---
title: Hypertext Transfer Protocol (HTTP) over QUIC
abbrev: HTTP over QUIC
docname: draft-ietf-quic-http-latest
date: {DATE}
category: std
ipr: trust200902
area: Transport
workgroup: QUIC

stand_alone: yes
pi: [toc, sortrefs, symrefs, docmapping]

author:
 -
    ins: M. Bishop
    name: Mike Bishop
    org: Microsoft
    email: Michael.Bishop@microsoft.com
    role: editor

normative:

  QUIC-TRANSPORT:
    title: "QUIC: A UDP-Based Multiplexed and Secure Transport"
    date: {DATE}
    seriesinfo:
      Internet-Draft: draft-ietf-quic-transport-latest
    author:
      -
        ins: J. Iyengar
        name: Jana Iyengar
        org: Google
        role: editor
      -
        ins: M. Thomson
        name: Martin Thomson
        org: Mozilla
        role: editor

informative:


--- 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 QUIC.

--- note_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>.

Working Group information can be found at <https://github.com/quicwg>; source
code and issues list for this draft can be found at
<https://github.com/quicwg/base-drafts/labels/http>.


--- middle


# Introduction

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

QUIC is described in {{QUIC-TRANSPORT}}.  For a full description of HTTP/2, see
{{!RFC7540}}.


## Notational Conventions

The words "MUST", "MUST NOT", "SHOULD", and "MAY" are used in this document.
It's not shouting; when they are capitalized, they have the special meaning
defined in {{!RFC2119}}.

Field definitions are given in Augmented Backus-Naur Form (ABNF), as defined in
{{!RFC5234}}.


# QUIC Advertisement

An HTTP origin advertises the availability of an equivalent HTTP/QUIC endpoint
via the Alt-Svc HTTP response header or the HTTP/2 ALTSVC frame ({{!RFC7838}}),
using the ALPN token defined in {{connection-establishment}}.

For example, an origin could indicate in an HTTP/1.1 or HTTP/2 response that
HTTP/QUIC was available on UDP port 50781 at the same hostname by including the
following header in any response:

~~~ example
Alt-Svc: hq=":50781"
~~~

On receipt of an Alt-Svc header indicating HTTP/QUIC support, a client MAY
attempt to establish a QUIC connection to the indicated host and port and, if
successful, send HTTP requests using the mapping described in this document.

Connectivity problems (e.g. firewall blocking UDP) can result in QUIC connection
establishment failure, in which case the client SHOULD continue using the
existing connection or try another alternative endpoint offered by the origin.

Servers MAY serve HTTP/QUIC on any UDP port.  Servers MUST use the same port
across all IP addresses that serve a single domain, and SHOULD NOT change this
port.

## QUIC Version Hints {#alt-svc-version-hint}

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

~~~ abnf
quic = version-number
version-number = 1*8HEXDIG; hex-encoded QUIC version
~~~

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

~~~ example
Alt-Svc: hq=":49288";quic=1;quic=51303334
~~~

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


# Connection Establishment {#connection-establishment}

HTTP/QUIC connections are established as described in {{QUIC-TRANSPORT}}. During
connection establishment, HTTP/QUIC support is indicated by selecting the ALPN
token "hq" in the crypto handshake.

While connection-level options pertaining to the core QUIC protocol are set in
the initial crypto handshake, HTTP-specific settings are conveyed
in the SETTINGS frame. After the QUIC connection is established, a SETTINGS
frame ({{frame-settings}}) MUST be sent as the initial frame of the HTTP control
stream (Stream ID 1, see {{stream-mapping}}).  The server MUST NOT send data on
any other stream until the client's SETTINGS frame has been received.

## Draft Version Identification

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

Only implementations of the final, published RFC can identify themselves as
"hq". Until such an RFC exists, implementations MUST NOT identify themselves
using this string.

Implementations of draft versions of the protocol MUST add the string "-" and
the corresponding draft number to the identifier. For example,
draft-ietf-quic-http-01 is identified using the string "hq-01".

Non-compatible experiments that are based on these draft versions MUST append
the string "-" and an experiment name to the identifier. For example, an
experimental implementation based on draft-ietf-quic-http-09 which reserves an
extra stream for unsolicited transmission of 1980s pop music might identify
itself as "hq-09-rickroll". Note that any label MUST conform to the "token"
syntax defined in Section 3.2.6 of [RFC7230]. Experimenters are encouraged to
coordinate their experiments on the quic@ietf.org mailing list.


# Stream Mapping and Usage {#stream-mapping}

A QUIC stream provides reliable in-order delivery of bytes, but makes no
guarantees about order of delivery with regard to bytes on other streams. On the
wire, data is framed into QUIC STREAM frames, but this framing is invisible to
the HTTP framing layer. A QUIC receiver buffers and orders received STREAM
frames, exposing the data contained within as a reliable byte stream to the
application.

QUIC reserves Stream 0 for crypto operations (the handshake, crypto config
updates). Stream 1 is reserved for sending and receiving HTTP control frames,
and is analogous to HTTP/2's Stream 0.  This control stream is considered
critical to the HTTP connection.  If the control stream is closed for any
reason, this MUST be treated as a connection error of type
QUIC_CLOSED_CRITICAL_STREAM.

When HTTP headers and data are sent over QUIC, the QUIC layer handles most of
the stream management. An HTTP request/response consumes a single stream: This
means that the client's first request occurs on QUIC stream 3, the second on
stream 5, and so on. The server's first push consumes stream 2.

This stream carries frames related to the request/response (see {{frames}}).
When a stream terminates cleanly, if the last frame on the stream was truncated,
this MUST be treated as a connection error (see HTTP_MALFORMED_* in
{{http-error-codes}}).  Streams which terminate abruptly may be reset at any
point in the frame.

Streams SHOULD be used sequentially, with no gaps.  Streams used for pushed
resources MAY be initiated out-of-order, but stream IDs SHOULD be allocated to
promised resources sequentially.

HTTP does not need to do any separate multiplexing when using QUIC - data sent
over a QUIC stream always maps to a particular HTTP transaction. Requests and
responses are considered complete when the corresponding QUIC stream is closed
in the appropriate direction.


##  Stream 1: Control Stream

Since most connection-level concerns will be managed by QUIC, the primary use of
Stream 1 will be for the SETTINGS frame when the connection opens and for
PRIORITY frames subsequently.

## HTTP Message Exchanges {#request-response}

A client sends an HTTP request on a new QUIC stream. A server sends an HTTP
response on the same stream as the request.

