C＃异步客户端-访问字符串冻结接收线程

Question

I am writing a C# client to connect to a Node.JS server. Things were working alright, but at one point the receive function stopped working. I was able to determine that accessing the string received by the client is freezing the thread. Some code excerpts:

Socket socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
byte[] byteData = new byte[2048];

... setup socket connection ...

socket.BeginReceive(byteData, 0, byteData.Length,
    SocketFlags.None, new AsyncCallback(OnReceive), null);

private void OnReceive(IAsyncResult ar)
{
    socket.EndReceive(ar);

    stringData = Encoding.ASCII.GetString(byteData).Trim();

    Console.WriteLine("Before string");
    Console.WriteLine(stringData);
    Console.WriteLine("After string");

    // always ready to asynchronously receive
    socket.BeginReceive(byteData, 0, byteData.Length,
        SocketFlags.None, new AsyncCallback(OnReceive), null);
}

This outputs the following when receiving 'OK' from Node.JS:

Before string
OK

And the newline isn't even even written by the console, since the system output continues directly after 'OK' on the same line. Any subsequent receives show nothing. I have no idea what might have caused this, and I can't seem to find anyone else that has run into this problem.

Answer 1

socket.EndReceive returns a value that tells you how many bytes were actually read. You need to get that value and pass it to the GetString method:

int bytesRead = socket.EndReceive(ar);
stringData = Encoding.ASCII.GetString(byteData, 0, bytesRead);

Otherwise, GetString will try to convert the entire string. That's going to give you all manner of garbage. Your existing call to Trim() is removing the trailing nul bytes that are caused by the way you're currently doing it, but that won't prevent you from getting garbage if you pass a partially-filled buffer to the next call.

That said, I see nothing there that would cause the thing to lock up. Are you certain that you didn't change some other part of the code, and that is causing the lockup?