[Docs] [txt|pdf|xml|html] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12

Network Working Group                                         J. Reschke
Internet-Draft                                                greenbytes
Intended status: Standards Track                               S. Loreto
Expires: September 18, 2016                                     Ericsson
                                                          March 17, 2016


                 'Out-Of-Band' Content Coding for HTTP
                   draft-reschke-http-oob-encoding-04

Abstract

   This document describes an Hypertext Transfer Protocol (HTTP) content
   coding that can be used to describe the location of a secondary
   resource that contains 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>.

   The changes in this draft are summarized in Appendix C.4.

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."




Reschke & Loreto       Expires September 18, 2016               [Page 1]


Internet-Draft    'Out-Of-Band' Content Coding for HTTP       March 2016


   This Internet-Draft will expire on September 18, 2016.

Copyright Notice

   Copyright (c) 2016 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.



































Reschke & Loreto       Expires September 18, 2016               [Page 2]


Internet-Draft    'Out-Of-Band' Content Coding for HTTP       March 2016


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Notational Conventions . . . . . . . . . . . . . . . . . . . .  4
   3.  'Out-Of-Band' Content Coding . . . . . . . . . . . . . . . . .  4
     3.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.2.  Definitions  . . . . . . . . . . . . . . . . . . . . . . .  5
     3.3.  Problem Reporting  . . . . . . . . . . . . . . . . . . . .  6
       3.3.1.  Server Not Reachable . . . . . . . . . . . . . . . . .  7
       3.3.2.  Resource Not Found . . . . . . . . . . . . . . . . . .  7
       3.3.3.  Payload Unusable . . . . . . . . . . . . . . . . . . .  7
     3.4.  Examples . . . . . . . . . . . . . . . . . . . . . . . . .  7
       3.4.1.  Basic Example  . . . . . . . . . . . . . . . . . . . .  7
       3.4.2.  Example involving an encrypted resource  . . . . . . .  9
       3.4.3.  Example For Problem Reporting  . . . . . . . . . . . . 10
   4.  Feature Discovery  . . . . . . . . . . . . . . . . . . . . . . 10
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
     5.1.  Content Modifications  . . . . . . . . . . . . . . . . . . 10
     5.2.  Content Stealing . . . . . . . . . . . . . . . . . . . . . 10
     5.3.  Use in Requests  . . . . . . . . . . . . . . . . . . . . . 11
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 11
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 12
   Appendix A.  Alternatives, or: why not a new Status Code?  . . . . 13
   Appendix B.  Open Issues . . . . . . . . . . . . . . . . . . . . . 13
     B.1.  Range Requests . . . . . . . . . . . . . . . . . . . . . . 13
     B.2.  Accessing the Secondary Resource Too Early . . . . . . . . 14
     B.3.  Resource maps  . . . . . . . . . . . . . . . . . . . . . . 14
     B.4.  Padding  . . . . . . . . . . . . . . . . . . . . . . . . . 14
   Appendix C.  Change Log (to be removed by RFC Editor before
                publication)  . . . . . . . . . . . . . . . . . . . . 15
     C.1.  Changes since draft-reschke-http-oob-encoding-00 . . . . . 15
     C.2.  Changes since draft-reschke-http-oob-encoding-01 . . . . . 15
     C.3.  Changes since draft-reschke-http-oob-encoding-02 . . . . . 15
     C.4.  Changes since draft-reschke-http-oob-encoding-03 . . . . . 15
   Appendix D.  Acknowledgements  . . . . . . . . . . . . . . . . . . 15














Reschke & Loreto       Expires September 18, 2016               [Page 3]


Internet-Draft    'Out-Of-Band' Content Coding for HTTP       March 2016


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 contains 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
   encryption, 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 a 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 payload

   5.  Client combines above representation with additional
       representation metadata obtained from the primary resource








Reschke & Loreto       Expires September 18, 2016               [Page 4]


Internet-Draft    'Out-Of-Band' Content Coding for HTTP       March 2016


     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) |---------------------------\
                           payload |
   (4) <---------------------------/

   (5)
      Client and combines payload 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 object describing secondary resources plus OPTIONAL
   additional metadata:

   'URIs'  A REQUIRED string array containing at least one URI reference
      (Section 4.1 of [RFC3986]) of a secondary resource.

   'fallback'  An OPTIONAL string containing a URI reference of a
      fallback resource (see Appendix B.2).  This URI reference, after
      resolution against the URI of the primary resource, MUST identify
      a resource on the same server as the primary resource.

