Hypertext Transfer Protocol Version 3 (HTTP/3)Akamaimbishop@evequefou.be
Transport
QUICThe 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 HTTP/3.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.HTTP semantics are used for a broad range of services on the Internet. These
semantics have commonly been used with two different TCP mappings, HTTP/1.1 and
HTTP/2. HTTP/3 supports the same semantics over a new transport protocol, QUIC.HTTP/1.1 is a TCP mapping which uses whitespace-delimited text fields to convey
HTTP messages. While these exchanges are human-readable, using whitespace for
message formatting leads to parsing difficulties and workarounds to be tolerant
of variant behavior. Because each connection can transfer only a single HTTP
request or response at a time in each direction, multiple parallel TCP
connections are often used, reducing the ability of the congestion controller to
accurately manage traffic between endpoints.HTTP/2 introduced a binary framing and multiplexing layer to improve latency
without modifying the transport layer. However, because the parallel nature of
HTTP/2’s multiplexing is not visible to TCP’s loss recovery mechanisms, a lost
or reordered packet causes all active transactions to experience a stall
regardless of whether that transaction was impacted by the lost packet.The QUIC transport protocol incorporates stream multiplexing and per-stream flow
control, similar to that provided by the HTTP/2 framing layer. By providing
reliability at the stream level and congestion control across the entire
connection, it has the capability to improve the performance of HTTP compared to
a TCP mapping. QUIC also incorporates TLS 1.3 at the transport layer, offering
comparable security to running TLS over TCP, with the improved connection setup
latency of TCP Fast Open .This document defines a mapping of HTTP semantics over the QUIC transport
protocol, drawing heavily on the design of HTTP/2. While delegating stream
lifetime and flow control issues to QUIC, a similar binary framing is used on
each stream. Some HTTP/2 features are subsumed by QUIC, while other features are
implemented atop QUIC.QUIC is described in . For a full description of HTTP/2, see
.HTTP/3 provides a transport for HTTP semantics using the QUIC transport protocol
and an internal framing layer similar to HTTP/2.Once a client knows that an HTTP/3 server exists at a certain endpoint, it opens
a QUIC connection. QUIC provides protocol negotiation, stream-based
multiplexing, and flow control. An HTTP/3 endpoint can be discovered using HTTP
Alternative Services; this process is described in greater detail in
.Within each stream, the basic unit of HTTP/3 communication is a frame
(). Each frame type serves a different purpose. For example, HEADERS
and DATA frames form the basis of HTTP requests and responses
().Multiplexing of requests is performed using the QUIC stream abstraction,
described in Section 2 of . Each request and response
consumes a single QUIC stream. Streams are independent of each other, so one
stream that is blocked or suffers packet loss does not prevent progress on other
streams.Server push is an interaction mode introduced in HTTP/2 which permits
a server to push a request-response exchange to a client in anticipation of the
client making the indicated request. This trades off network usage against a
potential latency gain. Several HTTP/3 frames are used to manage server push,
such as PUSH_PROMISE, DUPLICATE_PUSH, MAX_PUSH_ID, and CANCEL_PUSH.As in HTTP/2, request and response headers are compressed for transmission.
Because HPACK relies on in-order transmission of compressed
header blocks (a guarantee not provided by QUIC), HTTP/3 replaces HPACK with
QPACK . QPACK uses separate unidirectional streams to modify and track
header table state, while header blocks refer to the state of the table without
modifying it.The HTTP/3 specification is split into seven parts. The document begins
with a detailed overview of the connection lifecycle and key concepts:Connection Setup and Management () covers how an HTTP/3
endpoint is discovered and a connection is established.HTTP Request Lifecycle () describes how HTTP
semantics are expressed using frames.Connection Closure () describes how connections are
terminated, either gracefully or abruptly.The details of the wire protocol and interactions with the transport are
described in subsequent sections:Stream Mapping and Usage () describes the way QUIC streams
are used.HTTP Framing Layer () describes the frames used on
most streams.Error Handling () describes how error conditions are handled and
expressed, either on a particular stream or for the connection as a whole.Additional resources are provided in the final sections:Extensions to HTTP/3 () describes how new capabilities can be
added in future documents.A more detailed comparison between HTTP/2 and HTTP/3 can be found in
.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
.The following terms are used:
An abrupt termination of a connection or stream, possibly due to an error
condition.
The endpoint that initiates an HTTP/3 connection. Clients send HTTP requests
and receive HTTP responses.
A transport-layer connection between two endpoints, using QUIC as the
transport protocol.
An error that affects the entire HTTP/3 connection.
Either the client or server of the connection.
The smallest unit of communication on a stream in HTTP/3, consisting of a
header and a variable-length sequence of octets structured according to the
frame type.
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 CONNECTION_CLOSE
frames.” References without this preface refer to frames defined in
.
An endpoint. When discussing a particular endpoint, “peer” refers to the
endpoint that is remote to the primary subject of discussion.
An endpoint that is receiving frames.
An endpoint that is transmitting frames.
The endpoint that accepts an HTTP/3 connection. Servers receive HTTP requests
and send HTTP responses.
A bidirectional or unidirectional bytestream provided by the QUIC transport.
An error on the individual HTTP/3 stream.The term “payload body” is defined in Section 3.3 of .Finally, the terms “gateway”, “intermediary”, “proxy”, and “tunnel” are defined
in Section 2.3 of . Intermediaries act as both client and server at
different times.RFC Editor’s Note: Please remove this section prior to publication of a
final version of this document.HTTP/3 uses the token “h3” to identify itself in ALPN and Alt-Svc. Only
implementations of the final, published RFC can identify themselves as “h3”.
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 “h3-01”.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 “h3-09-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.An HTTP origin advertises the availability of an equivalent HTTP/3 endpoint via
the Alt-Svc HTTP response header field or the HTTP/2 ALTSVC frame
(), using the ALPN token defined in
.For example, an origin could indicate in an HTTP response that HTTP/3 was
available on UDP port 50781 at the same hostname by including the following
header field:On receipt of an Alt-Svc record indicating HTTP/3 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/3 on any UDP port, since an alternative always includes
an explicit port.This document defines the “quic” parameter for Alt-Svc, which MAY be used to
provide version-negotiation hints to HTTP/3 clients. QUIC versions are four-byte
sequences with no additional constraints on format. Leading zeros SHOULD be
omitted for brevity.Syntax:Where multiple versions are listed, the order of the values reflects the
server’s preference (with the first value being the most preferred version).
Reserved versions MAY be listed, but unreserved versions which are not supported
by the alternative SHOULD NOT be present in the list. Origins MAY omit supported
versions for any reason.Clients MUST ignore any included versions which they do not support. The “quic”
parameter MUST NOT occur more than once; clients SHOULD process only the first
occurrence.For example, suppose a server supported both version 0x00000001 and the version
rendered in ASCII as “Q034”. If it also opted to include the reserved version
(from Section 15 of ) 0x1abadaba, it could specify the
following header field:A client acting on this header field would drop the reserved version (not
supported), then attempt to connect to the alternative using the first version
in the list which it does support, if any.HTTP/3 relies on QUIC as the underlying transport. The QUIC version being used
MUST use TLS version 1.3 or greater as its handshake protocol. HTTP/3 clients
MUST indicate the target domain name during the TLS handshake. This may be done
using the Server Name Indication (SNI) extension to TLS or using
some other mechanism.QUIC connections are established as described in . During
connection establishment, HTTP/3 support is indicated by selecting the ALPN
token “h3” 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/3-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 (see ).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/3 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/3 endpoint is authoritative for other origins without an
explicit signal.Prior to making requests for an origin whose scheme is not “https,” the client
MUST ensure the server is willing to serve that scheme. If the client intends
to make requests for an origin whose scheme is “http”, this means that it MUST
obtain a valid http-opportunistic response for the origin as described in
prior to making any such requests. Other schemes might define
other mechanisms.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 ).The considerations discussed in Section 9.1 of also apply to the
management of HTTP/3 connections.A client sends an HTTP request on a client-initiated bidirectional QUIC stream.
