Expect: 100-continue not implemented for HTTP/2

Hyper (server) does not support sending 100 Continue upon receiving an HTTP/2 request with a Expect: 100-continue specified. This is currently blocking moving a project from HTTP/1.1 to HTTP2 for me.

I've been digging through the specs, and as far as I can tell;

• HTTP/2

HTTP's existing semantics remain unchanged.

• HTTP Semantics / Expect

An origin server MUST, upon receiving an HTTP/1.1 (or later)
request-line and a complete header section that contains a
100-continue expectation and indicates a request message body will
follow, either send an immediate response with a final status code,
if that status can be determined by examining just the request-line
and header fields, or send an immediate 100 (Continue) response to
encourage the client to send the request's message body. The origin
server MUST NOT wait for the message body before sending the 100
(Continue) response.

I think the simple solution here is to try to replicate the behavior hyper already expose for HTTP/1.1? https://github.com/hyperium/hyper/issues/838

Start by tracing Hyper's existing HTTP/1.1 handling for Expect: 100-continue and comparing it with the HTTP/2 request path. Confirm the behavior against the linked HTTP/2 and HTTP Semantics specifications. Done means an HTTP/2 request with Expect: 100-continue receives the appropriate immediate 100 Continue response before its body is sent.