One document matched: draft-reschke-http-oob-encoding-02.xml

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<rfc ipr="trust200902" docName="draft-reschke-http-oob-encoding-02" category="std">

  

	<front>
  <title>'Out-Of-Band' Content Coding for HTTP</title>
  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
    <organization abbrev="greenbytes">greenbytes GmbH</organization>
    <address>
      <postal>
        <street>Hafenweg 16</street>
        <city>Muenster</city><region>NW</region><code>48155</code>
        <country>Germany</country>
      </postal>
      <email>julian.reschke@greenbytes.de</email>	
      <uri>http://greenbytes.de/tech/webdav/</uri>	
    </address>
  </author>
  <author initials="S." surname="Loreto" fullname="Salvatore Loreto">
    <organization>Ericsson</organization>
    <address>
        <postal>
        <street>Hirsalantie 11</street>
        <code>02420</code> 
          <city>Jorvas</city> 
          <country>Finland</country>
        </postal>
        <email>salvatore.loreto@ericsson.com</email>
    </address>
  </author>

  <date year="2015" month="December" day="31"/>
  
  <area>Applications and Real-Time</area>
  <keyword>HTTP</keyword>
  <keyword>content coding</keyword>
  <keyword>ouf-of-band</keyword>

  <abstract>
    <t>
      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.
    </t>
  </abstract>
  

  <note title="Editorial Note (To be removed by RFC Editor before publication)">
    <t>
      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 <eref target="mailto:ietf-http-wg@w3.org">ietf-http-wg@w3.org</eref>,
      which may be joined by sending a message with subject 
      "subscribe" to <eref target="mailto:ietf-http-wg-request@w3.org?subject=subscribe">ietf-http-wg-request@w3.org</eref>.
    </t>
    <t>
      Discussions of the HTTPbis Working Group are archived at
      <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.               
    </t> 
    <t>
      XML versions, latest edits, and issue tracking for this document
      are available from <eref target="https://github.com/reschke/oobencoding"/> and
      <eref target="http://greenbytes.de/tech/webdav/#draft-reschke-http-oob-encoding"/>.
    </t>
    <t>
      The changes in this draft are summarized in <xref target="changes.since.01"/>.
    </t>
  </note>


  </front>

  <middle>

<section anchor="introduction" title="Introduction">
<t>
  This document describes an Hypertext Transfer Protocol (HTTP) content
  coding (Section 3.1.2.1 of <xref target="RFC7231"/>) that can be used
  to describe the location of a secondary resource that contains the payload.
</t>
<t>
  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
  <xref target="ENCRYPTENC"/>.
</t>
</section>  

<section anchor="notational.conventions" title="Notational Conventions">
<t>
   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 <xref target="RFC2119"/>.
</t>
<t>
   This document reuses terminology used in the base HTTP specifications,
   namely Section 2 of <xref target="RFC7230"/> and
   Section 3 of <xref target="RFC7231"/>.
</t>
</section>

