Handle case when provisional response is sent after a final one (#2350)

Handle case when provisional response is sent after a final one
- If 100rel is required, prevent retransmission if the initial send fails, since the retransmission will cause a crash later.
- Otherwise, return error instead of asserting in sip_transaction

pjsip/src/pjsip-ua/sip_100rel.c

@@ -600,7 +600,14 @@ static void on_retransmit(pj_timer_heap_t *timer_heap,
     final = tdata->msg->line.status.code >= 200;
 
     if (dd->uas_state->retransmit_count == 1) {
-	pjsip_tsx_send_msg(dd->inv->invite_tsx, tdata);
+	pj_status_t status;
+
+	status = pjsip_tsx_send_msg(dd->inv->invite_tsx, tdata);
+	if (status != PJ_SUCCESS) {
+	    PJ_PERROR(3, (THIS_FILE, status,
+			 "Failed to send message"));
+	    return;
+	}
     } else {
 	pjsip_tsx_retransmit_no_state(dd->inv->invite_tsx, tdata);
     }
@@ -809,7 +816,7 @@ PJ_DEF(pj_status_t) pjsip_100rel_tx_response(pjsip_inv_session *inv,
 	char rseq_str[32];
 	pj_str_t rseq;
 	tx_data_list_t *tl;
-	
+
 	/* Create UAS state if we don't have one */
 	if (dd->uas_state == NULL) {
 	    dd->uas_state = PJ_POOL_ZALLOC_T(inv->dlg->pool,

pjsip/src/pjsip/sip_transaction.c

@@ -3273,10 +3273,11 @@ static pj_status_t tsx_on_state_completed_uas( pjsip_transaction *tsx,
 	}
 
     } else {
-	/* Ignore request to transmit. */
-	PJ_ASSERT_RETURN(event->type == PJSIP_EVENT_TX_MSG && 
-			 event->body.tx_msg.tdata == tsx->last_tx, 
+	PJ_ASSERT_RETURN(event->type == PJSIP_EVENT_TX_MSG, 
 			 PJ_EINVALIDOP);
+	/* Ignore request to transmit a new message. */
+	if (event->body.tx_msg.tdata != tsx->last_tx)
+	    return PJ_EINVALIDOP;
     }
 
     return PJ_SUCCESS;