WebTransport over HTTP/3
draft-ietf-webtrans-http3-00
Network Working Group V. Vasiliev
Internet-Draft Google
Intended status: Standards Track 17 February 2021
Expires: 21 August 2021
WebTransport over HTTP/3
draft-ietf-webtrans-http3-00
Abstract
WebTransport [OVERVIEW] is a protocol framework that enables clients
constrained by the Web security model to communicate with a remote
server using a secure multiplexed transport. This document describes
a WebTransport protocol that is based on HTTP/3 [HTTP3] and provides
support for unidirectional streams, bidirectional streams and
datagrams, all multiplexed within the same HTTP/3 connection.
Note to Readers
Discussion of this draft takes place on the WebTransport mailing list
(webtransport@ietf.org), which is archived at
<https://mailarchive.ietf.org/arch/search/?email_list=webtransport>.
The repository tracking the issues for this draft can be found at
<https://github.com/ietf-wg-webtrans/draft-ietf-webtrans-http3/
issues>. The web API draft corresponding to this document can be
found at <https://w3c.github.io/webtransport/>.
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 21 August 2021.
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Copyright Notice
Copyright (c) 2021 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
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provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 3
3. Session Establishment . . . . . . . . . . . . . . . . . . . . 4
3.1. Establishing a Transport-Capable HTTP/3 Connection . . . 4
3.2. Extended CONNECT in HTTP/3 . . . . . . . . . . . . . . . 4
3.3. Creating a New Session . . . . . . . . . . . . . . . . . 5
3.4. Limiting the Number of Simultaneous Sessions . . . . . . 5
4. WebTransport Features . . . . . . . . . . . . . . . . . . . . 6
4.1. Unidirectional streams . . . . . . . . . . . . . . . . . 6
4.2. Client-Initiated Bidirectional Streams . . . . . . . . . 6
4.3. Server-Initiated Bidirectional Streams . . . . . . . . . 7
4.4. Datagrams . . . . . . . . . . . . . . . . . . . . . . . . 7
5. Session Termination . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7.1. Upgrade Token Registration . . . . . . . . . . . . . . . 9
7.2. HTTP/3 SETTINGS Parameter Registration . . . . . . . . . 9
7.3. Frame Type Registration . . . . . . . . . . . . . . . . . 9
7.4. Stream Type Registration . . . . . . . . . . . . . . . . 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1. Normative References . . . . . . . . . . . . . . . . . . 10
8.2. Informative References . . . . . . . . . . . . . . . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
HTTP/3 [HTTP3] is a protocol defined on top of QUIC [QUIC-TRANSPORT]
that can multiplex HTTP requests over a QUIC connection. This
document defines a mechanism for multiplexing non-HTTP data with
HTTP/3 in a manner that conforms with the WebTransport protocol
requirements and semantics [OVERVIEW]. Using the mechanism described
here, multiple WebTransport instances can be multiplexed
simultaneously with regular HTTP traffic on the same HTTP/3
connection.
1.1. Terminology
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
This document follows terminology defined in Section 1.2 of
[OVERVIEW]. Note that this document distinguishes between a
WebTransport server and an HTTP/3 server. An HTTP/3 server is the
server that terminates HTTP/3 connections; a WebTransport server is
an application that accepts WebTransport sessions, which can be
accessed via an HTTP/3 server.
2. Protocol Overview
WebTransport servers in general are identified by a pair of authority
value and path value (defined in [RFC3986] Sections 3.2 and 3.3
correspondingly).
When an HTTP/3 connection is established, both the client and server
have to send a SETTINGS_ENABLE_WEBTRANSPORT setting in order to
indicate that they both support WebTransport over HTTP/3.
WebTransport sessions are initiated inside a given HTTP/3 connection
by the client, who sends an extended CONNECT request [RFC8441]. If
the server accepts the request, an WebTransport session is
established. The resulting stream will be further referred to as a
_CONNECT stream_, and its stream ID is used to uniquely identify a
given WebTransport session within the connection. The ID of the
CONNECT stream that established a given WebTransport session will be
further referred to as a _Session ID_.
