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Why isn't TcpListener listening?

We have a C++ v100 application that is processing every event in our system, listening on port 1705, running off the Hostname. (it works perfectly for the C++ app, and we don't want to change anything in the c++ code) We are trying to intercept some of those events into a C# 4.5.2 solution, simply to display specific events in our new web system.
I have coded the following, in an attempt to listen to port 1705 traffic... but I never receive any data. (I can create events that get sent to 1705)
The following code runs, and it makes it to 'Waiting for a connection', but never makes it to 'Connected!'. If you see any reason in the following code as to why I wouldn't be receiving data, please let me know:
private void PortListener()
{
TcpListener server = null;
try
{
// Set the TcpListener on port 13000.
var port = 1705;
var localAddr = IPAddress.Parse(Dns.GetHostAddresses(Environment.MachineName)[0].ToString());
server = new TcpListener(localAddr, port);
// Start listening for client requests.
server.Start();
// Buffer for reading data
var bytes = new byte[256];
// Enter the listening loop.
while (true)
{
Console.Write("Waiting for a connection... ");
// Perform a blocking call to accept requests.
// You could also user server.AcceptSocket() here.
var client = server.AcceptTcpClient();
Console.WriteLine("Connected!");
// Get a stream object for reading and writing
var stream = client.GetStream();
int i;
// Loop to receive all the data sent by the client.
while ((i = stream.Read(bytes, 0, bytes.Length)) != 0)
{
// Translate data bytes to a ASCII string.
var data = System.Text.Encoding.ASCII.GetString(bytes, 0, i);
Console.WriteLine("Received: {0}", data);
// Process the data sent by the client.
data = data.ToUpper();
//TODO: Process the data
}
// Shutdown and end connection
client.Close();
}
}
catch (SocketException e)
{
Console.WriteLine("SocketException: {0}", e);
}
finally
{
// Stop listening for new clients.
server?.Stop();
}
}

Make sure that you are binding/listening to the right ip-address. If you bind/listen on localhost (127.0.0.1) you can only connect from the same host.
Check what
Dns.GetHostAddresses(Environment.MachineName)[0].ToString());
really produces.

I'm doing this all wrong. In order to listen to an already opened Port, I need to use a TcpClient to connect and listen. Only a single TcpListener is allowed per port. Several TcpClients can connect at once. Sigh.

Winsock server/client application in c#

I'm working to make a Client/Server Application in C# using winsock Control. I done every thing in that but i stuck the place of sending data from client to server. In my program server always listen the client using the ip and port. I send the data from the client to server.
1)When click the Listen button on the server form it open the server where client is connect.
2)In Client form 1st i click the connect button for that the server is connected Gives an message (Connect Event: ip) for this message we easly know that the client is connected to the server.
3)Then we enter some data in the Send Data text Box then click Send Button to send the data to server and also save in client.
Code Below:
SERVER:
using System;
using System.Collections.Generic;
using System.Windows.Forms;
using System.Net;
using System.Threading;
using System.Net.Sockets;
namespace Server
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
const string DEFAULT_SERVER = "ip";
const int DEFAULT_PORT = 120;
System.Net.Sockets.Socket serverSocket;
System.Net.Sockets.SocketInformation serverSocketInfo;
public string Startup()
{
IPHostEntry hostInfo = Dns.GetHostByName(DEFAULT_SERVER);
IPAddress serverAddr = hostInfo.AddressList[0];
var serverEndPoint = new IPEndPoint(serverAddr, DEFAULT_PORT);
serverSocket = new System.Net.Sockets.Socket(System.Net.Sockets.AddressFamily.InterNetwork, System.Net.Sockets.SocketType.Stream, System.Net.Sockets.ProtocolType.Tcp);
serverSocket.Bind(serverEndPoint);
return serverSocket.LocalEndPoint.ToString();
}
public string Listen()
{
int backlog = 0;
try
{
serverSocket.Listen(backlog);
return "Server listening";
}
catch (Exception ex)
{
return "Failed to listen" + ex.ToString();
}
}
public string ReceiveData()
{
System.Net.Sockets.Socket receiveSocket;
byte[] buffer = new byte[256];
receiveSocket = serverSocket.Accept();
var bytesrecd = receiveSocket.Receive(buffer);
receiveSocket.Close();
System.Text.Encoding encoding = System.Text.Encoding.UTF8;
return encoding.GetString(buffer);
}
private void Listen_Click(object sender, EventArgs e)
{
string serverInfo = Startup();
textBox1.Text = "Server started at:" + serverInfo;
serverInfo = Listen();
textBox1.Text = serverInfo;
//string datatosend = Console.ReadLine();
//SendData(datatosend);
serverInfo = ReceiveData();
textBox1.Text = serverInfo;
//Console.ReadLine();
}
private void winsock_DataArrival(object sender, AxMSWinsockLib.DMSWinsockControlEvents_DataArrivalEvent e)
{
ReceiveData();
Listen();
}
private void winsock_ConnectEvent(object sender, EventArgs e)
{
Listen();
}
}
}
This all are work perfectly But here my problem is that i get data form the client to server at only one time. When i send data again from the client to the server its not working and gives me some Message like
Additional information: Only one usage of each socket address
(protocol/network address/port) is normally permitted
In the server form
serverSocket.Bind(serverEndPoint);
Please someone help me to solve my problem.
Thank you.

