Is there a way we can see/log the actual forward proxy request's details?

[ChintanRaval]

dotnet 7
yarp 2.0.1

Hello!

Just like the app.UseHttpLogging() logs the request & response and you can control how much to log and see there, is there a way I can also log the proxy request that is being forwarded by YARP? Maybe it's this object RequestTransformContext.ProxyRequest? Or maybe it's some other object with the details?

However, i am struggling to log the details of the actual request that is being sent out by YARP. The closest I can get is by referencing the ReverseProxy.Metrics.Sample's HttpClientTelemetryConsumer's OnRequestStart method which har some of the details coming in as arguments which I could log by wiring up that class in the middleware (builder.Services.AddTelemetryConsumer<HttpClientTelemetryConsumer>();

It seems like a simple thing to see when using YARP, but I think I am definitely overlooking something that may be obviously available - so some help here is really appreciated 🙂

P.S.: Yes - I have tried searching the YARP repo, this discussion forum, YARP's documentation, search engine & chatGPT 😅

[ChintanRaval]

UPDATE: I think I may have found one way to access the forward proxy request by using a Custom Transformer as described here and then use HttpTransformer.TransformRequestAsync(...) method to access the HttpRequestMessage proxyRequest argument.

However, this seems to require moving away from the regular app.MapReverseProxy() call, is there a way one can log/see/access the forward request object without using direct forwarding?

[MihaZupan]

What information about the request are you looking to log?
Things like Uri/Host/Headers, or also the request body of POST requests?

There is nothing similar to UseHttpLogging built in, but most of the information on the outgoing request should be very similar to the original request that came in (minus Uri and header modifications done with transforms).

However, this seems to require moving away from the regular app.MapReverseProxy() call, is there a way one can log/see/access the forward request object without using direct forwarding?

You don't have to write a whole HttpTransformer or move to direct forwarding to do so.
E.g.

services.AddReverseProxy()
    .AddTransforms(transformBuilderContext =>
    {
        transformBuilderContext.AddRequestTransform(context =>
        {
            _logger.LogInformation("...", context.ProxyRequest.RequestUri.AbsoluteUri);

            return ValueTask.CompletedTask;
        });
    });

See https://microsoft.github.io/reverse-proxy/articles/transforms.html

If you are interested in logging the request body, I think the best option is to let ASP.NET Core's Http Logging do it for you.

[ChintanRaval]

thanks @MihaZupan that helps and solved my problem 🙂

[jakebanks]

Is there any way to see the egress request after transforms? I am working with @ChintanRaval and we are now looking to compare headers on the ingress request vs headers on the egress request.

One thing I tried was using a middleware but the request on the HttpContext is the ingress request.

Thank you.

[MihaZupan]

You could try inserting that logic as the last request transform, or write a DelegatingHandler that by definition runs after all request transforms.

[jakebanks]

Thanks @MihaZupan. We actually realized that comparing header values ingress/egress is essentially 'testing YARP' and we trust the headers are being copied over, so I won't be pursuing this line of thought further.