Question

I would like to encode the contents of my byte[] variable before sending it using asynchronous socket.

private void SendDatabaseObj(Socket handler, BuildHistoryClass buildHistoryQueryResult)
{
    byte[] byteData = ObjectToByteArray(buildHistoryQueryResult);

    // Begin sending the data to the remote device.
    handler.BeginSend(byteData, 0, byteData.Length, 0,
        new AsyncCallback(SendCallback), handler);
}

buildHistoryQueryResult is serialize using this function:

private byte[] ObjectToByteArray(BuildHistoryClass obj)
{
    BinaryFormatter bf = new BinaryFormatter();
    MemoryStream ms = new MemoryStream();
    bf.Serialize(ms, obj);
    return ms.ToArray();
}

What would be “proper” encoding format because I am getting an exception in my receiver:

SerializationException was caught
The input stream is not a valid binary format. The starting contents (in bytes) are: 04-00-00-00-06-0F-00-00-00-04-54-72-75-65-06-10-00 …

Receiving side:

        private void ReceiveCallback_onQuery(IAsyncResult ar)
        {
            try
            {
                // Retrieve the state object and the client socket 
                // from the asynchronous state object.
                StateObject state = (StateObject)ar.AsyncState;
                Socket client = state.workSocket;

                // Read data from the remote device.
                int bytesRead = client.EndReceive(ar);

                if (bytesRead > 0)
                {
                    // There might be more data, so store the data received so far.
                    state.sb.Append(state.buffer);

                    // Get the rest of the data.
                    client.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0,
                        new AsyncCallback(ReceiveCallback_onQuery), state);
                }
                else
                {
                    // All the data has arrived; put it in response.
                    if (state.sb.Length > 1)
                    {
                        response_onQueryHistory = ByteArrayToObject(state.buffer);
                    }
                    // Signal that all bytes have been received.
                    receiveDoneQuery.Set();
                }
            }
            catch (Exception e)
            {
                Console.WriteLine(e.ToString());
            }
        }

De-serializing function:

        private BuildHistoryClass ByteArrayToObject(byte[] arrayBytes)
        {
            MemoryStream ms = new MemoryStream();
            BinaryFormatter bf = new BinaryFormatter();
            ms.Write(arrayBytes, 0, arrayBytes.Length);
            ms.Seek(0, SeekOrigin.Begin);
            BuildHistoryClass obj = (BuildHistoryClass)bf.Deserialize(ms);
            return obj;
        }

Answer 1

Your own code has a bug, and it may be the cause of the SerializationException.
On the receiving side you have the following code and comment:

// There might be more data, so store the data received so far.
state.sb.Append(state.buffer);

Yet later (after all data has been received) you have the following:

// All the data has arrived; put it in response.
if (state.sb.Length > 1)
{
    response_onQueryHistory = ByteArrayToObject(state.buffer);
}

Note that you are de-serialising the state.buffer where you should be de-serialising whatever is in state.sb