[Feature] HttpClient Listener rewritten for performance

[JRAlexander]

HttpClient Listener rewritten for performance

For HttpClient, we built a new from-the-ground-up managed HttpClientHandler called SocketHttpHandler. As you can likely guess, it’s a C# implementation of HttpClient based on .NET sockets and Span.

The biggest win of SocketHttpHandler is performance. It is a lot faster than the existing implementation. There are other benefits:

Elimination of platform dependencies on libcurl (for linux) and WinHTTP (for Windows) – simplifies both development, deployment and servicing
Consistent behavior across platforms and platform/dependency versions.
You can opt-in to using the SocketHTTPHandler in one the following ways with Preview 1:

Environment variable: COMPlus_UseManagedHttpClientHandler=true
AppContext: System.Net.Http.UseManagedHttpClientHandler=true

Still Needed:

• Content Types
• Table of Contents
• Prioritization

If you know someone who can provide feedback, use '@' to ask them to review.

[mairaw]

Let's just add this to the what's new topic: https://docs.microsoft.com/en-us/dotnet/core/whats-new/dotnet-core-2-1