net/http: enable automatic HTTP/2 if TLSNextProto is nil

This enables HTTP/2 by default (for https only) if the user didn't
configure anything in their NPN/ALPN map. If they're using SPDY or an
alternate http2 or a newer http2 from x/net/http2, we do nothing
and don't use the standard library's vendored copy of x/net/http2.

Upstream remains golang.org/x/net/http2.

Update #6891

Change-Id: I69a8957a021a00ac353f9d7fdb9a40a5b69f2199
Reviewed-on: https://go-review.googlesource.com/15828
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

1 files changed, 11 insertions, 1 deletions

diff --git a/src/net/http/server.go b/src/net/http/server.go
index ae62e076dd..dc4f100e01 100644
--- a/src/net/http/server.go
+++ b/src/net/http/server.go
@@ -1806,7 +1806,8 @@ type Server struct {
 	// standard logger.
 	ErrorLog *log.Logger
 
-	disableKeepAlives int32 // accessed atomically.
+	disableKeepAlives int32     // accessed atomically.
+	nextProtoOnce     sync.Once // guards initialization of TLSNextProto in Serve
 }
 
 // A ConnState represents the state of a client connection to a server.
@@ -1896,6 +1897,7 @@ func (srv *Server) ListenAndServe() error {
 func (srv *Server) Serve(l net.Listener) error {
 	defer l.Close()
 	var tempDelay time.Duration // how long to sleep on accept failure
+	srv.nextProtoOnce.Do(srv.setNextProtoDefaults)
 	for {
 		rw, e := l.Accept()
 		if e != nil {
@@ -2052,6 +2054,14 @@ func (srv *Server) ListenAndServeTLS(certFile, keyFile string) error {
 	return srv.Serve(tlsListener)
 }
 
+func (srv *Server) setNextProtoDefaults() {
+	// Enable HTTP/2 by default if the user hasn't otherwise
+	// configured their TLSNextProto map.
+	if srv.TLSNextProto == nil {
+		http2ConfigureServer(srv, nil)
+	}
+}
+
 // TimeoutHandler returns a Handler that runs h with the given time limit.
 //
 // The new Handler calls h.ServeHTTP to handle each request, but if a