CLI.IPC

A .NET library that helps you implement a client/server architecture for command line interface applications. Using spkl.CLI.IPC, you can let your CLI application delegate its workload to a separate server process.

How does it work? When a user starts your client application, it sends its working directory, command line arguments and process ID to the server application. While processing the request, the server application can send console outputs (standard and error) back to the client. At the end, the server sends an exit code and closes the connection.

spkl.CLI.IPC was designed for clients and servers that run on the same machine, but because it is based on sockets, network communication between different machines can also be used.

Example Usage

Server

Start a server by calling Host.Start and supplying the following information:

• How will the connection be established (ITransport)? Any streaming socket is supported; support for TCP loopback and Unix Domain Sockets* is built-in.
• What will happen when a client connects (IClientConnectionHandler)?

* Unix Domain Sockets are not supported for .NET Standard 2.0 or before Windows 10.

In this example, lets implement a fictional database dump command:

static void Main(string[] args)
{
    Host host = Host.Start(new UdsTransport("path/to/socket_file"), new MyClientConnectionHandler());
    // [ wait until it is time to shut down the server ]
    host.Shutdown();
    host.WaitUntilAllClientsDisconnected();
}

private class MyClientConnectionHandler : IClientConnectionHandler
{
    public void HandleCall(IClientConnection connection)
    {
        if (connection.Properties.Arguments is [_, "dump-db", string fileName])
        {
            connection.Out.WriteLine("Dumping database to file...");
            Db.DumpTo(Path.Combine(connection.Properties.CurrentDirectory, fileName));
            connection.Exit(0);
            return;
        }

        connection.Error.WriteLine("Unknown command.");
        connection.Exit(1);
    }

    // [...]
}

Client

Implementing a client can be as easy as this one-liner:

Client.Attach(
    new UdsTransport("path/to/socket_file"),
    new DefaultHostConnectionHandler());

Just like for the server, you need to specify connection and behavior information (ITransport, IHostConnectionHandler2).

For most scenarios, the built-in DefaultHostConnectionHandler can be used. It writes the received outputs to the console and exits the application with the received exit code when the server closes the connection.

Other Features

SingletonApp: Starting a Server On Demand

A client application obviously can't connect to a server when the server is not running. If the server should be started on demand, i.e. when a client wants to connect, the SingletonApp class can help.

With SingletonApp, you can ensure that only one instance of the server is started, even when multiple clients ask for it simultaneously.

Usage as a client application: Call RequestInstance to ensure that an application instance is running before connecting to it.

IStartupBehavior startupBehavior = [...];
new SingletonApp(startupBehavior).RequestInstance();

Client.Attach([...]);

Usage as a server application: Call ReportInstanceRunning when ready for incoming connections. Call ReportInstanceShuttingDown before no longer accepting connections.

IStartupBehavior startupBehavior = [...];
SingletonApp singletonApp = new(startupBehavior);

Host host = Host.Start([...]);
singletonApp.ReportInstanceRunning();
// [...]
singletonApp.ReportInstanceShuttingDown();
// Consider adding a short waiting period here, to prevent clients that just started up from being denied service.
host.Shutdown();

Using the IStartupBehavior interface, you can customize the following aspects:

• How a server instance is started. Typically, by starting a new process.
• Which time period is used for polling whether a server is starting or running.
• After what timeout the RequestInstance or ReportInstanceRunning methods will fail.
• Which file path is used to determine server state (because SingletonApp uses file-based locking). This can be used to provide a server process per machine, per user, or arbitrarily.

AutoTransportSingletonApp: On Demand and Even Easier

AutoTransportSingletonApp does everything that SingletonApp does, plus it automatically connects your server and your client so you don't have to manage TCP ports or Unix Domain Socket paths.

Simply use the value of the AutoTransportSingletonApp.Transport property for the call to Host.Start and Client.Attach, and a connection can be established.