[DataChannelInterface] Introduce DataChannelInterface::SendAsync()

One problem with the existing Send() method is that it has a return
value that is problematic for a fully async implementation.

A second problem with Send() is that the return value is bool and not
RTCError (webrtc:13289), which is why OnSendComplete() uses RTCError.

Also, start deprecating `bool Send()` in favor of `void SendAsync()` and
adding `network_safety_` flag for posting async operations to the
network thread. This flag also takes over from the
`connected_to_transport_` which can now be removed.

Bug: webrtc:11547, webrtc:13289
Change-Id: I87bbc7e9b964a52684bdfe0e6ebc5230be254e8b
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/299760
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#39817}

api/data_channel_interface.cc

@@ -10,6 +10,8 @@
 
 #include "api/data_channel_interface.h"
 
+#include "rtc_base/checks.h"
+
 namespace webrtc {
 
 bool DataChannelInterface::ordered() const {
@@ -44,4 +46,17 @@ uint64_t DataChannelInterface::MaxSendQueueSize() {
   return 16 * 1024 * 1024;  // 16 MiB
 }
 
+// TODO(tommi): Remove method once downstream implementations have been removed.
+bool DataChannelInterface::Send(const DataBuffer& buffer) {
+  RTC_DCHECK_NOTREACHED();
+  return false;
+}
+
+// TODO(tommi): Remove implementation once method is pure virtual.
+void DataChannelInterface::SendAsync(
+    DataBuffer buffer,
+    absl::AnyInvocable<void(RTCError) &&> on_complete) {
+  RTC_DCHECK_NOTREACHED();
+}
+
 }  // namespace webrtc

api/data_channel_interface.h

@@ -19,6 +19,7 @@
 
 #include <string>
 
+#include "absl/functional/any_invocable.h"
 #include "absl/types/optional.h"
 #include "api/priority.h"
 #include "api/rtc_error.h"
@@ -198,7 +199,20 @@ class RTC_EXPORT DataChannelInterface : public rtc::RefCountInterface {
   // Returns false if the data channel is not in open state or if the send
   // buffer is full.
   // TODO(webrtc:13289): Return an RTCError with information about the failure.
-  virtual bool Send(const DataBuffer& buffer) = 0;
+  // TODO(tommi): Remove this method once downstream implementations don't refer
+  // to it.
+  virtual bool Send(const DataBuffer& buffer);
+
+  // Queues up an asynchronus send operation to run on a network thread.
+  // Once the operation has completed the `on_complete` callback is invoked,
+  // on the thread the send operation was done on. It's important that
+  // `on_complete` implementations do not block the current thread but rather
+  // post any expensive operations to other worker threads.
+  // TODO(tommi): Make pure virtual after updating mock class in Chromium.
+  // Deprecate `Send` in favor of this variant since the return value of `Send`
+  // is limiting for a fully async implementation (yet in practice is ignored).
+  virtual void SendAsync(DataBuffer buffer,
+                         absl::AnyInvocable<void(RTCError) &&> on_complete);
 
   // Amount of bytes that can be queued for sending on the data channel.
   // Those are bytes that have not yet been processed at the SCTP level.

api/test/mock_data_channel.h

@@ -51,6 +51,11 @@ class MockDataChannelInterface
   MOCK_METHOD(uint64_t, buffered_amount, (), (const, override));
   MOCK_METHOD(void, Close, (), (override));
   MOCK_METHOD(bool, Send, (const DataBuffer& buffer), (override));
+  MOCK_METHOD(void,
+              SendAsync,
+              (DataBuffer buffer,
+               absl::AnyInvocable<void(RTCError) &&> on_complete),
+              (override));
 
  protected:
   MockDataChannelInterface() = default;

pc/BUILD.gn

@@ -877,6 +877,7 @@ rtc_library("sctp_data_channel") {
     "../api:rtc_error",
     "../api:scoped_refptr",
     "../api:sequence_checker",
+    "../api/task_queue:pending_task_safety_flag",
     "../api/transport:datagram_transport_interface",
     "../media:media_channel",
     "../media:rtc_data_sctp_transport_internal",
@@ -2484,6 +2485,7 @@ if (rtc_include_tests && !build_with_chromium) {
       "../rtc_base/third_party/sigslot",
       "../system_wrappers:metrics",
       "../test:field_trial",
+      "../test:rtc_expect_death",
       "../test:run_loop",
       "../test:scoped_key_value_config",
       "../test/pc/sctp:fake_sctp_transport",

pc/data_channel_unittest.cc

@@ -32,6 +32,10 @@
 #include "test/gtest.h"
 #include "test/run_loop.h"
 
+#if RTC_DCHECK_IS_ON && GTEST_HAS_DEATH_TEST && !defined(WEBRTC_ANDROID)
+#include "test/testsupport/rtc_expect_death.h"
+#endif  // RTC_DCHECK_IS_ON && GTEST_HAS_DEATH_TEST && !defined(WEBRTC_ANDROID)
+
 namespace webrtc {
 
 namespace {
@@ -124,6 +128,20 @@ class SctpDataChannelTest : public ::testing::Test {
     channel_->RegisterObserver(observer_.get());
   }
 
