCP server; data received from the TCP server is packaged into DATA frames by the proxy. Note that the size and number of TCP segments is not guaranteed to map predictably to the size and number of HTTP DATA or QUIC STREAM frames. The TCP connection can be closed by either peer. When the client ends the request stream (that is, the receive stream at the proxy enters the “Data Recvd” state), the proxy will set the FIN bit on its connection to the TCP server. When the proxy receives a packet with the FIN bit set, it will terminate the send stream that it sends to client. TCP connections which remain half-closed in a single direction are not invalid, but are often handled poorly by servers, so clients SHOULD NOT cause send a STREAM frame with a FIN bit for connections on which they are still expecting data. A TCP connection error is signaled with RST_STREAM. A proxy treats any error in the TCP connection, which includes receiving a TCP segment with the RST bit set, as a stream error of type HTTP_CONNECT_ERROR (). Correspondingly, a proxy MUST send a TCP segment with the RST bit set if it detects an error with the stream or the QUIC connection.

HTTP/QUIC uses the priority scheme described in , Section 5.3. In this priority scheme, a given request can be designated as dependent upon another request, which expresses the preference that the latter stream (the “parent” request) be allocated resources before the former stream (the “dependent” request). Taken together, the dependencies across all requests in a connection form a dependency tree. The structure of the dependency tree changes as PRIORITY frames add, remove, or change the dependency links between requests. The PRIORITY frame identifies a request either by identifying the stream that carries a request or by using a Push ID (). Only a client can send PRIORITY frames. A server MUST NOT send a PRIORITY frame.

HTTP/QUIC supports server push as described in . During connection establishment, the client enables server push by sending a MAX_PUSH_ID frame (see ). A server cannot use server push until it receives a MAX_PUSH_ID frame. As with server push for HTTP/2, the server initiates a server push by sending a PUSH_PROMISE frame that includes request header fields attributed to the request. The PUSH_PROMISE frame is sent on the client-initiated, bidirectional stream that carried the request that generated the push. This allows the server push to be associated with a request. Ordering of a PUSH_PROMISE in relation to certain parts of the response is important (see Section 8.2.1 of ). Unlike HTTP/2, the PUSH_PROMISE does not reference a stream; it contains a Push ID. The Push ID uniquely identifies a server push (see ). This allows a server to fulfill promises in the order that best suits its needs. When a server later fulfills a promise, the server push response is conveyed on a push stream. A push stream is a server-initiated, unidirectional stream. A push stream always begins with a header (see ) that identifies the Push ID of the promise that it fulfills, encoded as a variable-length integer.

A server SHOULD use Push IDs sequentially, starting at 0. A client uses the MAX_PUSH_ID frame () to limit the number of pushes that a server can promise. A client MUST treat receipt of a push stream with a Push ID that is greater than the maximum Push ID as a connection error of type HTTP_PUSH_LIMIT_EXCEEDED. Each Push ID MUST only be used once in a push stream header. If a push stream header includes a Push ID that was used in another push stream header, the client MUST treat this as a connection error of type HTTP_DUPLICATE_PUSH. The same Push ID can be used in multiple PUSH_PROMISE frames (see ). After the push stream header, a push contains a response (), with response headers, a response body (if any) carried by DATA frames, then trailers (if any) carried by HEADERS frames. If a promised server push is not needed by the client, the client SHOULD send a CANCEL_PUSH frame; if the push stream is already open, a QUIC STOP_SENDING frame with an appropriate error code can be used instead (e.g., HTTP_PUSH_REFUSED, HTTP_PUSH_ALREADY_IN_CACHE; see ). This asks the server not to transfer the data and indicates that it will be discarded upon receipt.

Frames are used on each stream. This section describes HTTP framing in QUIC and highlights some differences from HTTP/2 framing. For more detail on differences from HTTP/2, see .

All frames have the following format:

A frame includes the following fields: A variable-length integer that describes the length of the Frame Payload. This length does not include the frame header. An 8-bit type for the frame. An 8-bit field containing flags. The Type field determines the semantics of flags. A payload, the semantics of which are determined by the Type field.

DATA frames (type=0x0) convey arbitrary, variable-length sequences of octets associated with an HTTP request or response payload. The DATA frame defines no flags. DATA frames MUST be associated with an HTTP request or response. If a DATA frame is received on either control stream, the recipient MUST respond with a connection error () of type HTTP_WRONG_STREAM. DATA frames MUST contain a non-zero-length payload. If a DATA frame is received with a payload length of zero, the recipient MUST respond with a stream error () of type HTTP_MALFORMED_FRAME.

The HEADERS frame (type=0x1) is used to carry a header block, compressed using HPACK . No flags are defined for the HEADERS frame. A HEADERS frame with any flags set MUST be treated as a connection error of type HTTP_MALFORMED_FRAME.

