Network Working Group H. Nielsen

Network Working Group H. Nielsen
Request for Comments: 2774 P. Leach
Category: Experimental Microsoft
S. Lawrence
Agranat Systems
February 2000

An HTTP Extension Framework

Status of this Memo

This memo defines an Experimental Protocol for the Internet
community. It does not specify an Internet standard of any kind.
Discussion and suggestions for improvement are requested.
Distribution of this memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (2000). All Rights Reserved.

IESG Note

This document was originally requested for Proposed Standard status.
However, due to mixed reviews during Last Call and within the HTTP
working group, it is being published as an Experimental document.
This is not necessarily an indication of technical flaws in the
document; rather, there is a more general concern about whether this
document actually represents community consensus regarding the
evolution of HTTP. Additional study and discussion are needed before
this can be determined.

Note also that when HTTP is used as a substrate for other protocols,
it may be necessary or appropriate to use other extension mechanisms
in addition to, or instead of, those defined here. This document
should therefore not be taken as a blueprint for adding extensions to
HTTP, but it defines mechanisms that might be useful in such
circumstances.

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RFC 2774 An HTTP Extension Framework February 2000

Abstract

A wide range of applications have proposed various extensions of the
HTTP protocol. Current efforts span an enormous range, including
distributed authoring, collaboration, printing, and remote procedure
call mechanisms. These HTTP extensions are not coordinated, since
there has been no standard framework for defining extensions and
thus, separation of concerns. This document describes a generic
extension mechanism for HTTP, which is designed to address the
tension between private agreement and public specification and to
accommodate extension of applications using HTTP clients, servers,
and proxies. The proposal associates each extension with a globally
unique identifier, and uses HTTP header fields to carry the extension
identifier and related information between the parties involved in
the extended communication.

Table of Contents

1. Introduction ...............................................3
2. Notational Conventions .....................................3
3. Extension Declarations .....................................4
3.1 Header Field Prefixes ...................................5
4. Extension Header Fields ....................................6
4.1 End-to-End Extensions ...................................7
4.2 Hop-by-Hop Extensions ...................................7
4.3 Extension Response Header Fields ........................8
5. Mandatory HTTP Requests ....................................8
5.1 Fulfilling a Mandatory Request .........................10
6. Mandatory HTTP Responses ..................................11
7. 510 Not Extended ..........................................11
8. Publishing an Extension ...................................11
9. Caching Considerations ....................................12
10. Security Considerations ...................................13
11. References ................................................13
12. Acknowledgements ..........................................14
13. Authors' Addresses ........................................14
14. Summary of Protocol Interactions ..........................15
15. Examples ..................................................16
15.1 User Agent to Origin Server ............................16
15.2 User Agent to Origin Server via HTTP/1.1 Proxy .........17
15.3 User Agent to Origin Server via HTTP/1.0 Proxy .........18
Full Copyright Statement ......................................20

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1. Introduction

This proposal is designed to address the tension between private
agreement and public specification; and to accommodate dynamic
extension of HTTP clients and servers by software components. The
kind of extensions capable of being introduced range from:

o extending a single HTTP message;

o introducing new encodings;

o initiating HTTP-derived protocols for new applications; to...

o switching to protocols which, once initiated, run independent
of the original protocol stack.

The proposal is intended to be used as follows:

o Some party designs and specifies an extension; the party
assigns the extension a globally unique URI, and makes one or
more representations of the extension available at that address
(see section 8).

o An HTTP client or server that implements this extension
mechanism (hereafter called an agent) declares the use of the
extension by referencing its URI in an extension declaration in
an HTTP message (see section 3).

o The HTTP application which the extension declaration is
intended for (hereafter called the ultimate recipient) can
deduce how to properly interpret the extended message based on
the extension declaration.

The proposal uses features in HTTP/1.1 but is compatible with
HTTP/1.0 applications in such a way that extended applications can
coexist with existing HTTP applications. Applications implementing
this proposal MUST be based on HTTP/1.1 (or later versions of HTTP).

