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
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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&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&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&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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Acknowledgment
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