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System.Net.Sockets.UdpClient

This API implements the UdpClient class with a pattern similar to the official .NET equivalent System.Net.Sockets.UdpClient. Beside the lack of the asynchronous methods the receive functions don't use an internal buffer like the .NET API but instead requires a buffer to be passed as part of the call.

Note: For the Receive methods if the buffer is smaller than the packet to receive it will be truncated to the buffer size without warning. Indeed "lwIP", the TCP/IP stack used commonly by RTOS, doesn't support the MSG_TRUNC socket option in calls to recvfrom to return the real length of the datagram when it is longer than the passed buffer opposite to common Un*x implementations.

Build status

Component	Build Status	NuGet Package
nanoFramework.System.Net.Sockets.UdpClient

Usage

Important: Obviously UdpClient requires a working network connection with a valid IP address. Please check the examples with the Network Helpers on how to connect to a network.

The UdpClient class provides simple methods for sending and receiving UDP datagrams on an IP network. The current implementation supports only IPv4. IPv6 isn't supported on nanoFramework currently.

Samples

Samples for UdpClient are present in the nanoFramework Sample repository.

Remote host

Because UDP is a connectionless protocol you don't need to establish a remote host connection before sending and receiving data. But you can define a default remote host that will be used for subsequent Send method calls. If you establish a default remote host, you cannot specify a different host when sending datagrams. You can define a default remote host with one of the following methods:

• Create your client using the UdpClient(string hostname,string remoteport) constructor.
• Create an instance and then call the Connect method.

Client usage

Using UdpClient in client mode is pretty easy. You create an UdpClient with one of the constructor, establish or not a default remote host (see above) then you can send and receive message from the network.

The following code show a typical client server exchange where you first send a message to the server and wait for the server answer:

// establish defaut host and port
UdpClient udpClient = new UdpClient("1.2.3.4", 5000);
udpClient.Send(Encoding.UTF8.GetBytes("Hello server"));

// receive message
byte[] buffer = new byte[1024];
IPEndPoint ipEndpoint = new IPEndPoint(IPAddress.Any, 0);
int length = udpClient.Receive(buffer, ref ipEndpoint);
Debug.WriteLine(Encoding.UTF8.GetString(buffer, 0, length));

Server usage

Working as server you bind your UdpClient on a local port then you wait for messages from clients. As a server you don't know beforehand the IP address of your clients so you shouldn't define any remote host.

The following code show a simple echo server:

// Run echo protocol on port 5000
UdpClient udpClient = new UdpClient(5000); 

// We limit ourself to a 1024 bytes buffer
byte[] buffer = new byte[1024];
IPEndPoint endpointClient = new IPEndPoint(IPAddress.Any, 0);

// We send back every request we get
while (true)
{
    int length = udpClient.Receive(buffer, ref endpointClient);
    udpClient.Send(buffer,endpointClient);
}

Multicast

If you want to use multicast ensure that you bind your UdpClient on the 0.0.0.0 (wilcard) address. If you bind your UdpClient to a specific IPAddress you won't receive the multicast datagrams.

Basically for a functional multicast client/server you need to:

• Create your UdpClient without binding it to a specific address.
• Join a Multicast group by a call to the JoinMulticastGroup method.
• Receive datagram sent to that group address with call to Receive
• Send message to the group multicast using Send
• Leave the Multicast group by calling the DropMulticastGroup method

The following sample illustrate that basic workflow:

// Create your UdpClient without binding it to a specific address
IPEndPoint iPEndpoint = new IPEndPoint(IPAddress.Any, 5000);
UdpClient client = new UdpClient(iPEndpoint);

// Join a Multicast group
IPAddress ipGroupMulticast = IPAddress.Parse("239.255.255.250");
client.JoinMulticastGroup(ipGroupMulticast);

bool StopListener = false;
byte[] buffer = new byte[2048];
while (!StopListener)
{
    IPEndPoint remote = new IPEndPoint(IPAddress.Any, 0);
    int length = client.Receive(buffer, ref remote);
    string result = Encoding.UTF8.GetString(buffer, 0, length);
    if (result == "Ping")
    {
        buffer = Encoding.UTF8.GetBytes("Present");
        client.Send(buffer,ipGroupMulticast);
    }
    StopListener = (result == "Exit");
}

// Leave the Multicast group
client.DropMulticastGroup(ipGroupMulticast);

If you want to receive your own messages you can enable this by setting the UdpClient.MulticastLoopback property to true.

Feedback and documentation

For documentation, providing feedback, issues and finding out how to contribute please refer to the Home repo.

Join our Discord community here.

Credits

The list of contributors to this project can be found at CONTRIBUTORS.

License

The nanoFramework Class Libraries are licensed under the MIT license.

Code of Conduct

This project has adopted the code of conduct defined by the Contributor Covenant to clarify expected behaviour in our community. For more information see the .NET Foundation Code of Conduct.

.NET Foundation

This project is supported by the .NET Foundation.