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QUIC M. Bishop, Ed.
Internet-Draft Akamai
Intended status: Standards Track 22 January 2020
Expires: 25 July 2020
Hypertext Transfer Protocol Version 3 (HTTP/3)
draft-ietf-quic-http-25
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.
Note to Readers
Discussion of this draft takes place on the QUIC working group
mailing list (quic@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/search/?email_list=quic
(https://mailarchive.ietf.org/arch/search/?email_list=quic).
Working Group information can be found at https://github.com/quicwg
(https://github.com/quicwg); source code and issues list for this
draft can be found at https://github.com/quicwg/base-drafts/labels/-
http (https://github.com/quicwg/base-drafts/labels/-http).
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 25 July 2020.
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Copyright Notice
Copyright (c) 2020 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 (https://trustee.ietf.org/
license-info) 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 Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Prior versions of HTTP . . . . . . . . . . . . . . . . . 4
1.2. Delegation to QUIC . . . . . . . . . . . . . . . . . . . 5
2. HTTP/3 Protocol Overview . . . . . . . . . . . . . . . . . . 5
2.1. Document Organization . . . . . . . . . . . . . . . . . . 6
2.2. Conventions and Terminology . . . . . . . . . . . . . . . 7
3. Connection Setup and Management . . . . . . . . . . . . . . . 8
3.1. Draft Version Identification . . . . . . . . . . . . . . 8
3.2. Discovering an HTTP/3 Endpoint . . . . . . . . . . . . . 8
3.3. Connection Establishment . . . . . . . . . . . . . . . . 9
3.4. Connection Reuse . . . . . . . . . . . . . . . . . . . . 9
4. HTTP Request Lifecycle . . . . . . . . . . . . . . . . . . . 10
4.1. HTTP Message Exchanges . . . . . . . . . . . . . . . . . 10
4.1.1. Header Formatting and Compression . . . . . . . . . . 12
4.1.2. Request Cancellation and Rejection . . . . . . . . . 13
4.1.3. Malformed Requests and Responses . . . . . . . . . . 14
4.2. The CONNECT Method . . . . . . . . . . . . . . . . . . . 14
4.3. HTTP Upgrade . . . . . . . . . . . . . . . . . . . . . . 15
4.4. Server Push . . . . . . . . . . . . . . . . . . . . . . . 15
5. Connection Closure . . . . . . . . . . . . . . . . . . . . . 17
5.1. Idle Connections . . . . . . . . . . . . . . . . . . . . 17
5.2. Connection Shutdown . . . . . . . . . . . . . . . . . . . 17
5.3. Immediate Application Closure . . . . . . . . . . . . . . 19
5.4. Transport Closure . . . . . . . . . . . . . . . . . . . . 19
6. Stream Mapping and Usage . . . . . . . . . . . . . . . . . . 19
6.1. Bidirectional Streams . . . . . . . . . . . . . . . . . . 20
6.2. Unidirectional Streams . . . . . . . . . . . . . . . . . 20
6.2.1. Control Streams . . . . . . . . . . . . . . . . . . . 22
6.2.2. Push Streams . . . . . . . . . . . . . . . . . . . . 22
6.2.3. Reserved Stream Types . . . . . . . . . . . . . . . . 23
7. HTTP Framing Layer . . . . . . . . . . . . . . . . . . . . . 23
7.1. Frame Layout . . . . . . . . . . . . . . . . . . . . . . 24
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7.2. Frame Definitions . . . . . . . . . . . . . . . . . . . . 25
7.2.1. DATA . . . . . . . . . . . . . . . . . . . . . . . . 25
7.2.2. HEADERS . . . . . . . . . . . . . . . . . . . . . . . 26
7.2.3. CANCEL_PUSH . . . . . . . . . . . . . . . . . . . . . 26
7.2.4. SETTINGS . . . . . . . . . . . . . . . . . . . . . . 27
7.2.5. PUSH_PROMISE . . . . . . . . . . . . . . . . . . . . 30
7.2.6. GOAWAY . . . . . . . . . . . . . . . . . . . . . . . 31
7.2.7. MAX_PUSH_ID . . . . . . . . . . . . . . . . . . . . . 32
7.2.8. DUPLICATE_PUSH . . . . . . . . . . . . . . . . . . . 32
7.2.9. Reserved Frame Types . . . . . . . . . . . . . . . . 33
8. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 34
8.1. HTTP/3 Error Codes . . . . . . . . . . . . . . . . . . . 34
9. Extensions to HTTP/3 . . . . . . . . . . . . . . . . . . . . 35
10. Security Considerations . . . . . . . . . . . . . . . . . . . 36
10.1. Traffic Analysis . . . . . . . . . . . . . . . . . . . . 37
10.2. Frame Parsing . . . . . . . . . . . . . . . . . . . . . 37
10.3. Early Data . . . . . . . . . . . . . . . . . . . . . . . 37
10.4. Migration . . . . . . . . . . . . . . . . . . . . . . . 37
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37
11.1. Registration of HTTP/3 Identification String . . . . . . 37
11.2. New Registries . . . . . . . . . . . . . . . . . . . . . 38
11.2.1. Frame Types . . . . . . . . . . . . . . . . . . . . 38
11.2.2. Settings Parameters . . . . . . . . . . . . . . . . 39
11.2.3. Error Codes . . . . . . . . . . . . . . . . . . . . 40
11.2.4. Stream Types . . . . . . . . . . . . . . . . . . . . 43
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 43
12.1. Normative References . . . . . . . . . . . . . . . . . . 43
12.2. Informative References . . . . . . . . . . . . . . . . . 45
Appendix A. Considerations for Transitioning from HTTP/2 . . . . 46
A.1. Streams . . . . . . . . . . . . . . . . . . . . . . . . . 46
A.2. HTTP Frame Types . . . . . . . . . . . . . . . . . . . . 47
A.2.1. Prioritization Differences . . . . . . . . . . . . . 47
A.2.2. Header Compression Differences . . . . . . . . . . . 47
A.2.3. Guidance for New Frame Type Definitions . . . . . . . 48
A.2.4. Mapping Between HTTP/2 and HTTP/3 Frame Types . . . . 48
A.3. HTTP/2 SETTINGS Parameters . . . . . . . . . . . . . . . 49
A.4. HTTP/2 Error Codes . . . . . . . . . . . . . . . . . . . 50
Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 51
B.1. Since draft-ietf-quic-http-24 . . . . . . . . . . . . . . 51
B.2. Since draft-ietf-quic-http-23 . . . . . . . . . . . . . . 51
B.3. Since draft-ietf-quic-http-22 . . . . . . . . . . . . . . 52
B.4. Since draft-ietf-quic-http-21 . . . . . . . . . . . . . . 53
B.5. Since draft-ietf-quic-http-20 . . . . . . . . . . . . . . 53
B.6. Since draft-ietf-quic-http-19 . . . . . . . . . . . . . . 54
B.7. Since draft-ietf-quic-http-18 . . . . . . . . . . . . . . 54
B.8. Since draft-ietf-quic-http-17 . . . . . . . . . . . . . . 54
B.9. Since draft-ietf-quic-http-16 . . . . . . . . . . . . . . 54
B.10. Since draft-ietf-quic-http-15 . . . . . . . . . . . . . . 55
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B.11. Since draft-ietf-quic-http-14 . . . . . . . . . . . . . . 55
B.12. Since draft-ietf-quic-http-13 . . . . . . . . . . . . . . 55
B.13. Since draft-ietf-quic-http-12 . . . . . . . . . . . . . . 55
B.14. Since draft-ietf-quic-http-11 . . . . . . . . . . . . . . 56
B.15. Since draft-ietf-quic-http-10 . . . . . . . . . . . . . . 56
B.16. Since draft-ietf-quic-http-09 . . . . . . . . . . . . . . 56
B.17. Since draft-ietf-quic-http-08 . . . . . . . . . . . . . . 56
B.18. Since draft-ietf-quic-http-07 . . . . . . . . . . . . . . 56
B.19. Since draft-ietf-quic-http-06 . . . . . . . . . . . . . . 56
B.20. Since draft-ietf-quic-http-05 . . . . . . . . . . . . . . 57
B.21. Since draft-ietf-quic-http-04 . . . . . . . . . . . . . . 57
B.22. Since draft-ietf-quic-http-03 . . . . . . . . . . . . . . 57
B.23. Since draft-ietf-quic-http-02 . . . . . . . . . . . . . . 57
B.24. Since draft-ietf-quic-http-01 . . . . . . . . . . . . . . 57
B.25. Since draft-ietf-quic-http-00 . . . . . . . . . . . . . . 58
B.26. Since draft-shade-quic-http2-mapping-00 . . . . . . . . . 58
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 58
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 58
1. Introduction
HTTP semantics are used for a broad range of services on the
Internet. These semantics have commonly been used with two different
TCP mappings, HTTP/1.1 and HTTP/2. HTTP/3 supports the same
semantics over a new transport protocol, QUIC.
1.1. Prior versions of HTTP
HTTP/1.1 is a TCP mapping which uses whitespace-delimited text fields
to convey HTTP messages. While these exchanges are human-readable,
using whitespace for message formatting leads to parsing difficulties
and workarounds to be tolerant of variant behavior. Because each
connection can transfer only a single HTTP request or response at a
time in each direction, multiple parallel TCP connections are often
used, reducing the ability of the congestion controller to accurately
manage traffic between endpoints.
HTTP/2 introduced a binary framing and multiplexing layer to improve
latency without modifying the transport layer. However, because the
parallel nature of HTTP/2's multiplexing is not visible to TCP's loss
recovery mechanisms, a lost or reordered packet causes all active
transactions to experience a stall regardless of whether that
transaction was impacted by the lost packet.