An HTTP message (request or response) consists of:

1. one header block (see {{frame-headers}}) containing the message headers (see
   {{!RFC7230}}, Section 3.2),

2. the payload body (see {{!RFC7230}}, Section 3.3), sent as a series of DATA
   frames (see {{frame-data}}),

3. optionally, one header block containing the trailer-part, if present (see
   {{!RFC7230}}, Section 4.1.2).

In addition, prior to sending the message header block indicated above, a
response may contain zero or more header blocks containing the message headers
of informational (1xx) HTTP responses (see {{!RFC7230}}, Section 3.2 and
{{!RFC7231}}, Section 6.2).

PUSH_PROMISE frames MAY be interleaved with the frames of a response message
indicating a pushed resource related to the response. These PUSH_PROMISE frames
are not part of the response, but carry the headers of a separate HTTP request
message.  See {{server-push}} for more details.

The "chunked" transfer encoding defined in Section 4.1 of {{!RFC7230}} MUST NOT
be used.

Trailing header fields are carried in an additional header block following the
body. Such a header block is a sequence of HEADERS frames with End Header Block
set on the last frame. Senders MUST send only one header block in the trailers
section; receivers MUST discard any subsequent header blocks.

An HTTP request/response exchange fully consumes a QUIC stream. After sending a
request, a client closes the stream for sending; after sending a response, the
server closes the stream for sending and the QUIC stream is fully closed.

A server can send a complete response prior to the client sending an entire
request if the response does not depend on any portion of the request that has
not been sent and received. When this is true, a server MAY request that the
client abort transmission of a request without error by triggering a QUIC
STOP_SENDING with error code HTTP_EARLY_RESPONSE, sending a complete response,
and cleanly closing its streams. Clients MUST NOT discard complete responses as
a result of having their request terminated abruptly, though clients can always
discard responses at their discretion for other reasons.  Servers MUST NOT
abort a response in progress as a result of receiving a solicited RST_STREAM.

### Header Compression

HTTP/QUIC uses HPACK header compression as described in {{!RFC7541}}. HPACK was
designed for HTTP/2 with the assumption of in-order delivery such as that
provided by TCP. A sequence of encoded header blocks must arrive (and be
decoded) at an endpoint in the same order in which they were encoded. This
ensures that the dynamic state at the two endpoints remains in sync.

QUIC streams provide in-order delivery of data sent on those streams, but there
are no guarantees about order of delivery between streams. QUIC anticipates
moving to a modified version of HPACK without this assumption.  In the meantime,
by fixing the size of the dynamic table at zero, HPACK can be used in an
unordered environment.


### The CONNECT Method

The pseudo-method CONNECT ({{!RFC7231}}, Section 4.3.6) is primarily used with
HTTP proxies to establish a TLS session with an origin server for the purposes
of interacting with "https" resources. In HTTP/1.x, CONNECT is used to convert
an entire HTTP connection into a tunnel to a remote host. In HTTP/2, the CONNECT
method is used to establish a tunnel over a single HTTP/2 stream to a remote
host for similar purposes.

A CONNECT request in HTTP/QUIC functions in the same manner as in HTTP/2. The
request MUST be formatted as described in {{!RFC7540}}, Section 8.3. A CONNECT
request that does not conform to these restrictions is malformed. The message
data 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 proxy sends a HEADERS frame containing a 2xx
series status code to the client, as defined in {{!RFC7231}}, Section 4.3.6.

All DATA frames on the request stream correspond to data sent on the TCP
connection. Any DATA frame sent by the client is transmitted by the proxy to the
TCP server; data received from the TCP server is packaged into DATA frames by
the proxy. Note that the size and number of TCP segments is not guaranteed to
map predictably to the size and number of HTTP DATA or QUIC STREAM frames.

The TCP connection can be closed by either peer. When the client half-closes the
request stream, 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
half-close the corresponding stream. TCP connections which remain half-closed in
a single direction are not invalid, but are often handled poorly by servers, so
clients SHOULD NOT half-close connections on which they are still expecting
data.

A TCP connection error is signaled with RST_STREAM. A proxy treats any error in
the TCP connection, which includes receiving a TCP segment with the RST bit set,
as a stream error of type HTTP_CONNECT_ERROR ({{http-error-codes}}).
Correspondingly, a proxy MUST send a TCP segment with the RST bit set if it
detects an error with the stream or the QUIC connection.

## Request Prioritization {#priority}

HTTP/QUIC uses the priority scheme described in {{!RFC7540}}, Section 5.3. In
this priority scheme, a given request can be designated as dependent upon
another request, which expresses the preference that the latter stream (the
"parent" request) be allocated resources before the former stream (the
"dependent" request). Taken together, the dependencies across all requests in a
connection form a dependency tree. The structure of the dependency tree changes
as PRIORITY frames add, remove, or change the dependency links between requests.

HTTP/2 defines its priorities in terms of streams whereas HTTP over QUIC
identifies requests.  The PRIORITY frame {{frame-priority}} identifies a request
either by identifying the stream that carries a request or by using a Push ID
({{frame-push-promise}}).  Other than the means of identifying requests, the
prioritization system is identical to that in HTTP/2.

Only a client can send PRIORITY frames.  A server MUST NOT send a PRIORITY
frame.


## Server Push

HTTP/QUIC supports server push as described in {{!RFC7540}}. During connection
establishment, the client enables server push by sending a MAX_PUSH_ID frame
(see {{frame-max-push-id}}).  A server cannot use server push until it receives
a MAX_PUSH_ID frame.

As with server push for HTTP/2, the server initiates a server push by sending a
PUSH_PROMISE frame that includes request header fields attributed to the
request. The PUSH_PROMISE frame is sent on a response stream.  Unlike HTTP/2,
the PUSH_PROMISE does not reference a stream; when a server fulfills a promise,
the stream that carries the stream headers references the PUSH_PROMISE.  This
allows a server to fulfill promises in the order that best suits its needs.