A client MUST send only a single request on a given stream. A server sends zero
or more non-final HTTP responses on the same stream as the request, followed by
a single final HTTP response, as detailed below.An HTTP message (request or response) consists of:the message header (see , Section 3.2), sent as a single HEADERS
frame (see ),optionally, the payload body, if present (see , Section 3.3),
sent as a series of DATA frames (see ),optionally, trailing headers, if present (see , Section 4.1.2),
sent as a single HEADERS frame.A server MAY send one or more PUSH_PROMISE frames (see )
before, after, or interleaved with the frames of a response message. These
PUSH_PROMISE frames are not part of the response; see for more
details.Frames of unknown types (), including reserved frames
() MAY be sent on a request or push stream before, after, or
interleaved with other frames described in this section.The HEADERS and PUSH_PROMISE frames might reference updates to the QPACK dynamic
table. While these updates are not directly part of the message exchange, they
must be received and processed before the message can be consumed. See
for more details.The “chunked” transfer encoding defined in Section 4.1 of MUST NOT
be used.A response MAY consist of multiple messages when and only when one or more
informational responses (1xx; see , Section 6.2) precede a final
response to the same request. Non-final responses do not contain a payload body
or trailers.If an endpoint receives an invalid sequence of frames on either a request or
a push stream, it MUST respond with a connection error of type
HTTP_FRAME_UNEXPECTED (). In particular, a DATA frame before any
HEADERS frame, or a HEADERS or DATA frame after the trailing HEADERS frame is
considered invalid.An HTTP request/response exchange fully consumes a bidirectional QUIC stream.
After sending a request, a client MUST close the stream for sending. Unless
using the CONNECT method (see ), clients MUST NOT make
stream closure dependent on receiving a response to their request. After sending
a final response, the server MUST close the stream for sending. At this point,
the QUIC stream is fully closed.When a stream is closed, this indicates the end of an HTTP message. Because some
messages are large or unbounded, endpoints SHOULD begin processing partial HTTP
messages once enough of the message has been received to make progress. If a
client stream terminates without enough of the HTTP message to provide a
complete response, the server SHOULD abort its response with the error code
HTTP_REQUEST_INCOMPLETE.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 abort reading the
request stream with error code HTTP_EARLY_RESPONSE, send a complete response,
and cleanly close the sending part of the stream. 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.HTTP message headers carry information as a series of key-value pairs, called
header fields. For a listing of registered HTTP header fields, see the “Message
Header Field” registry maintained at
https://www.iana.org/assignments/message-headers.Just as in previous versions of HTTP, header field names are strings of ASCII
characters that are compared in a case-insensitive fashion. Properties of HTTP
header field names and values are discussed in more detail in Section 3.2 of
, though the wire rendering in HTTP/3 differs. As in HTTP/2, header
field names MUST be converted to lowercase prior to their encoding. A request
or response containing uppercase header field names MUST be treated as
malformed ().As in HTTP/2, HTTP/3 uses special pseudo-header fields beginning with the ‘:’
character (ASCII 0x3a) to convey the target URI, the method of the request, and
the status code for the response. These pseudo-header fields are defined in
Section 8.1.2.3 and 8.1.2.4 of . Pseudo-header fields are not HTTP
header fields. Endpoints MUST NOT generate pseudo-header fields other than
those defined in . The restrictions on the use of pseudo-header
fields in Section 8.1.2.1 of also apply to HTTP/3.HTTP/3 uses QPACK header compression as described in , a variation of
HPACK which allows the flexibility to avoid header-compression-induced
head-of-line blocking. See that document for additional details.To allow for better compression efficiency, the cookie header field
MAY be split into separate header fields, each with one or more cookie-pairs,
before compression. If a decompressed header list contains multiple cookie
header fields, these MUST be concatenated before being passed into a non-HTTP/2,
non-HTTP/3 context, as described in , Section 8.1.2.5.An HTTP/3 implementation MAY impose a limit on the maximum size of the message
header it will accept on an individual HTTP message. A server that receives a
larger header field list than it is willing to handle can send an HTTP 431
(Request Header Fields Too Large) status code . A client can
discard responses that it cannot process. The size of a header field list is
calculated based on the uncompressed size of header fields, including the length
of the name and value in bytes plus an overhead of 32 bytes for each header
field.If an implementation wishes to advise its peer of this limit, it can be conveyed
as a number of bytes in the SETTINGS_MAX_HEADER_LIST_SIZE parameter. An
implementation which has received this parameter SHOULD NOT send an HTTP message
header which exceeds the indicated size, as the peer will likely refuse to
process it. However, because this limit is applied at each hop, messages below
this limit are not guaranteed to be accepted.Clients can cancel requests by resetting and aborting the request stream with an
error code of HTTP_REQUEST_CANCELLED (). When the client
aborts reading a response, it indicates that this response is no longer of
interest. Implementations SHOULD cancel requests by abruptly terminating any
directions of a stream that are still open.When the server rejects a request without performing any application processing,
it SHOULD abort its response stream with the error code HTTP_REQUEST_REJECTED.
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. The
client can treat requests rejected by the server as though they had never been
sent at all, thereby allowing them to be retried later on a new connection.
Servers MUST NOT use the HTTP_REQUEST_REJECTED error code for requests which
were partially or fully processed. When a server abandons a response after
partial processing, it SHOULD abort its response stream with the error code
HTTP_REQUEST_CANCELLED.When a client resets a request with the error code HTTP_REQUEST_CANCELLED, a
server MAY abruptly terminate the response using the error code
HTTP_REQUEST_REJECTED if no processing was performed. Clients MUST NOT use the
HTTP_REQUEST_REJECTED error code, except when a server has requested closure of
the request stream with this error code.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).A malformed request or response is one that is an otherwise valid sequence of
frames but is invalid due to the presence of extraneous frames, prohibited
header fields, the absence of mandatory header fields, or the inclusion of
uppercase header field names.A request or response that includes a payload body can include a
content-length header field. A request or response is also malformed if the
value of a content-length header field does not equal the sum of the DATA frame
payload lengths that form the body. A response that is defined to have no
payload, as described in Section 3.3.2 of can have a non-zero
content-length header field, even though no content is included in DATA frames.Intermediaries that process HTTP requests or responses (i.e., any intermediary
not acting as a tunnel) MUST NOT forward a malformed request or response.
