Network Working Group J. Reschke
Internet-Draft greenbytes
Intended status: Standards Track S. Loreto
Expires: December 6, 2015 Ericsson
June 4, 2015
'Out-Of-Band' Content Coding for HTTP
draft-reschke-http-oob-encoding-00
Abstract
This document describes an Hypertext Transfer Protocol (HTTP) content
coding that can be used to describe the location of a secondary
resource that contans the payload.
Editorial Note (To be removed by RFC Editor before publication)
Distribution of this document is unlimited. Although this is not a
work item of the HTTPbis Working Group, comments should be sent to
the Hypertext Transfer Protocol (HTTP) mailing list at
ietf-http-wg@w3.org [1], which may be joined by sending a message
with subject "subscribe" to ietf-http-wg-request@w3.org [2].
Discussions of the HTTPbis Working Group are archived at
<http://lists.w3.org/Archives/Public/ietf-http-wg/>.
XML versions, latest edits, and issue tracking for this document are
available from <https://github.com/reschke/oobencoding> and
<http://greenbytes.de/tech/webdav/#draft-reschke-http-oob-encoding>.
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 http://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 December 6, 2015.
Reschke & Loreto Expires December 6, 2015 [Page 1]
Internet-Draft 'Out-Of-Band' Content Coding for HTTP June 2015
Copyright Notice
Copyright (c) 2015 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
(http://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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3
3. 'Out-Of-Band' Content Coding . . . . . . . . . . . . . . . . . 3
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.2. Definitions . . . . . . . . . . . . . . . . . . . . . . . 4
3.3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.3.1. Basic Example . . . . . . . . . . . . . . . . . . . . 5
3.3.2. Example involving an encryted resource . . . . . . . . 7
4. Feature Discovery . . . . . . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
5.1. Use in Requests . . . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Normative References . . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . . 9
Appendix A. Alternatives, or: why not a new Status Code? . . . . 10
Appendix B. Open Issues . . . . . . . . . . . . . . . . . . . . . 10
B.1. Range Requests . . . . . . . . . . . . . . . . . . . . . . 10
Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 10
Reschke & Loreto Expires December 6, 2015 [Page 2]
Internet-Draft 'Out-Of-Band' Content Coding for HTTP June 2015
1. Introduction
This document describes an Hypertext Transfer Protocol (HTTP) content
coding (Section 3.1.2.1 of [RFC7231]) that can be used to describe
the location of a secondary resource that contans the payload.
The primary use case for this content coding is to enable origin
servers to delegate the delivery of content to a secondary server
that might be "closer" to the client (with respect to network
topology) and/or able to cache content, leveraging content encrytion,
as described in [ENCRYPTENC].
2. Notational Conventions
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 [RFC2119].
This document reuses terminology used in the base HTTP
specifications, namely Section 2 of [RFC7230] and Section 3 of
[RFC7231].
3. 'Out-Of-Band' Content Coding
3.1. Overview
The 'Out-Of-Band' content coding is used to direct the recipient to
retrieve the actual message representation (Section 3 of [RFC7231])
from a secondary resource, such as a public cache:
1. Client performs GET request
2. Received response specifies the 'out-of-band' content coding; the
payload of the response contains additional meta data, plus the
location of the secondary resource
3. Client performs GET request on secondary resource (usually again
via HTTP(s))
4. Secondary server provides wrapped HTTP message
5. Client unwraps that representation (obtaining a full HTTP
message)
6. Client combines above representation with additional
representation metadata obtained from the primary resource
Reschke & Loreto Expires December 6, 2015 [Page 3]
Internet-Draft 'Out-Of-Band' Content Coding for HTTP June 2015
Client Secondary Server Origin Server
sends GET request with Accept-Encoding: out-of-band
(1) |---------------------------------------------------------\
status 200 and Content-Coding: out-of-band |
(2) <---------------------------------------------------------/
GET to secondary server
(3) |---------------------------\
wrapped HTTP message |
(4) <---------------------------/
(5, 6)
Client and combines HTTP message received in (4)
with metadata received in (2).
3.2. Definitions
The name of the content coding is "out-of-band".
The payload format uses JavaScript Object Notation (JSON, [RFC7159]),
describing an array of objects describing secondary resources, each
containing some of the members below:
'URI' A REQUIRED string containing the URI reference (Section 4.1 of
[RFC3986]) of the secondary resource.
