RFC 9114: HTTP/3

RFC 9114: HTTP/3
RFC 9114
HTTP/3
June 2022
Bishop
Standards Track
[Page]
Stream:
Internet Engineering Task Force (IETF)
RFC:
9114
Category:
Standards Track
Published:
June 2022
ISSN:
2070-1721
Author:
M. Bishop,
Ed.
Akamai
RFC 9114
HTTP/3
Abstract
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 HTTP/3.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by
the Internet Engineering Steering Group (IESG). Further
information on Internet Standards is available in Section 2 of
RFC 7841.
Information about the current status of this document, any
errata, and how to provide feedback on it may be obtained at
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with
respect to this document. Code Components extracted from this
document must include Revised BSD License text as described in
Section 4.e of the Trust Legal Provisions and are provided without
warranty as described in the Revised BSD License.
Table of Contents
1.
Introduction
HTTP semantics (
HTTP
) are used for a broad range of services on the
Internet. These semantics have most commonly been used with HTTP/1.1 and HTTP/2.
HTTP/1.1 has been used over a variety of transport and session layers, while
HTTP/2 has been used primarily with TLS over TCP. HTTP/3 supports the same
semantics over a new transport protocol: QUIC.
1.1.
Prior Versions of HTTP
HTTP/1.1 (
HTTP/1.1
) uses whitespace-delimited text fields to convey HTTP
messages. While these exchanges are human readable, using whitespace for
message formatting leads to parsing complexity and excessive tolerance of
variant behavior.
Because HTTP/1.1 does not include a multiplexing layer, multiple TCP connections
are often used to service requests in parallel. However, that has a negative
impact on congestion control and network efficiency, since TCP does not share
congestion control across multiple connections.
HTTP/2 (
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 directly impacted
by the lost packet.
1.2.
Delegation to QUIC
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, QUIC has the capability to improve the performance of HTTP compared
to a TCP mapping. QUIC also incorporates TLS 1.3 (
TLS
) at the
transport layer, offering comparable confidentiality and integrity to running
TLS over TCP, with the improved connection setup latency of TCP Fast Open
TFO
).
This document defines HTTP/3: a mapping of HTTP semantics over the QUIC
transport protocol, drawing heavily on the design of HTTP/2. HTTP/3 relies on
QUIC to provide confidentiality and integrity protection of data; peer
authentication; and reliable, in-order, per-stream delivery. While delegating
stream lifetime and flow-control issues to QUIC, a binary framing similar to the
HTTP/2 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
QUIC-TRANSPORT
. For a full description of
HTTP/2, see
HTTP/2
2.
HTTP/3 Protocol Overview
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. Discovery of an HTTP/3 endpoint is described in
Section 3.1
Within each stream, the basic unit of HTTP/3 communication is a frame
Section 7.2
). Each frame type serves a different purpose. For example,
HEADERS
and
DATA
frames form the basis of HTTP requests and responses
Section 4.1
). Frames that apply to the entire connection are
conveyed on a dedicated
control stream
Multiplexing of requests is performed using the QUIC stream abstraction, which
is described in
Section 2
of [
QUIC-TRANSPORT
. Each request-response pair
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 (
HTTP/2
) that
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
MAX_PUSH_ID
, and
CANCEL_PUSH
As in HTTP/2, request and response fields are compressed for transmission.
Because HPACK (
HPACK
) relies on in-order transmission of
compressed field sections (a guarantee not provided by QUIC), HTTP/3 replaces
HPACK with QPACK (
QPACK
). QPACK uses separate unidirectional streams to
modify and track field table state, while encoded field sections refer to the
state of the table without modifying it.
2.1.
Document Organization
The following sections provide a detailed overview of the lifecycle of an HTTP/3
connection:
Connection Setup and Management
" (
Section 3
) covers how an HTTP/3
endpoint is discovered and an HTTP/3 connection is established.
Expressing HTTP Semantics in HTTP/3
" (
Section 4
) describes how HTTP
semantics are expressed using frames.
Connection Closure
" (
Section 5
) describes how HTTP/3
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
" (
Section 6
) describes the way QUIC streams
are used.
HTTP Framing Layer
" (
Section 7
) describes the frames used
on most streams.
Error Handling
" (
Section 8
) 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
" (
Section 9
) describes how new capabilities can be
added in future documents.
A more detailed comparison between HTTP/2 and HTTP/3 can be found in
Appendix A
2.2.
Conventions and Terminology
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
RFC2119
RFC8174
when, and only when, they
appear in all capitals, as shown here.
This document uses the variable-length integer encoding from
QUIC-TRANSPORT
The following terms are used:
abort:
An abrupt termination of a connection or stream, possibly due to an error
condition.
client:
The endpoint that initiates an HTTP/3 connection. Clients send HTTP requests
and receive HTTP responses.
connection:
A transport-layer connection between two endpoints using QUIC as the
transport protocol.
connection error
An error that affects the entire HTTP/3 connection.
endpoint:
Either the client or server of the connection.
frame:
The smallest unit of communication on a stream in HTTP/3, consisting of a
header and a variable-length sequence of bytes structured according to the
frame type.
Protocol elements called "frames" exist in both this document and
QUIC-TRANSPORT
. Where frames from
QUIC-TRANSPORT
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
Section 7.2
HTTP/3 connection:
A QUIC connection where the negotiated application protocol is HTTP/3.
peer:
An endpoint. When discussing a particular endpoint, "peer" refers to the
endpoint that is remote to the primary subject of discussion.
receiver:
An endpoint that is receiving frames.
sender:
An endpoint that is transmitting frames.
server:
The endpoint that accepts an HTTP/3 connection. Servers receive HTTP requests
and send HTTP responses.
stream:
A bidirectional or unidirectional bytestream provided by the QUIC transport.
All streams within an HTTP/3 connection can be considered "HTTP/3 streams",
but multiple stream types are defined within HTTP/3.
stream error
An application-level error on the individual stream.
The term "content" is defined in
Section 6.4
of [
HTTP
Finally, the terms "resource", "message", "user agent", "origin server",
"gateway", "intermediary", "proxy", and "tunnel" are defined in
Section 3
of [
HTTP
Packet diagrams in this document use the format defined in
Section 1.3
of [
QUIC-TRANSPORT
to illustrate the order and size of fields.
3.
Connection Setup and Management
3.1.
Discovering an HTTP/3 Endpoint
HTTP relies on the notion of an authoritative response: a response that has been
determined to be the most appropriate response for that request given the state
of the target resource at the time of response message origination by (or at the
direction of) the origin server identified within the target URI. Locating an
authoritative server for an HTTP URI is discussed in
Section 4.3
of [
HTTP
The "https" scheme associates authority with possession of a certificate that
the client considers to be trustworthy for the host identified by the authority
component of the URI. Upon receiving a server certificate in the TLS handshake,
the client
MUST
verify that the certificate is an acceptable match for the URI's
origin server using the process described in
Section 4.3.4
of [
HTTP
. If
the certificate cannot be verified with respect to the URI's origin server, the
client
MUST NOT
consider the server authoritative for that origin.
A client
MAY
attempt access to a resource with an "https" URI by resolving the
host identifier to an IP address, establishing a QUIC connection to that address
on the indicated port (including validation of the server certificate as
described above), and sending an HTTP/3 request message targeting the URI
to the server over that secured connection. Unless some other mechanism is used
to select HTTP/3, the token "h3" is used in the Application-Layer Protocol
Negotiation (ALPN; see
RFC7301
) extension during the TLS handshake.
Connectivity problems (e.g., blocking UDP) can result in a failure to establish
a QUIC connection; clients
SHOULD
attempt to use TCP-based versions of HTTP
in this case.
Servers
MAY
serve HTTP/3 on any UDP port; an alternative service advertisement
always includes an explicit port, and URIs contain either an explicit port or a
default port associated with the scheme.
3.1.1.
HTTP Alternative Services
An HTTP origin can advertise the availability of an equivalent HTTP/3 endpoint
via the Alt-Svc HTTP response header field or the HTTP/2 ALTSVC frame
ALTSVC
) using the "h3" ALPN token.
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:
Alt-Svc: h3=":50781"
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; if this
connection is successful, the client can send HTTP requests using the mapping
described in this document.
3.1.2.
Other Schemes
Although HTTP is independent of the transport protocol, the "http" scheme
associates authority with the ability to receive TCP connections on the
indicated port of whatever host is identified within the authority component.
Because HTTP/3 does not use TCP, HTTP/3 cannot be used for direct access to the
authoritative server for a resource identified by an "http" URI. However,
protocol extensions such as
ALTSVC
permit the authoritative server
to identify other services that are also authoritative and that might be
reachable over HTTP/3.
Prior to making requests for an origin whose scheme is not "https", the client
MUST
ensure the server is willing to serve that scheme. For origins whose scheme
is "http", an experimental method to accomplish this is described in
RFC8164
. Other mechanisms might be defined for various schemes in the
future.
3.2.
Connection Establishment
HTTP/3 relies on QUIC version 1 as the underlying transport. The use of other
QUIC transport versions with HTTP/3
MAY
be defined by future specifications.
QUIC version 1 uses TLS version 1.3 or greater as its handshake protocol.
HTTP/3 clients
MUST
support a mechanism to indicate the target host to the
server during the TLS handshake. If the server is identified by a domain name
DNS-TERMS
), clients
MUST
send the Server Name Indication (SNI;
RFC6066
) TLS extension unless an alternative mechanism to indicate the
target host is used.
QUIC connections are established as described in
QUIC-TRANSPORT
. 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, settings specific to HTTP/3 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
3.3.
Connection Reuse
HTTP/3 connections are persistent across multiple requests. For best
performance, it is expected that clients will not close connections until it is
determined that no further communication with a server is necessary (for
example, when a user navigates away from a particular web page) or until the
server closes the connection.
Once a connection to a server endpoint exists, this connection
MAY
be reused for
requests with multiple different URI authority components. To use an existing
connection for a new origin, clients
MUST
validate the certificate presented by
the server for the new origin server using the process described in
Section 4.3.4
of [
HTTP
. This implies that clients will need to retain the
server certificate and any additional information needed to verify that
certificate; clients that do not do so will be unable to reuse the connection
for additional origins.
If the certificate is not acceptable with regard to the new origin for any
reason, the connection
MUST NOT
be reused and a new connection
SHOULD
be
established for the new origin. If the reason the certificate cannot be
verified might apply to other origins already associated with the connection,
the client
SHOULD
revalidate the server certificate for those origins. For
instance, if validation of a certificate fails because the certificate has
expired or been revoked, this might be used to invalidate all other origins for
which that certificate was used to establish authority.
Clients
SHOULD NOT
open more than one HTTP/3 connection to a given IP address
and UDP port, where the IP address and port might be derived from a URI, a
selected alternative service (
ALTSVC
), a configured proxy, or name
resolution of any of these. A client
MAY
open multiple HTTP/3 connections to the
same IP address and UDP port using different transport or TLS configurations but
SHOULD
avoid creating multiple connections with the same configuration.
Servers are encouraged to maintain open HTTP/3 connections for as long as
possible but are permitted to terminate idle connections if necessary. When
either endpoint chooses to close the HTTP/3 connection, the terminating endpoint
SHOULD
first send a
GOAWAY
frame (
Section 5.2
) so that both
endpoints can reliably determine whether previously sent frames have been
processed and gracefully complete or terminate any necessary remaining tasks.
A server that does not wish clients to reuse HTTP/3 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 7.4
of [
HTTP
4.
Expressing HTTP Semantics in HTTP/3
4.1.
HTTP Message Framing
A client sends an HTTP request on a
request stream
, which is a client-initiated
bidirectional QUIC stream; see
Section 6.1
. A client
MUST
send only a
single request on a given stream. A server sends zero or more interim HTTP
responses on the same stream as the request, followed by a single final HTTP
response, as detailed below. See
Section 15
of [
HTTP
for a description
of interim and final HTTP responses.
Pushed responses are sent on a server-initiated unidirectional QUIC stream; see
Section 6.2.2
. A server sends zero or more interim HTTP responses, followed
by a single final HTTP response, in the same manner as a standard response.
Push is described in more detail in
Section 4.6
On a given stream, receipt of multiple requests or receipt of an additional HTTP
response following a final HTTP response
MUST
be treated as
malformed
An HTTP message (request or response) consists of:
the header section, including message control data, sent as a single
HEADERS
frame,
optionally, the content, if present, sent as a series of
DATA
frames, and
optionally, the trailer section, if present, sent as a single
HEADERS
frame.
Header and trailer sections are described in Sections
6.3
and
6.5
of
HTTP
; the content is described in
Section 6.4
of [
HTTP
Receipt of an invalid sequence of frames
MUST
be treated as a
connection error
of type
H3_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. Other frame types, especially unknown frame types,
might be permitted subject to their own rules; see
Section 9
A server
MAY
send one or more
PUSH_PROMISE
frames
before, after, or interleaved with the frames of a response message. These
PUSH_PROMISE
frames are not part of the response; see
Section 4.6
for more
details.