The server push response is conveyed on a push stream.  A push stream is a
server-initiated stream.  A push stream includes a header (see
{{fig-push-stream-header}}) that identifies the PUSH_PROMISE that it fulfills.
This header consists of a 32-bit Push ID, which identifies a server push (see
{{frame-push-promise}}).

~~~~~
 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 (32)                          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~~~~~
{: #fig-push-stream-header title="Push Stream Header"}

A push stream always starts with a 32-bit Push ID.  A client MUST treat
receiving a push stream that contains fewer than 4 octets as a connection error
of type HTTP_MALFORMED_PUSH.

A server SHOULD use Push IDs sequentially, starting at 0.  A client uses the
MAX_PUSH_ID frame ({{frame-max-push-id}}) to limit the number of pushes that a
server can promise.  A client MUST treat receipt of a push stream with a Push ID
that is greater than the maximum Push ID as a connection error of type
HTTP_MALFORMED_PUSH.

Each Push ID MUST only be used once in a push stream header.  If a push stream
header includes a Push ID that was used in another push stream header, the
client MUST treat this as a connection error of type HTTP_MALFORMED_PUSH.  The
same Push ID can be used in multiple PUSH_PROMISE frames (see
{{frame-push-promise}}).

After the push stream header, a push contains a response ({{request-response}}),
with response headers, a response body (if any) carried by DATA frames, then
trailers (if any) carried by HEADERS frames.

If a promised server push is not needed by the client, the client SHOULD send a
CANCEL_PUSH frame; if the push stream is already open, a QUIC STOP_SENDING frame
with an appropriate error code can be used instead (e.g., HTTP_PUSH_REFUSED,
HTTP_PUSH_ALREADY_IN_CACHE; see {{errors}}).  This asks the server not to
transfer the data and indicates that it will be discarded upon receipt.


# HTTP Framing Layer {#http-framing-layer}

Frames are used on each stream.  This section describes HTTP framing in QUIC and
highlights some differences from HTTP/2 framing.  For more detail on differences
from HTTP/2, see {{h2-frames}}.

## Frame Layout

All frames have the following format:

~~~~~~~~~~ drawing
    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Length (16)         |     Type (8)  |   Flags (8)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Frame Payload (*)                     ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~~~~~~~~~~
{: #fig-frame title="HTTP/QUIC frame format"}

## Frame Definitions {#frames}

### DATA {#frame-data}

DATA frames (type=0x0) convey arbitrary, variable-length sequences of octets
associated with an HTTP request or response payload.

The DATA frame defines no flags.

DATA frames MUST be associated with an HTTP request or response.  If a DATA
frame is received on the control stream, the recipient MUST respond with a
connection error ({{errors}}) of type HTTP_WRONG_STREAM.

DATA frames MUST contain a non-zero-length payload.  If a DATA frame is received
with a payload length of zero, the recipient MUST respond with a stream error
({{errors}}) of type HTTP_MALFORMED_DATA.

### HEADERS {#frame-headers}

The HEADERS frame (type=0x1) is used to carry part of a header set, compressed
using HPACK {{header-compression}}.

One flag is defined:

  End Header Block (0x4):
  : This frame concludes a header block.

A HEADERS frame with any other flags set MUST be treated as a connection error
of type HTTP_MALFORMED_HEADERS.

The next frame on the same stream after a HEADERS frame without the EHB flag set
MUST be another HEADERS frame. A receiver MUST treat the receipt of any other
type of frame as a stream error of type HTTP_INTERRUPTED_HEADERS. (Note that
QUIC can intersperse data from other streams between frames, or even during
transmission of frames, so multiplexing is not blocked by this requirement.)

A full header block is contained in a sequence of zero or more HEADERS frames
without EHB set, followed by a HEADERS frame with EHB set.


### PRIORITY {#frame-priority}

The PRIORITY (type=0x02) frame specifies the sender-advised priority of a stream
and is substantially different in format from {{!RFC7540}}.  In order to ensure
that prioritization is processed in a consistent order, PRIORITY frames MUST be
sent on the control stream.  A PRIORITY frame sent on any other stream MUST be
treated as a HTTP_WRONG_STREAM error.

The format has been modified to accommodate not being sent on a request stream,
to allow for identification of server pushes, and the larger stream ID space of
QUIC.  The semantics of the Stream Dependency, Weight, and E flag are otherwise
the same as in HTTP/2.

The flags defined are:

  PUSH_PRIORITIZED (0x04):
  : Indicates that the Prioritized Stream is a server push rather than a
    request.

  PUSH_DEPENDENT (0x02):
  : Indicates a dependency on a server push.

  E (0x01):
  : Indicates that the stream dependency is exclusive (see {{!RFC7540}}, Section
    5.3).

~~~~~~~~~~  drawing
    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Prioritized Request ID (32)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Stream Dependency ID (32)                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Weight (8)  |
   +-+-+-+-+-+-+-+-+
~~~~~~~~~~
{: #fig-priority title="PRIORITY frame payload"}

The PRIORITY frame payload has the following fields:

  Prioritized Request ID:
  : A 32-bit identifier for a request.  This contains the stream ID of a request
    stream when the PUSH_PRIORITIZED flag is clear, or a Push ID when the
    PUSH_PRIORITIZED flag is set.

  Stream Dependency ID:
  : A 32-bit stream identifier for a dependent request.  This contains the
    stream ID of a request stream when the PUSH_DEPENDENT flag is clear, or a
    Push ID when the PUSH_DEPENDENT flag is set.  A request stream ID of 0
    indicates a dependency on the root stream. For details of dependencies,
    see {{priority}} and {{!RFC7540}}, Section 5.3.

  Weight:
  : An unsigned 8-bit integer representing a priority weight for the stream (see
    {{!RFC7540}}, Section 5.3). Add one to the value to obtain a weight between
    1 and 256.

A PRIORITY frame identifies a request to priotize, and a request upon which that
request is dependent.  A Prioritized Request ID or Stream Dependency ID
identifies a client-initiated request using the corresponding stream ID when the
corresponding PUSH_PRIORITIZED or PUSH_DEPENDENT flag is not set.  Setting the
PUSH_PRIORITIZED or PUSH_DEPENDENT flag causes the Prioritized Request ID or
Stream Dependency ID (respectively) to identify a server push using a Push ID
(see {{frame-push-promise}} for details).

A PRIORITY frame MAY identify a Stream Dependency ID using a stream ID of 0; as
in {{!RFC7540}}, this makes the request dependent on the root of the dependency
tree.

Stream ID 0 and stream ID 1 cannot be reprioritized. A Prioritized Request ID
that identifies Stream 0 or 1 MUST be treated as a connection error of type
HTTP_MALFORMED_PRIORITY.

A PRIORITY frame that does not reference a request MUST be treated as a
HTTP_MALFORMED_PRIORITY error, unless it references stream ID 0.  A PRIORITY
that sets a PUSH_PRIORITIZED or PUSH_DEPENDENT flag, but then references a
non-existent Push ID MUST be treated as a HTTP_MALFORMED_PRIORITY error.

