Align the semantics of http.request.size with http.response.size

[qdongxu]

This PR is for Issue #7087

1. record replacer "http.request.size" as well as "http.response.size"
2. let metrics record accurate reqeust size by read from req.Body. ( metrics read from Content-Length field, which not applicable to web socket or chunked Body)
3. cache RequestRecorder to handle records in multiple modules. ( logRequest and metrics creates its own ResponseRecorder.)
4. refactor, put the recording function in a single place. lengthReader as a member of ResponseRecorder. it takes quite a time to understand when they separated and share a common int pointer.

[CLAassistant]

All committers have signed the CLA.

[mohammed90]

Just at first glance, is there any need for these fields to be exported? If not, could you lowercase them please?

[qdongxu]

Sure.

[mohammed90]

There are 2 things that are unclear to me:
1- can you explain the reasoning for the double pointer on http.Request?
2- I don't understand how could you have used the ` for the imports

[mholt]

I don't think we should/can change this signature at this point. I'm also not clear as to why this signature is better?

[qdongxu]

Some thinking as below.

[qdongxu]

There are 2 things that are unclear to me:
1- can you explain the reasoning for the double pointer on http.Request?
2- I don't understand how could you have used the ` for the imports

As for the import， it shocks me too🤣. It was mostly generated by the goland IDE. I am sorry I didn't check formattings before checking in.

As for the double pointer, the http.Request.WithContext works in a immutable way, it should returns a new instance when change the context. It looks cohensive to make the change inside the NewResponseRecorder implementation.

    c := context.WithValue(r.Context(), ResponseRecorderVarKey, rr)
    *req = r.WithContext(c)

A alternative way is to let the invoker to take care of the new r . The side effect is not obvious for the invoker(The input r changed??)

    func NewResponseRecorder(w http.ResponseWriter, req *http.Request, buf *bytes.Buffer,
	shouldBuffer ShouldBufferFunc) (wrec ResponseRecorder, newReq *http.Request , cached bool)
    // ....
    wrec, r, cached := NewResponseRecorder(w, r, nil, nil)

It's weird to input a double pointer but it's may get the invoker's attention as I had thought.

What's your opinion on the alternatives ?

[qdongxu]

I converted this PR to draft. During review the caching of responseRecorder, I found its better to decouple responseRecorder into responseBuffer and responseMeter. I will do some more investigation.