PUSH_PROMISE
frames are not permitted on
push streams
; a pushed
response that includes
PUSH_PROMISE
frames
MUST
be treated as a
connection error
of type
H3_FRAME_UNEXPECTED
Frames of unknown types (
Section 9
), including reserved frames
Section 7.2.8
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
Section 4.2
for more details.
Transfer codings (see
Section 7
of [
HTTP/1.1
) are not defined for HTTP/3;
the Transfer-Encoding header field
MUST NOT
be used.
A response
MAY
consist of multiple messages when and only when one or more
interim responses (1xx; see
Section 15.2
of [
HTTP
) precede a final
response to the same request. Interim responses do not contain content
or trailer sections.
An HTTP request/response exchange fully consumes a client-initiated
bidirectional QUIC stream. After sending a request, a client
MUST
close the
stream for sending. Unless using the CONNECT method (see
Section 4.4
), 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 the final 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-initiated stream terminates without enough of the HTTP
message to provide a complete response, the server
SHOULD
abort its response
stream with the error code
H3_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 the server does not need to receive the
remainder of the request, it
MAY
abort reading the
request stream
, send a
complete response, and cleanly close the sending part of the stream. The error
code
H3_NO_ERROR
SHOULD
be used when requesting that the client stop sending on
the
request 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. If the server sends a partial
or complete response but does not abort reading the request, clients
SHOULD
continue sending the content of the request and close the stream normally.
4.1.1.
Request Cancellation and Rejection
Once a
request stream
has been opened, the request
MAY
be cancelled by either
endpoint. Clients cancel requests if the response is no longer of interest;
servers cancel requests if they are unable to or choose not to respond. When
possible, it is
RECOMMENDED
that servers send an HTTP response with an
appropriate status code rather than cancelling a request it has already begun
processing.
Implementations
SHOULD
cancel requests by abruptly terminating any directions of
a stream that are still open. To do so, an implementation resets the sending
parts of streams and aborts reading on the receiving parts of streams; see
Section 2.4
of [
QUIC-TRANSPORT
When the server cancels a request without performing any application processing,
the request is considered "rejected". The server
SHOULD
abort its response
stream with the error code
H3_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.
Servers
MUST NOT
use the
H3_REQUEST_REJECTED
error code for requests that were
partially or fully processed. When a server abandons a response after partial
processing, it
SHOULD
abort its response stream with the error code
H3_REQUEST_CANCELLED
Client
SHOULD
use the error code
H3_REQUEST_CANCELLED
to cancel requests. Upon
receipt of this error code, a server
MAY
abruptly terminate the response using
the error code
H3_REQUEST_REJECTED
if no processing was performed. Clients
MUST NOT
use the
H3_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. Only
idempotent actions such as GET, PUT, or DELETE can be safely retried; a client
SHOULD NOT
automatically retry a request with a non-idempotent method unless it
has some means to know that the request semantics are idempotent
independent of the method or some means to detect that the original request was
never applied. See
Section 9.2.2
of [
HTTP
for more details.
4.1.2.
Malformed Requests and Responses
A malformed request or response is one that is an otherwise valid sequence of
frames but is invalid due to:
the presence of prohibited fields or pseudo-header fields,
the absence of mandatory pseudo-header fields,
invalid values for pseudo-header fields,
pseudo-header fields after fields,
an invalid sequence of HTTP messages,
the inclusion of uppercase field names, or
the inclusion of invalid characters in field names or values.
A request or response that is defined as having content when it contains a
Content-Length header field (
Section 8.6
of [
HTTP
) is malformed if the
value of the Content-Length header field does not equal the sum of the
DATA
frame lengths received. A response that is defined as never having content, even
when a Content-Length is present, 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
H3_MESSAGE_ERROR
For malformed requests, a server
MAY
send an HTTP response indicating the error
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.
4.2.
HTTP Fields
HTTP messages carry metadata as a series of key-value pairs called "HTTP
fields"; see Sections
6.3
and
6.5
of
HTTP
. For a listing of registered
HTTP fields, see the "Hypertext Transfer Protocol (HTTP) Field Name Registry"
maintained at
. Like HTTP/2, HTTP/3 has additional considerations related to
the use of characters in field names, the Connection header field, and
pseudo-header fields.
Field names are strings containing a subset of ASCII characters. Properties of
HTTP field names and values are discussed in more detail in
Section 5.1
of [
HTTP
. Characters in field names
MUST
be converted to lowercase prior to
their encoding. A request or response containing uppercase characters in field
names
MUST
be treated as
malformed
HTTP/3 does not use the Connection header field to indicate connection-specific
fields; in this protocol, connection-specific metadata is conveyed by other
means. An endpoint
MUST NOT
generate an HTTP/3 field section containing
connection-specific fields; any message containing connection-specific fields
MUST
be treated as
malformed
The only exception to this is the TE header field, which
MAY
be present in an
HTTP/3 request header; when it is, it
MUST NOT
contain any value other than
"trailers".
An intermediary transforming an HTTP/1.x message to HTTP/3
MUST
remove
connection-specific header fields as discussed in
Section 7.6.1
of [
HTTP
, or their messages will be treated by other HTTP/3 endpoints as
malformed
4.2.1.
Field Compression
QPACK
describes a variation of HPACK that gives an encoder some control
over how much head-of-line blocking can be caused by compression. This allows
an encoder to balance compression efficiency with latency. HTTP/3 uses QPACK to
compress header and trailer sections, including the control data present in the
header section.
To allow for better compression efficiency, the Cookie header field
MAY
be split into separate field lines, each with one or
more cookie-pairs, before compression. If a decompressed field section contains
multiple cookie field lines, these
MUST
be concatenated into a single byte
string using the two-byte delimiter of "
" (ASCII 0x3b, 0x20) before being
passed into a context other than HTTP/2 or HTTP/3, such as an HTTP/1.1
connection, or a generic HTTP server application.
4.2.2.
Header Size Constraints
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 section than it is willing to handle can send an HTTP 431 (Request
Header Fields Too Large) status code (
RFC6585
). A client can discard
responses that it cannot process. The size of a field list is calculated based
on the uncompressed size of fields, including the length of the name and value
in bytes plus an overhead of 32 bytes for each 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_FIELD_SECTION_SIZE
parameter. An
implementation that has received this parameter
SHOULD NOT
send an HTTP message
header that exceeds the indicated size, as the peer will likely refuse to
process it. However, an HTTP message can traverse one or more intermediaries
before reaching the origin server; see
Section 3.7
of [
HTTP
. Because
this limit is applied separately by each implementation that processes the
message, messages below this limit are not guaranteed to be accepted.
4.3.
HTTP Control Data
Like HTTP/2, HTTP/3 employs a series of pseudo-header fields, where the field
name begins with the
character (ASCII 0x3a). These pseudo-header fields
convey message control data; see
Section 6.2
of [
HTTP
Pseudo-header fields are not HTTP fields. Endpoints
MUST NOT
generate
pseudo-header fields other than those defined in this document. However, an
extension could negotiate a modification of this restriction; see
Section 9
Pseudo-header fields are only valid in the context in which they are defined.
Pseudo-header fields defined for requests
MUST NOT
appear in responses;
pseudo-header fields defined for responses
MUST NOT
appear in requests.
Pseudo-header fields
MUST NOT
appear in trailer sections. Endpoints
MUST
treat a
request or response that contains undefined or invalid pseudo-header fields as
malformed
All pseudo-header fields
MUST
appear in the header section before regular header
fields. Any request or response that contains a pseudo-header field that
appears in a header section after a regular header field
MUST
be treated as
malformed
4.3.1.
Request Pseudo-Header Fields
The following pseudo-header fields are defined for requests:
":method":
Contains the HTTP method (
Section 9
of [
HTTP
":scheme":
Contains the scheme portion of the target URI (
Section 3.1
of [
URI
).
The :scheme pseudo-header is not restricted to URIs with scheme "http" and
"https". A proxy or gateway can translate requests for non-HTTP schemes,
enabling the use of HTTP to interact with non-HTTP services.
See
Section 3.1.2
for guidance on using a scheme other than "https".
":authority":
Contains the authority portion of the target URI (
Section 3.2
of [
URI
).
The authority
MUST NOT
include the deprecated userinfo
subcomponent for URIs of scheme "http" or "https".
To ensure that the HTTP/1.1 request line can be reproduced accurately, this
pseudo-header field
MUST
be omitted when translating from an HTTP/1.1
request that has a request target in a method-specific form; see
Section 7.1
of [
HTTP
. Clients that generate HTTP/3 requests directly
SHOULD
use
the :authority pseudo-header field instead of the Host header field. An
intermediary that converts an HTTP/3 request to HTTP/1.1
MUST
create a Host
field if one is not present in a request by copying the value of the
:authority pseudo-header field.
":path":
Contains the path and query parts of the target URI (the "path-absolute"
production and optionally a
character (ASCII 0x3f) followed by the
"query" production; see Sections
3.3
and
3.4
of
URI
This pseudo-header field
MUST NOT
be empty for "http" or "https" URIs;
"http" or "https" URIs that do not contain a path component
MUST
include a
value of
(ASCII 0x2f). An OPTIONS request that does not include a path
component includes the value
(ASCII 0x2a) for the :path pseudo-header
field; see
Section 7.1
of [
HTTP
All HTTP/3 requests
MUST
include exactly one value for the :method, :scheme,
and :path pseudo-header fields, unless the request is a CONNECT request; see
Section 4.4
If the :scheme pseudo-header field identifies a scheme that has a mandatory
authority component (including "http" and "https"), the request
MUST
contain
either an :authority pseudo-header field or a Host header field. If these
fields are present, they
MUST NOT
be empty. If both fields are present, they
MUST
contain the same value. If the scheme does not have a mandatory authority
component and none is provided in the request target, the request
MUST NOT
contain the :authority pseudo-header or Host header fields.
An HTTP request that omits mandatory pseudo-header fields or contains invalid
values for those pseudo-header fields is
malformed
HTTP/3 does not define a way to carry the version identifier that is included in
the HTTP/1.1 request line. HTTP/3 requests implicitly have a protocol version
of "3.0".
4.3.2.
Response Pseudo-Header Fields
For responses, a single ":status" pseudo-header field is defined that carries
the HTTP status code; see
Section 15
of [
HTTP
. This pseudo-header
field
MUST
be included in all responses; otherwise, the response is
malformed
(see
Section 4.1.2
).
HTTP/3 does not define a way to carry the version or reason phrase that is
included in an HTTP/1.1 status line. HTTP/3 responses implicitly have a protocol
version of "3.0".
4.4.
The CONNECT Method
The CONNECT method requests that the recipient establish a tunnel to the
destination origin server identified by the request-target; see
Section 9.3.6
of [
HTTP
. It 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 and HTTP/3, the CONNECT method is used to establish
a tunnel over a single stream.
A CONNECT request
MUST
be constructed as follows:
The :method pseudo-header field is set to "CONNECT"
The :scheme and :path pseudo-header fields are omitted
The :authority pseudo-header field contains the host and port to connect to
(equivalent to the authority-form of the request-target of CONNECT requests;
see
Section 7.1
of [
HTTP
).
The
request stream
remains open at the end of the request to carry the data to
be transferred. A CONNECT request that does not conform to these restrictions
is
malformed
A proxy that supports CONNECT establishes a TCP connection (
RFC0793
) 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 15.3
of [
HTTP
All
DATA
frames on the stream correspond to data sent or received on the TCP
connection. The payload of 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 known frame type
MUST
be
treated as a
connection error
of type
H3_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 close the send stream
that it sends to the client. TCP connections that 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
H3_CONNECT_ERROR
Correspondingly, if a proxy detects an error with the stream or the QUIC
connection, it
MUST
close the TCP connection. If the proxy detects that the
client has reset the stream or aborted reading from the stream, it
MUST
close
the TCP connection. If the stream is reset or reading is aborted by the client,
a proxy
SHOULD
perform the same operation on the other direction in order to
ensure that both directions of the stream are cancelled. In all these cases, if
the underlying TCP implementation permits it, the proxy
SHOULD
send a TCP
segment with the RST bit set.
Since CONNECT creates a tunnel to an arbitrary server, proxies that support
CONNECT
SHOULD
restrict its use to a set of known ports or a list of safe
request targets; see
Section 9.3.6
of [
HTTP
for more details.
4.5.
HTTP Upgrade
HTTP/3 does not support the HTTP Upgrade mechanism (
Section 7.8
of [
HTTP
) or the 101 (Switching Protocols) informational status code
Section 15.2.2
of [
HTTP
).
4.6.
Server Push
Server push is an interaction mode that 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
Section 8.2
of [
HTTP/2
, but it uses different mechanisms.
