Report the correct os_error in the SOCKET_READ_ERROR event

net/socket/tcp_client_socket_win.cc

Index: net/socket/tcp_client_socket_win.cc
===================================================================
--- net/socket/tcp_client_socket_win.cc	(revision 187920)
+++ net/socket/tcp_client_socket_win.cc	(working copy)
@@ -957,7 +957,6 @@
   DWORD num_bytes, flags;
   BOOL ok = WSAGetOverlappedResult(socket_, &core_->read_overlapped_,
                                    &num_bytes, FALSE, &flags);
-  WSAResetEvent(core_->read_overlapped_.hEvent);
   waiting_read_ = false;
   int rv;
   if (ok) {
@@ -975,6 +974,7 @@
     net_log_.AddEvent(NetLog::TYPE_SOCKET_READ_ERROR,
                       CreateNetLogSocketErrorCallback(rv, os_error));
   }
+  WSAResetEvent(core_->read_overlapped_.hEvent);
   core_->read_iobuffer_ = NULL;
   core_->read_buffer_length_ = 0;
   DoReadCallback(rv);
@@ -1025,22 +1025,29 @@
   if (rv == SOCKET_ERROR) {
     os_error = WSAGetLastError();
     rv = MapSystemError(os_error);
-  } else if (network_events.lNetworkEvents & FD_READ) {
+  } else if (network_events.lNetworkEvents) {
+    DCHECK_EQ(network_events.lNetworkEvents & ~(FD_READ | FD_CLOSE), 0);
+    // If network_events.lNetworkEvents is FD_CLOSE and
+    // network_events.iErrorCode[FD_CLOSE_BIT] is 0, it is a graceful
+    // connection closure. It is tempting to directly set rv to 0 in
+    // this case, but the MSDN pages for WSAEventSelect and
+    // WSAAsyncSelect recommend we still call DoRead():
+    //   FD_CLOSE should only be posted after all data is read from a
+    //   socket, but an application should check for remaining data upon
+    //   receipt of FD_CLOSE to avoid any possibility of losing data.
+    //
+    // If network_events.iErrorCode[FD_READ_BIT] or
+    // network_events.iErrorCode[FD_CLOSE_BIT] is nonzero, still call
+    // DoRead() because recv() reports a more accurate error code
+    // (WSAECONNRESET vs. WSAECONNABORTED) when the connection was
+    // reset.
     rv = DoRead(core_->read_iobuffer_, core_->read_buffer_length_,
                 read_callback_);
     if (rv == ERR_IO_PENDING)
       return;
-  } else if (network_events.lNetworkEvents & FD_CLOSE) {
-    if (network_events.iErrorCode[FD_CLOSE_BIT]) {
-      rv = MapSystemError(network_events.iErrorCode[FD_CLOSE_BIT]);
-      net_log_.AddEvent(NetLog::TYPE_SOCKET_READ_ERROR,
-                        CreateNetLogSocketErrorCallback(rv, os_error));
-    } else {
-      rv = 0;
-    }
   } else {
-    // This should not happen but I have seen cases where we will get
-    // signaled but the network events flags are all clear (0).
+    // This may happen because Read() may succeed synchronously and
+    // consume all the received data without resetting the event object.
     core_->WatchForRead();
     return;
   }