#Sockets Plugin for Xamarin and Windows (PCL)

An abstraction over the socket helper classes of .NET and WinRT, providing a PCL-friendly socket library for projects targeting Xamarin iOS/Android/Forms, Xamarin.Mac/MonoMac, Windows Phone 8/8.1, Windows Store, UWP, and Windows Desktop. It allows you to write socket code in your PCL, simplifying cross-platform peer-to-peer communications significantly as well as enabling code sharing for many other use cases.

This library utilises the "Bait and Switch" pattern, so must be installed via NuGet in both the PCL and your native projects.

Get it on NuGet: Install-Package rda.SocketsForPCL

Classes

The plugin currently provides the following socket abstractions:

Class	Description	.NET Abstraction	WinRT Abstraction
TcpSocketListener	Bind to a port and accept TCP socket connections.	TcpListener	StreamSocketListener
TcpSocketClient	Connect to a TCP endpoint with bi-directional communication.	TcpClient	StreamSocket
UdpSocketReceiver	Bind to a port and receive UDP messages.	UdpClient	DatagramSocket
UdpSocketClient	Send messages to arbitrary endpoints over UDP.	UdpClient	DatagramSocket
UdpSocketMulticastClient	Send and receive UDP messages within a multicast group.	UdpClient	DatagramSocket

Apart from the decisions made in order to merge the two APIs, the abstraction aims to be relatively unopinionated. This means that there is little to no protection in the library against socket failures, reliablity, retry, and other considerations. sockethelpers-for-pcl is a longer term project with the aim of providing useful functionality around the base sockets-for-pcl classes, including hub-style communications, custom protocol helpers and support for typed messaging, and error handling/life cycle and reliability options.

Example Usage

TcpSocketListener and TcpSocketClient each expose ReadStream and WriteStream properties of type System.IO.Stream for receiving and sending data. UdpReceiver, UdpClient and UdpMulticastClient expose a MessageReceived event and a Send() method due to the nature of the transport and the underlying implementations.

A TCP listener

var listenPort = 11000;
var listener = new TcpSocketListener();
    
// when we get connections, read byte-by-byte from the socket's read stream
listener.ConnectionReceived += async (sender, args) => 
{
    var client = args.SocketClient; 
    
	var bytesRead = -1;
	var buf = new byte[1];
		
	while (bytesRead != 0)
	{
		bytesRead = await args.SocketClient.ReadStream.ReadAsync(buf, 0, 1);
		if (bytesRead > 0)
            Debug.Write(buf[0]);
	}
};
    
// bind to the listen port across all interfaces
await listener.StartListeningAsync(listenPort);

A TCP client

var address = "127.0.0.1";
var port = 11000;
var r = new Random(); 
    
var client = new TcpSocketClient();
await client.ConnectAsync(address, port);
    
// we're connected!
for (int i = 0; i<5; i++)
{
    // write to the 'WriteStream' property of the socket client to send data
    var nextByte = (byte) r.Next(0,254);
    client.WriteStream.WriteByte(nextByte);
    await client.WriteStream.FlushAsync();
      
    // wait a little before sending the next bit of data
    await Task.Delay(TimeSpan.FromMilliseconds(500)); 
}
    
await client.DisconnectAsync();

A UDP receiver

var listenPort = 11011;
var receiver = new UdpSocketReceiver();
    
receiver.MessageReceived += (sender, args) =>
{
    // get the remote endpoint details and convert the received data into a string
    var from = String.Format("{0}:{1}", args.RemoteAddress, args.RemotePort);
    var data = Encoding.UTF8.GetString(args.ByteData, 0, args.ByteData.Length);
      
    Debug.WriteLine("{0} - {1}", from, data);
};
    
// listen for udp traffic on listenPort
await receiver.StartListeningAsync(listenPort);

A UDP client

var port = 11011;
var address = "127.0.0.1";
    
var client = new UdpSocketClient();
    
// convert our greeting message into a byte array
var msg = "HELLO WORLD";
var msgBytes = Encoding.UTF8.GetBytes(msg);
    
