An HTTP/2 extension for bidirectional messaging communication
draft-xie-bidirectional-messaging-01
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Expired".
|
|
|---|---|---|---|
| Authors | Guowu Xie , Alan Frindell | ||
| Last updated | 2019-04-04 | ||
| RFC stream | (None) | ||
| Formats | |||
| Additional resources | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-xie-bidirectional-messaging-01
httpbis Working Group G. Xie
Internet-Draft F. Frindell
Intended status: Standards Track Facebook Inc.
Expires: 6 October 2019 4 April 2019
An HTTP/2 extension for bidirectional messaging communication
draft-xie-bidirectional-messaging-01
Abstract
This draft proposes a http2 protocol extension, which enables
bidirectional messaging communication between client and server.
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 October 2019.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.
Xie & Frindell Expires 6 October 2019 [Page 1]
Internet-Draft bidirectional messaging April 2019
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 2
3. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Routing Stream and ExStream . . . . . . . . . . . . . . 3
3.2. Bidirectional Messaging Communication . . . . . . . . . 3
3.3. States of RStream and ExStream . . . . . . . . . . . . 4
3.4. Negotiate the Extension through SETTINGS frame . . . . 5
3.5. Interaction with standard http2 features . . . . . . . 5
4. HTTP2 EX_HEADERS Frame . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5.1. FRAME TYPE Registry . . . . . . . . . . . . . . . . . . 6
5.2. Settings Registry . . . . . . . . . . . . . . . . . . . 6
5.3. Error Code Registry . . . . . . . . . . . . . . . . . . 7
6. Normative References . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
HTTP/2 is the de facto application protocol in Internet. The
optimizations developed in HTTP/2, like stream multiplexing, header
compression, and binary message framing are very generic. They can
be useful in non web browsing applications, for example, Publish/
Subscribe, RPC. However, the request/response from client to server
communication pattern limits HTTP/2 from wider use in these
applications. This draft proposes a HTTP/2 protocol extension, which
enables bidirectional messaging between client and server.
The only mechanism HTTP/2 provides for server to client communication
is PUSH_PROMISE. While this satisfies some use-cases, it is
unidirectional, i.g. the client cannot respond. In this draft, a new
frame is introduced which has the routing properties of PUSH_PROMISE
and the bi-directionality of HEADERS. Further, clients are also able
group streams together for routing purposes, such that each
individual stream does not need to carry additional routing
information.
2. Conventions and Terminology
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
document, are to be interpreted as described in [RFC2119].
All the terms defined in the Conventions and Terminology section in
[RFC7540] apply to this document.
Xie & Frindell Expires 6 October 2019 [Page 2]
Internet-Draft bidirectional messaging April 2019
3. Solution Overview
3.1. Routing Stream and ExStream
A routing stream (RStream) is a long lived HTTP/2 stream in nature.
RStreams are initiated by clients, and can be routed independently by
any intermediaries. Though an RStream is effectively a regular
HTTP/2 stream, RStreams are recommended for exchanging metadata, but
not user data.
A new HTTP/2 stream called ExStream is introduced for exchanging user
data. ExStreams are recommended for short lived transactions, so
intermediaries and servers can gracefully shutdown ExStreams within a
short time. The typical use case can be a subscription or publish
request/response in Publish/Subscribe use case, or an RPC call
between two endpoints.
An ExStream is opened by an EX_HEADERS frame, and continued by
CONTINUATION and DATA frames. An ExStream MUST be associated with an
open RStream, and MUST NOT be associated with any other ExStream.
ExStreams are routed according to their RStreams by intermediaries
and servers. Effectively, all ExStreams with the same RStream form a
logical stream group, and are routed to the same endpoint.
3.2. Bidirectional Messaging Communication
With RStreams and ExStreams, HTTP/2 can be used for bidirectional
messaging communication. As shown in the follow diagrams, after an
RStream is open from client to server, either endpoint can initiate
an ExStreams to its peer.
+--------+ RStream (5) +---------+ RStream (1) +--------+
| client |>--------------->| proxy |>---------------->| server |
+--------+ +---------+ +--------+
v ^ v ^
| ExStream(7, RS=5) | | ExStream(3, RS=1) |
+------------------------+ +------------------------+
Figure 1: Client initiates the ExStream to server, after an
RStream is open.
+--------+ RStream (5) +---------+ RStream (1) +--------+
| client |>--------------->| proxy |>---------------->| server |
+--------+ +---------+ +--------+
^ v ^ v
| ExStream(4, RS=5) | | ExStream(2, RS=1) |
+------------------------+ +------------------------+
Xie & Frindell Expires 6 October 2019 [Page 3]
Internet-Draft bidirectional messaging April 2019
Figure 2: Server initiates the ExStream to client, after an
RStream is open.
Beyond that, clients can multiplex RStreams, ExStreams and regular
HTTP/2 streams into one HTTP/2 connection. This enables clients to
access different services without initiating new TCP connections.
This avoids the latency cost of setting up new connections. This is
more desirable for mobile devices because they usually have longer
RTT and battery constraints. Multiplexing these services also allows
them to share a single TCP connection congestion control context.
As shown in the following diagram, the client can exchange data with
PubSub, RPC and CDN three different services with one TCP connection.
+--------+ RStream (5) +---------+ RStream (1) +----------+
| client |>--------------->| proxy |>---------------->| PUBSUB |
+--------+ +---------+ +----------+
v v ^ ^ v v
| | RStream (7) / | | \ RStream (5) +----------+
| +-------------------+ | | +---------------->| RPC |
| | | +----------+
| | |
| Stream (9) | | Stream (7) +----------+
+---------------------------+ +--------------------->| CDN |
+----------+
Figure 3: Client opens multiple RStreams and a HTTP/2 stream
within one HTTP/2 connection.