Malformed requests or responses that are detected MUST be treated as a stream
error () of type HTTP_GENERAL_PROTOCOL_ERROR.For malformed requests, a server MAY send an HTTP response prior to closing or
resetting the stream. Clients MUST NOT accept a malformed response. Note that
these requirements are intended to protect against several types of common
attacks against HTTP; they are deliberately strict because being permissive can
expose implementations to these vulnerabilities.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/3 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 (see
). The request stream MUST NOT be 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 stream correspond to data sent or received 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.Once the CONNECT method has completed, only DATA frames are permitted
to be sent on the stream. Extension frames MAY be used if specifically
permitted by the definition of the extension. Receipt of any other frame type
MUST be treated as a connection error of type HTTP_FRAME_UNEXPECTED.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 the 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 close a stream for sending while they still expect to receive
data from the target of the CONNECT.A TCP connection error is signaled by abruptly terminating the 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, if a proxy detects an error with the
stream or the QUIC connection, it MUST close the TCP connection. If the
underlying TCP implementation permits it, the proxy SHOULD send a TCP segment
with the RST bit set.HTTP/3 does not support the HTTP Upgrade mechanism (, Section 6.7) or
101 (Switching Protocols) informational status code (, Section 6.2.2).Server push is an interaction mode introduced in HTTP/2 which permits
a server to push a request-response exchange to a client in anticipation of the
client making the indicated request. This trades off network usage against a
potential latency gain. HTTP/3 server push is similar to what is described in
HTTP/2 , but uses different mechanisms.Each server push is identified by a unique Push ID. This Push ID is used in a
single PUSH_PROMISE frame (see ) which carries the request
headers, possibly included in one or more DUPLICATE_PUSH frames (see
), then included with the push stream which ultimately
fulfills those promises.Server push is only enabled on a connection when a client sends a MAX_PUSH_ID
frame (see ). A server cannot use server push until it
receives a MAX_PUSH_ID frame. A client sends additional MAX_PUSH_ID frames to
control the number of pushes that a server can promise. A server SHOULD use Push
IDs sequentially, starting at 0. 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_ID_ERROR.The header of the request message is carried by a PUSH_PROMISE frame (see
) on the request stream which generated the push. This
allows the server push to be associated with a client request. Promised
requests MUST conform to the requirements in Section 8.2 of .The same server push can be associated with additional client requests using a
DUPLICATE_PUSH frame (see ).Ordering of a PUSH_PROMISE or DUPLICATE_PUSH in relation to certain parts of the
response is important. The server SHOULD send PUSH_PROMISE or DUPLICATE_PUSH
frames prior to sending HEADERS or DATA frames that reference the promised
responses. This reduces the chance that a client requests a resource that will
be pushed by the server.When a server later fulfills a promise, the server push response is conveyed on
a push stream (see ). The push stream identifies the Push ID of
the promise that it fulfills, then contains a response to the promised request
using the same format described for responses in .Due to reordering, DUPLICATE_PUSH frames or push stream data can arrive before
the corresponding PUSH_PROMISE frame. When a client receives a DUPLICATE_PUSH
frame for an as-yet-unknown Push ID, the request headers of the push are not
immediately available. The client can either delay generating new requests for
content referenced following the DUPLICATE_PUSH frame until the request headers
become available, or can initiate requests for discovered resources and cancel
the requests if the requested resource is already being pushed. When a client
receives a new push stream with an as-yet-unknown Push ID, both the associated
client request and the pushed request headers are unknown. The client can
buffer the stream data in expectation of the matching PUSH_PROMISE. The client
can use stream flow control (see section 4.1 of ) to limit the
amount of data a server may commit to the pushed stream.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 or opens after sending the
CANCEL_PUSH frame, the client can abort reading the stream with an error code of
HTTP_REQUEST_CANCELLED. This asks the server not to transfer additional data and
indicates that it will be discarded upon receipt.Once established, an HTTP/3 connection can be used for many requests and
responses over time until the connection is closed. Connection closure can
happen in any of several different ways.Each QUIC endpoint declares an idle timeout during the handshake. If the
connection remains idle (no packets received) for longer than this duration, the
peer will assume that the connection has been closed. HTTP/3 implementations
will need to open a new connection for new requests if the existing connection
has been idle for longer than the server’s advertised idle timeout, and SHOULD
do so if approaching the idle timeout.HTTP clients are expected to request that the transport keep connections open
while there are responses outstanding for requests or server pushes, as
described in Section 19.2 of . If the client is not expecting
a response from the server, allowing an idle connection to time out is preferred
over expending effort maintaining a connection that might not be needed. A
gateway MAY maintain connections in anticipation of need rather than incur the
latency cost of connection establishment to servers. Servers SHOULD NOT actively
keep connections open.Even when a connection is not idle, either endpoint can decide to stop using the
connection and let the connection close gracefully. Since clients drive request
generation, clients perform a connection shutdown by not sending additional
requests on the connection; responses and pushed responses associated to
previous requests will continue to completion. Servers perform the same
function by communicating with clients.Servers initiate the shutdown of a connection by sending a GOAWAY frame
(). The GOAWAY frame indicates that client-initiated requests
on lower stream IDs were or might be processed in this connection, while
requests on the indicated stream ID and greater were rejected. This enables
client and server to agree on which requests were accepted prior to the
connection shutdown. This identifier MAY be zero if no requests were processed.
Servers SHOULD NOT permit additional QUIC streams after sending a GOAWAY frame.Clients MUST NOT send new requests on the connection after receiving GOAWAY;
a new connection MAY be established to send additional requests.Some requests might already be in transit. If the client has already sent
requests on streams with a Stream ID greater than or equal to that indicated in
the GOAWAY frame, those requests will not be processed and MAY be retried by the
client on a different connection. The client MAY cancel these requests. It is
RECOMMENDED that the server explicitly reject such requests (see
) in order to clean up transport state for the affected
streams.Requests on Stream IDs less than the Stream ID in the GOAWAY frame might have
been processed; their status cannot be known until a response is received, the
stream is reset individually, or the connection terminates. Servers MAY reject
individual requests on streams below the indicated ID if these requests were not
processed.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 request 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.A client that is unable to retry requests loses all requests that are in flight
when the server closes the connection. A server MAY send multiple GOAWAY frames
indicating different stream IDs, but MUST NOT increase the value they send in
the last Stream ID, since clients might already have retried unprocessed
requests on another 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 maximum value allowed by QUIC’s MAX_STREAMS and SHOULD NOT increase
the MAX_STREAMS limit 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 accepted requests have been processed, the server can permit the
connection to become idle, or MAY initiate an immediate closure of the
connection. An endpoint that completes a graceful shutdown SHOULD use the
HTTP_NO_ERROR code when closing the connection.If a client has consumed all available bidirectional stream IDs with requests,
the server need not send a GOAWAY frame, since the client is unable to make
further requests.An HTTP/3 implementation can immediately close the QUIC connection at any time.
This results in sending a QUIC CONNECTION_CLOSE frame to the peer; the error
code in this frame indicates to the peer why the connection is being closed.
See for error codes which can be used when closing a connection.Before closing the connection, a GOAWAY MAY be sent to allow the client to retry
some requests. Including the GOAWAY frame in the same packet as the QUIC
CONNECTION_CLOSE frame improves the chances of the frame being received by
clients.For various reasons, the QUIC transport could indicate to the application layer
that the connection has terminated. This might be due to an explicit closure
by the peer, a transport-level error, or a change in network topology which
interrupts connectivity.If a connection terminates without a GOAWAY frame, clients MUST assume that any
request which was sent, whether in whole or in part, might have been processed.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. The transport layer buffers and orders received QUIC
STREAM frames, exposing the data contained within as a reliable byte stream to
the application. Although QUIC permits out-of-order delivery within a stream,
HTTP/3 does not make use of this feature.QUIC streams can be either unidirectional, carrying data only from initiator to
receiver, or bidirectional. Streams can be initiated by either the client or
the server. For more detail on QUIC streams, see Section 2 of
.When HTTP headers and data are sent over QUIC, the QUIC layer handles most of
the stream management. 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 or connection context.All client-initiated bidirectional streams are used for HTTP requests and
responses. 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 0, with subsequent requests on stream 4, 8, and so on. In order
to permit these streams to open, an HTTP/3 server SHOULD configure non-zero
minimum values for the number of permitted streams and the initial stream flow
control window. It is RECOMMENDED that at least 100 requests be permitted at a
time, so as to not unnecessarily limit parallelism.HTTP/3 does not use server-initiated bidirectional streams, though an extension
could define a use for these streams. Clients MUST treat receipt of a
server-initiated bidirectional stream as a connection error of type
HTTP_STREAM_CREATION_ERROR unless such an extension has been negotiated.Unidirectional streams, in either direction, are used for a range of purposes.
