Filters, Context & Telemetry

Call filters

An IActorCallFilter runs around every call, local or remote. Use it for logging, validation, authorization and more.

actors.AddCallFilter<AuditFilter>();   // created by the container - or AddCallFilter(instance)

public sealed class AuditFilter : IActorCallFilter
{
    public async ValueTask InvokeAsync(ActorCallContext ctx, ActorCallDelegate next)
    {
        if (ActorRequestContext.Get("user") is null) throw new UnauthorizedAccessException();
        await next(ctx);   // ctx.Method, ctx.Arguments, ctx.Result (settable), ctx.ActorId
    }
}

• Filters run inside the actor’s turn, for both asks and one-way calls.
• ctx.Result can be read and replaced after next.
• An actor that implements IActorCallFilter itself filters its own calls, innermost.

Request context

ActorRequestContext.Set("user", "allan");
await actors.Get<IWallet>("allan").Deposit(10);   // the actor, and anything it calls, sees "user"

ActorRequestContext values flow into the call, onward to the actors it calls, and across remote calls in the x-actor-context header.

Telemetry

services.AddOpenTelemetry()
    .WithTracing(t => t.AddSource(ActorTelemetry.Name))
    .WithMetrics(m => m.AddMeter(ActorTelemetry.Name));

Both the ActivitySource and the Meter are named Shiny.Actors.

Traces. There’s one span per call, named {interface}/{method} and parented to the caller’s span. That holds across actors and across HTTP: the client span, then the server span, then the actor’s.

Metrics. None of them carry actor ids, because ids are unbounded:

• calls, by outcome
• call duration
• active, activated and deactivated actors
• queued calls
• state writes, write duration and conflicts
• reminders fired
• stream events