Raise an Error in ConfigureHttpClient when custom IForwarderHttpClientFactory is added

[Kahbazi]

What should we add or change to make your life better?

Throw an exception in ConfigureHttpClient when custom IForwarderHttpClientFactory is added stating that "You couldn't call ConfigureHttpClient when another type is added for IForwarderHttpClientFactory. "

Why is this important to you?

I had ConfigureHttpClient in my code to configure SslOptions and lately I added a custom IForwarderHttpClientFactory. Now this wouldn't work because ConfigureHttpClient would add its own IForwarderHttpClientFactory and ignore the DiagnosticsHandlerFactory. I couldn't figure out why DiagnosticsHandlerFactory wasn't working until I checked the source code.

I suggest to throw an exception in ConfigureHttpClient if any other implementation of IForwarderHttpClientFactory beside ForwarderHttpClientFactory is added, in order to reduce the debugging time for others.

Btw this is my code:

services.AddSingleton<IForwarderHttpClientFactory, DiagnosticsHandlerFactory>();
services.AddReverseProxy()
    .ConfigureHttpClient((context, handler) =>
    {
        handler.SslOptions = ...
    }

[adityamandaleeka]

@Kahbazi This sort of thing is difficult to do with the way the service collection works. Detecting the presence of the prior service might be tricky.

You're welcome to try an experiment to see if this would be practical.