The length of a PRIORITY frame is 9 octets.  A PRIORITY frame with any other
length MUST be treated as a connection error of type HTTP_MALFORMED_PRIORITY.


### CANCEL_PUSH {#frame-cancel-push}

The CANCEL_PUSH frame (type=0x3) is used to request cancellation of server push
prior to the push stream being created.  The CANCEL_PUSH frame identifies a
server push request by Push ID (see {{frame-push-promise}}).

When a server receives this frame, it aborts sending the response for the
identified server push.  If the server has not yet started to send the server
push, it can use the receipt of a CANCEL_PUSH frame to avoid opening a
stream.  If the push stream has been opened by the server, the server SHOULD
sent a QUIC RST_STREAM frame on those streams and cease transmission of the
response.

A server can send this frame to indicate that it won't be sending a response
prior to creation of a push stream.  Once the push stream has been created,
sending CANCEL_PUSH has no effect on the state of the push stream.  A QUIC
RST_STREAM frame SHOULD be used instead to cancel transmission of the server
push response.

A CANCEL_PUSH frame is sent on the control stream.  Sending a CANCEL_PUSH frame
on a stream other than the control stream MUST be treated as a stream error of
type HTTP_WRONG_STREAM.

The CANCEL_PUSH frame has no defined flags.

The CANCEL_PUSH frame carries a 32-bit Push ID that identifies the server push
that is being cancelled (see {{frame-push-promise}}).

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.

A server MUST treat a CANCEL_PUSH frame payload that is other than 4 octets in
length as a connection error of type HTTP_MALFORMED_CANCEL_PUSH.


### SETTINGS {#frame-settings}

The SETTINGS frame (type=0x4) conveys configuration parameters that affect how
endpoints communicate, such as preferences and constraints on peer behavior, and
is different from {{!RFC7540}}. Individually, a SETTINGS parameter can also be
referred to as a "setting".

SETTINGS parameters are not negotiated; they describe characteristics of the
sending peer, which can be used by the receiving peer. However, a negotiation
can be implied by the use of SETTINGS -- a peer uses SETTINGS to advertise a set
of supported values. The recipient can then choose which entries from this list
are also acceptable and proceed with the value it has chosen. (This choice could
be announced in a field of an extension frame, or in its own value in SETTINGS.)

Different values for the same parameter can be advertised by each peer. For
example, a client might be willing to consume very large response headers,
while servers are more cautious about request size.

Parameters MUST NOT occur more than once.  A receiver MAY treat the presence of
the same parameter more than once as a connection error of type
HTTP_MALFORMED_SETTINGS.

The SETTINGS frame defines no flags.

The payload of a SETTINGS frame consists of zero or more parameters, each
consisting of an unsigned 16-bit setting identifier and a length-prefixed binary
value.

~~~~~~~~~~~~~~~  drawing
    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 (16)        |         Length (16)           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Contents (?)                       ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~~~~~~~~~~~~~~~
{: #fig-ext-settings title="SETTINGS value format"}

A zero-length content indicates that the setting value is a Boolean and true.
False is indicated by the absence of the setting.

Non-zero-length values MUST be compared against the remaining length of the
SETTINGS frame.  Any value which purports to cross the end of the frame MUST
cause the SETTINGS frame to be considered malformed and trigger a connection
error of type HTTP_MALFORMED_SETTINGS.

An implementation MUST ignore the contents for any SETTINGS identifier it does
not understand.

SETTINGS frames always apply to a connection, never a single stream.  A SETTINGS
frame MUST be sent as the first frame of the control stream (see
{{stream-mapping}}) by each peer, and MUST NOT be sent subsequently or on any
other stream. If an endpoint receives an SETTINGS frame on a different stream,
the endpoint MUST respond with a connection error of type HTTP_WRONG_STREAM.  If
an endpoint receives a second SETTINGS frame, the endpoint MUST respond with a
connection error of type HTTP_MULTIPLE_SETTINGS.

The SETTINGS frame affects connection state. A badly formed or incomplete
SETTINGS frame MUST be treated as a connection error ({{errors}}) of type
HTTP_MALFORMED_SETTINGS.


#### Integer encoding

Settings which are integers are transmitted in network byte order.  Leading
zero octets are permitted, but implementations SHOULD use only as many bytes as
are needed to represent the value.  An integer MUST NOT be represented in more
bytes than would be used to transfer the maximum permitted value.

#### Defined SETTINGS Parameters {#settings-parameters}

The following settings are defined in HTTP/QUIC:

  SETTINGS_HEADER_TABLE_SIZE (0x1):
  : An integer with a maximum value of 2^32 - 1.  This value MUST be zero.

  SETTINGS_MAX_HEADER_LIST_SIZE (0x6):
  : An integer with a maximum value of 2^32 - 1

#### Usage in 0-RTT

When a 0-RTT QUIC connection is being used, the client's initial requests will
be sent before the arrival of the server's SETTINGS frame.  Clients SHOULD
cache at least the following settings about servers:

  - SETTINGS_HEADER_TABLE_SIZE
  - SETTINGS_MAX_HEADER_LIST_SIZE

Clients MUST comply with cached settings until the server's current settings are
received.  If a client does not have cached values, it SHOULD assume the
following values:

  - SETTINGS_HEADER_TABLE_SIZE:  0 octets
  - SETTINGS_MAX_HEADER_LIST_SIZE:  16,384 octets

Servers MAY continue processing data from clients which exceed its current
configuration during the initial flight.  In this case, the client MUST apply
the new settings immediately upon receipt.

If the connection is closed because these or other constraints were violated
during the 0-RTT flight (e.g. with HTTP_HPACK_DECOMPRESSION_FAILED), clients MAY
establish a new connection and retry any 0-RTT requests using the settings sent
by the server on the closed connection. (This assumes that only requests that
are safe to retry are sent in 0-RTT.) If the connection was closed before the
SETTINGS frame was received, clients SHOULD discard any cached values and use
the defaults above on the next connection.


### PUSH_PROMISE {#frame-push-promise}

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

~~~~~~~~~~  drawing
    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 (32)                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Header Block (*)                      ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~~~~~~~~~~
{: #fig-push-promise title="PUSH_PROMISE frame payload"}

The payload consists of:

Push ID:
: A 32-bit identifier for the server push request.  A push ID is used in push
  stream header ({{server-push}}), CANCEL_PUSH frames ({{frame-cancel-push}}),
  and PRIORITY frames ({{frame-priority}}).

