Support for TCP Fast open in Kestrel

[mjsabby]

TCP Fast Open (RFC 7413) is an extension to the TCP protocol.

Recent versions of Windows and Linux both support TCP Fast Open.

It'd be nice if we could put this on the Kestrel roadmap.

[benaadams]

Would need Fast Open support on corefx sockets https://github.com/dotnet/corefx/issues/16375 or SetRawSocketOption https://github.com/dotnet/corefx/issues/37122 as currently the PAL layer throws

[benaadams]

You can get around it by operating on the socket handle directly; but its not a great approach: https://github.com/benaadams/AspNetCore/blob/16ffdba0e4eee5c91d81ba0069062cb3aaf7d8d0/src/Servers/Kestrel/Transport.Sockets/src/Internal/SocketConnection.cs#L366-L381

[analogrelay]

As @benaadams said, we're blocked waiting on support from corefx here. Putting this on the backlog until we get support.

[chrisaut]

FYI SetRawSocketOption has been merged: dotnet/runtime#33261