TurnCustomizer - an interface for modifying stun messages sent by TurnPort

This patch adds an interface that allows modification of stun messages
sent by TurnPort. A user can inject a TurnCustomizer on the RTCConfig
and the TurnCustomizer will be invoked by TurnPort before sending
message. This allows user to e.g add custom attributes as described
in rtf5389.

BUG=webrtc:8313

Change-Id: I6f4333e9f8ff7fd20f32677be19285f15e1180b6
Reviewed-on: https://webrtc-review.googlesource.com/7618
Reviewed-by: Guido Urdaneta <guidou@webrtc.org>
Reviewed-by: Taylor Brandstetter <deadbeef@webrtc.org>
Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
Commit-Queue: Jonas Oreland <jonaso@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20233}

api/BUILD.gn

@@ -61,6 +61,7 @@ rtc_static_library("libjingle_peerconnection_api") {
     "rtpsenderinterface.h",
     "statstypes.cc",
     "statstypes.h",
+    "turncustomizer.h",
     "umametrics.h",
     "videosourceproxy.h",
   ]

api/peerconnectioninterface.h

@@ -83,6 +83,7 @@
 #include "api/rtpsenderinterface.h"
 #include "api/stats/rtcstatscollectorcallback.h"
 #include "api/statstypes.h"
+#include "api/turncustomizer.h"
 #include "api/umametrics.h"
 #include "call/callfactoryinterface.h"
 #include "logging/rtc_event_log/rtc_event_log_factory_interface.h"
@@ -474,6 +475,12 @@ class PeerConnectionInterface : public rtc::RefCountInterface {
     // interval specified in milliseconds by the uniform distribution [a, b].
     rtc::Optional<rtc::IntervalRange> ice_regather_interval_range;
 
+    // Optional TurnCustomizer.
+    // With this class one can modify outgoing TURN messages.
+    // The object passed in must remain valid until PeerConnection::Close() is
+    // called.
+    webrtc::TurnCustomizer* turn_customizer = nullptr;
+
     //
     // Don't forget to update operator== if adding something.
     //

api/turncustomizer.h

@@ -0,0 +1,46 @@
+/*
+ *  Copyright 2017 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef API_TURNCUSTOMIZER_H_
+#define API_TURNCUSTOMIZER_H_
+
+#include <stdlib.h>
+
+namespace cricket {
+class PortInterface;
+class StunMessage;
+}  // namespace cricket
+
+
+namespace webrtc {
+
+class TurnCustomizer {
+ public:
+  // This is called before a TURN message is sent.
+  // This could be used to add implementation specific attributes to a request.
+  virtual void MaybeModifyOutgoingStunMessage(
+      cricket::PortInterface* port,
+      cricket::StunMessage* message) = 0;
+
+  // TURN can send data using channel data messages or Send indication.
+  // This method should return false if |data| should be sent using
+  // a Send indication instead of a ChannelData message, even if a
+  // channel is bound.
+  virtual bool AllowChannelData(cricket::PortInterface* port,
+                                const void* data,
+                                size_t size,
+                                bool payload) = 0;
+
+  virtual ~TurnCustomizer() {}
+};
+
+}  // namespace webrtc
+
+#endif  // API_TURNCUSTOMIZER_H_