remoting: Obtain max message size dynamically.

Previously, clipboard messages were capped at the default safe size of
64KiB. This patchset raises the limit when the session descriptor
indicates that a larger size is supported.

Bug: 988865
Change-Id: I651c4e0a5aa96b84950eb4fa8f798af7579eff85
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1726277
Commit-Queue: Erik Jensen <rkjnsn@chromium.org>
Reviewed-by: Joe Downing <joedow@chromium.org>
Auto-Submit: Erik Jensen <rkjnsn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#682400}

remoting/protocol/host_control_dispatcher.cc

@@ -18,12 +18,6 @@
 namespace remoting {
 namespace protocol {
 
-namespace {
-// It seems Chrome currently only properly supports receiving messages up to
-// 64KiB.
-constexpr int kMaxSafeMessageSizeInBytes = 64 * 1024;
-}  // namespace
-
 HostControlDispatcher::HostControlDispatcher()
     : ChannelDispatcherBase(kControlChannelName) {}
 HostControlDispatcher::~HostControlDispatcher() = default;
@@ -58,9 +52,12 @@ void HostControlDispatcher::SetVideoLayout(const VideoLayout& layout) {
 void HostControlDispatcher::InjectClipboardEvent(const ClipboardEvent& event) {
   ControlMessage message;
   message.mutable_clipboard_event()->CopyFrom(event);
-  if (message.ByteSizeLong() > kMaxSafeMessageSizeInBytes) {
+  std::size_t message_size = message.ByteSizeLong();
+  if (message_size > max_message_size_) {
     // Better to drop the event than drop the connection, which can happen if
     // the browser receives a message larger than it can handle.
+    LOG(WARNING) << "Clipboard message dropped because message size "
+                 << message_size << " is larger than " << max_message_size_;
     return;
   }
   message_pipe()->Send(&message, base::Closure());

remoting/protocol/host_control_dispatcher.h

@@ -5,6 +5,8 @@
 #ifndef REMOTING_PROTOCOL_HOST_CONTROL_DISPATCHER_H_
 #define REMOTING_PROTOCOL_HOST_CONTROL_DISPATCHER_H_
 
+#include <cstddef>
+
 #include "base/macros.h"
 #include "remoting/protocol/channel_dispatcher_base.h"
 #include "remoting/protocol/client_stub.h"
@@ -48,11 +50,23 @@ class HostControlDispatcher : public ChannelDispatcherBase,
   // message. |host_stub| must outlive this object.
   void set_host_stub(HostStub* host_stub) { host_stub_ = host_stub; }
 
+  // Sets the maximum size of outgoing messages, which defaults to 64KiB. This
+  // is used to ensure we don't try to send any clipboard messages that the
+  // client can't receive. Clipboard updates that are larger than the maximum
+  // message size will be dropped.
+  void set_max_message_size(std::size_t max_message_size) {
+    LOG(INFO) << "Setting maximum message size to " << max_message_size;
+    max_message_size_ = max_message_size;
+  }
+
  private:
   void OnIncomingMessage(std::unique_ptr<CompoundBuffer> buffer) override;
 
   ClipboardStub* clipboard_stub_ = nullptr;
   HostStub* host_stub_ = nullptr;
+  // 64 KiB is the default message size expected to be supported in absence of
+  // a higher value negotiated via SDP.
+  std::size_t max_message_size_ = 64 * 1024;
 
   DISALLOW_COPY_AND_ASSIGN(HostControlDispatcher);
 };

remoting/protocol/webrtc_connection_to_client.cc

@@ -26,6 +26,7 @@
 #include "remoting/protocol/webrtc_video_stream.h"
 #include "third_party/webrtc/api/media_stream_interface.h"
 #include "third_party/webrtc/api/peer_connection_interface.h"
+#include "third_party/webrtc/api/sctp_transport_interface.h"
 
 namespace remoting {
 namespace protocol {
@@ -179,6 +180,14 @@ void WebrtcConnectionToClient::OnWebrtcTransportConnecting() {
 
 void WebrtcConnectionToClient::OnWebrtcTransportConnected() {
   DCHECK(thread_checker_.CalledOnValidThread());
+  auto sctp_transport = transport_->peer_connection()->GetSctpTransport();
+  if (sctp_transport) {
+    absl::optional<double> max_message_size =
+        sctp_transport->Information().MaxMessageSize();
+    if (max_message_size && *max_message_size > 0) {
+      control_dispatcher_->set_max_message_size(*max_message_size);
+    }
+  }
 }
 
 void WebrtcConnectionToClient::OnWebrtcTransportError(ErrorCode error) {