'metadata' An OPTIONAL object containing additional members,
representing header field values to be recombined with the
metadata from the secondary resource and which can not appear as
header fields in the response message itself (header fields that
occur multiple times need to be combined into a single field value
as per Section 3.2.2 of [RFC7230]; header field names are lower-
cased).
The payload format uses a JSON array so that the origin server can
specify multiple secondary resources. When a client receives a
response containing multiple entries, it is free to choose which of
these to use.
The representation of the secondary resource needs to use a media
type capable of representing a full HTTP message. For now the only
supported type is "application/http" (Section 8.3.2 of [RFC7230]).
The client then obtains the original message by:
Reschke & Loreto Expires December 6, 2015 [Page 4]
Internet-Draft 'Out-Of-Band' Content Coding for HTTP June 2015
1. Unwrap the encapsulated HTTP message by removing any transfer and
content codings.
The latter might require additional metadata that could be
present in the "metadata" object, such as the "Encryption-Key"
header field described in Section 4 of [ENCRYPTENC].
2. Replacing/setting any response header fields from the primary
response except for framing-related information such as Content-
Length, Transfer-Encoding and Content-Encoding.
3. Replacing/setting any header fields with those present as members
in the "metadata" object. [[anchor3: Do we have a use case for
this?]]
Note that although this mechanism causes the inclusion of external
content, it will not affect the application-level security properties
of the reconstructed message, such as its web origin ([RFC6454]).
The cacheability of the response for the secondary resource does not
affect the cacheability of the reconstructed response message, which
is the same as for the origin server's response.
3.3. Examples
3.3.1. Basic Example
Client request of primary resource:
GET /test HTTP/1.1
Host: www.example.com
Accept-Encoding: gzip, out-of-band
Reschke & Loreto Expires December 6, 2015 [Page 5]
Internet-Draft 'Out-Of-Band' Content Coding for HTTP June 2015
Response:
HTTP/1.1 200 OK
Date: Thu, 14 May 2015 18:52:00 GMT
Content-Type: text/plain
Cache-Control: max-age=10, public
Content-Encoding: out-of-band
Content-Length: 76
[{
"URI": "http://example.net/bae27c36-fa6a-11e4-ae5d-00059a3c7a00"
}]
(note that the Content-Type header field describes the media type of
the secondary's resource representation)
Client request for secondary resource:
GET /bae27c36-fa6a-11e4-ae5d-00059a3c7a00 HTTP/1.1
Host: example.net
Response:
HTTP/1.1 200 OK
Date: Thu, 14 May 2015 18:52:10 GMT
Content-Type: application/http
Cache-Control: private
Content-Length: 115
HTTP/1.1 200 OK
Date: Thu, 14 May 2015 17:00:00 GMT
Content-Length: 15
Content-Language: en
Hello, world.
Reschke & Loreto Expires December 6, 2015 [Page 6]
Internet-Draft 'Out-Of-Band' Content Coding for HTTP June 2015
Final message after recombining header fields:
HTTP/1.1 200 OK
Date: Thu, 14 May 2015 18:52:00 GMT
Content-Length: 15
Cache-Control: max-age=10, public
Content-Type: text/plain
Content-Language: en
Hello, world.
In this example, Cache-Control, Content-Length, and Date have been
set/overwritten with data from the primary resource's representation.
3.3.2. Example involving an encryted resource
Given the example HTTP message from Section 5.4 of [ENCRYPTENC], a
primary resource could use the "out-of-band" encoding to specify just
the location of the secondary resource plus the contents of the
"Encryption-Key" header field needed to decrypt the payload:
Response:
HTTP/1.1 200 OK
Date: Thu, 14 May 2015 18:52:00 GMT
Content-Encoding: out-of-band
Content-Type: text/plain
Content-Length: 192
[{
"URI": "http://example.net/bae27c36-fa6a-11e4-ae5d-00059a3c7a00"
"metadata": {
"encryption-key": "keyid=\"a1\";
key=\"9Z57YCb3dK95dSsdFJbkag\""
}
}]
(note that the Content-Type header field describes the media type of
the secondary's resource representation)
Reschke & Loreto Expires December 6, 2015 [Page 7]
Internet-Draft 'Out-Of-Band' Content Coding for HTTP June 2015
Response for secondary resource:
HTTP/1.1 200 OK
Date: Thu, 14 May 2015 18:52:10 GMT
Content-Type: application/http
Content-Length: ...