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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, it has the capability to
improve the performance of HTTP compared to a TCP mapping. QUIC also
incorporates TLS 1.3 at the transport layer, offering comparable
security to running TLS over TCP, with the improved connection setup
latency of TCP Fast Open [RFC7413].
This document defines a mapping of HTTP semantics over the QUIC
transport protocol, drawing heavily on the design of HTTP/2. While
delegating stream lifetime and flow control issues to QUIC, a similar
binary framing is used on each stream. Some HTTP/2 features are
subsumed by QUIC, while other features are implemented atop QUIC.
QUIC is described in [QUIC-TRANSPORT]. For a full description of
HTTP/2, see [HTTP2].
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. An HTTP/3
endpoint can be discovered using HTTP Alternative Services; this
process is described in greater detail in Section 3.2.
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).
Multiplexing of requests is performed using the QUIC stream
abstraction, 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 [HTTP2] which
permits a server to push a request-response exchange to a client in
anticipation of the client making the indicated request. This trades
off network usage against a potential latency gain. Several HTTP/3
frames are used to manage server push, such as PUSH_PROMISE,
DUPLICATE_PUSH, MAX_PUSH_ID, and CANCEL_PUSH.
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As in HTTP/2, request and response headers are compressed for
transmission. Because HPACK [HPACK] relies on in-order transmission
of compressed header blocks (a guarantee not provided by QUIC),
HTTP/3 replaces HPACK with QPACK [QPACK]. QPACK uses separate
unidirectional streams to modify and track header table state, while
header blocks refer to the state of the table without modifying it.
2.1. Document Organization
The following sections provide a detailed overview of the connection
lifecycle and key concepts:
* Connection Setup and Management (Section 3) covers how an HTTP/3
endpoint is discovered and a connection is established.
* HTTP Request Lifecycle (Section 4) describes how HTTP semantics
are expressed using frames.
* Connection Closure (Section 5) describes how connections are
terminated, either gracefully or abruptly.
The details of the wire protocol and interactions with the transport
are described in subsequent sections:
* Stream Mapping and Usage (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.
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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.
Field definitions are given in Augmented Backus-Naur Form (ABNF), as
defined in [RFC5234].
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.
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.
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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.
stream error: An error on the individual HTTP/3 stream.
The term "payload body" is defined in Section 3.3 of [RFC7230].
Finally, the terms "gateway", "intermediary", "proxy", and "tunnel"
are defined in Section 2.3 of [RFC7230]. Intermediaries act as both
client and server at different times.
3. Connection Setup and Management
3.1. Draft Version Identification
*RFC Editor's Note:* Please remove this section prior to
publication of a final version of this document.
HTTP/3 uses the token "h3" to identify itself in ALPN and Alt-Svc.
Only implementations of the final, published RFC can identify
themselves as "h3". Until such an RFC exists, implementations MUST
NOT identify themselves using this string.
Implementations of draft versions of the protocol MUST add the string
"-" and the corresponding draft number to the identifier. For
example, draft-ietf-quic-http-01 is identified using the string
"h3-01".
Non-compatible experiments that are based on these draft versions
MUST append the string "-" and an experiment name to the identifier.
For example, an experimental implementation based on draft-ietf-quic-
http-09 which reserves an extra stream for unsolicited transmission
of 1980s pop music might identify itself as "h3-09-rickroll". Note
that any label MUST conform to the "token" syntax defined in
Section 3.2.6 of [RFC7230]. Experimenters are encouraged to
coordinate their experiments on the quic@ietf.org mailing list.
3.2. Discovering an HTTP/3 Endpoint
An HTTP origin advertises the availability of an equivalent HTTP/3
endpoint via the Alt-Svc HTTP response header field or the HTTP/2
ALTSVC frame ([ALTSVC]), using the ALPN token defined in Section 3.3.
For example, an origin could indicate in an HTTP response that HTTP/3
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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 and, if successful, send HTTP requests using the mapping
described in this document.
Connectivity problems (e.g. firewall blocking UDP) can result in QUIC
connection establishment failure, in which case the client SHOULD
continue using the existing connection or try another alternative
endpoint offered by the origin.
Servers MAY serve HTTP/3 on any UDP port, since an alternative always
includes an explicit port.
3.3. Connection Establishment
HTTP/3 relies on QUIC as the underlying transport. The QUIC version
being used MUST use TLS version 1.3 or greater as its handshake
protocol. HTTP/3 clients MUST indicate the target domain name during
the TLS handshake. This may be done using the Server Name Indication
(SNI) [RFC6066] extension to TLS or using some other mechanism.
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, HTTP/3-specific settings are
conveyed in the SETTINGS frame. After the QUIC connection is
established, a SETTINGS frame (Section 7.2.4) MUST be sent by each
endpoint as the initial frame of their respective HTTP control stream
(see Section 6.2.1).
3.4. Connection Reuse
Once a connection exists to a server endpoint, this connection MAY be
reused for requests with multiple different URI authority components.
The client MAY send any requests for which the client considers the
server authoritative.
An authoritative HTTP/3 endpoint is typically discovered because the
client has received an Alt-Svc record from the request's origin which
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nominates the endpoint as a valid HTTP Alternative Service for that
origin. As required by [RFC7838], clients MUST check that the
nominated server can present a valid certificate for the origin
before considering it authoritative. Clients MUST NOT assume that an
HTTP/3 endpoint is authoritative for other origins without an
explicit signal.
Prior to making requests for an origin whose scheme is not "https,"
the client MUST ensure the server is willing to serve that scheme.
If the client intends to make requests for an origin whose scheme is
"http", this means that it MUST obtain a valid "http-opportunistic"
response for the origin as described in [RFC8164] prior to making any
such requests. Other schemes might define other mechanisms.
A server that does not wish clients to reuse connections for a
particular origin can indicate that it is not authoritative for a
request by sending a 421 (Misdirected Request) status code in
response to the request (see Section 9.1.2 of [HTTP2]).
The considerations discussed in Section 9.1 of [HTTP2] also apply to
the management of HTTP/3 connections.
4. HTTP Request Lifecycle
4.1. HTTP Message Exchanges
A client sends an HTTP request on a client-initiated bidirectional
QUIC stream. A client MUST send only a single request on a given
stream. A server sends zero or more non-final HTTP responses on the
same stream as the request, followed by a single final HTTP response,
as detailed below.
An HTTP message (request or response) consists of:
1. the message header (see Section 3.2 of [RFC7230]), sent as a
single HEADERS frame (see Section 7.2.2),
2. optionally, the payload body, if present (see Section 3.3 of
[RFC7230]), sent as a series of DATA frames (see Section 7.2.1),
3. optionally, trailing headers, if present (see Section 4.1.2 of
[RFC7230]), sent as a single HEADERS frame.
A server MAY send one or more PUSH_PROMISE (see Section 7.2.5) or
DUPLICATE_PUSH (see Section 7.2.8) frames before, after, or
interleaved with the frames of a response message. These
PUSH_PROMISE and DUPLICATE_PUSH frames are not part of the response;
see Section 4.4 for more details.
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Frames of unknown types (Section 9), including reserved frames
(Section 7.2.9) 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 4.1.1 for more details.
The "chunked" transfer encoding defined in Section 4.1 of [RFC7230]
MUST NOT be used.
A response MAY consist of multiple messages when and only when one or
more informational responses (1xx; see Section 6.2 of [RFC7231])
precede a final response to the same request. Non-final responses do
not contain a payload body or trailers.
If an endpoint receives an invalid sequence of frames on either a
request or a push stream, it MUST respond with a connection error of
type H3_FRAME_UNEXPECTED (Section 8). In particular, a DATA frame
before any HEADERS frame, or a HEADERS or DATA frame after the
trailing HEADERS frame is considered invalid.
An HTTP request/response exchange fully consumes a bidirectional QUIC
stream. After sending a request, a client MUST close the stream for
sending. Unless using the CONNECT method (see Section 4.2), clients
MUST NOT make stream closure dependent on receiving a response to
their request. After sending a final response, the server MUST close
the stream for sending. At this point, the QUIC stream is fully
closed.
When a stream is closed, this indicates the end of an HTTP message.
Because some messages are large or unbounded, endpoints SHOULD begin
processing partial HTTP messages once enough of the message has been
received to make progress. If a client stream terminates without
enough of the HTTP message to provide a complete response, the server
SHOULD abort its response with the error code 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.
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If the server sends a partial or complete response but does not abort
reading, clients SHOULD continue sending the body of the request and
close the stream normally.
4.1.1. Header Formatting and Compression
HTTP message headers carry information as a series of key-value
pairs, called header fields. For a listing of registered HTTP header
fields, see the "Message Header Field" registry maintained at
https://www.iana.org/assignments/message-headers
(https://www.iana.org/assignments/message-headers).
Just as in previous versions of HTTP, header field names are strings
of ASCII characters that are compared in a case-insensitive fashion.
Properties of HTTP header field names and values are discussed in
more detail in Section 3.2 of [RFC7230], though the wire rendering in
HTTP/3 differs. As in HTTP/2, header field names MUST be converted
to lowercase prior to their encoding. A request or response
containing uppercase header field names MUST be treated as malformed
(Section 4.1.3).
As in HTTP/2, HTTP/3 uses special pseudo-header fields beginning with
the ':' character (ASCII 0x3a) to convey the target URI, the method
of the request, and the status code for the response. These pseudo-
header fields are defined in Section 8.1.2.3 and 8.1.2.4 of [HTTP2].
Pseudo-header fields are not HTTP header fields. Endpoints MUST NOT
generate pseudo-header fields other than those defined in [HTTP2].
The restrictions on the use of pseudo-header fields in Section 8.1.2
of [HTTP2] also apply to HTTP/3. Messages which are considered
malformed under these restrictions are handled as described in
Section 4.1.3.