The purpose is indicated by a stream type, which is sent as a variable-length
integer at the start of the stream. The format and structure of data that
follows this integer is determined by the stream type.Some stream types are reserved (). Two stream types are
defined in this document: control streams () and push streams
(). Other stream types can be defined by extensions to HTTP/3;
see for more details.The performance of HTTP/3 connections in the early phase of their lifetime is
sensitive to the creation and exchange of data on unidirectional streams.
Endpoints that excessively restrict the number of streams or the flow control
window of these streams will increase the chance that the remote peer reaches
the limit early and becomes blocked. In particular, implementations should
consider that remote peers may wish to exercise reserved stream behavior
() with some of the unidirectional streams they are permitted
to use. To avoid blocking, the transport parameters sent by both clients and
servers MUST allow the peer to create at least one unidirectional stream for the
HTTP control stream plus the number of unidirectional streams required by
mandatory extensions (three being the minimum number required for the base
HTTP/3 protocol and QPACK), and SHOULD provide at least 1,024 bytes of flow
control credit to each stream.Note that an endpoint is not required to grant additional credits to create more
unidirectional streams if its peer consumes all the initial credits before
creating the critical unidirectional streams. Endpoints SHOULD create the HTTP
control stream as well as the unidirectional streams required by mandatory
extensions (such as the QPACK encoder and decoder streams) first, and then
create additional streams as allowed by their peer.If the stream header indicates a stream type which is not supported by the
recipient, the remainder of the stream cannot be consumed as the semantics are
unknown. Recipients of unknown stream types MAY abort reading of the stream with
an error code of HTTP_STREAM_CREATION_ERROR, but MUST NOT consider such streams
to be a connection error of any kind.Implementations MAY send stream types before knowing whether the peer supports
them. However, stream types which could modify the state or semantics of
existing protocol components, including QPACK or other extensions, MUST NOT be
sent until the peer is known to support them.A sender can close or reset a unidirectional stream unless otherwise specified.
A receiver MUST tolerate unidirectional streams being closed or reset prior to
the reception of the unidirectional stream header.A control stream is indicated by a stream type of 0x00. Data on this stream
consists of HTTP/3 frames, as defined in .Each side MUST initiate a single control stream at the beginning of the
connection and send its SETTINGS frame as the first frame on this stream. If
the first frame of the control stream is any other frame type, this MUST be
treated as a connection error of type HTTP_MISSING_SETTINGS. Only one control
stream per peer is permitted; receipt of a second stream which claims to be a
control stream MUST be treated as a connection error of type
HTTP_STREAM_CREATION_ERROR. The sender MUST NOT close the control stream, and
the receiver MUST NOT request that the sender close the control stream. If
either control stream is closed at any point, this MUST be treated as a
connection error of type HTTP_CLOSED_CRITICAL_STREAM.A pair of unidirectional streams is used rather than a single bidirectional
stream. This allows either peer to send data as soon as it is 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.Server push is an optional feature introduced in HTTP/2 that allows a server to
initiate a response before a request has been made. See for
more details.A push stream is indicated by a stream type of 0x01, followed by the Push ID
of the promise that it fulfills, encoded as a variable-length integer. The
remaining data on this stream consists of HTTP/3 frames, as defined in
, and fulfills a promised server push by zero or more non-final HTTP
responses followed by a single final HTTP response, as defined in
. Server push and Push IDs are described in
.Only servers can push; if a server receives a client-initiated push stream, this
MUST be treated as a connection error of type HTTP_STREAM_CREATION_ERROR.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_ID_ERROR.Stream types of the format 0x1f * N + 0x21 for integer values of N are
reserved to exercise the requirement that unknown types be ignored. These
streams have no semantics, and can be sent when application-layer padding is
desired. They MAY also be sent on connections where no data is currently being
transferred. Endpoints MUST NOT consider these streams to have any meaning upon
receipt.The payload and length of the stream are selected in any manner the
implementation chooses.HTTP frames are carried on QUIC streams, as described in .
HTTP/3 defines three stream types: control stream, request stream, and push
stream. This section describes HTTP/3 frame formats and the streams types on
which they are permitted; see for an overview. A
comparison between HTTP/2 and HTTP/3 frames is provided in .FrameControl StreamRequest StreamPush StreamSectionDATANoYesYesHEADERSNoYesYesCANCEL_PUSHYesNoNoSETTINGSYes (1)NoNoPUSH_PROMISENoYesNoGOAWAYYesNoNoMAX_PUSH_IDYesNoNoDUPLICATE_PUSHNoYesNoReservedYesYesYes{{frame-reserved}Certain frames can only occur as the first frame of a particular stream type;
these are indicated in with a (1). Specific guidance
is provided in the relevant section.Note that, unlike QUIC frames, HTTP/3 frames can span multiple packets.All frames have the following format:A frame includes the following fields:
A variable-length integer that identifies the frame type.
A variable-length integer that describes the length of the Frame Payload.
A payload, the semantics of which are determined by the Type field.Each frame’s payload MUST contain exactly the fields identified in its
description. A frame payload that contains additional bytes after the
identified fields or a frame payload that terminates before the end of the
identified fields MUST be treated as a connection error of type
HTTP_FRAME_ERROR.When a stream terminates cleanly, if the last frame on the stream was truncated,
this MUST be treated as a connection error () of type
HTTP_FRAME_ERROR. Streams which terminate abruptly may be reset at any point in
a frame.DATA frames (type=0x0) convey arbitrary, variable-length sequences of bytes
associated with an HTTP request or response payload.DATA frames MUST be associated with an HTTP request or response. If a DATA
frame is received on a control stream, the recipient MUST respond with a
connection error () of type HTTP_FRAME_UNEXPECTED.The HEADERS frame (type=0x1) is used to carry a header block, compressed using
QPACK. See for more details.HEADERS frames can only be sent on request / push streams. If a HEADERS frame
is received on a control stream, the recipient MUST respond with a connection
error () of type HTTP_FRAME_UNEXPECTED.The CANCEL_PUSH frame (type=0x3) is used to request cancellation of a server
push prior to the push stream being received. The CANCEL_PUSH frame identifies
a server push by Push ID (see ), encoded as 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 push
stream. If the push stream has been opened by the server, the server SHOULD
abruptly terminate that stream.A server can send the CANCEL_PUSH frame to indicate that it will not be
fulfilling a promise 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. The server SHOULD abruptly terminate the push stream instead.A CANCEL_PUSH frame is sent on the control stream. Receiving a CANCEL_PUSH
frame on a stream other than the control stream MUST be treated as a connection
error of type HTTP_FRAME_UNEXPECTED.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.The SETTINGS frame (type=0x4) conveys configuration parameters that affect how
endpoints communicate, such as preferences and constraints on peer behavior.
Individually, a SETTINGS parameter can also be referred to as a “setting”; the
identifier and value of each setting parameter can be referred to as a “setting
identifier” and a “setting value”.SETTINGS frames always apply to a connection, never a single stream. A SETTINGS
frame MUST be sent as the first frame of each control stream (see
) by each peer, and MUST NOT be sent subsequently. If
an endpoint receives a second SETTINGS frame on the control stream, the endpoint
MUST respond with a connection error of type HTTP_FRAME_UNEXPECTED.SETTINGS frames MUST NOT be sent on any stream other than the control stream.
