Add experiment to use ::recvmsg to receive packets on posix systems

Using ::recvmsg ensure packet timestamp can then be read directly when reading the buffer
instead of a separate system call and should also work on Ios/Mac.

The same experiment field trial flag will be "WebRTC-SCM-Timestamp/enabled/" and is also planned to be used for fixing webrtc:14066

Bug: webrtc:5773, webrtc:14066
Change-Id: I8a3749e87c686aa18fcee947472c1b602a0f63c8
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/279280
Reviewed-by: Evan Shrubsole <eshr@webrtc.org>
Commit-Queue: Per Kjellander <perkj@webrtc.org>
Reviewed-by: Jonas Oreland <jonaso@webrtc.org>
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#38585}

5 files changed, 132 insertions, 20 deletions

diff --git a/rtc_base/BUILD.gn b/rtc_base/BUILD.gn
index b171b162bf..c5b9024cc1 100644
--- a/rtc_base/BUILD.gn
+++ b/rtc_base/BUILD.gn
@@ -961,6 +961,7 @@ rtc_library("threading") {
     "../api/task_queue",
     "../api/task_queue:pending_task_safety_flag",
     "../api/units:time_delta",
+    "../system_wrappers:field_trial",
     "synchronization:mutex",
     "system:no_unique_address",
     "system:rtc_export",
@@ -1498,6 +1499,7 @@ if (rtc_include_tests) {
         ":timeutils",
         "../api/units:time_delta",
         "../system_wrappers",
+        "../test:field_trial",
         "../test:fileutils",
         "../test:test_main",
         "../test:test_support",
diff --git a/rtc_base/physical_socket_server.cc b/rtc_base/physical_socket_server.cc
index 7c01815d30..b7d69140e0 100644
--- a/rtc_base/physical_socket_server.cc
+++ b/rtc_base/physical_socket_server.cc
@@ -52,6 +52,7 @@
 #include "rtc_base/null_socket_server.h"
 #include "rtc_base/synchronization/mutex.h"
 #include "rtc_base/time_utils.h"
+#include "system_wrappers/include/field_trial.h"
 
 #if defined(WEBRTC_LINUX)
 #include <linux/sockios.h>
@@ -118,6 +119,12 @@ class ScopedSetTrue {
  private:
   bool* value_;
 };
+
+// Returns true if the the client is in the experiment to get timestamps
+// from the socket implementation.
+bool IsScmTimeStampExperimentEnabled() {
+  return webrtc::field_trial::IsEnabled("WebRTC-SCM-Timestamp");
+}
 }  // namespace
 
 namespace rtc {
@@ -127,7 +134,8 @@ PhysicalSocket::PhysicalSocket(PhysicalSocketServer* ss, SOCKET s)
       s_(s),
       error_(0),
       state_((s == INVALID_SOCKET) ? CS_CLOSED : CS_CONNECTED),
-      resolver_(nullptr) {
+      resolver_(nullptr),
+      read_scm_timestamp_experiment_(IsScmTimeStampExperimentEnabled()) {
   if (s_ != INVALID_SOCKET) {
     SetEnabledEvents(DE_READ | DE_WRITE);
 
@@ -395,7 +403,7 @@ int PhysicalSocket::SendTo(const void* buffer,
 
 int PhysicalSocket::Recv(void* buffer, size_t length, int64_t* timestamp) {
   int received =
-      ::recv(s_, static_cast<char*>(buffer), static_cast<int>(length), 0);
+      DoReadFromSocket(buffer, length, /*out_addr*/ nullptr, timestamp);
   if ((received == 0) && (length != 0)) {
     // Note: on graceful shutdown, recv can return 0.  In this case, we
     // pretend it is blocking, and then signal close, so that simplifying
@@ -407,9 +415,7 @@ int PhysicalSocket::Recv(void* buffer, size_t length, int64_t* timestamp) {
     SetError(EWOULDBLOCK);
     return SOCKET_ERROR;
   }
-  if (timestamp) {
-    *timestamp = GetSocketRecvTimestamp(s_);
-  }
+
   UpdateLastError();
   int error = GetError();
   bool success = (received >= 0) || IsBlockingError(error);
@@ -426,17 +432,8 @@ int PhysicalSocket::RecvFrom(void* buffer,
                              size_t length,
                              SocketAddress* out_addr,
                              int64_t* timestamp) {
-  sockaddr_storage addr_storage;
-  socklen_t addr_len = sizeof(addr_storage);
-  sockaddr* addr = reinterpret_cast<sockaddr*>(&addr_storage);
-  int received = ::recvfrom(s_, static_cast<char*>(buffer),
-                            static_cast<int>(length), 0, addr, &addr_len);
-  if (timestamp) {
-    *timestamp = GetSocketRecvTimestamp(s_);
-  }
+  int received = DoReadFromSocket(buffer, length, out_addr, timestamp);
   UpdateLastError();
-  if ((received >= 0) && (out_addr != nullptr))
-    SocketAddressFromSockAddrStorage(addr_storage, out_addr);
   int error = GetError();
   bool success = (received >= 0) || IsBlockingError(error);
   if (udp_ || success) {
@@ -448,6 +445,84 @@ int PhysicalSocket::RecvFrom(void* buffer,
   return received;
 }
 