HTTP/3 uses QPACK header compression as described in [QPACK], a
variation of HPACK which allows the flexibility to avoid header-
compression-induced head-of-line blocking. See that document for
additional details.
To allow for better compression efficiency, the cookie header field
[RFC6265] MAY be split into separate header fields, each with one or
more cookie-pairs, before compression. If a decompressed header list
contains multiple cookie header fields, these MUST be concatenated
before being passed into a non-HTTP/2, non-HTTP/3 context, as
described in Section 8.1.2.5 of [HTTP2].
An HTTP/3 implementation MAY impose a limit on the maximum size of
the message header it will accept on an individual HTTP message. A
server that receives a larger header field list than it is willing to
handle can send an HTTP 431 (Request Header Fields Too Large) status
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code [RFC6585]. A client can discard responses that it cannot
process. The size of a header field list is calculated based on the
uncompressed size of header fields, including the length of the name
and value in bytes plus an overhead of 32 bytes for each header
field.
If an implementation wishes to advise its peer of this limit, it can
be conveyed as a number of bytes in the
"SETTINGS_MAX_HEADER_LIST_SIZE" parameter. An implementation which
has received this parameter SHOULD NOT send an HTTP message header
which exceeds the indicated size, as the peer will likely refuse to
process it. However, because this limit is applied at each hop,
messages below this limit are not guaranteed to be accepted.
4.1.2. Request Cancellation and Rejection
Clients can cancel requests by resetting and aborting the request
stream with an error code of H3_REQUEST_CANCELLED (Section 8.1).
When the client aborts reading a response, it indicates that this
response is no longer of interest. Implementations SHOULD cancel
requests by abruptly terminating any directions of a stream that are
still open.
When the server rejects a request without performing any application
processing, it SHOULD abort its response stream with the error code
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 on a new connection.
Servers MUST NOT use the H3_REQUEST_REJECTED error code for requests
which were partially or fully processed. When a server abandons a
response after partial processing, it SHOULD abort its response
stream with the error code H3_REQUEST_CANCELLED.
When a client resets a request with the error code
H3_REQUEST_CANCELLED, 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. Automatically retrying such requests is
not possible, unless this is otherwise permitted (e.g., idempotent
actions like GET, PUT, or DELETE).
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4.1.3. 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 extraneous
frames, prohibited header fields, the absence of mandatory header
fields, or the inclusion of uppercase header field names.
A request or response that includes a payload body can include a
"content-length" header field. A request or response is also
malformed if the value of a content-length header field does not
equal the sum of the DATA frame payload lengths that form the body.
A response that is defined to have no payload, as described in
Section 3.3.2 of [RFC7230] 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 (Section 8) of type
H3_GENERAL_PROTOCOL_ERROR.
For malformed requests, a server MAY send an HTTP response prior to
closing or resetting the stream. Clients MUST NOT accept a malformed
response. Note that these requirements are intended to protect
against several types of common attacks against HTTP; they are
deliberately strict because being permissive can expose
implementations to these vulnerabilities.
4.2. The CONNECT Method
The pseudo-method CONNECT (Section 4.3.6 of [RFC7231]) is primarily
used with HTTP proxies to establish a TLS session with an origin
server for the purposes of interacting with "https" resources. In
HTTP/1.x, CONNECT is used to convert an entire HTTP connection into a
tunnel to a remote host. In HTTP/2, the CONNECT method is used to
establish a tunnel over a single HTTP/2 stream to a remote host for
similar purposes.
A CONNECT request in HTTP/3 functions in the same manner as in
HTTP/2. The request MUST be formatted as described in Section 8.3 of
[HTTP2]. A CONNECT request that does not conform to these
restrictions is malformed (see Section 4.1.3). The request stream
MUST NOT be closed at the end of the request.
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
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proxy sends a HEADERS frame containing a 2xx series status code to
the client, as defined in Section 4.3.6 of [RFC7231].
All DATA frames on the stream correspond to data sent or received on
the TCP connection. Any DATA frame sent by the client is transmitted
by the proxy to the TCP server; data received from the TCP server is
packaged into DATA frames by the proxy. Note that the size and
number of TCP segments is not guaranteed to map predictably to the
size and number of HTTP DATA or QUIC STREAM frames.
Once the CONNECT method has completed, only DATA frames are permitted
to be sent on the stream. Extension frames MAY be used if
specifically permitted by the definition of the extension. Receipt
of any other frame type MUST be treated as a connection error of type
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 terminate the send stream that it sends to
the client. TCP connections which remain half-closed in a single
direction are not invalid, but are often handled poorly by servers,
so clients SHOULD NOT close a stream for sending while they still
expect to receive data from the target of the CONNECT.
A TCP connection error is signaled by abruptly terminating the
stream. A proxy treats any error in the TCP connection, which
includes receiving a TCP segment with the RST bit set, as a stream
error of type H3_CONNECT_ERROR (Section 8.1). Correspondingly, if a
proxy detects an error with the stream or the QUIC connection, it
MUST close the TCP connection. If the underlying TCP implementation
permits it, the proxy SHOULD send a TCP segment with the RST bit set.
4.3. HTTP Upgrade
HTTP/3 does not support the HTTP Upgrade mechanism (Section 6.7 of
[RFC7230]) or 101 (Switching Protocols) informational status code
(Section 6.2.2 of [RFC7231]).
4.4. Server Push
Server push is an interaction mode introduced in HTTP/2 [HTTP2] which
permits a server to push a request-response exchange to a client in
anticipation of the client making the indicated request. This trades
off network usage against a potential latency gain. HTTP/3 server
push is similar to what is described in HTTP/2 [HTTP2], but uses
different mechanisms.
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Each server push is identified by a unique Push ID. This Push ID is
used in a single PUSH_PROMISE frame (see Section 7.2.5) which carries
the request headers, possibly included in one or more DUPLICATE_PUSH
frames (see Section 7.2.8), then included with the push stream which
ultimately fulfills those promises.
Server push is only enabled on a connection when a client sends a
MAX_PUSH_ID frame (see Section 7.2.7). A server cannot use server
push until it receives a MAX_PUSH_ID frame. A client sends
additional MAX_PUSH_ID frames to control the number of pushes that a
server can promise. A server SHOULD use Push IDs sequentially,
starting at 0. A client MUST treat receipt of a push stream with a
Push ID that is greater than the maximum Push ID as a connection
error of type H3_ID_ERROR.
The header of the request message is carried by a PUSH_PROMISE frame
(see Section 7.2.5) on the request stream which generated the push.
Promised requests MUST conform to the requirements in Section 8.2 of
[HTTP2].
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 DUPLICATE_PUSH
frame (see Section 7.2.8). These associations do not affect the
operation of the protocol, but MAY be used by user agents when
deciding how to use pushed resources.
Ordering of a PUSH_PROMISE or DUPLICATE_PUSH in relation to certain
parts of the response is important. The server SHOULD send
PUSH_PROMISE or DUPLICATE_PUSH frames prior to sending HEADERS or
DATA frames that reference the promised responses. This reduces the
chance that a client requests a resource that will be pushed by the
server.
When a server later fulfills a promise, the server push response is
conveyed on a push stream (see Section 6.2.2). The push stream
identifies the Push ID of the promise that it fulfills, then contains
a response to the promised request using the same format described
for responses in Section 4.1.
Due to reordering, DUPLICATE_PUSH frames or push stream data can
arrive before the corresponding PUSH_PROMISE frame. When a client
receives a DUPLICATE_PUSH frame for an as-yet-unknown Push ID, the
request headers of the push are not immediately available. The
client can either delay generating new requests for content
referenced following the DUPLICATE_PUSH frame until the request
headers become available, or can initiate requests for discovered
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resources and cancel the requests if the requested resource is
already being pushed. When a client receives a new push stream with
an as-yet-unknown Push ID, both the associated client request and the
pushed request headers are unknown. The client can buffer the stream
data in expectation of the matching PUSH_PROMISE. The client can use
stream flow control (see section 4.1 of [QUIC-TRANSPORT]) to limit
the amount of data a server may commit to the pushed stream.
If a promised server push is not needed by the client, the client
SHOULD send a CANCEL_PUSH frame. If the push stream is already open
or opens after sending the CANCEL_PUSH frame, the client can abort
reading the stream with an error code of H3_REQUEST_CANCELLED. This
asks the server not to transfer additional data and indicates that it
will be discarded upon receipt.
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 connection remains idle (no packets received) for longer than
this duration, the peer will assume that the connection has been
closed. HTTP/3 implementations will need to open a new connection
for new requests if the existing connection has been idle for longer
than the server's advertised idle timeout, and SHOULD do so if
approaching the idle timeout.
HTTP clients are expected to request that the transport keep
connections open while there are responses outstanding for requests
or server pushes, as described in Section 19.2 of [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 let the connection close gracefully.
Since clients drive request generation, clients perform a connection
shutdown by not sending additional requests on the connection;
responses and pushed responses associated to previous requests will
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continue to completion. Servers perform the same function by
communicating with clients.
Servers initiate the shutdown of a connection by sending a GOAWAY
frame (Section 7.2.6). The GOAWAY frame indicates that client-
initiated requests on lower stream IDs were or might be processed in
this connection, while requests on the indicated stream ID and
greater were rejected. This enables client and server to agree on
which requests were accepted prior to the connection shutdown. This
identifier MAY be zero if no requests were processed. Servers SHOULD
NOT permit additional QUIC streams after sending a GOAWAY frame.
Clients MUST NOT send new requests on the connection after receiving
GOAWAY; a new connection MAY be established to send additional
requests.
Some requests might already be in transit. If the client has already
sent requests on streams with a Stream ID greater than or equal to
that indicated in the GOAWAY frame, those requests will not be
processed and MAY be retried by the client on a different connection.