2. Notational Conventions

This specification uses the same notational conventions and basic
parsing constructs as RFC 2068 [5]. In particular the BNF constructs
"token", "quoted-string", "Request-Line", "field-name", and
"absoluteURI" in this document are to be interpreted as described in
RFC 2068 [5].

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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [6].

This proposal does not rely on particular features defined in URLs
[8] that cannot potentially be expressed using URNs (see section 8).
Therefore, the more generic term URI [8] is used throughout the
specification.

3. Extension Declarations

An extension declaration can be used to indicate that an extension
has been applied to a message and possibly to reserve a part of the
header namespace identified by a header field prefix (see 3.1). This
section defines the extension declaration itself; section 4 defines a
set of header fields using the extension declaration.

This specification does not define any ramifications of applying an
extension to a message nor whether two extensions can or cannot
logically coexist within the same message. It is simply a framework
for describing which extensions have been applied and what the
ultimate recipient either must or may do in order to properly
interpret any extension declarations within that message.

The grammar for an extension declaration is as follows:

ext-decl = <"> ( absoluteURI | field-name ) <">
[ namespace ] [ decl-extensions ]

namespace = ";" "ns" "=" header-prefix
header-prefix = 2*DIGIT

decl-extensions = *( decl-ext )
decl-ext = ";" token [ "=" ( token | quoted-string ) ]

An extension is identified by an absolute, globally unique URI or a
field-name. A field-name MUST specify a header field uniquely defined
in an IETF Standards Track RFC [3]. A URI can unambiguously be
distinguished from a field-name by the presence of a colon (":").

The support for header field names as extension identifiers provides
a transition strategy from decentralized extensions to extensions
defined by IETF Standards Track RFCs until a mapping between the
globally unique URI space and features defined in IETF Standards
Track RFCs has been defined according to the guidelines described in
section 8.

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Examples of extension declarations are

"http://www.company.com/extension"; ns=11
"Range"

An agent MAY use the decl-extensions mechanism to include optional
extension declaration parameters but cannot assume these parameters
to be recognized by the recipient. An agent MUST NOT use decl-
extensions to pass extension instance data, which MAY be passed using
header field prefix values (see section 3.1). Unrecognized decl-ext
parameters SHOULD be ignored and MUST NOT be removed by proxies when
forwarding the extension declaration.

3.1 Header Field Prefixes

The header-prefix is a dynamically generated string. All header
fields in the message that match this string, using string prefix-
matching, belong to that extension declaration. Header field prefixes
allow an extension declaration to dynamically reserve a subspace of
the header space in a protocol message in order to prevent header
field name clashes and to allow multiple declarations using the same
extension to be applied to the same message without conflicting.

Header fields using a header-prefix are of the form:

prefixed-header = prefix-match field-name
prefix-match = header-prefix "-"

Linear white space (LWS) MUST NOT be used between the header-prefix
and the dash ("-") or between the prefix-match and the field-name.
The string prefix matching algorithm is applied to the prefix-match
string.

The format of the prefix using a combination of digits and the dash
("-") guarantees that no extension declaration can reserve the whole
header field name space. The header-prefix mechanism was preferred
over other solutions for exchanging extension instance parameters
because it is header based and therefore allows for easy integration
of new extensions with existing HTTP features.

Agents MUST NOT reuse header-prefix values in the same message unless
explicitly allowed by the extension (see section 4.1 for a discussion
of the ultimate recipient of an extension declaration).

Clients SHOULD be as consistent as possible when generating header-
prefix values as this facilitates use of the Vary header field in
responses that vary as a function of the request extension
declaration(s) (see [5], section 13.6).

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Servers including prefixed-header header fields in a Vary header
field value MUST also include the corresponding extension declaration
field-name as part of that value. For example, if a response depends
on the value of the 16-use-transform header field defined by an
optional extension declaration in the request, the Vary header field
in the response could look like this:

Vary: Opt, 16-use-transform

Note, that header-prefix consistency is no substitute for including
an extension declaration in the message: header fields with header-
prefix values not defined by an extension declaration in the same
message are not defined by this specification.