3.3. States of RStream and ExStream
RStreams are regular HTTP/2 streams that follow the stream lifecycle
in [RFC7540], section 5.1. ExStreams use the same lifecycle as
regular HTTP/2 streams, but also depend on their RStreams. If a
RStream is reset, endpoints MUST reset the ExStreams associated with
that RStream. If the RStream is closed, endpoints SHOULD allow
existing ExStreams complete normally. The RStream SHOULD remain open
while communication is ongoing. Endpoints SHOULD refresh any
timeouts on the RStream while associated ExStreams are open.
A sender MUST NOT initiate new ExStreams if on an RStream that is in
the open or half closed (remote) state.
Endpoints process new ExStreams only when the RStream is open or half
closed (local) state. If an endpoint receives an EX_HEADERS frame
specifying an RStream in the closed or haf closed (remote) state, it
MUST respond with a connection error of type ROUTING_STREAM_ERROR.
Xie & Frindell Expires 6 October 2019 [Page 4]
Internet-Draft bidirectional messaging April 2019
3.4. Negotiate the Extension through SETTINGS frame
The extension SHOULD be disabled by default. Endpoints can negotiate
the use of the extension through the SETTINGS frame. If an
implementation supports the extension, it is RECOMMENDED to include
the ENABLE_EX_HEADERS setting in the initial SETTINGS frame. HTTP/2
compliant implementations will ignore the setting if it is unknown.
An endpoint can send EX_HEADERS frames immediately upon receiving a
SETTINGS frame with ENABLE_EX_HEADERS=1.
Endpoints MUST NOT send out EX_HEADERS before receiving a SETTINGS
frame with the ENABLE_EX_HEADERS=1. If a remote endpoint does not
support this extension, the EX_HEADERS will be ignored, making the
header compression contexts inconsistent between sender and receiver.
If an endpoint supports this extension, but receives EX_HEADERS
before ENABLE_EX_HEADERS, it MUST respond with a connection error
EX_HEADER_NOT_ENABLED_ERROR.
Intermediaries SHOULD send the ENABLE_EX_HEADERS setting to clients,
only if intermediaries and their upstream servers can support this
extension. If an intermediary receives an ExStream but discovers the
destination endpoint does not support the extension, it MUST reset
the stream with EX_HEADER_NOT_ENABLED_ERROR.
3.5. Interaction with standard http2 features
The extension implementation should apply stream and connection level
flow control, maximum concurrent streams limit, GOAWAY logic to both
RStreams and ExStreams.
4. HTTP2 EX_HEADERS Frame
The EX_HEADERS frame (type=0xfb) has all the fields and frame header
flags defined by HEADERS frame in HEADERS [RFC7540]. Moreover,
EX_HEADERS has one extra field, RStream ID. It is used to open an
ExStream, and additionally carries a header block fragment.
EX_HEADERS frames can be sent on a stream in the "idle", "open", or
"half-closed (remote)" state.
Like HEADERS, the CONTINUATION frame (type=0x9) is used to continue a
sequence of header block fragments, if the headers do not fit into
one EX_HEADERS frame.
Xie & Frindell Expires 6 October 2019 [Page 5]
Internet-Draft bidirectional messaging April 2019
+---------------+
|Pad Length? (8)|
+-+-------------+-----------------------------------------------+
|E| Stream Dependency? (31) |
+-+-------------+-----------------------------------------------+
| Weight? (8) |
+-+-------------+-----------------------------------------------+
|R| Routing Stream ID (31) |
+-+-------------+-----------------------------------------------+
| Header Block Fragment (*) ...
+---------------------------------------------------------------+
| Padding (*) ...
+---------------------------------------------------------------+
Figure 4: EX_HEADERS Frame Payload
The RStream specified in EX_HEADERS frames MUST be an open stream.
The recipient MUST respond with a connection error
ROUTING_STREAM_ERROR PROTOCOL_ERROR, if the specified RStream is
missing; or is an ExStream rather than a stream; or is closed or
half-closed (remote). Otherwise, the states maintained for header
compression or flow control) may be out of sync.
5. IANA Considerations
This document establishes a registry for a new frame type, setting,
and error code.
5.1. FRAME TYPE Registry
The entry in the following table are registered by this document.
+---------------+------+--------------+
| Frame Type | Code | Section |
+---------------+------+--------------+
| EX_HEADERS | 0xfb | |
+---------------+------+--------------+
5.2. Settings Registry
The entry in the following table are registered by this document.
+------------------------+--------+---------------+---------------+
| Name | Code | Initial Value | Specification |
+------------------------+--------+---------------+---------------+
| ENABLE_EX_HEADERS | 0xfbfb | 0 | |
+------------------------+--------+---------------+---------------+
Xie & Frindell Expires 6 October 2019 [Page 6]
Internet-Draft bidirectional messaging April 2019
5.3. Error Code Registry
The entry in the following table are registered by this document.
+----------------------+------+-------------------+---------------+
| Name | Code | Description | Specification |
+----------------------+------+-------------------+---------------+
| ROUTING_STREAM_ERROR | 0xfb | Routing stream is | |
| | | not open | |
| EX_HEADERS_NOT_ | 0xfc | EX_HEADERS is not | |
| ENABLED_ERROR | | enabled yet | |
+----------------------+------+-------------------+---------------+
6. Normative References
[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>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<https://www.rfc-editor.org/info/rfc7540>.
Authors' Addresses
Guowu Xie
Facebook Inc.
1 Hacker Way
Menlo Park
Email: woo@fb.com
Alan Frindell
Facebook Inc.
Email: afrind@fb.com
Xie & Frindell Expires 6 October 2019 [Page 7]