   'metadata'  An OPTIONAL object containing additional members,
      representing header field values 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 URIs, it is free to choose which of
   these to use.

   New specifications can define new OPTIONAL header fields, thus
   clients MUST ignore unknown fields.  Extension specifications will
   have to update this specification. [[anchor3: or we define a
   registry]]



Reschke & Loreto       Expires September 18, 2016               [Page 5]


Internet-Draft    'Out-Of-Band' Content Coding for HTTP       March 2016


   The client then obtains the original message by:

   1.  Unwrapping the encapsulated HTTP message by removing any transfer
       and content codings.

   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. [[anchor4: Do we have a use case for
       this?]]

   If the client is unable to retrieve the secondary resource's
   representation (host can't be reached, non 2xx response status code,
   payload failing integrity check, etc.), it can choose an alternate
   secondary resource (if specified), try the fallback URI (if given),
   or simply retry the request to the origin server without including
   "out-of-band" in the Accept-Encoding request header field.  In the
   latter case, it can be useful to inform the origin server about what
   problems were encountered when trying to access the secondary
   resource; see Section 3.3 for details.

   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.

   Note that because the server's response depends on the request's
   Accept-Encoding header field, the response usually will need to be
   declared to vary on that.  See Section 7.1.4 of [RFC7231] and Section
   2.3 of [RFC7232] for details.

3.3.  Problem Reporting

   When the client fails to obtain the secondary resource, it can be
   useful to inform the origin server about the condition.  This can be
   accomplished by adding a "Link" header field ([RFC5988]) to a
   subsequent request to the origin server, detailing the URI of the
   secondary resource and the failure reason.

   The following link extension relations are defined:






Reschke & Loreto       Expires September 18, 2016               [Page 6]


Internet-Draft    'Out-Of-Band' Content Coding for HTTP       March 2016


3.3.1.  Server Not Reachable

   Used in case the server was not reachable.

   Link relation:

   http://purl.org/NET/linkrel/not-reachable

3.3.2.  Resource Not Found

   Used in case the server responded, but the object could not be
   obtained.

   Link relation:

   http://purl.org/NET/linkrel/resource-not-found

3.3.3.  Payload Unusable

   Used in case the the payload could be obtained, but wasn't usable
   (for instance, because integrity checks failed).

   Link relation:

   http://purl.org/NET/linkrel/payload-unusable

3.4.  Examples

3.4.1.  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 September 18, 2016               [Page 7]


Internet-Draft    'Out-Of-Band' Content Coding for HTTP       March 2016


   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: 145
     Vary: Accept-Encoding

     {
       "URIs": [
         "http://example.net/bae27c36-fa6a-11e4-ae5d-00059a3c7a00"
       ],
       "fallback": "/c/bae27c36-fa6a-11e4-ae5d-00059a3c7a00"
     }

   (note that the Content-Type header field describes the media type of
   the secondary's resource representation, and the origin server
   supplied a fallback URI)

   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
     Cache-Control: private
     Content-Length: 15

     Hello, world.

   (Note no Content-Type header field is present here because the
   secondary server truly does not know the media type of the payload)

   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

     Hello, world.



Reschke & Loreto       Expires September 18, 2016               [Page 8]


Internet-Draft    'Out-Of-Band' Content Coding for HTTP       March 2016


3.4.2.  Example involving an encrypted 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
   "Crypto-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: aesgcm128, out-of-band
     Content-Type: text/plain
     Encryption: keyid="a1"; salt="vr0o6Uq3w_KDWeatc27mUg"
     Crypto-Key: keyid="a1"; aesgcm128="csPJEXBYA5U-Tal9EdJi-w"
     Content-Length: 87
     Vary: Accept-Encoding

     {
       "URIs": [
         "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)

   Response for secondary resource:

     HTTP/1.1 200 OK
     Date: Thu, 14 May 2015 18:52:10 GMT
     Content-Length: ...
     Cache-Control: private

     fuag8ThIRIazSHKUqJ5OduR75UgEUuM76J8UFwadEvg
   (payload body shown in base64 here)

   Final message undoing all content codings:

     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






Reschke & Loreto       Expires September 18, 2016               [Page 9]


Internet-Draft    'Out-Of-Band' Content Coding for HTTP       March 2016


      Note: in this case, the ability to undo the "aescgm128" is needed
      to process the response.  If "aescgm128" wasn't listed as
      acceptable content encoding in the request, the origin server
      wouldn't be able to use the "out-of-band" mechanism.

