x/net/http2: export more tunable knobs

[ayanamist]

There are several default window settings in transport.go:

    // transportDefaultConnFlow is how many connection-level flow control
    // tokens we give the server at start-up, past the default 64k.
    transportDefaultConnFlow = 1 << 30

    // transportDefaultStreamFlow is how many stream-level flow
    // control tokens we announce to the peer, and how many bytes
    // we buffer per stream.
    transportDefaultStreamFlow = 4 << 20

    // transportDefaultStreamMinRefresh is the minimum number of bytes we'll send
    // a stream-level WINDOW_UPDATE for at a time.
    transportDefaultStreamMinRefresh = 4 << 10

NewClientConn method will use these without looking up other places. However, these default values are not suitable for all situations like high-latency high-throughput network.

Can you provide some setters to change these values instead of rewrite the whole thing using Framer or forking and rewriting this repo?

[jared2501]

Hey @bradfitz - this would be very handy. As mentioned in #30277, the default settings are too high if you have a low-latency requirement on a proxy that proxies a fast link into a slow link (i.e. I'm streaming live video over HTTP/2 through a Go proxy to LTE clients).

Current work around is to fork net/http2. Would be great to put these on the http2.Transport. Would you accept PR for this?