Examples of header-prefix values are

12
15
23

Old applications may introduce header fields independent of this
extension mechanism, potentially conflicting with header fields
introduced by the prefix mechanism. In order to minimize this risk,
prefixes MUST contain at least 2 digits.

4. Extension Header Fields

This proposal introduces two types of extension declaration strength:
mandatory and optional, and two types of extension declaration scope:
hop-by-hop and end-to-end (see section 4.1 and 4.2).

A mandatory extension declaration indicates that the ultimate
recipient MUST consult and adhere to the rules given by the extension
when processing the message or reporting an error (see section 5 and
7).

An optional extension declaration indicates that the ultimate
recipient of the extension MAY consult and adhere to the rules given
by the extension when processing the message, or ignore the extension
declaration completely. An agent may not be able to distinguish
whether the ultimate recipient does not understand an extension
referred to by an optional extension or simply ignores the extension
declaration.

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The combination of the declaration strength and scope defines a 2x2
matrix which is distinguished by four new general HTTP header fields:
Man, Opt, C-Man, and C-Opt. (See sections 4.1 and 4.2; also see
appendix 14, which has a table of interactions with origin servers
and proxies.)

The header fields are general header fields as they describe which
extensions actually are applied to an HTTP message. Optional
declarations MAY be applied to any HTTP message if appropriate (see
section 5 for how to apply mandatory extension declarations to
requests and section 6 for how to apply them to responses).

4.1 End-to-End Extensions

End-to-end declarations MUST be transmitted to the ultimate recipient
of the declaration. The Man and the Opt general header fields are
end- to-end header fields and are defined as follows:

mandatory = "Man" ":" 1#ext-decl
optional = "Opt" ":" 1#ext-decl

For example

HTTP/1.1 200 OK
Content-Length: 421
Opt: "http://www.digest.org/Digest"; ns=15
15-digest: "snfksjgor2tsajkt52"
...

The ultimate recipient of a mandatory end-to-end extension
declaration MUST handle that extension declaration as described in
section 5 and 6.

4.2 Hop-by-Hop Extensions

Hop-by-hop extension declarations are meaningful only for a single
HTTP connection. In HTTP/1.1, C-Man, C-Opt, and all header fields
with matching header-prefix values defined by C-Man and C-Opt MUST be
protected by a Connection header field. That is, these header fields
are to be included as Connection header field directives (see [5],
section 14.10). The two header fields have the following grammar:

c-mandatory = "C-Man" ":" 1#ext-decl
c-optional = "C-Opt" ":" 1#ext-decl

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For example

M-GET / HTTP/1.1
Host: some.host
C-Man: "http://www.digest.org/ProxyAuth"; ns=14
14-Credentials="g5gj262jdw@4df"
Connection: C-Man, 14-Credentials

The ultimate recipient of a mandatory hop-by-hop extension
declaration MUST handle that extension declaration as described in
section 5 and 6.

4.3 Extension Response Header Fields

Two extension response header fields are used to indicate that a
request containing mandatory extension declarations has been
fulfilled by the ultimate recipient as described in section 5.1. The
extension response header fields are exclusively intended to serve as
extension acknowledgements, and can not carry any other information.

The Ext header field is used to indicate that all end-to-end
mandatory extension declarations in the request were fulfilled:

ext = "Ext" ":"

The C-Ext response header field is used to indicate that all hop-by-
hop mandatory extension declarations in the request were fulfilled.

c-ext = "C-Ext" ":"

In HTTP/1.1, the C-Ext header fields MUST be protected by a
Connection header (see [5], section 14.10).

The Ext and the C-Ext header fields are not mutually exclusive; they
can both occur within the same message as described in section 5.1.