3.4.3.  Example For Problem Reporting

   Client requests primary resource as in Section 3.4.1, but the attempt
   to access the secondary resource fails.

   Response:

     HTTP/1.1 404 Not Found
     Date: Thu, 08 September 2015 16:49:00 GMT
     Content-Type: text/plain
     Content-Length: 20

     Resource Not Found

   Client retries with the origin server and includes Link header field
   reporting the problem:

     GET /test HTTP/1.1
     Host: www.example.com
     Accept-Encoding: gzip, out-of-band
     Link: <http://example.net/bae27c36-fa6a-11e4-ae5d-00059a3c7a00>;
           rel="http://purl.org/NET/linkrel/resource-not-found"


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

5.1.  Content Modifications

   This specification does not define means to verify that the payload
   obtained from the secondary resource really is what the origin server
   expects it to be.  Content signatures can address this concern (see
   [CONTENTSIG] and [MICE]).

5.2.  Content Stealing

   The Out-Of-Band content coding could be used to circumvent the same-
   origin policy ([RFC6454], Section 3) of user agents: an attacking



Reschke & Loreto       Expires September 18, 2016              [Page 10]


Internet-Draft    'Out-Of-Band' Content Coding for HTTP       March 2016


   site which knows the URI of a secondary resource would use the out-
   of-band coding to trick the user agent to read the contents of the
   secondary resource, which then, due to the security properties of
   out-of-band codings, would be handled as if it originated from the
   origin's resource.

   This problem is not yet addressed by this specification.  Possible
   defenses would be to rely on signatures and encryption, or to add an
   indication to the secondary resource's response that would prevent
   further processing in responses from "bad" origins (not unlike the
   "Access-Control-Allow-Origin" header field defined in Section 5.1 of
   [CORS]).

5.3.  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).

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>.




Reschke & Loreto       Expires September 18, 2016              [Page 11]


Internet-Draft    'Out-Of-Band' Content Coding for HTTP       March 2016


   [RFC5988]     Nottingham, M., "Web Linking", RFC 5988, DOI 10.17487/
                 RFC5988, October 2010,
                 <http://www.rfc-editor.org/info/rfc5988>.

   [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

   [CONTENTSIG]  Thomson, M., "Content-Signature Header Field for HTTP",
                 draft-thomson-http-content-signature-00 (work in
                 progress), July 2015.

   [CORS]        van Kesteren, A., "Cross-Origin Resource Sharing", W3C
                 Recommendation REC-cors-20140116, January 2014,
                 <http://www.w3.org/TR/2014/REC-cors-20140116/>.

                 Latest version available at
                 <http://www.w3.org/TR/cors/>.

   [ENCRYPTENC]  Thomson, M., "Encrypted Content-Encoding for HTTP",
                 draft-ietf-httpbis-encryption-encoding-00 (work in
                 progress), December 2015.

   [MICE]        Thomson, M., "Merkle Integrity Content Encoding",
                 draft-thomson-http-mice-00 (work in progress),
                 January 2016.

   [RFC2017]     Freed, N. and K. Moore, "Definition of the URL MIME
                 External-Body Access-Type", RFC 2017, DOI 10.17487/
                 RFC2017, October 1996,
                 <http://www.rfc-editor.org/info/rfc2017>.

   [RFC4483]     Burger, E., "A Mechanism for Content Indirection in
                 Session Initiation Protocol (SIP) Messages", RFC 4483,
                 DOI 10.17487/RFC4483, May 2006,
                 <http://www.rfc-editor.org/info/rfc4483>.



Reschke & Loreto       Expires September 18, 2016              [Page 12]


Internet-Draft    'Out-Of-Band' Content Coding for HTTP       March 2016


   [RFC6454]     Barth, A., "The Web Origin Concept", RFC 6454,
                 DOI 10.17487/RFC6454, December 2011,
                 <http://www.rfc-editor.org/info/rfc6454>.

   [RFC7232]     Fielding, R., Ed. and J. Reschke, Ed., "Hypertext
                 Transfer Protocol (HTTP/1.1): Conditional Requests",
                 RFC 7232, DOI 10.17487/RFC7232, June 2014,
                 <http://www.rfc-editor.org/info/rfc7232>.

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.

   o  The origin-preserving nature of using a content coding woudld be
      lost.

   Another alternative would be to implement the indirection on the
   level of the media type using something similar to the type "message/
   external-body", defined in [RFC2017] and refined for use in the
   Session Initiation Protocol (SIP) in [RFC4483].  This approach though
   would share most of the drawbacks of the status code approach
   mentioned above.