The PRIORITY (type=0x02) frame specifies the sender-advised priority of a stream and is substantially different in format from . In order to ensure that prioritization is processed in a consistent order, PRIORITY frames MUST be sent on the control stream. A PRIORITY frame sent on any other stream MUST be treated as a HTTP_WRONG_STREAM error. The format has been modified to accommodate not being sent on a request stream, to allow for identification of server pushes, and the larger stream ID space of QUIC. The semantics of the Stream Dependency, Weight, and E flag are otherwise the same as in HTTP/2. The flags defined are: Indicates that the Prioritized Stream is a server push rather than a request. Indicates a dependency on a server push. Indicates that the stream dependency is exclusive (see , Section 5.3).

The PRIORITY frame payload has the following fields: A variable-length integer that identifies a request. This contains the Stream ID of a request stream when the PUSH_PRIORITIZED flag is clear, or a Push ID when the PUSH_PRIORITIZED flag is set. A variable-length integer that identifies a dependent request. This contains the Stream ID of a request stream when the PUSH_DEPENDENT flag is clear, or a Push ID when the PUSH_DEPENDENT flag is set. A request Stream ID of 0 indicates a dependency on the root stream. For details of dependencies, see and , Section 5.3. An unsigned 8-bit integer representing a priority weight for the stream (see , Section 5.3). Add one to the value to obtain a weight between 1 and 256. A PRIORITY frame identifies a request to prioritize, and a request upon which that request is dependent. A Prioritized Request ID or Stream Dependency ID identifies a client-initiated request using the corresponding stream ID when the corresponding PUSH_PRIORITIZED or PUSH_DEPENDENT flag is not set. Setting the PUSH_PRIORITIZED or PUSH_DEPENDENT flag causes the Prioritized Request ID or Stream Dependency ID (respectively) to identify a server push using a Push ID (see for details). A PRIORITY frame MAY identify a Stream Dependency ID using a Stream ID of 0; as in , this makes the request dependent on the root of the dependency tree. A PRIORITY frame MUST identify a client-initiated, bidirectional stream. A server MUST treat receipt of PRIORITY frame with a Stream ID of any other type as a connection error of type HTTP_MALFORMED_FRAME. Stream ID 0 cannot be reprioritized. A Prioritized Request ID that identifies Stream 0 MUST be treated as a connection error of type HTTP_MALFORMED_FRAME. A PRIORITY frame that does not reference a request MUST be treated as a HTTP_MALFORMED_FRAME error, unless it references Stream ID 0. A PRIORITY that sets a PUSH_PRIORITIZED or PUSH_DEPENDENT flag, but then references a non-existent Push ID MUST be treated as a HTTP_MALFORMED_FRAME error. A PRIORITY frame MUST contain only the identified fields. A PRIORITY frame that contains more or fewer fields, or a PRIORITY frame that includes a truncated integer encoding MUST be treated as a connection error of type HTTP_MALFORMED_FRAME.

The CANCEL_PUSH frame (type=0x3) is used to request cancellation of server push prior to the push stream being created. The CANCEL_PUSH frame identifies a server push request by Push ID (see ) using a variable-length integer. When a server receives this frame, it aborts sending the response for the identified server push. If the server has not yet started to send the server push, it can use the receipt of a CANCEL_PUSH frame to avoid opening a stream. If the push stream has been opened by the server, the server SHOULD sent a QUIC RST_STREAM frame on those streams and cease transmission of the response. A server can send this frame to indicate that it won’t be sending a response prior to creation of a push stream. Once the push stream has been created, sending CANCEL_PUSH has no effect on the state of the push stream. A QUIC RST_STREAM frame SHOULD be used instead to cancel transmission of the server push response. A CANCEL_PUSH frame is sent on the control stream. Sending a CANCEL_PUSH frame on a stream other than the control stream MUST be treated as a stream error of type HTTP_WRONG_STREAM. The CANCEL_PUSH frame has no defined flags. The CANCEL_PUSH frame carries a Push ID encoded as a variable-length integer. The Push ID identifies the server push that is being cancelled (see ). If the client receives a CANCEL_PUSH frame, that frame might identify a Push ID that has not yet been mentioned by a PUSH_PROMISE frame. An endpoint MUST treat a CANCEL_PUSH frame which does not contain exactly one properly-formatted variable-length integer as a connection error of type HTTP_MALFORMED_FRAME.

The SETTINGS frame (type=0x4) conveys configuration parameters that affect how endpoints communicate, such as preferences and constraints on peer behavior, and is different from . Individually, a SETTINGS parameter can also be referred to as a “setting”. SETTINGS parameters are not negotiated; they describe characteristics of the sending peer, which can be used by the receiving peer. However, a negotiation can be implied by the use of SETTINGS – a peer uses SETTINGS to advertise a set of supported values. The recipient can then choose which entries from this list are also acceptable and proceed with the value it has chosen. (This choice could be announced in a field of an extension frame, or in its own value in SETTINGS.) Different values for the same parameter can be advertised by each peer. For example, a client might be willing to consume very large response headers, while servers are more cautious about request size. Parameters MUST NOT occur more than once. A receiver MAY treat the presence of the same parameter more than once as a connection error of type HTTP_MALFORMED_FRAME. The SETTINGS frame defines no flags. The payload of a SETTINGS frame consists of zero or more parameters, each consisting of an unsigned 16-bit setting identifier and a length-prefixed binary value.