+  // Wait for queued up methods to run on the network thread.
+  void FlushNetworkThread() {
+    RTC_DCHECK_RUN_ON(run_loop_.task_queue());
+    network_thread_.BlockingCall([] {});
+  }
+
+  // Used to complete pending methods on the network thread
+  // that might queue up methods on the signaling (main) thread
+  // that are run too.
+  void FlushNetworkThreadAndPendingOperations() {
+    FlushNetworkThread();
+    run_loop_.Flush();
+  }
+
   test::RunLoop run_loop_;
   rtc::Thread network_thread_;
   InternalDataChannelInit init_;
@@ -207,6 +225,48 @@ TEST_F(SctpDataChannelTest, StateTransition) {
 // Tests that DataChannel::buffered_amount() is correct after the channel is
 // blocked.
 TEST_F(SctpDataChannelTest, BufferedAmountWhenBlocked) {
+  AddObserver();
+  SetChannelReady();
+  DataBuffer buffer("abcd");
+  size_t successful_sends = 0;
+  auto send_complete = [&](RTCError err) {
+    EXPECT_TRUE(err.ok());
+    ++successful_sends;
+  };
+  channel_->SendAsync(buffer, send_complete);
+  FlushNetworkThreadAndPendingOperations();
+  EXPECT_EQ(channel_->buffered_amount(), 0u);
+  size_t successful_send_count = 1;
+  EXPECT_EQ(successful_send_count, successful_sends);
+  EXPECT_EQ(successful_send_count,
+            observer_->on_buffered_amount_change_count());
+
+  controller_->set_send_blocked(true);
+  const int number_of_packets = 3;
+  for (int i = 0; i < number_of_packets; ++i) {
+    channel_->SendAsync(buffer, send_complete);
+    ++successful_send_count;
+  }
+  FlushNetworkThreadAndPendingOperations();
+  EXPECT_EQ(buffer.data.size() * number_of_packets,
+            channel_->buffered_amount());
+  EXPECT_EQ(successful_send_count, successful_sends);
+
+  // An event should not have been fired for buffered amount.
+  EXPECT_EQ(1u, observer_->on_buffered_amount_change_count());
+
+  // Now buffered amount events should get fired and the value
+  // get down to 0u.
+  controller_->set_send_blocked(false);
+  run_loop_.Flush();
+  EXPECT_EQ(channel_->buffered_amount(), 0u);
+  EXPECT_EQ(successful_send_count, successful_sends);
+  EXPECT_EQ(successful_send_count,
+            observer_->on_buffered_amount_change_count());
+}
+
+// TODO(tommi): This test uses `Send()`. Remove once fully deprecated.
+TEST_F(SctpDataChannelTest, DeprecatedBufferedAmountWhenBlocked) {
   AddObserver();
   SetChannelReady();
   DataBuffer buffer("abcd");
@@ -232,7 +292,7 @@ TEST_F(SctpDataChannelTest, BufferedAmountWhenBlocked) {
   controller_->set_send_blocked(false);
   run_loop_.Flush();
   successful_send_count += number_of_packets;
-  EXPECT_EQ(0U, channel_->buffered_amount());
+  EXPECT_EQ(channel_->buffered_amount(), 0u);
   EXPECT_EQ(successful_send_count,
             observer_->on_buffered_amount_change_count());
 }
@@ -240,6 +300,28 @@ TEST_F(SctpDataChannelTest, BufferedAmountWhenBlocked) {
 // Tests that the queued data are sent when the channel transitions from blocked
 // to unblocked.
 TEST_F(SctpDataChannelTest, QueuedDataSentWhenUnblocked) {
+  AddObserver();
+  SetChannelReady();
+  DataBuffer buffer("abcd");
+  controller_->set_send_blocked(true);
+  size_t successful_send = 0u;
+  auto send_complete = [&](RTCError err) {
+    EXPECT_TRUE(err.ok());
+    ++successful_send;
+  };
+  channel_->SendAsync(buffer, send_complete);
+  FlushNetworkThreadAndPendingOperations();
+  EXPECT_EQ(1U, successful_send);
+  EXPECT_EQ(0U, observer_->on_buffered_amount_change_count());
+
+  controller_->set_send_blocked(false);
+  SetChannelReady();
+  EXPECT_EQ(channel_->buffered_amount(), 0u);
+  EXPECT_EQ(observer_->on_buffered_amount_change_count(), 1u);
+}
+
+// TODO(tommi): This test uses `Send()`. Remove once fully deprecated.
+TEST_F(SctpDataChannelTest, DeprecatedQueuedDataSentWhenUnblocked) {
   AddObserver();
   SetChannelReady();
   DataBuffer buffer("abcd");
@@ -257,6 +339,34 @@ TEST_F(SctpDataChannelTest, QueuedDataSentWhenUnblocked) {
 // Tests that no crash when the channel is blocked right away while trying to
 // send queued data.
 TEST_F(SctpDataChannelTest, BlockedWhenSendQueuedDataNoCrash) {
+  AddObserver();
+  SetChannelReady();
+  DataBuffer buffer("abcd");
+  controller_->set_send_blocked(true);
+  size_t successful_send = 0u;
+  auto send_complete = [&](RTCError err) {
+    EXPECT_TRUE(err.ok());
+    ++successful_send;
+  };
+  channel_->SendAsync(buffer, send_complete);
+  FlushNetworkThreadAndPendingOperations();
+  EXPECT_EQ(1U, successful_send);
+  EXPECT_EQ(0U, observer_->on_buffered_amount_change_count());
+
+  // Set channel ready while it is still blocked.
+  SetChannelReady();
+  EXPECT_EQ(buffer.size(), channel_->buffered_amount());
+  EXPECT_EQ(0U, observer_->on_buffered_amount_change_count());
+
+  // Unblock the channel to send queued data again, there should be no crash.
+  controller_->set_send_blocked(false);
+  SetChannelReady();
+  EXPECT_EQ(0U, channel_->buffered_amount());
+  EXPECT_EQ(1U, observer_->on_buffered_amount_change_count());
+}
+
+// TODO(tommi): This test uses `Send()`. Remove once fully deprecated.
+TEST_F(SctpDataChannelTest, DeprecatedBlockedWhenSendQueuedDataNoCrash) {
   AddObserver();
   SetChannelReady();
   DataBuffer buffer("abcd");
@@ -294,6 +404,55 @@ TEST_F(SctpDataChannelTest, VerifyMessagesAndBytesSent) {
   EXPECT_EQ(0U, channel_->messages_sent());
   EXPECT_EQ(0U, channel_->bytes_sent());
 