Header Block:
: HPACK-compressed request headers for the promised response.

A server MUST NOT use a Push ID that is larger than the client has provided in a
MAX_PUSH_ID frame ({{frame-max-push-id}}).  A client MUST treat receipt of a
PUSH_PROMISE that contains a larger Push ID than the client has advertised as a
connection error of type HTTP_MALFORMED_PUSH_PROMISE.

A server MAY use the same Push ID in multiple PUSH_PROMISE frames.  This allows
the server to use the same server push in response to multiple concurrent
requests.  Referencing the same server push ensures that a PUSH_PROMISE can be
made in relation to every response in which server push might be needed without
duplicating pushes.

A server that uses the same Push ID in multiple PUSH_PROMISE frames MUST include
the same header fields each time.  The octets of the header block MAY be
different due to differing encoding, but the header fields and their values MUST
be identical.  Note that ordering of header fields is significant.  A client
MUST treat receipt of a PUSH_PROMISE with conflicting header field values for
the same Push ID as a connection error of type HTTP_MALFORMED_PUSH_PROMISE.

Allowing duplicate references to the same Push ID is primarily to reduce
duplication caused by concurrent requests.  A server SHOULD avoid reusing a Push
ID over a long period.  Clients are likely to consume server push responses and
not retain them for reuse over time.  Clients that see a PUSH_PROMISE that uses
a Push ID that they have since consumed and discarded are forced to ignore the
PUSH_PROMISE.


### GOAWAY {#frame-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.  (Note that clients do not need to send GOAWAY to gracefully
close a connection; they simply stop making new requests.)

The GOAWAY frame does not define any flags, and the payload is a QUIC stream
identifier.  The GOAWAY frame applies to the connection, not a specific stream.
An endpoint MUST treat a GOAWAY frame on a stream other than the control stream
as a connection error ({{errors}}) of type HTTP_WRONG_STREAM.

New client requests might already have been sent before the client receives the
server's GOAWAY frame.  The GOAWAY frame contains the stream identifier of the
last client-initiated request that was or might be processed in this connection,
which enables client and server to agree on which requests were accepted prior
to the connection shutdown.  This identifier MAY be lower than the stream limit
identified by a QUIC MAX_STREAM_ID frame, and MAY be zero if no requests were
processed.  Servers SHOULD NOT increase the MAX_STREAM_ID limit after sending a
GOAWAY frame.

  Note:
  : In this context, "processed" means that some data from the stream was
    passed to some higher layer of software that might have taken some action as
    a result.

Once sent, the server will refuse requests sent on streams with an identifier
higher than the included last stream identifier.  Clients MUST NOT send new
requests on the connection after receiving GOAWAY, although requests might
already be in transit. A new connection can be established for new requests.

If the client has sent requests on streams with a higher stream identifier than
indicated in the GOAWAY frame, those requests were not and will not be
processed.  Endpoints SHOULD reset any streams above this ID with the error code
HTTP_REQUEST_CANCELLED.  Servers MAY also reset streams below the indicated ID
with HTTP_REQUEST_CANCELLED if the associated requests were not processed.
Servers MUST NOT use the HTTP_REQUEST_CANCELLED status for requests which were
partially or fully processed.

The client can treat requests cancelled by the server as though they had never
been sent at all, thereby allowing them to be retried later on a new connection.
If a stream is cancelled after receiving a complete response, the client MAY
ignore the cancellation and use the response.  However, if a stream is cancelled
after receiving a partial response, the response SHOULD NOT be used.
Automatically retrying such requests is not possible, unless this is otherwise
permitted (e.g. idempotent actions like GET, PUT, or DELETE).  Requests on
stream IDs less than or equal to the stream ID in the GOAWAY frame might have
been processed; their status cannot be known until they are completed
successfully, reset individually, or the connection terminates.

Servers SHOULD send a GOAWAY frame when the closing of a connection is known
in advance, even if the advance notice is small, so that the remote peer can
know whether a stream has been partially processed or not.  For example, if an
HTTP client sends a POST at the same time that a server closes a QUIC
connection, the client cannot know if the server started to process that POST
request if the server does not send a GOAWAY frame to indicate what streams it
might have acted on.

For unexpected closures caused by error conditions, a QUIC CONNECTION_CLOSE
frame MUST be used.  However, a GOAWAY MAY be sent first to provide additional
detail to clients.  If a connection terminates without a GOAWAY frame, the last
stream identifier is effectively the highest possible stream identifier (as
determined by QUIC's MAX_STREAM_ID).

An endpoint MAY send multiple GOAWAY frames if circumstances change. For
instance, an endpoint that sends GOAWAY without an error code during graceful
shutdown could subsequently encounter an error condition.  The last stream
identifier from the last GOAWAY frame received indicates which streams could
have been acted upon.  Endpoints MUST NOT increase the value they send in the
last stream identifier, since the peers might already have retried unprocessed
requests on another connection.

A client that is unable to retry requests loses all requests that are in flight
when the server closes the connection.  A server that is attempting to
gracefully shut down a connection SHOULD send an initial GOAWAY frame with the
last stream identifier set to the current value of QUIC's MAX_STREAM_ID and
SHOULD NOT increase the MAX_STREAM_ID thereafter.  This signals to the client
that a shutdown is imminent and that initiating further requests is prohibited.
After allowing time for any in-flight requests (at least one round-trip time),
the server MAY send another GOAWAY frame with an updated last stream identifier.
This ensures that a connection can be cleanly shut down without losing requests.


### MAX_PUSH_ID {#frame-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 a PUSH_PROMISE frame.  Consequently, this
also limits the number of push streams that the server can initiate in addition
to the limit set by the QUIC MAX_STREAM_ID frame.

The MAX_PUSH_ID frame is always sent on the control stream.  Receipt of a
MAX_PUSH_ID frame on any other stream MUST be treated as a connection error of
type HTTP_WRONG_STREAM.

A server MUST NOT send a MAX_PUSH_ID frame.  A client MUST treat the receipt of
a MAX_PUSH_ID frame as a connection error of type HTTP_MALFORMED_MAX_PUSH_ID.

The maximum Push ID is unset when a connection is created, meaning that a server
cannot push until it receives a MAX_PUSH_ID frame.  A client that wishes to
manage the number of promised server pushes can increase the maximum Push ID by
sending a MAX_PUSH_ID frame as the server fulfills or cancels server pushes.

