Example of how to interpose yourself in a message stream.

ipc/ipc_sync_channel.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ipc/ipc_sync_channel.h"
 
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/message_loop.h"
 #include "base/threading/thread_local.h"
@@ skipping 382 matching lines @@
 
 void SyncChannel::SetRestrictDispatchToSameChannel(bool value) {
   sync_context()->set_restrict_dispatch(value);
 }
 
 bool SyncChannel::Send(Message* message) {
   return SendWithTimeout(message, base::kNoTimeout);
 }
 
 bool SyncChannel::SendWithTimeout(Message* message, int timeout_ms) {
+  if (outgoing_message_filter())

[jam, 2011/05/02 20:06:11]

this should be done in ChannelProxy::Send

+    message = outgoing_message_filter()->Rewrite(message);
+
   if (!message->is_sync()) {
     ChannelProxy::Send(message);
     return true;
   }
 
   // *this* might get deleted in WaitForReply.
   scoped_refptr<SyncContext> context(sync_context());
   if (context->shutdown_event()->IsSignaled()) {
     delete message;
     return false;
@@ skipping 90 matching lines @@
 void SyncChannel::OnWaitableEventSignaled(WaitableEvent* event) {
   DCHECK(event == sync_context()->GetDispatchEvent());
   // The call to DispatchMessages might delete this object, so reregister
   // the object watcher first.
   event->Reset();
   dispatch_watcher_.StartWatching(event, this);
   sync_context()->DispatchMessages();
 }
 
 }  // namespace IPC