Customized SocketsHttpHandler does not support diagnostics tracking

[rangp]

I want to use custom HttpConnectionSettings for my requests since I need to decrease DefaultMaxConnectionsPerServer. As far as I know HttpConnectionSettings are only exposed when creating a new SocketsHttpHandler. However if I create a new handler with custom settings and use the handler as message handler for my HttpClient I lose my dependency tracking.

Upon debugging I noticed that the default message handler is HttpClientHandler which includes a DiagnosticsHandler that is not publicly exposed.

How can I customize HttpConnectionSettings while still seeing request diagnostics?

I don't necessarily want to copy DiagnosticsHandler into my code to accomplish this.

On first glance I could see two possible solutions:

1. Expose DiagnosticsHandler publicly, so consumers can wrap their custom HttpHandlers with it.
2. Provide a way to customize HttpConnectionSettings without creating a new message handler, so consumers can use the HttpClientHandler while still being able to configure connection behavior.

[stephentoub]

cc: @lmolkova

[scalablecory]

Can you give more detail on how explicitly using a SocketsHttpHandler breaks dependency tracking?

Max connections per server can be customized via the HttpClientHandler API already, if your goal is to continue using diagnostics:

using var handler = new HttpClientHandler { MaxConnectionsPerServer = 10 };
using var client = new HttpClient(handler);

[stephentoub]

@scalablecory, DiagnosticHandler is created and wrapped around SocketsHttpHandler in HttpClientHandler, e.g.
https://github.com/dotnet/corefx/blob/a3f71bfe819463e388fa7afe77a579ebf99ac866/src/System.Net.Http/src/System/Net/Http/HttpClientHandler.Windows.cs#L31
If you construct a different handler than HttpClientHandler, DiagnosticHandler isn't created.

[scalablecory]

@stephentoub yes, that is clear.

[rangp]

@scalablecory Thanks for the info, I didn't see that HttpClientHandler is customizable this way. However I would also like to adjust MaxResponseDrainSize which I can't see as a property of HttpClientHandler.

I think that my dependency tracking is broken because DiagnosticsHandler is missing around my SocketsHttpHandler. I'm using application insights' automatic dependency tracking that seems to integrate with the diagnostics propagated by DiagnosticsHandler.

In general I would like the freedom to adjust the settings of the SocketsHttpHandler contained in my HttpClient without losing the diagnostics. The issue I'm having is that I can't access the SocketsHttpHandler that's automatically created by HttpClientHandler and as explained I can't just create a SocketsHttpHandler myself without losing diagnostic information.

I just posted this as an issue because I expected to be able to adjust the full set of HttpConnectionSettings without trade-offs like losing dependency tracking

[ctaggart]

The dotnet ApplicationInsights SDK also builds on this. If we create a custom SocketsHttpHandler, we loose http request tracking.

[karelz]

Triage: We should do something -- there is multiple options - expose it as type (not a very interesting one), static factory, or HttpClient property to enable it.
Xamarin workloads have native handlers and that's why we need to make it work outside of just SocketsHttpHandler.

We should make it happen in 5.0 as AppInsights is important scenario for custom handler -- Xamarin and SocketsHttpHandler.