The MAX_PUSH_ID frame has no defined flags.

The MAX_PUSH_ID frame carries a 32-bit Push ID that identifies the maximum value
for a Push ID that the server can use (see {{frame-push-promise}}).  A
MAX_PUSH_ID frame cannot reduce the maximum Push ID; receipt of a MAX_PUSH_ID
that contains a smaller value than previously received MUST be treated as a
connection error of type HTTP_MALFORMED_MAX_PUSH_ID.

A server MUST treat a MAX_PUSH_ID frame payload that is other than 4 octets in
length as a connection error of type HTTP_MALFORMED_MAX_PUSH_ID.


# Connection Management

QUIC connections are persistent.  All of the considerations in Section 9.1 of
{{?RFC7540}} apply to the management of QUIC connections.

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


# Error Handling {#errors}

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}}.

This section describes HTTP-specific error codes which can be used to express
the cause of a connection or stream error.

## HTTP/QUIC Error Codes {#http-error-codes}

The following error codes are defined for use in QUIC RST_STREAM, STOP_SENDING,
and CONNECTION_CLOSE frames when using HTTP/QUIC.

STOPPING (0x00):
: This value is reserved by the transport to be used in response to QUIC
  STOP_SENDING frames.

HTTP_NO_ERROR (0x01):
: No error.  This is used when the connection or stream needs to be closed, but
  there is no error to signal.

HTTP_PUSH_REFUSED (0x02):
: The server has attempted to push content which the client will not accept
  on this connection.

HTTP_INTERNAL_ERROR (0x03):
: An internal error has occurred in the HTTP stack.

HTTP_PUSH_ALREADY_IN_CACHE (0x04):
: The server has attempted to push content which the client has cached.

HTTP_REQUEST_CANCELLED (0x05):
: The client no longer needs the requested data.

HTTP_HPACK_DECOMPRESSION_FAILED (0x06):
: HPACK failed to decompress a frame and cannot continue.

HTTP_CONNECT_ERROR (0x07):
: The connection established in response to a CONNECT request was reset or
  abnormally closed.

HTTP_EXCESSIVE_LOAD (0x08):
: The endpoint detected that its peer is exhibiting a behavior that might be
  generating excessive load.

HTTP_VERSION_FALLBACK (0x09):
: The requested operation cannot be served over HTTP/QUIC.  The peer should
  retry over HTTP/2.

HTTP_MALFORMED_HEADERS (0x0A):
: A HEADERS frame has been received with an invalid format.

HTTP_MALFORMED_PRIORITY (0x0B):
: A PRIORITY frame has been received with an invalid format.

HTTP_MALFORMED_SETTINGS (0x0C):
: A SETTINGS frame has been received with an invalid format.

HTTP_MALFORMED_PUSH_PROMISE (0x0D):
: A PUSH_PROMISE frame has been received with an invalid format.

HTTP_MALFORMED_DATA (0x0E):
: A DATA frame has been received with an invalid format.

HTTP_INTERRUPTED_HEADERS (0x0F):
: A HEADERS frame without the End Header Block flag was followed by a frame
  other than HEADERS.

HTTP_WRONG_STREAM (0x10):
: A frame was received on stream where it is not permitted.

HTTP_MULTIPLE_SETTINGS (0x11):
: More than one SETTINGS frame was received.

HTTP_MALFORMED_PUSH (0x12):
: A push stream header was malformed or included an invalid Push ID.

HTTP_MALFORMED_MAX_PUSH_ID (0x13):
: A MAX_PUSH_ID frame has been received with an invalid format.


# Considerations for Transitioning from HTTP/2

HTTP/QUIC is strongly informed by HTTP/2, and bears many similarities.  This
section describes the approach taken to design HTTP/QUIC, points out important
differences from HTTP/2, and describes how to map HTTP/2 extensions into
HTTP/QUIC.

HTTP/QUIC begins from the premise that HTTP/2 code reuse is a useful feature,
but not a hard requirement.  HTTP/QUIC departs from HTTP/2 primarily where
necessary to accommodate the differences in behavior between QUIC and TCP (lack
of ordering, support for streams).  We intend to avoid gratuitous changes which
make it difficult or impossible to build extensions with the same semantics
applicable to both protocols at once.

These departures are noted in this section.

## HTTP Frame Types {#h2-frames}

Many framing concepts from HTTP/2 can be elided away on QUIC, because the
transport deals with them. Because frames are already on a stream, they can omit
the stream number. Because frames do not block multiplexing (QUIC's multiplexing
occurs below this layer), the support for variable-maximum-length packets can be
removed. Because stream termination is handled by QUIC, an END_STREAM flag is
not required.

Frame payloads are largely drawn from {{!RFC7540}}. However, QUIC includes many
features (e.g. flow control) which are also present in HTTP/2. In these cases,
the HTTP mapping does not re-implement them. As a result, several HTTP/2 frame
types are not required in HTTP/QUIC. Where an HTTP/2-defined frame is no longer
used, the frame ID has been reserved in order to maximize portability between
HTTP/2 and HTTP/QUIC implementations. However, even equivalent frames between
the two mappings are not identical.

Many of the differences arise from the fact that HTTP/2 provides an absolute
ordering between frames across all streams, while QUIC provides this guarantee
on each stream only.  As a result, if a frame type makes assumptions that frames
from different streams will still be received in the order sent, HTTP/QUIC will
break them.

For example, implicit in the HTTP/2 prioritization scheme is the notion of
in-order delivery of priority changes (i.e., dependency tree mutations): since
operations on the dependency tree such as reparenting a subtree are not
commutative, both sender and receiver must apply them in the same order to
ensure that both sides have a consistent view of the stream dependency tree.
HTTP/2 specifies priority assignments in PRIORITY frames and (optionally) in
HEADERS frames. To achieve in-order delivery of priority changes in HTTP/QUIC,
PRIORITY frames are sent on the control stream and the PRIORITY section is
removed from the HEADERS frame.

Other than this issue, frame type HTTP/2 extensions are typically portable to
QUIC simply by replacing Stream 0 in HTTP/2 with Stream 1 in HTTP/QUIC.
HTTP/QUIC extensions will not assume ordering, but would not be harmed by
ordering, and would be portable to HTTP/2 in the same manner.

Below is a listing of how each HTTP/2 frame type is mapped:

DATA (0x0):
: Padding is not defined in HTTP/QUIC frames.  See {{frame-data}}.

