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Peter Saint-Andre 2013-10-23 12:36:23 -06:00
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xep-0156.xml
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@ -11,6 +11,7 @@
&LEGALNOTICE; &LEGALNOTICE;
<number>0156</number> <number>0156</number>
<status>Draft</status> <status>Draft</status>
<interim/>
<type>Standards Track</type> <type>Standards Track</type>
<sig>Standards</sig> <sig>Standards</sig>
<approver>Council</approver> <approver>Council</approver>
@ -24,6 +25,13 @@
<registry/> <registry/>
&hildjj; &hildjj;
&stpeter; &stpeter;
&lance;
<revision>
<version>1.1</version>
<date>2013-10-22</date>
<initials>ls/psa</initials>
<remark><p>Defined HTTP lookup methods using well-known URIs as specified in RFC 5785.</p></remark>
</revision>
<revision> <revision>
<version>1.0</version> <version>1.0</version>
<date>2007-06-12</date> <date>2007-06-12</date>
@ -92,53 +100,120 @@
</revision> </revision>
</header> </header>
<section1 topic='Introduction' anchor='intro'> <section1 topic='Introduction' anchor='intro'>
<p>Although &xmppcore; specifies the use of TCP as the method of connecting to an XMPP server, alternative connection methods exist, including the &xep0124; method for which &xep0206; is the XMPP profile, the &xep0025; method (now deprecated), and less common methods such as &wap;. For some of these methods, it is necessary to discover further parameters before connecting, such as the HTTP URL of an alternative connection manager. Currently, if a client application needs to discover alternative connection methods before connecting to an XMPP service, the relevant information needs to be provided manually by a human user, which is cumbersome and error-prone. Thankfully, there are several potential ways to complete this pre-connection service discovery in an automated fashion:</p> <p>Although &xmppcore; specifies the use of TCP as the method of connecting to an XMPP server, alternative connection methods exist, including the &xep0124; method (for which &xep0206; is the XMPP profile) and &xmppoverwebsocket;. For some of these methods, it is necessary to discover further parameters before connecting, such as the HTTP URL of an alternative connection manager. Without ways to auto-discovering alternative connection methods, the relevant information would need to be provided manually by a human user, which is cumbersome and error-prone.</p>
<p>This document defines two ways to encapsulate information about alternative connection methods for auto-discovery:</p>
<ol> <ol>
<li><p>Define a &w3wsdl; definition (or other XML file format) and a canonical URL for that definition at a domain that offers XMPP services. Unfortunately, this approach requires access to the HTTP server for the domain (and quite possibly to the root directory thereof), which can be difficult for XMPP server administrators to arrange. In addition, it requires a client to retrieve the relevant file via HTTP before performing DNS lookups and XMPP connection; it would be more efficient to use recognized DNS methods since DNS lookups are already required by <cite>RFC 6120</cite>.</p></li> <li>DNS TXT resource records</li>
<li><p>Define a way to specify alternative connection methods as part of the existing DNS SRV records (see &rfc2782;) for a domain that offers XMPP services. While this approach sounds promising, it is not feasible since the DNS SRV Target field can be used only to specify domain names and cannot be used to specify full URIs (such as the URL for an HTTP connection manager).</p></li> <li>Link entries in a server's "host-meta" file</li>
<li><p>Define a way to specify alternative connection methods using the "straightforward NAPTR" (S-NAPTR) profile of the Dynamic Delegation Discovery System (see &rfc3958; and &rfc3401;). Unfortunately, S-NAPTR also does not allow inclusion of full URIs, and thus does not meet the requirements for discovery of alternative connection methods.</p></li>
<li><p>Define a way to specify alternative connection methods using the "URI-enabled NAPTR" (U-NAPTR) profile of the Dynamic Delegation Discovery System (see &rfc4848;). While this is a valid approach that is worth pursuing, the authors are concerned about the deployability of such an approach given the rarity of support for DDDS and U-NAPTR, especially in client-side applications (the main focus of this specification).</p></li>
<li><p>Define a way to specify alternative connection methods via properly-formatted DNS TXT records (see &rfc1464;). While this approach requires an update to the DNS records for the server domain, that is usually necessary in order to establish XMPP services in the first place. Furthermore, although there are some perils to be avoided in the use of DNS TXT records (e.g., wildcards), the technology is well understood and widely deployed (e.g., it is used by the <link url='http://www.openspf.org/'>Sender Policy Framework</link> and <link url='http://www.microsoft.com/mscorp/safety/technologies/senderid/default.mspx'>SenderID</link> email server verification technologies).</p></li>