If an endpoint receives a SETTINGS frame on a different stream, the endpoint
MUST respond with a connection error of type HTTP_FRAME_UNEXPECTED.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 - each peer uses SETTINGS to advertise a
set of supported values. The definition of the setting would describe how each
peer combines the two sets to conclude which choice will be used. SETTINGS does
not provide a mechanism to identify when the choice takes effect.Different values for the same parameter can be advertised by each peer. For
example, a client might be willing to consume a very large response header,
while servers are more cautious about request size.The same setting identifier MUST NOT occur more than once in the SETTINGS frame.
A receiver MAY treat the presence of duplicate setting identifiers as a
connection error of type HTTP_SETTINGS_ERROR.The payload of a SETTINGS frame consists of zero or more parameters. Each
parameter consists of a setting identifier and a value, both encoded as QUIC
variable-length integers.An implementation MUST ignore the contents for any SETTINGS identifier it does
not understand.The following settings are defined in HTTP/3:
The default value is unlimited. See for usage.Setting identifiers of the format 0x1f * N + 0x21 for integer values of N are
reserved to exercise the requirement that unknown identifiers be ignored. Such
settings have no defined meaning. Endpoints SHOULD include at least one such
setting in their SETTINGS frame. Endpoints MUST NOT consider such settings to
have any meaning upon receipt.Because the setting has no defined meaning, the value of the setting can be any
value the implementation selects.Additional settings can be defined by extensions to HTTP/3; see
for more details.An HTTP implementation MUST NOT send frames or requests which would be invalid
based on its current understanding of the peer’s settings.All settings begin at an initial value. Each endpoint SHOULD use these initial
values to send messages before the peer’s SETTINGS frame has arrived, as packets
carrying the settings can be lost or delayed. When the SETTINGS frame arrives,
any settings are changed to their new values.This removes the need to wait for the SETTINGS frame before sending messages.
Endpoints MUST NOT require any data to be received from the peer prior to
sending the SETTINGS frame; settings MUST be sent as soon as the transport is
ready to send data.For servers, the initial value of each client setting is the default value.For clients using a 1-RTT QUIC connection, the initial value of each server
setting is the default value. 1-RTT keys will always become available prior to
SETTINGS arriving, even if the server sends SETTINGS immediately. Clients SHOULD
NOT wait indefinitely for SETTINGS to arrive before sending requests, but SHOULD
process received datagrams in order to increase the likelihood of processing
SETTINGS before sending the first request.When a 0-RTT QUIC connection is being used, the initial value of each server
setting is the value used in the previous session. Clients SHOULD store the
settings the server provided in the connection where resumption information was
provided, but MAY opt not to store settings in certain cases (e.g., if the
session ticket is received before the SETTINGS frame). A client MUST comply with
stored settings – or default values, if no values are stored – when attempting
0-RTT. Once a server has provided new settings, clients MUST comply with those
values.A server can remember the settings that it advertised, or store an
integrity-protected copy of the values in the ticket and recover the information
when accepting 0-RTT data. A server uses the HTTP/3 settings values in
determining whether to accept 0-RTT data. If the server cannot determine that
the settings remembered by a client are compatible with its current settings, it
MUST NOT accept 0-RTT data. Remembered settings are compatible if a client
complying with those settings would not violate the server’s current settings.A server MAY accept 0-RTT and subsequently provide different settings in its
SETTINGS frame. If 0-RTT data is accepted by the server, its SETTINGS frame MUST
NOT reduce any limits or alter any values that might be violated by the client
with its 0-RTT data. The server MUST include all settings which differ from
their default values. If a server accepts 0-RTT, but then sends a SETTINGS
frame which reduces a setting the client understands or omits a value that was
previously specified to have a non-default value, this MUST be treated as a
connection error of type HTTP_SETTINGS_ERROR.The PUSH_PROMISE frame (type=0x5) is used to carry a promised request header
set from server to client on a request stream, as in HTTP/2.The payload consists of:
A variable-length integer that identifies the server push operation. A Push
ID is used in push stream headers (), CANCEL_PUSH frames
(), and DUPLICATE_PUSH frames ().
QPACK-compressed request header fields for the promised response. See
for more details.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 frame that contains a larger Push ID than the client has advertised
as a connection error of HTTP_ID_ERROR.A server MUST NOT use the same Push ID in multiple PUSH_PROMISE frames. A client
MUST treat receipt of a Push ID which has already been promised as a connection
error of type HTTP_ID_ERROR.If a PUSH_PROMISE frame is received on the control stream, the client MUST
respond with a connection error () of type HTTP_FRAME_UNEXPECTED.A client MUST NOT send a PUSH_PROMISE frame. A server MUST treat the receipt
of a PUSH_PROMISE frame as a connection error of type HTTP_FRAME_UNEXPECTED.See for a description of the overall server push mechanism.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 is always sent on the control stream. It carries a QUIC Stream
ID for a client-initiated bidirectional stream encoded as a variable-length
integer. A client MUST treat receipt of a GOAWAY frame containing a Stream ID
of any other type as a connection error of type HTTP_ID_ERROR.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 on any
stream as a connection error () of type HTTP_FRAME_UNEXPECTED.The GOAWAY frame applies to the connection, not a specific stream. A client
MUST treat a GOAWAY frame on a stream other than the control stream as a
connection error () of type HTTP_FRAME_UNEXPECTED.See for more information on the use of the GOAWAY frame.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 maintained by the QUIC transport.The MAX_PUSH_ID frame is always sent on the control stream. Receipt of a
MAX_PUSH_ID frame on any other stream MUST be treated as a connection error of
type HTTP_FRAME_UNEXPECTED.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_FRAME_UNEXPECTED.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 MAX_PUSH_ID frames as the server fulfills or cancels server pushes.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_ID_ERROR.The DUPLICATE_PUSH frame (type=0xE) is used by servers to indicate that an
existing pushed resource is related to multiple client requests.The DUPLICATE_PUSH frame is always sent on a request stream. Receipt of a
DUPLICATE_PUSH frame on any other stream MUST be treated as a connection error
of type HTTP_FRAME_UNEXPECTED.A client MUST NOT send a DUPLICATE_PUSH frame. A server MUST treat the receipt
of a DUPLICATE_PUSH frame as a connection error of type HTTP_FRAME_UNEXPECTED.The DUPLICATE_PUSH frame carries a single variable-length integer that
identifies the Push ID of a resource that the server has previously promised
(see ), though that promise might not be received before
this frame. 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 DUPLICATE_PUSH that contains a larger Push ID than the client has
advertised as a connection error of type HTTP_ID_ERROR.This frame allows the server to use the same server push in response to multiple
concurrent requests. Referencing the same server push ensures that a promise
can be made in relation to every response in which server push might be needed
without duplicating request headers or pushed responses.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 DUPLICATE_PUSH that
uses a Push ID that they have since consumed and discarded are forced to ignore
the DUPLICATE_PUSH.Frame types of the format 0x1f * N + 0x21 for integer values of N are reserved
to exercise the requirement that unknown types be ignored ().
