title: C# sending byte array over socket
body: <p>I've been trying to send a byte array from client to server to build a authentication server.</p>
  
  <p>I have send the byte array succesfully using the Microsoft asynchronous server socket example. <a href="https://docs.microsoft.com/en-us/dotnet/framework/network-programming/asynchronous-server-socket-example" rel="nofollow noreferrer">link</a>
  But in their example they are using string to indiate end of byte transfer. </p>
  
  <pre><code>content.IndexOf("&lt;EOF&gt;") &gt; -1
  </code></pre>
  
  <p>I don't like this approach and removed it, so the server keeps waiting for a messages from the client until the client or server packet handler decides to close the socket.</p>
  
  <p><strong>I don't understand the need of a string to indicate the end of transfer</strong>. I can check this by array length?
  <strong>Is the approach I am using safe enough to ensure the data integrity?</strong></p>
  
  <p>My code server side:
  The changes are made in the method: ReadCallback</p>
  
  <pre><code>public class AsynchronousSocketListener
  {
      // Thread signal.  
      public static ManualResetEvent allDone = new ManualResetEvent(false);
  
      public AsynchronousSocketListener()
      {
      }
  
      public static void StartListening(String hostname, int port)
      {
          // Establish the local endpoint for the socket.  
          // The DNS name of the computer  
          // example running the listener is "localhost".  
          IPHostEntry ipHostInfo = Dns.GetHostEntry(hostname);
          IPAddress ipAddress = ipHostInfo.AddressList[0];
          IPEndPoint localEndPoint = new IPEndPoint(ipAddress, port);
  
          // Create a TCP/IP socket.  
          Socket listener = new Socket(ipAddress.AddressFamily,
              SocketType.Stream, ProtocolType.Tcp);
  
          try
          {
              // Bind the socket to the local endpoint and listen for incoming connections.  
              listener.Bind(localEndPoint);
              listener.Listen(100);
  
              // Do not stop after one connection
              while (true)
              {
                  // Set the event to nonsignaled state.  
                  allDone.Reset();
  
                  // Start an asynchronous socket to listen for connections.  
                  Console.WriteLine("Listening for new connection");
                  listener.BeginAccept(
                      new AsyncCallback(AcceptCallback),
                      listener);
  
                  // Wait until a connection is made before listening again
                  // for a new connection.  
                  allDone.WaitOne();
                  Console.WriteLine("Connection established.");
  
              }
  
          }
          catch (Exception e)
          {
              Console.WriteLine(e.ToString());
          }
  
          Console.WriteLine("\nPress ENTER to continue...");
          Console.Read();
  
      }
  
      public static void AcceptCallback(IAsyncResult ar)
      {
          // Signal the main thread to continue.  
          allDone.Set();
  
          // Get the socket that handles the client request.  
          Socket listener = (Socket)ar.AsyncState;
          Socket handler = listener.EndAccept(ar);
  
          // Create the state object.  
          StateObject state = new StateObject();
          state.workSocket = handler;
          handler.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0,
              new AsyncCallback(ReadCallback), state);
      }
  
      public static void ReadCallback(IAsyncResult ar)
      {
          String content = String.Empty;
  
          // Retrieve the state object and the handler socket  
          // from the asynchronous state object.  
          StateObject state = (StateObject)ar.AsyncState;
          Socket handler = state.workSocket;
  
          // Read data from the client socket.
          //int bytesRead = handler.EndReceive(ar);
  
          // New way, handles forcibly disconnect.
          SocketError errorCode;
          int bytesRead = 0;
          try
          {
              bytesRead = handler.EndReceive(ar, out errorCode);
  
          }
          catch (Exception ex)
          {
              Console.WriteLine(ex);
          }
  
          if (bytesRead &gt; 0)
          {
              // There  might be more data, so store the data received so far.  
              state.sb.Append(Encoding.ASCII.GetString(
                  state.buffer, 0, bytesRead));
  
              PacketHandler.CheckPacket(
                  handler: handler,
                  data:  state.buffer,
                  length: bytesRead
                  );
  
              // Check for end-of-file tag. If it is not there, read
              // more data.  
              content = state.sb.ToString();
  
              Console.WriteLine("Read {0} bytes from socket. \n Data : {1}",
              content.Length, content);
  
  
              // Keep listening to the socket for messages while the socket is connected.
              if (handler.Connected)
              {
                  // Empty the previous message
                  state.sb.Clear();
  
                  try
                  {
                      // Recursieve? Calling itself til socket is disposed off.
                      handler.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0,
                          new AsyncCallback(ReadCallback), state);
                  }
                  catch (Exception ex)
                  {
                      Console.WriteLine(ex.Message);
                  }
                  Thread.Sleep(1000);
  
              }
  
              // If it got this far, means socket is closed. Double checking before disposing of the socket.
              if (!handler.Connected)
              {
  
                  try
                  {
                      // https://stackoverflow.com/questions/4160347/close-vs-shutdown-socket
                      handler.Shutdown(SocketShutdown.Both);
                      handler.Close();
                      Console.WriteLine("Closed socket");
  
                  }
                  catch (Exception ex)
                  {
                      Console.WriteLine("Failed close socket. " + ex.Message);
                  }
              }
  
  
  
              //if (content.IndexOf("&lt;EOF&gt;") &gt; -1)
              //{
              //    // All the data has been read from the
              //    // client. Display it on the console.  
              //    Console.WriteLine("Read {0} bytes from socket. \n Data : {1}",
              //        content.Length, content);
              //    // Echo the data back to the client.  
              //    Send(handler, content);
              //}
              //else
              //{
              //    // Not all data received. Get more.  
              //    handler.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0,
              //    new AsyncCallback(ReadCallback), state);
              //}
          }
      }
  
      public static void Send(Socket handler, String data)
      {
          // Convert the string data to byte data using ASCII encoding.  
          byte[] byteData = Encoding.ASCII.GetBytes(data);
  
          // Begin sending the data to the remote device.  
          handler.BeginSend(byteData, 0, byteData.Length, 0,
              new AsyncCallback(SendCallback), handler);
      }
  
      private static void SendCallback(IAsyncResult ar)
      {
          try
          {
              // Retrieve the socket from the state object.  
              Socket handler = (Socket)ar.AsyncState;
  
              // Complete sending the data to the remote device.  
              int bytesSent = handler.EndSend(ar);
              Console.WriteLine("Sent {0} bytes to client.", bytesSent);
  
              handler.Shutdown(SocketShutdown.Both);
              handler.Close();
  
          }
          catch (Exception e)
          {
              Console.WriteLine(e.ToString());
          }
      }
  }
  </code></pre>