+  // Send three buffers while not blocked.
+  controller_->set_send_blocked(false);
+  for (int i : {0, 1, 2}) {
+    channel_->SendAsync(buffers[i], nullptr);
+  }
+  FlushNetworkThreadAndPendingOperations();
+
+  size_t bytes_sent = buffers[0].size() + buffers[1].size() + buffers[2].size();
+  EXPECT_EQ_WAIT(0U, channel_->buffered_amount(), kDefaultTimeout);
+  EXPECT_EQ(3U, channel_->messages_sent());
+  EXPECT_EQ(bytes_sent, channel_->bytes_sent());
+
+  // Send three buffers while blocked, queuing the buffers.
+  controller_->set_send_blocked(true);
+  for (int i : {3, 4, 5}) {
+    channel_->SendAsync(buffers[i], nullptr);
+  }
+  FlushNetworkThreadAndPendingOperations();
+  size_t bytes_queued =
+      buffers[3].size() + buffers[4].size() + buffers[5].size();
+  EXPECT_EQ(bytes_queued, channel_->buffered_amount());
+  EXPECT_EQ(3U, channel_->messages_sent());
+  EXPECT_EQ(bytes_sent, channel_->bytes_sent());
+
+  // Unblock and make sure everything was sent.
+  controller_->set_send_blocked(false);
+  EXPECT_EQ_WAIT(0U, channel_->buffered_amount(), kDefaultTimeout);
+  bytes_sent += bytes_queued;
+  EXPECT_EQ(6U, channel_->messages_sent());
+  EXPECT_EQ(bytes_sent, channel_->bytes_sent());
+}
+
+// TODO(tommi): This test uses `Send()`. Remove once fully deprecated.
+TEST_F(SctpDataChannelTest, DeprecatedVerifyMessagesAndBytesSent) {
+  AddObserver();
+  SetChannelReady();
+  std::vector<DataBuffer> buffers({
+      DataBuffer("message 1"),
+      DataBuffer("msg 2"),
+      DataBuffer("message three"),
+      DataBuffer("quadra message"),
+      DataBuffer("fifthmsg"),
+      DataBuffer("message of the beast"),
+  });
+
+  // Default values.
+  EXPECT_EQ(0U, channel_->messages_sent());
+  EXPECT_EQ(0U, channel_->bytes_sent());
+
   // Send three buffers while not blocked.
   controller_->set_send_blocked(false);
   EXPECT_TRUE(channel_->Send(buffers[0]));
@@ -369,6 +528,35 @@ TEST_F(SctpDataChannelTest, SendUnorderedAfterReceivesOpenAck) {
 
   EXPECT_EQ_WAIT(DataChannelInterface::kOpen, proxy->state(), 1000);
 
+  // Sends a message and verifies it's ordered.
+  DataBuffer buffer("some data");
+  proxy->SendAsync(buffer, nullptr);
+  EXPECT_TRUE(controller_->last_send_data_params().ordered);
+
+  // Emulates receiving an OPEN_ACK message.
+  rtc::CopyOnWriteBuffer payload;
+  WriteDataChannelOpenAckMessage(&payload);
+  network_thread_.BlockingCall(
+      [&] { dc->OnDataReceived(DataMessageType::kControl, payload); });
+
+  // Sends another message and verifies it's unordered.
+  proxy->SendAsync(buffer, nullptr);
+  FlushNetworkThreadAndPendingOperations();
+  EXPECT_FALSE(controller_->last_send_data_params().ordered);
+}
+
+// TODO(tommi): This test uses `Send()`. Remove once fully deprecated.
+TEST_F(SctpDataChannelTest, DeprecatedSendUnorderedAfterReceivesOpenAck) {
+  SetChannelReady();
+  InternalDataChannelInit init;
+  init.id = 1;
+  init.ordered = false;
+  rtc::scoped_refptr<SctpDataChannel> dc =
+      controller_->CreateDataChannel("test1", init);
+  auto proxy = webrtc::SctpDataChannel::CreateProxy(dc, signaling_safety_);
+
+  EXPECT_EQ_WAIT(DataChannelInterface::kOpen, proxy->state(), 1000);
+
   // Sends a message and verifies it's ordered.
   DataBuffer buffer("some data");
   ASSERT_TRUE(proxy->Send(buffer));
@@ -398,6 +586,29 @@ TEST_F(SctpDataChannelTest, SendUnorderedAfterReceiveData) {
 