After the session is established, the peers can exchange data using
the following mechanisms:
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* A client can create a bidirectional stream using a special
indefinite-length HTTP/3 frame that transfers ownership of the
stream to WebTransport.
* A server can create a bidirectional stream, which is possible
since HTTP/3 does not define any semantics for server-initiated
bidirectional streams.
* Both client and server can create a unidirectional stream using a
special stream type.
* A datagram can be sent using a QUIC DATAGRAM frame
[QUIC-DATAGRAM].
An WebTransport session is terminated when the CONNECT stream that
created it is closed.
3. Session Establishment
3.1. Establishing a Transport-Capable HTTP/3 Connection
In order to indicate support for WebTransport, both the client and
the server MUST send a SETTINGS_ENABLE_WEBTRANSPORT value set to "1"
in their SETTINGS frame. Endpoints MUST NOT use any WebTransport-
related functionality unless the parameter has been negotiated.
If SETTINGS_ENABLE_WEBTRANSPORT is negotiated, support for the QUIC
DATAGRAMs within HTTP/3 MUST be negotiated as described in
[HTTP3-DATAGRAM]; negotiating WebTransport support without
negotiating QUIC DATAGRAM extension SHALL result in a
H3_SETTINGS_ERROR error.
[HTTP3] requires client's "initial_max_bidi_streams" transport
parameter to be set to zero. Existing implementation might enforce
this requirement before negotiating settings; thus, the client MUST
send a non-zero MAX_STREAMS for client-initiated bidirectional
streams after receiving an appropriate SETTINGS frame from the
server.
3.2. Extended CONNECT in HTTP/3
[RFC8441] defines an extended CONNECT method in Section 4, enabled by
the SETTINGS_ENABLE_CONNECT_PROTOCOL parameter. That parameter is
only defined for HTTP/2. This document does not create a new multi-
purpose parameter to indicate support for extended CONNECT in HTTP/3;
instead, the SETTINGS_ENABLE_WEBTRANSPORT setting implies that an
endpoint supports extended CONNECT.
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3.3. Creating a New Session
As WebTransport sessions are established over HTTP/3, they are
identified using the "https" URI scheme [RFC7230].
In order to create a new WebTransport session, a client can send an
HTTP CONNECT request. The ":protocol" pseudo-header field
([RFC8441]) MUST be set to "webtransport". The ":scheme" field MUST
be "https". Both the ":authority" and the ":path" value MUST be set;
those fields indicate the desired WebTransport server. An "Origin"
header [RFC6454] MUST be provided within the request.
Upon receiving an extended CONNECT request with a ":protocol" field
set to "webtransport", the HTTP/3 server can check if it has a
WebTransport server associated with the specified ":authority" and
":path" values. If it does not, it SHOULD reply with status code 404
(Section 6.5.4, [RFC7231]). If it does, it MAY accept the session by
replying with status code 200. The WebTransport server MUST verify
the "Origin" header to ensure that the specified origin is allowed to
access the server in question.
From the client's perspective, a WebTransport session is established
when the client receives a 200 response. From the server's
perspective, a session is established once it sends a 200 response.
Both endpoints MUST NOT open any streams or send any datagrams on a
given session before that session is established. WebTransport over
HTTP/3 does not support 0-RTT.
3.4. Limiting the Number of Simultaneous Sessions
From the flow control perspective, WebTransport sessions count
against the stream flow control just like regular HTTP requests,
since they are established via an HTTP CONNECT request. This
document does not make any effort to introduce a separate flow
control mechanism for sessions, nor to separate HTTP requests from
WebTransport data streams. If the server needs to limit the rate of
incoming requests, it has alternative mechanisms at its disposal:
* "HTTP_REQUEST_REJECTED" error code defined in [HTTP3] indicates to
the receiving HTTP/3 stack that the request was not processed in
any way.