</ol>
<p>This document defines a way to encapsulate information about alternative connection methods in DNS TXT resource records. However, the authors will monitor the availability of DDDS-based systems supporting U-NAPTR, and might request deprecation of the DNS TXT methods defined in this document at some point in the future.</p>
</section1>
<section1 topic='Record Format' anchor='format'>
<p>The following format for DNS TXT resource records is specified in <cite>RFC 1464</cite>:</p>
<code><![CDATA[
<owner> <class> <ttl> <TXT> <"attribute name=attribute value">
]]></code>
<p>This document specifies that the following additional rules apply for DNS TXT resource records used to specify alternative connection methods:</p>
<ol>
<li>It is RECOMMENDED for the owner to be "_xmppconnect".</li>
<li>The class field SHOULD be IN.</li>
<li>The ttl field is OPTIONAL.</li>
<li>The attribute name SHOULD begin with the string "_xmpp-client-" or "_xmpp-server-" and SHOULD be registered as described in the <link url='#registrar'>XMPP Registrar Considerations</link> section of this document.</li>
<li>If the txt-data field contains only an attribute name (i.e., no unquoted "=" character followed by additional characters), the receiving application SHOULD interpret it as indicating the presence of the attribute or feature with no defined value.</li>
<li>If the txt-data field contains an unquoted "=" character, it MUST also contain an attribute value.</li>
</ol> </ol>
</section1> </section1>
<section1 topic='Business Rules' anchor='bizrules'>
<p>The following business rules apply:</p> <section1 topic='DNS Lookup Method' anchor='dns'>
<ol start='1'>
<li>TXT lookups MUST be used only as a fallback after the methods specified in <cite>RFC 6120</cite> have been exhausted. <note>The point of this rule is to prevent someone from defining a new XEP-0156 connection method like "_xmpp-client-tcp" to override the SRV records defined in the core XMPP specification.</note></li> <section2 topic='Record Format' anchor='dnsformat'>
<li>A domain SHOULD NOT present information in DNS TXT records that is available via the DNS SRV records defined in <cite>RFC 6120</cite>.</li> <p>The following format for DNS TXT resource records is specified in <cite>RFC 1464</cite>:</p>
<li>The order of DNS TXT records SHOULD NOT be interpreted as significant by the presenting domain or the receiving entity.</li> <code><![CDATA[
</ol> <owner> <class> <ttl> <TXT> <"attribute name=attribute value">
</section1> ]]></code>
<section1 topic='Examples' anchor='examples'> <p>This document specifies that the following additional rules apply for DNS TXT resource records used to specify alternative connection methods:</p>
<p>The following examples show two DNS TXT resource records: the first indicates support for the XMPP Over BOSH connection method defined in <cite>XEP-0124</cite> and <cite>XEP-0206</cite> and the second indicates support for WAP connections (the latter connection method is not yet defined).</p> <ol>
<example caption='TXT Resource Records'><![CDATA[ <li>It is RECOMMENDED for the owner to be "_xmppconnect".</li>
<li>The class field SHOULD be IN.</li>
<li>The ttl field is OPTIONAL.</li>
<li>The attribute name SHOULD begin with the string "_xmpp-client-" or "_xmpp-server-" and SHOULD be registered as described in the <link url='#registrar'>XMPP Registrar Considerations</link> section of this document.</li>
<li>If the txt-data field contains only an attribute name (i.e., no unquoted "=" character followed by additional characters), the receiving application SHOULD interpret it as indicating the presence of the attribute or feature with no defined value.</li>
<li>If the txt-data field contains an unquoted "=" character, it MUST also contain an attribute value.</li>
</ol>
</section2>
<section2 topic='Business Rules' anchor='dnsbizrules'>
<p>The following business rules apply:</p>
<ol start='1'>
<li>TXT lookups MUST be used only as a fallback after the methods specified in <cite>RFC 6120</cite> have been exhausted. <note>The point of this rule is to prevent someone from defining a new XEP-0156 connection method like "_xmpp-client-tcp" to override the SRV records defined in the core XMPP specification.</note></li>
<li>A domain SHOULD NOT present information in DNS TXT records that is available via the DNS SRV records defined in <cite>RFC 6120</cite>.</li>
<li>The order of DNS TXT records SHOULD NOT be interpreted as significant by the presenting domain or the receiving entity.</li>
</ol>
</section2>
<section2 topic='Examples' anchor='dnsexamples'>
<p>The following examples show two DNS TXT resource records: the first indicates support for the XMPP Over BOSH connection method defined in <cite>XEP-0124</cite> and <cite>XEP-0206</cite> and the second indicates support for WAP connections (the latter connection method is not yet defined).</p>
<example caption='TXT Resource Records'><![CDATA[
_xmppconnect IN TXT "_xmpp-client-xbosh=https://bosh.jabber.org:5280/bind" _xmppconnect IN TXT "_xmpp-client-xbosh=https://bosh.jabber.org:5280/bind"