5. Mandatory HTTP Requests

An HTTP request is called a mandatory request if it includes at least
one mandatory extension declaration (using the Man or the C-Man
header fields). The method name of a mandatory request MUST be
prefixed by "M-". For example, a client might express the binding
rights- management constraints in an HTTP PUT request as follows:

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M-PUT /a-resource HTTP/1.1
Man: "http://www.copyright.org/rights-management"; ns=16
16-copyright: http://www.copyright.org/COPYRIGHT.html
16-contributions: http://www.copyright.org/PATCHES.html
Host: www.w3.org
Content-Length: 1203
Content-Type: text/html

<!doctype html ...

An ultimate recipient conforming to this specification receiving a
mandatory request MUST process the request by performing the
following actions in the order listed below:

1. Identify all mandatory extension declarations (both hop-by-hop
and end-to-end); the server MAY ignore optional declarations
without affecting the result of processing the HTTP message;

2. Examine all extensions identified in 1) and determine if they
are supported for this message. If not, respond with a 510 (Not
Extended) status-code (see section 7);

3. If 2) did not result in a 510 (Not Extended) status code, then
process the request according to the semantics of the
extensions and of the existing HTTP method name as defined in
HTTP/1.1 [5] or later versions of HTTP. The HTTP method name
can be obtained by ignoring the "M-" method name prefix.

4. If the evaluation in 3) was successful and the mandatory
request fulfilled, the server MUST respond as defined in
section 5.1. A server MUST NOT fulfill a request without
understanding and obeying all mandatory extension
declaration(s) in a request.

A proxy that does not act as the ultimate recipient of a mandatory
extension declaration MUST NOT remove the extension declaration or
the "M-" method name prefix when forwarding the message (see section
5.1 for how to detect when a mandatory extension has been fulfilled).

A server receiving an HTTP/1.0 (or earlier versions of HTTP) message
that includes a Connection header MUST, for each connection-token in
this field, remove and ignore any header field(s) from the message
with the same name as the connection-token.

A server receiving a mandatory request including the "M-" method name
prefix without any mandatory extension declarations to follow MUST
return a 510 (Not Extended) response.

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The "M-" prefix is reserved by this proposal and MUST NOT be used by
other HTTP extensions.

5.1 Fulfilling a Mandatory Request

A server MUST NOT claim to have fulfilled any mandatory request
unless it understood and obeyed all the mandatory extension
declarations in the request. This section defines a mechanism for
conveying this information to the client in such a way that it
interoperates with existing HTTP applications and prevents broken
servers from giving the false impression that an extended request was
fulfilled by responding with a 200 (Ok) response without
understanding the method.

If any end-to-end mandatory extension declarations were among the
fulfilled extensions then the server MUST include an Ext response
header field in the response. In order to avoid that the Ext header
field inadvertently is cached in an HTTP/1.1 cache, the response MUST
contain a no-cache cache-control directive. If the response is
otherwise cachable, the no-cache cache-control directive SHOULD be
limited to only affect the Ext header field:

HTTP/1.1 200 OK
Ext:
Cache-Control: no-cache="Ext"
...

If the mandatory request has been forwarded by an HTTP/1.0
intermediary proxy then this is indicated either directly in the
Request-Line or by the presence of an HTTP/1.1 Via header field. In
this case, the server MUST include an Expires header field with a
date equal to or earlier than the value of the Date header field (see
section 9 for a discussion on caching considerations):

HTTP/1.1 200 OK
Date: Sun, 25 Oct 1998 08:12:31 GMT
Expires: Sun, 25 Oct 1998 08:12:31 GMT
Ext:
Cache-Control: no-cache="Ext", max-age=3600
...

If any hop-by-hop mandatory extension declarations were among the
fulfilled extensions then the server MUST include a C-Ext response
header field in the response. The C-Ext header field MUST be
protected by a Connection header field (see [5], section 14.10).

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RFC 2774 An HTTP Extension Framework February 2000

HTTP/1.1 200 OK
C-Ext:
Connection: C-Ext

Note, that the Ext and C-Ext header fields are not mutually
exclusive; they can be both be present in a response when fulfilling
mandatory request containing both hop-by-hop as well as end-to-end
mandatory extension declarations.

