<abstract>This specification defines an XMPP protocol extension for including small bits of binary data in an XML stanza.</abstract>
&LEGALNOTICE;
<number>0231</number>
<status>Experimental</status>
<type>Standards Track</type>
<sig>Standards</sig>
<approver>Council</approver>
<dependencies>
<spec>XMPP Core</spec>
<spec>RFC 2045</spec>
<spec>RFC 2111</spec>
<spec>RFC 4648</spec>
</dependencies>
<supersedes/>
<supersededby/>
<shortname>NOT YET ASSIGNED</shortname>
&stpeter;
<revision>
<version>0.1</version>
<date>2008-01-30</date>
<initials>psa</initials>
<remark><p>Initial published version.</p></remark>
</revision>
<revision>
<version>0.0.4</version>
<date>2008-01-29</date>
<initials>psa</initials>
<remark><p>Separately described service discovery feature for inclusion of the data element in file previews.</p></remark>
</revision>
<revision>
<version>0.0.3</version>
<date>2007-12-27</date>
<initials>psa</initials>
<remark><p>Described use cases for previewing data to be exchanged in file transfers and for inclusion of media information in data forms.</p></remark>
</revision>
<revision>
<version>0.0.2</version>
<date>2007-12-18</date>
<initials>psa</initials>
<remark><p>Changed syntax to not use data: URL scheme; added cid and type attributes; described use cases for messaging and data retrieval.</p></remark>
</revision>
<revision>
<version>0.0.1</version>
<date>2007-11-09</date>
<initials>psa</initials>
<remark><p>First draft.</p></remark>
</revision>
</header>
<section1topic='Introduction'anchor='intro'>
<p>Sometimes it is desirable to include a small bit of binary data in an XMPP stanza. Typical use cases might be inclusion of an icon or emoticon in a message, a thumbnail in a file transfer request, a rasterized image in a whiteboarding session, or a small bit of media in a data form. At present, there is no lightweight method for including such data in an XMPP stanza, since existing methods (e.g., &xep0047;) are designed for larger blobs of data and therefore require some form of negotiation (e.g., via &xep0096; or &xep0166;). Therefore, this document specifies just such a lightweight method, using a <data/> element that provides semantics similar to the data: URL scheme defined in &rfc2397;.</p>
</section1>
<section1topic='Format'anchor='format'>
<p>The format for including binary data is straightforward: the data is encapsulated as the XML character data of a <data/> element, where the data MUST be encoded as Base64 in accordance with Section 4 of &rfc4648; (note: the Base64 output MUST NOT include whitespace and MUST set the number of pad bits to zero).</p>
<p>The <data/> element SHOULD be used only to encapsulate small bits of binary data and SHOULD NOT be used for large data transfers. Naturally the definition of "small" and "large" is rather loose. In general, it is recommended that the data should not be more than 4 kilobytes and that dedicated file transfer methods should be used for exchanging blobs of data larger than 4 kilobytes. Naturally, implementations or deployments may impose their own limits.</p>
<p>The following attributes are defined for the <data/> element.</p>
<tablecaption='Defined Attributes'>
<tr>
<th>Attribute</th>
<th>Description</th>
<th>Inclusion</th>
</tr>
<tr>
<td>alt</td>
<td>A human-readable description of the data.</td>
<td>RECOMMENDED</td>
</tr>
<tr>
<td>cid</td>
<td>A Content-ID that can be mapped to a cid: URL as specified in &rfc2111;.</td>
<td>RECOMMENDED</td>
</tr>
<tr>
<td>type</td>
<td>The MIME type of the data (e.g., "image/png") as described in &rfc2045;.</td>
<td>REQUIRED</td>
</tr>
</table>
<p>The following example illustrates the format (line endings are provided for readability only).</p>
<p>The <data/> element can be used in conjunction with &xep0071; and the cid: URL scheme to point to binary data that is provided in-band within a &MESSAGE; stanza.</p>
<examplecaption='A message with included data'><