[sr-dev] [tracker] Task changed: tracked initial requests ended prematurely by stateless responses are not cleaned up

[sip-router]

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FS#154 - tracked initial requests ended prematurely by stateless responses are not cleaned up
User who did this: Timo Reimann (tr)
Task details edited:
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If the initial request to a dialog tracked using dlg_manage() is not delivered further downstream but ended by a stateless response from the proxy the associated dialog will not be cleaned up properly.

Example flow:

Caller ---> INVITE ---> Proxy

Caller <--- 4xx(s-less) --- Proxy
         

The reason for this behavior is that the dialog module expects a transaction to conclude when a call is being tracked. By returning the failure response statelessly, no transaction will be created and thus, the dialog structure never removed.

Possible fixes to the problem:

(1) On return of a stateless response, let the sl module call a function in the dialog module to clean up such dialogs. This is an ugly approach because it touches two modules and increases inter-module dependency; on the other side, it is expected to work.
(2) Within the dialog module, register a to-be-implemented function on completed execution of the configuration script which is to detect and cleanup all "unconfirmed" dialogs that were ended prematurely by means of stateless responding. While this is a more elegant approach than (1), a method needs to be determined which is capable of detecting the problematic state. Introducing a new dialog state (e.g., DLG_STATE_UNCONFIRMED_SENT) could be one way to do this.


Workarounds:

(1) Refrain from tracking dialogs using dlg_manage() until you are sure no stateless response will be emitted.
(2) Return responses statefully, i.e., call t_newtran() followed by t_reply().
(3) Track dialogs using the dialog flag instead of dlg_manage(). Although I haven't verified this solution, it should work.
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More information can be found at the following URL:
http://sip-router.org/tracker/index.php?do=details&task_id=154

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