Try this. It helps you
delegate void AddTextCallback(string text);
public Form1()
{
InitializeComponent();
}
private void ButtonConnected_Click(object sender, EventArgs e)
{
ThreadPool.QueueUserWorkItem(new WaitCallback(ServerHandler));
}
private void ServerHandler(object state)
{
TcpListener _listner = new TcpListener(IPAddress.Parse("12.2.54.658"), 145);
_listner.Start();
AddText("Server started - Listening on port 145");
Socket _sock = _listner.AcceptSocket();
//AddText("User from IP " + _sock.RemoteEndPoint);
while (_sock.Connected)
{
byte[] _Buffer = new byte[1024];
int _DataReceived = _sock.Receive(_Buffer);
if (_DataReceived == 0)
{
break;
}
AddText("Message Received...");
string _Message = Encoding.ASCII.GetString(_Buffer);
AddText(_Message);
}
_sock.Close();
AddText("Client Disconnected.");
_listner.Stop();
AddText("Server Stop.");
}
private void AddText(string text)
{
if (this.listBox1.InvokeRequired)
{
AddTextCallback d = new AddTextCallback(AddText);
this.Invoke(d, new object[] { text });
}
else
{
this.listBox1.Items.Add(text);
}
}
I'm also have the same problem like you on last month but i solve that using this Receive multiple different messages TcpListener C# from stackoverflow. This helps me lot hope it helps to solve your problem also.

I'm not 100% sure you understand TCP sockets so here goes.
When you use a TCP listener socket you first bind to a port so that clients have a fixed, known point to connect to. This reserves the port for your socket until you give it up by calling Close() on that socket.
Next you Listen in order to begin the process of accepting clients on the port you bound to. You can do both this and the first step in one but as you haven't I haven't here.
Next you call Accept(). This blocks (halts execution) until a client connects and then it returns a socket which is dedicated to communication with that client. If you want to allow another client to connect, you have to call Accept() again.
You can then communicate with your client using the socket that was returned by Accept() until you're done, at which point you call Close() on that socket.
When you're done listening for new connections you call Close() on your listener socket.
However when you press your listen button the following happens:
You bind correctly, you begin listening correctly and then your call to ReceiveData() blocks on the Accept call until a client is received. You then receive some data (though this is TCP so that might not be the whole data!) and then you instantly close the connection to your client.
I presume to get the error you're getting you must then press listen again on your server. This therefore restarts the whole listener socket and when you get to bind to the port the second time your previous listener is still bound to it and thus the call fails because something's already allocated on that port.
Solution wise you need to keep the socket returned from the Accept() call open until you're done with it. Have the client handle the close by calling the Shutdown() method on their socket or establish some convention for marking the end of communication.
You're also going to run into trouble when you try and have multiple users connected and so at some point you're either going to require threads or some asynchronous sockets but I feel that's out the scope of this question.