A zero-length content indicates that the setting value is a Boolean and true. False is indicated by the absence of the setting. Non-zero-length values MUST be compared against the remaining length of the SETTINGS frame. Any value which purports to cross the end of the frame MUST cause the SETTINGS frame to be considered malformed and trigger a connection error of type HTTP_MALFORMED_FRAME. An implementation MUST ignore the contents for any SETTINGS identifier it does not understand. SETTINGS frames always apply to a connection, never a single stream. A SETTINGS frame MUST be sent as the first frame of either control stream (see ) by each peer, and MUST NOT be sent subsequently or on any other stream. If an endpoint receives an SETTINGS frame on a different stream, the endpoint MUST respond with a connection error of type HTTP_WRONG_STREAM. If an endpoint receives a second SETTINGS frame, the endpoint MUST respond with a connection error of type HTTP_MALFORMED_FRAME. The SETTINGS frame affects connection state. A badly formed or incomplete SETTINGS frame MUST be treated as a connection error () of type HTTP_MALFORMED_FRAME.

Settings which are integers use the QUIC variable-length integer encoding.

The following settings are defined in HTTP/QUIC: An integer with a maximum value of 2^30 - 1. This value MUST be zero. An integer with a maximum value of 2^30 - 1

When a 0-RTT QUIC connection is being used, the client’s initial requests will be sent before the arrival of the server’s SETTINGS frame. Clients SHOULD cache at least the following settings about servers: SETTINGS_HEADER_TABLE_SIZE SETTINGS_MAX_HEADER_LIST_SIZE Clients MUST comply with cached settings until the server’s current settings are received. If a client does not have cached values, it SHOULD assume the following values: SETTINGS_HEADER_TABLE_SIZE: 0 octets SETTINGS_MAX_HEADER_LIST_SIZE: 16,384 octets Servers MAY continue processing data from clients which exceed its current configuration during the initial flight. In this case, the client MUST apply the new settings immediately upon receipt. If the connection is closed because these or other constraints were violated during the 0-RTT flight (e.g. with HTTP_HPACK_DECOMPRESSION_FAILED), clients MAY establish a new connection and retry any 0-RTT requests using the settings sent by the server on the closed connection. (This assumes that only requests that are safe to retry are sent in 0-RTT.) If the connection was closed before the SETTINGS frame was received, clients SHOULD discard any cached values and use the defaults above on the next connection.

The PUSH_PROMISE frame (type=0x05) is used to carry a request header set from server to client, as in HTTP/2. The PUSH_PROMISE frame defines no flags.

The payload consists of: A variable-length integer that identifies the server push request. A push ID is used in push stream header (), CANCEL_PUSH frames (), and PRIORITY frames (). HPACK-compressed request headers for the promised response. A server MUST NOT use a Push ID that is larger than the client has provided in a MAX_PUSH_ID frame (). A client MUST treat receipt of a PUSH_PROMISE that contains a larger Push ID than the client has advertised as a connection error of type HTTP_MALFORMED_FRAME. A server MAY use the same Push ID in multiple PUSH_PROMISE frames. This allows the server to use the same server push in response to multiple concurrent requests. Referencing the same server push ensures that a PUSH_PROMISE can be made in relation to every response in which server push might be needed without duplicating pushes. A server that uses the same Push ID in multiple PUSH_PROMISE frames MUST include the same header fields each time. The octets of the header block MAY be different due to differing encoding, but the header fields and their values MUST be identical. Note that ordering of header fields is significant. A client MUST treat receipt of a PUSH_PROMISE with conflicting header field values for the same Push ID as a connection error of type HTTP_MALFORMED_FRAME. Allowing duplicate references to the same Push ID is primarily to reduce duplication caused by concurrent requests. A server SHOULD avoid reusing a Push ID over a long period. Clients are likely to consume server push responses and not retain them for reuse over time. Clients that see a PUSH_PROMISE that uses a Push ID that they have since consumed and discarded are forced to ignore the PUSH_PROMISE.

