blocks|key|476315|text|在XMPP中，消息只能一次性传递：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|476316|对于共享最高优先级的在线资源，|unordered-list-item|476317|通过脱机消息传递连接到第一个客户端。|476318|但是，如果您希望其他客户端重新同步，则应该依赖XEP-0313:消息存档管理。此规范描述了客户端如何访问消息历史记录并重新同步其状态。|offset|length|476319|例如，您可以使用查询给定时间后的所有消息存档。这将允许连接的客户端获取自上次联机以来错过的所有消息：|476320|<iq+type='set'+id='juliet1'>
++<query+xmlns='urn:xmpp:mam:0'>
++++<x+xmlns='jabber:x:data'>
++++++<field+var='FORM_TYPE'>
++++++++<value>urn:xmpp:mam:0</value>
++++++</field>
++++++<field+var='start'>
++++++++<value>2010-08-07T00:00:00Z</value>
++++++</field>
++++</x>
++</query>
</iq>|code-block|syntax|javascript|476321|entityMap|0|LINK|mutability|MUTABLE|url|http://xmpp.org/extensions/xep-0313.html|1|http://xmpp.org/extensions/xep-0313.html#filter-time^0|0|0|0|N|F|0|0|8|E|1|0|0^^$0|@$1|2|3|4|5|6|7|11|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|12|8|@]|9|@]|A|$]]|$1|E|3|F|5|D|7|13|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|14|8|@]|9|@$I|15|J|16|1|17]]|A|$]]|$1|K|3|L|5|6|7|18|8|@]|9|@$I|19|J|1A|1|1B]]|A|$]]|$1|M|3|N|5|O|7|1C|8|@]|9|@]|A|$P|Q]]|$1|R|3|-4|5|6|7|1D|8|@]|9|@]|A|$]]]|S|$T|$5|U|V|W|A|$X|Y]]|Z|$5|U|V|W|A|$X|10]]]]

In XMPP, the message are only delivered in a single go either:

<ul>
<li>to the online resources sharing the highest priority, </li>
<li>to the first client that connect through offline message delivery.</li>
</ul>

However, if you want other clients to resync, you should rely on <a href="http://xmpp.org/extensions/xep-0313.html" rel="nofollow">XEP-0313: Message Archive Management</a>. This specifications describe how a client can access a message history and resync its state.

You can for example <a href="http://xmpp.org/extensions/xep-0313.html#filter-time" rel="nofollow">query the message archive for all messages after a given time</a>. This will allow the client that connect to get all the messages it missed since it was last online:

<pre><code>&lt;iq type='set' id='juliet1'&gt;
 &lt;query xmlns='urn:xmpp:mam:0'&gt;
 &lt;x xmlns='jabber:x:data'&gt;
 &lt;field var='FORM_TYPE'&gt;
 &lt;value&gt;urn:xmpp:mam:0&lt;/value&gt;
 &lt;/field&gt;
 &lt;field var='start'&gt;
 &lt;value&gt;2010-08-07T00:00:00Z&lt;/value&gt;
 &lt;/field&gt;
 &lt;/x&gt;
 &lt;/query&gt;
&lt;/iq&gt;
</code></pre>

blocks|key|586499|text|除了Mickael的回答，你应该知道一些事情。如果指定一个完整的JID作为要处理的地址，则该消息将仅传递到该单个端点。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|586500|只有在下列情况下才会为同一用户传递消息到多个资源|586501|要地址是空的JID|unordered-list-item|586502|所有连接都有相同的优先级。|586503|服务器被配置为传送到多个端点。|586504|最后一点至关重要。根据规范，服务器可以通过两种方式处理发送到裸JID的消息。|586505|发送到具有最高优先级的连接之一。哪一个是由服务器决定的，它可以是第一个连接的，也可以是最后一个连接，或者是一个随机的选择，如果有多个具有相同优先级的连接。|586506|向所有具有最高优先级的连接发送。|586507|因此，除非您知道您的服务器支持并配置为允许第二种选择，否则无论如何您都无法完成您想要做的事情。|586508|entityMap^0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|W|8|@]|9|@]|A|$]]|$1|G|3|H|5|F|7|X|8|@]|9|@]|A|$]]|$1|I|3|J|5|F|7|Y|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|Z|8|@]|9|@]|A|$]]|$1|M|3|N|5|F|7|10|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|11|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|12|8|@]|9|@]|A|$]]|$1|S|3|-4|5|6|7|13|8|@]|9|@]|A|$]]]|T|$]]

In addition to Mickael's answer, you should be aware of a few things. If you specify a full JID as your to address, then the message will only be delivered to that single endpoint.

Message deliver to multiple resources for the same user will only occur if 

<ul>
<li>The to address is the bare JID</li>
<li>All connections have the same priority</li>
<li>The server is configured to deliver to multiple endpoints.</li>
</ul>

That last point is crucial. According to the specification, the server can handle messages sent to the bare JID in 2 ways.