Cache-Control: private
HTTP/1.1 200 OK
Content-Length: 31
Content-Encoding: aesgcm-128
Encryption: keyid="a1"; salt="ibZx1RNz537h1XNkRcPpjA"
zK3kpG__Z8whjIkG6RYgPz11oUkTKcxPy9WP-VPMfuc
(payload body shown in base64 here)
Final message after recombining header fields:
HTTP/1.1 200 OK
Date: Thu, 14 May 2015 18:52:00 GMT
Content-Length: 15
Content-Type: text/plain
I am the walrus
4. Feature Discovery
New content codings can be deployed easily, as the client can use the
"Accept-Encoding" header field (Section 5.3.4 of [RFC7231]) to signal
which content codings are supported.
5. Security Considerations
[[tbd.security: Such as: how is the secondary resource safe from
being modified without knowledge of the primary resource?]]
5.1. Use in Requests
In general, content codings can be used in both requests and
responses. This particular content coding has been designed for
responses. When supported in requests, it creates a new attack
vector where the receiving server can be tricked into including
content that the client might not have access to otherwise (such as
HTTP resources behind a firewall).
Reschke & Loreto Expires December 6, 2015 [Page 8]
Internet-Draft 'Out-Of-Band' Content Coding for HTTP June 2015
6. IANA Considerations
The IANA "HTTP Content Coding Registry", located at
<http://www.iana.org/assignments/http-parameters>, needs to be
updated with the registration below:
Name: out-of-band
Description: Payload needs to be retrieved from a secondary resource
Reference: Section 3 of this document
7. References
7.1. 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,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter,
"Uniform Resource Identifier (URI): Generic Syntax",
STD 66, RFC 3986, DOI 10.17487/RFC3986, January 2005,
<http://www.rfc-editor.org/info/rfc3986>.
[RFC7159] Bray, T., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, DOI 10.17487/RFC7159,
March 2014, <http://www.rfc-editor.org/info/rfc7159>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Message Syntax and
Routing", RFC 7230, DOI 10.17487/RFC7230, June 2014,
<http://www.rfc-editor.org/info/rfc7230>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Semantics and Content",
RFC 7231, DOI 10.17487/RFC7231, June 2014,
<http://www.rfc-editor.org/info/rfc7231>.
7.2. Informative References
[ENCRYPTENC] Thomson, M., "Encrypted Content-Encoding for HTTP",
draft-thomson-http-encryption-00 (work in progress),
May 2015.
[RFC6454] Barth, A., "The Web Origin Concept", RFC 6454,
DOI 10.17487/RFC6454, December 2011,
Reschke & Loreto Expires December 6, 2015 [Page 9]
Internet-Draft 'Out-Of-Band' Content Coding for HTTP June 2015
<http://www.rfc-editor.org/info/rfc6454>.
URIs
[1] <mailto:ietf-http-wg@w3.org>
[2] <mailto:ietf-http-wg-request@w3.org?subject=subscribe>
Appendix A. Alternatives, or: why not a new Status Code?
A plausible alternative approach would be to implement this
functionality one level up, using a new redirect status code (Section
6.4 of [RFC7231]). However, this would have several drawbacks:
o Servers will need to know whether a client understands the new
status code; thus some additional signal to opt into this protocol
would always be needed.
o In redirect messages, representation metadata (Section 3.1 of
[RFC7231]), namely "Content-Type", applies to the response
message, not the redirected-to resource.
Appendix B. Open Issues
B.1. Range Requests
We probably need to handle Range Requests. How would this work?
Passing down the Range request header field to the secondary
resource?
What about codes other than 200 and 206?
Appendix C. Acknowledgements
Thanks to Goran Eriksson, Mark Nottingham, and Martin Thomson for
feedback on this document.
Authors' Addresses
Julian F. Reschke
greenbytes GmbH
Hafenweg 16
Muenster, NW 48155
Germany
EMail: julian.reschke@greenbytes.de
URI: http://greenbytes.de/tech/webdav/
Reschke & Loreto Expires December 6, 2015 [Page 10]
Internet-Draft 'Out-Of-Band' Content Coding for HTTP June 2015
Salvatore Loreto
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
EMail: salvatore.loreto@ericsson.com
Reschke & Loreto Expires December 6, 2015 [Page 11]