The GOAWAY frame (type=0x7) is used to initiate graceful shutdown of a connection by a server. GOAWAY allows a server to stop accepting new requests while still finishing processing of previously received requests. This enables administrative actions, like server maintenance. GOAWAY by itself does not close a connection. The GOAWAY frame does not define any flags, and the payload is a QUIC Stream ID for a client-initiated, bidirectional stream encoded as a variable-length integer. Clients do not need to send GOAWAY to initiate a graceful shutdown; they simply stop making new requests. A server MUST treat receipt of a GOAWAY frame as a connection error () of type HTTP_UNEXPECTED_GOAWAY. A client MUST treat receipt of a GOAWAY frame containing a Stream ID of any other type as a connection error of type HTTP_MALFORMED_FRAME. The GOAWAY frame applies to the connection, not a specific stream. An endpoint MUST treat a GOAWAY frame on a stream other than the control stream as a connection error () of type HTTP_WRONG_STREAM. New client requests might already have been sent before the client receives the server’s GOAWAY frame. The GOAWAY frame contains the Stream ID of the last client-initiated request that was or might be processed in this connection, which enables client and server to agree on which requests were accepted prior to the connection shutdown. This identifier MAY be lower than the stream limit identified by a QUIC MAX_STREAM_ID frame, and MAY be zero if no requests were processed. Servers SHOULD NOT increase the MAX_STREAM_ID limit after sending a GOAWAY frame. In this context, “processed” means that some data from the stream was passed to some higher layer of software that might have taken some action as a result. Once sent, the server will refuse requests sent on streams with an identifier higher than the included last Stream ID. Clients MUST NOT send new requests on the connection after receiving GOAWAY, although requests might already be in transit. A new connection can be established for new requests. If the client has sent requests on streams with a higher Stream ID than indicated in the GOAWAY frame, those requests were not and will not be processed. Endpoints SHOULD reset any streams above this ID with the error code HTTP_REQUEST_CANCELLED. Servers MAY also reset streams below the indicated ID with HTTP_REQUEST_CANCELLED if the associated requests were not processed. Servers MUST NOT use the HTTP_REQUEST_CANCELLED status for requests which were partially or fully processed. The client can treat requests cancelled by the server as though they had never been sent at all, thereby allowing them to be retried later on a new connection. If a stream is cancelled after receiving a complete response, the client MAY ignore the cancellation and use the response. However, if a stream is cancelled after receiving a partial response, the response SHOULD NOT be used. Automatically retrying such requests is not possible, unless this is otherwise permitted (e.g., idempotent actions like GET, PUT, or DELETE). Requests on Stream IDs less than or equal to the Stream ID in the GOAWAY frame might have been processed; their status cannot be known until they are completed successfully, reset individually, or the connection terminates. Servers SHOULD send a GOAWAY frame when the closing of a connection is known in advance, even if the advance notice is small, so that the remote peer can know whether a stream has been partially processed or not. For example, if an HTTP client sends a POST at the same time that a server closes a QUIC connection, the client cannot know if the server started to process that POST request if the server does not send a GOAWAY frame to indicate what streams it might have acted on. For unexpected closures caused by error conditions, a QUIC CONNECTION_CLOSE or APPLICATION_CLOSE frame MUST be used. However, a GOAWAY MAY be sent first to provide additional detail to clients and to allow the client to retry requests. Including the GOAWAY frame in the same packet as the QUIC CONNECTION_CLOSE or APPLICATION_CLOSE frame improves the chances of the frame being received by clients. If a connection terminates without a GOAWAY frame, the last Stream ID is effectively the highest possible Stream ID (as determined by QUIC’s MAX_STREAM_ID). An endpoint MAY send multiple GOAWAY frames if circumstances change. For instance, an endpoint that sends GOAWAY without an error code during graceful shutdown could subsequently encounter an error condition. The last stream identifier from the last GOAWAY frame received indicates which streams could have been acted upon. A server MUST NOT increase the value they send in the last Stream ID, since clients might already have retried unprocessed requests on another connection. A client that is unable to retry requests loses all requests that are in flight when the server closes the connection. A server that is attempting to gracefully shut down a connection SHOULD send an initial GOAWAY frame with the last Stream ID set to the current value of QUIC’s MAX_STREAM_ID and SHOULD NOT increase the MAX_STREAM_ID thereafter. This signals to the client that a shutdown is imminent and that initiating further requests is prohibited. After allowing time for any in-flight requests (at least one round-trip time), the server MAY send another GOAWAY frame with an updated last Stream ID. This ensures that a connection can be cleanly shut down without losing requests. Once all requests on streams at or below the identified stream number have been completed or cancelled, and all promised server push responses associated with those requests have been completed or cancelled, the connection can be closed using an Immediate Close (see ). An endpoint that completes a graceful shutdown SHOULD use the QUIC APPLICATION_CLOSE frame with the HTTP_NO_ERROR code.