These frames have no semantics, and can be sent on any open stream when
application-layer padding is desired. They MAY also be sent on connections where
no data is currently being transferred. Endpoints MUST NOT consider these frames
to have any meaning upon receipt.The payload and length of the frames are selected in any manner the
implementation chooses.Frame types which were used in HTTP/2 where there is no corresponding HTTP/3
frame have also been reserved (). These frame types MUST NOT be
sent, and receipt MAY be treated as an error of type HTTP_UNEXPECTED_FRAME.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
. An endpoint MAY choose to treat a stream error as a
connection error.Because new error codes can be defined without negotiation (see ),
receipt of an unknown error code or use of an error code in an unexpected
context MUST NOT be treated as an error. However, closing a stream can
constitute an error regardless of the error code (see ).This section describes HTTP/3-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 when abruptly terminating streams,
aborting reading of streams, or immediately closing connections.
No error. This is used when the connection or stream needs to be closed, but
there is no error to signal.
Peer violated protocol requirements in a way which doesn’t match a more
specific error code, or endpoint declines to use the more specific error code.
An internal error has occurred in the HTTP stack.
The endpoint detected that its peer created a stream that it will not accept.
A stream required by the connection was closed or reset.
A frame was received which was not permitted in the current state or on the
current stream.
A frame that fails to satisfy layout requirements or with an invalid size
was received.
The endpoint detected that its peer is exhibiting a behavior that might be
generating excessive load.
A Stream ID or Push ID was used incorrectly, such as exceeding a limit,
reducing a limit, or being reused.
An endpoint detected an error in the payload of a SETTINGS frame.
No SETTINGS frame was received at the beginning of the control stream.
A server rejected a request without performing any application processing.
The request or its response (including pushed response) is cancelled.
The client’s stream terminated without containing a fully-formed request.
The remainder of the client’s request is not needed to produce a response.
For use in STOP_SENDING only.
The connection established in response to a CONNECT request was reset or
abnormally closed.
The requested operation cannot be served over HTTP/3. The peer should
retry over HTTP/1.1.HTTP/3 permits extension of the protocol. Within the limitations described in
this section, protocol extensions can be used to provide additional services or
alter any aspect of the protocol. Extensions are effective only within the
scope of a single HTTP/3 connection.This applies to the protocol elements defined in this document. This does not
affect the existing options for extending HTTP, such as defining new methods,
status codes, or header fields.Extensions are permitted to use new frame types (), new settings
(), new error codes (), or new unidirectional
stream types (). Registries are established for
managing these extension points: frame types (), settings
(), error codes (), and stream types
().Implementations MUST ignore unknown or unsupported values in all extensible
protocol elements. Implementations MUST discard frames and unidirectional
streams that have unknown or unsupported types. This means that any of these
extension points can be safely used by extensions without prior arrangement or
negotiation. However, where a known frame type is required to be in a specific
location, such as the SETTINGS frame as the first frame of the control stream
(see ), an unknown frame type does not satisfy that
requirement and SHOULD be treated as an error.Extensions that could change the semantics of existing protocol components MUST
be negotiated before being used. For example, an extension that changes the
layout of the HEADERS frame cannot be used until the peer has given a positive
signal that this is acceptable. In this case, it could also be necessary to
coordinate when the revised layout comes into effect.This document doesn’t mandate a specific method for negotiating the use of an
extension but notes that a setting () could be used for
that purpose. If both peers set a value that indicates willingness to use the
extension, then the extension can be used. If a setting is used for extension
negotiation, the default value MUST be defined in such a fashion that the
extension is disabled if the setting is omitted.The security considerations of HTTP/3 should be comparable to those of HTTP/2
with TLS; the considerations from Section 10 of apply in addition to
those listed here.When HTTP Alternative Services is used for discovery for HTTP/3 endpoints, the
security considerations of also apply.Where HTTP/2 employs PADDING frames and Padding fields in other frames to make a
connection more resistant to traffic analysis, HTTP/3 can either rely on
transport-layer padding or employ the reserved frame and stream types discussed
in and . These methods of padding produce
different results in terms of the granularity of padding, the effect of packet
loss and recovery, and how an implementation might control padding.Several protocol elements contain nested length elements, typically in the form
of frames with an explicit length containing variable-length integers. This
could pose a security risk to an incautious implementer. An implementation MUST
ensure that the length of a frame exactly matches the length of the fields it
contains.The use of 0-RTT with HTTP/3 creates an exposure to replay attack. The
anti-replay mitigations in MUST be applied when using
HTTP/3 with 0-RTT.Certain HTTP implementations use the client address for logging or
access-control purposes. Since a QUIC client’s address might change during a
connection (and future versions might support simultaneous use of multiple
addresses), such implementations will need to either actively retrieve the
client’s current address or addresses when they are relevant or explicitly
accept that the original address might change.This document creates a new registration for the identification of
HTTP/3 in the “Application Layer Protocol Negotiation (ALPN)
Protocol IDs” registry established in .The “h3” string identifies HTTP/3:
HTTP/3
0x68 0x33 (“h3”)
This documentThis 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/3 frame type codes. The “HTTP/3
Frame Type” registry governs a 62-bit space. This space is split into three
spaces that are governed by different policies. Values between 0x00 and 0x3f
(in hexadecimal) are assigned via the Standards Action or IESG Review policies
. Values from 0x40 to 0x3fff operate on the Specification
Required policy . All other values are assigned to Private Use
.While this registry is separate from the “HTTP/2 Frame Type” registry defined in
, it is preferable that the assignments parallel each other where the
code spaces overlap. 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 62-bit code assigned to the frame type.
A reference to a specification that includes a description of the frame layout
and its semantics, including any parts of the frame that are conditionally
present.The entries in the following table are registered by this document.Frame TypeCodeSpecificationDATA0x0HEADERS0x1Reserved0x2N/ACANCEL_PUSH0x3SETTINGS0x4PUSH_PROMISE0x5Reserved0x6N/AGOAWAY0x7Reserved0x8N/AReserved0x9N/AMAX_PUSH_ID0xDDUPLICATE_PUSH0xEAdditionally, each code of the format 0x1f * N + 0x21 for integer values of N
(that is, 0x21, 0x40, …, through 0x3FFFFFFFFFFFFFFE) MUST NOT be
assigned by IANA.This document establishes a registry for HTTP/3 settings. The “HTTP/3 Settings”
registry governs a 62-bit space. This space is split into three spaces that are
governed by different policies. Values between 0x00 and 0x3f (in
hexadecimal) are assigned via the Standards Action or IESG Review policies
. Values from 0x40 to 0x3fff operate on the Specification
Required policy . All other values are assigned to Private 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 62-bit code assigned to the setting.
An optional reference to a specification that describes the use of the
setting.
