Jingle XMPP stanza对应的XML schema-优快云博客

本文链接：https://blog.youkuaiyun.com/iteye_3854/article/details/82027698

本文解析了JingleXMPPStanza的典型结构，包括<iq>元素下的<jingle>子元素及其子元素<content>、<description>、<payload-type>和<transport>的使用方式，并讨论了Libjingle实现时的设计考虑。

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一个典型的Jingle XMPP stanza:

<iq from='romeo@montague.lit/orchard'
    id='xs51r0k4'
    to='juliet@capulet.lit/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:1'
          action='session-initiate'
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <content creator='initiator' name='voice'>
      <description xmlns='urn:xmpp:jingle:apps:rtp:1' media='audio'>
        <payload-type id='96' name='speex' clockrate='16000'/>
        <payload-type id='97' name='speex' clockrate='8000'/>
        <payload-type id='18' name='G729'/>
        <payload-type id='0' name='PCMU' />
        <payload-type id='103' name='L16' clockrate='16000' channels='2'/>
        <payload-type id='98' name='x-ISAC' clockrate='8000'/>
      </description>
      <transport xmlns='urn:xmpp:jingle:transports:ice-udp:1'
                 pwd='asd88fgpdd777uzjYhagZg'
                 ufrag='8hhy'>
        <candidate component='1'
                   foundation='1'
                   generation='0'
                   id='el0747fg11'
                   ip='10.0.1.1'
                   network='1'
                   port='8998'
                   priority='2130706431'
                   protocol='udp'
                   type='host'/>
        <candidate component='1'
                   foundation='2'
                   generation='0'
                   id='y3s2b30v3r'
                   ip='192.0.2.3'
                   network='1'
                   port='45664'
                   priority='1694498815'
                   protocol='udp'
                   rel-addr='10.0.1.1'
                   rel-port='8998'
                   type='srflx'/>
      </transport>
    </content>
  </jingle>
</iq>

从XEP-0166的XML Schema可以看出, <jingle>元素下的<content>元素minOccurs为0, maxOccurs为无限. 而<content>元素下的子元素未定义, 需要到别的XEP去看, minOccurs为0, maxOccurs为无限.

从XEP-0167的XML Schema可以看出, <description>元素下的<payload-type>元素minOccurs为0, maxOccurs为无限.

从XEP-0176的XML Schema可以看出, <transport>元素下的<candidate>元素minOccurs为1, maxOccurs为无限.

结合起来, 意味着<jingle>元素作为<iq>元素的子元素, 其下面可以包含任意多个<content>子元素, 而<content>子元素下面可以包含任意的<description>元素和<transport>元素.

所以, Libjingle在实现Jingle协议的时候, 设计了对应的数据结构来实现各种可能的情况, 导致代码看起来很晦涩, 其实对照Jingle的XML Schema来看, 就很容易理解了.