WebTransport over WebSocket
draft-richter-webtransport-websocket-00
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Author | Marten Richter | ||
| Last updated | 2024-01-03 | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
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| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
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draft-richter-webtransport-websocket-00
webtrans M. Richter
Internet-Draft Technische Universität Berlin
Intended status: Standards Track 3 January 2024
Expires: 6 July 2024
WebTransport over WebSocket
draft-richter-webtransport-websocket-00
Abstract
WebTransport [OVERVIEW], a protocol framework within the Web security
model, empowers Web clients to initiate secure multiplexed transport
for low-level client-server interactions with remote servers. This
document outlines a protocol, based on WebSocket [WEBSOCKET],
offering WebTransport capabilities similar to the HTTP/2 variant
[WEBTRANSPORT-H2]. It serves as an alternative when UDP-based
protocols are inaccessible, and the client environment exclusively
supports WebSocket [WEBSOCKET].
Discussion Venues
This note is to be removed before publishing as an RFC.
Source for this draft and an issue tracker can be found at
https://github.com/martenrichter/draft-ietf-webtransport-websocket.
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 6 July 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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 Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Connection and version negotiation . . . . . . . . . . . 3
3.2. Data framing . . . . . . . . . . . . . . . . . . . . . . 4
3.3. Capsule frames . . . . . . . . . . . . . . . . . . . . . 4
3.4. Replacement for SETTINGS . . . . . . . . . . . . . . . . 5
4. Implementation Status . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6.1. WebSocket Subprotocol Name Registry . . . . . . . . . . . 6
6.2. WebTransport WebSocket Protocol Version Registry . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.1. Normative References . . . . . . . . . . . . . . . . . . 7
7.2. Informative References . . . . . . . . . . . . . . . . . 8
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
WebTransport [OVERVIEW] is designed to facilitate communication for
Web clients over HTTP/3 [HTTP3], leveraging QUIC [QUIC] semantics
with streams or datagrams [DATAGRAM]. In cases where UDP-based
traffic is restricted, HTTP/2 protocol [WEBTRANSPORT-H2] serves as an
alternative built solely on HTTP semantics.
Both [WEBTRANSPORT-H2] and [WEBTRANSPORT-H3] variants require a
native WebClient implementation due to the usual unavailability of
plain UDP and TCP/IP socket access for scripts within WebClients
This document defines a protocol implementable on the WebClient using
available scripting languages, without altering the WebClient's
native code. It uses the widespread WebSocket protocol as the base
without modification. However, a direct implementation in a
WebClient is possible.
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The protocol utilizes capsule semantics derived from
[WEBTRANSPORT-H2] and translates them into WebSocket frames. By
relying on WebSockets, also intermediates such as proxies unaware of
WebTransports can apply application layer processing.
An implementation should support both WebSocket over http/1 and
http/2. The server should incorporate WebTransport flow control
constraints and capsule processing into its WebSocket parser code.
Therefore, using unmodified existing WebSocket code is not
recommended.
2. Conventions and Definitions
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.
The document follows the terminology defined in Section 1.2 of
[OVERVIEW].
3. Protocol Overview
WebTransport servers are identified by an HTTPS URI per Section 4.2.2
of [HTTP].
The protocol uses [WEBTRANSPORT-H2] semantics with the following
modifications.
3.1. Connection and version negotiation
The WebSocket connection is established according to Section 4 of
[WEBSOCKET] or [WEBSOCKET-H2].
When a WebSocket connection is established, both the client and
server select the WebTransport-Websocket protocol by setting |Sec-
WebSocket-Protocol| Section 1.9 of [WEBSOCKET] to the supported
versions. The protocol names follow the scheme
"webtransport_VERSIONAME", where VERSIONNAME identifies the
particular protocol version. For this protocol VERSIONAME would be
"kDraft1" and the |Sec-WebSocket-Protocol| field would include
"webtransport_kDraft1". The protocol negotiation follows the
procedures as described in Section 4.1 of [WEBSOCKET] and
Section 4.2.2 of [WEBSOCKET]. No protocol extensions MUST BE
negotiated.
