SlimFaasClient 0.84.9

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SlimFaasClient

C# library to connect Jobs or virtual functions to SlimFaas via WebSocket. Lets any process receive async requests and publish/subscribe events without exposing an HTTP port.

Links:

• NuGet package: https://www.nuget.org/packages/SlimFaasClient
• GitHub repository: https://github.com/SlimPlanet/SlimFaas
• SlimFaas website: https://slimfaas.dev/

Installation

dotnet add package SlimFaasClient

Quick start

using SlimFaasClient;

var config = new SlimFaasClientConfig
{
    FunctionName = "my-job",
    SubscribeEvents = [new SubscribeEventConfig { Name = "order-created" }],
    DefaultVisibility = FunctionVisibility.Public,
    NumberParallelRequest = 5,
};

await using var client = new SlimFaasClient.SlimFaasClient(
    new Uri("ws://slimfaas:5003/ws"), config);

// Async request handler — return the HTTP status code SlimFaas should record
client.OnAsyncRequest = async req =>
{
    Console.WriteLine($"Request: {req.Method} {req.Path}{req.Query}");
    // Body is available as a byte[]? decoded from base64
    return 200;
};

// Publish/subscribe event handler
client.OnPublishEvent = async evt =>
    Console.WriteLine($"Event: {evt.EventName}");

// Sync streaming handler (HTTP-over-WebSocket)
client.OnSyncRequest = async req =>
{
    await req.Response.StartAsync(200, new() { ["Content-Type"] = ["text/plain"] });
    await req.Response.WriteAsync(System.Text.Encoding.UTF8.GetBytes("Hello"));
    await req.Response.CompleteAsync();
};

using var cts = new CancellationTokenSource();
Console.CancelKeyPress += (_, e) => { e.Cancel = true; cts.Cancel(); };
await client.RunForeverAsync(cts.Token);

Full configuration

Connection options

var options = new SlimFaasClientOptions
{
    ReconnectDelay = 5.0,
    PingInterval = 30.0,
    ReceiveBufferSize = 64 * 1024,
};

await using var client = new SlimFaasClient.SlimFaasClient(
    new Uri("ws://slimfaas:5003/ws"), config, options);

Connection lifecycle

RunForeverAsync(ct) owns the connection until ct is cancelled:

• After a clean close by the server it reconnects immediately; after a network error or an unreachable server it waits ReconnectDelay seconds and retries, forever.
• It returns normally when ct is cancelled, whether the cancellation happens while connected, while connecting or during the reconnect delay. It never surfaces an OperationCanceledException for its own token.
• It throws SlimFaasRegistrationException when SlimFaas refuses the registration (name already used by a Kubernetes function, configuration mismatch): this is fatal and is not retried.
• IsConnected is true only between a successful registration and the next disconnection; ConnectionId is null outside that window. SendCallbackAsync and the sync response methods throw InvalidOperationException while disconnected.

Long-running requests (status 202)

Return 202 from the handler to acknowledge the request without completing it yet, then call SendCallbackAsync when the work is done:

client.OnAsyncRequest = async req =>
{
    _ = Task.Run(async () =>
    {
        await LongProcessAsync(req);
        await client.SendCallbackAsync(req.ElementId, 200);
    });
    return 202; // "I'll handle it — will call back"
};

Dependency injection

// Register in your DI container (e.g. ASP.NET Core)
builder.Services.AddSingleton(sp =>
{
    var logger = sp.GetRequiredService<ILogger<SlimFaasClient.SlimFaasClient>>();
    var config = new SlimFaasClientConfig { FunctionName = "my-job" };
    return new SlimFaasClient.SlimFaasClient(
        new Uri("ws://slimfaas:5003/ws"), config, logger: logger);
});

// Access other services inside handlers via a scoped service provider
client.OnAsyncRequest = async req =>
{
    using var scope = app.Services.CreateScope();
    var db = scope.ServiceProvider.GetRequiredService<IMyDatabase>();
    await db.SaveAsync(req.Body);
    return 200;
};

Important rules

1. FunctionName must not match an existing Kubernetes Deployment name. SlimFaas will reject the registration with a SlimFaasRegistrationException.

2. All clients sharing the same FunctionName must use the exact same configuration. Mismatches are rejected on connection.

Running the tests

dotnet test

The suite in tests/SlimFaasClient.Tests contains unit tests for the models and serialization, plus end-to-end protocol tests: SlimFaasClientWebSocketTests starts an in-process Kestrel WebSocket server (FakeSlimFaasServer) that speaks the SlimFaas protocol and drives a real SlimFaasClient through registration, async requests and callbacks, publish events, streamed sync requests, keepalive pings, malformed frames and reconnection. No running SlimFaas instance is needed.