Node.js, protobuffer, buffer.lentgh.. how to send structured buffer/message trough tcp?

I had wrote a node/ssjs program that makes:

• Tcp connection to data server(Apache MIMA), using TLS module. (OK)
• Encode/decode(serialize/deserialize) messages through protobuffer module.. (OK)
• Send serialized message to server and get response. (Not OK).

The server´s manual types:

Structure of message:
[ Length | Header length | Header (| Body length |Body) ]
Length – message length = fixed size (4 bytes). Note that this is only the size of
         following message (not the prefix itself);
Header  length – fixed size (4 bytes);
Header – contains message metadata (e.g. messageId);
Body length – fixed size (4 bytes, optional). If body is not required, body size is 
              not serialized. In such case, message is 4 (message length) + 4 
              (header length) + length(header) bytes long.
Body – the message payload (optional). If body is not present (e.g. response
       notification without data) it is not serialized.

Length [bytes]  Content    
4               Whole message length       
4               Header message length (H_LEN)      
H_LEN           Protocol Buffers encoded MessageHeaderProto    
4               Body message length (B_LEN), optional      
B_LEN           Protocol Buffers encoded Message

My questions are:

• How to get the 4-bytes-length of a protobuffer?
• How to concatenate those buffers before send?
• How to send?
• Is it possible to do with JavaScript? Observation: The server uses Little Endian byte order, client side too.

Thank you all...