   EXPECT_EQ_WAIT(DataChannelInterface::kOpen, proxy->state(), 1000);
 
+  // Emulates receiving a DATA message.
+  DataBuffer buffer("data");
+  network_thread_.BlockingCall(
+      [&] { dc->OnDataReceived(DataMessageType::kText, buffer.data); });
+
+  // Sends a message and verifies it's unordered.
+  proxy->SendAsync(buffer, nullptr);
+  FlushNetworkThreadAndPendingOperations();
+  EXPECT_FALSE(controller_->last_send_data_params().ordered);
+}
+
+// TODO(tommi): This test uses `Send()`. Remove once fully deprecated.
+TEST_F(SctpDataChannelTest, DeprecatedSendUnorderedAfterReceiveData) {
+  SetChannelReady();
+  InternalDataChannelInit init;
+  init.id = 1;
+  init.ordered = false;
+  rtc::scoped_refptr<SctpDataChannel> dc =
+      controller_->CreateDataChannel("test1", init);
+  auto proxy = webrtc::SctpDataChannel::CreateProxy(dc, signaling_safety_);
+
+  EXPECT_EQ_WAIT(DataChannelInterface::kOpen, proxy->state(), 1000);
+
   // Emulates receiving a DATA message.
   DataBuffer buffer("data");
   network_thread_.BlockingCall(
@@ -426,6 +637,24 @@ TEST_F(SctpDataChannelTest, OpenWaitsForOpenMesssage) {
 TEST_F(SctpDataChannelTest, QueuedCloseFlushes) {
   DataBuffer buffer("foo");
 
+  controller_->set_send_blocked(true);
+  SetChannelReady();
+  EXPECT_EQ(DataChannelInterface::kConnecting, channel_->state());
+  controller_->set_send_blocked(false);
+  EXPECT_EQ_WAIT(DataChannelInterface::kOpen, channel_->state(), 1000);
+  controller_->set_send_blocked(true);
+  channel_->SendAsync(buffer, nullptr);
+  channel_->Close();
+  controller_->set_send_blocked(false);
+  EXPECT_EQ_WAIT(DataChannelInterface::kClosed, channel_->state(), 1000);
+  EXPECT_TRUE(channel_->error().ok());
+  EXPECT_EQ(DataMessageType::kText, controller_->last_send_data_params().type);
+}
+
+// TODO(tommi): This test uses `Send()`. Remove once fully deprecated.
+TEST_F(SctpDataChannelTest, DeprecatedQueuedCloseFlushes) {
+  DataBuffer buffer("foo");
+
   controller_->set_send_blocked(true);
   SetChannelReady();
   EXPECT_EQ(DataChannelInterface::kConnecting, channel_->state());
@@ -442,6 +671,16 @@ TEST_F(SctpDataChannelTest, QueuedCloseFlushes) {
 
 // Tests that messages are sent with the right id.
 TEST_F(SctpDataChannelTest, SendDataId) {
+  SetChannelSid(inner_channel_, StreamId(1));
+  SetChannelReady();
+  DataBuffer buffer("data");
+  channel_->SendAsync(buffer, nullptr);
+  FlushNetworkThreadAndPendingOperations();
+  EXPECT_EQ(1, controller_->last_sid());
+}
+
+// TODO(tommi): This test uses `Send()`. Remove once fully deprecated.
+TEST_F(SctpDataChannelTest, DeprecatedSendDataId) {
   SetChannelSid(inner_channel_, StreamId(1));
   SetChannelReady();
   DataBuffer buffer("data");
@@ -564,6 +803,36 @@ TEST_F(SctpDataChannelTest, OpenAckRoleInitialization) {
 // Tests that that Send() returns false if the sending buffer is full
 // and the channel stays open.
 TEST_F(SctpDataChannelTest, OpenWhenSendBufferFull) {
+  AddObserver();
+  SetChannelReady();
+
+  const size_t packetSize = 1024;
+
+  rtc::CopyOnWriteBuffer buffer(packetSize);
+  memset(buffer.MutableData(), 0, buffer.size());
+
+  DataBuffer packet(buffer, true);
+  controller_->set_send_blocked(true);
+  size_t successful_send = 0u, failed_send = 0u;
+  auto send_complete = [&](RTCError err) {
+    err.ok() ? ++successful_send : ++failed_send;
+  };
+
+  size_t count = DataChannelInterface::MaxSendQueueSize() / packetSize;
+  for (size_t i = 0; i < count; ++i) {
+    channel_->SendAsync(packet, send_complete);
+  }
+
+  // The sending buffer should be full, `Send()` returns false.
+  channel_->SendAsync(packet, std::move(send_complete));
+  FlushNetworkThreadAndPendingOperations();
+  EXPECT_TRUE(DataChannelInterface::kOpen == channel_->state());
+  EXPECT_EQ(successful_send, count);
+  EXPECT_EQ(failed_send, 1u);
+}
+
+// TODO(tommi): This test uses `Send()`. Remove once fully deprecated.
+TEST_F(SctpDataChannelTest, DeprecatedOpenWhenSendBufferFull) {
   SetChannelReady();
 
   const size_t packetSize = 1024;
@@ -590,6 +859,20 @@ TEST_F(SctpDataChannelTest, ClosedOnTransportError) {
   DataBuffer buffer("abcd");
   controller_->set_transport_error();
 