The client MAY cancel these requests. It is RECOMMENDED that the
server explicitly reject such requests (see Section 4.1.2) in order
to clean up transport state for the affected streams.
Requests on Stream IDs less than the Stream ID in the GOAWAY frame
might have been processed; their status cannot be known until a
response is received, the stream is reset individually, or the
connection terminates. Servers MAY reject individual requests on
streams below the indicated ID if these requests were not processed.
Servers SHOULD send a GOAWAY frame when the closing of a connection
is known in advance, even if the advance notice is small, so that the
remote peer can know whether a request has been partially processed
or not. For example, if an HTTP client sends a POST at the same time
that a server closes a QUIC connection, the client cannot know if the
server started to process that POST request if the server does not
send a GOAWAY frame to indicate what streams it might have acted on.
A client that is unable to retry requests loses all requests that are
in flight when the server closes the connection. A server MAY send
multiple GOAWAY frames indicating different stream IDs, but MUST NOT
increase the value they send in the last Stream ID, since clients
might already have retried unprocessed requests on another
connection.
A server that is attempting to gracefully shut down a connection can
send an initial GOAWAY frame with the last Stream ID set to the
maximum possible value for a client-initiated, bidirectional stream
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(i.e. 2^62-4 in case of QUIC version 1). This GOAWAY frame signals
to the client that shutdown is imminent and that initiating further
requests is prohibited. After allowing time for any in-flight
requests to reach the server, the server can send another GOAWAY
frame indicating which requests it will accept before the end of the
connection. This ensures that a connection can be cleanly shut down
without causing requests to fail.
Once all accepted requests have been processed, the server can permit
the connection to become idle, or MAY initiate an immediate closure
of the connection. An endpoint that completes a graceful shutdown
SHOULD use the H3_NO_ERROR code when closing the connection.
If a client has consumed all available bidirectional stream IDs with
requests, the server need not send a GOAWAY frame, since the client
is unable to make further requests.
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; the error code in this frame indicates to the peer why the
connection is being closed. See Section 8 for error codes which can
be used when closing a connection.
Before closing the connection, a GOAWAY MAY be sent to allow the
client to retry some requests. Including the GOAWAY frame in the
same packet as the QUIC CONNECTION_CLOSE frame improves the chances
of the frame being received by clients.
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 which interrupts connectivity.
If a connection terminates without a GOAWAY frame, clients MUST
assume that any request which was sent, whether in whole or in part,
might have been processed.
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. On the wire, data is framed into QUIC STREAM frames, but
this framing is invisible to the HTTP framing layer. The transport
layer buffers and orders received QUIC STREAM frames, exposing the
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data contained within as a reliable byte stream to the application.
Although QUIC permits out-of-order delivery within a stream, HTTP/3
does not make use of this feature.
QUIC streams can be either unidirectional, carrying data only from
initiator to receiver, or bidirectional. Streams can be initiated by
either the client or the server. For more detail on QUIC streams,
see Section 2 of [QUIC-TRANSPORT].
When HTTP headers and data are sent over QUIC, the QUIC layer handles
most of the stream management. HTTP does not need to do any separate
multiplexing when using QUIC - data sent over a QUIC stream always
maps to a particular HTTP transaction or connection context.
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. This means that the client's
first request occurs on QUIC stream 0, with subsequent requests on
stream 4, 8, and so on. In order to permit these streams to open, an
HTTP/3 server SHOULD configure non-zero minimum values for the number
of permitted streams and the initial stream flow control window. So
as to not unnecessarily limit parallelism, at least 100 requests
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.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Stream Type (i) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Unidirectional Stream Header
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Some stream types are reserved (Section 6.2.3). 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.
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. To avoid blocking, the transport parameters sent
by both clients and servers MUST allow the peer to create at least
one unidirectional stream for the HTTP control stream plus the number
of unidirectional streams required by mandatory extensions (three
being the minimum number required for the base HTTP/3 protocol and
QPACK), and SHOULD provide at least 1,024 bytes of flow control
credit to each stream.
Note that an endpoint is not required to grant additional credits to
create more unidirectional streams if its peer consumes all the
initial credits before creating the critical unidirectional streams.
Endpoints SHOULD create the HTTP control stream as well as the
unidirectional streams required by mandatory extensions (such as the
QPACK encoder and decoder streams) first, and then create additional
streams as allowed by their peer.
If the stream header indicates a stream type which is not supported
by the recipient, the remainder of the stream cannot be consumed as
the semantics are unknown. Recipients of unknown stream types MAY
abort reading of the stream with an error code of
H3_STREAM_CREATION_ERROR, but MUST NOT consider such streams to be a
connection error of any kind.
Implementations MAY send stream types before knowing whether the peer
supports them. However, stream types which could modify the state or
semantics of existing protocol components, including QPACK or other
extensions, MUST NOT be sent until the peer is known to support them.
A sender can close or reset a unidirectional stream unless otherwise
specified. A receiver MUST tolerate unidirectional streams being
closed or reset prior to the reception of the unidirectional stream
header.
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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 which claims 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.
A pair of unidirectional streams is used rather than a single
bidirectional stream. This allows either peer to send data as soon
as it is able. Depending on whether 0-RTT is enabled on the
connection, either client or server might be able to send stream data
first after the cryptographic handshake completes.
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 4.4 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 non-final HTTP responses followed by a single
final HTTP response, as defined in Section 4.1. Server push and Push
IDs are described in Section 4.4.
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.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x01 (i) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Push ID (i) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 2: Push Stream Header
Each Push ID MUST only be used once in a push stream header. If a
push stream header includes a Push ID that was used in another push
stream header, the client MUST treat this as a connection error of
type H3_ID_ERROR.
6.2.3. Reserved Stream Types
Stream types of the format "0x1f * N + 0x21" for integer values of N
are reserved to exercise the requirement that unknown types be
ignored. These streams have no semantics, and can be sent when
application-layer padding is desired. They MAY also be sent on
connections where no data is currently being transferred. Endpoints
MUST NOT consider these streams to have any meaning upon receipt.
The payload and length of the stream are selected in any manner the
implementation chooses. Implementations MAY terminate these streams
cleanly, or MAY abruptly terminate them. When terminating abruptly,
the error code H3_NO_ERROR 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 the
streams types on which they are permitted; see Table 1 for an
overview. A comparison between HTTP/2 and HTTP/3 frames is provided
in Appendix A.2.
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+----------------+----------------+---------+--------+---------+
| Frame | Control Stream | Request | Push | Section |
| | | Stream | Stream | |
+================+================+=========+========+=========+
| 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 |
+----------------+----------------+---------+--------+---------+
| DUPLICATE_PUSH | No | Yes | No | Section |
| | | | | 7.2.8 |
+----------------+----------------+---------+--------+---------+
| Reserved | Yes | Yes | Yes | Section |
| | | | | 7.2.9 |
+----------------+----------------+---------+--------+---------+
Table 1: HTTP/3 Frames and Stream Type Overview
Certain frames can only occur as the first frame of a particular
stream type; these are 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:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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.
When a stream terminates cleanly, if the last frame on the stream was
truncated, this MUST be treated as a connection error (Section 8) of
type H3_FRAME_ERROR. Streams which terminate abruptly may be reset
at any point in a frame.
7.2. Frame Definitions
7.2.1. DATA
DATA frames (type=0x0) convey arbitrary, variable-length sequences of
bytes associated with an HTTP request or response payload.
DATA frames MUST be associated with an HTTP request or response. If
a DATA frame is received on a control stream, the recipient MUST
respond with a connection error (Section 8) of type
H3_FRAME_UNEXPECTED.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload (*) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: DATA Frame Payload
7.2.2. HEADERS
The HEADERS frame (type=0x1) is used to carry a header block,
compressed using QPACK. See [QPACK] for more details.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Header Block (*) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: HEADERS Frame Payload
HEADERS frames can only be sent on request / push streams. If a
HEADERS frame is received on a control stream, the recipient MUST
respond with a connection error (Section 8) of type
H3_FRAME_UNEXPECTED.
7.2.3. CANCEL_PUSH
The CANCEL_PUSH frame (type=0x3) is used to request cancellation of a
server push prior to the push stream being received. The CANCEL_PUSH
frame identifies a server push by Push ID (see Section 7.2.5),
encoded as a variable-length integer.
When a client sends CANCEL_PUSH, 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.
When a server sends CANCEL_PUSH, it is indicating that it will not be
fulfilling a promise and has not created a push stream. The client
should not expect the corresponding promise to be fulfilled.
Sending CANCEL_PUSH has no direct effect on the state of existing
push streams. A server SHOULD NOT send a CANCEL_PUSH when it has
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already created a corresponding push stream, and a client SHOULD NOT
send a CANCEL_PUSH when it has already received a corresponding push
stream.
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.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Push ID (i) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: CANCEL_PUSH Frame Payload
The CANCEL_PUSH frame carries a Push ID encoded as a variable-length
integer. The Push ID identifies the server push that is being
cancelled (see Section 7.2.5). If a CANCEL_PUSH frame is received
which 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=0x4) conveys configuration parameters that
affect how endpoints communicate, such as preferences and constraints
on peer behavior. Individually, a SETTINGS parameter can also be
referred to as a "setting"; the identifier and value of each setting
parameter can be referred to as a "setting identifier" and a "setting
value".
SETTINGS frames always apply to a connection, never a single stream.
A SETTINGS frame MUST be sent as the first frame of each control
stream (see Section 6.2.1) by each peer, and MUST NOT be sent
subsequently. If an endpoint receives a second SETTINGS frame on the
control stream, the endpoint MUST respond with a connection error of
type 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
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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, which can be used by the receiving peer.
