WatsonTcp is the fastest, easiest, most efficient way to build TCP-based clients and servers in C# with integrated framing, reliable transmission, and fast disconnect detection.

IMPORTANT WatsonTcp provides framing to ensure message-level delivery which also dictates that you must either 1) use WatsonTcp for both the server and the client, or, 2) ensure that your client/server exchange messages with the WatsonTcp node using WatsonTcp's framing. Refer to FRAMING.md for a reference on WatsonTcp message structure.

• If you want a library that doesn't use framing, but has a similar implementation, use SuperSimpleTcp
• If you want a library that doesn't use framing and provides explicit control over how much data to read, use CavemanTcp

This project is part of the .NET Foundation along with other projects like the .NET Runtime.

Special thanks to the following people for their support and contributions to this project!

@brudo @MrMikeJJ @mikkleini @pha3z @crushedice @marek-petak @ozrecsec @developervariety @NormenSchwettmann @karstennilsen @motridox @AdamFrisby @Job79 @Dijkstra-ru @playingoDEERUX @DuAell @syntacs @zsolt777 @broms95 @Antwns @MartyIX @Jyck @Memphizzz @nirajgenius @cee-sharp @jeverz @cbarraco @DenisBalan @Markonius @Ahmed310 @markashleybell @thechosensausage @JVemon @eatyouroats @bendablegears @Laiteux @fisherman6v6 @wesoos @YorVeX @tovich37 @sancheolz @lunedis

If you'd like to contribute, please jump right into the source code and create a pull request, or, file an issue with your enhancement request.

• Remove unsupported frameworks
• Async version of SyncMessageReceived callback
• Moving usings inside namespace
• Remove obsolete methods
• Mark non-async APIs obsolete
• Modified test projects to use async
• Ensured background tasks honored cancellation tokens
• Ability to specify a client's GUID before attempting to connect
• Remove obsolete methods

Test projects for both client and server are included which will help you understand and exercise the class library.

WatsonTcp supports data exchange with or without SSL. The server and client classes include constructors that allow you to include fields for the PFX certificate file and password. An example certificate can be found in the test projects, which has a password of 'password'.

WatsonTcp allows you to receive messages using either byte arrays or streams. Set Events.MessageReceived if you wish to consume a byte array, or, set Events.StreamReceived if you wish to consume a stream.

It is important to note the following:

• When using Events.MessageReceived
  • The message payload is read from the stream and sent to your application
  • The event is fired asynchronously and Watson can continue reading messages while your application processes
• When using Events.StreamReceived
  • If the message payload is smaller than Settings.MaxProxiedStreamSize, the data is read into a MemoryStream and sent to your application asynchronously
  • If the message payload is larger than Settings.MaxProxiedStreamSize, the underlying data stream is sent to your application synchronously, and WatsonTcp will wait until your application responds before continuing to read
• Only one of Events.MessageReceived and Events.StreamReceived should be set; Events.MessageReceived will be used if both are set

Should you with to include metadata with any message, use the Send or SendAsync method that allows you to pass in metadata (Dictionary<string, object>). Refer to the TestClient, TestServer, TestClientStream, and TestServerStream projects for a full example. Keys must be of type string.

Note: if you use a class instance as either the value, you'll need to deserialize on the receiving end from JSON.

object myVal = args.Metadata["myKey"];
MyClass instance = myVal.ToObject<MyClass>();

This is not necessary if you are using simple types (int, string, etc). Simply cast to the simple type.

IMPORTANT

Identifying the demarcation between message header and payload is CPU intensive and requires evaluation of the tail end of an internally-managed buffer. This process of evaluation is performed for each byte read until the end of the header is reached. Thus, is it recommended that the metadata property be used sparingly and with very small amounts of data (less than 1KB). When used with large amounts of data, CPU utilization will increase dramatically and response time will be very slow.

IMPORTANT

• If you specify 127.0.0.1 as the listener IP address in WatsonTcpServer, it will only be able to accept connections from within the local host.
• To accept connections from other machines:
  • Use a specific interface IP address, or
  • Use null, *, +, or 0.0.0.0 for the listener IP address (requires admin privileges to listen on any IP address)
• Make sure you create a permit rule on your firewall to allow inbound connections on that port
• If you use a port number under 1024, admin privileges will be required

.NET Core should always be the preferred option for multi-platform deployments. However, WatsonTcp works well in Mono environments with the .NET Framework to the extent that we have tested it. It is recommended that when running under Mono, you execute the containing EXE using --server and after using the Mono Ahead-of-Time Compiler (AOT). Note that TLS 1.2 is hard-coded, which may need to be downgraded to TLS in Mono environments.