<section anchor="ouf-of-band.content.coding" title="'Out-Of-Band' Content Coding">
<section title="Overview">
<t>
  The 'Out-Of-Band' content coding is used to direct the recipient to retrieve the
  actual message representation (Section 3 of <xref target="RFC7231"/>)
  from a secondary resource, such as a public cache:
</t>
<t>
  <list style="numbers">
    <t anchor="flow.get.request">Client performs GET request</t>
    <t anchor="flow.get.response">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</t>
    <t anchor="flow.get.request2">Client performs GET request on secondary resource (usually again via HTTP(s))</t>
    <t anchor="flow.get.response2">Secondary server provides wrapped HTTP message</t>
    <t anchor="flow.unwrap">Client unwraps that representation (obtaining a full HTTP message)</t>
    <t anchor="flow.combine">Client combines above representation with additional representation metadata
    obtained from the primary resource</t>
  </list>
</t>
<figure><artwork type="drawing"><![CDATA[
  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).]]></artwork></figure>
</section>
<section title="Definitions">
<t>
  The name of the content coding is "out-of-band". 
</t>
<t>
  The payload format uses JavaScript Object Notation (JSON, <xref target="RFC7159"/>),
  describing an array of objects describing secondary resources, each containing
  some of the members below:
</t>
<t>
  <list style="hanging">
    <t hangText="'URI'">
      A REQUIRED string containing the URI reference (Section 4.1 of <xref target="RFC3986"/>) of the secondary resource.
    </t>
    <t hangText="'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 <xref target="RFC7230"/>; header field names are lower-cased).
    </t>
  </list>
</t>
<t>
  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.
</t>
<t>
  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 <xref target="RFC7230"/>).
</t>
<t>
  The client then obtains the original message by:
</t>
<t>
  <list style="numbers">
    <t>
        Unwrapping the encapsulated HTTP message by removing any transfer and content codings.
      <vspace blankLines="1"/>
        The latter might require
        additional metadata that could be present in the "metadata" object,
        such as the "Crypto-Key" header field described in Section 4 of <xref target="ENCRYPTENC"/>.
      </t>
    <t>
        Replacing/setting any response header fields from the primary
        response except for framing-related information such as
        Content-Length, Transfer-Encoding and Content-Encoding.
      </t>
    <t>
        Replacing/setting any header fields with those present as members
        in the "metadata" object.
        <cref>Do we have a use case for this?</cref>
      </t>
  </list>
</t>
<t>
  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), 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 <xref target="problem.reporting"/>
  for details.
</t>
<t>
  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 (<xref target="RFC6454"/>).
</t>
<t>
  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.
</t>
<t>
  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 <xref target="RFC7231"/> and
  Section 2.3 of <xref target="RFC7232"/> for details.
</t>
</section>

<section anchor="problem.reporting" title="Problem Reporting">
<t>
  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 (<xref target="RFC5988"/>) to a subsequent request to the origin server,
  detailing the URI of the secondary resource and the failure reason.
</t>
<t>
  The following link extension relations are defined:
</t>

<section anchor="rel-not-reachable" title="Server Not Reachable">
<t>
  Used in case the server was not reachable.
</t>
<figure>
<preamble>Link relation:</preamble>
<artwork type="example"><![CDATA[
http://purl.org/NET/linkrel/not-reachable]]></artwork>
</figure>
</section>

<section anchor="rel-resource-not-found" title="Resource Not Found">
<t>
  Used in case the server responded, but the object could not be obtained.
</t>
<figure>
<preamble>Link relation:</preamble>
<artwork type="example"><![CDATA[
http://purl.org/NET/linkrel/resource-not-found]]></artwork>
</figure>
</section>

<section anchor="rel-payload-unusable" title="Payload Unusable">
<t>
  Used in case the the payload could be obtained, but wasn't usable
  (for instance, because integrity checks failed).
</t>
<figure>
<preamble>Link relation:</preamble>
<artwork type="example"><![CDATA[
http://purl.org/NET/linkrel/payload-unusable]]></artwork>
</figure>
</section>

</section>

<section title="Examples">
<section anchor="basic.example" title="Basic Example">
<figure>
<preamble>Client request of primary resource:</preamble>
<artwork type="message/http; msgtype="request""><![CDATA[
  GET /test HTTP/1.1
  Host: www.example.com
  Accept-Encoding: gzip, out-of-band
  
  ]]></artwork></figure>
<figure>
<preamble>Response:</preamble>
<artwork type="message/http; msgtype="request""><![CDATA[
  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
  Vary: Accept-Encoding
  
  [{
    "URI": "http://example.net/bae27c36-fa6a-11e4-ae5d-00059a3c7a00"
  }]
  ]]></artwork>
<postamble>
  (note that the Content-Type header field describes the media type of the
  secondary's resource representation)
</postamble>
</figure>
<figure>
<preamble>Client request for secondary resource:</preamble>
<artwork type="message/http; msgtype="request""><![CDATA[
  GET /bae27c36-fa6a-11e4-ae5d-00059a3c7a00 HTTP/1.1
  Host: example.net
  
  ]]></artwork></figure>
<figure>
<preamble>Response:</preamble>
<artwork type="message/http; msgtype="request""><![CDATA[
  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.
  