Each server push is assigned a unique push ID by the server. The push ID is
used to refer to the push in various contexts throughout the lifetime of the
HTTP/3 connection.
The push ID space begins at zero and ends at a maximum value set by the
MAX_PUSH_ID
frame. In particular, a server is not
able to push until after the client sends a
MAX_PUSH_ID
frame. A client sends
MAX_PUSH_ID
frames to control the number of pushes that a server can promise. A
server
SHOULD
use push IDs sequentially, beginning from zero. A client
MUST
treat receipt of a
push stream
as a
connection error
of type
H3_ID_ERROR
when no
MAX_PUSH_ID
frame has been sent or when the stream
references a push ID that is greater than the maximum push ID.
The push ID is used in one or more
PUSH_PROMISE
frames that carry the control
data and header fields of the request message. These frames are sent on the
request stream
that generated the push. This allows the server push to be
associated with a client request. When the same push ID is promised on multiple
request streams
, the decompressed request field sections
MUST
contain the same
fields in the same order, and both the name and the value in each field
MUST
be
identical.
The push ID is then included with the
push stream
that ultimately fulfills
those promises. The
push stream
identifies the push ID of
the promise that it fulfills, then contains a response to the promised request
as described in
Section 4.1
Finally, the push ID can be used in
CANCEL_PUSH
frames; see
Section 7.2.3
. Clients use this frame to indicate they do not wish to
receive a promised resource. Servers use this frame to indicate they will not
be fulfilling a previous promise.
Not all requests can be pushed. A server
MAY
push requests that have the
following properties:
cacheable; see
Section 9.2.3
of [
HTTP
safe; see
Section 9.2.1
of [
HTTP
does not include request content or a trailer section
The server
MUST
include a value in the :authority pseudo-header field for
which the server is authoritative. If the client has not yet validated the
connection for the origin indicated by the pushed request, it
MUST
perform the
same verification process it would do before sending a request for that origin
on the connection; see
Section 3.3
. If this verification fails,
the client
MUST NOT
consider the server authoritative for that origin.
Clients
SHOULD
send a
CANCEL_PUSH
frame upon receipt of a
PUSH_PROMISE
frame
carrying a request that is not cacheable, is not known to be safe, that
indicates the presence of request content, or for which it does not consider the
server authoritative. Any corresponding responses
MUST NOT
be used or cached.
Each pushed response is associated with one or more client requests. The push
is associated with the
request stream
on which the
PUSH_PROMISE
frame was
received. The same server push can be associated with additional client
requests using a
PUSH_PROMISE
frame with the same push ID on multiple
request
streams
. These associations do not affect the operation of the protocol, but
they
MAY
be considered by user agents when deciding how to use pushed resources.
Ordering of a
PUSH_PROMISE
frame in relation to certain parts of the response is
important. The server
SHOULD
send
PUSH_PROMISE
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.
Due to reordering,
push stream
data can arrive before the corresponding
PUSH_PROMISE
frame. When a client receives a new
push stream
with an
as-yet-unknown push ID, both the associated client request and the pushed
request header fields are unknown. The client can buffer the stream data in
expectation of the matching
PUSH_PROMISE
. The client can use stream flow control
Section 4.1
of [
QUIC-TRANSPORT
) to limit the amount of data a server may
commit to the pushed stream. Clients
SHOULD
abort reading and discard data
already read from
push streams
if no corresponding
PUSH_PROMISE
frame is
processed in a reasonable amount of time.
Push stream data can also arrive after a client has cancelled a push. In this
case, the client can abort reading the stream with an error code of
H3_REQUEST_CANCELLED
. This asks the server not to transfer additional data and
indicates that it will be discarded upon receipt.
Pushed responses that are cacheable (see
Section 3
of [
HTTP-CACHING
) can be
stored by the client, if it implements an HTTP cache. Pushed responses are
considered successfully validated on the origin server (e.g., if the "no-cache"
cache response directive is present; see
Section 5.2.2.4
of [
HTTP-CACHING
) at the
time the pushed response is received.
Pushed responses that are not cacheable
MUST NOT
be stored by any HTTP cache.
They
MAY
be made available to the application separately.
5.
Connection Closure
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.
5.1.
Idle Connections
Each QUIC endpoint declares an idle timeout during the handshake. If the QUIC
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 HTTP/3 connection for new requests if the existing
connection has been idle for longer than the idle timeout negotiated during the
QUIC handshake, and they
SHOULD
do so if approaching the idle timeout; see
Section 10.1
of [
QUIC-TRANSPORT
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 10.1.2
of [
QUIC-TRANSPORT
. 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.
5.2.
Connection Shutdown
Even when a connection is not idle, either endpoint can decide to stop using the
connection and initiate a graceful connection close. Endpoints initiate the
graceful shutdown of an HTTP/3 connection by sending a
GOAWAY
frame. The
GOAWAY
frame contains an identifier that indicates to the receiver the range of
requests or pushes that were or might be processed in this connection. The
server sends a client-initiated bidirectional stream ID; the client sends a
push
ID
. Requests or pushes with the indicated identifier or greater are rejected
Section 4.1.1
) by the sender of the
GOAWAY
. This identifier
MAY
be
zero if no requests or pushes were processed.
The information in the
GOAWAY
frame enables a client and server to agree on
which requests or pushes were accepted prior to the shutdown of the HTTP/3
connection. Upon sending a
GOAWAY
frame, the endpoint
SHOULD
explicitly cancel
(see Sections
4.1.1
and
7.2.3
) any requests
or pushes that have identifiers greater than or equal to the one indicated, in
order to clean up transport state for the affected streams. The endpoint
SHOULD
continue to do so as more requests or pushes arrive.
Endpoints
MUST NOT
initiate new requests or promise new pushes on the connection
after receipt of a
GOAWAY
frame from the peer. Clients
MAY
establish a new
connection to send additional requests.
Some requests or pushes might already be in transit:
Upon receipt of a
GOAWAY
frame, if the client has already sent requests with
a stream ID greater than or equal to the identifier contained in the
GOAWAY
frame, those requests will not be processed. Clients can safely retry
unprocessed requests on a different HTTP connection. A client that is
unable to retry requests loses all requests that are in flight when the
server closes the connection.
Requests on stream IDs less than the stream ID in a
GOAWAY
frame from the
server might have been processed; their status cannot be known until a
response is received, the stream is reset individually, another
GOAWAY
is
received with a lower stream ID than that of the request in question,
or the connection terminates.
Servers
MAY
reject individual requests on streams below the indicated ID if
these requests were not processed.
If a server receives a
GOAWAY
frame after having promised pushes with a
push
ID
greater than or equal to the identifier contained in the
GOAWAY
frame,
those pushes will not be accepted.
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 or not a request has been partially processed. 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.
An endpoint
MAY
send multiple
GOAWAY
frames indicating different identifiers,
but the identifier in each frame
MUST NOT
be greater than the identifier in any
previous frame, since clients might already have retried unprocessed requests on
another HTTP connection. Receiving a
GOAWAY
containing a larger identifier than
previously received
MUST
be treated as a
connection error
of type
H3_ID_ERROR
An endpoint that is attempting to gracefully shut down a connection can send a
GOAWAY
frame with a value set to the maximum possible value (2
62
-4
for servers, 2
62
-1 for clients). This ensures that the peer stops
creating new requests or pushes. After allowing time for any in-flight requests
or pushes to arrive, the endpoint can send another
GOAWAY
frame indicating which
requests or pushes it might accept before the end of the connection. This
ensures that a connection can be cleanly shut down without losing requests.
A client has more flexibility in the value it chooses for the Push ID field in a
GOAWAY
that it sends. A value of 2
62
-1 indicates that the server can
continue fulfilling pushes that have already been promised. A smaller value
indicates the client will reject pushes with push IDs greater than or equal to
this value. Like the server, the client
MAY
send subsequent
GOAWAY
frames so
long as the specified
push ID
is no greater than any previously sent value.
Even when a
GOAWAY
indicates that a given request or push will not be processed
or accepted upon receipt, the underlying transport resources still exist. The
endpoint that initiated these requests can cancel them to clean up transport
state.
Once all accepted requests and pushes have been processed, the endpoint can
permit the connection to become idle, or it
MAY
initiate an immediate closure of
the connection. An endpoint that completes a graceful shutdown
SHOULD
use the
H3_NO_ERROR
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.
5.3.
Immediate Application Closure
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 indicating
that the application layer has terminated the connection. The application error
code in this frame indicates to the peer why the connection is being closed.
See
Section 8
for error codes that can be used when closing a connection in
HTTP/3.
Before closing the connection, a
GOAWAY
frame
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.
If there are open streams that have not been explicitly closed, they are
implicitly closed when the connection is closed; see
Section 10.2
of [
QUIC-TRANSPORT
5.4.
Transport Closure
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 that
interrupts connectivity.
If a connection terminates without a
GOAWAY
frame, clients
MUST
assume that any
request that was sent, whether in whole or in part, might have been processed.
6.
Stream Mapping and Usage
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. In
version 1 of QUIC, the stream data containing HTTP frames is carried by QUIC
STREAM frames, but this framing is invisible to the HTTP framing layer. The
transport layer buffers and orders received stream data, exposing 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, carrying data in both directions. Streams can be
initiated by either the client or the server. For more detail on QUIC streams,
see
Section 2
of [
QUIC-TRANSPORT
When HTTP fields 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 to the entire HTTP/3 connection context.
6.1.
Bidirectional Streams
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. These streams are referred to as request streams.
This means that the client's first request occurs on QUIC stream 0, with
subsequent requests on streams 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. So as
to not unnecessarily limit parallelism, at least 100 request streams
SHOULD
be
permitted at a time.
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
H3_STREAM_CREATION_ERROR
unless such an extension has been
negotiated.
6.2.
Unidirectional Streams
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.
Unidirectional Stream Header {
Stream Type (i),
Figure 1
Unidirectional Stream Header
Two stream types are defined in this document:
control streams
Section 6.2.1
) and
push streams
Section 6.2.2
).
QPACK
defines
two additional stream types. Other stream types can be defined by extensions to
HTTP/3; see
Section 9
for more details. Some stream types are reserved
Section 6.2.3
).
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
Section 6.2.3
) with some of the unidirectional streams they are permitted
to use.
Each endpoint needs to create at least one unidirectional stream for the HTTP
control stream
. QPACK requires two additional unidirectional streams, and other
extensions might require further streams. Therefore, the transport parameters
sent by both clients and servers
MUST
allow the peer to create at least three
unidirectional streams. These transport parameters
SHOULD
also provide at least
1,024 bytes of flow-control credit to each unidirectional 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 that is not supported by the
recipient, the remainder of the stream cannot be consumed as the semantics are
unknown. Recipients of unknown stream types
MUST
either abort reading of the
stream or discard incoming data without further processing. If reading is
aborted, the recipient
SHOULD
use the
H3_STREAM_CREATION_ERROR
error code or a
reserved error code (
Section 8.1
). The recipient
MUST NOT
consider
unknown stream types to be a
connection error
of any kind.
As certain stream types can affect connection state, a recipient
SHOULD NOT
discard data from incoming unidirectional streams prior to reading the stream
type.
Implementations
MAY
send stream types before knowing whether the peer supports
them. However, stream types that 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.
6.2.1.
Control Streams
A control stream is indicated by a stream type of 0x00. Data on this stream
consists of HTTP/3 frames, as defined in
Section 7.2
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
H3_MISSING_SETTINGS
. Only one control
stream per peer is permitted; receipt of a second stream claiming to be a
control stream
MUST
be treated as a
connection error
of type
H3_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
H3_CLOSED_CRITICAL_STREAM
. Connection errors are described in
Section 8
Because the contents of the control stream are used to manage the behavior of
other streams, endpoints
SHOULD
provide enough flow-control credit to keep the
peer's control stream from becoming blocked.
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 available on the QUIC connection, either client or server
might be able to send stream data first.
6.2.2.
Push Streams
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
Section 4.6
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
Section 7.2
, and fulfills a promised server push by zero or more interim HTTP
responses followed by a single final HTTP response, as defined in
Section 4.1
. Server push and push IDs are described in
Section 4.6
Only servers can push; if a server receives a client-initiated push stream, this
MUST
be treated as a
connection error
of type
H3_STREAM_CREATION_ERROR
Push Stream Header {
Stream Type (i) = 0x01,
Push ID (i),
Figure 2
Push Stream Header
A client
SHOULD NOT
abort reading on a push stream prior to reading the push
stream header, as this could lead to disagreement between client and server on
which push IDs have already been consumed.
Each
push ID
MUST
only be used once in a push stream header. If a client detects
that 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
H3_ID_ERROR
6.2.3.
Reserved Stream Types
Stream types of the format
0x1f * N + 0x21
for non-negative integer values of
are reserved to exercise the requirement that unknown types be ignored.
