Network Working Group W. Tarreau
Internet-Draft Exceliance
Expires: July 20, 2013 E. Stephan
Orange
G. Montenegro
Microsoft
January 16, 2013
HTTP 2.0 Negotiation
draft-montenegro-httpbis-http2-negotiation-01
Abstract
This document describes an Upgrade-based protocol negotiation
proposal for HTTP 2.0.
Status of this Memo
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This Internet-Draft will expire on July 20, 2013.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Negotiation . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Optimizing the Handshake . . . . . . . . . . . . . . . . . . . 5
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
5. Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1. Normative References . . . . . . . . . . . . . . . . . . . 8
6.2. Informative References . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
User agents interact with numerous servers from different domains
using different versions of HTTP. In particular, the co-existence of
HTTP/1.x and HTTP/2.x requires a protocol negotiation mechanism
transparent to the user agents. This document specifies an Upgrade-
based HTTP 2.0 connection negotiation.
HTTP/2.0 will have the capability (but not the requirement) to use
the same ports as HTTP/1.X, typically, but not limited to, 80 (in the
clear) and 443 (when over TLS/SSL). Of course, it is possible for a
client to somehow acquire knowledge that a server implements HTTP/2.0
at a given port. In such a case, the client can immediately begin
sending HTTP/2.0 binary frames to the server, and the server can
immediately respond with the corresponding HTTP/2.0 frames. How that
knowledge is acquired is not the subject of this note. It could be
acquired by some out-of-band means such as using the DNS, or by some
configuration prior to the HTTP/2.0 exchange. Or it could have been
aquired earlier in-band in a previous exchange using, for example,
the Upgrade-based mechanism specified in this document. It could
have also been acquired at an earlier phase of this same exchange,
for example, at a lower protocol layer that precedes the overall HTTP
sequence, such as in the TLS handshake (if using TLS).
Nevertheless, there may be some situations, in which the client can
only assume that a server speaks HTTP/1.X. In such cases, a
connection upgrade mechanism to opportunistically attempt switching
to HTTP/2.0 is essential. Otherwise, the exchange will remain at
HTTP/1.X despite both client and server being willing to speak
HTTP/2.0.
This document specifies such a connection upgrade for HTTP/2.0. This
handshake does not incur any extra delay in obtaining a response in
HTTP/2.0, as the protocol switch is immediate and effective within
the first round trip. There is no delay either if there is no
protocol switch, as the server is capable to respond via HTTP/1.1
also within the first initial round trip.
This handshake uses the Upgrade header defined in HTTP/1.1
[I-D.ietf-httpbis-p1-messaging]. This Upgrade header is also in wide
use by the WebSocket protocol for similar purposes [RFC6455].
The goal of this document is to propose additional text to the
HTTP/2.0 specification. The starting point for HTTP/2.0, the initial
version of [I-D.ietf-httpbis-http2], has no language with respect to
a connection upgrade procedure. Hence, the text below could be
incorporated as a new section or sections within the HTTP/2.0
document.
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2. Negotiation
If a client has no knowledge about a server's support for HTTP/2.0,
it starts with HTTP/1.1 and attempt an upgrade to HTTP/2.0 as
follows:
GET /default.htm HTTP/1.1
Host: server.example.com
Connection: Upgrade
Upgrade: HTTP/2.0
If the server does not support the new protocol, it will simply
respond to the client using HTTP/1.1:
HTTP/1.1 200 OK
Content-length: 243
Content-type: text/html
...
If the server switches to the new protocol, it will signal so via a
101 response. The server switches to HTTP/2.0 immediately after the
empty line which terminates the 101 response
[I-D.ietf-httpbis-p2-semantics].
HTTP/1.1 101 Switching Protocols
Connection: Upgrade
Upgrade: HTTP/2.0
[ HTTP/2.0 frame ]
In the above, the string "HTTP/2.0" represents the final version of
the protocol defined in [I-D.ietf-httpbis-http2]. However, per
guidance in that document, preliminary revisions of that document
(either draft or experimental) are denoted by adding the
corresponding version or revision number. For example, if the above
handshake were negotiating the use of the 03 version of the draft
(draft-ietf-httpbis-http2-03), then, instead of using "HTTP/2.0"
above, the handshake would use "HTTP-03/2.0" instead.
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3. Optimizing the Handshake
This handshake may be further optimized by the definition of HTTP
headers of the form "HTTP2-header_name". These "HTTP2" headers would
be meant to be interpreted exclusively by HTTP/2.0 servers and
applied upon a successful Upgrade to further optimize or proactively
configure the subsequent HTTP/2.0 exchanges. These headers would be
ignored by HTTP/1.1 servers. The HTTP2 headers are for future
revisions of this document.
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4. Acknowledgements
This document incorporates material from
[I-D.tarreau-httpbis-network-friendly] and
[I-D.montenegro-httpbis-speed-mobility].
This document was produced using the xml2rfc tool [RFC2629].
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5. Appendix
This Upgrade-based handshake may have issues with certain proxies and
intermediaries, particularly those that are not aware of its use and
don't obey its semantics. Some heuristics that have been observed to
help in this respect is to turn off caching by adding the following
to the client request:
Pragma: no-cache
Cache-Control: no-cache
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6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[I-D.ietf-httpbis-p1-messaging]
Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
(HTTP/1.1): Message Syntax and Routing",
draft-ietf-httpbis-p1-messaging-21 (work in progress),
October 2012.
[I-D.ietf-httpbis-p2-semantics]
Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
(HTTP/1.1): Semantics and Content",
draft-ietf-httpbis-p2-semantics-21 (work in progress),
October 2012.
6.2. Informative References
[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
June 1999.
[RFC6455] Fette, I. and A. Melnikov, "The WebSocket Protocol",
RFC 6455, December 2011.
[I-D.ietf-httpbis-http2]
Belshe, M., Peon, R., Thomson, M., and A. Melnikov, "SPDY
Protocol", draft-ietf-httpbis-http2-00 (work in progress),
November 2012.
[I-D.montenegro-httpbis-speed-mobility]
Trace, R., Foresti, A., Singhal, S., Mazahir, O., Nielsen,
H., Raymor, B., Rao, R., and G. Montenegro, "HTTP Speed+
Mobility", draft-montenegro-httpbis-speed-mobility-02
(work in progress), June 2012.
[I-D.tarreau-httpbis-network-friendly]
Tarreau, W., Jeffries, A., and A. Croy, "Proposal for a
Network-Friendly HTTP Upgrade",
draft-tarreau-httpbis-network-friendly-00 (work in
progress), March 2012.
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Authors' Addresses
Willy Tarreau
Exceliance
Email: w@1wt.eu
Emile Stephan
Orange
Email: emile.stephan@orange.com
Gabriel Montenegro
Microsoft
Email: Gabriel.Montenegro@microsoft.com
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