Detect HTTP/2 connection sent to HTTP/1.1 endpoint

[JamesNK]

Related to #39358 except an HTTP/2 connection sent to HTTP/1.1 endpoint.

[JamesNK]

I'm not sure about this. Need somewhere to flush the HTTP/2 GOAWAY frame content written in TryParseRequest.

[halter73]

It does feal weird to flush a response when _connectionAborted is true. If we stick with writing a GOAWAY for h2c connections to an HTTP/1.1 endpoint, I'd probably just make this virtual (it only gets called once per connection anyway) and use a new flag in DetectHttp2Preface (_isInvalidH2cConnection?). If set, I'd write the Http2GoAwayProtocolErrorBytes here and flush it and skip the default behavior. Otherwise, I'd just call into the base implementation.

That way you wouldn't have to set _connectionAborted in DetectHttp2Preface either which feels like a win.

[JamesNK]

Done.

I'm not resetting the new flag in OnReset. Is that ok? I'm not familiar with HTTP/1.1 reuse so I'm not sure whether it will get reused after keep-alive is set to false.

[Tratcher]

If you can sort out the flush logic with Stephen

[davidfowl]

Did this affect the performance of the HTTP/1.1 connection close benchmark?

cc @sebastienros

[davidfowl]

Ah I see this only affects the error case.