C# Socket Receive messes up data

Question

I am trying to create a client/server application which communicates through Sockets. But when I receive data it randomly messed up and does not always (sometimes) show the correct data. The code I use to receive data:

private static void ReceiveCallback(IAsyncResult AR) { try { Socket socket = (Socket)AR.AsyncState; if (SocketConnected(socket)) { int received = socket.EndReceive(AR); byte[] dataBuf = new byte[received]; Array.Copy(_buffer, dataBuf, received); string text = Encoding.ASCII.GetString(dataBuf); if (!text.Contains("GET") && !text.Contains("HTTP") && text != null) { Console.WriteLine(DateTime.Now.ToString("h:mm:ss tt") + ":" + text); } socket.BeginReceive(_buffer, 0, _buffer.Length, SocketFlags.None, new AsyncCallback(ReceiveCallback), socket); } } catch { } }

can someone explain me why this happends? Thanks in advance!

Also, I have tried to check untill it finds a character (which is on the end of every response '-' but that did not work). Unfortunatley this was the result:

The way that your Begin and End Receive methods are structured is strange. And you call the same method as a callback. It would be better if you broke out the structure of your code into more methods and handle the begin and end calls separately. May help you debug your issue here, if the code was better structured. — ManoDestra
– ManoDestra, Commented Apr 12, 2016 at 18:34
didnot get it BeginReceive after EndReceive. Does that works.... — devprashant
– devprashant, Commented Apr 27, 2016 at 9:28

Luaan · Accepted Answer · 2016-04-12 18:55:53Z

I assume your socket is a TCP socket, since you're dealing with something like HTTP.

TCP deals with streams, not messages. So when you do your read, at most _buffer.Length bytes are read from the stream. This means that you can easily read just a part of the response - or rather, the response will be split between multiple callbacks. When you read enough by chance, everything works as expected. This is especially true when testing on localhost, because Windows treats localhost TCP very differently from the non-localhost case. But when it so happens that you don't read enough, text will not contain the whole response - and your data is broken.

Additionally, when received is zero, it means the other side has closed the stream and you should stop doing BeginReceive.

I understand what you mean but I cant find a possible solution. Thanks tho!

aaaa bbbb · Accepted Answer · 2016-04-12 21:19:48Z

You have to loop on the socket receive until you get your entire message.

This also means that you must have an application level protocol. What defines a message?

A termination character? Then loop on the read until you get that character.

A count of characters? Then loop on the read until you get that many characters.

Is the length of the message at the front of the message? Then loop until you get enough bytes to get the length, then loop until you get the entire message.

The server sends a command to all clients and the clients send an response. I tried to add a termination char but that did not work out for me (i've edited the original post) also the count of the chars is not always the same so that is not an option.

MSE · Accepted Answer · 2016-04-21 12:25:46Z

Your socket code looks fine to me. Characters encoding format in the .Net world is "Unicode", you should convert the bytes you receive to Unicode instead of ASCII :

string text = Encoding.Unicode.GetString(dataBuf);

You should use the same encoding that the sender used. If that's unknown then ask or consult a specification; use guessing only when you've failed.

Collectives™ on Stack Overflow

C# Socket Receive messes up data

3 Answers 3

1 Comment

1 Comment

1 Comment

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

1 Comment

1 Comment

Related