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3.2. Data framing
The protocol uses the data frames as defined in Section 5 of
[WEBSOCKET]. PING and PONG frame handling is not changed Section 5.5
of [WEBSOCKET].
The CLOSE frame Section 5.5.1 of [WEBSOCKET] replaces the mechanism
invoked after CONNECT stream closure in Section 2 of
[WEBTRANSPORT-H2]. The body MUST include a UTF-8 encoded reason
string when transmitted by a protocol-aware client or server. The
reason string has the form "CODE:REASONSTRING", where CODE is a text
representation of an unsigned 32-bit decimal integer in the range of
between 0x00000000 and 0xffffffff Section 4.3 of [WEBTRANSPORT-H3].
REASONSTRING is the actual reason transmitted through WebTransport.
A close FRAME without a reason may be sent by protocol-unaware
WebClients or proxies. In such instances, the CODE and REASONSTRING
are reconstructed using the WebSocket Close Code Number as specified
in the WebSocketCloseCode Registry outlined in Section 11.7 of
[WEBSOCKET].
Data Frames containing Text are reserved for future use and MUST NOT
be sent. Binary Data Frames transport CAPSULE content defined in
[WEBTRANSPORT-H2] and [DATAGRAM]. For details, refer to the next
section Section 3.3. Their length is limited by WebTransport flow
control, and a violation SHOULD lead to connection termination.
CONTINUATION frames are processed per [WEBSOCKET] specifications.
Given the streaming nature of the content, partial DATA frames or
CONTINUATION frames should be promptly forwarded to corresponding
streams reducing latency.
3.3. Capsule frames
This protocol adopts the mechanisms and intrinsic elements outlined
in [WEBTRANSPORT-H2], which itself is constructed upon the CAPSULE
protocol originating from [DATAGRAM].
A CAPSULE has the form in [DATAGRAM]:
Capsule {
Capsule Type (i),
Capsule Length (i),
Capsule Value (..),
}
where Capsule Type and Length are variable-length integers. The
Capsule Value represents the payload of the capsule, and its
semantics are determined by the payload type
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In the context of WebTransport over WebSockets, CAPSULEs are
substituted by binary DATA FRAMES of WebSockets, following the
format:
WebSocketDataFrameCapsule {
FrameHeader (..),
PayloadData (..)
}
FrameHeader contains the first two bytes of the FRAME, and if present
the extended payload length and masking key as defined in Section 5.2
of [WEBSOCKET]. PayloadData is defined as:
PayloadData {
Capsule Type (i),
Capsule Value (..)
}
with the variable length integer Capsule Type and Capsule Value as in
the CAPSULE protocol.
Capsule length can be calculated from the Payload Length as set in
Section 5.2 of [WEBSOCKET]:
Capsule Length = Payload Length - sizeof(Capsule Type),
as no Extension Data is allowed.
3.4. Replacement for SETTINGS
Section 3.1 of [WEBTRANSPORT-H2] requires sending an
SETTINGS_WEBTRANSPORT_MAX_SESSIONS settings parameter. This is not
required here, as the protocol type is negotiated using the
subprotocol mechanism of WebSockets and
SETTINGS_WEBTRANSPORT_MAX_SESSIONS equal to 1 is assumed per
WebSocket connection(HTTP1)/stream(HTTP2). Subsections of
Section 3.4 of [WEBTRANSPORT-H2] require sending initial SETTINGS for
flow control. As SETTINGS are not accessible for the WebSocket
protocol using the existing WebSocket interfaces, a replacement is
required.
Therefore client and server MUST send the initial flow control values
using CAPSULES immediately before ANY other capsules such as
WT_STREAM or DATAGRAM capsules have been sent.
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4. Implementation Status
The protocol is implemented in a node.js package (https://github.com/
fails-components/webtransport).