The value of the setting unless otherwise indicated. SHOULD be the most
restrictive possible value.The entries in the following table are registered by this document.Setting NameCodeSpecificationDefaultReserved0x2N/AN/AReserved0x3N/AN/AReserved0x4N/AN/AReserved0x5N/AN/AMAX_HEADER_LIST_SIZE0x6UnlimitedAdditionally, each code of the format 0x1f * N + 0x21 for integer values of N
(that is, 0x21, 0x40, …, through 0x3FFFFFFFFFFFFFFE) MUST NOT be
assigned by IANA.This document establishes a registry for HTTP/3 error codes. The “HTTP/3 Error
Code” registry manages a 62-bit space. The “HTTP/3 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 62-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.NameCodeDescriptionSpecificationHTTP_NO_ERROR0x0100No errorHTTP_GENERAL_PROTOCOL_ERROR0x0101General protocol errorHTTP_INTERNAL_ERROR0x0102Internal errorHTTP_STREAM_CREATION_ERROR0x0103Stream creation errorHTTP_CLOSED_CRITICAL_STREAM0x0104Critical stream was closedHTTP_FRAME_UNEXPECTED0x0105Frame not permitted in the current stateHTTP_FRAME_ERROR0x0106Frame violated layout or size rulesHTTP_EXCESSIVE_LOAD0x0107Peer generating excessive loadHTTP_ID_ERROR0x0108An identifier was used incorrectlyHTTP_SETTINGS_ERROR0x0109SETTINGS frame contained invalid valuesHTTP_MISSING_SETTINGS0x010ANo SETTINGS frame receivedHTTP_REQUEST_REJECTED0x010BRequest not processedHTTP_REQUEST_CANCELLED0x010CData no longer neededHTTP_REQUEST_INCOMPLETE0x010DStream terminated earlyHTTP_EARLY_RESPONSE0x010ERemainder of request not neededHTTP_CONNECT_ERROR0x010FTCP reset or error on CONNECT requestHTTP_VERSION_FALLBACK0x0110Retry over HTTP/1.1This document establishes a registry for HTTP/3 unidirectional stream types. The
“HTTP/3 Stream Type” registry governs a 62-bit space. This space is split into
three spaces that are governed by different policies. Values between 0x00 and
0x3f (in hexadecimal) are assigned via the Standards Action or IESG Review
policies . Values from 0x40 to 0x3fff operate on the
Specification Required policy . All other values are assigned to
Private Use .New entries in this registry require the following information:
A name or label for the stream type.
The 62-bit code assigned to the stream type.
A reference to a specification that includes a description of the stream type,
including the layout semantics of its payload.
Which endpoint on a connection may initiate a stream of this type. Values are
“Client”, “Server”, or “Both”.The entries in the following table are registered by this document.Stream TypeCodeSpecificationSenderControl Stream0x00BothPush Stream0x01ServerAdditionally, each code of the format 0x1f * N + 0x21 for integer values of N
(that is, 0x21, 0x40, …, through 0x3FFFFFFFFFFFFFFE) MUST NOT be
assigned by IANA.QUIC: A UDP-Based Multiplexed and Secure TransportFastlyMozillaQPACK: Header Compression for HTTP over QUICGoogle, IncAkamai TechnologiesFacebookHypertext Transfer Protocol Version 2 (HTTP/2)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.Key words for use in RFCs to Indicate Requirement LevelsIn 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.Ambiguity of Uppercase vs Lowercase in RFC 2119 Key WordsRFC 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.Augmented BNF for Syntax Specifications: ABNFInternet 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]Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and RoutingThe 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.HTTP Alternative ServicesThis 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.Transport Layer Security (TLS) Extensions: Extension DefinitionsThis 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]Opportunistic Security for HTTP/2This document describes how "http" URIs can be accessed using Transport Layer Security (TLS) and HTTP/2 to mitigate pervasive monitoring attacks. This mechanism not a replacement for "https" URIs; it is vulnerable to active attacks.Hypertext Transfer Protocol (HTTP/1.1): Semantics and ContentThe 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.HTTP State Management MechanismThis document defines the HTTP Cookie and Set-Cookie header fields. These header fields can be used by HTTP servers to store state (called cookies) at HTTP user agents, letting the servers maintain a stateful session over the mostly stateless HTTP protocol. Although cookies have many historical infelicities that degrade their security and privacy, the Cookie and Set-Cookie header fields are widely used on the Internet. This document obsoletes RFC 2965. [STANDARDS-TRACK]Transmission Control ProtocolUsing Early Data in HTTPUsing TLS early data creates an exposure to the possibility of a replay attack. This document defines mechanisms that allow clients to communicate with servers about HTTP requests that are sent in early data. Techniques are described that use these mechanisms to mitigate the risk of replay.HTTP Alternative ServicesThis 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.Guidelines for Writing an IANA Considerations Section in RFCsMany 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.TCP Fast OpenThis document describes an experimental TCP mechanism called TCP Fast Open (TFO). TFO allows data to be carried in the SYN and SYN-ACK packets and consumed by the receiving end during the initial connection handshake, and saves up to one full round-trip time (RTT) compared to the standard TCP, which requires a three-way handshake (3WHS) to complete before data can be exchanged. However, TFO deviates from the standard TCP semantics, since the data in the SYN could be replayed to an application in some rare circumstances. Applications should not use TFO unless they can tolerate this issue, as detailed in the Applicability section.HPACK: Header Compression for HTTP/2This specification defines HPACK, a compression format for efficiently representing HTTP header fields, to be used in HTTP/2.Additional HTTP Status CodesThis document specifies additional HyperText Transfer Protocol (HTTP) status codes for a variety of common situations. [STANDARDS-TRACK]Transport Layer Security (TLS) Application-Layer Protocol Negotiation ExtensionThis 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.HTTP/3 is strongly informed by HTTP/2, and bears many similarities. This
section describes the approach taken to design HTTP/3, points out important
differences from HTTP/2, and describes how to map HTTP/2 extensions into HTTP/3.HTTP/3 begins from the premise that similarity to HTTP/2 is preferable, but not
a hard requirement. HTTP/3 departs from HTTP/2 where QUIC differs from TCP,
either to take advantage of QUIC features (like streams) or to accommodate
important shortcomings (such as a lack of total ordering). These differences
make HTTP/3 similar to HTTP/2 in key aspects, such as the relationship of
requests and responses to streams. However, the details of the HTTP/3 design are
substantially different than HTTP/2.These departures are noted in this section.HTTP/3 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 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. This permits the removal of the Flags field from the generic
frame layout.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/3. 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/3 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/3 will
break them.Some examples of feature adaptations are described below, as well as general
guidance to extension frame implementors converting an HTTP/2 extension to
HTTP/3.HTTP/2 specifies priority assignments in PRIORITY frames and (optionally) in
HEADERS frames. HTTP/3 does not provide a means of signaling priority.Note that while there is no explicit signaling for priority, this does not mean
that prioritization is not important for achieving good performance.HPACK was designed with the assumption of in-order delivery. 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.Because this total ordering is not provided by QUIC, HTTP/3 uses a modified
version of HPACK, called QPACK. QPACK uses a single unidirectional stream to
make all modifications to the dynamic table, ensuring a total order of updates.
All frames which contain encoded headers merely reference the table state at a
given time without modifying it. provides additional details.Frame type definitions in HTTP/3 often use the QUIC variable-length integer
encoding. In particular, Stream IDs use this encoding, which allows for a
larger range of possible values than the encoding used in HTTP/2. Some frames
in HTTP/3 use an identifier rather than a Stream ID (e.g., Push
IDs). Redefinition of the encoding of extension frame types might be necessary
if the encoding includes a Stream ID.Because the Flags field is not present in generic HTTP/3 frames, those frames
which depend on the presence of flags need to allocate space for flags as part
of their frame payload.Other than this issue, frame type HTTP/2 extensions are typically portable to
QUIC simply by replacing Stream 0 in HTTP/2 with a control stream in HTTP/3.
HTTP/3 extensions will not assume ordering, but would not be harmed by ordering,
and would be portable to HTTP/2 in the same manner.
Padding is not defined in HTTP/3 frames. See .
The PRIORITY region of HEADERS is not defined in HTTP/3 frames. Padding is not
defined in HTTP/3 frames. See .
As described in , HTTP/3 does not provide a means of
signaling priority.
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.Frame types defined by extensions to HTTP/2 need to be separately registered for
HTTP/3 if still applicable. The IDs of frames defined in have been
reserved for simplicity. Note that the frame type space in HTTP/3 is
substantially larger (62 bits versus 8 bits), so many HTTP/3 frame types have no
equivalent HTTP/2 code points. See .An important difference from HTTP/2 is that settings are sent once, as the first
frame of the control stream, 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/3. The HTTP-level options that
are retained in HTTP/3 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/3. Specifying it in the SETTINGS frame
is an error.