_xmppconnect IN TXT "_xmpp-client-wap=http://wap.jabber.org/connector" _xmppconnect IN TXT "_xmpp-client-wap=http://wap.jabber.org/connector"
]]></example> ]]></example>
</section2>
</section1> </section1>
<section1 topic='HTTP Lookup Method' anchor='http'>
<section2 topic='Link Format' anchor='httpformat'>
<p>The HTTP lookup method uses Web Host Metadata &rfc6415; to categorize and list the URIs of alternative connection methods. It is primarily intended for use by clients in environments where the ability to perform DNS queries is restricted, such as in web browsers.</p>
<p>Each alternative connection method is specified in the host-meta (XRD) file using a distinctive link relation &rfc5988;. This specification defines several extension relation types:</p>
<ul>
<li>urn:xmpp:alt-connections:httppoll</li>
<li>urn:xmpp:alt-connections:websocket</li>
<li>urn:xmpp:alt-connections:xbosh</li>
</ul>
</section2>
<section2 topic='Business Rules' anchor='httpbizrules'>
<p>The following business rules apply:</p>
<ol start='1'>
<li>HTTP queries for host-meta information MUST be used only as a fallback after the methods specified in <cite>RFC 6120</cite> have been exhausted.</li>
<li>A domain SHOULD NOT present information in host-meta link records that is available via the DNS SRV records defined in <cite>RFC 6120</cite>.</li>
<li>The order of XMPP related link entries in the host-meta file records SHOULD NOT be interpreted as significant by the presenting domain or the receiving entity.</li>
</ol>
</section2>
<section2 topic='Examples' anchor='httpexamples'>
<p>The following examples show two host-meta link records: the first indicates support for the XMPP Over BOSH connection method defined in <cite>XEP-0124</cite> and <cite>XEP-0206</cite> and the second indicates support for the &xmppoverwebsocket; connection method.</p>
<example caption='Result for /.well-known/host-meta'><![CDATA[<?xml version='1.0' encoding=utf-9'?>
<XRD xmlns='http://docs.oasis-open.org/ns/xri/xrd-1.0'>
...
<Link rel="urn:xmpp:alt-connections:xbosh"
href="https://example.com:5280/bosh" />
<Link rel="urn:xmpp:alt-connections:websocket"
href="wss://example.com:5280/websocket" />
...
</XRD>
]]></example>
<p>It is possible to use an alternative JSON format for host-meta information, in which case the above example would be presented as:</p>
<example caption='Result for /.well-known/host-meta.json'><![CDATA[{
...
"links": [
...
{
"rel": "urn:xmpp:alt-connections:xbosh",
"href": "https://example.com:5280/bosh"
},
{
"rel": "urn:xmpp:alt-connections:websocket",
"href": "wss://example.com:5280/websocket"
},
...
]
}
]]></example>
</section2>
</section1>
<section1 topic='Security Considerations' anchor='security'> <section1 topic='Security Considerations' anchor='security'>
<p>It is possible that advertisement of alternative connection methods can introduce security vulnerabilities, since a connecting entity (usually a client) might deliberately seek to connect using the method with the weakest security mechanisms (e.g., no channel encryption or relatively weak authentication). Care needs to be taken in determining which alternative connection methods are appropriate to advertise.</p> <p>It is possible that advertisement of alternative connection methods can introduce security vulnerabilities, since a connecting entity (usually a client) might deliberately seek to connect using the method with the weakest security mechanisms (e.g., no channel encryption or relatively weak authentication). Care needs to be taken in determining which alternative connection methods are appropriate to advertise.</p>
</section1> </section1>
<section1 topic='IANA Considerations' anchor='iana'> <section1 topic='IANA Considerations' anchor='iana'>
<p>This document requires no interaction with &IANA;.</p> <p>Because the link relations specified here are extension relation types rather than registered relation types (see Section 4 of RFC 5988), this document requires no interaction with &IANA;.</p>
</section1> </section1>
<section1 topic='XMPP Registrar Considerations' anchor='registrar'> <section1 topic='XMPP Registrar Considerations' anchor='registrar'>
<section2 topic='Namespaces' anchor='ns'>
<p>The &REGISTRAR; shall include 'urn:xmpp:alt-connections' in its registry of protocol namespaces (see &NAMESPACES;).</p>
<ul>
<li>urn:xmpp:alt-connections</li>
</ul>
</section2>
<section2 topic='Alternative Connection Methods Registry' anchor='registrar-altconn'> <section2 topic='Alternative Connection Methods Registry' anchor='registrar-altconn'>
<p>The &REGISTRAR; maintains a registry of attributes for use in DNS TXT resource records that advertise alternative XMPP connection methods (see &ALTCONN;).</p> <p>The &REGISTRAR; maintains a registry of attributes for use in DNS TXT resource records that advertise alternative XMPP connection methods (see &ALTCONN;).</p>
<section3 topic='Process' anchor='registrar-altconn-process'> <section3 topic='Process' anchor='registrar-altconn-process'>