These streams have no semantics, and they 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 sending
implementation chooses. When sending a reserved stream type, the implementation
MAY
either terminate the stream cleanly or reset it. When resetting the stream,
either the
H3_NO_ERROR
error code or a reserved error code
Section 8.1
SHOULD
be used.
7.
HTTP Framing Layer
HTTP frames are carried on QUIC streams, as described in
Section 6
HTTP/3 defines three stream types:
control stream
request stream
, and
push
stream
. This section describes HTTP/3 frame formats and their permitted stream
types; see
Table 1
for an overview. A comparison between
HTTP/2 and HTTP/3 frames is provided in
Appendix A.2
Table 1
HTTP/3 Frames and Stream Type Overview
Frame
Control Stream
Request Stream
Push Stream
Section
DATA
No
Yes
Yes
Section 7.2.1
HEADERS
No
Yes
Yes
Section 7.2.2
CANCEL_PUSH
Yes
No
No
Section 7.2.3
SETTINGS
Yes (1)
No
No
Section 7.2.4
PUSH_PROMISE
No
Yes
No
Section 7.2.5
GOAWAY
Yes
No
No
Section 7.2.6
MAX_PUSH_ID
Yes
No
No
Section 7.2.7
Reserved
Yes
Yes
Yes
Section 7.2.8
The
SETTINGS
frame can only occur as the first frame of a Control stream; this
is indicated in
Table 1
with a (1). Specific guidance
is provided in the relevant section.
Note that, unlike QUIC frames, HTTP/3 frames can span multiple packets.
7.1.
Frame Layout
All frames have the following format:
HTTP/3 Frame Format {
Type (i),
Length (i),
Frame Payload (..),
Figure 3
HTTP/3 Frame Format
A frame includes the following fields:
Type:
A variable-length integer that identifies the frame type.
Length:
A variable-length integer that describes the length in bytes of
the Frame Payload.
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
H3_FRAME_ERROR
. In particular, redundant length encodings
MUST
be verified to be self-consistent; see
Section 10.8
When a stream terminates cleanly, if the last frame on the stream was truncated,
this
MUST
be treated as a
connection error
of type
H3_FRAME_ERROR
. Streams that
terminate abruptly may be reset at any point in a frame.
7.2.
Frame Definitions
7.2.1.
DATA
DATA frames (type=0x00) convey arbitrary, variable-length sequences of bytes
associated with HTTP request or response content.
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
H3_FRAME_UNEXPECTED
DATA Frame {
Type (i) = 0x00,
Length (i),
Data (..),
Figure 4
DATA Frame
7.2.2.
HEADERS
The HEADERS frame (type=0x01) is used to carry an HTTP field section that is
encoded using QPACK. See
QPACK
for more details.
HEADERS Frame {
Type (i) = 0x01,
Length (i),
Encoded Field Section (..),
Figure 5
HEADERS Frame
HEADERS frames can only be sent on
request streams
or
push streams
. If a
HEADERS frame is received on a
control stream
, the recipient
MUST
respond with a
connection error
of type
H3_FRAME_UNEXPECTED
7.2.3.
CANCEL_PUSH
The CANCEL_PUSH frame (type=0x03) 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
Section 4.6
), encoded as a variable-length
integer.
When a client sends a CANCEL_PUSH frame, it is indicating that it does not wish
to receive the promised resource. The server
SHOULD
abort sending the resource,
but the mechanism to do so depends on the state of the corresponding
push
stream
. If the server has not yet created a
push stream
, it does not create
one. If the
push stream
is open, the server
SHOULD
abruptly terminate that
stream. If the
push stream
has already ended, the server
MAY
still abruptly
terminate the stream or
MAY
take no action.
A server sends a CANCEL_PUSH frame to indicate that it will not be fulfilling a
promise that was previously sent. The client cannot expect the corresponding
promise to be fulfilled, unless it has already received and processed the
promised response. Regardless of whether a
push stream
has been opened, a server
SHOULD
send a CANCEL_PUSH frame when it determines that promise will not be
fulfilled. If a stream has already been opened, the server can abort sending on
the stream with an error code of
H3_REQUEST_CANCELLED
Sending a CANCEL_PUSH frame has no direct effect on the state of existing
push
streams
. A client
SHOULD NOT
send a CANCEL_PUSH frame when it has already
received a corresponding
push stream
. A
push stream
could arrive after a client
has sent a CANCEL_PUSH frame, because a server might not have processed the
CANCEL_PUSH. The client
SHOULD
abort reading the stream with an error code of
H3_REQUEST_CANCELLED
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
H3_FRAME_UNEXPECTED
CANCEL_PUSH Frame {
Type (i) = 0x03,
Length (i),
Push ID (i),
Figure 6
CANCEL_PUSH Frame
The CANCEL_PUSH frame carries a
push ID
encoded as a variable-length integer.
The Push ID field identifies the server push that is being cancelled; see
Section 4.6
. If a CANCEL_PUSH frame is received that references a
push ID
greater than currently allowed on the connection, this
MUST
be treated as a
connection error
of type
H3_ID_ERROR
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 due to reordering. If a
server receives a CANCEL_PUSH frame for a
push ID
that has not yet been
mentioned by a
PUSH_PROMISE
frame, this
MUST
be treated as a
connection error
of
type
H3_ID_ERROR
7.2.4.
SETTINGS
The SETTINGS frame (type=0x04) 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 an entire HTTP/3 connection, never a single
stream. A SETTINGS frame
MUST
be sent as the first frame of each
control stream
(see
Section 6.2.1
) by each peer, and it
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
H3_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
H3_FRAME_UNEXPECTED
SETTINGS parameters are not negotiated; they describe characteristics of the
sending peer that 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 field
section, 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
H3_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.
Setting {
Identifier (i),
Value (i),

SETTINGS Frame {
Type (i) = 0x04,
Length (i),
Setting (..) ...,
Figure 7
SETTINGS Frame
An implementation
MUST
ignore any parameter with an identifier it does
not understand.
7.2.4.1.
Defined SETTINGS Parameters
The following settings are defined in HTTP/3:
SETTINGS_MAX_FIELD_SECTION_SIZE (0x06)
The default value is unlimited. See
Section 4.2.2
for usage.
Setting identifiers of the format
0x1f * N + 0x21
for non-negative integer
values of
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.
Setting identifiers that were defined in
HTTP/2
where there is no
corresponding HTTP/3 setting have also been reserved (
Section 11.2.2
). These
reserved settings
MUST NOT
be sent, and their receipt
MUST
be treated as a
connection error
of type
H3_SETTINGS_ERROR
Additional settings can be defined by extensions to HTTP/3; see
Section 9
for more details.
7.2.4.2.
Initialization
An HTTP implementation
MUST NOT
send frames or requests that 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
the packet containing SETTINGS being processed by QUIC, even if the server sends
SETTINGS immediately. Clients
SHOULD NOT
wait indefinitely for SETTINGS to
arrive before sending requests, but they
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 HTTP/3 connection where resumption
information was provided, but they
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 that differ from
their default values. If a server accepts 0-RTT but then sends settings that
are not compatible with the previously specified settings, this
MUST
be treated
as a
connection error
of type
H3_SETTINGS_ERROR
. If a server accepts 0-RTT but
then sends a SETTINGS frame that omits a setting value that the client
understands (apart from reserved setting identifiers) that was previously
specified to have a non-default value, this
MUST
be treated as a
connection
error
of type
H3_SETTINGS_ERROR
7.2.5.
PUSH_PROMISE
The PUSH_PROMISE frame (type=0x05) is used to carry a promised request header
section from server to client on a
request stream
PUSH_PROMISE Frame {
Type (i) = 0x05,
Length (i),
Push ID (i),
Encoded Field Section (..),
Figure 8
PUSH_PROMISE Frame
The payload consists of:
Push ID:
A variable-length integer that identifies the server push operation. A
push
ID
is used in
push stream
headers (
Section 4.6
) and
CANCEL_PUSH
frames.
Encoded Field Section:
QPACK-encoded request header fields for the promised response. See
QPACK
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 (
Section 7.2.7
). 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
H3_ID_ERROR
A server
MAY
use the same
push ID
in multiple PUSH_PROMISE frames. If so, the
decompressed request header sets
MUST
contain the same fields in the same order,
and both the name and the value in each field
MUST
be exact matches. Clients
SHOULD
compare the request header sections for resources promised multiple
times. If a client receives a
push ID
that has already been promised and detects
a mismatch, it
MUST
respond with a
connection error
of type
H3_GENERAL_PROTOCOL_ERROR
. If the decompressed field sections match exactly, the
client
SHOULD
associate the pushed content with each stream on which a
PUSH_PROMISE frame was received.
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 frame that
uses a
push ID
that they have already consumed and discarded are forced to
ignore the promise.
If a PUSH_PROMISE frame is received on the
control stream
, the client
MUST
respond with a
connection error
of type
H3_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
H3_FRAME_UNEXPECTED
See
Section 4.6
for a description of the overall server push mechanism.
7.2.6.
GOAWAY
The GOAWAY frame (type=0x07) is used to initiate graceful shutdown of an HTTP/3
connection by either endpoint. GOAWAY allows an endpoint to stop accepting new
requests or pushes while still finishing processing of previously received
requests and pushes. This enables administrative actions, like server
maintenance. GOAWAY by itself does not close a connection.
GOAWAY Frame {
Type (i) = 0x07,
Length (i),
Stream ID/Push ID (i),
Figure 9
GOAWAY Frame
The GOAWAY frame is always sent on the
control stream
. In the server-to-client
direction, 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
H3_ID_ERROR
In the client-to-server direction, the GOAWAY frame carries a
push ID
encoded as
a variable-length integer.
The GOAWAY frame applies to the entire 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
H3_FRAME_UNEXPECTED
See
Section 5.2
for more information on the use of the GOAWAY frame.
7.2.7.
MAX_PUSH_ID
The MAX_PUSH_ID frame (type=0x0d) 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
PUSH_PROMISE
and
CANCEL_PUSH
frames.
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
H3_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
H3_FRAME_UNEXPECTED
The maximum
push ID
is unset when an HTTP/3 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.
MAX_PUSH_ID Frame {
Type (i) = 0x0d,
Length (i),
Push ID (i),
Figure 10
MAX_PUSH_ID Frame
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
Section 4.6
. A
MAX_PUSH_ID frame cannot reduce the maximum
push ID
; receipt of a MAX_PUSH_ID
frame that contains a smaller value than previously received
MUST
be treated as
connection error
of type
H3_ID_ERROR
7.2.8.
Reserved Frame Types
Frame types of the format
0x1f * N + 0x21
for non-negative integer values of
are reserved to exercise the requirement that unknown types be ignored
Section 9
). These frames have no semantics, and they
MAY
be sent on any
stream where frames are allowed to be sent. This enables their use for
application-layer padding. 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 that were used in HTTP/2 where there is no corresponding HTTP/3
frame have also been reserved (
Section 11.2.1
). These frame types
MUST NOT
be
sent, and their receipt
MUST
be treated as a
connection error
of type
H3_FRAME_UNEXPECTED
8.
Error Handling
When a stream cannot be completed successfully, QUIC allows the application to
abruptly terminate (reset) that stream and communicate a reason; see
Section 2.4
of [
QUIC-TRANSPORT
. This is referred to as a "stream error". An HTTP/3
implementation can decide to close a QUIC stream and communicate the type of
error. Wire encodings of error codes are defined in
Section 8.1
Stream errors are distinct from HTTP status codes that indicate error
conditions. Stream errors indicate that the sender did not transfer or consume
the full request or response, while HTTP status codes indicate the result of a
request that was successfully received.
If an entire connection needs to be terminated, QUIC similarly provides
mechanisms to communicate a reason; see
Section 5.3
of [
QUIC-TRANSPORT
. This
is referred to as a "connection error". Similar to stream errors, an HTTP/3
implementation can terminate a QUIC connection and communicate the reason using
an error code from
Section 8.1
Although the reasons for closing streams and connections are called "errors",
these actions do not necessarily indicate a problem with the connection or
either implementation. For example, a stream can be reset if the requested
resource is no longer needed.
An endpoint
MAY
choose to treat a stream error as a connection error under
certain circumstances, closing the entire connection in response to a condition
on a single stream. Implementations need to consider the impact on outstanding
requests before making this choice.
Because new error codes can be defined without negotiation (see
Section 9
),
use of an error code in an unexpected context or receipt of an unknown error
code
MUST
be treated as equivalent to
H3_NO_ERROR
. However, closing a stream
can have other effects regardless of the error code; for example, see
Section 4.1
8.1.
HTTP/3 Error Codes
The following error codes are defined for use when abruptly terminating streams,
aborting reading of streams, or immediately closing HTTP/3 connections.
