Remove transport_name_ from Channel.

Because of this (seemingly simple) change, I had to change the return
type of transport_name from `const std::string&` to `absl::string_view`
to handle the case when there's no transport assigned.
That in turn caused an avalanche of required updates.

Bug: webrtc:12230, webrtc:11993
Change-Id: I16ec6c6a5fc2f5f7c7de572355a3c6ca924bb9d4
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/244084
Reviewed-by: Niels Moller <nisse@webrtc.org>
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#35617}

media/base/fake_media_engine.h

@@ -275,7 +275,7 @@ class RtpHelper : public Base {
   }
   void OnPacketSent(const rtc::SentPacket& sent_packet) override {}
   void OnReadyToSend(bool ready) override { ready_to_send_ = ready; }
-  void OnNetworkRouteChanged(const std::string& transport_name,
+  void OnNetworkRouteChanged(absl::string_view transport_name,
                              const rtc::NetworkRoute& network_route) override {
     last_network_route_ = network_route;
     ++num_network_route_changes_;

media/base/media_channel.h

@@ -187,7 +187,7 @@ class MediaChannel {
   virtual void OnReadyToSend(bool ready) = 0;
   // Called when the network route used for sending packets changed.
   virtual void OnNetworkRouteChanged(
-      const std::string& transport_name,
+      absl::string_view transport_name,
       const rtc::NetworkRoute& network_route) = 0;
   // Creates a new outgoing media stream with SSRCs and CNAME as described
   // by sp.

media/engine/webrtc_video_engine.cc

@@ -1864,11 +1864,12 @@ void WebRtcVideoChannel::OnReadyToSend(bool ready) {
 }
 
 void WebRtcVideoChannel::OnNetworkRouteChanged(
-    const std::string& transport_name,
+    absl::string_view transport_name,
     const rtc::NetworkRoute& network_route) {
   RTC_DCHECK_RUN_ON(&network_thread_checker_);
   worker_thread_->PostTask(ToQueuedTask(
-      task_safety_, [this, name = transport_name, route = network_route] {
+      task_safety_,
+      [this, name = std::string(transport_name), route = network_route] {
         RTC_DCHECK_RUN_ON(&thread_checker_);
         webrtc::RtpTransportControllerSendInterface* transport =
             call_->GetTransportControllerSend();

media/engine/webrtc_video_engine.h

@@ -167,7 +167,7 @@ class WebRtcVideoChannel : public VideoMediaChannel,
                         int64_t packet_time_us) override;
   void OnPacketSent(const rtc::SentPacket& sent_packet) override;
   void OnReadyToSend(bool ready) override;
-  void OnNetworkRouteChanged(const std::string& transport_name,
+  void OnNetworkRouteChanged(absl::string_view transport_name,
                              const rtc::NetworkRoute& network_route) override;
   void SetInterface(NetworkInterface* iface) override;
 

media/engine/webrtc_voice_engine.cc

@@ -2284,14 +2284,15 @@ void WebRtcVoiceMediaChannel::OnPacketSent(const rtc::SentPacket& sent_packet) {
 }
 
 void WebRtcVoiceMediaChannel::OnNetworkRouteChanged(
-    const std::string& transport_name,
+    absl::string_view transport_name,
     const rtc::NetworkRoute& network_route) {
   RTC_DCHECK_RUN_ON(&network_thread_checker_);
 
   call_->OnAudioTransportOverheadChanged(network_route.packet_overhead);
 
   worker_thread_->PostTask(ToQueuedTask(
-      task_safety_, [this, name = transport_name, route = network_route] {
+      task_safety_,
+      [this, name = std::string(transport_name), route = network_route] {
         RTC_DCHECK_RUN_ON(worker_thread_);
         call_->GetTransportControllerSend()->OnNetworkRouteChanged(name, route);
       }));

media/engine/webrtc_voice_engine.h

@@ -209,7 +209,7 @@ class WebRtcVoiceMediaChannel final : public VoiceMediaChannel,
   void OnPacketReceived(rtc::CopyOnWriteBuffer packet,
                         int64_t packet_time_us) override;
   void OnPacketSent(const rtc::SentPacket& sent_packet) override;
-  void OnNetworkRouteChanged(const std::string& transport_name,
+  void OnNetworkRouteChanged(absl::string_view transport_name,
                              const rtc::NetworkRoute& network_route) override;
   void OnReadyToSend(bool ready) override;
   bool GetStats(VoiceMediaInfo* info, bool get_and_clear_legacy_stats) override;

pc/channel.cc

@@ -232,8 +232,6 @@ bool BaseChannel::SetRtpTransport(webrtc::RtpTransportInternal* rtp_transport) {
 
   rtp_transport_ = rtp_transport;
   if (rtp_transport_) {
-    transport_name_ = rtp_transport_->transport_name();
-
     if (!ConnectToRtpTransport()) {
       RTC_LOG(LS_ERROR) << "Failed to connect to the new RtpTransport for "
                         << ToString() << ".";
@@ -369,7 +367,7 @@ void BaseChannel::OnNetworkRouteChanged(
   // use the same transport name and MediaChannel::OnNetworkRouteChanged cannot
   // work correctly. Intentionally leave it broken to simplify the code and
   // encourage the users to stop using non-muxing RTCP.
-  media_channel_->OnNetworkRouteChanged(transport_name_, new_route);
+  media_channel_->OnNetworkRouteChanged(transport_name(), new_route);
 }
 
 void BaseChannel::SetFirstPacketReceivedCallback(

pc/channel.h

@@ -124,12 +124,11 @@ class BaseChannel : public ChannelInterface,
   rtc::Thread* network_thread() const { return network_thread_; }
   const std::string& content_name() const override { return content_name_; }
   // TODO(deadbeef): This is redundant; remove this.
-  const std::string& transport_name() const override {
+  absl::string_view transport_name() const override {
     RTC_DCHECK_RUN_ON(network_thread());
     if (rtp_transport_)
       return rtp_transport_->transport_name();
-    // TODO(tommi): Delete this variable.
+    return "";
-    return transport_name_;
   }
 
