Receive messages continuously using udpClient

Question

I was looking for the best solution to receive and process messages via UdpClient class in C#. Does anyone have any solutions for this?

What have you tried so far? What do you not like about it/make you believe there is a "better" solution? — dtb, Sep 01 '11 at 04:42

score 45 · Accepted Answer · edited Jul 24 '15 at 21:05

45

Try this code :

//Client uses as receive udp client
UdpClient Client = new UdpClient(Port);

try
{
     Client.BeginReceive(new AsyncCallback(recv), null);
}
catch(Exception e)
{
     MessageBox.Show(e.ToString());
}

//CallBack
private void recv(IAsyncResult res)
{
    IPEndPoint RemoteIpEndPoint = new IPEndPoint(IPAddress.Any, 8000);
    byte[] received = Client.EndReceive(res, ref RemoteIpEndPoint);

    //Process codes

    MessageBox.Show(Encoding.UTF8.GetString(received));
    Client.BeginReceive(new AsyncCallback(recv), null);
}

edited Jul 24 '15 at 21:05

unloco

6,274
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answered Sep 14 '11 at 22:52

Hossein Mobasher

4,269
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24

+1: A couple of notes. First, it's probably not a good idea to call `MessageBox.Show` for error handling, especially in an async callback. But I'll assume you just meant that as, "for example." Second, you probably want to issue the next `BeginReceive` immediately after calling `EndReceive` -- *before* processing the item. Otherwise you can miss messages that arrive while you're processing. Of course, then your async callback has to be re-entrant (i.e. thread safe), but then it already should be. – Jim Mischel Sep 14 '11 at 23:02
is this code work for multiple clients which send request asynchronously.i m stuck in same issue where i have to write the code for multiple client.here my question http://stackoverflow.com/questions/32837887/udp-client-server – SANDEEP Oct 01 '15 at 06:28
1

What is `recv`? – EgoPingvina Dec 07 '16 at 16:27
private void recv(IAsyncResult res) – Matteo TeoMan Mangano Apr 29 '19 at 09:58
recv is shorthand for receive. – person27 Jun 21 '19 at 02:49
recv is the method private void recv(IAsyncResult res) should really have been private void Recv(IAsyncResult ar) but to each their own. – Levon Ravel Jun 22 '19 at 05:10
@JimMischel thank you very much for bringing up the re-entrancy issue. I did receive doubles of the same packet in some cases, sometimes even incomplete packets until I protected my EndReceive callback against re-entrancy. – henon Jan 03 '20 at 12:10
The new async and await methods are so much better than the old way described here. – C Johnson Aug 18 '20 at 04:26

score 21 · Answer 2 · answered Jun 11 '14 at 04:33

For newer methods using TAP instead of Begin/End method you can use the following in .Net 4.5

Quite simple!

Asynchronous Method

    private static void UDPListener()
    {
        Task.Run(async () =>
        {
            using (var udpClient = new UdpClient(11000))
            {
                string loggingEvent = "";
                while (true)
                {
                    //IPEndPoint object will allow us to read datagrams sent from any source.
                    var receivedResults = await udpClient.ReceiveAsync();
                    loggingEvent += Encoding.ASCII.GetString(receivedResults.Buffer);
                }
            }
        });
    }

Synchronous Method

As appose to the asynchronous method above, this can be also implemented in synchronous method in a very similar fashion:

    private static void UDPListener()
    {
        Task.Run(() =>
        {
            using (var udpClient = new UdpClient(11000))
            {
                string loggingEvent = "";
                while (true)
                {
                    //IPEndPoint object will allow us to read datagrams sent from any source.
                    var remoteEndPoint = new IPEndPoint(IPAddress.Any, 0);
                    var receivedResults = udpClient.Receive(ref remoteEndPoint);
                    loggingEvent += Encoding.ASCII.GetString(receivedResults);
                }
            }
        });
    }

Yes, this probably runs. But consider an environment such as Unity 3D where you do not have multitasking / multithreading. What do you do in this case? — Slesa, Jul 31 '15 at 15:06
@Slesa Late response but you can use multitasking/multithreading in Unity. You just need to access Unity stuff on main thread, everything else can be done on other threads. — Alexander, Jun 09 '17 at 12:00
any idea why .net is missing IPEndPoint from ReceiveAsync method? how would you send a message back to the sender? — scape, Dec 09 '20 at 21:29
@scape it will be in the result UdpReceiveResult->RemoteEndPoint. in a synchronous method, it is not in vain that the RemoteEndPoint parameter is passed through "ref" — Gardes, Jan 28 '22 at 06:32

score 0 · Answer 3 · edited Jan 15 '18 at 19:09

I can recommend two links about this solution which were helpful for me.

PC Related

Stack Overflow

The first one is really easy solution but be careful at modifying because the continual receiving will work only if some UDP packet is sent as first to the "remote" device. For continual listening add the code line "udp.BeginReceive(new AsyncCallback(UDP_IncomingData), udp_ep);" after each reading of incomming data to enable new receiving of UDP packets.

The second one is nice solution for using the Multicast IP-addresses (239.255.255.255 - 240.0.0.0)

Receive messages continuously using udpClient

3 Answers3

Asynchronous Method

Synchronous Method

Linked