mirror of
https://github.com/moparisthebest/xeps
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306 lines
14 KiB
XML
306 lines
14 KiB
XML
<?xml version='1.0' encoding='UTF-8'?>
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<!DOCTYPE xep SYSTEM 'xep.dtd' [
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<!ENTITY % ents SYSTEM 'xep.ent'>
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%ents;
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]>
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<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
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<xep>
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<header>
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<title>Stream Compression</title>
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<abstract>This document defines an XMPP protocol extension for negotiating compression of XML streams, especially in situations where standard TLS compression cannot be negotiated. The protocol provides a modular framework that can accommodate a wide range of compression algorithms; the ZLIB compression algorithm is mandatory-to-implement, but implementations may support other algorithms in addition.</abstract>
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&LEGALNOTICE;
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<number>0138</number>
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<status>Final</status>
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<type>Standards Track</type>
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<sig>Standards</sig>
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<dependencies>
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<spec>XMPP Core</spec>
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</dependencies>
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<supersedes/>
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<supersededby/>
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<shortname>compress</shortname>
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<schemaloc>
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<ns>compress</ns>
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<url>http://www.xmpp.org/schemas/compress.xsd</url>
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</schemaloc>
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<schemaloc>
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<ns>feature</ns>
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<url>http://www.xmpp.org/schemas/compress-feature.xsd</url>
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</schemaloc>
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<registry/>
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&hildjj;
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&stpeter;
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<revision>
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<version>2.0</version>
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<date>2009-05-27</date>
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<initials>psa</initials>
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<remark><p>Per a vote of the XMPP Council, advanced status to Final.</p></remark>
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</revision>
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<revision>
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<version>1.3</version>
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<date>2007-09-26</date>
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<initials>psa</initials>
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<remark><p>Moved specification of LZW algorithm to XEP-0229.</p></remark>
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</revision>
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<revision>
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<version>1.2</version>
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<date>2007-08-22</date>
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<initials>psa</initials>
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<remark><p>Clarified when compression shall be considered to start; per XEP-0170, specified that compression should be negotiated after SASL.</p></remark>
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</revision>
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<revision>
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<version>1.1</version>
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<date>2005-12-14</date>
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<initials>psa</initials>
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<remark><p>More completely specified error handling; mentioned LZW (DCLZ) method.</p></remark>
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</revision>
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<revision>
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<version>1.0</version>
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<date>2005-06-16</date>
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<initials>psa</initials>
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<remark><p>Per a vote of the Jabber Council, advanced status to Draft.</p></remark>
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</revision>
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<revision>
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<version>0.5</version>
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<date>2005-05-18</date>
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<initials>psa</initials>
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<remark><p>Modifications to address Council feedback: used RFC 3920 terminology; specified error conditions; specified ZLIB as mandatory to implement.</p></remark>
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</revision>
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<revision>
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<version>0.4</version>
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<date>2005-05-11</date>
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<initials>psa</initials>
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<remark><p>Corrected several errors in the schemas.</p></remark>
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</revision>
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<revision>
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<version>0.3</version>
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<date>2005-03-28</date>
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<initials>psa</initials>
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<remark><p>Specified compression methods registry.</p></remark>
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</revision>
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<revision>
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<version>0.2</version>
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<date>2004-09-28</date>
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<initials>psa</initials>
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<remark><p>Fixed TLS text per list discussion.</p></remark>
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</revision>
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<revision>
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<version>0.1</version>
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<date>2004-07-16</date>
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<initials>jjh/psa</initials>
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<remark><p>Initial version.</p></remark>
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</revision>
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</header>
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<section1 topic='Introduction' anchor='intro'>
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<p>&xmppcore; specifies the use of Transport Layer Security (TLS; see &rfc5246;) for encryption of XML streams, and TLS includes the ability to compress encrypted traffic (see &rfc3749;). However, not all computing platforms are able to implement TLS, and traffic compression may be desirable for communication by applications on such computing platforms. This document defines a mechanism for negotiating the compression of XML streams outside the context of TLS.</p>
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</section1>
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<section1 topic='Use Case' anchor='usecase'>
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<p>The protocol flow is as follows:</p>
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<example caption='Receiving Entity Offers Stream Compression Feature'><![CDATA[
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<stream:features>
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<starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>
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<compression xmlns='http://jabber.org/features/compress'>
