[Pidgin] #16524: XMPP group chat history is duplicated

[Pidgin]

#16524: XMPP group chat history is duplicated
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 Reporter:  ralfj    |       Owner:  EionRobb
     Type:  defect   |      Status:  new
Milestone:           |   Component:  unclassified
  Version:  2.10.11  |  Resolution:
 Keywords:           |
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Comment (by ralfj):

 I attached a first proposal for a patch implementing this - it's ready for
 review!

 I should probably explain my change to pidgin_conv_write_conv: The purpose
 of this is to achieve the following behavior.

 * Log in to a bunch of group chats
 * Disconnect from LAN
 * Reconnect
 * If no new message has been posted, then the Pidgin status icon does
 *not* turn into "there are unseen messages"

 This behavior is desirable as otherwise, being in several chats
 permanently becomes pretty annoying with Pidgin: Each time I come back
 from standby, or change WiFi, I have to click away the "new" messages from
 all chats, even though there's not actually anything "new".

 Not getting duplicate history is only one half to the story here. There
 are still system status messages that Pidgin itself adds to the
 conversation on every reconnect:

 {{{
 (18:23:55) The account has disconnected and you are no longer in this
 chat. You will automatically rejoin the chat when the account reconnects.
 (18:23:58) %s has set the topic to: %s
 }}}

 The second of these triggers the "unseen messages" behavior. By excluding
 SYSTEM messages from this, I obtain the desired behavior.

 I realize this may not be what you want. I'd actually prefer a solution
 where the topic message is not added needlessly, e.g. if the topic did not
 even change. But I found so such solution so far. In any case the rest of
 this patch should be useful independently, and any feedback is welcome.

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Ticket URL: <https://developer.pidgin.im/ticket/16524#comment:1>
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