Expose Protocol identification API in Lua scripts

[ramaraochavali]

Description:
While it is possible to identify the type of protocol (H1/H2 etc) and whether TLS is used on a given request using c++ API in filters, Lua does not expose this. It would be useful to expose this information in Lua so that Lua filter can make some decisions.

[dio]

@ramaraochavali for my own education, while the type of protocol can be inferred from RequestInfo, how to check whether TLS is being used in current request?

Probably I could extend the RequestInfo wrapper here #3627 to return the protocol (e.g. the API maybe something like: request_handle:requestInfo():protocol()) but not sure about the flag for TLS.

Is it from StreamDecoderFilterCallbacks::connection()?

[ramaraochavali]

@dio yes. I think it is from this API https://github.com/envoyproxy/envoy/blob/master/include/envoy/network/connection.h#L182.
Are you actively working on the above PR?

[ramaraochavali]

@dio sorry..I just checked the PR, looks like you are working actively on it. I will follow the PR on the progress,

[dio]

😬yeah, it was stale a bit. Will try to cover this use-case too.