improvement: net/http: reuse connection if entire unread body is in buffer

[canoriz]

Currently, if an HTTP response body is closed before fully read (fully means till EOF),
the underlying HTTP connection won't be reused. But in the current implementation,
body is first read into bufio buffer by bufio reader, then from buffer by body Reader.
So even if the body is closed before fully read, as long as the entire body has been
read into buffer, after discard buffer, the connection can be reused.

This will be useful when go client only read body if status is 200 while server sends
HTTP body in a non 200 status response.

I filed a PR #75303, reviewer suggests opening an issue and discuss it first, so here it is.

[canoriz]

new proposal issue

[canoriz]

new proposal issue

[gabyhelp]

Related Issues

• net/http: Response.Body.Close() has nothing to do with re-use persistent connection #29886 (closed)
• net/http: fix docs on Transport connection reuse specifics #22954 (closed)
• net/http: support bufio.Reader body retries #52603 (closed)

Related Code Changes

• net/http: reuse connection if entire unread body is in buffer
• net/http: clarify Transport connection reuse docs a bit
• net/http: fix race when request body is reused before being read to EOF
• net/http: reuse HTTP/1 Transport conns more for gzipped responses
• net/http: add test confirming a connection reuse case
• net/http: support bufio.Reader body retries
• net/http: add ways to unblock pending I/O on Body.

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}