However, a negotiation can be implied by the use of SETTINGS - each
peer uses SETTINGS to advertise a set of supported values. The
definition of the setting would describe how each peer combines the
two sets to conclude which choice will be used. SETTINGS does not
provide a mechanism to identify when the choice takes effect.
Different values for the same parameter can be advertised by each
peer. For example, a client might be willing to consume a very large
response header, while servers are more cautious about request size.
The same setting identifier MUST NOT occur more than once in the
SETTINGS frame. A receiver MAY treat the presence of duplicate
setting identifiers as a connection error of type 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.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier (i) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value (i) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: SETTINGS Parameter Format
An implementation MUST ignore the contents for any SETTINGS
identifier it does not understand.
7.2.4.1. Defined SETTINGS Parameters
The following settings are defined in HTTP/3:
SETTINGS_MAX_HEADER_LIST_SIZE (0x6): The default value is unlimited.
See Section 4.1.1 for usage.
Setting identifiers of the format "0x1f * N + 0x21" for integer
values of N are reserved to exercise the requirement that unknown
identifiers be ignored. Such settings have no defined meaning.
Endpoints SHOULD include at least one such setting in their SETTINGS
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frame. Endpoints MUST NOT consider such settings to have any meaning
upon receipt.
Because the setting has no defined meaning, the value of the setting
can be any value the implementation selects.
Additional settings can be defined by extensions to HTTP/3; see
Section 9 for more details.
7.2.4.2. Initialization
An HTTP implementation MUST NOT send frames or requests which would
be invalid based on its current understanding of the peer's settings.
All settings begin at an initial value. Each endpoint SHOULD use
these initial values to send messages before the peer's SETTINGS
frame has arrived, as packets carrying the settings can be lost or
delayed. When the SETTINGS frame arrives, any settings are changed
to their new values.
This removes the need to wait for the SETTINGS frame before sending
messages. Endpoints MUST NOT require any data to be received from
the peer prior to sending the SETTINGS frame; settings MUST be sent
as soon as the transport is ready to send data.
For servers, the initial value of each client setting is the default
value.
For clients using a 1-RTT QUIC connection, the initial value of each
server setting is the default value. 1-RTT keys will always become
available prior to SETTINGS arriving, even if the server sends
SETTINGS immediately. Clients SHOULD NOT wait indefinitely for
SETTINGS to arrive before sending requests, but SHOULD process
received datagrams in order to increase the likelihood of processing
SETTINGS before sending the first request.
When a 0-RTT QUIC connection is being used, the initial value of each
server setting is the value used in the previous session. Clients
SHOULD store the settings the server provided in the connection where
resumption information was provided, but MAY opt not to store
settings in certain cases (e.g., if the session ticket is received
before the SETTINGS frame). A client MUST comply with stored
settings - or default values, if no values are stored - when
attempting 0-RTT. Once a server has provided new settings, clients
MUST comply with those values.
A server can remember the settings that it advertised, or store an
integrity-protected copy of the values in the ticket and recover the
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information when accepting 0-RTT data. A server uses the HTTP/3
settings values in determining whether to accept 0-RTT data. If the
server cannot determine that the settings remembered by a client are
compatible with its current settings, it MUST NOT accept 0-RTT data.
Remembered settings are compatible if a client complying with those
settings would not violate the server's current settings.
A server MAY accept 0-RTT and subsequently provide different settings
in its SETTINGS frame. If 0-RTT data is accepted by the server, its
SETTINGS frame MUST NOT reduce any limits or alter any values that
might be violated by the client with its 0-RTT data. The server MUST
include all settings which differ from their default values. If a
server accepts 0-RTT but then sends 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=0x5) is used to carry a promised request
header set from server to client on a request stream, as in HTTP/2.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Push ID (i) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Header Block (*) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: PUSH_PROMISE Frame Payload
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 4.4), CANCEL_PUSH frames (Section 7.2.3), and
DUPLICATE_PUSH frames (Section 7.2.8).
Header Block: QPACK-compressed 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
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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 MUST NOT use the same Push ID in multiple PUSH_PROMISE
frames. A client MUST treat receipt of a Push ID which has already
been promised as a connection error of type H3_ID_ERROR.
If a PUSH_PROMISE frame is received on the control stream, the client
MUST respond with a connection error (Section 8) 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 4.4 for a description of the overall server push
mechanism.
7.2.6. GOAWAY
The GOAWAY frame (type=0x7) is used to initiate graceful shutdown of
a connection by a server. GOAWAY allows a server to stop accepting
new requests while still finishing processing of previously received
requests. This enables administrative actions, like server
maintenance. GOAWAY by itself does not close a connection.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Stream ID (i) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: GOAWAY Frame Payload
The GOAWAY frame is always sent on the control stream. It carries a
QUIC Stream ID for a client-initiated bidirectional stream encoded as
a variable-length integer. A client MUST treat receipt of a GOAWAY
frame containing a Stream ID of any other type as a connection error
of type H3_ID_ERROR.
Clients do not need to send GOAWAY to initiate a graceful shutdown;
they simply stop making new requests. A server MUST treat receipt of
a GOAWAY frame on any stream as a connection error (Section 8) of
type H3_FRAME_UNEXPECTED.
The GOAWAY frame applies to the connection, not a specific stream. A
client MUST treat a GOAWAY frame on a stream other than the control
stream as a connection error (Section 8) of type H3_FRAME_UNEXPECTED.
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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=0xD) is used by clients to control the
number of server pushes that the server can initiate. This sets the
maximum value for a Push ID that the server can use in 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 a connection is created, meaning
that a server cannot push until it receives a MAX_PUSH_ID frame. A
client that wishes to manage the number of promised server pushes can
increase the maximum Push ID by sending MAX_PUSH_ID frames as the
server fulfills or cancels server pushes.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Push ID (i) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: MAX_PUSH_ID Frame Payload
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 7.2.5). A MAX_PUSH_ID frame cannot reduce the maximum
Push ID; receipt of a MAX_PUSH_ID that contains a smaller value than
previously received MUST be treated as a connection error of type
H3_ID_ERROR.
7.2.8. DUPLICATE_PUSH
The DUPLICATE_PUSH frame (type=0xE) is used by servers to indicate
that an existing pushed resource is related to multiple client
requests.
The DUPLICATE_PUSH frame is always sent on a request stream. Receipt
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of a DUPLICATE_PUSH frame on any other stream MUST be treated as a
connection error of type H3_FRAME_UNEXPECTED.
A client MUST NOT send a DUPLICATE_PUSH frame. A server MUST treat
the receipt of a DUPLICATE_PUSH frame as a connection error of type
H3_FRAME_UNEXPECTED.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Push ID (i) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: DUPLICATE_PUSH Frame Payload
The DUPLICATE_PUSH frame carries a single variable-length integer
that identifies the Push ID of a resource that the server has
previously promised (see Section 7.2.5), though that promise might
not be received before this frame. A server MUST NOT use a Push ID
that is larger than the client has provided in a MAX_PUSH_ID frame
(Section 7.2.7). A client MUST treat receipt of a DUPLICATE_PUSH
that contains a larger Push ID than the client has advertised as a
connection error of type H3_ID_ERROR.
This frame allows the server to use the same server push in response
to multiple concurrent requests. Referencing the same server push
ensures that a promise can be made in relation to every response in
which server push might be needed without duplicating request headers
or pushed responses.
Allowing duplicate references to the same Push ID is primarily to
reduce duplication caused by concurrent requests. A server SHOULD
avoid reusing a Push ID over a long period. Clients are likely to
consume server push responses and not retain them for reuse over
time. Clients that see a DUPLICATE_PUSH that uses a Push ID that
they have since consumed and discarded are forced to ignore the
DUPLICATE_PUSH.
7.2.9. Reserved Frame Types
Frame types of the format "0x1f * N + 0x21" for integer values of N
are reserved to exercise the requirement that unknown types be
ignored (Section 9). These frames have no semantics, and can be sent
on any open stream when application-layer padding is desired. They
MAY also be sent on connections where no data is currently being
transferred. Endpoints MUST NOT consider these frames to have any
meaning upon receipt.
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The payload and length of the frames are selected in any manner the
implementation chooses.
Frame types which were used in HTTP/2 where there is no corresponding
HTTP/3 frame have also been reserved (Section 11.2.1). These frame
types MUST NOT be sent, and receipt MAY be treated as an error of
type H3_FRAME_UNEXPECTED.
8. Error Handling
QUIC allows the application to abruptly terminate (reset) individual
streams or the entire connection when an error is encountered. These
are referred to as "stream errors" or "connection errors" and are
described in more detail in [QUIC-TRANSPORT].
An endpoint MAY choose to treat a stream error as a connection error
under certain circumstances. 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 (see Section 4.1).
This section describes HTTP/3-specific error codes which can be used
to express the cause of a connection or stream error.
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 connections.
H3_NO_ERROR (0x100): 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 (0x101): Peer violated protocol
requirements in a way which doesn't match a more specific error
code, or endpoint declines to use the more specific error code.
H3_INTERNAL_ERROR (0x102): An internal error has occurred in the
HTTP stack.
H3_STREAM_CREATION_ERROR (0x103): The endpoint detected that its
peer created a stream that it will not accept.
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H3_CLOSED_CRITICAL_STREAM (0x104): A stream required by the
connection was closed or reset.
H3_FRAME_UNEXPECTED (0x105): A frame was received which was not
permitted in the current state or on the current stream.
H3_FRAME_ERROR (0x106): A frame that fails to satisfy layout
requirements or with an invalid size was received.
H3_EXCESSIVE_LOAD (0x107): The endpoint detected that its peer is
exhibiting a behavior that might be generating excessive load.
H3_ID_ERROR (0x108): A Stream ID or Push ID was used incorrectly,
such as exceeding a limit, reducing a limit, or being reused.
