| Network Working Group | J. Reschke |
| Internet-Draft | greenbytes |
| Intended status: Standards Track | S. Loreto |
| Expires: December 6, 2015 | Ericsson |
| June 4, 2015 |
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.¶
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, which may be joined by sending a message with subject "subscribe" to ietf-http-wg-request@w3.org.¶
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>.¶
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.¶
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.¶
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].¶
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:¶
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).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:¶
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:¶
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].
Replacing/setting any response header fields from the primary response except for framing-related information such as Content-Length, Transfer-Encoding and Content-Encoding.
Replacing/setting any header fields with those present as members in the "metadata" object. [rfc.comment.1: 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.¶
Client request of primary resource:
GET /test HTTP/1.1 Host: www.example.com Accept-Encoding: gzip, out-of-band
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.
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.
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)
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 walrusNew 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.¶
[tbd.security: Such as: how is the secondary resource safe from being modified without knowledge of the primary resource?] ¶
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).¶
The IANA "HTTP Content Coding Registry", located at <http://www.iana.org/assignments/http-parameters>, needs to be updated with the registration below:¶
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:¶
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?¶
Thanks to Goran Eriksson, Mark Nottingham, and Martin Thomson for feedback on this document.¶