   // This function returns true if using SRTP (DTLS-based keying or SDES).
@@ -304,14 +303,6 @@ class BaseChannel : public ChannelInterface,
   std::function<void()> on_first_packet_received_
       RTC_GUARDED_BY(network_thread());
 
-  // Won't be set when using raw packet transports. SDP-specific thing.
-  // TODO(bugs.webrtc.org/12230): Written on network thread, read on
-  // worker thread (at least).
-  // TODO(tommi): Remove this variable and instead use rtp_transport_ to
-  // return the transport name. This variable is currently required for
-  // "for_test" methods.
-  std::string transport_name_;
-
   webrtc::RtpTransportInternal* rtp_transport_
       RTC_GUARDED_BY(network_thread()) = nullptr;
 

pc/channel_interface.h

@@ -14,6 +14,7 @@
 #include <string>
 #include <vector>
 
+#include "absl/strings/string_view.h"
 #include "api/jsep.h"
 #include "api/media_types.h"
 #include "media/base/media_channel.h"
@@ -32,8 +33,11 @@ class ChannelInterface {
 
   virtual MediaChannel* media_channel() const = 0;
 
+  // Returns a string view for the transport name. Fetching the transport name
+  // must be done on the network thread only and note that the lifetime of
+  // the returned object should be assumed to only be the calling scope.
   // TODO(deadbeef): This is redundant; remove this.
-  virtual const std::string& transport_name() const = 0;
+  virtual absl::string_view transport_name() const = 0;
 
   virtual const std::string& content_name() const = 0;
 

pc/peer_connection.cc

@@ -2666,8 +2666,8 @@ void PeerConnection::ReportTransportStats() {
       media_types_by_transport_name;
   for (const auto& transceiver : rtp_manager()->transceivers()->UnsafeList()) {
     if (transceiver->internal()->channel()) {
-      const std::string& transport_name =
+      std::string transport_name(
-          transceiver->internal()->channel()->transport_name();
+          transceiver->internal()->channel()->transport_name());
       media_types_by_transport_name[transport_name].insert(
           transceiver->media_type());
     }
@@ -2827,7 +2827,8 @@ bool PeerConnection::OnTransportChanged(
     if (dtls_transport) {
       signaling_thread()->PostTask(ToQueuedTask(
           signaling_thread_safety_.flag(),
-          [this, name = dtls_transport->internal()->transport_name()] {
+          [this,
+           name = std::string(dtls_transport->internal()->transport_name())] {
             RTC_DCHECK_RUN_ON(signaling_thread());
             sctp_transport_name_s_ = std::move(name);
           }));

pc/rtc_stats_collector.cc

@@ -2148,7 +2148,7 @@ void RTCStatsCollector::PrepareTransceiverStatsInfosAndCallStats_s_w_n() {
       }
 
       stats.mid = channel->content_name();
-      stats.transport_name = channel->transport_name();
+      stats.transport_name = std::string(channel->transport_name());
 
       if (media_type == cricket::MEDIA_TYPE_AUDIO) {
         auto* voice_channel = static_cast<cricket::VoiceChannel*>(channel);

pc/stats_collector.cc

@@ -887,7 +887,7 @@ StatsCollector::SessionStats StatsCollector::ExtractSessionInfo_n(
     cricket::ChannelInterface* channel = transceiver->internal()->channel();
     if (channel) {
       stats.transport_names_by_mid[channel->content_name()] =
-          channel->transport_name();
+          std::string(channel->transport_name());
     }
   }
 

pc/test/fake_peer_connection_for_stats.h

@@ -101,7 +101,7 @@ class VoiceChannelForTesting : public cricket::VoiceChannel {
         test_transport_name_(std::move(transport_name)) {}
 
  private:
-  const std::string& transport_name() const override {
+  absl::string_view transport_name() const override {
     return test_transport_name_;
   }
 
@@ -130,7 +130,7 @@ class VideoChannelForTesting : public cricket::VideoChannel {
         test_transport_name_(std::move(transport_name)) {}
 
  private:
-  const std::string& transport_name() const override {
+  absl::string_view transport_name() const override {
     return test_transport_name_;
   }
 

pc/test/mock_channel_interface.h

@@ -26,7 +26,7 @@ class MockChannelInterface : public cricket::ChannelInterface {
  public:
   MOCK_METHOD(cricket::MediaType, media_type, (), (const, override));
   MOCK_METHOD(MediaChannel*, media_channel, (), (const, override));
-  MOCK_METHOD(const std::string&, transport_name, (), (const, override));
+  MOCK_METHOD(absl::string_view, transport_name, (), (const, override));
   MOCK_METHOD(const std::string&, content_name, (), (const, override));
   MOCK_METHOD(void, Enable, (bool), (override));
   MOCK_METHOD(void,

pc/test/mock_voice_media_channel.h

@@ -40,7 +40,7 @@ class MockVoiceMediaChannel : public VoiceMediaChannel {
   MOCK_METHOD(void, OnReadyToSend, (bool ready), (override));
   MOCK_METHOD(void,
               OnNetworkRouteChanged,
-              (const std::string& transport_name,
+              (absl::string_view transport_name,
                const rtc::NetworkRoute& network_route),
               (override));
   MOCK_METHOD(bool, AddSendStream, (const StreamParams& sp), (override));