NOTE: Windows accepts '0.0.0.0' as an IP address representing any interface. On Mac and Linux you must be specified ('127.0.0.1' is also acceptable, but '0.0.0.0' is NOT).

mono --aot=nrgctx-trampolines=8096,nimt-trampolines=8096,ntrampolines=4048 --server myapp.exe
mono --server myapp.exe

The following examples show a simple client and server example using WatsonTcp without SSL and consuming messages using byte arrays instead of streams. For full examples, please refer to the Test.* projects.

using WatsonTcp;

static void Main(string[] args)
{
    WatsonTcpServer server = new WatsonTcpServer("127.0.0.1", 9000);
    server.Events.ClientConnected += ClientConnected;
    server.Events.ClientDisconnected += ClientDisconnected;
    server.Events.MessageReceived += MessageReceived; 
    server.Callbacks.SyncRequestReceivedAsync = SyncRequestReceived;
    server.Start();

    // list clients
    IEnumerable<ClientMetadata> clients = server.ListClients();

    // send a message
    await server.SendAsync([guid], "Hello, client!");

    // send a message with metadata
    Dictionary<string, object> md = new Dictionary<string, object>();
    md.Add("foo", "bar");
    await server.SendAsync([guid], "Hello, client!  Here's some metadata!", md);

    // send and wait for a response
    try
    {
        SyncResponse resp = await server.SendAndWaitAsync(
            [guid], 
            5000, 
            "Hey, say hello back within 5 seconds!");

        Console.WriteLine("My friend says: " + Encoding.UTF8.GetString(resp.Data));
    }
    catch (TimeoutException)
    {
        Console.WriteLine("Too slow...");
    } 
}

static void ClientConnected(object sender, ConnectionEventArgs args)
{
    Console.WriteLine("Client connected: " + args.Client.ToString());
}

static void ClientDisconnected(object sender, DisconnectionEventArgs args)
{
    Console.WriteLine(
        "Client disconnected: " 
        + args.Client.ToString() 
        + ": " 
        + args.Reason.ToString());
}

static void MessageReceived(object sender, MessageReceivedEventArgs args)
{
    Console.WriteLine(
        "Message from " 
        + args.Client.ToString() 
        + ": " 
        + Encoding.UTF8.GetString(args.Data));
}

static async Task<SyncResponse> SyncRequestReceived(SyncRequest req)
{
    return new SyncResponse(req, "Hello back at you!");
}

using WatsonTcp;

static void Main(string[] args)
{
    WatsonTcpClient client = new WatsonTcpClient("127.0.0.1", 9000);
    client.Events.ServerConnected += ServerConnected;
    client.Events.ServerDisconnected += ServerDisconnected;
    client.Events.MessageReceived += MessageReceived; 
    client.Callbacks.SyncRequestReceivedAsync = SyncRequestReceived;
    client.Connect();

    // check connectivity
    Console.WriteLine("Am I connected?  " + client.Connected);

    // send a message
    client.Send("Hello!");

    // send a message with metadata
    Dictionary<string, object> md = new Dictionary<string, object>();
    md.Add("foo", "bar");
    await client.SendAsync("Hello, client!  Here's some metadata!", md);

    // send and wait for a response
    try
    {
        SyncResponse resp = await client.SendAndWaitAsync(
            5000, 
            "Hey, say hello back within 5 seconds!");

        Console.WriteLine("My friend says: " + Encoding.UTF8.GetString(resp.Data));
    }
    catch (TimeoutException)
    {
        Console.WriteLine("Too slow...");
    }  
}

static void MessageReceived(object sender, MessageReceivedEventArgs args)
{
    Console.WriteLine("Message from server: " + Encoding.UTF8.GetString(args.Data));
}

static void ServerConnected(object sender, ConnectionEventArgs args)
{
    Console.WriteLine("Server connected");
}

static void ServerDisconnected(object sender, DisconnectionEventArgs args)
{
    Console.WriteLine("Server disconnected");
}

static async Task<SyncResponse> SyncRequestReceived(SyncRequest req)
{
    return new SyncResponse(req, "Hello back at you!");
}

The examples above can be modified to use SSL as follows. No other changes are needed. Ensure that the certificate is exported as a PFX file and is resident in the directory of execution.

// server
WatsonTcpServer server = new WatsonTcpServer("127.0.0.1", 9000, "test.pfx", "password"); 
server.Settings.AcceptInvalidCertificates = true;
server.Settings.MutuallyAuthenticate = true;
server.Start();

// client
WatsonTcpClient client = new WatsonTcpClient("127.0.0.1", 9000, "test.pfx", "password"); 
client.Settings.AcceptInvalidCertificates = true;
client.Settings.MutuallyAuthenticate = true;
client.Connect();

Refer to the Test.ClientStream and Test.ServerStream projects for a full example.