6. Mandatory HTTP Responses

A server MUST NOT include mandatory extension declarations in an HTTP
response unless it is responding to a mandatory HTTP request whose
definition allowed for the mandatory response or the server has some
a priori knowledge that the recipient can handle the extended
response. A server MAY include optional extension declarations in
any HTTP response (see section 4).

If a client is the ultimate recipient of a mandatory HTTP response
containing mandatory extension declarations that either the client
does not understand or does not want to use, then it SHOULD discard
the complete response as if it were a 500 (Internal Server Error)
response.

7. 510 Not Extended

The policy for accessing the resource has not been met in the
request. The server should send back all the information necessary
for the client to issue an extended request. It is outside the scope
of this specification to specify how the extensions inform the
client.

If the 510 response contains information about extensions that were
not present in the initial request then the client MAY repeat the
request if it has reason to believe it can fulfill the extension
policy by modifying the request according to the information provided
in the 510 response. Otherwise the client MAY present any entity
included in the 510 response to the user, since that entity may
include relevant diagnostic information.

8. Publishing an Extension

While the protocol extension definition should be published at the
address of the extension identifier, this specification does not
require it. The only absolute requirement is that extension
identifiers MUST be globally unique identifiers, and that distinct
names be used for distinct semantics.

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Likewise, applications are not required to attempt resolving
extension identifiers included in an extension declaration. The only
absolute requirement is that an application MUST NOT claim
conformance with an extension that it does not recognize (regardless
of whether it has tried to resolve the extension identifier or not).
This document does not provide any policy for how long or how often
an application may attempt to resolve an extension identifier.

The association between the extension identifier and the
specification might be made by distributing a specification, which
references the extension identifier.

It is strongly recommended that the integrity and persistence of the
extension identifier be maintained and kept unquestioned throughout
the lifetime of the extension. Care should be taken not to distribute
conflicting specifications that reference the same name. Even when an
extension specification is made available at the address of the URI,
care must be taken that the specification made available at that
address does not change over time. One agent may associate the
identifier with the old semantics, while another might associate it
with the new semantics.

The extension definition may be made available in different
representations ranging from

o a human-readable specification defining the extension semantics
(see for example [7]),

o downloadable code which implements the semantics defined by the
extension,

o a formal interface description provided by the extension, to

o a machine-readable specification defining the extension
semantics.

For example, a software component that implements the specification
may reside at the same address as a human-readable specification
(distinguished by content negotiation). The human-readable
representation serves to document the extension and encourage
deployment, while the software component would allow clients and
servers to be dynamically extended.

9. Caching Considerations

Use of extensions using the syntax defined by this document may have
additional implications on the cachability of HTTP response messages
other than the ones described in section 5.1.

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The originator of an extended message should be able to determine
from the semantics of the extension whether or not the extension's
presence impacts the caching constraints of the response message. If
an extension does require tighter constraints on the cachebility of
the response, the originator MUST include the appropriate combination
of cache header fields (Cache-Control, Vary, Expires) corresponding
to the required level of constraints of the extended semantics.

10. Security Considerations

Dynamic installation of extension facilities as described in the
introduction involves software written by one party (the provider of
the implementation) to be executed under the authority of another
(the party operating the host software). This opens the host party to
a variety of "Trojan horse" attacks by the provider, or a malicious
third party that forges implementations under a provider's name. See,
for example RFC2046 [4], section 4.5.2 for a discussion of these
risks.

11. References

[1] Crocker, D., "Standard for the Format of ARPA Internet Text
Messages", STD 11, RFC 822, August 1982.

[2] Berners-Lee, T., Fielding, R. and H. Frystyk, "Hypertext
Transfer Protocol -- HTTP/1.0", RFC 1945, May 1996.

[3] Bradner, S., "The Internet Standards Process -- Revision 3", BCP
9, RFC 2026, October 1996.

[4] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046, November
1996.

[5] Fielding, R., Gettys, J., Mogul, J., Frystyk, H. and T.
Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC
2068, January 1997.

[6] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.