H3_NO_ERROR (0x0100)
No error. This is used when the connection or stream needs to be closed, but
there is no error to signal.
H3_GENERAL_PROTOCOL_ERROR (0x0101)
Peer violated protocol requirements in a way that does not match a more
specific error code or endpoint declines to use the more specific error code.
H3_INTERNAL_ERROR (0x0102)
An internal error has occurred in the HTTP stack.
H3_STREAM_CREATION_ERROR (0x0103)
The endpoint detected that its peer created a stream that it will not accept.
H3_CLOSED_CRITICAL_STREAM (0x0104)
A stream required by the HTTP/3 connection was closed or reset.
H3_FRAME_UNEXPECTED (0x0105)
A frame was received that was not permitted in the current state or on the
current stream.
H3_FRAME_ERROR (0x0106)
A frame that fails to satisfy layout requirements or with an invalid size
was received.
H3_EXCESSIVE_LOAD (0x0107)
The endpoint detected that its peer is exhibiting a behavior that might be
generating excessive load.
H3_ID_ERROR (0x0108)
A stream ID or
push ID
was used incorrectly, such as exceeding a limit,
reducing a limit, or being reused.
H3_SETTINGS_ERROR (0x0109)
An endpoint detected an error in the payload of a
SETTINGS
frame.
H3_MISSING_SETTINGS (0x010a)
No
SETTINGS
frame was received at the beginning of the
control stream
H3_REQUEST_REJECTED (0x010b)
A server rejected a request without performing any application processing.
H3_REQUEST_CANCELLED (0x010c)
The request or its response (including pushed response) is cancelled.
H3_REQUEST_INCOMPLETE (0x010d)
The client's stream terminated without containing a fully formed request.
H3_MESSAGE_ERROR (0x010e)
An HTTP message was
malformed
and cannot be processed.
H3_CONNECT_ERROR (0x010f)
The TCP connection established in response to a CONNECT request was reset or
abnormally closed.
H3_VERSION_FALLBACK (0x0110)
The requested operation cannot be served over HTTP/3. The peer should
retry over HTTP/1.1.
Error codes of the format
0x1f * N + 0x21
for non-negative integer values of
are reserved to exercise the requirement that unknown error codes be treated
as equivalent to
H3_NO_ERROR
Section 9
). Implementations
SHOULD
select an
error code from this space with some probability when they would have sent
H3_NO_ERROR
9.
Extensions to HTTP/3
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 fields.
Extensions are permitted to use new frame types (
Section 7.2
), new settings
Section 7.2.4.1
), new error codes (
Section 8
), or new unidirectional
stream types (
Section 6.2
). Registries are established for
managing these extension points: frame types (
Section 11.2.1
), settings
Section 11.2.2
), error codes (
Section 11.2.3
), and stream types
Section 11.2.4
).
Implementations
MUST
ignore unknown or unsupported values in all extensible
protocol elements. Implementations
MUST
discard data or abort reading on
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
Section 6.2.1
), 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. Coordinating when such a revised layout comes
into effect could prove complex. As such, allocating new identifiers for
new definitions of existing protocol elements is likely to be more effective.
This document does not mandate a specific method for negotiating the use of an
extension, but it notes that a setting (
Section 7.2.4.1
) 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.
10.
Security Considerations
The security considerations of HTTP/3 should be comparable to those of HTTP/2
with TLS. However, many of the considerations from
Section 10
of [
HTTP/2
apply to
QUIC-TRANSPORT
and are discussed in that document.
10.1.
Server Authority
HTTP/3 relies on the HTTP definition of authority. The security considerations
of establishing authority are discussed in
Section 17.1
of [
HTTP
10.2.
Cross-Protocol Attacks
The use of ALPN in the TLS and QUIC handshakes establishes the target
application protocol before application-layer bytes are processed. This ensures
that endpoints have strong assurances that peers are using the same protocol.
This does not guarantee protection from all cross-protocol attacks.
Section 21.5
of [
QUIC-TRANSPORT
describes some ways in which the plaintext of QUIC
packets can be used to perform request forgery against endpoints that don't use
authenticated transports.
10.3.
Intermediary-Encapsulation Attacks
The HTTP/3 field encoding allows the expression of names that are not valid
field names in the syntax used by HTTP (
Section 5.1
of [
HTTP
). Requests or
responses containing invalid field names
MUST
be treated as
malformed
Therefore, an intermediary cannot translate an HTTP/3 request or response
containing an invalid field name into an HTTP/1.1 message.
Similarly, HTTP/3 can transport field values that are not valid. While most
values that can be encoded will not alter field parsing, carriage return (ASCII
0x0d), line feed (ASCII 0x0a), and the null character (ASCII 0x00) might be
exploited by an attacker if they are translated verbatim. Any request or
response that contains a character not permitted in a field value
MUST
be
treated as
malformed
. Valid characters are defined by the
"field-content" ABNF rule in
Section 5.5
of [
HTTP
10.4.
Cacheability of Pushed Responses
Pushed responses do not have an explicit request from the client; the request is
provided by the server in the
PUSH_PROMISE
frame.
Caching responses that are pushed is possible based on the guidance provided by
the origin server in the Cache-Control header field. However, this can cause
issues if a single server hosts more than one tenant. For example, a server
might offer multiple users each a small portion of its URI space.
Where multiple tenants share space on the same server, that server
MUST
ensure
that tenants are not able to push representations of resources that they do not
have authority over. Failure to enforce this would allow a tenant to provide a
representation that would be served out of cache, overriding the actual
representation that the authoritative tenant provides.
Clients are required to reject pushed responses for which an origin server is
not authoritative; see
Section 4.6
10.5.
Denial-of-Service Considerations
An HTTP/3 connection can demand a greater commitment of resources to operate
than an HTTP/1.1 or HTTP/2 connection. The use of field compression and flow
control depend on a commitment of resources for storing a greater amount of
state. Settings for these features ensure that memory commitments for these
features are strictly bounded.
The number of
PUSH_PROMISE
frames is constrained in a similar fashion. A client
that accepts server push
SHOULD
limit the number of push IDs it issues at a
time.
Processing capacity cannot be guarded as effectively as state capacity.
The ability to send undefined protocol elements that the peer is required to
ignore can be abused to cause a peer to expend additional processing time. This
might be done by setting multiple undefined
SETTINGS
parameters, unknown frame
types, or unknown stream types. Note, however, that some uses are entirely
legitimate, such as optional-to-understand extensions and padding to increase
resistance to traffic analysis.
Compression of field sections also offers some opportunities to waste processing
resources; see
Section 7
of [
QPACK
for more details on potential abuses.
All these features -- i.e., server push, unknown protocol elements, field
compression -- have legitimate uses. These features become a burden only when
they are used unnecessarily or to excess.
An endpoint that does not monitor such behavior exposes itself to a risk of
denial-of-service attack. Implementations
SHOULD
track the use of these
features and set limits on their use. An endpoint
MAY
treat activity that is
suspicious as a
connection error
of type
H3_EXCESSIVE_LOAD
, but
false positives will result in disrupting valid connections and requests.
10.5.1.
Limits on Field Section Size
A large field section (
Section 4.1
) can cause an implementation to
commit a large amount of state. Header fields that are critical for routing can
appear toward the end of a header section, which prevents streaming of the
header section to its ultimate destination. This ordering and other reasons,
such as ensuring cache correctness, mean that an endpoint likely needs to buffer
the entire header section. Since there is no hard limit to the size of a field
section, some endpoints could be forced to commit a large amount of available
memory for header fields.
An endpoint can use the
SETTINGS_MAX_FIELD_SECTION_SIZE
Section 4.2.2
) setting to advise peers of limits that might apply
on the size of field sections. This setting is only advisory, so endpoints
MAY
choose to send field sections that exceed this limit and risk having the request
or response being treated as
malformed
. This setting is specific to an HTTP/3
connection, so any request or response could encounter a hop with a lower,
unknown limit. An intermediary can attempt to avoid this problem by passing on
values presented by different peers, but they are not obligated to do so.
A server that receives a larger field section than it is willing to handle can
send an HTTP 431 (Request Header Fields Too Large) status code (
RFC6585
).
A client can discard responses that it cannot process.
10.5.2.
CONNECT Issues
The CONNECT method can be used to create disproportionate load on a proxy, since
stream creation is relatively inexpensive when compared to the creation and
maintenance of a TCP connection. Therefore, a proxy that supports CONNECT might
be more conservative in the number of simultaneous requests it accepts.
A proxy might also maintain some resources for a TCP connection beyond the
closing of the stream that carries the CONNECT request, since the outgoing TCP
connection remains in the TIME_WAIT state. To account for this, a proxy might
delay increasing the QUIC stream limits for some time after a TCP connection
terminates.
10.6.
Use of Compression
Compression can allow an attacker to recover secret data when it is compressed
in the same context as data under attacker control. HTTP/3 enables compression
of fields (
Section 4.2
); the following concerns also apply to the use
of HTTP compressed content-codings; see
Section 8.4.1
of [
HTTP
There are demonstrable attacks on compression that exploit the characteristics
of the web (e.g.,
BREACH
). The attacker induces multiple requests
containing varying plaintext, observing the length of the resulting ciphertext
in each, which reveals a shorter length when a guess about the secret is
correct.
Implementations communicating on a secure channel
MUST NOT
compress content that
includes both confidential and attacker-controlled data unless separate
compression contexts are used for each source of data. Compression
MUST NOT
be
used if the source of data cannot be reliably determined.
Further considerations regarding the compression of field sections are
described in
QPACK
10.7.
Padding and Traffic Analysis
Padding can be used to obscure the exact size of frame content and is provided
to mitigate specific attacks within HTTP, for example, attacks where compressed
content includes both attacker-controlled plaintext and secret data (e.g.,
BREACH
).
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 Sections
7.2.8
and
6.2.3
. These methods of
padding produce different results in terms of the granularity of padding, how
padding is arranged in relation to the information that is being protected,
whether padding is applied in the case of packet loss, and how an implementation
might control padding.
Reserved stream types can be used to give the appearance of sending traffic even
when the connection is idle. Because HTTP traffic often occurs in bursts,
apparent traffic can be used to obscure the timing or duration of such bursts,
even to the point of appearing to send a constant stream of data. However, as
such traffic is still flow controlled by the receiver, a failure to promptly
drain such streams and provide additional flow-control credit can limit the
sender's ability to send real traffic.
To mitigate attacks that rely on compression, disabling or limiting compression
might be preferable to padding as a countermeasure.
Use of padding can result in less protection than might seem immediately
obvious. Redundant padding could even be counterproductive. At best, padding
only makes it more difficult for an attacker to infer length information by
increasing the number of frames an attacker has to observe. Incorrectly
implemented padding schemes can be easily defeated. In particular, randomized
padding with a predictable distribution provides very little protection;
similarly, padding payloads to a fixed size exposes information as payload sizes
cross the fixed-sized boundary, which could be possible if an attacker can
control plaintext.
10.8.
Frame Parsing
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.
10.9.
Early Data
The use of 0-RTT with HTTP/3 creates an exposure to replay attack. The
anti-replay mitigations in
HTTP-REPLAY
MUST
be applied when using
HTTP/3 with 0-RTT. When applying
HTTP-REPLAY
to HTTP/3, references to the
TLS layer refer to the handshake performed within QUIC, while all references to
application data refer to the contents of streams.
10.10.
Migration
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.
10.11.
Privacy Considerations
Several characteristics of HTTP/3 provide an observer an opportunity to
correlate actions of a single client or server over time. These include the
value of settings, the timing of reactions to stimulus, and the handling of any
features that are controlled by settings.
As far as these create observable differences in behavior, they could be used as
a basis for fingerprinting a specific client.
HTTP/3's preference for using a single QUIC connection allows correlation of a
user's activity on a site. Reusing connections for different origins allows
for correlation of activity across those origins.
Several features of QUIC solicit immediate responses and can be used by an
endpoint to measure latency to their peer; this might have privacy implications
in certain scenarios.
11.
IANA Considerations
This document registers a new ALPN protocol ID (
Section 11.1
) and creates new
registries that manage the assignment of code points in HTTP/3.
11.1.
Registration of HTTP/3 Identification String
This document creates a new registration for the identification of
HTTP/3 in the "TLS Application-Layer Protocol Negotiation (ALPN)
Protocol IDs" registry established in
RFC7301
The "h3" string identifies HTTP/3:
Protocol:
HTTP/3
Identification Sequence:
0x68 0x33 ("h3")
Specification:
This document
11.2.
New Registries
New registries created in this document operate under the QUIC registration
policy documented in
Section 22.1
of [
QUIC-TRANSPORT
. These registries all
include the common set of fields listed in
Section 22.1.1
of [
QUIC-TRANSPORT
These registries are collected under the "Hypertext Transfer Protocol version 3
(HTTP/3)" heading.