+  channel_->SendAsync(buffer, nullptr);
+
+  EXPECT_EQ(DataChannelInterface::kClosed, channel_->state());
+  EXPECT_FALSE(channel_->error().ok());
+  EXPECT_EQ(RTCErrorType::NETWORK_ERROR, channel_->error().type());
+  EXPECT_EQ(RTCErrorDetailType::NONE, channel_->error().error_detail());
+}
+
+// TODO(tommi): This test uses `Send()`. Remove once fully deprecated.
+TEST_F(SctpDataChannelTest, DeprecatedClosedOnTransportError) {
+  SetChannelReady();
+  DataBuffer buffer("abcd");
+  controller_->set_transport_error();
+
   EXPECT_TRUE(channel_->Send(buffer));
 
   EXPECT_EQ(DataChannelInterface::kClosed, channel_->state());
@@ -622,6 +905,17 @@ TEST_F(SctpDataChannelTest, SendEmptyData) {
   SetChannelReady();
   EXPECT_EQ(DataChannelInterface::kOpen, channel_->state());
 
+  DataBuffer buffer("");
+  channel_->SendAsync(buffer, nullptr);
+  EXPECT_EQ(DataChannelInterface::kOpen, channel_->state());
+}
+
+// TODO(tommi): This test uses `Send()`. Remove once fully deprecated.
+TEST_F(SctpDataChannelTest, DeprecatedSendEmptyData) {
+  SetChannelSid(inner_channel_, StreamId(1));
+  SetChannelReady();
+  EXPECT_EQ(DataChannelInterface::kOpen, channel_->state());
+
   DataBuffer buffer("");
   EXPECT_TRUE(channel_->Send(buffer));
   EXPECT_EQ(DataChannelInterface::kOpen, channel_->state());
@@ -646,6 +940,34 @@ TEST_F(SctpDataChannelTest, UnusedTransitionsDirectlyToClosed) {
 // Test that the data channel goes to the "closed" state (and doesn't crash)
 // when its transport goes away, even while data is buffered.
 TEST_F(SctpDataChannelTest, TransportDestroyedWhileDataBuffered) {
+  AddObserver();
+  SetChannelReady();
+
+  rtc::CopyOnWriteBuffer buffer(1024);
+  memset(buffer.MutableData(), 0, buffer.size());
+  DataBuffer packet(buffer, true);
+
+  // Send a packet while sending is blocked so it ends up buffered.
+  controller_->set_send_blocked(true);
+  channel_->SendAsync(packet, nullptr);
+
+  // Tell the data channel that its transport is being destroyed.
+  // It should then stop using the transport (allowing us to delete it) and
+  // transition to the "closed" state.
+  RTCError error(RTCErrorType::OPERATION_ERROR_WITH_DATA, "");
+  error.set_error_detail(RTCErrorDetailType::SCTP_FAILURE);
+  network_thread_.BlockingCall(
+      [&] { inner_channel_->OnTransportChannelClosed(error); });
+  controller_.reset(nullptr);
+  EXPECT_EQ_WAIT(DataChannelInterface::kClosed, channel_->state(),
+                 kDefaultTimeout);
+  EXPECT_FALSE(channel_->error().ok());
+  EXPECT_EQ(RTCErrorType::OPERATION_ERROR_WITH_DATA, channel_->error().type());
+  EXPECT_EQ(RTCErrorDetailType::SCTP_FAILURE, channel_->error().error_detail());
+}
+
+// TODO(tommi): This test uses `Send()`. Remove once fully deprecated.
+TEST_F(SctpDataChannelTest, DeprecatedTransportDestroyedWhileDataBuffered) {
   SetChannelReady();
 
   rtc::CopyOnWriteBuffer buffer(1024);
@@ -762,5 +1084,69 @@ TEST_F(SctpSidAllocatorTest, SctpIdReusedForRemovedDataChannel) {
   EXPECT_EQ(even_id.stream_id_int() + 6, allocated_id.stream_id_int());
 }
 
