Expose Http.Sys fast delegation proxying

[Tratcher]

Http.Sys server exposes a feature that lets you examine a request and then quickly 'proxy' it to another service on the same machine by transferring it to a different queue.

We could expose this as optional middleware that reads cluster/destination data and forwards requests using this mechanic.

Pros:

• Very fast/efficient
• Interops with IIS

Cons:

• You can't modify the request or observe the response.

Supported on .NET 6 and Win11.

Example:
dotnet/aspnetcore@f72785f#diff-66e5582beb1ea1594e35e4e0457f4676e3453bb34efecd2a9e69005ff17f06bbR55-R61

[davidni]

Related but different: we might also want to look into socket handoff support in Kestrel to enable scenarios like Envoy's hot restart. Obviously that works at the connection level as opposed to per-request, but could still be useful... particularly when routing table is based on connection-level predicates such as host name only.

[NGloreous]

My team would like this support (we were originally planning on doing it ourselves). Happy to help out if needed. We wanted to ship this sometime this year to flesh out any issues before we will depend on this next year.

[adityamandaleeka]

Triage: the prerequisite for this already shipped in .NET 6 so we should be able to implement this as a new middleware now.

@NGloreous Great! We'd love to chat more about your use case.