  ]]></artwork>
</figure>
<figure>
<preamble>Final message after recombining header fields:</preamble>
<artwork type="message/http; msgtype="request""><![CDATA[
  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.
  ]]></artwork>
<postamble>In this example, Cache-Control, Content-Length, and Date have been set/overwritten with data from the primary resource's representation.</postamble>
</figure>
</section>
<section title="Example involving an encrypted resource">
<t>
  Given the example HTTP message from Section 5.4 of <xref target="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: 
</t>
<figure>
<preamble>Response:</preamble>
<artwork type="message/http; msgtype="request""><![CDATA[
  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: 194
  Vary: Accept-Encoding
  
  [{
    "URI": "http://example.net/bae27c36-fa6a-11e4-ae5d-00059a3c7a00"
    "metadata": {
      "crypto-key": "keyid=\"a1\";
                         aesgcm128=\"csPJEXBYA5U-Tal9EdJi-w\""
    }
  }]
  ]]></artwork>
<postamble>
  (note that the Content-Type header field describes the media type of the
  secondary's resource representation)
</postamble>
</figure>
<figure>
<preamble>Response for secondary resource:</preamble>
<artwork type="message/http; msgtype="request""><![CDATA[
  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: 32
  Content-Encoding: aesgcm128
  Encryption: keyid="a1"; salt="vr0o6Uq3w_KDWeatc27mUg"
  
  fuag8ThIRIazSHKUqJ5OduR75UgEUuM76J8UFwadEvg]]></artwork>
<postamble>(payload body shown in base64 here)</postamble>
</figure>
<figure>
<preamble>Final message after recombining header fields:</preamble>
<artwork type="message/http; msgtype="request""><![CDATA[
  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]]></artwork>
</figure>
</section>

<section title="Example For Problem Reporting">
<t>
  Client requests primary resource as in <xref target="basic.example"/>, but the
  attempt to access the secondary resource fails.
</t>
<figure>
<preamble>Response:</preamble>
<artwork type="message/http; msgtype="request""><![CDATA[
  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
  ]]></artwork>
</figure>
<figure>
<preamble>Client retries with the origin server and includes Link
header field reporting the problem:</preamble>
<artwork type="message/http; msgtype="request""><![CDATA[
  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"
  
  ]]></artwork></figure>
</section>
</section>
</section>

<section anchor="feature.discovery" title="Feature Discovery">
<t>
  New content codings can be deployed easily, as the client can use
  the "Accept-Encoding" header field (Section 5.3.4 of <xref target="RFC7231"/>)
  to signal which content codings are supported.
</t>
</section>

<section anchor="security.considerations" title="Security Considerations">
<section title="Content Modifications">
<t>
  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 <xref target="CONTENTSIG"/>).
</t>  
</section>
<section title="Use in Requests">
<t>
  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).
</t>
</section>
</section>

<section anchor="iana.considerations" title="IANA Considerations">
<t>
  The IANA "HTTP Content Coding Registry", located at <eref target="http://www.iana.org/assignments/http-parameters"/>,
  needs to be updated with the registration below:
</t>
<t>
  <list style="hanging">
    <t hangText="Name:">out-of-band</t>
    <t hangText="Description:">Payload needs to be retrieved from a secondary resource</t>
    <t hangText="Reference:"><xref target="ouf-of-band.content.coding"/> of this document</t>
  </list>
</t>
</section>