+// Code coverage tests for default implementations in data_channel_interface.*.
+namespace {
+class NoImplDataChannel : public DataChannelInterface {
+ public:
+  NoImplDataChannel() = default;
+  // Send and SendAsync implementations are public and implementation
+  // is in data_channel_interface.cc.
+
+ private:
+  // Implementation for pure virtual methods, just for compilation sake.
+  void RegisterObserver(DataChannelObserver* observer) override {}
+  void UnregisterObserver() override {}
+  std::string label() const override { return ""; }
+  bool reliable() const override { return false; }
+  int id() const override { return -1; }
+  DataState state() const override { return DataChannelInterface::kClosed; }
+  uint32_t messages_sent() const override { return 0u; }
+  uint64_t bytes_sent() const override { return 0u; }
+  uint32_t messages_received() const override { return 0u; }
+  uint64_t bytes_received() const override { return 0u; }
+  uint64_t buffered_amount() const override { return 0u; }
+  void Close() override {}
+};
+
+class NoImplObserver : public DataChannelObserver {
+ public:
+  NoImplObserver() = default;
+
+ private:
+  void OnStateChange() override {}
+  void OnMessage(const DataBuffer& buffer) override {}
+};
+}  // namespace
+
+TEST(DataChannelInterfaceTest, Coverage) {
+  auto channel = rtc::make_ref_counted<NoImplDataChannel>();
+  EXPECT_FALSE(channel->ordered());
+  EXPECT_EQ(channel->maxRetransmitTime(), 0u);
+  EXPECT_EQ(channel->maxRetransmits(), 0u);
+  EXPECT_FALSE(channel->maxRetransmitsOpt());
+  EXPECT_FALSE(channel->maxPacketLifeTime());
+  EXPECT_TRUE(channel->protocol().empty());
+  EXPECT_FALSE(channel->negotiated());
+  EXPECT_EQ(channel->MaxSendQueueSize(), 16u * 1024u * 1024u);
+
+  NoImplObserver observer;
+  observer.OnBufferedAmountChange(0u);
+  EXPECT_FALSE(observer.IsOkToCallOnTheNetworkThread());
+}
+
+#if RTC_DCHECK_IS_ON && GTEST_HAS_DEATH_TEST && !defined(WEBRTC_ANDROID)
+
+TEST(DataChannelInterfaceDeathTest, SendDefaultImplDchecks) {
+  auto channel = rtc::make_ref_counted<NoImplDataChannel>();
+  RTC_EXPECT_DEATH(channel->Send(DataBuffer("Foo")), "Check failed: false");
+}
+
+TEST(DataChannelInterfaceDeathTest, SendAsyncDefaultImplDchecks) {
+  auto channel = rtc::make_ref_counted<NoImplDataChannel>();
+  RTC_EXPECT_DEATH(channel->SendAsync(DataBuffer("Foo"), nullptr),
+                   "Check failed: false");
+}
+#endif  // RTC_DCHECK_IS_ON && GTEST_HAS_DEATH_TEST && !defined(WEBRTC_ANDROID)
+
 }  // namespace
 }  // namespace webrtc

pc/sctp_data_channel.cc

@@ -60,6 +60,10 @@ PROXY_SECONDARY_CONSTMETHOD0(uint64_t, bytes_received)
 PROXY_SECONDARY_CONSTMETHOD0(uint64_t, buffered_amount)
 PROXY_SECONDARY_METHOD0(void, Close)
 PROXY_SECONDARY_METHOD1(bool, Send, const DataBuffer&)
+BYPASS_PROXY_METHOD2(void,
+                     SendAsync,
+                     DataBuffer,
+                     absl::AnyInvocable<void(RTCError) &&>)
 END_PROXY_MAP(DataChannel)
 }  // namespace
 
@@ -261,6 +265,8 @@ class SctpDataChannel::ObserverAdapter : public DataChannelObserver {
         }));
   }
 
+  bool IsOkToCallOnTheNetworkThread() override { return true; }
+
   rtc::Thread* signaling_thread() const { return signaling_thread_; }
   rtc::Thread* network_thread() const { return channel_->network_thread_; }
 
@@ -320,14 +326,16 @@ SctpDataChannel::SctpDataChannel(
       negotiated_(config.negotiated),
       ordered_(config.ordered),
       observer_(nullptr),
-      controller_(std::move(controller)),
+      controller_(std::move(controller)) {
-      connected_to_transport_(connected_to_transport) {
   RTC_DCHECK_RUN_ON(network_thread_);
   // Since we constructed on the network thread we can't (yet) check the
   // `controller_` pointer since doing so will trigger a thread check.
   RTC_UNUSED(network_thread_);
   RTC_DCHECK(config.IsValid());
 
+  if (connected_to_transport)
+    network_safety_->SetAlive();
+
   switch (config.open_handshake_role) {
     case InternalDataChannelInit::kNone:  // pre-negotiated
       handshake_state_ = kHandshakeReady;
@@ -465,9 +473,6 @@ bool SctpDataChannel::negotiated() const {
 
 int SctpDataChannel::id() const {
   RTC_DCHECK_RUN_ON(network_thread_);
-  // TODO(tommi): Once an ID has been assigned, it won't change (can be
-  // considered const). We could do special handling of this and allow bypassing
-  // the proxy so that we can return a valid id without thread hopping.
   return id_n_.stream_id_int();
 }
 
@@ -554,22 +559,53 @@ uint64_t SctpDataChannel::bytes_received() const {
 
 bool SctpDataChannel::Send(const DataBuffer& buffer) {
   RTC_DCHECK_RUN_ON(network_thread_);
+  RTCError err = SendImpl(buffer);
+  if (err.type() == RTCErrorType::INVALID_STATE ||
+      err.type() == RTCErrorType::RESOURCE_EXHAUSTED) {
+    return false;
+  }
 