[7] Masinter, L., "Hyper Text Coffee Pot Control Protocol
(HTCPCP/1.0)", RFC 2324, 1 April 1998.

[8] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource
Identifiers (URI): Generic Syntax", RFC 2396, August 1998.

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[9] Nielsen, H., Connolly, D. and R. Khare, "PEP - an extension
mechanism for HTTP", Work in Progress.

12. Acknowledgements

Roy Fielding, Rohit Khare, Yaron Y. Goland, and Koen Holtman, deserve
special recognition for their efforts in commenting in all phases of
this specification. Also thanks to Josh Cohen, Ross Patterson, Jim
Gettys, Larry Masinter, and to the people involved in PEP [9].

The contribution of World Wide Web Consortium (W3C) staff is part of
the W3C HTTP Activity (see "http://www.w3.org/Protocols/Activity").

13. Authors' Addresses

Henrik Frystyk Nielsen
Microsoft Corporation
1 Microsoft Way
Redmond, WA 98052, USA

EMail: [email protected]

Paul J. Leach
Microsoft Corporation
1 Microsoft Way
Redmond, WA 98052, USA

EMail: [email protected]

Scott Lawrence
Agranat Systems, Inc.
5 Clocktower Place, Suite 400
Maynard, MA 01754, USA

EMail: [email protected]

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RFC 2774 An HTTP Extension Framework February 2000

Appendices

14. Summary of Protocol Interactions

The following tables summarize the outcome of strength and scope rules
of the mandatory proposal of compliant and non-compliant HTTP proxies
and origin servers. The summary is intended as a guide and index to
the text, but is necessarily cryptic and incomplete. This summary
should never be used or referenced separately from the complete
specification.

Table 1: Origin Server

Scope Hop-by-hop End-to-end

Strength Optional Required Optional Required
(may) (must) (may) (must)

Mandatory Standard 501 (Not Standard 501 (Not
unsupported processing Implemented) processing Implemented)

Extension Standard 510 (Not Standard 510 (Not
unsupported processing Extended) processing Extended)
Extension Extended Extended Extended Extended
supported processing processing processing processing

Table 2: Proxy Server

Scope Hop-by-hop End-to-end

Strength Optional Required Optional Required
(may) (must) (may) (must)

Mandatory Strip 501 (Not Forward 501 (Not
unsupported extension Implemented) extension Implemented)
or tunnel or tunnel

Extension Strip 510 (Not Forward Forward
unsupported extension Extended) extension extension

Extension Extended Extended Extended Extended
supported processing processing processing, processing,
and strip and strip may strip may strip

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15. Examples

The following examples show various scenarios using mandatory in
HTTP/1.1 requests and responses. Information not essential for
illustrating the examples is left out (referred to as "...")

15.1 User Agent to Origin Server

Table 3: User Agent directly to origin server

Client issues a request M-GET /some-document HTTP/1.1
with one optional and Opt: "http://www.my.com/tracking"
one mandatory extension Man: "http://www.foo.com/privacy"
...

Origin server accepts HTTP/1.1 200 OK
the mandatory extension Ext:
but ignores the Cache-Control: max-age=120, no-cache="Ext"
optional one. The ...
client can not see in
this case that the
optional extension was
ignored.

Table 4: Origin server with Vary header field

Client issues a request M-GET /p/q HTTP/1.1
with one mandatory Man: "http://www.x.y/transform"; ns=16
extension 16-use-transform: xyzzy
...

Origin server accepts HTTP/1.1 200 OK
the mandatory but Ext:
indicates that the Vary: Man, 16-use-transform
response varies on the Date: Sun, 25 Oct 1998 08:12:31 GMT
request extension Expires: Sun, 25 Oct 1998 08:12:31 GMT
declaration Cache-Control: no-cache="Ext", max-age=1000
...

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15.2 User Agent to Origin Server via HTTP/1.1 Proxy

These two examples show how an extended request interacts with an
HTTP/1.1 proxy.