I suggest you do not use AxMSWinsockLib.. Have a look at socket example given here where it shows how to create a client socket and server socket - https://msdn.microsoft.com/en-us/library/kb5kfec7(v=vs.110).aspx AND this one - https://msdn.microsoft.com/en-us/library/6y0e13d3(v=vs.110).aspx

stream was not writable when trying to write to Networkstream

I'm new with socket and trying to write a Client-Server application
My applicationhas those two main methods :
SERVER running on separate Thread :
public void socketListener()
{
byte[] StreamMessage = new byte[9632];
Socket listener = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
IPEndPoint localEndPoint =new IPEndPoint(IPAddress.Any , ControlLayer.GlobalParam.PEER2PEER_PORT);
listener.Bind(localEndPoint);
listener.Listen(10);
while (true)
{
Socket Handler = listener.Accept();
//int ByteRec = Handler.Receive(StreamMessage);
int MessageLength;
MessageLength = Handler.Receive(StreamMessage, 0, StreamMessage.Length, SocketFlags.None);
//return MessageLength;
// string message = System.Text.Encoding.Default.GetString(StreamMessage);
string message = System.Text.Encoding.UTF8.GetString(StreamMessage);
OnDataRecievedFromRemotePeer(this, message, "TcpServer");//send data to screen
Task.Run(() => { ParseMessage(message, Handler); });
}
}
once data arrives I prase it collect data and send it using Client
CLIENT :
public void Write(string message)
{
ThreadPool.QueueUserWorkItem(new WaitCallback(CreateClient), message);
}
private void CreateClient(object message)
{
try
{
peerClient = new TcpClient();
peerClient.Connect(remoteIP, 6001/*TODO remove this */);
netStream = peerClient.GetStream();//<- Exception
StreamWriter sw = new StreamWriter(netStream);
sw.Write((string)(message));
netStream.Close();
peerClient.Close();
}
catch(Exception ex)
{
//TODO :
}
}
Each station is symmetrical and have those two methods
I can tell that the server is working and accepting socket and data
but once I want to respond back I get exception in the Line marked in the CreateClient
stream was not writable and when looking on the netStream it is written that I have ObjectDisposed Exception .
What can be the cause of that ?
Also please inform me if more code is needed

You have a classical race here between the server closing the connection before the client has processed the response of the server.
TCP is a "polite" protocol, which means that you can not perform a fire and forget action on the server. The connection needs to be alive on both ends until both sides have processed all messages. Thus either the client needs to send an acknowledge/logout, so that the server can close the connection or at least the server has to wait x seconds until closing it.

SocketException An existing connection was forcibly closed by the remote host

I've decided to take a look at network messaging etc and my first port of call was UDP.
The problem i have is when i attempt to send a message. I'm trying to hit an IP on a specifc port, but the application errors with the error
"SocketException An existing connection was forcibly closed by the remote host".
Here is the code.
User ME = new User();
UdpClient MyUDPClient;
private void Form1_Load(object sender, EventArgs e)
{
ME.Username = Environment.UserName;
}
private void StartUDP_Click(object sender, EventArgs e)
{
CreateUDPClient();
}
private void CreateUDPClient()
{
IPHostEntry host = Dns.GetHostEntry(Dns.GetHostName());
foreach (IPAddress ip in host.AddressList)
{
if (ip.AddressFamily == AddressFamily.InterNetwork)
{
int Port = int.Parse(txt_Port.Text);
ME.UserIP = new IPEndPoint(ip, Port);
break;
}
}
MyUDPClient = new UdpClient(ME.UserIP);
UDPListening();
}
public void UDPListening()
{
MyUDPClient.BeginReceive(ReceiveMessage, new object());
}
private void ReceiveMessage(IAsyncResult IAR)
{
byte[] B = MyUDPClient.EndReceive(IAR, ref ME.UserIP);
ProcessMSG(Encoding.ASCII.GetString(B));
UDPListening();
}
delegate void MessageDelegate(String MSG);
public void ProcessMSG(String M)
{
if (this.lbl_Messages.InvokeRequired)
{
MessageDelegate Del = new MessageDelegate(ProcessMSG);
this.Invoke(Del, M);
}
else
{
lbl_Messages.Text = M;
}
}
//Send Data to Another version of this program elsewhere.
private void btn_SendtoTarget_Click(object sender, EventArgs e)
{
IPEndPoint TargetIP = new IPEndPoint(IPAddress.Parse(txt_Send2IP.Text),int.Parse(txt_Send2Port.Text));
byte[] Message = Encoding.ASCII.GetBytes("TEST TEST TEST");
MyUDPClient.Send(Message, Message.Length, TargetIP);
}
}
thanks for the help.
Not sure if this helps but...
The Application is running on machine which is set to listen is on 192.168.0.25:5555
the Send is trying to send to Machine 192.168.0.50:10001
T
From further reading, I think my specific issue is the creation of the UDPclient object. It is created and is then listening on the ip 192.168.0.25:5555. When i attempt to send a message I'm attempting to use the same UDPClient but sending to a new IP. I'm getting the vibe that this is not the correct procedure and thus its trying to close the previous down??? I'm sure someone can comfirm this. So that would suggest to me that to have effective UDP networking (UP and Down) i'd need to have a UDPclient receiving and a second UDP to be able to send (which is dynamic to each target address i want to hit). Once again this is all guess work, and if i have this i hope someone could provide some pointers.