The initial allocations in these registries are all assigned permanent status
and list a change controller of the IETF and a contact of the HTTP working group
(ietf-http-wg@w3.org).
11.2.1.
Frame Types
This document establishes a registry for HTTP/3 frame type codes. The "HTTP/3
Frame Types" registry governs a 62-bit space. This registry follows the QUIC
registry policy; see
Section 11.2
. Permanent registrations in this registry
are assigned using the Specification Required policy (
RFC8126
), except for
values between 0x00 and 0x3f (in hexadecimal; inclusive), which are assigned
using Standards Action or IESG Approval as defined in
Sections
4.9
and
4.10
of
RFC8126
While this registry is separate from the "HTTP/2 Frame Type" registry defined in
HTTP/2
, 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. Expert reviewers
MAY
reject unrelated registrations that would
conflict with the same value in the corresponding registry.
In addition to common fields as described in
Section 11.2
, permanent
registrations in this registry
MUST
include the following field:
Frame Type:
A name or label for the frame type.
Specifications of frame types
MUST
include a description of the frame layout and
its semantics, including any parts of the frame that are conditionally present.
The entries in
Table 2
are registered by this document.
Table 2
Initial HTTP/3 Frame Types
Frame Type
Value
Specification
DATA
0x00
Section 7.2.1
HEADERS
0x01
Section 7.2.2
Reserved
0x02
This document
CANCEL_PUSH
0x03
Section 7.2.3
SETTINGS
0x04
Section 7.2.4
PUSH_PROMISE
0x05
Section 7.2.5
Reserved
0x06
This document
GOAWAY
0x07
Section 7.2.6
Reserved
0x08
This document
Reserved
0x09
This document
MAX_PUSH_ID
0x0d
Section 7.2.7
Each code of the format
0x1f * N + 0x21
for non-negative integer values of
(that is, 0x21, 0x40, ..., through 0x3ffffffffffffffe)
MUST NOT
be assigned by
IANA and
MUST NOT
appear in the listing of assigned values.
11.2.2.
Settings Parameters
This document establishes a registry for HTTP/3 settings. The "HTTP/3 Settings"
registry governs a 62-bit space. This registry follows the QUIC registry
policy; see
Section 11.2
. Permanent registrations in this registry are
assigned using the Specification Required policy (
RFC8126
), except for
values between 0x00 and 0x3f (in hexadecimal; inclusive), which are assigned
using Standards Action or IESG Approval as defined in
Sections
4.9
and
4.10
of
RFC8126
While this registry is separate from the "HTTP/2 Settings" registry defined in
HTTP/2
, 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. Expert reviewers
MAY
reject unrelated registrations that would conflict with the same value in
the corresponding registry.
In addition to common fields as described in
Section 11.2
, permanent
registrations in this registry
MUST
include the following fields:
Setting Name:
A symbolic name for the setting. Specifying a setting name is optional.
Default:
The value of the setting unless otherwise indicated. A default
SHOULD
be the
most restrictive possible value.
The entries in
Table 3
are registered by this document.
Table 3
Initial HTTP/3 Settings
Setting Name
Value
Specification
Default
Reserved
0x00
This document
N/A
Reserved
0x02
This document
N/A
Reserved
0x03
This document
N/A
Reserved
0x04
This document
N/A
Reserved
0x05
This document
N/A
MAX_FIELD_SECTION_SIZE
0x06
Section 7.2.4.1
Unlimited
For formatting reasons, setting names can be abbreviated by removing the
'SETTINGS_' prefix.
Each code of the format
0x1f * N + 0x21
for non-negative integer values of
(that is, 0x21, 0x40, ..., through 0x3ffffffffffffffe)
MUST NOT
be assigned by
IANA and
MUST NOT
appear in the listing of assigned values.
11.2.3.
Error Codes
This document establishes a registry for HTTP/3 error codes. The "HTTP/3 Error
Codes" registry manages a 62-bit space. This registry follows the QUIC registry
policy; see
Section 11.2
. Permanent registrations in this registry are
assigned using the Specification Required policy (
RFC8126
), except for
values between 0x00 and 0x3f (in hexadecimal; inclusive), which are assigned
using Standards Action or IESG Approval as defined in
Sections
4.9
and
4.10
of
RFC8126
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. Use of values that are registered in the "HTTP/2
Error Code" registry is discouraged, and expert reviewers
MAY
reject such
registrations.
In addition to common fields as described in
Section 11.2
, this registry
includes two additional fields. Permanent registrations in this registry
MUST
include the following field:
Name:
A name for the error code.
Description:
A brief description of the error code semantics.
The entries in
Table 4
are registered by this document. These
error codes were selected from the range that operates on a Specification
Required policy to avoid collisions with HTTP/2 error codes.
Table 4
Initial HTTP/3 Error Codes
Name
Value
Description
Specification
H3_NO_ERROR
0x0100
No error
Section 8.1
H3_GENERAL_PROTOCOL_ERROR
0x0101
General protocol error
Section 8.1
H3_INTERNAL_ERROR
0x0102
Internal error
Section 8.1
H3_STREAM_CREATION_ERROR
0x0103
Stream creation error
Section 8.1
H3_CLOSED_CRITICAL_STREAM
0x0104
Critical stream was closed
Section 8.1
H3_FRAME_UNEXPECTED
0x0105
Frame not permitted in the current state
Section 8.1
H3_FRAME_ERROR
0x0106
Frame violated layout or size rules
Section 8.1
H3_EXCESSIVE_LOAD
0x0107
Peer generating excessive load
Section 8.1
H3_ID_ERROR
0x0108
An identifier was used incorrectly
Section 8.1
H3_SETTINGS_ERROR
0x0109
SETTINGS
frame contained invalid values
Section 8.1
H3_MISSING_SETTINGS
0x010a
No
SETTINGS
frame received
Section 8.1
H3_REQUEST_REJECTED
0x010b
Request not processed
Section 8.1
H3_REQUEST_CANCELLED
0x010c
Data no longer needed
Section 8.1
H3_REQUEST_INCOMPLETE
0x010d
Stream terminated early
Section 8.1
H3_MESSAGE_ERROR
0x010e
Malformed message
Section 8.1
H3_CONNECT_ERROR
0x010f
TCP reset or error on CONNECT request
Section 8.1
H3_VERSION_FALLBACK
0x0110
Retry over HTTP/1.1
Section 8.1
Each code of the format
0x1f * N + 0x21
for non-negative integer values of
(that is, 0x21, 0x40, ..., through 0x3ffffffffffffffe)
MUST NOT
be assigned by
IANA and
MUST NOT
appear in the listing of assigned values.
11.2.4.
Stream Types
This document establishes a registry for HTTP/3 unidirectional stream types. The
"HTTP/3 Stream Types" registry governs a 62-bit space. This registry follows
the QUIC registry policy; see
Section 11.2
. Permanent registrations in this
registry are assigned using the Specification Required policy (
RFC8126
),
except for values between 0x00 and 0x3f (in hexadecimal; inclusive), which are
assigned using Standards Action or IESG Approval as defined in Sections
4.9
and
4.10
of
RFC8126
In addition to common fields as described in
Section 11.2
, permanent
registrations in this registry
MUST
include the following fields:
Stream Type:
A name or label for the stream type.
Sender:
Which endpoint on an HTTP/3 connection may initiate a stream of this type.
Values are "Client", "Server", or "Both".
Specifications for permanent registrations
MUST
include a description of the
stream type, including the layout and semantics of the stream contents.
The entries in
Table 5
are registered by this document.
Table 5
Initial Stream Types
Stream Type
Value
Specification
Sender
Control Stream
0x00
Section 6.2.1
Both
Push Stream
0x01
Section 4.6
Server
Each code of the format
0x1f * N + 0x21
for non-negative integer values of
(that is, 0x21, 0x40, ..., through 0x3ffffffffffffffe)
MUST NOT
be assigned by
IANA and
MUST NOT
appear in the listing of assigned values.
12.
References
12.1.
Normative References
[ALTSVC]
Nottingham, M.
McManus, P.
, and
J. Reschke
"HTTP Alternative Services"
RFC 7838
DOI 10.17487/RFC7838
April 2016
[COOKIES]
Barth, A.
"HTTP State Management Mechanism"
RFC 6265
DOI 10.17487/RFC6265
April 2011
[HTTP]
Fielding, R., Ed.
Nottingham, M., Ed.
, and
J. Reschke, Ed.
"HTTP Semantics"
STD 97
RFC 9110
DOI 10.17487/RFC9110
June 2022
[HTTP-CACHING]
Fielding, R., Ed.
Nottingham, M., Ed.
, and
J. Reschke, Ed.
"HTTP Caching"
STD 98
RFC 9111
DOI 10.17487/RFC9111
June 2022
[HTTP-REPLAY]
Thomson, M.
Nottingham, M.
, and
W. Tarreau
"Using Early Data in HTTP"
RFC 8470
DOI 10.17487/RFC8470
September 2018
[QPACK]
Krasic, C.
Bishop, M.
, and
A. Frindell, Ed.
"QPACK: Field Compression for HTTP/3"
RFC 9204
DOI 10.17487/RFC9204
June 2022
[QUIC-TRANSPORT]
Iyengar, J., Ed.
and
M. Thomson, Ed.
"QUIC: A UDP-Based Multiplexed and Secure Transport"
RFC 9000
DOI 10.17487/RFC9000
May 2021
[RFC0793]
Postel, J.
"Transmission Control Protocol"
STD 7
RFC 793
DOI 10.17487/RFC0793
September 1981
[RFC2119]
Bradner, S.
"Key words for use in RFCs to Indicate Requirement Levels"
BCP 14
RFC 2119
DOI 10.17487/RFC2119
March 1997
[RFC6066]
Eastlake 3rd, D.
"Transport Layer Security (TLS) Extensions: Extension Definitions"
RFC 6066
DOI 10.17487/RFC6066
January 2011
[RFC7301]
Friedl, S.
Popov, A.
Langley, A.
, and
E. Stephan
"Transport Layer Security (TLS) Application-Layer Protocol Negotiation Extension"
RFC 7301
DOI 10.17487/RFC7301
July 2014
[RFC8126]
Cotton, M.
Leiba, B.
, and
T. Narten
"Guidelines for Writing an IANA Considerations Section in RFCs"
BCP 26
RFC 8126
DOI 10.17487/RFC8126
June 2017
[RFC8174]
Leiba, B.
"Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words"
BCP 14
RFC 8174
DOI 10.17487/RFC8174
May 2017
[URI]
Berners-Lee, T.
Fielding, R.
, and
L. Masinter
"Uniform Resource Identifier (URI): Generic Syntax"
STD 66
RFC 3986
DOI 10.17487/RFC3986
January 2005
12.2.
Informative References
[BREACH]
Gluck, Y.
Harris, N.
, and
A. Prado
"BREACH: Reviving the CRIME Attack"
July 2013
[DNS-TERMS]
Hoffman, P.
Sullivan, A.
, and
K. Fujiwara
"DNS Terminology"
BCP 219
RFC 8499
DOI 10.17487/RFC8499
January 2019
[HPACK]
Peon, R.
and
H. Ruellan
"HPACK: Header Compression for HTTP/2"
RFC 7541
DOI 10.17487/RFC7541
May 2015
[HTTP/1.1]
Fielding, R., Ed.
Nottingham, M., Ed.
, and
J. Reschke, Ed.
"HTTP/1.1"
STD 99
RFC 9112
DOI 10.17487/RFC9112
June 2022
[HTTP/2]
Thomson, M., Ed.
and
C. Benfield, Ed.
"HTTP/2"
RFC 9113
DOI 10.17487/RFC9113
June 2022
[RFC6585]
Nottingham, M.
and
R. Fielding
"Additional HTTP Status Codes"
RFC 6585
DOI 10.17487/RFC6585
April 2012
[RFC8164]
Nottingham, M.
and
M. Thomson
"Opportunistic Security for HTTP/2"
RFC 8164
DOI 10.17487/RFC8164
May 2017
[TFO]
Cheng, Y.
Chu, J.
Radhakrishnan, S.
, and
A. Jain
"TCP Fast Open"
RFC 7413
DOI 10.17487/RFC7413
December 2014
[TLS]
Rescorla, E.
"The Transport Layer Security (TLS) Protocol Version 1.3"
RFC 8446
DOI 10.17487/RFC8446
August 2018
Appendix A.
Considerations for Transitioning from HTTP/2
HTTP/3 is strongly informed by HTTP/2, and it 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). While HTTP/3 is
similar to HTTP/2 in key aspects, such as the relationship of requests and
responses to streams, the details of the HTTP/3 design are substantially
different from HTTP/2.
Some important departures are noted in this section.
A.1.
Streams
HTTP/3 permits use of a larger number of streams (2
62
-1) than HTTP/2.
The same 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.
