<abstract>While a protocol has been described for initiating a file transfer from one user to another, there is not yet a defined way for users to designate a set of files as available for retrieval by other users of their choosing. This extension defines a common syntax for this purpose which is based on PubSub Collections.</abstract>
<p>This document defines a common format which allows a Jabber user to submit, find, and retrieve files within XMPP. The file listing itself is stored on a &xep0060; server, allowing multiple users to manage the same listing. Other features specified by this extension include file metadata, revisions, and download mirrors.</p>
<p>Retrieval of files provided in a listing MAY be performed through any relevant protocol for transferring data (http, ftp, etc). This protocol standardizes the use of &xep0137; to establish the file transfer, but also allows for usage of outside protocols such as http or ftp.</p>
<li>Publication of a list of available files to a PubSub server, with support for hierarchical listings, file metadata, user privileges, and file versioning.</li>
<td>A Root-level Pubsub Collection Node, containing information about files and/or subsections which a user or group of users have published.</td>
</tr>
<tr>
<th>Subsection</th>
<td>A Non-Root Collection Node which contains files and/or other subsections.</td>
</tr>
<tr>
<th>File</th>
<td>A Pubsub Node, stored within a File Listing, which describes all revisions of a given file. The filename and (optional) description are provided here.</td>
</tr>
<tr>
<th>Revision</th>
<td>A Pubsub Item which describes a given file revision. Other metadata which can vary between revisions, such as filesize, checksum, or available mirrors, is provided here.</td>
</tr>
<tr>
<th>Mirror</th>
<td>A location which has a given Revision available for download. Additional information about a Mirror MAY be specified in instances where the protocol requires it. A list of example file transfer protocols is provided below, but others may also be deployed.</td>
<p>The following use cases describe tasks which are already covered by &xep0060; in a more generic context. These tasks are again being provided here in order to demonstrate the functionality provided by this protocol and convey the structure and syntax of the file listing. As a result of this close relationship, many details of PubSub are omitted here for brevity. Consult &xep0060; and &xep0248; for the full specification of node and user management commands as well as their server responses.</p>
<p>Juliet wishes to make her sonnets available for retrieval by the public. She creates a Root Pubsub Collection Node which will contain her file listing:</p>
<examplecaption='Creating a New File Listing'><code><![CDATA[<iqtype='set'
<p>Juliet has just finished a new sonnet and wishes to announce its availability on her File Listing. She adds the sonnet as a new PubSub Node stored in her Collection Node, then inserts a first revision of her sonnet as an Item within that Node:</p>
<p>The Item ID is set to 1, signifying the first revision for this file. Subsequent revisions/items will have incremented ID values, like one would see in a versioning system such as CVS or SVN. Implementations MAY follow this convention, but are not required to do so. For example, a given implementation may instead mark revisions using version numbers ("Beta 1", "6.2", etc) or use other arbitrary strings. However, no two revisions of a given file may share the same ID.</p>
<p>Node IDs MAY take the form of "path/to/file.ext", rather than the randomized string "a6190c5d38e22452041d1c5798eff3f5" provided in the above use case. For example, Juliet's sonnet MAY instead use a Node ID of "juliets_sonnets/sonnet.txt", as long as this ID is unique within the PubSub server. Randomized strings are used in this document to illustrate that Node IDs SHOULD NOT be used for providing information about files.</p>
<tr><th>Modified</th><td>The last modified time of the revision. Follows the format described in &xep0082;. If a publisher prefers to only make a single revision available to clients, the publisher MAY instead update this value (and others, such as size and/or checksum) to announce that a new version of the file is available.</td></tr>
<tr><th>Checksum</th><td>A checksum of the revision, using the specified hash algorithm. Acceptable types are "sha512", "sha1", "md5", and "crc32".</td></tr>
<tr><th>Description</th><td>Description text for the revision. As an example, could contain release notes.</td></tr>
<tr><th>Mirrors</th><td>A list of mirrors; their properties are defined below. If no downloads are available, MAY be left empty or removed entirely.</td></tr>
</table>
<p>Because Romeo is now subscribed, he receives notice of Juliet's addition:</p>
<examplecaption='Notification of Addition'><code><![CDATA[<message from='pubsub.shakespeare.lit' to='romeo@montague.net' id='create4'>
<p>The above examples give a listing of several possible file transfer protocols in example configurations. Only the sipub mirror type is REQUIRED; the other types are OPTIONAL. Here is a full listing of those protocols and their available settings:</p>
<p>The Description field is where an arbitrary description of the mirror MAY be placed. For example, if a File Listing is advertising mirrors which are located in different geographic locations, then this field may be used to specify those locations.</p>
<p>The Ref field is a unique address or identifier for retrieving the file from the mirror server. In the above examples, it is used as a path to the file.</p>
<p>The address and port fields describe the server where the file may be retrieved using the specified protocol. If a port is not provided, the default value (specified in parentheses) MAY be assumed.</p>
<p>The User and Pass fields are for providing credentials which, if given by the File Listing, SHOULD be used when requesting the file. For example, an sftp mirror MAY require that the user log in using specified credentials before the file may be retrieved.</p>
<p>Juliet has revised her sonnet and wishes to publish the new version, while still leaving the original copy available for retrieval. To do this, she inserts a new Item, representing her new revision, into the file's Node:</p>
<examplecaption='Adding a new Revision'><code><![CDATA[<iqtype='set'
<p>Juliet has uploaded a copy of her revised sonnet to a new mirror, and wishes to let her subscribers know about this secondary source. She is able to do this by modifying the revision in question to include a reference to her website, overwriting the existing mirrors in the Item with an updated list:</p>
<examplecaption='Modifying a Revision'><code><![CDATA[<iqtype='set'
<mirrortype='http'description='Shakespeare.lit Boston Mirror'
address='www.capulet.com'
ref='~juliet/sonnet2.txt'/>
</mirrors>
</entry>
</item>
</publish>
</pubsub>
</iq>
]]></code></example>
<p>Juliet now wishes to allow others to contribute to her sonnet collection. She gives owner access for the entire Listing to Romeo, and publisher access to her nurse:</p>
<p>Romeo is interested in seeing what files Juliet has made available. To do this, Romeo sends a request to Juliet for repositories which she is associated with:</p>
<p>Juliet responds with a list of PubSub nodes where she has published files or which she believes would be interesting to Romeo. If no such locations exist, Juliet SHOULD respond with an empty list.</p>
<p>After browsing Juliet's repository, Romeo has chosen to download her sonnet. The most recent revision of this file contains a listing of available mirrors, and Romeo sees that one of them is an SI stream. Romeo sends an SI request to that mirror:</p>
<p>Since PubSub is used for the File Listing, the access models described in &xep0060; and &xep0248; MUST be followed. Users MUST NOT be able to view or control information in the File Listing to which they do not have access.</p>
<p>If user access to files is restricted, the Mirror servers and the PubSub server MUST be able to synchronize these restrictions between them. See <linkurl='#security'>Security Considerations</link>.</p>
<p>When restricted files are being distributed, mirrors need to know which users have sufficient privileges to access which files. If mirrors are not kept up to date on user privileges, unauthorized users could access files directly from those mirrors, thus bypassing any restrictions being set on the PubSub server.</p>