// send to address:port, 
// no guarantee that anyone is there 
// or that the message is delivered.
await client.SendToAsync(msgBytes, address, port);

A multicast UDP client

var port = 11811;
var address = "239.192.0.1"; // must be a valid multicast address
    
// typical instantiation
var receiver = new UdpSocketMulticastClient();
receiver.TTL = 5;
    
receiver.MessageReceived += (sender, args) =>
{
    var from = String.Format("{0}:{1}", args.RemoteAddress, args.RemotePort);
    var data = Encoding.UTF8.GetString(args.ByteData, 0, args.ByteData.Length);
      
    Debug.WriteLine("{0} - {1}", from, data);
};
    
// join the multicast address:port
await receiver.JoinMulticastGroupAsync(address, port);

var msg = "HELLO MULTIVERSE";
var msgBytes = Encoding.UTF8.GetBytes(msg);
    
// send a message that will be received by all listening in
// the same multicast group. 
await receiver.SendMulticastAsync(msgBytes);

Binding to a specific interface

For a majority of mobile use cases, binding to all interfaces is a good approach. However, when working with multicast or on a machine with many interfaces, it may be useful to bind to a specific interface. The TcpSocketListener, UdpSocketReceiver and UdpSocketMulitcastClient classes include an optional CommsInterface parameter on their listen/join methods, allowing them to be bound to a specific interface only. If this parameter is not specified, all interfaces will be bound. CommsInterface has a static method GetAllInterfacesAsync that can be used to enumerate the available interfaces.

// retrieve the list of interfaces from the device
var allInterfaces = await CommsInterface.GetAllInterfacesAsync();
    
// get the first interface with an ip address
var firstUsable = allInterfaces.FirstOrDefault(ci => ci.IsUsable);
    
if (firstUsable == null)
    return; // no connected interfaces, too bad!
        
var listener = new TcpSocketListener(); 
await listener.StartListeningAsync(11000, firstUsable); 
    
Console.WriteLine("Listening on interface with ip: {0}", firstUsable.IpAddress);

TLS Support

TcpSocketClient supports TLS connections (server certificate only). Pass true to the optional parameter useTls on ConnectAsync to enable secure communication.

Platform Considerations

• Xamarin.Mac Unified and MonoMac should work out of the box. For Xamarin.Mac Classic projects, after installing sockets-for-pcl you must manually alter the <HintPath> entries for Sockets.Plugin and Sockets.Plugin.Abstractions in your .csproj file, to replace references to net45 with Xamarin.Mac.Classic. Without this, code interacting with portions of the System.Net namespace not implemented in mono, including methods on some classes required by CommsInterface, will fail.
• On Windows Phone, you will require appropriate permissions in your app manifest. Depending on whether you are listening or sending, this could include a combination of privateNetworkClientServer, internetClient and/or internetClientServer capabilities.
• On Windows Phone/Store, there are restrictions regarding passing traffic over loopback between separate apps (i.e. no IPC)
• Binding to specific interfaces is not supported on Windows Phone 8.0 (8.1 is fine). All interfaces will be bound, even if a specific CommsInterface is provided.

Additional 'higher level' features will likely end up in the sockethelpers-for-pcl project mentioned earlier.

Contributions

Many members of the community have contributed to improving sockets-for-pcl:

• @rdavisau
• @jamesmontemagno (project and NuGet templates)
• @galvesribeiro (TLS support)
• @SatoshiARA (Mac support)
• @aghajani (bugfixes)
• @danielcweber (GetStream(), PCL-friendly SocketException)
• @xen2 (configurable and consistent buffering between .NET and WinRT)
• @NVentimiglia (bugfixes, design considerations)
• @fubar-coder (auto/ephemeral port selection, support for getting connected interface)
• @mattleibow (Xamarin Component Store submission)
• @Waty (proper events, bugfixes)
• @SparkStream (TcpSocketClient cancellation support, service name support)
• @usasos000 (bugfixes)
• @jasells (udpclient design considerations)

If you have a bugfix or a feature you'd like to add, please open an issue. All pull requests should be opened against the dev branch.

Sponsors

Thanks to Xamarin and ReSharper who provide open-source licenses for the project.