In contrast to HTTP/2, stream concurrency in HTTP/3 is managed by QUIC. QUIC
considers a stream closed when all data has been received and sent data has been
acknowledged by the peer. HTTP/2 considers a stream closed when the frame
containing the END_STREAM bit has been committed to the transport. As a result,
the stream for an equivalent exchange could remain "active" for a longer period
of time. HTTP/3 servers might choose to permit a larger number of concurrent
client-initiated bidirectional streams to achieve equivalent concurrency to
HTTP/2, depending on the expected usage patterns.
In HTTP/2, only request and response bodies (the frame payload of
DATA
frames)
are subject to flow control. All HTTP/3 frames are sent on QUIC streams, so all
frames on all streams are flow controlled in HTTP/3.
Due to the presence of other unidirectional stream types, HTTP/3 does not rely
exclusively on the number of concurrent unidirectional streams to control the
number of concurrent in-flight pushes. Instead, HTTP/3 clients use the
MAX_PUSH_ID
frame to control the number of pushes received from an HTTP/3
server.
A.2.
HTTP Frame Types
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
HTTP/2
. However, QUIC includes many
features (e.g., flow control) that 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 frame types that appear in
both mappings do not have identical semantics.
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.
A.2.1.
Prioritization Differences
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.
A.2.2.
Field Compression Differences
HPACK was designed with the assumption of in-order delivery. A sequence of
encoded field sections 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 that contain encoded fields merely reference the table state at a
given time without modifying it.
QPACK
provides additional details.
A.2.3.
Flow-Control Differences
HTTP/2 specifies a stream flow-control mechanism. Although all HTTP/2 frames are
delivered on streams, only the
DATA
frame payload is subject to flow control.
QUIC provides flow control for stream data and all HTTP/3 frame types defined in
this document are sent on streams. Therefore, all frame headers and payload are
subject to flow control.
A.2.4.
Guidance for New Frame Type Definitions
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 other 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
that depend on the presence of flags need to allocate space for flags as part
of their frame payload.
Other than these issues, 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 are expected to be portable to HTTP/2.
A.2.5.
Comparison of HTTP/2 and HTTP/3 Frame Types
DATA
(0x00)
Padding is not defined in HTTP/3 frames. See
Section 7.2.1
HEADERS
(0x01)
The PRIORITY region of
HEADERS
is not defined in HTTP/3 frames. Padding is not
defined in HTTP/3 frames. See
Section 7.2.2
PRIORITY (0x02):
As described in
Appendix A.2.1
, HTTP/3 does not provide a means of
signaling priority.
RST_STREAM (0x03):
RST_STREAM frames do not exist in HTTP/3, since QUIC provides stream lifecycle
management. The same code point is used for the
CANCEL_PUSH
frame
Section 7.2.3
).
SETTINGS
(0x04)
SETTINGS
frames are sent only at the beginning of the connection. See
Section 7.2.4
and
Appendix A.3
PUSH_PROMISE
(0x05)
The
PUSH_PROMISE
frame does not reference a stream; instead, the
push stream
references the
PUSH_PROMISE
frame using a
push ID
. See
Section 7.2.5
PING (0x06):
PING frames do not exist in HTTP/3, as QUIC provides equivalent
functionality.
GOAWAY
(0x07)
GOAWAY
does not contain an error code. In the client-to-server direction,
it carries a
push ID
instead of a server-initiated stream ID.
See
Section 7.2.6
WINDOW_UPDATE (0x08):
WINDOW_UPDATE frames do not exist in HTTP/3, since QUIC provides flow control.
CONTINUATION (0x09):
CONTINUATION frames do not exist in HTTP/3; 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
HTTP/2
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
Section 11.2.1
A.3.
HTTP/2 SETTINGS Parameters
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 setting that
is retained in HTTP/3 has the same value as in HTTP/2. The superseded
settings are reserved, and their receipt is an error. See
Section 7.2.4.1
for discussion of both the retained and reserved values.
Below is a listing of how each HTTP/2
SETTINGS
parameter is mapped:
SETTINGS_HEADER_TABLE_SIZE (0x01):
See
QPACK
SETTINGS_ENABLE_PUSH (0x02):
This is removed in favor of the
MAX_PUSH_ID
frame, which provides a more
granular control over server push. Specifying a setting with the identifier
0x02 (corresponding to the SETTINGS_ENABLE_PUSH parameter) in the HTTP/3
SETTINGS
frame is an error.
SETTINGS_MAX_CONCURRENT_STREAMS (0x03):
QUIC controls the largest open stream ID as part of its flow-control logic.
Specifying a setting with the identifier 0x03 (corresponding to the
SETTINGS_MAX_CONCURRENT_STREAMS parameter) in the HTTP/3
SETTINGS
frame is an
error.
SETTINGS_INITIAL_WINDOW_SIZE (0x04):
QUIC requires both stream and connection flow-control window sizes to be
specified in the initial transport handshake. Specifying a setting with the
identifier 0x04 (corresponding to the SETTINGS_INITIAL_WINDOW_SIZE parameter)
in the HTTP/3
SETTINGS
frame is an error.
SETTINGS_MAX_FRAME_SIZE (0x05):
This setting has no equivalent in HTTP/3. Specifying a setting with the
identifier 0x05 (corresponding to the SETTINGS_MAX_FRAME_SIZE parameter) in
the HTTP/3
SETTINGS
frame is an error.
SETTINGS_MAX_HEADER_LIST_SIZE (0x06):
This setting identifier has been renamed
SETTINGS_MAX_FIELD_SECTION_SIZE
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 that
use the full 32-bit space. Settings ported from HTTP/2 might choose to redefine
their value to limit it to 30 bits for more efficient encoding or to make use
of the 62-bit space if more than 30 bits are required.
Settings need to be defined separately for HTTP/2 and HTTP/3. The IDs of
settings defined in
HTTP/2
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
Section 11.2.2
As QUIC streams might arrive out of order, endpoints are advised not to wait for
the peers' settings to arrive before responding to other streams. See
Section 7.2.4.2
A.4.
HTTP/2 Error Codes
QUIC has the same concepts of "stream" and "connection" errors that HTTP/2
provides. However, the differences between HTTP/2 and HTTP/3 mean that error
codes are not directly portable between versions.
The HTTP/2 error codes defined in
Section 7
of [
HTTP/2
logically map to
the HTTP/3 error codes as follows:
NO_ERROR (0x00):
H3_NO_ERROR
in
Section 8.1
PROTOCOL_ERROR (0x01):
This is mapped to
H3_GENERAL_PROTOCOL_ERROR
except in cases where more
specific error codes have been defined. Such cases include
H3_FRAME_UNEXPECTED
H3_MESSAGE_ERROR
, and
H3_CLOSED_CRITICAL_STREAM
defined
in
Section 8.1
INTERNAL_ERROR (0x02):
H3_INTERNAL_ERROR
in
Section 8.1
FLOW_CONTROL_ERROR (0x03):
Not applicable, since QUIC handles flow control.
SETTINGS_TIMEOUT (0x04):
Not applicable, since no acknowledgment of
SETTINGS
is defined.
STREAM_CLOSED (0x05):
Not applicable, since QUIC handles stream management.
FRAME_SIZE_ERROR (0x06):
H3_FRAME_ERROR
error code defined in
Section 8.1
REFUSED_STREAM (0x07):
H3_REQUEST_REJECTED
(in
Section 8.1
) is used to indicate that a
request was not processed. Otherwise, not applicable because QUIC handles
stream management.
CANCEL (0x08):
H3_REQUEST_CANCELLED
in
Section 8.1
COMPRESSION_ERROR (0x09):
Multiple error codes are defined in
QPACK
CONNECT_ERROR (0x0a):
H3_CONNECT_ERROR
in
Section 8.1
ENHANCE_YOUR_CALM (0x0b):
H3_EXCESSIVE_LOAD
in
Section 8.1
INADEQUATE_SECURITY (0x0c):
Not applicable, since QUIC is assumed to provide sufficient security on all
connections.
HTTP_1_1_REQUIRED (0x0d):
H3_VERSION_FALLBACK
in
Section 8.1
Error codes need to be defined for HTTP/2 and HTTP/3 separately. See
Section 11.2.3
A.4.1.
Mapping between HTTP/2 and HTTP/3 Errors
An intermediary that converts between HTTP/2 and HTTP/3 may encounter error
conditions from either upstream. It is useful to communicate the occurrence of
errors to the downstream, but error codes largely reflect connection-local
problems that generally do not make sense to propagate.
An intermediary that encounters an error from an upstream origin can indicate
this by sending an HTTP status code such as 502 (Bad Gateway), which is suitable
for a broad class of errors.
There are some rare cases where it is beneficial to propagate the error by
mapping it to the closest matching error type to the receiver. For example, an
intermediary that receives an HTTP/2
stream error
of type REFUSED_STREAM from
the origin has a clear signal that the request was not processed and that the
request is safe to retry. Propagating this error condition to the client as an
HTTP/3
stream error
of type
H3_REQUEST_REJECTED
allows the client to take the
action it deems most appropriate. In the reverse direction, the intermediary
might deem it beneficial to pass on client request cancellations that are
indicated by terminating a stream with
H3_REQUEST_CANCELLED
; see
Section 4.1.1
Conversion between errors is described in the logical mapping. The error codes
are defined in non-overlapping spaces in order to protect against accidental
conversion that could result in the use of inappropriate or unknown error codes
for the target version. An intermediary is permitted to promote
stream errors
to
connection errors
but they should be aware of the cost to the HTTP/3 connection
for what might be a temporary or intermittent error.
Acknowledgments
Robbie Shade
and
Mike Warres
were the authors of
draft-shade-quic-http2-mapping, a precursor of this document.
The IETF QUIC Working Group received an enormous amount of support from many
people. Among others, the following people provided substantial contributions to
this document:
Bence Beky
Daan De Meyer
Martin Duke
Roy Fielding
Alan Frindell
Alessandro Ghedini
Nick Harper
Ryan Hamilton
Christian Huitema
Subodh Iyengar
Robin Marx
Patrick McManus
Luca Niccolini
奥 一穂
Kazuho Oku
Lucas Pardue
Roberto Peon
Julian Reschke
Eric Rescorla
Martin Seemann
Ben Schwartz
Ian Swett
Willy Taureau
Martin Thomson
Dmitri Tikhonov
Tatsuhiro Tsujikawa
A portion of
Mike Bishop
's contribution was supported by Microsoft during
his employment there.