5. Security Considerations
The security considerations of Section 10 of [WEBSOCKET] also apply
here. The last paragraph of Section 8 of [WEBTRANSPORT-H2] is
equally applicable to this protocol.
6. IANA Considerations
6.1. WebSocket Subprotocol Name Registry
All possible subprotocol names following the format
"webtransport_VERSION," where VERSION is an alphanumeric string
denoting the subprotocol version of this protocol, are added to the
registry as domains for this protocol and its successors.
6.2. WebTransport WebSocket Protocol Version Registry
This specification establishes a new IANA registry for WebTransort
Protocol Version names, intended for use with the WebSocket
WebTransport Protocol, in alignment with the principles outlined in
[RFC5226].
As part of this registry, IANA manages the following information
(similar to [WEBSOCKET] versions):
Version String The version string name as part of the subprotocol
defined in Section 6.1 and Section 3.1. The value must only include
alphanumeric characters.
Reference The RFC requesting a new version number or a draft name
with version number (see below).
Status Either "Interim" or "Standard". See below for a description.
A version string can be either "Interim" or "Standard".
A "Standard" version string is part of an RFC and identifies a major,
stable version of the WebTransport-WebSocket protocol. The "IETF
Review" IANA registration policy [RFC5226] applies to "Standard"
version string.
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An Internet-Draft documents an "Interim" version string. Internet-
Drafts helps implementors to identify and interoperate with the
WebTransport-WebSocket protocol, as this current draft. The "Expert
Review" IANA registration policy [RFC5226] applies to the "Interim"
version names. The initial Designated Experts need to be determined.
7. References
7.1. Normative References
[HTTP] Fielding, R. T., Nottingham, M., and J. Reschke, "HTTP
Semantics", Work in Progress, Internet-Draft, draft-ietf-
httpbis-semantics-19, 12 September 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
semantics-19>.
[OVERVIEW] Vasiliev, V., "The WebTransport Protocol Framework", Work
in Progress, Internet-Draft, draft-ietf-webtrans-overview-
06, 6 September 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-
webtrans-overview-06>.
[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/rfc/rfc2119>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<https://www.rfc-editor.org/rfc/rfc5226>.
[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/rfc/rfc8174>.
[WEBSOCKET]
Fette, I. and A. Melnikov, "The WebSocket Protocol",
RFC 6455, DOI 10.17487/RFC6455, December 2011,
<https://www.rfc-editor.org/rfc/rfc6455>.
[WEBSOCKET-H2]
McManus, P., "Bootstrapping WebSockets with HTTP/2",
RFC 8441, DOI 10.17487/RFC8441, September 2018,
<https://www.rfc-editor.org/rfc/rfc8441>.
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[WEBTRANSPORT-H2]
Frindell, A., Kinnear, E., Pauly, T., Thomson, M.,
Vasiliev, V., and G. Xie, "WebTransport over HTTP/2", Work
in Progress, Internet-Draft, draft-ietf-webtrans-http2-07,
23 October 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-webtrans-http2-07>.
[WEBTRANSPORT-H3]
Frindell, A., Kinnear, E., and V. Vasiliev, "WebTransport
over HTTP/3", Work in Progress, Internet-Draft, draft-
ietf-webtrans-http3-08, 23 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-
webtrans-http3-08>.
7.2. Informative References
[DATAGRAM] Pauly, T., Kinnear, E., and D. Schinazi, "An Unreliable
Datagram Extension to QUIC", RFC 9221,
DOI 10.17487/RFC9221, March 2022,
<https://www.rfc-editor.org/rfc/rfc9221>.
[HTTP3] Bishop, M., "HTTP/3", Work in Progress, Internet-Draft,
draft-ietf-quic-http-34, 2 February 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-quic-
http-34>.
[QUIC] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/rfc/rfc9000>.
Acknowledgments
Parts of the text were rephrased using ChatGPT. Portions of this
document are based upon a modification of text parts from the
underlying standards.
Author's Address
Marten Richter
Technische Universität Berlin
Email: marten.richter@tu-berlin.de
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