Send data from UWP client applications to server crash with error System.Runtime.InteropServices.COMException (0x8007274D)

Question

I want to create a server so that HoloLens, UWP app, could connect to it and send data to it.

So to create the server, I created a Console Application in Visual Studio and followed the example here

And from the client side, UWP application, I created the below class:

using UnityEngine;
#if !UNITY_EDITOR && UNITY_METRO
using System;
using System.Text;
using System.Collections;
using System.Collections.Generic;
using Windows.Networking.Sockets;
using Windows.Storage.Streams;
using Windows.Networking;
using Windows.Foundation;
#endif

public class SendSocketStreamClient {
    // The port number for the remote device.  
    private int port;
    private string serverIP;

    public SendSocketStreamClient(int portNum, string ip){
        port = portNum;
        serverIP = ip;
    }

#if !UNITY_EDITOR && UNITY_METRO
    private StreamSocket networkConnection;

    // The response from the remote device.  
    private static String response = String.Empty;

    public void StartClient()
    {
        // Setup a connection to the server.
        HostName networkHost = new HostName(serverIP);
        networkConnection = new StreamSocket();

        IAsyncAction outstandingAction = networkConnection.ConnectAsync(networkHost, port.ToString());
        AsyncActionCompletedHandler aach = new AsyncActionCompletedHandler(NetworkConnectedHandler);
        outstandingAction.Completed = aach;
    }

    public void NetworkConnectedHandler(IAsyncAction asyncInfo, AsyncStatus status)
    {
        // Status completed is successful.
        if (status == AsyncStatus.Completed)
        {
            DataWriter networkDataWriter;

            // Since we are connected, we can send the data we set aside when establishing the connection.
            using (networkDataWriter = new DataWriter(networkConnection.OutputStream))
            {

                networkDataWriter.WriteBytes(Encoding.ASCII.GetBytes("Sending Trial 1"));

                // Again, this is an async operation, so we'll set a callback.
                DataWriterStoreOperation dswo = networkDataWriter.StoreAsync();
                dswo.Completed = new AsyncOperationCompletedHandler<uint>(DataSentHandler);
            }
        }
        else
        {
            // TODO resend
            Debug.Log("Failed to establish connection. Error Code: " + asyncInfo.ErrorCode);
            networkConnection.Dispose();
        }
    }

    public void DataSentHandler(IAsyncOperation<uint> operation, AsyncStatus status)
    {
        if (status == AsyncStatus.Error)
        {
            // didn't send, so requeue
            Debug.Log("Error while sending " + operation.ErrorCode);
        }
        // Always disconnect here since we will reconnect when sending the next data.  
        networkConnection.Dispose();
    }
#endif
}

I then call this class in a C# script:

#if !UNITY_EDITOR && UNITY_METRO
        SendSocketStreamClient newClient = new SendSocketStreamClient(ConnectionPort, ServerIP.Trim());
        newClient.StartClient();
#endif

But I always get the error below.

Failed to establish connection. Error Code: System.Runtime.InteropServices.COMException (0x8007274D): No connection could be made because the target machine actively refused it.

Any idea what I am doing wrong or how to send data from HoloLens to the server? Is there something wrong with the server?

-----Edit----

Failed to establish connection. Error Code: System.Runtime.InteropServices.COMException (0x8007274C): A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.

The error changed to the above when I set the serverIP to be the IP address of my machine instead of 127.0.0.1. So I think giving it the right IP address solved this error but now it does not connect to the server.

Does that mean the way I created the server is not right?

Answer 1

As said in the comments above and as here I found that in the server I am using

 IPAddress ipAddress = IPAddress.Loopback;

instead of

IPHostEntry ipHostInfo = Dns.Resolve(Dns.GetHostName());  
IPAddress ipAddress = ipHostInfo.AddressList[0];

Changing that solved my problem and I was able to connect to the server from HoloLens and receive data.