net/http: HTTP/2 retry loop broken when net/http manages dials

[neild]

http2.Transport.RoundTripOpt retries requests under some circumstances (transport.go#492):

for retry := 0; ; retry++ {
  cc, err := t.connPool().GetClientConn(req, addr)
   if err != nil {
    t.vlogf("http2: Transport failed to get client conn for %s: %v", addr, err)
    return nil, err
  }
  // ...

When using the bundled HTTP/2 support in net/http, however, GetClientConn does not dial connections when none are available. Instead, it returns ErrNoCachedConn and net/http handles the dial.

This results in an infinite retry loop when the server immediately hangs up on a retryable request.

[WGH-]

I can easily reproduce this with nginx special return code 444 ("close connection"):

location /nginx-444 {
    return 444;
}

package main

import (
	"log"
	"net/http"
)

func main() {
	resp, err := http.Get("https://chireiden.torlan.ru/nginx-444")
	if err != nil {
		log.Fatal(err)
	}
	defer resp.Body.Close()
	log.Printf("%s", resp.Status)
}