* HTTP status code 429 indicates that the request was rejected due
to rate limiting [RFC6585]. Unlike the previous method, this
signal is directly propagated to the application.
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4. WebTransport Features
WebTransport over HTTP/3 provides the following features described in
[OVERVIEW]: unidirectional streams, bidirectional streams and
datagrams, initiated by either endpoint.
Session IDs are used to demultiplex streams and datagrams belonging
to different WebTransport sessions. On the wire, session IDs are
encoded using the QUIC variable length integer scheme described in
[QUIC-TRANSPORT].
4.1. Unidirectional streams
Once established, both endpoints can open unidirectional streams.
The HTTP/3 unidirectional stream type SHALL be 0x54. The body of the
stream SHALL be the stream type, followed by the session ID, encoded
as a variable-length integer, followed by the user-specified stream
data (Figure 1).
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x54 (i) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session ID (i) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Stream Body ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Unidirectional WebTransport stream format
4.2. Client-Initiated Bidirectional Streams
WebTransport clients can initiate bidirectional streams by opening an
HTTP/3 bidirectional stream and sending an HTTP/3 frame with type
"WEBTRANSPORT_STREAM" (type=0x41). The format of the frame SHALL be
the frame type, followed by the session ID, encoded as a variable-
length integer, followed by the user-specified stream data
(Figure 2). The frame SHALL last until the end of the stream.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x41 (i) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session ID (i) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Stream Body ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: WEBTRANSPORT_STREAM frame format
4.3. Server-Initiated Bidirectional Streams
WebTransport servers can initiate bidirectional streams by opening a
bidirectional stream within the HTTP/3 connection. Note that since
HTTP/3 does not define any semantics for server-initiated
bidirectional streams, this document is a normative reference for the
semantics of such streams for all HTTP/3 connections in which the
SETTINGS_ENABLE_WEBTRANSPORT option is negotiated. The format of
those streams SHALL be the session ID, encoded as a variable-length
integer, followed by the user-specified stream data (Figure 3).
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session ID (i) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Stream Body ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Server-initiated bidirectional stream format
4.4. Datagrams
Datagrams can be sent using the DATAGRAM frame as defined in
[QUIC-DATAGRAM] and [HTTP3-DATAGRAM]. For all HTTP/3 connections in
which the SETTINGS_ENABLE_WEBTRANSPORT option is negotiated, the Flow
Identifier is set to the session ID. In other words, the format of
datagrams SHALL be the session ID, followed by the user-specified
payload (Figure 4).
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session ID (i) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Datagram Body ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Datagram format
In QUIC, a datagram frame can span at most one packet. Because of
that, the applications have to know the maximum size of the datagram
they can send. However, when proxying the datagrams, the hop-by-hop
MTUs can vary. TODO: Describe how the path MTU can be computed,
specifically propagation across HTTP proxies.
5. Session Termination
An WebTransport session over HTTP/3 is terminated when either
endpoint closes the stream associated with the CONNECT request that
initiated the session. Upon learning about the session being
terminated, the endpoint MUST stop sending new datagrams and reset
all of the streams associated with the session.
6. Security Considerations
WebTransport over HTTP/3 satisfies all of the security requirements
imposed by [OVERVIEW] on WebTransport protocols, thus providing a
secure framework for client-server communication in cases when the
client is potentially untrusted.
WebTransport over HTTP/3 requires explicit opt-in through the use of
a QUIC transport parameter; this avoids potential protocol confusion
attacks by ensuring the HTTP/3 server explicitly supports it. It
also requires the use of the Origin header, providing the server with
the ability to deny access to Web-based clients that do not originate
from a trusted origin.
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Just like HTTP traffic going over HTTP/3, WebTransport pools traffic
to different origins within a single connection. Different origins
imply different trust domains, meaning that the implementations have
to treat each transport as potentially hostile towards others on the
same connection. One potential attack is a resource exhaustion
attack: since all of the transports share both congestion control and
flow control context, a single client aggressively using up those
resources can cause other transports to stall. The user agent thus
SHOULD implement a fairness scheme that ensures that each transport
within connection gets a reasonable share of controlled resources;
this applies both to sending data and to opening new streams.