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?



Reschke & Loreto       Expires September 18, 2016              [Page 13]


Internet-Draft    'Out-Of-Band' Content Coding for HTTP       March 2016


B.2.  Accessing the Secondary Resource Too Early

   One use-case for this protocol is to enable a system of "blind
   caches", which would serve the secondary resources.  These caches
   might only be populated on demand, thus it could happen that whatever
   mechanism is used to populate the cache hasn't finished when the
   client hits it (maybe due to race conditions, or because the cache is
   behind a middlebox which doesn't allow the origin server to push
   content to it).

   In this particular case, it can be useful if the client was able to
   "piggyback" the URI of the fallback for the primary resource, giving
   the secondary server a means by which it could obtain the payload
   itself.  This information could be provided in yet another Link
   header field:

     GET bae27c36-fa6a-11e4-ae5d-00059a3c7a00 HTTP/1.1
     Host: example.net
     Link: <http://example.com/c/bae27c36-fa6a-11e4-ae5d-00059a3c7a00>;
           rel="http://purl.org/NET/linkrel/primary-resource"


   (continuing the example from Section 3.4.1)

B.3.  Resource maps

   When out-of-band encoding is used as part of a caching solution, the
   additional round trips to the origin server can be a significant
   performance problem; in particular, when many small resources need to
   be loaded (such as scripts, images, or video fragments).  In cases
   like these, it could be useful for the origin server to provide a
   "resource map", allowing to skip the round trips to the origin server
   for these mapped resources.  Plausible ways to transmit the resource
   map could be:

   o  as extension in the out-of-band encoding JSON payload, or

   o  as separate resource identified by a "Link" response header field.

   This specification does not define a format, nor a mechanism to
   transport the map, but it's a given that some specification using
   "out-of-band" encoding will do.

B.4.  Padding

   It might be a good idea to allow padding in the secondary resource's
   payload, in order to even hide the precise content length.  This
   could be accomplished by adding range information to the out-of-band



Reschke & Loreto       Expires September 18, 2016              [Page 14]


Internet-Draft    'Out-Of-Band' Content Coding for HTTP       March 2016


   metadata, allowing the client to throw away parts of the payload when
   reconstructing the response body.

Appendix C.  Change Log (to be removed by RFC Editor before publication)

C.1.  Changes since draft-reschke-http-oob-encoding-00

   Mention media type approach.

   Explain that clients can always fall back not to use oob when the
   secondary resource isn't available.

   Add Vary response header field to examples and mention that it'll
   usually be needed
   (<https://github.com/reschke/oobencoding/issues/6>).

   Experimentally add problem reporting using piggy-backed Link header
   fields (<https://github.com/reschke/oobencoding/issues/7>).

C.2.  Changes since draft-reschke-http-oob-encoding-01

   Updated ENCRYPTENC reference.

C.3.  Changes since draft-reschke-http-oob-encoding-02

   Add MICE reference.

   Remove the ability of the secondary resource to contain anything but
   the payload (<https://github.com/reschke/oobencoding/issues/11>).

   Changed JSON payload to be an object containing an array of URIs plus
   additional members.  Specify "fallback" as one of these additional
   members, and update Appendix B.2 accordingly).

   Discuss extensibility a bit.

C.4.  Changes since draft-reschke-http-oob-encoding-03

   Mention "Content Stealing" thread.

   Mention padding.

Appendix D.  Acknowledgements

   Thanks to Christer Holmberg, Daniel Lindstrom, Goran Eriksson, John
   Mattsson, Kevin Smith, Magnus Westerlund, Mark Nottingham, Martin
   Thomson, and Roland Zink for feedback on this document.




Reschke & Loreto       Expires September 18, 2016              [Page 15]


Internet-Draft    'Out-Of-Band' Content Coding for HTTP       March 2016


Authors' Addresses

   Julian F. Reschke
   greenbytes GmbH
   Hafenweg 16
   Muenster, NW  48155
   Germany

   EMail: julian.reschke@greenbytes.de
   URI:   http://greenbytes.de/tech/webdav/


   Salvatore Loreto
   Ericsson
   Torshamnsgatan 21
   Stochholm  16483
   Sweden

   EMail: salvatore.loreto@ericsson.com
































Reschke & Loreto       Expires September 18, 2016              [Page 16]


Html markup produced by rfcmarkup 1.129b, available from https://tools.ietf.org/tools/rfcmarkup/