HEADERS (0x1):
: As described above, the PRIORITY region of HEADERS is not supported. A
  separate PRIORITY frame MUST be used. Padding is not defined in HTTP/QUIC
  frames.  See {{frame-headers}}.

PRIORITY (0x2):
: As described above, the PRIORITY frame is sent on the control stream.  See
  {{frame-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
  ({{frame-cancel-push}}).

SETTINGS (0x4):
: SETTINGS frames are sent only at the beginning of the connection.  See
  {{frame-settings}} and {{h2-settings}}.

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
  {{frame-push-promise}}.

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 {{frame-goaway}}.

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, and HEADERS frames can be used in series.

Frame types defined by extensions to HTTP/2 need to be separately registered for
HTTP/QUIC if still applicable.  The IDs of frames defined in {{!RFC7540}} have
been reserved for simplicity.  See {{iana-frames}}.

## HTTP/2 SETTINGS Parameters {#h2-settings}

An important difference from HTTP/2 is that settings are sent once, at the
beginning of the connection, and thereafter cannot change.  This eliminates
many corner cases around synchronization of changes.

Some transport-level options that HTTP/2 specifies via the SETTINGS frame are
superseded by QUIC transport parameters in HTTP/QUIC. The HTTP-level options
that are retained in HTTP/QUIC have the same value as in HTTP/2.

Below is a listing of how each HTTP/2 SETTINGS parameter is mapped:

SETTINGS_HEADER_TABLE_SIZE:
: See {{settings-parameters}}.

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 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/QUIC.  Specifying it in the SETTINGS
  frame is an error.

SETTINGS_MAX_HEADER_LIST_SIZE:
: See {{settings-parameters}}.

Settings need to be defined separately for HTTP/2 and  HTTP/QUIC.  The IDs of
settings defined in {{!RFC7540}} have been reserved for simplicity.  See
{{iana-settings}}.


## HTTP/2 Error Codes

QUIC has the same concepts of "stream" and "connection" errors that HTTP/2
provides. However, because the error code space is shared between multiple
components, there is no direct portability of HTTP/2 error codes.

The HTTP/2 error codes defined in Section 7 of {{!RFC7540}} map to the HTTP over
QUIC error codes as follows:

NO_ERROR (0x0):
: HTTP_NO_ERROR in {{http-error-codes}}.

PROTOCOL_ERROR (0x1):
: No single mapping.  See new HTTP_MALFORMED_* error codes defined in
  {{http-error-codes}}.

INTERNAL_ERROR (0x2):
: HTTP_INTERNAL_ERROR in {{http-error-codes}}.

FLOW_CONTROL_ERROR (0x3):
: Not applicable, since QUIC handles flow control.  Would provoke a
  QUIC_FLOW_CONTROL_RECEIVED_TOO_MUCH_DATA from the QUIC layer.

SETTINGS_TIMEOUT (0x4):
: Not applicable, since no acknowledgement of SETTINGS is defined.

STREAM_CLOSED (0x5):
: Not applicable, since QUIC handles stream management.  Would provoke a
  QUIC_STREAM_DATA_AFTER_TERMINATION from the QUIC layer.

FRAME_SIZE_ERROR (0x6)
: No single mapping.  See new error codes defined in {{http-error-codes}}.

REFUSED_STREAM (0x7):
: Not applicable, since QUIC handles stream management.  Would provoke a
  QUIC_TOO_MANY_OPEN_STREAMS from the QUIC layer.

CANCEL (0x8):
: HTTP_REQUEST_CANCELLED in {{http-error-codes}}.

COMPRESSION_ERROR (0x9):
: HTTP_HPACK_DECOMPRESSION_FAILED in {{http-error-codes}}.

CONNECT_ERROR (0xa):
: HTTP_CONNECT_ERROR in {{http-error-codes}}.

ENHANCE_YOUR_CALM (0xb):
: HTTP_EXCESSIVE_LOAD in {{http-error-codes}}.

INADEQUATE_SECURITY (0xc):
: Not applicable, since QUIC is assumed to provide sufficient security on all
  connections.

HTTP_1_1_REQUIRED (0xd):
: HTTP_VERSION_FALLBACK in {{http-error-codes}}.

Error codes need to be defined for HTTP/2 and HTTP/QUIC separately.  See
{{iana-error-codes}}.

# Security Considerations

The security considerations of HTTP over QUIC should be comparable to those of
HTTP/2.

The modified SETTINGS format contains nested length elements, which could pose
a security risk to an uncautious implementer.  A SETTINGS frame parser MUST
ensure that the length of the frame exactly matches the length of the settings
it contains.


# IANA Considerations

## Registration of HTTP/QUIC Identification String

This document creates a new registration for the identification of HTTP/QUIC in
the "Application Layer Protocol Negotiation (ALPN) Protocol IDs" registry
established in {{?RFC7301}}.

The "hq" string identifies HTTP/QUIC:

  Protocol:
  : HTTP over QUIC

  Identification Sequence:
  : 0x68 0x71 ("hq")

  Specification:
  : This document

## Registration of QUIC Version Hint Alt-Svc Parameter

This document creates a new registration for version-negotiation hints in the
"Hypertext Transfer Protocol (HTTP) Alt-Svc Parameter" registry established in
{{!RFC7838}}.

  Parameter:
  : "quic"

  Specification:
  : This document, {{alt-svc-version-hint}}

## Frame Types {#iana-frames}

This document establishes a registry for HTTP/QUIC frame type codes. The
"HTTP/QUIC Frame Type" registry manages an 8-bit space.  The "HTTP/QUIC Frame
Type" registry operates under either of the "IETF Review" or "IESG Approval"
policies {{?RFC8126}} for values between 0x00 and 0xef, with values between 0xf0
and 0xff being reserved for Experimental Use.

While this registry is separate from the "HTTP/2 Frame Type" registry defined in
{{RFC7540}}, it is preferable that the assignments parallel each other.  If an
entry is present in only one registry, every effort SHOULD be made to avoid
assigning the corresponding value to an unrelated operation.

New entries in this registry require the following information:

Frame Type:
: A name or label for the frame type.

Code:
: The 8-bit code assigned to the frame type.

Specification:
: A reference to a specification that includes a description of the frame
  layout, its semantics, and flags that the frame type uses, including any parts
  of the frame that are conditionally present based on the value of flags.