+int PhysicalSocket::DoReadFromSocket(void* buffer,
+                                     size_t length,
+                                     SocketAddress* out_addr,
+                                     int64_t* timestamp) {
+  sockaddr_storage addr_storage;
+  socklen_t addr_len = sizeof(addr_storage);
+  sockaddr* addr = reinterpret_cast<sockaddr*>(&addr_storage);
+
+#if defined(WEBRTC_POSIX)
+  int received = 0;
+  if (read_scm_timestamp_experiment_) {
+    iovec iov = {.iov_base = buffer, .iov_len = length};
+    msghdr msg = {.msg_iov = &iov, .msg_iovlen = 1};
+    if (out_addr) {
+      out_addr->Clear();
+      msg.msg_name = addr;
+      msg.msg_namelen = addr_len;
+    }
+    char control[CMSG_SPACE(sizeof(struct timeval))] = {};
+    if (timestamp) {
+      *timestamp = -1;
+      msg.msg_control = &control;
+      msg.msg_controllen = sizeof(control);
+    }
+    received = ::recvmsg(s_, &msg, 0);
+    if (received <= 0) {
+      // An error occured or shut down.
+      return received;
+    }
+    if (timestamp) {
+      struct cmsghdr* cmsg;
+      for (cmsg = CMSG_FIRSTHDR(&msg); cmsg; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
+        if (cmsg->cmsg_level != SOL_SOCKET)
+          continue;
+        if (cmsg->cmsg_type == SCM_TIMESTAMP) {
+          timeval* ts = reinterpret_cast<timeval*>(CMSG_DATA(cmsg));
+          *timestamp =
+              rtc::kNumMicrosecsPerSec * static_cast<int64_t>(ts->tv_sec) +
+              static_cast<int64_t>(ts->tv_usec);
+          break;
+        }
+      }
+    }
+    if (out_addr) {
+      SocketAddressFromSockAddrStorage(addr_storage, out_addr);
+    }
+  } else {  // !read_scm_timestamp_experiment_
+    if (out_addr) {
+      received = ::recvfrom(s_, static_cast<char*>(buffer),
+                            static_cast<int>(length), 0, addr, &addr_len);
+      SocketAddressFromSockAddrStorage(addr_storage, out_addr);
+    } else {
+      received =
+          ::recv(s_, static_cast<char*>(buffer), static_cast<int>(length), 0);
+    }
+    if (timestamp) {
+      *timestamp = GetSocketRecvTimestamp(s_);
+    }
+  }
+  return received;
+
+#else
+  int received = 0;
+  if (out_addr) {
+    received = ::recvfrom(s_, static_cast<char*>(buffer),
+                          static_cast<int>(length), 0, addr, &addr_len);
+    SocketAddressFromSockAddrStorage(addr_storage, out_addr);
+  } else {
+    received =
+        ::recv(s_, static_cast<char*>(buffer), static_cast<int>(length), 0);
+  }
+  if (timestamp) {
+    *timestamp = -1;
+  }
+  return received;
+#endif
+}
+
 int PhysicalSocket::Listen(int backlog) {
   int err = ::listen(s_, backlog);
   UpdateLastError();
@@ -643,7 +718,16 @@ bool SocketDispatcher::Initialize() {
   ioctlsocket(s_, FIONBIO, &argp);
 #elif defined(WEBRTC_POSIX)
   fcntl(s_, F_SETFL, fcntl(s_, F_GETFL, 0) | O_NONBLOCK);
+  if (IsScmTimeStampExperimentEnabled()) {
+    int value = 1;
+    // Attempt to get receive packet timestamp from the socket.
+    if (::setsockopt(s_, SOL_SOCKET, SO_TIMESTAMP, &value, sizeof(value)) !=
+        0) {
+      RTC_DLOG(LS_ERROR) << "::setsockopt failed. errno: " << LAST_SYSTEM_ERROR;
+    }
+  }
 #endif
+
 #if defined(WEBRTC_IOS)
   // iOS may kill sockets when the app is moved to the background
   // (specifically, if the app doesn't use the "voip" UIBackgroundMode). When
@@ -651,7 +735,9 @@ bool SocketDispatcher::Initialize() {
   // default will terminate the process, which we don't want. By specifying
   // this socket option, SIGPIPE will be disabled for the socket.
   int value = 1;
-  ::setsockopt(s_, SOL_SOCKET, SO_NOSIGPIPE, &value, sizeof(value));
+  if (::setsockopt(s_, SOL_SOCKET, SO_NOSIGPIPE, &value, sizeof(value)) != 0) {
+    RTC_DLOG(LS_ERROR) << "::setsockopt failed. errno: " << LAST_SYSTEM_ERROR;
+  }
 #endif
   ss_->Add(this);
   return true;
diff --git a/rtc_base/physical_socket_server.h b/rtc_base/physical_socket_server.h
index f97271f422..5a3acbf84f 100644
--- a/rtc_base/physical_socket_server.h
+++ b/rtc_base/physical_socket_server.h
@@ -190,6 +190,11 @@ class PhysicalSocket : public Socket, public sigslot::has_slots<> {
                        const struct sockaddr* dest_addr,
                        socklen_t addrlen);
 