The MAX_PUSH_ID frame (type=0xD) is used by clients to control the number of server pushes that the server can initiate. This sets the maximum value for a Push ID that the server can use in a PUSH_PROMISE frame. Consequently, this also limits the number of push streams that the server can initiate in addition to the limit set by the QUIC MAX_STREAM_ID frame. The MAX_PUSH_ID frame is always sent on a control stream. Receipt of a MAX_PUSH_ID frame on any other stream MUST be treated as a connection error of type HTTP_WRONG_STREAM. A server MUST NOT send a MAX_PUSH_ID frame. A client MUST treat the receipt of a MAX_PUSH_ID frame as a connection error of type HTTP_MALFORMED_FRAME. The maximum Push ID is unset when a connection is created, meaning that a server cannot push until it receives a MAX_PUSH_ID frame. A client that wishes to manage the number of promised server pushes can increase the maximum Push ID by sending a MAX_PUSH_ID frame as the server fulfills or cancels server pushes. The MAX_PUSH_ID frame has no defined flags. The MAX_PUSH_ID frame carries a single variable-length integer that identifies the maximum value for a Push ID that the server can use (see ). A MAX_PUSH_ID frame cannot reduce the maximum Push ID; receipt of a MAX_PUSH_ID that contains a smaller value than previously received MUST be treated as a connection error of type HTTP_MALFORMED_FRAME. A server MUST treat a MAX_PUSH_ID frame payload that does not contain a single variable-length integer as a connection error of type HTTP_MALFORMED_FRAME.

QUIC connections are persistent. All of the considerations in Section 9.1 of apply to the management of QUIC connections. HTTP clients are expected to use QUIC PING frames to keep connections open. Servers SHOULD NOT use PING frames to keep a connection open. A client SHOULD NOT use PING frames for this purpose unless there are responses outstanding for requests or server pushes. If the client is not expecting a response from the server, allowing an idle connection to time out (based on the idle_timeout transport parameter) is preferred over expending effort maintaining a connection that might not be needed. A gateway MAY use PING to maintain connections in anticipation of need rather than incur the latency cost of connection establishment to servers.

QUIC allows the application to abruptly terminate (reset) individual streams or the entire connection when an error is encountered. These are referred to as “stream errors” or “connection errors” and are described in more detail in . This section describes HTTP-specific error codes which can be used to express the cause of a connection or stream error.

The following error codes are defined for use in QUIC RST_STREAM, STOP_SENDING, and CONNECTION_CLOSE frames when using HTTP/QUIC. This value is reserved by the transport to be used in response to QUIC STOP_SENDING frames. No error. This is used when the connection or stream needs to be closed, but there is no error to signal. The server has attempted to push content which the client will not accept on this connection. An internal error has occurred in the HTTP stack. The server has attempted to push content which the client has cached. The client no longer needs the requested data. HPACK failed to decompress a frame and cannot continue. The connection established in response to a CONNECT request was reset or abnormally closed. The endpoint detected that its peer is exhibiting a behavior that might be generating excessive load. The requested operation cannot be served over HTTP/QUIC. The peer should retry over HTTP/2. A frame was received on stream where it is not permitted. A Push ID greater than the current maximum Push ID was referenced. A Push ID was referenced in two different stream headers. An error in a specific frame type. The frame type is included as the last octet of the error code. For example, an error in a MAX_PUSH_ID frame would be indicated with the code (0x10D).

HTTP/QUIC is strongly informed by HTTP/2, and bears many similarities. This section describes the approach taken to design HTTP/QUIC, points out important differences from HTTP/2, and describes how to map HTTP/2 extensions into HTTP/QUIC. HTTP/QUIC begins from the premise that HTTP/2 code reuse is a useful feature, but not a hard requirement. HTTP/QUIC departs from HTTP/2 primarily where necessary to accommodate the differences in behavior between QUIC and TCP (lack of ordering, support for streams). We intend to avoid gratuitous changes which make it difficult or impossible to build extensions with the same semantics applicable to both protocols at once. These departures are noted in this section.

HTTP/QUIC permits use of a larger number of streams (2^62-1) than HTTP/2. The considerations about exhaustion of stream identifier space apply, though the space is significantly larger such that it is likely that other limits in QUIC are reached first, such as the limit on the connection flow control window.

