TCP Server Windows 10 IOT

Question

I am having problems getting a TCP server to connect. I tried to pull apart the sample and thought I had everything correct. For some reason the server never accepts the incoming connection.

Code:

 public async void StartServer()
    {
        StreamSocketListener listener = new StreamSocketListener();
        listener.ConnectionReceived += OnConnection;
        listener.Control.KeepAlive = true;

        try
        {
            await listener.BindServiceNameAsync(RX_Connection_Port.Text);
        }
        catch
        {

        }
    }

    private async void OnConnection(
       StreamSocketListener sender,
       StreamSocketListenerConnectionReceivedEventArgs args)
    {
        DataReader reader = new DataReader(args.Socket.InputStream);
        try
        {
            while (true)
            {
                // Read first 4 bytes (length of the subsequent string).
                uint sizeFieldCount = await reader.LoadAsync(sizeof(uint));
                if (sizeFieldCount != sizeof(uint))
                {
                    // The underlying socket was closed before we were able to read the whole data.
                    return;
                }

                // Read the string.
                uint stringLength = reader.ReadUInt32();
                uint actualStringLength = await reader.LoadAsync(stringLength);
                if (stringLength != actualStringLength)
                {
                    // The underlying socket was closed before we were able to read the whole data.
                    return;
                }

                string recieved = reader.ReadString(actualStringLength);

                SynthPlayback(recieved);

            }
        }
        catch (Exception exception)
        {
            // If this is an unknown status it means that the error is fatal and retry will likely fail.
            if (Windows.Networking.Sockets.SocketError.GetStatus(exception.HResult) == SocketErrorStatus.Unknown)
            {
                throw;
            }


        }
    }

Any ideas to what I missed. The ipaddress and port are correct in the connection?

Update:

Added a text block to see the error

 public async void StartServer()
    {
        StreamSocketListener listener = new StreamSocketListener();
        listener.ConnectionReceived += OnConnection;
        listener.Control.KeepAlive = true;

        try
        {
            await listener.BindServiceNameAsync(RX_Connection_Port.Text);
        }
        catch (Exception exception)
        {
            if (SocketError.GetStatus(exception.HResult) == SocketErrorStatus.Unknown)
            {
                throw;
            }
            ErrorReport.Text = "Start listening failed with error: " + exception.Message;
        }
    }

Result: Start listening failed with error: The specified class was not found.

not sure what is happening. Any ideas?

Update: Narrowing this down. Got the first problem fixed and now have another.When the client connects to the listener it immediately starts to process before data has come in. I need to wait for data to come in not start on the connection. I am basing this off of this block of code:

 while (true)
            {
                uint sizeFieldCount = await reader.LoadAsync(sizeof(uint));

                if (sizeFieldCount != sizeof(uint))
                {
                    // The underlying socket was closed before we were able to read the whole data.
                    return;
                }
                // Read the string.
                uint stringLength = reader.ReadUInt32();

                uint actualStringLength = await reader.LoadAsync(stringLength);//This is where the code breaks.

                if (stringLength != actualStringLength)
                {
                    // The underlying socket was closed before we were able to read the whole data.
                    return;
                }

                ErrorReport.Text = String.Format("Received data: \"{0}\"", reader.ReadString(actualStringLength));
            }

maybe I need to do this differently. I just need a server to sit there and listen to incoming data. Then read the data to a string for use later. I have looked through so many examples my head is spinning. I am in overload. Any one have a snippit of working server class?

Answer 1

Assuming you are sending a control uint32 saying how many bytes you are about to send, something like in your connected event handler this should get you going.

using(DataReader reader = new DataReader(args.Socket.InputStream))
{
    //get the number of bytes you are expecting
    await reader.LoadAsync(sizeof(uint));
    uint expected = reader.ReadUInt32();

    // then load the buffer with those bytes
    await reader.LoadAsync(expected);
    byte[] buffer = new byte[expected];
    reader.ReadBytes(buffer); // grab them into a buffer

    //output the buffer to the console
    Debug.WriteLine(ASCIIEncoding.ASCII.GetString(buffer));
}

It doesn't handle sending nothing, or expections or anything like that and I am assuming you are sending in Ascii (if not swap that for utf-8 or whatever) but otherwise this should grab your length int then wait until its received all the rest.

My test client was this python 3.4+ code from a remote host (to get over the UWP localhost problem). It breaks the sends to demo the waiting bit.

import socket;

ip, port = 'x.x.x.x', 5001
message = b"What a lot of horses there are in that field"
i = len(message).to_bytes(4, byteorder='big')

sk = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
try:
    sk.connect((ip, port))
    sk.sendall(i)
    sk.sendall(message[0:5])
    sk.sendall(message[5:len(message)])
    reply = sk.recv(4096)
    print(reply)
except Exception as e:
    print(e)

which does the job.
Stop laughing.