+  int DoReadFromSocket(void* buffer,
+                       size_t length,
+                       SocketAddress* out_addr,
+                       int64_t* timestamp);
+
   void OnResolveResult(AsyncResolverInterface* resolver);
 
   void UpdateLastError();
@@ -216,6 +221,7 @@ class PhysicalSocket : public Socket, public sigslot::has_slots<> {
 #endif
 
  private:
+  const bool read_scm_timestamp_experiment_;
   uint8_t enabled_events_ = 0;
 };
 
diff --git a/rtc_base/physical_socket_server_unittest.cc b/rtc_base/physical_socket_server_unittest.cc
index 3da777a235..5d1ab5a4fd 100644
--- a/rtc_base/physical_socket_server_unittest.cc
+++ b/rtc_base/physical_socket_server_unittest.cc
@@ -23,6 +23,7 @@
 #include "rtc_base/socket_unittest.h"
 #include "rtc_base/test_utils.h"
 #include "rtc_base/thread.h"
+#include "test/field_trial.h"
 #include "test/gtest.h"
 
 namespace rtc {
@@ -460,8 +461,9 @@ TEST_F(PhysicalSocketTest, TestGetSetOptionsIPv6) {
 
 #if defined(WEBRTC_POSIX)
 
-// We don't get recv timestamps on Mac.
 #if !defined(WEBRTC_MAC)
+// We don't get recv timestamps on Mac without the experiment
+// WebRTC-SCM-Timestamp
 TEST_F(PhysicalSocketTest, TestSocketRecvTimestampIPv4) {
   MAYBE_SKIP_IPV4;
   SocketTest::TestSocketRecvTimestampIPv4();
@@ -472,6 +474,16 @@ TEST_F(PhysicalSocketTest, TestSocketRecvTimestampIPv6) {
 }
 #endif
 
+TEST_F(PhysicalSocketTest, TestSocketRecvTimestampIPv4ScmExperiment) {
+  MAYBE_SKIP_IPV4;
+  webrtc::test::ScopedFieldTrials trial("WebRTC-SCM-Timestamp/Enabled/");
+  SocketTest::TestSocketRecvTimestampIPv4();
+}
+
+TEST_F(PhysicalSocketTest, TestSocketRecvTimestampIPv6ScmExperiment) {
+  webrtc::test::ScopedFieldTrials trial("WebRTC-SCM-Timestamp/Enabled/");
+  SocketTest::TestSocketRecvTimestampIPv6();
+}
 // Verify that if the socket was unable to be bound to a real network interface
 // (not loopback), Bind will return an error.
 TEST_F(PhysicalSocketTest,
diff --git a/rtc_base/socket_unittest.cc b/rtc_base/socket_unittest.cc
index ea6407ae6e..8e76d343f6 100644
--- a/rtc_base/socket_unittest.cc
+++ b/rtc_base/socket_unittest.cc
@@ -1070,25 +1070,31 @@ void SocketTest::GetSetOptionsInternal(const IPAddress& loopback) {
 }
 
 void SocketTest::SocketRecvTimestamp(const IPAddress& loopback) {
+  StreamSink sink;
   std::unique_ptr<Socket> socket(
       socket_factory_->CreateSocket(loopback.family(), SOCK_DGRAM));
   EXPECT_EQ(0, socket->Bind(SocketAddress(loopback, 0)));
   SocketAddress address = socket->GetLocalAddress();
+  sink.Monitor(socket.get());
 
   int64_t send_time_1 = TimeMicros();
   socket->SendTo("foo", 3, address);
+
   int64_t recv_timestamp_1;
+  // Wait until data is available.
+  EXPECT_TRUE_WAIT(sink.Check(socket.get(), SSE_READ), kTimeout);
   char buffer[3];
-  socket->RecvFrom(buffer, 3, nullptr, &recv_timestamp_1);
-  EXPECT_GT(recv_timestamp_1, -1);
+  ASSERT_GT(socket->RecvFrom(buffer, 3, nullptr, &recv_timestamp_1), 0);
 
   const int64_t kTimeBetweenPacketsMs = 100;
   Thread::SleepMs(kTimeBetweenPacketsMs);
 
   int64_t send_time_2 = TimeMicros();
   socket->SendTo("bar", 3, address);
+  // Wait until data is available.
+  EXPECT_TRUE_WAIT(sink.Check(socket.get(), SSE_READ), kTimeout);
   int64_t recv_timestamp_2;
-  socket->RecvFrom(buffer, 3, nullptr, &recv_timestamp_2);
+  ASSERT_GT(socket->RecvFrom(buffer, 3, nullptr, &recv_timestamp_2), 0);
 
   int64_t system_time_diff = send_time_2 - send_time_1;
   int64_t recv_timestamp_diff = recv_timestamp_2 - recv_timestamp_1;