Create new class "CastTransport", which encapsulates the message read and write event loops.

extensions/browser/api/cast_channel/cast_message_util.cc

 // Copyright 2014 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 "extensions/browser/api/cast_channel/cast_message_util.h"
 
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/values.h"
@@ skipping 44 matching lines @@
       }
       break;
     default:
       // Unknown value type.  message_proto will remain uninitialized because
       // payload_type is unset.
       break;
   }
   return message_proto->IsInitialized();
 }
 
+bool ValidateCastMessage(const CastMessage& message_proto) {

[mark a. foltz, 2014/09/11 06:47:45]

I think there are also restrictions on namespace (non-empty string), sourceId
and destinationId (both non-empty, with legal values).

Is the intention for this to catch all semantic errors?

[Kevin M, 2014/09/11 18:07:58]

Yes. Done.

+  return (message_proto.payload_type() == CastMessage_PayloadType_STRING &&
+          message_proto.has_payload_utf8()) ||
+         (message_proto.payload_type() == CastMessage_PayloadType_BINARY &&
+          message_proto.has_payload_binary());
+}
+
 bool CastMessageToMessageInfo(const CastMessage& message_proto,
                               MessageInfo* message) {
   DCHECK(message);
   message->source_id = message_proto.source_id();
   message->destination_id = message_proto.destination_id();
   message->namespace_ = message_proto.namespace_();
   // Determine the type of the payload and fill base::Value appropriately.
   scoped_ptr<base::Value> value;
   switch (message_proto.payload_type()) {
   case CastMessage_PayloadType_STRING:
@@ skipping 66 matching lines @@
   message_proto->set_payload_binary(auth_message_string);
 }
 
 bool IsAuthMessage(const CastMessage& message) {
   return message.namespace_() == kAuthNamespace;
 }
 
 }  // namespace cast_channel
 }  // namespace core_api
 }  // namespace extensions