ms-turn: don't wait for a reply to STUN_SEND request

As per [MS-TURN] Section 2.2.1, TURN message type 0x0104 "Send request
response" isn't supported and the TURN server MUST NOT send them. Thus,
libnice should not remember Send requests in agent->sent_ids because
without replies coming, the number of allowed pending transaction gets
quickly exhausted, causing our data packets to be dropped until a
request timeout frees some space in the queue.

This behavior resulted in choppy reception of our audio on a Lync client
when connected via Lync Edge (TURN) Server.

Maniphest Tasks: T126

Reviewers: pwithnall

Projects: #libnice

Reviewed By: pwithnall

Subscribers: pwithnall

Differential Revision: https://phabricator.freedesktop.org/D223

2 files changed, 16 insertions, 3 deletions

diff --git a/socket/udp-turn.c b/socket/udp-turn.c
index 2b20142..12f90a0 100644
--- a/socket/udp-turn.c
+++ b/socket/udp-turn.c
@@ -816,7 +816,8 @@ socket_send_message (NiceSocket *sock, const NiceAddress *to,
     /* Finish the message. */
     msg_len = stun_agent_finish_message (&priv->agent, &msg,
         priv->password, priv->password_len);
-    if (msg_len > 0 && stun_message_get_class (&msg) == STUN_REQUEST) {
+    if (msg_len > 0 && stun_message_get_class (&msg) == STUN_REQUEST &&
+        priv->compatibility != NICE_TURN_SOCKET_COMPATIBILITY_OC2007) {
       SendRequest *req = g_slice_new0 (SendRequest);
 
       req->priv = priv;
diff --git a/stun/stunagent.c b/stun/stunagent.c
index 2abcc29..bd243cb 100644
--- a/stun/stunagent.c
+++ b/stun/stunagent.c
@@ -513,8 +513,20 @@ size_t stun_agent_finish_message (StunAgent *agent, StunMessage *msg,
   uint32_t fpr;
   int saved_id_idx = 0;
   uint8_t md5[16];
+  bool remember_transaction;
 
-  if (stun_message_get_class (msg) == STUN_REQUEST) {
+  remember_transaction = (stun_message_get_class (msg) == STUN_REQUEST);
+
+  if (agent->compatibility == STUN_COMPATIBILITY_OC2007 &&
+      stun_message_get_method (msg) == STUN_SEND) {
+    /* As per [MS-TURN] Section 2.2.1, the TURN server doesn't send responses to
+     * STUN_SEND requests, so don't bother waiting for them. More details at
+     * https://msdn.microsoft.com/en-us/library/dd946797%28v=office.12%29.aspx.
+     */
+    remember_transaction = FALSE;
+  }
+
+  if (remember_transaction) {
     for (saved_id_idx = 0; saved_id_idx < STUN_AGENT_MAX_SAVED_IDS; saved_id_idx++) {
       if (agent->sent_ids[saved_id_idx].valid == FALSE) {
         break;
@@ -620,7 +632,7 @@ size_t stun_agent_finish_message (StunAgent *agent, StunMessage *msg,
   }
 
 
-  if (stun_message_get_class (msg) == STUN_REQUEST) {
+  if (remember_transaction) {
     stun_message_id (msg, agent->sent_ids[saved_id_idx].id);
     agent->sent_ids[saved_id_idx].method = stun_message_get_method (msg);
     agent->sent_ids[saved_id_idx].key = (uint8_t *) key;