H3_SETTINGS_ERROR (0x109): An endpoint detected an error in the
payload of a SETTINGS frame.
H3_MISSING_SETTINGS (0x10A): No SETTINGS frame was received at the
beginning of the control stream.
H3_REQUEST_REJECTED (0x10B): A server rejected a request without
performing any application processing.
H3_REQUEST_CANCELLED (0x10C): The request or its response (including
pushed response) is cancelled.
H3_REQUEST_INCOMPLETE (0x10D): The client's stream terminated
without containing a fully-formed request.
H3_CONNECT_ERROR (0x10F): The connection established in response to
a CONNECT request was reset or abnormally closed.
H3_VERSION_FALLBACK (0x110): 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 integer values of N
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.
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This applies to the protocol elements defined in this document. This
does not affect the existing options for extending HTTP, such as
defining new methods, status codes, or header fields.
Extensions are permitted to use new frame types (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 frames
and unidirectional streams that have unknown or unsupported types.
This means that any of these extension points can be safely used by
extensions without prior arrangement or negotiation. However, where
a known frame type is required to be in a specific location, such as
the SETTINGS frame as the first frame of the control stream (see
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 doesn't mandate a specific method for negotiating the
use of an extension but 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; the considerations from Section 10 of [HTTP2]
apply in addition to those listed here.
When HTTP Alternative Services is used for discovery for HTTP/3
endpoints, the security considerations of [ALTSVC] also apply.
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10.1. Traffic Analysis
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 Section 7.2.9 and
Section 6.2.3. These methods of padding produce different results in
terms of the granularity of padding, the effect of packet loss and
recovery, and how an implementation might control padding.
10.2. 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.
10.3. 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.
10.4. 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.
11. IANA Considerations
This document registers a new ALPN protocol ID (Section 11.1) and
creates new registries that manage the assignment of codepoints 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 "Application Layer Protocol Negotiation (ALPN) Protocol
IDs" registry established in [RFC7301].
The "h3" string identifies HTTP/3:
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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].
The initial allocations in these registries created in this document
are all assigned permanent status and list as contact both the IESG
(iesg@ietf.org) and 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 Type" 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 Section 4.9 and 4.10
of [RFC8126].
While this registry is separate from the "HTTP/2 Frame Type" registry
defined in [HTTP2], 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.
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.
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+----------------+-------+---------------+
| Frame Type | Value | Specification |
+================+=======+===============+
| DATA | 0x0 | Section 7.2.1 |
+----------------+-------+---------------+
| HEADERS | 0x1 | Section 7.2.2 |
+----------------+-------+---------------+
| Reserved | 0x2 | N/A |
+----------------+-------+---------------+
| CANCEL_PUSH | 0x3 | Section 7.2.3 |
+----------------+-------+---------------+
| SETTINGS | 0x4 | Section 7.2.4 |
+----------------+-------+---------------+
| PUSH_PROMISE | 0x5 | Section 7.2.5 |
+----------------+-------+---------------+
| Reserved | 0x6 | N/A |
+----------------+-------+---------------+
| GOAWAY | 0x7 | Section 7.2.6 |
+----------------+-------+---------------+
| Reserved | 0x8 | N/A |
+----------------+-------+---------------+
| Reserved | 0x9 | N/A |
+----------------+-------+---------------+
| MAX_PUSH_ID | 0xD | Section 7.2.7 |
+----------------+-------+---------------+
| DUPLICATE_PUSH | 0xE | Section 7.2.8 |
+----------------+-------+---------------+
Table 2: Initial HTTP/3 Frame Types
Additionally, each code of the format "0x1f * N + 0x21" for integer
values of N (that is, "0x21", "0x40", ..., through
"0x3FFFFFFFFFFFFFFE") MUST NOT be assigned by IANA.
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 Section 4.9 and 4.10 of
[RFC8126].
While this registry is separate from the "HTTP/2 Settings" registry
defined in [HTTP2], it is preferable that the assignments parallel
each other. If an entry is present in only one registry, every
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effort SHOULD be made to avoid assigning the corresponding value to
an unrelated operation.
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.
+----------------------+-------+-----------------+-----------+
| Setting Name | Value | Specification | Default |
+======================+=======+=================+===========+
| Reserved | 0x2 | N/A | N/A |
+----------------------+-------+-----------------+-----------+
| Reserved | 0x3 | N/A | N/A |
+----------------------+-------+-----------------+-----------+
| Reserved | 0x4 | N/A | N/A |
+----------------------+-------+-----------------+-----------+
| Reserved | 0x5 | N/A | N/A |
+----------------------+-------+-----------------+-----------+
| MAX_HEADER_LIST_SIZE | 0x6 | Section 7.2.4.1 | Unlimited |
+----------------------+-------+-----------------+-----------+
Table 3: Initial HTTP/3 Settings
Additionally, each code of the format "0x1f * N + 0x21" for integer
values of N (that is, "0x21", "0x40", ..., through
"0x3FFFFFFFFFFFFFFE") MUST NOT be assigned by IANA.
11.2.3. Error Codes
This document establishes a registry for HTTP/3 error codes. The
"HTTP/3 Error Code" 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 Section 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
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registrations for possible duplication with existing error codes.
Use of existing registrations is to be encouraged, but not mandated.
In addition to common fields as described in Section 11.2, permanent
registrations in this registry MUST include the following fields:
Name: A name for the error code. Specifying an error code name is
optional.
Description: A brief description of the error code semantics.
The entries in the Table 4 are registered by this document.
+---------------------------+--------+--------------+---------------+
| Name | Value | Description | Specification |
+===========================+========+==============+===============+
| H3_NO_ERROR | 0x0100 | No error | Section 8.1 |
+---------------------------+--------+--------------+---------------+
| H3_GENERAL_PROTOCOL_ERROR | 0x0101 | General | Section 8.1 |
| | | protocol | |
| | | error | |
+---------------------------+--------+--------------+---------------+
| H3_INTERNAL_ERROR | 0x0102 | Internal | Section 8.1 |
| | | error | |
+---------------------------+--------+--------------+---------------+
| H3_STREAM_CREATION_ERROR | 0x0103 | Stream | Section 8.1 |
| | | creation | |
| | | error | |
+---------------------------+--------+--------------+---------------+
| H3_CLOSED_CRITICAL_STREAM | 0x0104 | Critical | Section 8.1 |
| | | stream was | |
| | | closed | |
+---------------------------+--------+--------------+---------------+
| H3_FRAME_UNEXPECTED | 0x0105 | Frame not | Section 8.1 |
| | | permitted | |
| | | in the | |
| | | current | |
| | | state | |
+---------------------------+--------+--------------+---------------+
| H3_FRAME_ERROR | 0x0106 | Frame | Section 8.1 |
| | | violated | |
| | | layout or | |
| | | size rules | |
+---------------------------+--------+--------------+---------------+
| H3_EXCESSIVE_LOAD | 0x0107 | Peer | Section 8.1 |
| | | generating | |
| | | excessive | |
| | | load | |
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+---------------------------+--------+--------------+---------------+
| H3_ID_ERROR | 0x0108 | An | Section 8.1 |
| | | identifier | |
| | | was used | |
| | | incorrectly | |
+---------------------------+--------+--------------+---------------+
| H3_SETTINGS_ERROR | 0x0109 | SETTINGS | Section 8.1 |
| | | frame | |
| | | contained | |
| | | invalid | |
| | | values | |
+---------------------------+--------+--------------+---------------+
| H3_MISSING_SETTINGS | 0x010A | No SETTINGS | Section 8.1 |
| | | frame | |
| | | received | |
+---------------------------+--------+--------------+---------------+
| H3_REQUEST_REJECTED | 0x010B | Request not | Section 8.1 |
| | | processed | |
+---------------------------+--------+--------------+---------------+
| H3_REQUEST_CANCELLED | 0x010C | Data no | Section 8.1 |
| | | longer | |
| | | needed | |
+---------------------------+--------+--------------+---------------+
| H3_REQUEST_INCOMPLETE | 0x010D | Stream | Section 8.1 |
| | | terminated | |
| | | early | |
+---------------------------+--------+--------------+---------------+
| H3_CONNECT_ERROR | 0x010F | TCP reset | Section 8.1 |
| | | or error on | |
| | | CONNECT | |
| | | request | |
+---------------------------+--------+--------------+---------------+
| H3_VERSION_FALLBACK | 0x0110 | Retry over | Section 8.1 |
| | | HTTP/1.1 | |
+---------------------------+--------+--------------+---------------+
Table 4: Initial HTTP/3 Error Codes
Additionally, each code of the format "0x1f * N + 0x21" for integer
values of N (that is, "0x21", "0x40", ..., through
"0x3FFFFFFFFFFFFFFE") MUST NOT be assigned by IANA.
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11.2.4. Stream Types
This document establishes a registry for HTTP/3 unidirectional stream
types. The "HTTP/3 Stream Type" 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 Section 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 a 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 semantics of the stream
contents.
The entries in the following table are registered by this document.
+----------------+-------+---------------+--------+
| Stream Type | Value | Specification | Sender |
+================+=======+===============+========+
| Control Stream | 0x00 | Section 6.2.1 | Both |
+----------------+-------+---------------+--------+
| Push Stream | 0x01 | Section 4.4 | Server |
+----------------+-------+---------------+--------+
Table 5
Additionally, each code of the format "0x1f * N + 0x21" for integer
values of N (that is, "0x21", "0x40", ..., through
"0x3FFFFFFFFFFFFFFE") MUST NOT be assigned by IANA.
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, <https://www.rfc-editor.org/info/rfc7838>.
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[HTTP-REPLAY]
Thomson, M., Nottingham, M., and W. Tarreau, "Using Early
Data in HTTP", RFC 8470, DOI 10.17487/RFC8470, September
2018, <https://www.rfc-editor.org/info/rfc8470>.