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<method>zlib</method>
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<method>lzw</method>
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</compression>
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</stream:features>
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]]></example>
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<p>Note: The <compression/> element MUST contain at least one <method/> child element. Each <method/> element MUST contain XML character data that specifies the name of a compression method, and such method names SHOULD be registered as described in the <link url='#registrar-methods'>Compression Methods Registry</link> section of this document. The methods SHOULD be provided in order of preference.</p>
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<p>The initiating entity then MAY request compression by specifying one of the methods advertised by the receiving entity:</p>
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<example caption='Initiating Entity Requests Stream Compression'><![CDATA[
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<compress xmlns='http://jabber.org/protocol/compress'>
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<method>zlib</method>
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</compress>
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]]></example>
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<p>Note: If the initiating entity did not understand any of the advertised compression methods, it SHOULD ignore the compression option and proceed as if no compression methods were advertised.</p>
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<p>If the initiating entity requests a stream compression method that is not supported by the receiving entity, the receiving entity MUST return an <unsupported-method/> error:</p>
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<example caption='Receiving Entity Reports That Method is Unsupported'><![CDATA[
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<failure xmlns='http://jabber.org/protocol/compress'>
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<unsupported-method/>
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</failure>
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]]></example>
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<p>If the receiving entity finds the requested method unacceptable or unworkable for any other reason, it MUST return a <setup-failed/> error:</p>
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<example caption='Receiving Entity Reports That Negotiation of Stream Compression Failed'><![CDATA[
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<failure xmlns='http://jabber.org/protocol/compress'>
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<setup-failed/>
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</failure>
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]]></example>
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<p>Note: Failure of the negotiation SHOULD NOT be treated as an unrecoverable error and therefore SHOULD NOT result in a stream error. In particular, the initiating entity is free to retry the compression negotiation if it fails.</p>
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<p>If no error occurs, the receiving entity MUST inform the initiating entity that compression has been successfully negotiated:</p>
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<example caption='Receiving Entity Acknowledges Negotiation of Stream Compression'><![CDATA[
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<compressed xmlns='http://jabber.org/protocol/compress'/>
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]]></example>
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<p>Both entities MUST now consider the previous (uncompressed) stream to be null and void, just as with TLS negotiation and SASL negotiation (as specified in <cite>RFC 3920</cite>) and MUST begin compressed communications with a new (compressed) stream. Therefore the initiating entity MUST initiate a new stream to the receiving entity:</p>
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<example caption='Initiating Entity Initiates New (Compressed) Stream'><![CDATA[
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<stream:stream
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xmlns='jabber:client'
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xmlns:stream='http://etherx.jabber.org/streams'
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to='shakespeare.lit'>
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]]></example>
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<p>If compression processing fails after the new (compressed) stream has been established, the entity that detects the error SHOULD generate a stream error and close the stream:</p>
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<example caption='Entity Closes Stream Because of a Processing Error'><![CDATA[
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<stream:error>
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<undefined-condition xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
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<failure xmlns='http://jabber.org/protocol/compress'>
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<processing-failed/>
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</failure>
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</stream:error>
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</stream:stream>
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]]></example>
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</section1>
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<section1 topic='Business Rules' anchor='bizrules'>
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<p>The following business rules apply:</p>
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<ul>
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<li>If stream compression is negotiated, it MUST be used in both directions.</li>
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<li>TLS compression and stream compression SHOULD NOT be used simultaneously.</li>
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<li>Stream compression MAY be offered after TLS negotiation if TLS compression is not used.</li>
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</ul>
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<p>For detailed recommendations regarding the order of stream feature negotiation, refer to &xep0170;.</p>
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</section1>
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<section1 topic='Mandatory-to-Implement Technologies' anchor='mandatory'>
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<p>Support for the ZLIB compression method as specified in &rfc1950; is REQUIRED.</p>
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<p>All other methods are OPTIONAL; such methods may be defined in future specifications or by registration as described in the <link url='#registrar-methods'>Compression Methods Registry</link> section of this document.</p>
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</section1>
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<section1 topic='Optional Technologies' anchor='optional'>
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<p>Implementations MAY support the following methods in addition to ZLIB:</p>
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<ul>
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<li>&xep0229;</li>
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</ul>
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</section1>
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<section1 topic='Implementation Notes' anchor='impl'>
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<p>When using ZLIB for compression, the sending application SHOULD complete a partial flush of ZLIB when its current send is complete. Note that this statement is deliberately somewhat vague: the sending application may end up performing this partial flush after sending every XML stanza, but on the other hand may perform the partial flush only after sending a group of stanzas that have been queued up for delivery. When to flush the state of the compression application is up to the sending application.</p>
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</section1>
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<section1 topic='Security Considerations' anchor='security'>
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<p>Stream encryption via TLS (as defined in <cite>RFC 3920</cite>) and stream compression (as defined herein) are not mutually exclusive, but stream encryption via TLS MUST be negotiated before negotiation of stream compression in order to secure the stream.</p>
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<p>Many of the security considerations related to TLS compression (see Section 6 of <cite>RFC 3749</cite>) also apply to stream compression.</p>
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</section1>
