IHttpForwarder and cancellation

[Tratcher]

IHttpForwarder.SendAsync does not directly accept a CancellationToken to abort it. It supports canceling if the ForwarderRequestConfig.ActivityTimeout expires, or if HttpContext.RequestAborted triggers (client disconnect).
https://github.com/microsoft/reverse-proxy/blob/79c88ce07f9b88a283e10fc4cc45287b2efa6750/src/ReverseProxy/Forwarder/IHttpForwarder.cs#L25-L26

A customer that wanted to add their own cancellation condition did so by replacing HttpContext.RequestAborted. However, this caused an issue where they were leaking resources because they were no longer responding to the original RequestAborted token. The fix was to chain the two tokens.

Feedback: Having a CancellationToken parameter on IHttpForwarder.SendAsync would make this less error prone.

[MihaZupan]

Having a CancellationToken parameter on IHttpForwarder.SendAsync would make this less error prone

I agree with this from the perspective of runtime APIs, but this doesn't seem to be the pattern AspNet follows to my knowledge:

• Middleware don't give you CancellationTokens explicitly - you are expected to use HttpContext.RequestAborted
• Same thing for MVC controllers
• You can't inject a CT into minimal APIs

app.MapGet("/delay1", async (CancellationToken ct) => // blows up at runtime
{
    while (true)
    {
        Console.WriteLine(ct.IsCancellationRequested);
        await Task.Delay(1000);
    }
});

app.MapGet("/delay2", async (HttpContext context) =>
{
    while (true)
    {
        Console.WriteLine(context.RequestAborted.IsCancellationRequested);
        await Task.Delay(1000);
    }
});

With YARP being in the middle between runtime and AspNet, do we believe YARP users are more error-prone to this than those of other web apps?

[Tratcher]

The main difference I see is that Middleware isn't invoked by users, it's invoked by the runtime that doesn't need to customize parameters. IHttpForwarder is an API invoked by the user more like HttpClient that does take a CT.

[davidfowl]

@MihaZupan

You can't inject a CT into minimal APIs

You can and also into MVC controller actions.

[MihaZupan]

You can and also into MVC controller actions.

Oh was that added in 7?

[davidfowl]

6.0 supports cancellation tokens but MVC always supported it.