How to read and write data in tcp socket client/server

Question

I was trying to accept some data from client, send it to the server and also send feedback from server to the client again. When server only gets some data, everething works fine. While trying to implement two-way communication, server just hungs. Server's code:

var tcpListener = new TcpListener(IPAddress.Any, 8888);
try
{
    tcpListener.Start();
    Console.WriteLine("Server is currently run, waiting for incoming connections");
    while (true)
    {
        using var tcpClient = await tcpListener.AcceptTcpClientAsync();
        await using var stream = tcpClient.GetStream();
        
        var incomeData = await DeserializeHelper.ConverteToBytes(stream);
        var incomePerson = MessagePackSerializer.Deserialize<Person>(incomeData);
        Console.WriteLine($"Income message from {incomePerson.Name}: '{incomePerson.Message}'");

        var responseMessage = $"Thank you, {incomePerson.Name} for the message";
        var responceData = MessagePackSerializer.Serialize(responseMessage);
        await stream.WriteAsync(responceData);
    }
}
finally
{
    tcpListener.Stop();
}

Client's code:

using TcpClient tcpClient = new TcpClient();
await tcpClient.ConnectAsync("127.1.199.250",8888);

Console.WriteLine("Hello, client!");

try
{
    var stream = tcpClient.GetStream();
    Console.WriteLine("Enter your name");
    var name = Console.ReadLine();
    Console.WriteLine("Enter message");
    var message = Console.ReadLine();
    Person tom = new Person(name, message);
    
    var sentData = MessagePackSerializer.Serialize(tom);
    await stream.WriteAsync(sentData);
    Console.WriteLine("Message was sent to the server");

    var incomeResponce = await DeserializeHelper.ConverteToBytes(stream);
    var incomeResponceMessage = MessagePackSerializer.Deserialize<string>(incomeResponce);
    Console.WriteLine($"Server's message: {incomeResponce}");
}
catch (Exception e)
{
    Console.WriteLine(e.Message);
}

Also all of them using my own static method ConverteToBytes, here it's code:

public static async Task<byte[]> ConverteToBytes(NetworkStream stream)
{
    await using var ms = new MemoryStream();
    byte[] bytesData = null;
    int count = 0;
    do
    {
        byte[] buffer = new byte[1024];
        count = await stream.ReadAsync(buffer,0,1024);
        ms.Write(buffer,0,count);
    } while (stream.CanRead && count > 0);
    
    return bytesData = ms.ToArray();
}

I guess the problem is with not correct stream using, but don't know what exactly is wrong. Thank's everyone!

I kind of wonder why there are so many questions about TCP on SO. Is it because it is the only protocol they learn about in school? Because they think it is easier due to being lower level? Or because it is so difficult to get right compared to most other protocols? As Stephen Cleary points out, if you don't have any specific reason to use raw TCP, use something else, it will save you a lot of time. — JonasH
– JonasH, Commented Dec 2, 2022 at 15:00

Stephen Cleary · Accepted Answer · 2022-12-02 12:52:20Z

1

I strongly recommend not using TCP/IP in the first place. If possible, use a well-established protocol with good library support, e.g., HTTP or WebSockets. Writing a correct TCP/IP application is extremely difficult.

If you must use TCP/IP, then I recommend watching my video series on the subject and reading my TCP/IP .NET Sockets FAQ.

Of particular note is that network streams are streams of bytes, not streams of messages. So there's no built-in way to know when a message completes. So you'll have to add that to your protocol yourself, i.e., using message framing. I describe message framing on my blog, and the video series linked above shows a more modern way to do it.

Without message framing, your server is likely just waiting for more bytes to arrive from the client connection.

answered Dec 2, 2022 at 12:52

Stephen Cleary

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