[HTTP2] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<https://www.rfc-editor.org/info/rfc7540>.
[QPACK] Krasic, C., Bishop, M., and A. Frindell, Ed., "QPACK:
Header Compression for HTTP over QUIC", Work in Progress,
Internet-Draft, draft-ietf-quic-qpack-12, 22 January 2020,
<https://tools.ietf.org/html/draft-ietf-quic-qpack-12>.
[QUIC-TRANSPORT]
Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", Work in Progress,
Internet-Draft, draft-ietf-quic-transport-25, 22 January
2020, <https://tools.ietf.org/html/draft-ietf-quic-
transport-25>.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066,
DOI 10.17487/RFC6066, January 2011,
<https://www.rfc-editor.org/info/rfc6066>.
[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
DOI 10.17487/RFC6265, April 2011,
<https://www.rfc-editor.org/info/rfc6265>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
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RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
<https://www.rfc-editor.org/info/rfc7231>.
[RFC7838] Nottingham, M., McManus, P., and J. Reschke, "HTTP
Alternative Services", RFC 7838, DOI 10.17487/RFC7838,
April 2016, <https://www.rfc-editor.org/info/rfc7838>.
[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,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8164] Nottingham, M. and M. Thomson, "Opportunistic Security for
HTTP/2", RFC 8164, DOI 10.17487/RFC8164, May 2017,
<https://www.rfc-editor.org/info/rfc8164>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
12.2. Informative References
[HPACK] Peon, R. and H. Ruellan, "HPACK: Header Compression for
HTTP/2", RFC 7541, DOI 10.17487/RFC7541, May 2015,
<https://www.rfc-editor.org/info/rfc7541>.
[RFC6585] Nottingham, M. and R. Fielding, "Additional HTTP Status
Codes", RFC 6585, DOI 10.17487/RFC6585, April 2012,
<https://www.rfc-editor.org/info/rfc6585>.
[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, <https://www.rfc-editor.org/info/rfc7301>.
[RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP
Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014,
<https://www.rfc-editor.org/info/rfc7413>.
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Appendix A. Considerations for Transitioning from HTTP/2
HTTP/3 is strongly informed by HTTP/2, and bears many similarities.
This section describes the approach taken to design HTTP/3, points
out important differences from HTTP/2, and describes how to map
HTTP/2 extensions into HTTP/3.
HTTP/3 begins from the premise that similarity to HTTP/2 is
preferable, but not a hard requirement. HTTP/3 departs from HTTP/2
where QUIC differs from TCP, either to take advantage of QUIC
features (like streams) or to accommodate important shortcomings
(such as a lack of total ordering). These differences make HTTP/3
similar to HTTP/2 in key aspects, such as the relationship of
requests and responses to streams. However, the details of the
HTTP/3 design are substantially different than HTTP/2.
These departures are noted in this section.
A.1. Streams
HTTP/3 permits use of a larger number of streams (2^62-1) than
HTTP/2. The considerations about exhaustion of stream identifier
space apply, though the space is significantly larger such that it is
likely that other limits in QUIC are reached first, such as the limit
on the connection flow control window.
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.
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.
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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 [HTTP2]. However, QUIC
includes many features (e.g., flow control) which are also present in
HTTP/2. In these cases, the HTTP mapping does not re-implement them.
As a result, several HTTP/2 frame types are not required in HTTP/3.
Where an HTTP/2-defined frame is no longer used, the frame ID has
been reserved in order to maximize portability between HTTP/2 and
HTTP/3 implementations. However, even equivalent frames between the
two mappings are not identical.
Many of the differences arise from the fact that HTTP/2 provides an
absolute ordering between frames across all streams, while QUIC
provides this guarantee on each stream only. As a result, if a frame
type makes assumptions that frames from different streams will still
be received in the order sent, HTTP/3 will break them.
Some examples of feature adaptations are described below, as well as
general guidance to extension frame implementors converting an HTTP/2
extension to HTTP/3.
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. Header Compression Differences
HPACK was designed with the assumption of in-order delivery. A
sequence of encoded header blocks must arrive (and be decoded) at an
endpoint in the same order in which they were encoded. This ensures
that the dynamic state at the two endpoints remains in sync.
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Because this total ordering is not provided by QUIC, HTTP/3 uses a
modified version of HPACK, called QPACK. QPACK uses a single
unidirectional stream to make all modifications to the dynamic table,
ensuring a total order of updates. All frames which contain encoded
headers merely reference the table state at a given time without
modifying it.
[QPACK] provides additional details.
A.2.3. 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 rather than a
Stream ID (e.g., Push IDs). Redefinition of the encoding of
extension frame types might be necessary if the encoding includes a
Stream ID.
Because the Flags field is not present in generic HTTP/3 frames,
those frames which depend on the presence of flags need to allocate
space for flags as part of their frame payload.
Other than this issue, frame type HTTP/2 extensions are typically
portable to QUIC simply by replacing Stream 0 in HTTP/2 with a
control stream in HTTP/3. HTTP/3 extensions will not assume
ordering, but would not be harmed by ordering, and would be portable
to HTTP/2 in the same manner.
A.2.4. Mapping Between HTTP/2 and HTTP/3 Frame Types
DATA (0x0): Padding is not defined in HTTP/3 frames. See
Section 7.2.1.
HEADERS (0x1): 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 (0x2): As described in Appendix A.2.1, HTTP/3 does not
provide a means of signaling priority.
RST_STREAM (0x3): RST_STREAM frames do not exist, since QUIC
provides stream lifecycle management. The same code point is used
for the CANCEL_PUSH frame (Section 7.2.3).
SETTINGS (0x4): SETTINGS frames are sent only at the beginning of
the connection. See Section 7.2.4 and Appendix A.3.
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PUSH_PROMISE (0x5): The PUSH_PROMISE does not reference a stream;
instead the push stream references the PUSH_PROMISE frame using a
Push ID. See Section 7.2.5.
PING (0x6): PING frames do not exist, since QUIC provides equivalent
functionality.
GOAWAY (0x7): GOAWAY is sent only from server to client and does not
contain an error code. See Section 7.2.6.
WINDOW_UPDATE (0x8): WINDOW_UPDATE frames do not exist, since QUIC
provides flow control.
CONTINUATION (0x9): CONTINUATION frames do not exist; instead,
larger HEADERS/PUSH_PROMISE frames than HTTP/2 are permitted.
Frame types defined by extensions to HTTP/2 need to be separately
registered for HTTP/3 if still applicable. The IDs of frames defined
in [HTTP2] 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 options that are retained in HTTP/3 have the same value as
in HTTP/2.
Below is a listing of how each HTTP/2 SETTINGS parameter is mapped:
SETTINGS_HEADER_TABLE_SIZE: See [QPACK].
SETTINGS_ENABLE_PUSH: This is removed in favor of the MAX_PUSH_ID
which provides a more granular control over server push.
SETTINGS_MAX_CONCURRENT_STREAMS: QUIC controls the largest open
Stream ID as part of its flow control logic. Specifying
SETTINGS_MAX_CONCURRENT_STREAMS in the SETTINGS frame is an error.
SETTINGS_INITIAL_WINDOW_SIZE: QUIC requires both stream and
connection flow control window sizes to be specified in the
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initial transport handshake. Specifying
SETTINGS_INITIAL_WINDOW_SIZE in the SETTINGS frame is an error.
SETTINGS_MAX_FRAME_SIZE: This setting has no equivalent in HTTP/3.
Specifying it in the SETTINGS frame is an error.
SETTINGS_MAX_HEADER_LIST_SIZE: See Section 7.2.4.1.
In HTTP/3, setting values are variable-length integers (6, 14, 30, or
62 bits long) rather than fixed-length 32-bit fields as in HTTP/2.
This will often produce a shorter encoding, but can produce a longer
encoding for settings which use the full 32-bit space. Settings
ported from HTTP/2 might choose to redefine 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 [HTTP2] 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 to
not 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, there is no direct portability of HTTP/2
error codes to HTTP/3 error codes; the values are shifted in order to
prevent accidental or implicit conversion.
The HTTP/2 error codes defined in Section 7 of [HTTP2] logically map
to the HTTP/3 error codes as follows:
NO_ERROR (0x0): H3_NO_ERROR in Section 8.1.
PROTOCOL_ERROR (0x1): This is mapped to H3_GENERAL_PROTOCOL_ERROR
except in cases where more specific error codes have been defined.
This includes H3_FRAME_UNEXPECTED and H3_CLOSED_CRITICAL_STREAM
defined in Section 8.1.
INTERNAL_ERROR (0x2): H3_INTERNAL_ERROR in Section 8.1.
FLOW_CONTROL_ERROR (0x3): Not applicable, since QUIC handles flow
control.
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SETTINGS_TIMEOUT (0x4): Not applicable, since no acknowledgement of
SETTINGS is defined.
STREAM_CLOSED (0x5): Not applicable, since QUIC handles stream
management.
FRAME_SIZE_ERROR (0x6): H3_FRAME_ERROR error code defined in
Section 8.1.
REFUSED_STREAM (0x7): 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 (0x8): H3_REQUEST_CANCELLED in Section 8.1.
COMPRESSION_ERROR (0x9): Multiple error codes are defined in
[QPACK].
CONNECT_ERROR (0xa): H3_CONNECT_ERROR in Section 8.1.
ENHANCE_YOUR_CALM (0xb): H3_EXCESSIVE_LOAD in Section 8.1.
INADEQUATE_SECURITY (0xc): Not applicable, since QUIC is assumed to
provide sufficient security on all connections.
H3_1_1_REQUIRED (0xd): 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.
Appendix B. Change Log
*RFC Editor's Note:* Please remove this section prior to
publication of a final version of this document.