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<section1 topic='IANA Considerations' anchor='iana'>
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<p>This document requires no interaction with &IANA;. </p>
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</section1>
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<section1 topic='XMPP Registrar Considerations' anchor='registrar'>
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<section2 topic='Stream Features' anchor='registrar-stream'>
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<p>The ®ISTRAR; includes 'http://jabber.org/features/compress' in its registry of stream features.</p>
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</section2>
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<section2 topic='Protocol Namespaces' anchor='registrar-ns'>
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<p>The XMPP Registrar includes 'http://jabber.org/protocol/compress' in its registry of protocol namespaces.</p>
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</section2>
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<section2 topic='Compression Methods Registry' anchor='registrar-methods'>
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<p>The XMPP Registrar maintains a registry of compression methods at &COMPRESSMETHODS;.</p>
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<section3 topic='Process' anchor='registrar-methods-process'>
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®PROCESS;
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<code><![CDATA[
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<method>
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<name>the XML character data of the method element</name>
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<desc>a natural-language description of the compression method</desc>
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<doc>the document that specifies or registers the compression method</doc>
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</method>
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]]></code>
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<p>The registrant may register more than one compression method at a time, each contained in a separate <method/> element.</p>
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</section3>
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<section3 topic='Registration' anchor='registrar-methods-init'>
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<code><![CDATA[
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<method>
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<name>zlib</name>
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<desc>the ZLIB compression method</desc>
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<doc>RFC 1950</doc>
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</method>
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]]></code>
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</section3>
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</section2>
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</section1>
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<section1 topic='XML Schemas' anchor='schemas'>
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<section2 topic='Stream Feature' anchor='schemas-stream'>
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<code><![CDATA[
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<?xml version='1.0' encoding='UTF-8'?>
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<xs:schema
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xmlns:xs='http://www.w3.org/2001/XMLSchema'
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targetNamespace='http://jabber.org/features/compress'
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xmlns='http://jabber.org/features/compress'
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elementFormDefault='qualified'>
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<xs:annotation>
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<xs:documentation>
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The protocol documented by this schema is defined in
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XEP-0138: http://www.xmpp.org/extensions/xep-0138.html
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</xs:documentation>
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</xs:annotation>
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<xs:element name='compression'>
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<xs:complexType>
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<xs:sequence>
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<xs:element name='method' type='xs:NCName' maxOccurs='unbounded'/>
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</xs:sequence>
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</xs:complexType>
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</xs:element>
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</xs:schema>
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]]></code>
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</section2>
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<section2 topic='Protocol Namespace' anchor='schemas-protocol'>
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<code><![CDATA[
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<?xml version='1.0' encoding='UTF-8'?>
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<xs:schema
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xmlns:xs='http://www.w3.org/2001/XMLSchema'
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targetNamespace='http://jabber.org/protocol/compress'
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xmlns='http://jabber.org/protocol/compress'
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elementFormDefault='qualified'>
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<xs:annotation>
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<xs:documentation>
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The protocol documented by this schema is defined in
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XEP-0138: http://www.xmpp.org/extensions/xep-0138.html
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</xs:documentation>
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</xs:annotation>
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<xs:import namespace='urn:ietf:params:xml:ns:xmpp-stanzas'
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schemaLocation='http://xmpp.org/schemas/stanzaerror.xsd'/>
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<xs:element name='compress'>
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<xs:complexType>
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<xs:sequence>
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<xs:element name='method' type='xs:NCName' minOccurs='1' maxOccurs='unbounded'/>
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</xs:sequence>
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</xs:complexType>
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</xs:element>
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<xs:element name='compressed' type='empty'/>
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<xs:element name='failure'>
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<xs:complexType>
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<xs:choice>
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<xs:element name='setup-failed' type='empty'/>
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<xs:element name='processing-failed' type='empty'/>
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<xs:element name='unsupported-method' type='empty'/>
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<xs:sequence xmlns:err='urn:ietf:params:xml:ns:xmpp-stanzas'>
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<xs:group ref='err:stanzaErrorGroup'/>
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<xs:element ref='err:text' minOccurs='0'/>
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</xs:sequence>
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</xs:choice>
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</xs:complexType>
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</xs:element>
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<xs:simpleType name='empty'>
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<xs:restriction base='xs:string'>
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<xs:enumeration value=''/>
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</xs:restriction>
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</xs:simpleType>
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</xs:schema>
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]]></code>
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</section2>
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</section1>
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</xep>
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