Several problems above.
Don't use ME in C#, it is this. Me is VB. The code above would not compile, as written, if using C#, since you left out your User() class you define as ME. I am not sure why you think you need that, since all it seems to hold is UserIP and UserName. The IP is part of a Socket, so you should just use that if you ever needed it:
IPAddress ip = IPAddress.Parse(socket.RemoteEndPoint);
And UserName could be made a global string variable - doesn't have to be part of a class.
Maybe I'm being nitpicky, but I didn't see where it was required to have either of those variables in the User() object like that and just mucked things up, for me, trying to decipher the code.
Always define your Socket, connect to it, then do your .Send(). You are missing the first 2 steps in your button click - you just do your .Send(). UdpClient is not a Socket, and I think it's better to do this as a Socket and define your connection type later. I think you could be right that you are trying to do your .Send() using the UdpClient you defined as your listener. Don't use the same object for your send and your listening! Normally you would, but you have 2 different addresses and ports for each event.
Don't use a foreach in your CreateUDPClient() function to get your IPAddress to assign to your IPEndPoint. You already knew your IP. Assign it directly. It's wasting processing time.
IPAddress ip = IPAddress.Parse("192.168.0.25");
IPEndPoint endPoint = new IPEndPoint(ip, port);
If you only had the host name, you would do:
string hostName = "MyComputerName";
int port = 5555; // or int.Parse(txt_Port.Text); ???
IPHostEntry hostEntry = Dns.GetHostAddresses(hostName);
IPEndPoint endPoint = new IPEndPoint(hostEntry[0], port);
Don't use Dns.GetHostEntry() -- if there's no reverse-lookup (PTR) record for that name, it will fail. Use Dns.GetHostAddresses(). And I have no idea why you think you needed the loop unless you have IPv6 addresses for the same host name you were providing. If not, just use [0] - it should be the first and only IP that will be returned that you'll be using if not using IPv6. But again, since you already have the IP, just plug that in - no need to do the lookup. It helps you eliminate Dns.GetHostName(), too - just use 192.168.0.25.
For your reference, MSDN has a procedure for your synchronous socket send/receive here:
https://msdn.microsoft.com/en-us/library/kb5kfec7(v=vs.110).aspx
and asynchronous socket send/receive here:
http://msdn.microsoft.com/en-us/library/bew39x2a(v=vs.110).aspx
Since I despise link only answers, and you seem to be mixing these 2 methods by using Send() and EndReceive(), respectively to the links above, I will endeavor to describe its contents succinctly and help fix your code:
Basically they say to use a StateObject class, instead of the global variable MyUDPClient you have:
public class StateObject
{
public byte[] buffer = new byte[1024];
public Socket workSocket;
public StringBuilder sb = new StringBuilder();
}
You would create a socket and add it to that. Buffer serves as a way to tell the Receive() or EndReceive() the size of the chunk you want to read back from the response at one time, and sb will serve as a placeholder for the response.
It looks like you have a lot going on here: a SendtoTarget_Click to do a one-off test from the form, and your listener. Your SendtoTarget button does a synchronous send, your StartUDP_Click() does an asynchronous receive.
You would change your SendtoTarget_Click() event to be this (which never defined your socket, before, and you must connect to it before sending):
private void btn_SendtoTarget_Click(object sender, EventArgs e)
{
IPEndPoint TargetIP = new IPEndPoint(IPAddress.Parse(txt_Send2IP.Text),int.Parse(txt_Send2Port.Text));
byte[] Message = Encoding.ASCII.GetBytes("TEST TEST TEST");
// Create a UDP socket.
Socket sender = new Socket(AddressFamily.InterNetwork,
SocketType.Stream, ProtocolType.Udp);
try
{
// Connect to the remote endpoint.
sender.Connect(TargetIP);
// Send message -- already contains the endpoint so no need to
// specify again
sender.Send(Message, 0, Message.Length, SocketFlags.None);
sender.Close();
}
catch (Exception)
{
// do something here...
}
}
For your listener, you can do:
private void CreateUDPClient()
{
IPEndPoint TargetIP = new IPEndPoint(IPAddress.Parse("192.168.0.25"), 5555);
// Create a UDP socket.
Socket receiver = new Socket(AddressFamily.InterNetwork,
SocketType.Stream, ProtocolType.Udp);
try {
// Create the state object.
StateObject state = new StateObject();
state.workSocket = receiver;
// Begin receiving the data from the remote device.
receiver.BeginReceive(state.buffer, 0, 256, 0,
new AsyncCallback(ReceiveMessage), state);
} catch (Exception e) {
Console.WriteLine(e.ToString());
}
}
and your function called ReceiveMessage(), does this:
private void ReceiveMessage(IAsyncResult IAR)
{
string response = String.Empty;
try {
// Retrieve the state object and the client socket
// from the asynchronous state object.
StateObject state = (StateObject) IAR.AsyncState;
Socket client = state.workSocket;
// Read data from the remote device.
int bytesRead = client.EndReceive(IAR);
if (bytesRead > 0) {
// There might be more data, so store the data received so far.
state.sb.Append(Encoding.ASCII.GetString(state.buffer, 0, bytesRead));
// Get the rest of the data.
client.BeginReceive(state.buffer, 0, 256, 0,
new AsyncCallback(ReceiveCallback), state);
} else {
// All the data has arrived; put it in response.
if (state.sb.Length > 1) {
response = state.sb.ToString();
}
// Signal that all bytes have been received.
client.Close();
}
ProcessMSG(response);
CreateUDPClient(); // personally, I would re-create than calling BeginReceive directly
} catch (Exception e) {
Console.WriteLine(e.ToString());
}
}
Did my best to integrate your code with MSDN's in a way that should work. You might be able to get away with assigning that socket to the StateObject and calling BeginReceive() on it, again - not sure. But don't re-use the UdpClient object like that. Use the StateObject class like on MSDN and use it ONLY as your listener.