Many framing concepts from HTTP/2 can be elided away on QUIC, because the transport deals with them. Because frames are already on a stream, they can omit the stream number. Because frames do not block multiplexing (QUIC’s multiplexing occurs below this layer), the support for variable-maximum-length packets can be removed. Because stream termination is handled by QUIC, an END_STREAM flag is not required. Frame payloads are largely drawn from . However, QUIC includes many features (e.g. flow control) which are also present in HTTP/2. In these cases, the HTTP mapping does not re-implement them. As a result, several HTTP/2 frame types are not required in HTTP/QUIC. Where an HTTP/2-defined frame is no longer used, the frame ID has been reserved in order to maximize portability between HTTP/2 and HTTP/QUIC implementations. However, even equivalent frames between the two mappings are not identical. Many of the differences arise from the fact that HTTP/2 provides an absolute ordering between frames across all streams, while QUIC provides this guarantee on each stream only. As a result, if a frame type makes assumptions that frames from different streams will still be received in the order sent, HTTP/QUIC will break them. For example, implicit in the HTTP/2 prioritization scheme is the notion of in-order delivery of priority changes (i.e., dependency tree mutations): since operations on the dependency tree such as reparenting a subtree are not commutative, both sender and receiver must apply them in the same order to ensure that both sides have a consistent view of the stream dependency tree. HTTP/2 specifies priority assignments in PRIORITY frames and (optionally) in HEADERS frames. To achieve in-order delivery of priority changes in HTTP/QUIC, PRIORITY frames are sent on the control stream and the PRIORITY section is removed from the HEADERS frame. Frame type definitions in HTTP/QUIC often use the QUIC variable-length integer encoding. In particular, Stream IDs use this encoding, which allow for a larger range of possible values than the encoding used in HTTP/2. Some frames in HTTP/QUIC use an identifier rather than a Stream ID (e.g. Push IDs in PRIORITY frames). Redefinition of the encoding of extension frame types might be necessary if the encoding includes a Stream ID. Other than this issue, frame type HTTP/2 extensions are typically portable to QUIC simply by replacing Stream 0 in HTTP/2 with Stream 2 or 3 in HTTP/QUIC. HTTP/QUIC extensions will not assume ordering, but would not be harmed by ordering, and would be portable to HTTP/2 in the same manner. Below is a listing of how each HTTP/2 frame type is mapped: Padding is not defined in HTTP/QUIC frames. See . As described above, the PRIORITY region of HEADERS is not supported. A separate PRIORITY frame MUST be used. Padding is not defined in HTTP/QUIC frames. See . As described above, the PRIORITY frame is sent on the control stream and can reference either a Stream ID or a Push ID. See . RST_STREAM frames do not exist, since QUIC provides stream lifecycle management. The same code point is used for the CANCEL_PUSH frame (). SETTINGS frames are sent only at the beginning of the connection. See and . The PUSH_PROMISE does not reference a stream; instead the push stream references the PUSH_PROMISE frame using a Push ID. See . PING frames do not exist, since QUIC provides equivalent functionality. GOAWAY is sent only from server to client and does not contain an error code. See . WINDOW_UPDATE frames do not exist, since QUIC provides flow control. CONTINUATION frames do not exist; instead, larger HEADERS/PUSH_PROMISE frames than HTTP/2 are permitted, and HEADERS frames can be used in series. Frame types defined by extensions to HTTP/2 need to be separately registered for HTTP/QUIC if still applicable. The IDs of frames defined in have been reserved for simplicity. See .

An important difference from HTTP/2 is that settings are sent once, at the beginning of the connection, and thereafter cannot change. This eliminates many corner cases around synchronization of changes. Some transport-level options that HTTP/2 specifies via the SETTINGS frame are superseded by QUIC transport parameters in HTTP/QUIC. The HTTP-level options that are retained in HTTP/QUIC have the same value as in HTTP/2. Below is a listing of how each HTTP/2 SETTINGS parameter is mapped: See . This is removed in favor of the MAX_PUSH_ID which provides a more granular control over server push. QUIC controls the largest open Stream ID as part of its flow control logic. Specifying SETTINGS_MAX_CONCURRENT_STREAMS in the SETTINGS frame is an error. QUIC requires both stream and connection flow control window sizes to be specified in the initial transport handshake. Specifying SETTINGS_INITIAL_WINDOW_SIZE in the SETTINGS frame is an error. This setting has no equivalent in HTTP/QUIC. Specifying it in the SETTINGS frame is an error. See . Settings need to be defined separately for HTTP/2 and HTTP/QUIC. The IDs of settings defined in have been reserved for simplicity. See .

QUIC has the same concepts of “stream” and “connection” errors that HTTP/2 provides. However, because the error code space is shared between multiple components, there is no direct portability of HTTP/2 error codes. The HTTP/2 error codes defined in Section 7 of map to the HTTP over QUIC error codes as follows: HTTP_NO_ERROR in . No single mapping. See new HTTP_MALFORMED_FRAME error codes defined in . HTTP_INTERNAL_ERROR in . Not applicable, since QUIC handles flow control. Would provoke a QUIC_FLOW_CONTROL_RECEIVED_TOO_MUCH_DATA from the QUIC layer. Not applicable, since no acknowledgement of SETTINGS is defined. Not applicable, since QUIC handles stream management. Would provoke a QUIC_STREAM_DATA_AFTER_TERMINATION from the QUIC layer. No single mapping. See new error codes defined in . Not applicable, since QUIC handles stream management. Would provoke a QUIC_TOO_MANY_OPEN_STREAMS from the QUIC layer. HTTP_REQUEST_CANCELLED in . HTTP_HPACK_DECOMPRESSION_FAILED in . HTTP_CONNECT_ERROR in . HTTP_EXCESSIVE_LOAD in . Not applicable, since QUIC is assumed to provide sufficient security on all connections. HTTP_VERSION_FALLBACK in . Error codes need to be defined for HTTP/2 and HTTP/QUIC separately. See .