// server
WatsonTcpServer server = new WatsonTcpServer("127.0.0.1", 9000);
server.Events.ClientConnected += ClientConnected;
server.Events.ClientDisconnected += ClientDisconnected;
server.Events.StreamReceived += StreamReceived; 
server.Start();

static void StreamReceived(object sender, StreamReceivedEventArgs args)
{
    long bytesRemaining = args.ContentLength;
    int bytesRead = 0;
    byte[] buffer = new byte[65536];

    using (MemoryStream ms = new MemoryStream())
    {
        while (bytesRemaining > 0)
        {
            bytesRead = args.DataStream.Read(buffer, 0, buffer.Length);
            if (bytesRead > 0)
            {
                ms.Write(buffer, 0, bytesRead);
                bytesRemaining -= bytesRead;
            }
        }
    }

    Console.WriteLine(
        "Stream received from " 
        + args.Client.ToString() 
        + ": " 
        + Encoding.UTF8.GetString(ms.ToArray())); 
}

// client
WatsonTcpClient client = new WatsonTcpClient("127.0.0.1", 9000);
client.Events.ServerConnected += ServerConnected;
client.Events.ServerDisconnected += ServerDisconnected;
client.Events.StreamReceived += StreamReceived; 
client.Connect();

static void StreamReceived(object sender, StreamReceivedEventArgs args)
{
    long bytesRemaining = args.ContentLength;
    int bytesRead = 0;
    byte[] buffer = new byte[65536];

    using (MemoryStream ms = new MemoryStream())
    {
        while (bytesRemaining > 0)
        {
            bytesRead = args.DataStream.Read(buffer, 0, buffer.Length);
            if (bytesRead > 0)
            {
                ms.Write(buffer, 0, bytesRead);
                bytesRemaining -= bytesRead;
            }
        }
    }

    Console.WriteLine("Stream received from server: " + Encoding.UTF8.GetString(ms.ToArray())); 
}

If you wish to specify a client's GUID, you can modify WatsonTcpClient.Settings.Guid prior to calling WatsonTcpClient.Connect().

WatsonTcpClient client = new WatsonTcpClient("127.0.0.1", 9000);
client.Events.ServerConnected += ServerConnected;
client.Events.ServerDisconnected += ServerDisconnected;
client.Events.StreamReceived += StreamReceived; 
client.Settings.Guid = Guid.Parse("12345678-1234-1234-123456781234");
client.Connect();

The first step in troubleshooting is to implement a logging method and attach it to Settings.Logger, and as a general best practice while debugging, set Settings.DebugMessages to true.

client.Settings.DebugMessages = true;
client.Settings.Logger = MyLoggerMethod;

private void MyLoggerMethod(Severity sev, string msg)
{
    Console.WriteLine(sev.ToString() + ": " + msg);
}

Additionally it is recommended that you implement the Events.ExceptionEncountered event.

client.Events.ExceptionEncountered += MyExceptionEvent;

private void MyExceptionEvent(object sender, ExceptionEventArgs args)
{
    Console.WriteLine(args.Json);
}

The project TcpTest (https://github.com/jchristn/TcpTest) was built specifically to provide a reference for WatsonTcp to handle a variety of disconnection scenarios. The disconnection tests for which WatsonTcp is evaluated include:

Additionally, as of v4.3.0, support for TCP keepalives has been added to WatsonTcp, primarily to address the issue of a network interface being shut down, the cable unplugged, or the media otherwise becoming unavailable. It is important to note that keepalives are supported in .NET Core and .NET Framework, but NOT .NET Standard. As of this release, .NET Standard provides no facilities for TCP keepalives.

TCP keepalives are NOT enabled by default. To enable and configure:

server.Keepalive.EnableTcpKeepAlives = true;
server.Keepalive.TcpKeepAliveInterval = 5;      // seconds to wait before sending subsequent keepalive
server.Keepalive.TcpKeepAliveTime = 5;          // seconds to wait before sending a keepalive
server.Keepalive.TcpKeepAliveRetryCount = 5;    // number of failed keepalive probes before terminating connection

Some important notes about TCP keepalives:

• Keepalives only work in .NET Core and .NET Framework
• Keepalive.TcpKeepAliveRetryCount is only applicable to .NET Core; for .NET Framework, this value is forced to 10

If you wish to have WatsonTcpServer automatically disconnect clients that have been idle for a period of time, set WatsonTcpServer.IdleClientTimeoutSeconds to a positive integer. Receiving a message from a client automatically resets their timeout. Client timeouts are evaluated every 5 seconds by Watson, so the disconnection may not be precise (for instance, if you use 7 seconds as your disconnect interval).

If you would like to financially support my efforts, first of all, thank you! Please refer to DONATIONS.md.

Please refer to CHANGELOG.md for details.