select() function in C#

im new to C# and any help/feedback would be appreciated. im trying to develop a a client-server program in c#, however i do have different clients sending information to the server side. Is there any function similar to the c language select() such that can help to get all the information from every client side in C#?
here is my server side code:
// Create the listening socket...
m_mainSocket = new Socket(AddressFamily.InterNetwork,
SocketType.Stream, ProtocolType.Tcp);
IPEndPoint ipLocal = new IPEndPoint(IPAddress.Any, 9051);
// Bind to local IP Address...
m_mainSocket.Bind(ipLocal);
// Start listening...
m_mainSocket.Listen(10);
Socket clientSock = m_mainSocket.Accept();
byte[] clientData = new byte[1024];
int receivedBytesLen = clientSock.Receive(clientData);
string clientDataInString =
Encoding.ASCII.GetString(clientData, 0, receivedBytesLen);
string clientStr = "Client Data Received: " + clientDataInString;
byte[] sendData = new byte[1024];
sendData = Encoding.ASCII.GetBytes(clientStr);
clientSock.Send(sendData);
clientSock.Close();

There are higher level constructs, but if you want to get pretty low level, you are probably looking for Socket.Accept:
http://msdn.microsoft.com/en-us/library/system.net.sockets.socket.accept.aspx

You want to accept connections from more than one client, so you have to call the blocking Accept method again after acception a connection:
while (true)
{
var clientSocket = s.Accept();
beginReceive(clientSocket);
}
After accepting you might want to start receiving data in an async manner:
private static void beginReceive(Socket clientSocket)
{
byte[] buffer = new byte[1000];
clientSocket.BeginReceive(
buffer, 0, 1000, SocketFlags.None, OnReceiveData, clientSocket);
}
And finally here is the callback method which is called by the framework on another thread when data arrives. You have to finish the async call with EndReceive:
private static void OnReceiveData(IAsyncResult ar)
{
int bytesReceived = ((Socket) ar.AsyncState).EndReceive(ar);
// process data...
}
Of cause you have to store your buffer somewhere else and maintain one receive buffer per client. Maybe you should write an own class for managing a connected client.

Here is a code project with some nice diagrams and examples. The underlying "select" is handled by the .NET framework so you have to think / work at a higher level.
At a high level you socket.accept create a thread to process the connection.
http://msdn.microsoft.com/en-us/library/system.net.sockets.socket.accept.aspx
http://www.codeproject.com/KB/IP/dotnettcp.aspx