The security considerations of HTTP over QUIC should be comparable to those of HTTP/2. The modified SETTINGS format contains nested length elements, which could pose a security risk to an uncautious implementer. A SETTINGS frame parser MUST ensure that the length of the frame exactly matches the length of the settings it contains.

This document creates a new registration for the identification of HTTP/QUIC in the “Application Layer Protocol Negotiation (ALPN) Protocol IDs” registry established in . The “hq” string identifies HTTP/QUIC: HTTP over QUIC 0x68 0x71 (“hq”) This document

This document creates a new registration for version-negotiation hints in the “Hypertext Transfer Protocol (HTTP) Alt-Svc Parameter” registry established in . “quic” This document,

This document establishes a registry for HTTP/QUIC frame type codes. The “HTTP/QUIC Frame Type” registry manages an 8-bit space. The “HTTP/QUIC Frame Type” registry operates under either of the “IETF Review” or “IESG Approval” policies for values between 0x00 and 0xef, with values between 0xf0 and 0xff being reserved for Experimental Use. While this registry is separate from the “HTTP/2 Frame Type” registry defined in , it is preferable that the assignments parallel each other. If an entry is present in only one registry, every effort SHOULD be made to avoid assigning the corresponding value to an unrelated operation. New entries in this registry require the following information: A name or label for the frame type. The 8-bit code assigned to the frame type. A reference to a specification that includes a description of the frame layout, its semantics, and flags that the frame type uses, including any parts of the frame that are conditionally present based on the value of flags. The entries in the following table are registered by this document. Frame Type Code Specification DATA 0x0 HEADERS 0x1 PRIORITY 0x2 CANCEL_PUSH 0x3 SETTINGS 0x4 PUSH_PROMISE 0x5 Reserved 0x6 N/A GOAWAY 0x7 Reserved 0x8 N/A Reserved 0x9 N/A MAX_PUSH_ID 0xD

This document establishes a registry for HTTP/QUIC settings. The “HTTP/QUIC Settings” registry manages a 16-bit space. The “HTTP/QUIC Settings” registry operates under the “Expert Review” policy for values in the range from 0x0000 to 0xefff, with values between and 0xf000 and 0xffff being reserved for Experimental Use. The designated experts are the same as those for the “HTTP/2 Settings” registry defined in . While this registry is separate from the “HTTP/2 Settings” registry defined in , it is preferable that the assignments parallel each other. If an entry is present in only one registry, every effort SHOULD be made to avoid assigning the corresponding value to an unrelated operation. New registrations are advised to provide the following information: A symbolic name for the setting. Specifying a setting name is optional. The 16-bit code assigned to the setting. An optional reference to a specification that describes the use of the setting. The entries in the following table are registered by this document. Setting Name Code Specification HEADER_TABLE_SIZE 0x1 Reserved 0x2 N/A Reserved 0x3 N/A Reserved 0x4 N/A Reserved 0x5 N/A MAX_HEADER_LIST_SIZE 0x6

This document establishes a registry for HTTP/QUIC error codes. The “HTTP/QUIC Error Code” registry manages a 16-bit space. The “HTTP/QUIC Error Code” registry operates under the “Expert Review” policy . Registrations for error codes are required to include a description of the error code. An expert reviewer is advised to examine new registrations for possible duplication with existing error codes. Use of existing registrations is to be encouraged, but not mandated. New registrations are advised to provide the following information: A name for the error code. Specifying an error code name is optional. The 16-bit error code value. A brief description of the error code semantics, longer if no detailed specification is provided. An optional reference for a specification that defines the error code. The entries in the following table are registered by this document. Name Code Description Specification STOPPING 0x0000 Reserved by QUIC HTTP_NO_ERROR 0x0001 No error HTTP_PUSH_REFUSED 0x0002 Client refused pushed content HTTP_INTERNAL_ERROR 0x0003 Internal error HTTP_PUSH_ALREADY_IN_CACHE 0x0004 Pushed content already cached HTTP_REQUEST_CANCELLED 0x0005 Data no longer needed HTTP_HPACK_DECOMPRESSION_FAILED 0x0006 HPACK cannot continue HTTP_CONNECT_ERROR 0x0007 TCP reset or error on CONNECT request HTTP_EXCESSIVE_LOAD 0x0008 Peer generating excessive load HTTP_VERSION_FALLBACK 0x0009 Retry over HTTP/2 HTTP_WRONG_STREAM 0x000A A frame was sent on the wrong stream HTTP_PUSH_LIMIT_EXCEEDED 0x000B Maximum Push ID exceeded HTTP_DUPLICATE_PUSH 0x000C Push ID was fulfilled multiple times HTTP_MALFORMED_FRAME 0x01XX Error in frame formatting or use

