res_pjsip: Handle invocation of callback on outgoing request when error occurs.

There are some error cases in PJSIP when sending a request that will
result in the callback for the request being invoked.  The code did not
handle this case and assumed on every error case that the callback was not
invoked.

The code has been changed to check whether the callback has been invoked
and if so to absorb the error and treat it as a success.

ASTERISK-26679
ASTERISK-26699

Change-Id: I563982ba204da5aa1428989a11c06dd9087fea91

res/res_pjsip.c

@@ -3404,6 +3404,8 @@ struct send_request_wrapper {
 	void (*callback)(void *token, pjsip_event *e);
 	/*! Non-zero when the callback is called. */
 	unsigned int cb_called;
+	/*! Non-zero if endpt_send_request_cb() was called. */
+	unsigned int send_cb_called;
 	/*! Timeout timer. */
 	pj_timer_entry *timeout_timer;
 	/*! Original timeout. */
@@ -3421,6 +3423,12 @@ static void endpt_send_request_cb(void *token, pjsip_event *e)
 	struct send_request_wrapper *req_wrapper = token;
 	unsigned int cb_called;
 
+	/*
+	 * Needed because we cannot otherwise tell if this callback was
+	 * called when pjsip_endpt_send_request() returns error.
+	 */
+	req_wrapper->send_cb_called = 1;
+
 	if (e->body.tsx_state.type == PJSIP_EVENT_TIMER) {
 		ast_debug(2, "%p: PJSIP tsx timer expired\n", req_wrapper);
 
@@ -3604,12 +3612,10 @@ static pj_status_t endpt_send_request(struct ast_sip_endpoint *endpoint,
 	if (ret_val != PJ_SUCCESS) {
 		char errmsg[PJ_ERR_MSG_SIZE];
 
-		/*
-		 * endpt_send_request_cb is not expected to ever be called
-		 * because the request didn't get far enough to attempt
-		 * sending.
-		 */
-		ao2_ref(req_wrapper, -1);
+		if (!req_wrapper->send_cb_called) {
+			/* endpt_send_request_cb is not expected to ever be called now. */
+			ao2_ref(req_wrapper, -1);
+		}
 
 		/* Complain of failure to send the request. */
 		pj_strerror(ret_val, errmsg, sizeof(errmsg));
@@ -3646,6 +3652,13 @@ static pj_status_t endpt_send_request(struct ast_sip_endpoint *endpoint,
 				req_wrapper->cb_called = 1;
 			}
 			ao2_unlock(req_wrapper);
+		} else if (req_wrapper->cb_called) {
+			/*
+			 * We cannot report any error.  The callback has
+			 * already freed any resources associated with
+			 * token.
+			 */
+			ret_val = PJ_SUCCESS;
 		}
 	}