[asterisk-dev] [Code Review] Add update callback to dnsmgr since chan_sip peers need to be re-linked in peers_by_ip when the IP changes

[Terry Wilson]

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https://reviewboard.asterisk.org/r/1691/
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Review request for Asterisk Developers.


Summary
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Asterisk's dnsmgr currently takes a pointer to an ast_sockaddr and updates it anytime an address resolves to something different. There are a couple of issues with this. First, the ast_sockaddr is usually the address of an ast_sockaddr inside a refcounted struct and we never bump the refcount of those structs when using dnsmgr. This makes it possible that a refresh could happen after the destructor for that object is called (despite ast_dnsmgr_release being called in that destructor). Second, the module using dnsmgr cannot be aware of an address changing without polling for it in the code. If an action needs to be taken on address update (like re-linking a SIP peer in the peers_by_ip table), then polling for this change negates many of the benefits of having dnsmgr in the first place.

This patch adds an update callback that is called if a pointer to a callback function is provided to ast_dnsmgr_lookup(). It also moves calls to ast_dnsmgr_release outside of the destructor functions and into cleanup functions that are called when we no longer need the objects and increments the refcount of the objects using dnsmgr since those objects are stored on the ast_dnsmgr_entry struct. A helper function for returning the proper default SIP port (non-tls vs tls) is also added and used.

The current implementation in the patch is backward compatible with code that doesn't use the update callback. Seeing as this is only two calls in chan_iax2, it might be better to just update chan_iax2 and insist on using the update callback. This would allow us to stop passing in the ast_sockaddr pointer altogether. I'll update the documentation of the dnsmgr functions (and CHANGES) after we decide on the aforementioned point.

This patch also builds on the registry fixes suggested Timo Teräs in issue ASTERISK-19106 re: the port number being 0 after a dnsmgr update.


This addresses bug ASTERISK-19106.
    https://issues.asterisk.org/jira/browse/ASTERISK-19106


Diffs
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  /branches/1.8/channels/chan_iax2.c 352519 
  /branches/1.8/channels/chan_sip.c 352551 
  /branches/1.8/include/asterisk/dnsmgr.h 352519 
  /branches/1.8/main/dnsmgr.c 352519 

Diff: https://reviewboard.asterisk.org/r/1691/diff


Testing
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I have tested registration via register => x at peer and via peers defined with callbackextension by having the host=invalid.address and selectively defining invalid.address in /etc/hosts with and without dnsmgr enabled. Timo Teräs in ASTERISK-19106 also reports that it fixes the issues he was experiencing.


Thanks,

Terry

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