<ul>
<li>Send to one of the connections with the highest priority. Which one is determined by the server, it could be the first one connected, the last one, or a random choice if there are multiple connections with the same priority.</li>
<li>Send to all of the connections with the highest priority.</li>
</ul>

So, unless you know your server supports and is configured to allow the second choice, you can't accomplish what you are trying to do anyway.

blocks|key|477296|text|为了参与即时消息传递和存在活动，客户端(即设备)应该在服务器上建立会话。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|477297|如XMPP文档中所示|offset|length|477298|如果已经有同名的活动资源，服务器必须(1)终止活动资源并允许新请求的会话，或者(2)不允许新请求的会话并维护活动资源。这些服务器中的哪一个取决于实现，尽管建议实现case+#1。在案例1中，服务器应该向活动资源发送流错误，终止XML流和活动资源的底层TCP连接，并向新请求的会话返回类型为“resource”(表示成功)的IQ节。在第二种情况下，服务器应该向新请求的会话发送一个节错误，但是维护该连接的XML流，以便新请求的会话在发送另一个会话请求之前有机会协商一个不冲突的资源标识符。|blockquote|477299|(https://www.rfc-editor.org/rfc/rfc6120#section-7.7.2.2)|477300|因此，您应该根据应用程序的要求，首先决定处理会话的方式。现在，由于您使用的是Ejabberd，所以可以通过定义选项资源来配置它。|477301|但是，如果仍然希望使用多个会话，则可以使用Management+XEP-0313|477302|这样您就可以在服务器上存储聊天历史记录，然后检索。这可以通过使用选项国防部在ejabberd中进行配置。|477303|entityMap|0|LINK|mutability|MUTABLE|url|https://xmpp.org/rfcs/rfc3921.html|1|https://www.rfc-editor.org/rfc/rfc6120#section-7.7.2.2|2|https://docs.ejabberd.im/admin/configuration/|3|https://xmpp.org/extensions/xep-0313.html|4|https://docs.ejabberd.im/admin/configuration/#mod-mam^0|0|1|6|0|0|0|1|1I|1|0|1L|2|2|0|W|8|3|0|Y|3|4|0^^$0|@$1|2|3|4|5|6|7|16|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|17|8|@]|9|@$D|18|E|19|1|1A]]|A|$]]|$1|F|3|G|5|H|7|1B|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|1C|8|@]|9|@$D|1D|E|1E|1|1F]]|A|$]]|$1|K|3|L|5|6|7|1G|8|@]|9|@$D|1H|E|1I|1|1J]]|A|$]]|$1|M|3|N|5|6|7|1K|8|@]|9|@$D|1L|E|1M|1|1N]]|A|$]]|$1|O|3|P|5|6|7|1O|8|@]|9|@$D|1P|E|1Q|1|1R]]|A|$]]|$1|Q|3|-4|5|6|7|1S|8|@]|9|@]|A|$]]]|R|$S|$5|T|U|V|A|$W|X]]|Y|$5|T|U|V|A|$W|Z]]|10|$5|T|U|V|A|$W|11]]|12|$5|T|U|V|A|$W|13]]|14|$5|T|U|V|A|$W|15]]]]

In order to participate in the instant messaging and presence activities, a client (i.e device) should establish a session on the server.
As given in <a href="https://xmpp.org/rfcs/rfc3921.html" rel="nofollow noreferrer">XMPP Documentation</a>
<blockquote>
If there is already an active resource of the same name, the server
MUST either (1) terminate the active resource and allow the
newly-requested session, or (2) disallow the newly-requested session
and maintain the active resource. Which of these the server does is up
to the implementation, although it is RECOMMENDED to implement case #1. In case #1, the server SHOULD send a stream error to the active resource, terminate the XML stream and underlying TCP
connection for the active resource, and return a IQ stanza of type
&quot;result&quot; (indicating success) to the newly-requested session. In case #2, the server SHOULD send a stanza error to the newly-requested session but maintain the XML stream for that
connection so that the newly-requested session has an opportunity to
negotiate a non-conflicting resource identifier before sending another
request for session establishment.
</blockquote>
(<a href="https://www.rfc-editor.org/rfc/rfc6120#section-7.7.2.2" rel="nofollow noreferrer">https://www.rfc-editor.org/rfc/rfc6120#section-7.7.2.2</a>)
Therefore you should first decide the way you are going to handle the sessions, according to the app requirement.
Now since you are using Ejabberd you can configure it by defining the option <a href="https://docs.ejabberd.im/admin/configuration/" rel="nofollow noreferrer">resource_conflict</a>
However, if you still want to use multiple sessions you can use Message Archive Management - <a href="https://xmpp.org/extensions/xep-0313.html" rel="nofollow noreferrer">XEP-0313</a>
So you can store chat history on the server and then retrieve. This can be configured in ejabberd by using the option <a href="https://docs.ejabberd.im/admin/configuration/#mod-mam" rel="nofollow noreferrer">mod_mam</a>

I am developing Android Chat Application.

My requirement is to deliver messages to multiple devices.

Consider this scenario between two users User A and User B:

<pre><code>User A logs in and sends message to User B.
User B logs in from Device 1 and receives message from User A.
User B logs in from Device 2 but does not get message from User A.
</code></pre>

According to my requirement User B should get message from User A in Device 2 as well.

How can I achieve this?

Thanks.

Multi Device support in XMPP Smack Chat Application

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我正在开发Android聊天应用程序。我的要求是向多个设备传递消息。考虑两个用户(用户A和用户B)之间的这种情况：User A logs in and sends message to User B.User B logs in from Device 1 and receives message from User ...

问XMPP Smack Chat应用中的多设备支持
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