Network Working Group E. Kinnear
Internet-Draft T. Pauly
Intended status: Standards Track Apple Inc.
Expires: March 14, 2019 September 10, 2018
Using HTTP/2 as a Transport for Arbitrary Bytestreams
draft-kinnear-httpbis-http2-transport-00
Abstract
HTTP/2 provides multiplexing of HTTP requests over a single
underlying transport connection. HTTP/2 Transport defines a
transport abstraction provided by HTTP/2 framing that is separate
from HTTP semantics.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 2
2. The STREAM HTTP/2 Frame . . . . . . . . . . . . . . . . . . . 2
2.1. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Advertising Support for STREAM Frames . . . . . . . . . . 4
2.3. Processing STREAM Frames . . . . . . . . . . . . . . . . 4
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5
6. Normative References . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
HTTP/2 [RFC7540] provides a framing layer that describes the exchange
of HTTP messages following HTTP semantics. This framing layer
provides multiplexing of multiple streams on a single underlying
transport connection, flow control, stream dependencies and
priorities, and exchange of configuration information between
endpoints. HTTP/2 also defines the mapping of HTTP semantics onto
that framing layer.
This document defines the use of the HTTP/2 framing layer as a
transport for arbitrary byte streams without the use of HTTP
semantics.
1.1. Notational Conventions
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.
2. The STREAM HTTP/2 Frame
This document defines a new HTTP/2 frame type called STREAM, that
allows endpoints to open HTTP/2 streams without header values.
Either endpoint can send this frame to open a stream. STREAM frames
are treated in all ways as HEADERS frames, including in the stream
state machine, but are not required to contain any header values.
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2.1. Syntax
The STREAM frame type is 0xd (decimal 13) and contains similar fields
to that of the HEADERS frame.
A STREAM frame is shown below.
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
+---------------+
|Pad Length? (8)|
+-+-------------+-----------------------------------------------+
|E| Stream Dependency? (31) |
+-+-------------+-----------------------------------------------+
| Weight? (8) |
+-+-------------+-----------------------------------------------+
| Padding (*) ...
+---------------------------------------------------------------+
Figure 1: STREAM Frame Format
The STREAM frame contains the following fields:
Pad Length: An 8-bit field containing the length of the frame
padding in units of octets. This field is only present if the
PADDED flag is set.
E: A single-bit flag indicating that the stream dependency is
exclusive (see Section 5.3 of [RFC7540]). This field is only
present if the PRIORITY flag is set.
Stream Dependency: A 31-bit stream identifier for the stream that
this stream depends on (see Section 5.3 of [RFC7540]). This field
is only present if the PRIORITY flag is set.
Weight: An unsigned 8-bit integer representing a priority weight for
the stream (see Section 5.3 of [RFC7540]). Add one to the value
to obtain a weight between 1 and 256. This field is only present
if the PRIORITY flag is set.
Padding: Padding octets.
The STREAM frame defines the following flags:
PADDED (0x8): When set, bit 3 indicates that the Pad Length field
and any padding that it describes are present.
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PRIORITY (0x20): When set, bit 5 indicates that the Exclusive Flag
(E), Stream Dependency, and Weight fields are present; see
Section 5.3 of [RFC7540].
STREAM frames MUST be associated with a stream. If a STREAM frame is
received whose stream identifier field is 0x0, the recipient MUST
respond with a connection error of type PROTOCOL_ERROR.
The STREAM frame can include padding. Padding fields and flags are
identical to those defined for DATA frames.
Prioritization information in a STREAM frame is logically equivalent
to a separate PRIORITY frame, but inclusion in a STREAM frame avoids
the potential for churn in stream prioritization when new streams are
created. Prioritization fields in STREAM frames subsequent to the
first on a stream reprioritize the stream (Section 5.3.3 of
[RFC7540]).
2.2. Advertising Support for STREAM Frames
As defined in [RFC7540], both endpoints can send
SETTINGS_MAX_CONCURRENT_STREAMS in SETTINGS frames to indicate the
number of streams that the sender permits the receiver to create.
This limit applies to streams created via the STREAM frame as well as
streams created via HEADERS frames.
2.3. Processing STREAM Frames
The STREAM frame is a non-critical extension to HTTP/2. Endpoints
that do not support this frame can safely ignore it upon receipt.
When received by a client that implements support, the STREAM frame
behaves in the same manner as a HEADERS frame, but does not carry any
header blocks. This changes the connection state in the same manner
as a HEADERS frame, described in Section 4.3 of [RFC7540].
STREAM frames can be sent on a stream in the "idle", "reserved
(local)", "open", or "half-closed (remote)" state. STREAM frames can
be sent by either endpoint on a connection.
Streams created via a STREAM frame are multiplexed in the same manner
on the underlying transport connection as streams created via a
HEADERS frame. Flow control also applies to these streams in the
same way. Flow control, stream dependencies, and priorities continue
to apply to streams as defined by [RFC7540].
Anywhere an endpoint would be permitted to send a HEADERS frame by
[RFC7540], it is likewise permitted to send a STREAM frame.
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A stream is closed via a RST_STREAM frame or by setting the
END_STREAM flag on a DATA frame.
3. IANA Considerations
This specification adds an entry to the "HTTP/2 Frame Type" registry.
o Frame Type: STREAM
o Code: 0xd
o Specification: [[RFC Editor: Please fill in this value with the
RFC number for this document.]]
4. Security Considerations
5. Acknowledgments
Thanks to Anthony Chivetta, Joshua Otto, and Valentin Pistol for
their contributions in the design and prototyping of this work.
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>.
[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>.
Authors' Addresses
Eric Kinnear
Apple Inc.
One Apple Park Way
Cupertino, California 95014
United States of America
Email: ekinnear@apple.com
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Tommy Pauly
Apple Inc.
One Apple Park Way
Cupertino, California 95014
United States of America
Email: tpauly@apple.com
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