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Is it necessary or recommended to make a UDP send-only socket async?

I am using a UDP socket to send eventlog data to a log analysis server, and don't want to block threads unnecessarily. The sending application is a Windows background service using a default threadpool.
// Should this be async? It's UDP only...
public static void LogUDP(string message)
{
try
{
var hostname = ConfigurationManager.AppSettings.Get<string>("SyslogUDPHostName", string.Empty);
var portString = ConfigurationManager.AppSettings.Get<string>("SyslogUDPHostPort", string.Empty);
var port = Convert.ToInt32(portString);
var ipParse = System.Net.Dns.GetHostAddresses(hostname);
var ip = ipParse.First();
// Create Endpoint
var udpEndpoint = new System.Net.IPEndPoint(ip, port);
// Create Socket
var socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
socket.Ttl = 26;
// Connect the socket
socket.Connect(udpEndpoint);
// Create the encoded buffer
var buffer = System.Text.Encoding.ASCII.GetBytes(message);
// Send the buffer
var sent = socket.Send(buffer);
}
catch (Exception ex)
{
}
}
Is it necessary or recommended to use Async for UDP based outbound-only messages?
I'm looking through the sample Microsoft-provided code to learn how to write equivalent Async code, but not sure if it's needed. My doubt is reaffirmed when I look at the overloads for BeginSend and every method has an AsyncCallback, and in the case of UDP, I'm not sure what to put there (null?)?
Advice welcome.

Client Socket not getting reponse bytes in .NET

I am creating and sending a message on server socket and not getting any response in return , I would like to know what could be possible reasons for the same. Below is my sample code for client socket
static void Main()
{
int _DCPport = 9090;
IPHostEntry ipHostInfo = Dns.GetHostEntry("HostName");
Console.WriteLine("Got the IP Host Info" , ipHostInfo.ToString ());
IPAddress ipAddress = ipHostInfo.AddressList[0];
Console.WriteLine("Got the IP hadress Info");
//End point of the host where the socket will be connected
IPEndPoint remoteDAPEndPoint = new IPEndPoint(ipAddress, _DCPport);
// Create a clientSocket that connects to host
Socket clientDAP = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
clientDAP.Connect(remoteDAPEndPoint);
Console.WriteLine("Client socket connected to remote end point");
#region Input variables
string requestString = "Hello";
string responseString = "";
byte[] requestByte = System.Text.Encoding.UTF8.GetBytes(requestString);
byte[] responseByte = new byte[1024];
StringBuilder messageBuilder = new StringBuilder();
int byteResult = 0;
#endregion
try
{
//sending the string as bytes over the socket
Console.WriteLine("Sending the input " + requestString);
clientDAP.Send(requestByte);
}
catch (SocketException eX)
{
Console.WriteLine(eX.Message);
}
try
{
//recieving the response bytes
byteResult = clientDAP.Receive(responseByte, clientDAP.Available, SocketFlags.None);
Console.WriteLine("Recieved {0} bytes as response from remote end point" , byteResult);
if (clientDAP.Connected)
{
responseString = Encoding.UTF8.GetString(responseByte);
messageBuilder.Append(responseString);
}
}
catch (SocketException eX)
{
Console.WriteLine(eX.Message);
}
clientDAP.Shutdown(SocketShutdown.Both);
clientDAP.Disconnect(true);
string sResult = messageBuilder.ToString();
Console.WriteLine(sResult);
}
I am not getting any bytes when i call socket.Recieve() , Any reasons why such is happening ?

From Socket.Send:
There is also no guarantee that the data you send will appear on the network immediately. To increase network efficiency, the underlying system may delay transmission until a significant amount of outgoing data is collected. A successful completion of the Send method means that the underlying system has had room to buffer your data for a network send
Which means that the data may not have even arrived at the server yet when your call to Send has completed. Let alone that the server has had time to process your data and return a response.
And yet your code charges straight ahead to try to receive the server's response. This isn't unreasonable, in and of itself. Your call to Receive would have blocked until it had received some data if you had specified the size of your buffer, rather than using Available, which will happily return 0 if there's no data yet available. So your Receive call is asking for up to 0 bytes and that's how many you're being given.
So change this line
byteResult = clientDAP.Receive(responseByte, 1024, SocketFlags.None);
(Or better yet, introduce a constant and/or use responseByte.Length or switch to an overload where you don't explicitly specify how many bytes you want)