  </middle>
  <back>
  
<references title="Normative References">

<reference anchor="RFC2119" target="http://www.rfc-editor.org/info/rfc2119"><front>
    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
    <author initials="S." surname="Bradner" fullname="Scott Bradner"/>
    <date month="March" year="1997"/>
  </front><seriesInfo name="BCP" value="14"/><seriesInfo name="RFC" value="2119"/><seriesInfo name="DOI" value="10.17487/RFC2119"/></reference>

<reference anchor="RFC3986" target="http://www.rfc-editor.org/info/rfc3986"><front>
  <title abbrev="URI Generic Syntax">Uniform Resource Identifier (URI): Generic Syntax</title>
  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee"/>
  <author initials="R." surname="Fielding" fullname="Roy T. Fielding"/>
  <author initials="L." surname="Masinter" fullname="Larry Masinter"/>
  <date month="January" year="2005"/>
 </front><seriesInfo name="STD" value="66"/><seriesInfo name="RFC" value="3986"/><seriesInfo name="DOI" value="10.17487/RFC3986"/></reference>

<reference anchor="RFC5988" target="http://www.rfc-editor.org/info/rfc5988"><front>
    <title>Web Linking</title>
    <author initials="M." surname="Nottingham" fullname="M. Nottingham"/>
    <date year="2010" month="October"/>
  </front><seriesInfo name="RFC" value="5988"/><seriesInfo name="DOI" value="10.17487/RFC5988"/></reference>

<reference anchor="RFC7159" target="http://www.rfc-editor.org/info/rfc7159"><front>
    <title>The JavaScript Object Notation (JSON) Data Interchange Format</title>
    <author initials="T." surname="Bray" fullname="Tim Bray"/>
    <date year="2014" month="March"/>
  </front><seriesInfo name="RFC" value="7159"/><seriesInfo name="DOI" value="10.17487/RFC7159"/></reference>

<reference anchor="RFC7230" target="http://www.rfc-editor.org/info/rfc7230"><front>
    <title>Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing</title>
    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor"/>
    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor"/>
    <date month="June" year="2014"/>
  </front><seriesInfo name="RFC" value="7230"/><seriesInfo name="DOI" value="10.17487/RFC7230"/></reference>

<reference anchor="RFC7231" target="http://www.rfc-editor.org/info/rfc7231"><front>
    <title>Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content</title>
    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor"/>
    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor"/>
    <date month="June" year="2014"/>
  </front><seriesInfo name="RFC" value="7231"/><seriesInfo name="DOI" value="10.17487/RFC7231"/></reference>

</references>

<references title="Informative References">

<reference anchor="RFC2017" target="http://www.rfc-editor.org/info/rfc2017"><front>
    <title abbrev="URL Access-Type">Definition of the URL MIME External-Body Access-Type</title>
    <author initials="N." surname="Freed" fullname="Ned Freed"/>
    <author initials="K." surname="Moore" fullname="Keith Moore"/>
    <date year="1996" month="October"/>
  </front><seriesInfo name="RFC" value="2017"/><seriesInfo name="DOI" value="10.17487/RFC2017"/></reference>

<reference anchor="RFC4483" target="http://www.rfc-editor.org/info/rfc4483"><front>
    <title>A Mechanism for Content Indirection in Session Initiation Protocol (SIP) Messages</title>
    <author initials="E." surname="Burger" fullname="E. Burger"/>
    <date year="2006" month="May"/>
  </front><seriesInfo name="RFC" value="4483"/><seriesInfo name="DOI" value="10.17487/RFC4483"/></reference>

<reference anchor="RFC6454" target="http://www.rfc-editor.org/info/rfc6454"><front>
    <title>The Web Origin Concept</title>
    <author initials="A." surname="Barth" fullname="A. Barth"/>
    <date year="2011" month="December"/>
  </front><seriesInfo name="RFC" value="6454"/><seriesInfo name="DOI" value="10.17487/RFC6454"/></reference>

<reference anchor="RFC7232" target="http://www.rfc-editor.org/info/rfc7232"><front>
    <title>Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests</title>
    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor"/>
    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor"/>
    <date month="June" year="2014"/>
  </front><seriesInfo name="RFC" value="7232"/><seriesInfo name="DOI" value="10.17487/RFC7232"/></reference>