Part 2

If you don't know how many bytes you'll be sent you can try the following using the regular System.IO streams API. There are a host of readers and buffers and things but since at this point you are mostly stuck at reading chunks then you should be able to get by with this sort of approach.

private async void OnConnection(StreamSocketListener sender, StreamSocketListenerConnectionReceivedEventArgs args)
{
    const int BufferSize = 64;
    Stream strm = args.Socket.InputStream.AsStreamForRead();
    StringBuilder builder = new StringBuilder();
    byte[] buffer = new byte[BufferSize];
    int read = -1;
    while(read != 0)
    {
        read = strm.Read(buffer, 0, BufferSize);
        builder.Append(ASCIIEncoding.ASCII.GetString(buffer, 0, read));
    }

    Debug.WriteLine(builder.ToString());

    DataWriter writer = new DataWriter(args.Socket.OutputStream);
    writer.WriteString("ok");
    await writer.StoreAsync();
    await writer.DetachStream().FlushAsync();
}

You can adjust that BufferSize const to a suitable value, say if you know you usually get at least 128 bytes, then up it for efficiency. The caller needs to close their end to signal the end of the stream or this will just sit waiting for a while. You can junk the writer bit at the end if you don't need to return anything.

The Python test client code for this was

import socket;

ip, port = 'x.x.x.x', 5001
m1 = b"The quick brown fox jumps over the lazy dog"
m2 = b"another quick brown fox jumps over the lazy dog"
m3 = b"yet another quick brown fox jumps over the lazy dog"

sk = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
try:
    sk.connect((ip, port))
    sk.sendall(m1)
    sk.sendall(m2)
    sk.sendall(m3)
    sk.shutdown(1)
    print(sk.recv(128))
except Exception as e:
    print(e)

Answer 2

this part of code now works as expected.

 public async void StartServer()
    {

        StreamSocketListener listener = new StreamSocketListener();
        listener.ConnectionReceived += OnConnection;
        listener.Control.KeepAlive = false;

        try
        {
            string ServerName = RX_Connection_Port.Text.ToString();
            await listener.BindServiceNameAsync(ServerName);
        }
        catch (Exception exception)
        {
            if (SocketError.GetStatus(exception.HResult) == SocketErrorStatus.Unknown)
            {
                throw;
            }
            ErrorReport.Text = "Start listening failed with error: " + exception.Message;
        }
    }

The only problem I am having now is getting the input string and reading it. The string is sent from another device that sends the strings in a format like:

"Hello this is a test string"(without quotes).

All samples I have tried want a uint to specify the string length. Unfortunately this is not an option currently as I cannot control the device output. It sends in plain ASCII strings.

Answer 3

I am still working on this and have narrowed it down further but cant figure out what is happening.

The code:

 private async void DataListener_ConnectionReceived(StreamSocketListener sender, StreamSocketListenerConnectionReceivedEventArgs args)
    {
        DataReader DataListener_Reader;
        StringBuilder DataListener_StrBuilder;
        string DataReceived;

        using (DataListener_Reader = new DataReader(args.Socket.InputStream))
            try
            {
                {
                    DataListener_StrBuilder = new StringBuilder();
                    DataListener_Reader.InputStreamOptions = InputStreamOptions.Partial;
                    DataListener_Reader.UnicodeEncoding = Windows.Storage.Streams.UnicodeEncoding.Utf8;
                    DataListener_Reader.ByteOrder = ByteOrder.LittleEndian;
                    await DataListener_Reader.LoadAsync(256);
                    while (DataListener_Reader.UnconsumedBufferLength > 0)
                    {
                        DataListener_StrBuilder.Append(DataListener_Reader.ReadString(DataListener_Reader.UnconsumedBufferLength));
                        await DataListener_Reader.LoadAsync(256);
                    }
                    DataListener_Reader.DetachStream();
                    DataReceived = DataListener_StrBuilder.ToString();
                }

                if (DataReceived != null)
                {
                    Debug.WriteLine("[SERVER] I've received " + DataReceived + " from " + args.Socket.Information.RemoteHostName);
                    // ServerResult.Text = "[SERVER] I've received " + DataReceived + " from " + args.Socket.Information.RemoteHostName;
                    ProcessRecievedData(DataReceived); 

                }
                else
                {
                     Debug.WriteLine("Received data was empty. Check if you sent data.");
                }
            }
            catch (Exception exception)
            {

                ServerResult.Text = "Incoming Data failed with error: " + exception.Message;

            }

    }

When the code hits the If(DataRecieved != null), the debug prints the information perfect. However if I try to send the data to another method of print the result in a text box the catch is triggered. If I only use the debug it processes with no problems. Any ideas to what could be causing this. I want to send the data to a text box and also use for other methods. The code does work as I get the incoming data. Just cant do anything with it. What could be causing this?

Answer 4

Solved:

 await Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
                    {
                        this.ServerResult.Text = incoming;
                        SynthPlayback(
                    });

Added this to by code and it fixed the problem.