Make Communicator::push() works with multiple message wrappers.

src/kernel/Communicator.cc

@@ -2004,7 +2004,7 @@ int Communicator::push(const void *buf, size_t size, CommSession *session)
 		(!session->passive && in->entry->session == session) ||
 		session->passive == 1)
 	{
-		ret = in->CommMessageIn::feedback(buf, size);
+		ret = in->inner()->feedback(buf, size);
 	}
 	else
 	{

src/kernel/Communicator.h

@@ -116,6 +116,9 @@ protected:
 	/* In append(), reset the begin time of receiving to current time. */
 	virtual void renew();
 
+	/* Return the deepest wrapped message. */
+	virtual CommMessageIn *inner() { return this; }
+
 private:
 	struct CommConnEntry *entry;
 

src/protocol/ProtocolMessage.h

@@ -89,6 +89,8 @@ protected:
 			return this->CommMessageIn::renew();
 	}
 
+	virtual ProtocolMessage *inner() { return this; }
+
 protected:
 	size_t size_limit;
 
@@ -145,6 +147,12 @@ protected:
 		return this->msg->append(buf, size);
 	}
 
+protected:
+	virtual ProtocolMessage *inner()
+	{
+		return this->msg->inner();
+	}
+
 protected:
 	ProtocolMessage *msg;