The entries in the following table are registered by this document.

|----------------|------|--------------------------|
| Frame Type     | Code | Specification            |
|----------------|:----:|--------------------------|
| DATA           | 0x0  | {{frame-data}}           |
| HEADERS        | 0x1  | {{frame-headers}}        |
| PRIORITY       | 0x2  | {{frame-priority}}       |
| CANCEL_PUSH    | 0x3  | {{frame-cancel-push}}    |
| SETTINGS       | 0x4  | {{frame-settings}}       |
| PUSH_PROMISE   | 0x5  | {{frame-push-promise}}   |
| Reserved       | 0x6  | N/A                      |
| GOAWAY         | 0x7  | {{frame-goaway}}         |
| Reserved       | 0x8  | N/A                      |
| Reserved       | 0x9  | N/A                      |
| MAX_PUSH_ID    | 0xD  | {{frame-max-push-id}}    |
|----------------|------|--------------------------|

## Settings Parameters {#iana-settings}

This document establishes a registry for HTTP/QUIC settings.  The "HTTP/QUIC
Settings" registry manages a 16-bit space.  The "HTTP/QUIC Settings" registry
operates under the "Expert Review" policy {{?RFC8126}} for values in the range
from 0x0000 to 0xefff, with values between and 0xf000 and 0xffff being reserved
for Experimental Use.  The designated experts are the same as those for the
"HTTP/2 Settings" registry defined in {{RFC7540}}.

While this registry is separate from the "HTTP/2 Settings" registry defined in
{{RFC7540}}, it is preferable that the assignments parallel each other.  If an
entry is present in only one registry, every effort SHOULD be made to avoid
assigning the corresponding value to an unrelated operation.

New registrations are advised to provide the following information:

Name:
: A symbolic name for the setting.  Specifying a setting name is optional.

Code:
: The 16-bit code assigned to the setting.

Specification:
: An optional reference to a specification that describes the use of the
  setting.

The entries in the following table are registered by this document.

|----------------------------|------|-------------------------|
| Setting Name               | Code | Specification           |
|----------------------------|:----:|-------------------------|
| HEADER_TABLE_SIZE          | 0x1  | {{settings-parameters}} |
| Reserved                   | 0x2  | N/A                     |
| Reserved                   | 0x3  | N/A                     |
| Reserved                   | 0x4  | N/A                     |
| Reserved                   | 0x5  | N/A                     |
| MAX_HEADER_LIST_SIZE       | 0x6  | {{settings-parameters}} |
|----------------------------|------|-------------------------|

## Error Codes {#iana-error-codes}

This document establishes a registry for HTTP/QUIC error codes.  The
"HTTP/QUIC Error Code" registry manages a 16-bit space.  The "HTTP/QUIC
Error Code" registry operates under the "Expert Review" policy
{{?RFC8126}}.

Registrations for error codes are required to include a description
of the error code.  An expert reviewer is advised to examine new
registrations for possible duplication with existing error codes.
Use of existing registrations is to be encouraged, but not mandated.

New registrations are advised to provide the following information:

Name:
: A name for the error code.  Specifying an error code name is optional.

Code:
: The 16-bit error code value.

Description:
: A brief description of the error code semantics, longer if no detailed
  specification is provided.

Specification:
: An optional reference for a specification that defines the error code.

The entries in the following table are registered by this document.

|-----------------------------------|--------|----------------------------------------|----------------------|
| Name                              | Code   | Description                            | Specification        |
|-----------------------------------|--------|----------------------------------------|----------------------|
|  STOPPING                         |  0x00  |  Reserved by QUIC                      | {{QUIC-TRANSPORT}}  |
|  HTTP_NO_ERROR                    |  0x01  |  No error                              | {{http-error-codes}} |
|  HTTP_PUSH_REFUSED                |  0x02  |  Client refused pushed content         | {{http-error-codes}} |
|  HTTP_INTERNAL_ERROR              |  0x03  |  Internal error                        | {{http-error-codes}} |
|  HTTP_PUSH_ALREADY_IN_CACHE       |  0x04  |  Pushed content already cached         | {{http-error-codes}} |
|  HTTP_REQUEST_CANCELLED           |  0x05  |  Data no longer needed                 | {{http-error-codes}} |
|  HTTP_HPACK_DECOMPRESSION_FAILED  |  0x06  |  HPACK cannot continue                 | {{http-error-codes}} |
|  HTTP_CONNECT_ERROR               |  0x07  |  TCP reset or error on CONNECT request | {{http-error-codes}} |
|  HTTP_EXCESSIVE_LOAD              |  0x08  |  Peer generating excessive load        | {{http-error-codes}} |
|  HTTP_VERSION_FALLBACK            |  0x09  |  Retry over HTTP/2                     | {{http-error-codes}} |
|  HTTP_MALFORMED_HEADERS           |  0x0A  |  Invalid HEADERS frame                 | {{http-error-codes}} |
|  HTTP_MALFORMED_PRIORITY          |  0x0B  |  Invalid PRIORITY frame                | {{http-error-codes}} |
|  HTTP_MALFORMED_SETTINGS          |  0x0C  |  Invalid SETTINGS frame                | {{http-error-codes}} |
|  HTTP_MALFORMED_PUSH_PROMISE      |  0x0D  |  Invalid PUSH_PROMISE frame            | {{http-error-codes}} |
|  HTTP_MALFORMED_DATA              |  0x0E  |  Invalid DATA frame                    | {{http-error-codes}} |
|  HTTP_INTERRUPTED_HEADERS         |  0x0F  |  Incomplete HEADERS block              | {{http-error-codes}} |
|  HTTP_WRONG_STREAM                |  0x10  |  A frame was sent on the wrong stream  | {{http-error-codes}} |
|  HTTP_MULTIPLE_SETTINGS           |  0x11  |  Multiple SETTINGS frames              | {{http-error-codes}} |
|  HTTP_MALFORMED_PUSH              |  0x12  |  Invalid push stream header            | {{http-error-codes}} |
|  HTTP_MALFORMED_MAX_PUSH_ID       |  0x13  |  Invalid MAX_PUSH_ID frame             | {{http-error-codes}} |
|-----------------------------------|--------|----------------------------------------|----------------------|


--- back

# Contributors

The original authors of this specification were Robbie Shade and Mike Warres.

# Change Log

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

## Since draft-ietf-quic-http-06

Nothing yet.

## 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)

## 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)

## Since draft-ietf-quic-http-03

None.

## Since draft-ietf-quic-http-02

- Track changes in transport draft

## 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

- 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)

## 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)


## Since draft-shade-quic-http2-mapping-00

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