<reference anchor="ENCRYPTENC"><front>
    <title>Encrypted Content-Encoding for HTTP</title>
    <author initials="M." surname="Thomson" fullname="Martin Thomson"/>
    <date month="December" year="2015"/>
  </front><seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-encryption-encoding-00"/></reference>

<reference anchor="CONTENTSIG"><front>
    <title>Content-Signature Header Field for HTTP</title>
    <author initials="M." surname="Thomson" fullname="Martin Thomson"/>
    <date month="July" year="2015"/>
  </front><seriesInfo name="Internet-Draft" value="draft-thomson-http-content-signature-00"/></reference>
</references>

<section anchor="alternatives" title="Alternatives, or: why not a new Status Code?">
<t>
  A plausible alternative approach would be to implement this functionality one level
  up, using a new redirect status code (Section 6.4 of <xref target="RFC7231"/>). However, 
  this would have several drawbacks:
</t>
<t>
  <list style="symbols">
    <t>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.</t>
    <t>In redirect messages, representation metadata (Section 3.1 of <xref target="RFC7231"/>),
    namely "Content-Type", applies to the response message, not the redirected-to
    resource.</t>
    <t>The origin-preserving nature of using a content coding woudld be lost.</t>
  </list>
</t>
<t>
  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 <xref target="RFC2017"/> and refined for use in the 
  Session Initiation Protocol (SIP) in <xref target="RFC4483"/>. This approach
  though would share most of the drawbacks of the status code approach mentioned 
  above.
</t>
</section>

<section title="Open Issues">
<section title="Range Requests">
<t>
  We probably need to handle Range Requests. How would this work? Passing down
  the Range request header field to the secondary resource?
</t>
<t>
  What about codes other than 200 and 206?
</t>
</section>

<section title="Accessing the Secondary Resource Too Early">
<t>
  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).
</t>
<t>
  In this particular case, it can be useful if the client was able to 
  "piggyback" the URI of 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:
</t>
<figure>
<artwork type="message/http; msgtype="request""><![CDATA[
  GET bae27c36-fa6a-11e4-ae5d-00059a3c7a00 HTTP/1.1
  Host: example.net
  Link: <http://example.com/test>;
        rel="http://purl.org/NET/linkrel/primary-resource"
  
  ]]></artwork>
<postamble>
(continuing the example from <xref target="basic.example"/>)
</postamble>
</figure>
<t>
  What's unclear is whether it's ok for the client to reveal the URI
  if the primary resource, and under which conditions it's ok for the secondary
  server to access it. All it needs is the potentially encrypted payload,
  so maybe yet another URI on the origin server is needed.
</t>
</section>
</section>

<section anchor="change.log" title="Change Log (to be removed by RFC Editor before publication)">
<section anchor="changes.since.00" title="Changes since draft-reschke-http-oob-encoding-00">
<t>
  Mention media type approach.
</t>
<t>
  Explain that clients can always fall back not to use oob when the secondary
  resource isn't available.
</t>
<t>
  Add Vary response header field to examples and mention that it'll
  usually be needed
  (<eref target="https://github.com/reschke/oobencoding/issues/6"/>).
</t>
<t>
  Experimentally add problem reporting using piggy-backed Link header fields
  (<eref target="https://github.com/reschke/oobencoding/issues/7"/>).
</t>
</section>
<section anchor="changes.since.01" title="Changes since draft-reschke-http-oob-encoding-01">
<t>
  Updated ENCRYPTENC reference.
</t>
</section>
</section>

<section title="Acknowledgements">
<t>
  Thanks to Christer Holmberg, Daniel Lindstrom, Goran Eriksson, John Mattsson, Kevin Smith, Mark Nottingham, Martin Thomson,
  and Roland Zink for feedback on this document.
</t>
</section>

  </back>

</rfc>