Index
CANCEL_PUSH
Section 2, Paragraph 5
Section 4.6, Paragraph 6
Section 4.6, Paragraph 10
Table 1
Section 7.2.3
Section 7.2.5, Paragraph 4.2.1
Section 7.2.7, Paragraph 1
Table 2
Appendix A.2.5, Paragraph 1.8.1
connection error
Section 2.2
Section 4.1, Paragraph 7
Section 4.1, Paragraph 8
Section 4.4, Paragraph 8
Section 4.4, Paragraph 10
Section 4.6, Paragraph 3
Section 5.2, Paragraph 7
Section 6.1, Paragraph 3
Section 6.2, Paragraph 7
Section 6.2.1, Paragraph 2
Section 6.2.1, Paragraph 2
Section 6.2.1, Paragraph 2
Section 6.2.2, Paragraph 3
Section 6.2.2, Paragraph 6
Section 7.1, Paragraph 5
Section 7.1, Paragraph 6
Section 7.2.1, Paragraph 2
Section 7.2.2, Paragraph 3
Section 7.2.3, Paragraph 5
Section 7.2.3, Paragraph 7
Section 7.2.3, Paragraph 8
Section 7.2.4, Paragraph 2
Section 7.2.4, Paragraph 3
Section 7.2.4, Paragraph 6
Section 7.2.4.1, Paragraph 5
Section 7.2.4.2, Paragraph 8
Section 7.2.4.2, Paragraph 8
Section 7.2.5, Paragraph 5
Section 7.2.5, Paragraph 6
Section 7.2.5, Paragraph 8
Section 7.2.5, Paragraph 9
Section 7.2.6, Paragraph 3
Section 7.2.6, Paragraph 5
Section 7.2.7, Paragraph 2
Section 7.2.7, Paragraph 3
Section 7.2.7, Paragraph 6
Section 7.2.8, Paragraph 3
Section 8
Section 10.5, Paragraph 7
Appendix A.4.1, Paragraph 4
control stream
Section 2, Paragraph 3
Section 3.2, Paragraph 4
Section 6.2, Paragraph 3
Section 6.2, Paragraph 5
Section 6.2, Paragraph 6
Section 6.2.1
Section 7, Paragraph 1
Section 7.2.1, Paragraph 2
Section 7.2.2, Paragraph 3
Section 7.2.3, Paragraph 5
Section 7.2.3, Paragraph 5
Section 7.2.4, Paragraph 2
Section 7.2.4, Paragraph 2
Section 7.2.4, Paragraph 3
Section 7.2.5, Paragraph 8
Section 7.2.6, Paragraph 3
Section 7.2.6, Paragraph 5
Section 7.2.7, Paragraph 2
Section 8.1, Paragraph 2.22.1
Section 9, Paragraph 4
Appendix A.2.4, Paragraph 3
Appendix A.3, Paragraph 1
DATA
Section 2, Paragraph 3
Section 4.1, Paragraph 5, Item 2
Section 4.1, Paragraph 7
Section 4.1, Paragraph 7
Section 4.1.2, Paragraph 3
Section 4.1.2, Paragraph 3
Section 4.4, Paragraph 7
Section 4.4, Paragraph 7
Section 4.4, Paragraph 7
Section 4.4, Paragraph 7
Section 4.4, Paragraph 8
Section 4.6, Paragraph 12
Table 1
Section 7.2.1
Table 2
Appendix A.1, Paragraph 3
Appendix A.2.3, Paragraph 1
Appendix A.2.5
GOAWAY
Section 3.3, Paragraph 5
Section 5.2, Paragraph 1
Section 5.2, Paragraph 1
Section 5.2, Paragraph 1
Section 5.2, Paragraph 2
Section 5.2, Paragraph 2
Section 5.2, Paragraph 3
Section 5.2, Paragraph 5.1.1
Section 5.2, Paragraph 5.1.1
Section 5.2, Paragraph 5.1.2
Section 5.2, Paragraph 5.1.2
Section 5.2, Paragraph 5, Item 2
Section 5.2, Paragraph 5, Item 2
Section 5.2, Paragraph 6
Section 5.2, Paragraph 6
Section 5.2, Paragraph 7
Section 5.2, Paragraph 7
Section 5.2, Paragraph 8
Section 5.2, Paragraph 8
Section 5.2, Paragraph 9
Section 5.2, Paragraph 9
Section 5.2, Paragraph 10
Section 5.2, Paragraph 12
Section 5.3, Paragraph 2
Section 5.3, Paragraph 2
Section 5.4, Paragraph 2
Table 1
Section 7.2.6
Table 2
Appendix A.2.5
Appendix A.2.5, Paragraph 1.16.1
H3_CLOSED_CRITICAL_STREAM
Section 6.2.1, Paragraph 2
Section 8.1
Table 4
Appendix A.4, Paragraph 3.4.1
H3_CONNECT_ERROR
Section 4.4, Paragraph 10
Section 8.1
Table 4
Appendix A.4, Paragraph 3.22.1
H3_EXCESSIVE_LOAD
Section 8.1
Section 10.5, Paragraph 7
Table 4
Appendix A.4, Paragraph 3.24.1
H3_FRAME_ERROR
Section 7.1, Paragraph 5
Section 7.1, Paragraph 6
Section 8.1
Table 4
Appendix A.4, Paragraph 3.14.1
H3_FRAME_UNEXPECTED
Section 4.1, Paragraph 7
Section 4.1, Paragraph 8
Section 4.4, Paragraph 8
Section 7.2.1, Paragraph 2
Section 7.2.2, Paragraph 3
Section 7.2.3, Paragraph 5
Section 7.2.4, Paragraph 2
Section 7.2.4, Paragraph 3
Section 7.2.5, Paragraph 8
Section 7.2.5, Paragraph 9
Section 7.2.6, Paragraph 5
Section 7.2.7, Paragraph 2
Section 7.2.7, Paragraph 3
Section 7.2.8, Paragraph 3
Section 8.1
Table 4
Appendix A.4, Paragraph 3.4.1
H3_GENERAL_PROTOCOL_ERROR
Section 7.2.5, Paragraph 6
Section 8.1
Table 4
Appendix A.4, Paragraph 3.4.1
H3_ID_ERROR
Section 4.6, Paragraph 3
Section 5.2, Paragraph 7
Section 6.2.2, Paragraph 6
Section 7.2.3, Paragraph 7
Section 7.2.3, Paragraph 8
Section 7.2.5, Paragraph 5
Section 7.2.6, Paragraph 3
Section 7.2.7, Paragraph 6
Section 8.1
Table 4
H3_INTERNAL_ERROR
Section 8.1
Table 4
Appendix A.4, Paragraph 3.6.1
H3_MESSAGE_ERROR
Section 4.1.2, Paragraph 4
Section 8.1
Table 4
Appendix A.4, Paragraph 3.4.1
H3_MISSING_SETTINGS
Section 6.2.1, Paragraph 2
Section 8.1
Table 4
H3_NO_ERROR
Section 4.1, Paragraph 15
Section 5.2, Paragraph 11
Section 6.2.3, Paragraph 2
Section 8, Paragraph 5
Section 8.1
Section 8.1, Paragraph 3
Section 8.1, Paragraph 3
Table 4
Appendix A.4, Paragraph 3.2.1
H3_REQUEST_CANCELLED
Section 4.1.1, Paragraph 4
Section 4.1.1, Paragraph 5
Section 4.6, Paragraph 14
Section 7.2.3, Paragraph 3
Section 7.2.3, Paragraph 4
Section 8.1
Table 4
Appendix A.4, Paragraph 3.18.1
Appendix A.4.1, Paragraph 3
H3_REQUEST_INCOMPLETE
Section 4.1, Paragraph 14
Section 8.1
Table 4
H3_REQUEST_REJECTED
Section 4.1.1, Paragraph 3
Section 4.1.1, Paragraph 4
Section 4.1.1, Paragraph 5
Section 4.1.1, Paragraph 5
Section 8.1
Table 4
Appendix A.4, Paragraph 3.16.1
Appendix A.4.1, Paragraph 3
H3_SETTINGS_ERROR
Section 7.2.4, Paragraph 6
Section 7.2.4.1, Paragraph 5
Section 7.2.4.2, Paragraph 8
Section 7.2.4.2, Paragraph 8
Section 8.1
Table 4
H3_STREAM_CREATION_ERROR
Section 6.1, Paragraph 3
Section 6.2, Paragraph 7
Section 6.2.1, Paragraph 2
Section 6.2.2, Paragraph 3
Section 8.1
Table 4
H3_VERSION_FALLBACK
Section 8.1
Table 4
Appendix A.4, Paragraph 3.28.1
HEADERS
Section 2, Paragraph 3
Section 4.1, Paragraph 5, Item 1
Section 4.1, Paragraph 5, Item 3
Section 4.1, Paragraph 7
Section 4.1, Paragraph 7
Section 4.1, Paragraph 7
Section 4.1, Paragraph 10
Section 4.4, Paragraph 6
Section 4.6, Paragraph 12
Table 1
Section 7.2.2
Section 9, Paragraph 5
Table 2
Appendix A.2.1, Paragraph 1
Appendix A.2.5
Appendix A.2.5, Paragraph 1.4.1
Appendix A.2.5, Paragraph 1.20.1
malformed
Section 4.1, Paragraph 3
Section 4.1.2
Section 4.2, Paragraph 2
Section 4.2, Paragraph 3
Section 4.2, Paragraph 5
Section 4.3, Paragraph 3
Section 4.3, Paragraph 4
Section 4.3.1, Paragraph 5
Section 4.3.2, Paragraph 1
Section 4.4, Paragraph 5
Section 8.1, Paragraph 2.30.1
Section 10.3, Paragraph 1
Section 10.3, Paragraph 2
Section 10.5.1, Paragraph 2
MAX_PUSH_ID
Section 2, Paragraph 5
Section 4.6, Paragraph 3
Section 4.6, Paragraph 3
Section 4.6, Paragraph 3
Section 4.6, Paragraph 3
Table 1
Section 7.2.5, Paragraph 5
Section 7.2.7
Table 2
Appendix A.1, Paragraph 4
Appendix A.3, Paragraph 4.4.1
push ID
Section 4.6
Section 5.2, Paragraph 1
Section 5.2, Paragraph 5, Item 2
Section 5.2, Paragraph 9
Section 6.2.2, Paragraph 2
Section 6.2.2, Paragraph 6
Section 6.2.2, Paragraph 6
Section 7.2.3, Paragraph 1
Section 7.2.3, Paragraph 7
Section 7.2.3, Paragraph 7
Section 7.2.3, Paragraph 8
Section 7.2.3, Paragraph 8
Section 7.2.5, Paragraph 4.2.1
Section 7.2.5, Paragraph 5
Section 7.2.5, Paragraph 5
Section 7.2.5, Paragraph 6
Section 7.2.5, Paragraph 6
Section 7.2.5, Paragraph 7
Section 7.2.5, Paragraph 7
Section 7.2.5, Paragraph 7
Section 7.2.6, Paragraph 4
Section 7.2.7, Paragraph 1
Section 7.2.7, Paragraph 4
Section 7.2.7, Paragraph 4
Section 7.2.7, Paragraph 6
Section 7.2.7, Paragraph 6
Section 8.1, Paragraph 2.18.1
Appendix A.2.5, Paragraph 1.12.1
Appendix A.2.5, Paragraph 1.16.1
push stream
Section 4.1, Paragraph 8
Section 4.1, Paragraph 9
Section 4.6, Paragraph 3
Section 4.6, Paragraph 5
Section 4.6, Paragraph 5
Section 4.6, Paragraph 13
Section 4.6, Paragraph 13
Section 4.6, Paragraph 13
Section 6.2, Paragraph 3
Section 6.2.2
Section 7, Paragraph 1
Section 7.2.2, Paragraph 3
Section 7.2.3, Paragraph 1
Section 7.2.3, Paragraph 2
Section 7.2.3, Paragraph 2
Section 7.2.3, Paragraph 2
Section 7.2.3, Paragraph 2
Section 7.2.3, Paragraph 3
Section 7.2.3, Paragraph 4
Section 7.2.3, Paragraph 4
Section 7.2.3, Paragraph 4
Section 7.2.5, Paragraph 4.2.1
Section 7.2.7, Paragraph 1
Appendix A.2.5, Paragraph 1.12.1
PUSH_PROMISE
Section 2, Paragraph 5
Section 4.1, Paragraph 8
Section 4.1, Paragraph 8
Section 4.1, Paragraph 8
Section 4.1, Paragraph 8
Section 4.1, Paragraph 10
Section 4.6, Paragraph 4
Section 4.6, Paragraph 10
Section 4.6, Paragraph 11
Section 4.6, Paragraph 11
Section 4.6, Paragraph 12
Section 4.6, Paragraph 12
Section 4.6, Paragraph 13
Section 4.6, Paragraph 13
Section 4.6, Paragraph 13
Table 1
Section 7.2.3, Paragraph 8
Section 7.2.3, Paragraph 8
Section 7.2.5
Section 7.2.7, Paragraph 1
Section 10.4, Paragraph 1
Section 10.5, Paragraph 2
Table 2
Appendix A.2.5
Appendix A.2.5, Paragraph 1.12.1
Appendix A.2.5, Paragraph 1.12.1
Appendix A.2.5, Paragraph 1.20.1
request stream
Section 4.1, Paragraph 1
Section 4.1, Paragraph 15
Section 4.1, Paragraph 15
Section 4.1.1, Paragraph 1
Section 4.1.1, Paragraph 5
Section 4.4, Paragraph 5
Section 4.4, Paragraph 9
Section 4.6, Paragraph 4
Section 4.6, Paragraph 4
Section 4.6, Paragraph 11
Section 4.6, Paragraph 11
Section 6.1
Section 7, Paragraph 1
Section 7.2.2, Paragraph 3
Section 7.2.5, Paragraph 1
SETTINGS
Section 3.2, Paragraph 4
Section 3.2, Paragraph 4
Section 6.2.1, Paragraph 2
Table 1
Section 7, Paragraph 3
Section 7.2.4
Section 8.1, Paragraph 2.20.1
Section 8.1, Paragraph 2.22.1
Section 9, Paragraph 4
Section 10.5, Paragraph 4
Table 2
Table 4
Table 4
Appendix A.2.5
Appendix A.2.5, Paragraph 1.10.1
Appendix A.3, Paragraph 2
Appendix A.3, Paragraph 3
Appendix A.3, Paragraph 4.4.1
Appendix A.3, Paragraph 4.6.1
Appendix A.3, Paragraph 4.8.1
Appendix A.3, Paragraph 4.10.1
Appendix A.4, Paragraph 3.10.1
SETTINGS_MAX_FIELD_SECTION_SIZE
Section 4.2.2, Paragraph 2
Section 7.2.4.1
Section 10.5.1, Paragraph 2
Appendix A.3, Paragraph 4.12.1
stream error
Section 2.2
Section 4.1.2, Paragraph 4
Section 4.4, Paragraph 10
Section 8
Appendix A.4.1, Paragraph 3
Appendix A.4.1, Paragraph 3
Appendix A.4.1, Paragraph 4
Author's Address
Mike Bishop (
editor
Akamai
Email:
mbishop@evequefou.be