+  // Always return true for SCTP DataChannel per the spec.
+  return true;
+}
+
+// RTC_RUN_ON(network_thread_);
+RTCError SctpDataChannel::SendImpl(DataBuffer buffer) {
   if (state_ != kOpen) {
     error_ = RTCError(RTCErrorType::INVALID_STATE);
-    return false;
+    return error_;
   }
 
   // If the queue is non-empty, we're waiting for SignalReadyToSend,
   // so just add to the end of the queue and keep waiting.
   if (!queued_send_data_.Empty()) {
-    return QueueSendDataMessage(buffer);
+    error_ = QueueSendDataMessage(buffer)
+                 ? RTCError::OK()
+                 : RTCError(RTCErrorType::RESOURCE_EXHAUSTED);
+    return error_;
   }
 
-  SendDataMessage(buffer, true);
+  return SendDataMessage(buffer, true);
+}
 
-  // Always return true for SCTP DataChannel per the spec.
+void SctpDataChannel::SendAsync(
-  return true;
+    DataBuffer buffer,
+    absl::AnyInvocable<void(RTCError) &&> on_complete) {
+  // Note: at this point, we do not know on which thread we're being called
+  // since this method bypasses the proxy. On Android the thread might be VM
+  // owned, on other platforms it might be the signaling thread, or in Chrome
+  // it can be the JS thread. We also don't know if it's consistently the same
+  // thread. So we always post to the network thread (even if the current thread
+  // might be the network thread - in theory a call could even come from within
+  // the `on_complete` callback).
+  network_thread_->PostTask(SafeTask(
+      network_safety_, [this, buffer = std::move(buffer),
+                        on_complete = std::move(on_complete)]() mutable {
+        RTC_DCHECK_RUN_ON(network_thread_);
+        RTCError err = SendImpl(std::move(buffer));
+        if (on_complete)
+          std::move(on_complete)(err);
+      }));
 }
 
 void SctpDataChannel::SetSctpSid_n(StreamId sid) {
@@ -608,7 +644,7 @@ void SctpDataChannel::OnClosingProcedureComplete() {
 
 void SctpDataChannel::OnTransportChannelCreated() {
   RTC_DCHECK_RUN_ON(network_thread_);
-  connected_to_transport_ = true;
+  network_safety_->SetAlive();
 }
 
 void SctpDataChannel::OnTransportChannelClosed(RTCError error) {
@@ -697,10 +733,8 @@ void SctpDataChannel::OnTransportReady() {
   // what triggers the callback to `OnTransportReady()`.
   // These steps are currently accomplished via two separate PostTask calls to
   // the signaling thread, but could simply be done in single method call on
-  // the network thread (which incidentally is the thread that we'll need to
+  // the network thread.
-  // be on for the below `Send*` calls, which currently do a BlockingCall
+  RTC_DCHECK(connected_to_transport());
-  // from the signaling thread to the network thread.
-  RTC_DCHECK(connected_to_transport_);
   RTC_DCHECK(id_n_.HasValue());
 
   SendQueuedControlMessages();
@@ -716,7 +750,7 @@ void SctpDataChannel::CloseAbruptlyWithError(RTCError error) {
     return;
   }
 
-  connected_to_transport_ = false;
+  network_safety_->SetNotAlive();
 
   // Closing abruptly means any queued data gets thrown away.
   queued_send_data_.Clear();
@@ -746,7 +780,7 @@ void SctpDataChannel::UpdateState() {
 
   switch (state_) {
     case kConnecting: {
-      if (connected_to_transport_ && controller_) {
+      if (connected_to_transport() && controller_) {
         if (handshake_state_ == kHandshakeShouldSendOpen) {
           rtc::CopyOnWriteBuffer payload;
           WriteDataChannelOpenMessage(label_, protocol_, priority_, ordered_,
@@ -774,7 +808,7 @@ void SctpDataChannel::UpdateState() {
       break;
     }
     case kClosing: {
-      if (connected_to_transport_ && controller_) {
+      if (connected_to_transport() && controller_) {
         // Wait for all queued data to be sent before beginning the closing
         // procedure.
         if (queued_send_data_.Empty() && queued_control_data_.Empty()) {
@@ -840,7 +874,7 @@ void SctpDataChannel::SendQueuedDataMessages() {
 
   while (!queued_send_data_.Empty()) {
     std::unique_ptr<DataBuffer> buffer = queued_send_data_.PopFront();
-    if (!SendDataMessage(*buffer, false)) {
+    if (!SendDataMessage(*buffer, false).ok()) {
       // Return the message to the front of the queue if sending is aborted.
       queued_send_data_.PushFront(std::move(buffer));
       break;
@@ -849,12 +883,12 @@ void SctpDataChannel::SendQueuedDataMessages() {
 }
 