B.1. Since draft-ietf-quic-http-24
* Removed H3_EARLY_RESPONSE error code; H3_NO_ERROR is recommended
instead (#3130,#3208)
* Unknown error codes are equivalent to H3_NO_ERROR (#3276,#3331)
* Some error codes are reserved for greasing (#3325,#3360)
B.2. Since draft-ietf-quic-http-23
* Removed "quic" Alt-Svc parameter (#3061,#3118)
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* Clients need not persist unknown settings for use in 0-RTT
(#3110,#3113)
* Clarify error cases around CANCEL_PUSH (#2819,#3083)
B.3. Since draft-ietf-quic-http-22
* Removed priority signaling (#2922,#2924)
* Further changes to error codes (#2662,#2551):
- Error codes renumbered
- HTTP_MALFORMED_FRAME replaced by HTTP_FRAME_ERROR,
HTTP_ID_ERROR, and others
* Clarify how unknown frame types interact with required frame
sequence (#2867,#2858)
* Describe interactions with the transport in terms of defined
interface terms (#2857,#2805)
* Require the use of the "http-opportunistic" resource (RFC 8164)
when scheme is "http" (#2439,#2973)
* Settings identifiers cannot be duplicated (#2979)
* Changes to SETTINGS frames in 0-RTT (#2972,#2790,#2945):
- Servers must send all settings with non-default values in their
SETTINGS frame, even when resuming
- If a client doesn't have settings associated with a 0-RTT
ticket, it uses the defaults
- Servers can't accept early data if they cannot recover the
settings the client will have remembered
* Clarify that Upgrade and the 101 status code are prohibited
(#2898,#2889)
* Clarify that frame types reserved for greasing can occur on any
stream, but frame types reserved due to HTTP/2 correspondence are
prohibited (#2997,#2692,#2693)
* Unknown error codes cannot be treated as errors (#2998,#2816)
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B.4. Since draft-ietf-quic-http-21
No changes
B.5. Since draft-ietf-quic-http-20
* Prohibit closing the control stream (#2509, #2666)
* Change default priority to use an orphan node (#2502, #2690)
* Exclusive priorities are restored (#2754, #2781)
* Restrict use of frames when using CONNECT (#2229, #2702)
* Close and maybe reset streams if a connection error occurs for
CONNECT (#2228, #2703)
* Encourage provision of sufficient unidirectional streams for QPACK
(#2100, #2529, #2762)
* Allow extensions to use server-initiated bidirectional streams
(#2711, #2773)
* Clarify use of maximum header list size setting (#2516, #2774)
* Extensive changes to error codes and conditions of their sending
- Require connection errors for more error conditions (#2511,
#2510)
- Updated the error codes for illegal GOAWAY frames (#2714,
#2707)
- Specified error code for HEADERS on control stream (#2708)
- Specified error code for servers receiving PUSH_PROMISE (#2709)
- Specified error code for receiving DATA before HEADERS (#2715)
- Describe malformed messages and their handling (#2410, #2764)
- Remove HTTP_PUSH_ALREADY_IN_CACHE error (#2812, #2813)
- Refactor Push ID related errors (#2818, #2820)
- Rationalize HTTP/3 stream creation errors (#2821, #2822)
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B.6. Since draft-ietf-quic-http-19
* SETTINGS_NUM_PLACEHOLDERS is 0x9 (#2443,#2530)
* Non-zero bits in the Empty field of the PRIORITY frame MAY be
treated as an error (#2501)
B.7. Since draft-ietf-quic-http-18
* Resetting streams following a GOAWAY is recommended, but not
required (#2256,#2457)
* Use variable-length integers throughout (#2437,#2233,#2253,#2275)
- Variable-length frame types, stream types, and settings
identifiers
- Renumbered stream type assignments
- Modified associated reserved values
* Frame layout switched from Length-Type-Value to Type-Length-Value
(#2395,#2235)
* Specified error code for servers receiving DUPLICATE_PUSH (#2497)
* Use connection error for invalid PRIORITY (#2507, #2508)
B.8. Since draft-ietf-quic-http-17
* HTTP_REQUEST_REJECTED is used to indicate a request can be retried
(#2106, #2325)
* Changed error code for GOAWAY on the wrong stream (#2231, #2343)
B.9. Since draft-ietf-quic-http-16
* Rename "HTTP/QUIC" to "HTTP/3" (#1973)
* Changes to PRIORITY frame (#1865, #2075)
- Permitted as first frame of request streams
- Remove exclusive reprioritization
- Changes to Prioritized Element Type bits
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* Define DUPLICATE_PUSH frame to refer to another PUSH_PROMISE
(#2072)
* Set defaults for settings, allow request before receiving SETTINGS
(#1809, #1846, #2038)
* Clarify message processing rules for streams that aren't closed
(#1972, #2003)
* Removed reservation of error code 0 and moved HTTP_NO_ERROR to
this value (#1922)
* Removed prohibition of zero-length DATA frames (#2098)
B.10. Since draft-ietf-quic-http-15
Substantial editorial reorganization; no technical changes.
B.11. Since draft-ietf-quic-http-14
* Recommend sensible values for QUIC transport parameters
(#1720,#1806)
* Define error for missing SETTINGS frame (#1697,#1808)
* Setting values are variable-length integers (#1556,#1807) and do
not have separate maximum values (#1820)
* Expanded discussion of connection closure (#1599,#1717,#1712)
* HTTP_VERSION_FALLBACK falls back to HTTP/1.1 (#1677,#1685)
B.12. Since draft-ietf-quic-http-13
* Reserved some frame types for grease (#1333, #1446)
* Unknown unidirectional stream types are tolerated, not errors;
some reserved for grease (#1490, #1525)
* Require settings to be remembered for 0-RTT, prohibit reductions
(#1541, #1641)
* Specify behavior for truncated requests (#1596, #1643)
B.13. Since draft-ietf-quic-http-12
* TLS SNI extension isn't mandatory if an alternative method is used
(#1459, #1462, #1466)
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* Removed flags from HTTP/3 frames (#1388, #1398)
* Reserved frame types and settings for use in preserving
extensibility (#1333, #1446)
* Added general error code (#1391, #1397)
* Unidirectional streams carry a type byte and are extensible
(#910,#1359)
* Priority mechanism now uses explicit placeholders to enable
persistent structure in the tree (#441,#1421,#1422)
B.14. Since draft-ietf-quic-http-11
* Moved QPACK table updates and acknowledgments to dedicated streams
(#1121, #1122, #1238)
B.15. Since draft-ietf-quic-http-10
* Settings need to be remembered when attempting and accepting 0-RTT
(#1157, #1207)
B.16. Since draft-ietf-quic-http-09
* Selected QCRAM for header compression (#228, #1117)
* The server_name TLS extension is now mandatory (#296, #495)
* Specified handling of unsupported versions in Alt-Svc (#1093,
#1097)
B.17. Since draft-ietf-quic-http-08
* Clarified connection coalescing rules (#940, #1024)
B.18. Since draft-ietf-quic-http-07
* Changes for integer encodings in QUIC (#595,#905)
* Use unidirectional streams as appropriate (#515, #240, #281, #886)
* Improvement to the description of GOAWAY (#604, #898)
* Improve description of server push usage (#947, #950, #957)
B.19. Since draft-ietf-quic-http-06
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* Track changes in QUIC error code usage (#485)
B.20. Since draft-ietf-quic-http-05
* Made push ID sequential, add MAX_PUSH_ID, remove
SETTINGS_ENABLE_PUSH (#709)
* Guidance about keep-alive and QUIC PINGs (#729)
* Expanded text on GOAWAY and cancellation (#757)
B.21. Since draft-ietf-quic-http-04
* Cite RFC 5234 (#404)
* Return to a single stream per request (#245,#557)
* Use separate frame type and settings registries from HTTP/2 (#81)
* SETTINGS_ENABLE_PUSH instead of SETTINGS_DISABLE_PUSH (#477)
* Restored GOAWAY (#696)
* Identify server push using Push ID rather than a stream ID
(#702,#281)
* DATA frames cannot be empty (#700)
B.22. Since draft-ietf-quic-http-03
None.
B.23. Since draft-ietf-quic-http-02
* Track changes in transport draft
B.24. Since draft-ietf-quic-http-01
* SETTINGS changes (#181):
- SETTINGS can be sent only once at the start of a connection; no
changes thereafter
- SETTINGS_ACK removed
- Settings can only occur in the SETTINGS frame a single time
- Boolean format updated
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* Alt-Svc parameter changed from "v" to "quic"; format updated
(#229)
* Closing the connection control stream or any message control
stream is a fatal error (#176)
* HPACK Sequence counter can wrap (#173)
* 0-RTT guidance added
* Guide to differences from HTTP/2 and porting HTTP/2 extensions
added (#127,#242)
B.25. Since draft-ietf-quic-http-00
* Changed "HTTP/2-over-QUIC" to "HTTP/QUIC" throughout (#11,#29)
* Changed from using HTTP/2 framing within Stream 3 to new framing
format and two-stream-per-request model (#71,#72,#73)
* Adopted SETTINGS format from draft-bishop-httpbis-extended-
settings-01
* Reworked SETTINGS_ACK to account for indeterminate inter-stream
order (#75)
* Described CONNECT pseudo-method (#95)
* Updated ALPN token and Alt-Svc guidance (#13,#87)
* Application-layer-defined error codes (#19,#74)
B.26. Since draft-shade-quic-http2-mapping-00
* Adopted as base for draft-ietf-quic-http
* Updated authors/editors list
Acknowledgements
The original authors of this specification were Robbie Shade and Mike
Warres.
A substantial portion of Mike's contribution was supported by
Microsoft during his employment there.
Author's Address
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Mike Bishop (editor)
Akamai
Email: mbishop@evequefou.be
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