See .In HTTP/3, setting values are variable-length integers (6, 14, 30, or 62 bits
long) rather than fixed-length 32-bit fields as in HTTP/2. This will often
produce a shorter encoding, but can produce a longer encoding for settings which
use the full 32-bit space. Settings ported from HTTP/2 might choose to redefine
the format of their settings to avoid using the 62-bit encoding.Settings need to be defined separately for HTTP/2 and HTTP/3. The IDs of
settings defined in have been reserved for simplicity. Note that
the settings identifier space in HTTP/3 is substantially larger (62 bits versus
16 bits), so many HTTP/3 settings have no equivalent HTTP/2 code point. See
.As QUIC streams might arrive out-of-order, endpoints are advised to not wait for
the peers’ settings to arrive before responding to other streams. See
.QUIC has the same concepts of “stream” and “connection” errors that HTTP/2
provides. However, there is no direct portability of HTTP/2 error codes to
HTTP/3 error codes; the values are shifted in order to prevent accidental
or implicit conversion.The HTTP/2 error codes defined in Section 7 of logically map to
the HTTP/3 error codes as follows:
HTTP_NO_ERROR in .
This is mapped to HTTP_GENERAL_PROTOCOL_ERROR except in cases where more
specific error codes have been defined. This includes HTTP_FRAME_UNEXPECTED
and HTTP_CLOSED_CRITICAL_STREAM defined in .
HTTP_INTERNAL_ERROR in .
Not applicable, since QUIC handles flow control.
Not applicable, since no acknowledgement of SETTINGS is defined.
Not applicable, since QUIC handles stream management.
HTTP_FRAME_ERROR error code defined in .
HTTP_REQUEST_REJECTED (in ) is used to indicate that a
request was not processed. Otherwise, not applicable because QUIC handles
stream management.
HTTP_REQUEST_CANCELLED in .
Multiple error codes are defined 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/3 separately. See
.RFC Editor’s Note: Please remove this section prior to publication of a
final version of this document.Removed priority signaling (#2922,#2924)Further changes to error codes (#2662,#2551):
Error codes renumberedHTTP_MALFORMED_FRAME replaced by HTTP_FRAME_ERROR, HTTP_ID_ERROR, and othersClarify how unknown frame types interact with required frame sequence
(#2867,#2858)Describe interactions with the transport in terms of defined interface terms
(#2857,#2805)Require the use of the http-opportunistic resource (RFC 8164) when scheme is
http (#2439,#2973)Settings identifiers cannot be duplicated (#2979)Changes to SETTINGS frames in 0-RTT (#2972,#2790,#2945):
Servers must send all settings with non-default values in their SETTINGS
frame, even when resumingIf a client doesn’t have settings associated with a 0-RTT ticket, it uses
the defaultsServers can’t accept early data if they cannot recover the settings the
client will have rememberedClarify that Upgrade and the 101 status code are prohibited (#2898,#2889)Clarify that frame types reserved for greasing can occur on any stream, but
frame types reserved due to HTTP/2 correspondence are prohibited
(#2997,#2692,#2693)Unknown error codes cannot be treated as errors (#2998,#2816)No changesProhibit closing the control stream (#2509, #2666)Change default priority to use an orphan node (#2502, #2690)Exclusive priorities are restored (#2754, #2781)Restrict use of frames when using CONNECT (#2229, #2702)Close and maybe reset streams if a connection error occurs for CONNECT (#2228,
#2703)Encourage provision of sufficient unidirectional streams for QPACK (#2100,
#2529, #2762)Allow extensions to use server-initiated bidirectional streams (#2711, #2773)Clarify use of maximum header list size setting (#2516, #2774)Extensive changes to error codes and conditions of their sending
Require connection errors for more error conditions (#2511, #2510)Updated the error codes for illegal GOAWAY frames (#2714, #2707)Specified error code for HEADERS on control stream (#2708)Specified error code for servers receiving PUSH_PROMISE (#2709)Specified error code for receiving DATA before HEADERS (#2715)Describe malformed messages and their handling (#2410, #2764)Remove HTTP_PUSH_ALREADY_IN_CACHE error (#2812, #2813)Refactor Push ID related errors (#2818, #2820)Rationalize HTTP/3 stream creation errors (#2821, #2822)SETTINGS_NUM_PLACEHOLDERS is 0x9 (#2443,#2530)Non-zero bits in the Empty field of the PRIORITY frame MAY be treated as an
error (#2501)Resetting streams following a GOAWAY is recommended, but not required
(#2256,#2457)Use variable-length integers throughout (#2437,#2233,#2253,#2275)
Variable-length frame types, stream types, and settings identifiersRenumbered stream type assignmentsModified associated reserved valuesFrame layout switched from Length-Type-Value to Type-Length-Value
(#2395,#2235)Specified error code for servers receiving DUPLICATE_PUSH (#2497)Use connection error for invalid PRIORITY (#2507, #2508)HTTP_REQUEST_REJECTED is used to indicate a request can be retried (#2106,
#2325)Changed error code for GOAWAY on the wrong stream (#2231, #2343)Rename “HTTP/QUIC” to “HTTP/3” (#1973)Changes to PRIORITY frame (#1865, #2075)
Permitted as first frame of request streamsRemove exclusive reprioritizationChanges to Prioritized Element Type bitsDefine DUPLICATE_PUSH frame to refer to another PUSH_PROMISE (#2072)Set defaults for settings, allow request before receiving SETTINGS (#1809,
#1846, #2038)Clarify message processing rules for streams that aren’t closed (#1972, #2003)Removed reservation of error code 0 and moved HTTP_NO_ERROR to this value
(#1922)Removed prohibition of zero-length DATA frames (#2098)Substantial editorial reorganization; no technical changes.Recommend sensible values for QUIC transport parameters (#1720,#1806)Define error for missing SETTINGS frame (#1697,#1808)Setting values are variable-length integers (#1556,#1807) and do not have
separate maximum values (#1820)Expanded discussion of connection closure (#1599,#1717,#1712)HTTP_VERSION_FALLBACK falls back to HTTP/1.1 (#1677,#1685)Reserved some frame types for grease (#1333, #1446)Unknown unidirectional stream types are tolerated, not errors; some reserved
for grease (#1490, #1525)Require settings to be remembered for 0-RTT, prohibit reductions (#1541,
#1641)Specify behavior for truncated requests (#1596, #1643)TLS SNI extension isn’t mandatory if an alternative method is used (#1459,
#1462, #1466)Removed flags from HTTP/3 frames (#1388, #1398)Reserved frame types and settings for use in preserving extensibility (#1333,
#1446)Added general error code (#1391, #1397)Unidirectional streams carry a type byte and are extensible (#910,#1359)Priority mechanism now uses explicit placeholders to enable persistent
structure in the tree (#441,#1421,#1422)Moved QPACK table updates and acknowledgments to dedicated streams (#1121,
#1122, #1238)Settings need to be remembered when attempting and accepting 0-RTT (#1157,
#1207)Selected QCRAM for header compression (#228, #1117)The server_name TLS extension is now mandatory (#296, #495)Specified handling of unsupported versions in Alt-Svc (#1093, #1097)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 draftSETTINGS changes (#181):
SETTINGS can be sent only once at the start of a connection;
no changes thereafterSETTINGS_ACK removedSettings can only occur in the SETTINGS frame a single timeBoolean format updatedAlt-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 addedGuide 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-01Reworked 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-httpUpdated authors/editors listThe 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.