 // RTC_RUN_ON(network_thread_).
-bool SctpDataChannel::SendDataMessage(const DataBuffer& buffer,
+RTCError SctpDataChannel::SendDataMessage(const DataBuffer& buffer,
-                                      bool queue_if_blocked) {
+                                          bool queue_if_blocked) {
   SendDataParams send_params;
   if (!controller_) {
     error_ = RTCError(RTCErrorType::INVALID_STATE);
-    return false;
+    return error_;
   }
 
   send_params.ordered = ordered_;
@@ -879,12 +913,16 @@ bool SctpDataChannel::SendDataMessage(const DataBuffer& buffer,
     if (observer_ && buffer.size() > 0) {
       observer_->OnBufferedAmountChange(buffer.size());
     }
-    return true;
+    return error_;
   }
 
   if (error_.type() == RTCErrorType::RESOURCE_EXHAUSTED) {
-    if (!queue_if_blocked || QueueSendDataMessage(buffer)) {
+    if (!queue_if_blocked)
-      return false;
+      return error_;
+
+    if (QueueSendDataMessage(buffer)) {
+      error_ = RTCError::OK();
+      return error_;
     }
   }
   // Close the channel if the error is not SDR_BLOCK, or if queuing the
@@ -895,7 +933,7 @@ bool SctpDataChannel::SendDataMessage(const DataBuffer& buffer,
   CloseAbruptlyWithError(
       RTCError(RTCErrorType::NETWORK_ERROR, "Failure to send data"));
 
-  return false;
+  return error_;
 }
 
 // RTC_RUN_ON(network_thread_).
@@ -924,7 +962,7 @@ void SctpDataChannel::SendQueuedControlMessages() {
 
 // RTC_RUN_ON(network_thread_).
 bool SctpDataChannel::SendControlMessage(const rtc::CopyOnWriteBuffer& buffer) {
-  RTC_DCHECK(connected_to_transport_);
+  RTC_DCHECK(connected_to_transport());
   RTC_DCHECK(id_n_.HasValue());
   RTC_DCHECK(controller_);
 

pc/sctp_data_channel.h

@@ -23,6 +23,7 @@
 #include "api/rtc_error.h"
 #include "api/scoped_refptr.h"
 #include "api/sequence_checker.h"
+#include "api/task_queue/pending_task_safety_flag.h"
 #include "api/transport/data_channel_transport_interface.h"
 #include "pc/data_channel_utils.h"
 #include "pc/sctp_utils.h"
@@ -171,6 +172,8 @@ class SctpDataChannel : public DataChannelInterface {
   uint32_t messages_received() const override;
   uint64_t bytes_received() const override;
   bool Send(const DataBuffer& buffer) override;
+  void SendAsync(DataBuffer buffer,
+                 absl::AnyInvocable<void(RTCError) &&> on_complete) override;
 
   // Close immediately, ignoring any queued data or closing procedure.
   // This is called when the underlying SctpTransport is being destroyed.
@@ -247,13 +250,14 @@ class SctpDataChannel : public DataChannelInterface {
     kHandshakeReady
   };
 
+  RTCError SendImpl(DataBuffer buffer) RTC_RUN_ON(network_thread_);
   void UpdateState() RTC_RUN_ON(network_thread_);
   void SetState(DataState state) RTC_RUN_ON(network_thread_);
 
   void DeliverQueuedReceivedData() RTC_RUN_ON(network_thread_);
 
   void SendQueuedDataMessages() RTC_RUN_ON(network_thread_);
-  bool SendDataMessage(const DataBuffer& buffer, bool queue_if_blocked)
+  RTCError SendDataMessage(const DataBuffer& buffer, bool queue_if_blocked)
       RTC_RUN_ON(network_thread_);
   bool QueueSendDataMessage(const DataBuffer& buffer)
       RTC_RUN_ON(network_thread_);
@@ -262,6 +266,10 @@ class SctpDataChannel : public DataChannelInterface {
   bool SendControlMessage(const rtc::CopyOnWriteBuffer& buffer)
       RTC_RUN_ON(network_thread_);
 
+  bool connected_to_transport() const RTC_RUN_ON(network_thread_) {
+    return network_safety_->alive();
+  }
+
   rtc::Thread* const signaling_thread_;
   rtc::Thread* const network_thread_;
   StreamId id_n_ RTC_GUARDED_BY(network_thread_);
@@ -286,7 +294,6 @@ class SctpDataChannel : public DataChannelInterface {
       RTC_GUARDED_BY(network_thread_);
   HandshakeState handshake_state_ RTC_GUARDED_BY(network_thread_) =
       kHandshakeInit;
-  bool connected_to_transport_ RTC_GUARDED_BY(network_thread_) = false;
   // Did we already start the graceful SCTP closing procedure?
   bool started_closing_procedure_ RTC_GUARDED_BY(network_thread_) = false;
   // Control messages that always have to get sent out before any queued
@@ -294,6 +301,8 @@ class SctpDataChannel : public DataChannelInterface {
   PacketQueue queued_control_data_ RTC_GUARDED_BY(network_thread_);
   PacketQueue queued_received_data_ RTC_GUARDED_BY(network_thread_);
   PacketQueue queued_send_data_ RTC_GUARDED_BY(network_thread_);
+  rtc::scoped_refptr<PendingTaskSafetyFlag> network_safety_ =
+      PendingTaskSafetyFlag::CreateDetachedInactive();
 };
 
 }  // namespace webrtc