7. IANA Considerations
7.1. Upgrade Token Registration
The following entry is added to the "Hypertext Transfer Protocol
(HTTP) Upgrade Token Registry" registry established by [RFC7230]:
The "webtransport" label identifies HTTP/3 used as a protocol for
WebTransport:
Value: webtransport
Description: WebTransport over HTTP/3
Reference: This document and [I-D.kinnear-webtransport-http2]
7.2. HTTP/3 SETTINGS Parameter Registration
The following entry is added to the "HTTP/3 Settings" registry
established by [HTTP3]:
The "SETTINGS_ENABLE_WEBTRANSPORT" parameter indicates that the
specified HTTP/3 connection is WebTransport-capable.
Setting Name: ENABLE_WEBTRANSPORT
Value: 0x2b603742
Default: 0
Specification: This document
7.3. Frame Type Registration
The following entry is added to the "HTTP/3 Frame Type" registry
established by [HTTP3]:
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The "WEBTRANSPORT_STREAM" frame allows HTTP/3 client-initiated
bidirectional streams to be used by WebTransport:
Code: 0x54
Frame Type: WEBTRANSPORT_STREAM
Specification: This document
7.4. Stream Type Registration
The following entry is added to the "HTTP/3 Stream Type" registry
established by [HTTP3]:
The "WebTransport stream" type allows unidirectional streams to be
used by WebTransport:
Code: 0x41
Stream Type: WebTransport stream
Specification: This document
Sender: Both
8. References
8.1. Normative References
[HTTP3] Bishop, M., Ed., "Hypertext Transfer Protocol Version 3
(HTTP/3)", Work in Progress, Internet-Draft, draft-ietf-
quic-http,
<https://tools.ietf.org/html/draft-ietf-quic-http>.
[HTTP3-DATAGRAM]
Schinazi, D. and L. Pardue, "Using QUIC Datagrams with
HTTP/3", Work in Progress, Internet-Draft, draft-schinazi-
masque-h3-datagram-04, 5 January 2021,
<http://www.ietf.org/internet-drafts/draft-schinazi-
masque-h3-datagram-04.txt>.
[OVERVIEW] Vasiliev, V., "The WebTransport Protocol Framework", Work
in Progress, Internet-Draft, draft-ietf-webtrans-overview-
latest, <https://tools.ietf.org/html/draft-ietf-webtrans-
overview-latest>.
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[QUIC-DATAGRAM]
Pauly, T., Kinnear, E., and D. Schinazi, "An Unreliable
Datagram Extension to QUIC", Work in Progress, Internet-
Draft, draft-pauly-quic-datagram,
<https://tools.ietf.org/html/draft-pauly-quic-datagram>.
[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,
<https://tools.ietf.org/html/draft-ietf-quic-transport>.
[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>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[RFC6454] Barth, A., "The Web Origin Concept", RFC 6454,
DOI 10.17487/RFC6454, December 2011,
<https://www.rfc-editor.org/info/rfc6454>.
[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>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
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>.
[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>.
[RFC8441] McManus, P., "Bootstrapping WebSockets with HTTP/2",
RFC 8441, DOI 10.17487/RFC8441, September 2018,
<https://www.rfc-editor.org/info/rfc8441>.
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8.2. Informative References
[I-D.kinnear-webtransport-http2]
Frindell, A., Kinnear, E., Pauly, T., Vasiliev, V., and G.
Xie, "WebTransport using HTTP/2", Work in Progress,
Internet-Draft, draft-kinnear-webtransport-http2-01, 13
July 2020, <http://www.ietf.org/internet-drafts/draft-
kinnear-webtransport-http2-01.txt>.
Author's Address
Victor Vasiliev
Google
Email: vasilvv@google.com
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