Make TCPConnectedSocketObserver an optional param

There are users of TCP socket APIs who do not care about the specific read/write
errors. One example is net::HttpServer.
This CL makes the observer param optional.

Bug: 721401
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_mojo
Change-Id: I028a01b6b8e3dea87a3865b704cc15347a3f2793
Reviewed-on: https://chromium-review.googlesource.com/978033Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Matt Menke <mmenke@chromium.org>
Commit-Queue: Helen Li <xunjieli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#546095}

services/network/public/mojom/network_service.mojom

@@ -213,14 +213,15 @@ interface NetworkContext {
                         TCPServerSocket& socket)
       => (int32 result, net.interfaces.IPEndPoint? local_addr_out);
 
-  // Creates a TCP socket connected to |remote_addr|. |observer| will be used
-  // to listen for any network connection error on the newly established
-  // connection. The socket created can only be used for the purpose specified
-  // in |traffic_annotation|, and cannot be re-used for other purposes.
-  // |local_addr| should be set to null unless the caller wants to bind the
-  // socket to a specific address and port. On success, |result| is net::OK.
-  // Caller is to use |send_stream| to send data and |receive_stream| to receive
-  // data over the connection. On failure, |result| is a network error code.
+  // Creates a TCP socket connected to |remote_addr|. |observer| if non-null
+  // will be used to listen for any network connection error on the newly
+  // established connection. The socket created can only be used for the purpose
+  // specified in |traffic_annotation|, and cannot be re-used for other
+  // purposes. |local_addr| should be set to null unless the caller wants to
+  // bind the socket to a specific address and port. On success, |result| is
+  // net::OK. Caller is to use |send_stream| to send data and |receive_stream|
+  // to receive data over the connection. On failure, |result| is a network
+  // error code.
   //
   // Any sockets that are created but are yet to be destroyed will be destroyed
   // when NetworkContext goes away.
@@ -229,7 +230,7 @@ interface NetworkContext {
       net.interfaces.AddressList remote_addr_list,
       MutableNetworkTrafficAnnotationTag traffic_annotation,
       TCPConnectedSocket& socket,
-      TCPConnectedSocketObserver observer)
+      TCPConnectedSocketObserver? observer)
      => (int32 result,
          handle<data_pipe_consumer>? receive_stream,
          handle<data_pipe_producer>? send_stream);

services/network/public/mojom/tcp_socket.mojom

@@ -35,16 +35,17 @@ interface TCPConnectedSocketObserver {
 // Represents a TCP server socket that has been successfully bound to a local
 // address. Caller can close the socket by destroying the interface pointer.
 interface TCPServerSocket {
-  // Waits for an incoming connection request. On success, returns net::OK,
-  // |remote_addr| represents the peer address, |connected_socket| is the new
-  // connection established. Caller uses |send_stream| to send data and
-  // |receive_stream| for receiving data over the new connection. On failure,
-  // |net_error| is a net error code and other fields are null.
-  // Up to |backlog| Accept()s can be pending at a time. |backlog| is a
-  // number that is specified when requesting TCPServerSocket. If more than
-  // |backlog| number of Accept()s are outstanding,
+  // Waits for an incoming connection request. |observer| if non-null will be
+  // used to listen for any network connection error on the newly established
+  // connection. On success, returns net::OK, |remote_addr| represents the peer
+  // address, |connected_socket| is the new connection established. Caller uses
+  // |send_stream| to send data and |receive_stream| for receiving data over the
+  // new connection. On failure, |net_error| is a net error code and other
+  // fields are null. Up to |backlog| Accept()s can be pending at a time.
+  // |backlog| is a number that is specified when requesting TCPServerSocket. If
+  // more than |backlog| number of Accept()s are outstanding,
   // net::ERR_INSUFFICIENT_RESOUCES will be returned.
-  Accept(TCPConnectedSocketObserver observer)
+  Accept(TCPConnectedSocketObserver? observer)
       => (int32 net_error,
           net.interfaces.IPEndPoint? remote_addr,
           TCPConnectedSocket? connected_socket,

services/network/tcp_connected_socket.cc

@@ -27,9 +27,6 @@ TCPConnectedSocket::TCPConnectedSocket(
       writable_handle_watcher_(FROM_HERE,
                                mojo::SimpleWatcher::ArmingPolicy::MANUAL),
       traffic_annotation_(traffic_annotation) {
-  // TODO(xunjieli): Consider supporting null |observer_|, if there are
-  // consumers who do not care about read/write errors.
-  DCHECK(observer_);
 }
 
 TCPConnectedSocket::TCPConnectedSocket(
@@ -165,7 +162,7 @@ void TCPConnectedSocket::OnReceiveStreamWritable(MojoResult result) {
 void TCPConnectedSocket::OnNetworkReadCompleted(int bytes_read) {
   DCHECK(pending_receive_);
 
-  if (bytes_read < 0)
+  if (bytes_read < 0 && observer_)
     observer_->OnReadError(bytes_read);
 
   if (bytes_read <= 0) {
@@ -225,7 +222,7 @@ void TCPConnectedSocket::OnSendStreamReadable(MojoResult result) {
 void TCPConnectedSocket::OnNetworkWriteCompleted(int bytes_written) {
   DCHECK(pending_send_);
 
-  if (bytes_written < 0)
+  if (bytes_written < 0 && observer_)
     observer_->OnWriteError(bytes_written);
   if (bytes_written <= 0) {
     ShutdownSend();