Reading from closed NetworkStream doesn't cause any exception

I'm trying to create a rather simple client-server application, but for communication I want to use binary serialized objects. The communication itself seems rather fine, but when I close the stream on the client's side, the server doesn't really notice it and keeps on trying to read the stream.
server side (class Server, executed in separate thread):
listening for connections
listener = new TcpListener(IPAddress.Parse("127.0.0.1"), this.Port);
listener.Start();
while (!interrupted)
{
Console.WriteLine("Waiting for client");
TcpClient client = listener.AcceptTcpClient();
AddClient(client);
Console.WriteLine("Client connected");
}
adding the client:
public void AddClient(TcpClient socket)
{
Client client = new Client(this, socket);
this.clients.Add(client);
client.Start();
}
listening for messages (deep inside Client class):
BinaryFormatter deserializer = new BinaryFormatter();
while (!interrupted)
{
System.Diagnostics.Debug.WriteLine("Waiting for the message...");
AbstractMessage msg = (AbstractMessage)deserializer.Deserialize(stream);
System.Diagnostics.Debug.WriteLine("Message arrived: " + msg.GetType());
raiseEvent(msg);
}
unit test:
Server server = new Server(6666);
server.Start();
Thread.Sleep(500);
TcpClient client = new TcpClient("127.0.0.1", 6666);
var message = new IntroductionMessage();
byte[] arr = message.Serialize();
client.GetStream().Write(arr, 0, arr.Length);
Thread.Sleep(500);
Assert.AreEqual(1, server.Clients.Count);
client.GetStream().Close();
client.Close();
Thread.Sleep(1000);
Assert.AreEqual(0, server.Clients.Count);
server.Stop();
so the message gets read properly, but then, when I close the stream, deserializer.Deserialize(stream) doesn't appear to throw any exceptions... so should it just not be read this way, or should I close the client in a different way?

Assuming the stream used in the Server for deserializing the message is a NetworkStream (which is the type of the stream returned by TcpClient.GetStream()), you should do two things:
Define a specific message for "connection ends". When the server receives and deserializes this message, exit the while-loop. To make this work, the client obviously needs to send such a message before closing its TcpClient connection. (You might choose a different mechanism working in a similar manner -- but why not using the message mechanism you already have in place...)
Set a ReadTimeout on the NetworkStream, so in case the connection gets lost and the client is unable to send a "connection ends" message, the server will hit the timeout and realize that the client is "dead".
The code in your server for listening to client messages should look similar to this:
//
// Time-out after 1 minute after receiving last message
//
stream.ReadTimeOut = 60 * 1000;
BinaryFormatter deserializer = new BinaryFormatter();
try
{
while (!interrupted)
{
System.Diagnostics.Debug.WriteLine("Waiting for the message...");
AbstractMessage msg = (AbstractMessage)deserializer.Deserialize(stream);
System.Diagnostics.Debug.WriteLine("Message arrived: " + msg.GetType());
//
// Exit while-loop when receiving a "Connection ends" message.
// Adapt this if condition to whatever is appropriate for
// your AbstractMessage type.
//
if (msg == ConnectionEndsMessage) break;
raiseEvent(msg);
}
}
catch (IOException ex)
{
... handle timeout and other IOExceptions here...
}

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.

Knowing which UDP client is which

Is it possible to identify an earlier UDP client without keeping the socket open? I want to link an integer ID to each unique client, but I don't want to keep any additional threads open.
//Receive (Server)
private static Int32 port = 11000;
private static UdpClient udpClient = new UdpClient(port);
public static void receive_threaded()
{
Thread t = new Thread(() =>
{
while (true)
{
IPEndPoint remoteIPEndPoint = new IPEndPoint(IPAddress.Any, port);
byte[] content = udpClient.Receive(ref remoteIPEndPoint);
if (content.Length > 0)
{
string message = Encoding.UTF8.GetString(content);
if (action_message_receive != null) action_message_receive(String.Format("Recv({0}): {1}", remoteIPEndPoint.Port, message));
parseMessage(message);
}
}
});
t.Start();
}
//Send (Client)
private static void send_message(string ip, string message)
{
byte[] packetData = System.Text.UTF8Encoding.UTF8.GetBytes(message);
int port = 11000;
IPEndPoint ep = new IPEndPoint(IPAddress.Parse(ip), port);
Socket client = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
client.SendTo(packetData, ep);
if (action_message_send != null) action_message_send("Send: " + message);
}
A client can request a (temporary) userID from the server, and the server will add it to it's database and notify the client when it's done doing that. However, I can't have the client send it's own userID when it's making requests because any memory altering application would mean a 'hacker' could gain access to other user's stuff.
Since the socket doesn't stay open, the IPEndPoint.Port changes every time the client sends something to the server, so I can't keep track of it with that. I could get it done by creating a username/pass on a userID request and having those sent on every single request involving the userID thereafter, but that would be silly.
So is there any way to do this without keeping a thread open for each client? I'm probably doing something really weird here because UDP is supposed to be a one way street, but I'm here to learn so I just had to ask.

You will need to introduce some sort of unique identifier chosen by the server and sent to the client for it to "behave and send it back for identification purposes". A random long integer should suffice.
UDP has neither connections nor identification/authentication mechanisms. If you want those, use TCP (but those can be bruteforced also...)