Use errors in custom middleware

[christopherpross]

Hey,
I have some Middlewares in yarp and I want to generate errors and then modify my flow or not proxy the request.
I read about the "IProxyErrorFeature" but it doesn't exist anymore.
Is there an other way to do that?
all the best,
Christopher

[alnikola]

Hi. IProxyErrorFeature was renamed to ForwaderErrorFeature. Please, find it here.

[Tratcher]

Broken link?

[alnikola]

Sorry. My mistake. Fixed.

[christopherpross]

That means:
I need to implement the interface IForwarderErrorFeature and can then set / get it in my middleware to look whether there was are an exception or not?
Does yarp generate this also this way? I know that HttpForwarder generate this, but I only use middleware.
My target is, to react on any exception / error that can happen, custom or yarp. On the best way.

[alnikola]

I'm not sure if I completely understood your question, but I'd like to clarify that IForwarderErrorFeature is specific to ForwarderMiddleware and HttpForwader types. It's not a generic error reporting mechanism.

[MihaZupan]

YARP will implement the interface, you just have to get it inside your middleware. HttpForwarder will set the IForwarderErrorFeature on the context before returning, so you can inspect the error even if you are using the middleware and not the forwarder directly.

endpoints.MapReverseProxy(proxyPipeline =>
{
    proxyPipeline.Use(CustomMiddleware);
});

public async Task CustomMiddleware(HttpContext context, Func<Task> next)
{
    try
    {
        await next();

        var error = context.Features.Get<IForwarderErrorFeature>();
        if (error is not null)
        {
            // We couldn't proxy the request for some reason
            // May include the underlying exception
            Console.WriteLine($"Error: {error.Error} ({error.Exception?.Message})");
        }
    }
    catch (Exception ex)
    {
        // Something even more unexpected happened
        // For example a transform threw an exeception
    }
}