Google Mozilla This specification describes an optimized expression of the semantics of the Hypertext Transfer Protocol (HTTP), referred to as HTTP version 2 (HTTP/2). HTTP/2 enables a more efficient use of network resources and a reduced perception of latency by introducing header field compression and allowing multiple concurrent exchanges on the same connection. It also introduces unsolicited push of representations from servers to clients.This specification is an alternative to, but does not obsolete, the HTTP/1.1 message syntax. HTTP's existing semantics remain unchanged. In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Internet technical specifications often need to define a formal syntax. Over the years, a modified version of Backus-Naur Form (BNF), called Augmented BNF (ABNF), has been popular among many Internet specifications. The current specification documents ABNF. It balances compactness and simplicity with reasonable representational power. The differences between standard BNF and ABNF involve naming rules, repetition, alternatives, order-independence, and value ranges. This specification also supplies additional rule definitions and encoding for a core lexical analyzer of the type common to several Internet specifications. [STANDARDS-TRACK] This document specifies "Alternative Services" for HTTP, which allow an origin's resources to be authoritatively available at a separate network location, possibly accessed with a different protocol configuration. This document provides specifications for existing TLS extensions. It is a companion document for RFC 5246, "The Transport Layer Security (TLS) Protocol Version 1.2". The extensions specified are server_name, max_fragment_length, client_certificate_url, trusted_ca_keys, truncated_hmac, and status_request. [STANDARDS-TRACK] The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document provides an overview of HTTP architecture and its associated terminology, defines the "http" and "https" Uniform Resource Identifier (URI) schemes, defines the HTTP/1.1 message syntax and parsing requirements, and describes related security concerns for implementations. The Hypertext Transfer Protocol (HTTP) is a stateless \%application- level protocol for distributed, collaborative, hypertext information systems. This document defines the semantics of HTTP/1.1 messages, as expressed by request methods, request header fields, response status codes, and response header fields, along with the payload of messages (metadata and body content) and mechanisms for content negotiation. This specification defines HPACK, a compression format for efficiently representing HTTP header fields, to be used in HTTP/2. This document describes a Transport Layer Security (TLS) extension for application-layer protocol negotiation within the TLS handshake. For instances in which multiple application protocols are supported on the same TCP or UDP port, this extension allows the application layer to negotiate which protocol will be used within the TLS connection. Many protocols make use of points of extensibility that use constants to identify various protocol parameters. To ensure that the values in these fields do not have conflicting uses and to promote interoperability, their allocations are often coordinated by a central record keeper. For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA).To make assignments in a given registry prudently, guidance describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made, is needed. This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry.This is the third edition of this document; it obsoletes RFC 5226.

The original authors of this specification were Robbie Shade and Mike Warres. A substantial portion of Mike’s contribution was supported by Microsoft during his employment there.

RFC Editor’s Note: Please remove this section prior to publication of a final version of this document.

Clarified connection coalescing rules (#940, #1024)

Changes for integer encodings in QUIC (#595,#905) Use unidirectional streams as appropriate (#515, #240, #281, #886) Improvement to the description of GOAWAY (#604, #898) Improve description of server push usage (#947, #950, #957)

Track changes in QUIC error code usage (#485)

Made push ID sequential, add MAX_PUSH_ID, remove SETTINGS_ENABLE_PUSH (#709) Guidance about keep-alive and QUIC PINGs (#729) Expanded text on GOAWAY and cancellation (#757)

Cite RFC 5234 (#404) Return to a single stream per request (#245,#557) Use separate frame type and settings registries from HTTP/2 (#81) SETTINGS_ENABLE_PUSH instead of SETTINGS_DISABLE_PUSH (#477) Restored GOAWAY (#696) Identify server push using Push ID rather than a stream ID (#702,#281) DATA frames cannot be empty (#700)

None.

Track changes in transport draft

SETTINGS changes (#181): SETTINGS can be sent only once at the start of a connection; no changes thereafter SETTINGS_ACK removed Settings can only occur in the SETTINGS frame a single time Boolean format updated Alt-Svc parameter changed from “v” to “quic”; format updated (#229) Closing the connection control stream or any message control stream is a fatal error (#176) HPACK Sequence counter can wrap (#173) 0-RTT guidance added Guide to differences from HTTP/2 and porting HTTP/2 extensions added (#127,#242)

Changed “HTTP/2-over-QUIC” to “HTTP/QUIC” throughout (#11,#29) Changed from using HTTP/2 framing within Stream 3 to new framing format and two-stream-per-request model (#71,#72,#73) Adopted SETTINGS format from draft-bishop-httpbis-extended-settings-01 Reworked SETTINGS_ACK to account for indeterminate inter-stream order (#75) Described CONNECT pseudo-method (#95) Updated ALPN token and Alt-Svc guidance (#13,#87) Application-layer-defined error codes (#19,#74)

Adopted as base for draft-ietf-quic-http Updated authors/editors list