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Network Working Group                                           R. Sayre
Internet-Draft                                          October 22, 2005
Expires: April 25, 2006


               Feed Seek for the Atom Publishing Protocol
                draft-sayre-atompub-protocol-seek-00.txt

Status of this Memo

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   This Internet-Draft will expire on April 25, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This memo presents a set of URI parameters used identify segments of
   an Atom Publishing Protocol feed.  It also presents a syntax for
   declaring the placement of those parameters in a URI.









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Table of Contents

   1.   Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.   Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.   The 'app:seek' Attribute . . . . . . . . . . . . . . . . . . . 4
   4.   Security Considerations  . . . . . . . . . . . . . . . . . . . 5
   5.   IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 5
   6.   Informative References . . . . . . . . . . . . . . . . . . . . 5
        Author's Address . . . . . . . . . . . . . . . . . . . . . . . 6
   A.   Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 6
   B.   Change History . . . . . . . . . . . . . . . . . . . . . . . . 6
        Intellectual Property and Copyright Statements . . . . . . . . 7







































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1.  Introduction

   When Atom Publishing Protocol [APP-Basic] clients encounter an APP
   collection, they may require smaller or larger frames of entries than
   the server provides by default.  Most servers provide between 5 and
   25 entries per Atom Feed Document [AtomFormat].  This frame can be
   far too large for a bandwidth and resource-constrained device, which
   might only have room to display two or three titles at a time.  This
   frame can be far too small for a client attempting to sync up with a
   collection that contains many thousands of members.

2.  Parameters

   HTTP URIs [RFC3986] provide a useful mechanism for composing
   parameterized requests--the query string [RFC2616].  This document
   outlines four parameters that are generally useful to APP clients,
   but may not be useful for every APP collection.

   count:  The maximum number of Atom Entries to be included in the
      response.  The field is an integer.
   offset:  The offset at which to begin the sequence of entries that
      match a given request.  The field is an integer.
   begin:  Atom entries in the returned feed have an atom:updated date
      later in time than the 'begin' date.  The field matches the syntax
      of an Atom Date Construct [AtomFormat].
   end:  Atom entries in the returned feed have an atom:updated date
      equal or earlier in time than the 'end' date.  The field matches
      the syntax of an Atom Date Construct [AtomFormat].

   None of the parameters are required, and servers could add additional
   parameters.

   Example Selection URI (disregard line break)

        http://example.com/foo?begin=2003-12-13T18:30:02Z\
        &end=2003-12-25T18:30:02Z&offset=2&count=4

   Seek URIs are templated by surrounding the field names in brackets.
   For example, the 'count' field would appear as '{count}' in a
   template.

   An example seek template:

        http://example.com/app?b={begin}&e={end}&i={offset}&c={count}

   All parameters are optional, so servers interpret requests with
   missing parameters using the list below:




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   If no 'end' field is present:  The 'end' date is considered to be the
      updated date of the collection's most recently updated member
      resource.
   If no 'begin' field is present:  The 'begin' date is considered to be
      the update date of the collection's least recently updated member
      resource.
   If no 'offset' field is present:  The 'offset' integer is considered
      to be 0.
   If no 'count' field is present:  The 'count' integer is determined by
      the server.

3.  The 'app:seek' Attribute

   The "app:seek" attribute can be added to an anchor element contained
   in a server's XOXO Service Outline [XOXO].  When present, this
   namespace-qualified attribute provides a template for the
   parameterized GET requests described by this document.  After
   substitution of the appropriate parameters, the resulting URI
   reference is interpreted relative to the in-scope base URI.  The APP
   namespace is "http://purl.org/atom/app#".  This document refers to it
   by using the prefix "app", but that prefix is arbitrary.






























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   An example Service Outline with an app:seek attribute:

   <ul class="xoxo" xmlns:app="http://purl.org/atom/app#">
    <li>
     <a href="/entries"
        app:select="/entries?b={begin}&e={end}&i={offset}&c={count}"
        rel="entry" type="application/atom+xml">Main Blog</a>
       <ul>
        <li><a href="/app/collection.py?id=2&amp;type=media"
               rel="media" type="application/atom+xml">Photos</a>
        </li>
        <li><a href="/app/collection.py?id=14"
               rel="entry" type="application/atom+xml">Drafts</a>
        </li>
      </ul>
    </li>
    <li>
     <a href="/app.py?id=3&amp;type=entries"
        app:select="/app.py?id=3&b={begin}&e={end}&i={offset}&c={count}"
        rel="entry" type="application/atom+xml">Side Bar Blog</a>
     <ul>
      <li><a href="/app/collection.py?id=4&amp;type=media"
             rel="media" type="application/atom+xml">Stuff</a>
      </li>
     </ul>
    </li>
   </ul>



4.  Security Considerations

   Malicious or buggy clients could mount a Denial-of-Service attack by
   sending large date ranges or integers as parameter values.

5.  IANA Considerations

   None

6.  Informative References

   [APP-Basic]
              Sayre, R., "The Atom Publishing Protocol (Basic)",  work-
              in-progress, October 2005.

   [AtomFormat]
              Nottingham, M. and R. Sayre, "The Atom Syndication
              Format",  work-in-progress, August 2005.



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   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

   [XOXO]     Marks, K., Celik, T., Pilgrim, M., and M. Peterson, "XOXO
              1.0: Extensible Open XHTML Outlines", October 2004.


Author's Address

   Robert Sayre

   Email: rfsayre@boswijck.com
   URI:   http://boswijck.com

Appendix A.  Contributors

   This draft is a variant of the in-progress Atom Publishing Protocol
   specification from the IETF Atompub WG, and owes a debt to the WG's
   members.

Appendix B.  Change History

   -00:  Split from draft-sayre-atompub-protocol-basic-00 / -02























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Intellectual Property Statement

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Acknowledgment

   Funding for the RFC Editor function is currently provided by the
   Internet Society.















































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