Table 5: HTTP/1.1 Proxy forwards extended request

Client issues a request M-GET /some-document HTTP/1.1
with one optional and C-Opt: "http://www.meter.org/hits"
one mandatory hop-by- C-Man: "http://www.copy.org/rights"
hop extension Connection: C-Opt, C-Man
...

HTTP/1.1 proxy forwards M-GET /some-document HTTP/1.1
the request and takes Via: 1.1 new
out the connection ...
headers

Origin server fails as HTTP/1.1 510 Not Extended
the request does not ...
contain any information
belonging to the M-GET
method

Table 6: HTTP/1.1 Proxy does not forward extended request

Client issues a request M-GET /some-document HTTP/1.1
with one optional and C-Opt: "http://www.meter.org/hits"
one mandatory hop-by- C-Man: "http://www.copy.org/rights"
hop extension Connection: C-Opt, C-Man
...

HTTP/1.1 proxy refuses HTTP/1.1 501 Not Implemented
to forward the M-GET ...
method and returns an
error

Origin server never
sees the extended
request

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15.3 User Agent to Origin Server via HTTP/1.0 Proxy

These two examples show how an extended request interacts with an
HTTP/1.0 proxy in the message path

Table 7: HTTP/1.0 Proxy forwards extended request

Client issues a request M-GET /some-document HTTP/1.1
with one mandatory Man: "http://www.price.com/sale"
extension ...

HTTP/1.0 proxy forwards M-GET /some-document HTTP/1.0
the request as a Man: "http://www.price.com/sale"
HTTP/1.0 request ...
without changing the
method

Origin server accepts HTTP/1.1 200 OK
declaration and returns Ext:
a 200 response and an Date: Sun, 25 Oct 1998 08:12:31 GMT
extension Expires: Sun, 25 Oct 1998 08:12:31 GMT
acknowledgement. The Cache-Control: no-cache="Ext", max-age=600
response can be cached ...
by HTTP/1.1 caches for
10 minutes.

Table 8: HTTP/1.0 and HTTP/1.1 Proxy Chain

Client issues request M-GET /some-document HTTP/1.1
with one mandatory and Man: "http://www.copy.org/rights"
one hop-by-hop optional C-Opt: "http://www.ads.org/noads"
extension Connection: C-Opt
...

HTTP/1.0 proxy forwards M-GET /some-document HTTP/1.0
request as HTTP/1.0 Man: "http://www.copy.org/rights"
request without C-Opt: "http://www.ads.org/noads"
changing the method and Connection: C-Man
without honoring the ...
Connection directives

HTTP/1.1 proxy deletes M-GET /some-document HTTP/1.1
(and ignores) optional Man: "http://www.copy.org/rights"
extension and forwards C-Man: "http://www.ads.org/givemeads"
the rest including a Connection: C-Man
via header field. It Via: 1.0 new
also add a hop-by-hop ...
mandatory extension

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RFC 2774 An HTTP Extension Framework February 2000

Origin server accepts HTTP/1.1 200 OK
both mandatory Ext:
extensions. The C-Ext
response is not Connection: C-Ext
cachable by the Date: Sun, 25 Oct 1998 08:12:31 GMT
HTTP/1.0 cache but can Expires: Sun, 25 Oct 1998 08:12:31 GMT
be cached for 1 hour by Cache-Control: no-cache="Ext", max-age=3600
HTTP/1.1 caches. ...

HTTP/1.1 proxy removes HTTP/1.1 200 OK
the hop-by-hop Ext:
extension Date: Sun, 25 Oct 1998 08:12:31 GMT
acknowledgement and Expires: Sun, 25 Oct 1998 08:12:31 GMT
forwards the remainder Cache-Control: no-cache="Ext", max-age=3600
of the response. ...

Nielsen, et al. Experimental [Page 19]

RFC 2774 An HTTP Extension Framework February 2000

Full Copyright Statement

Copyright (C) The Internet Society (2000). All Rights Reserved.

This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
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This document and the information contained herein is provided on an
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Acknowledgement

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Nielsen, et al. Experimental [Page 20]