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>

src/cmd/api/goapi.go

@@ -428,10 +428,15 @@ func (w *Walker) Import(name string) (*types.Package, error) {
 	}
 	w.imported[name] = &importing
 
+	root := w.root
+	if strings.HasPrefix(name, "golang.org/x/") {
+		root = filepath.Join(root, "vendor")
+	}
+
 	// Determine package files.
-	dir := filepath.Join(w.root, filepath.FromSlash(name))
+	dir := filepath.Join(root, filepath.FromSlash(name))
 	if fi, err := os.Stat(dir); err != nil || !fi.IsDir() {
-		log.Fatalf("no source in tree for package %q", pkg)
+		log.Fatalf("no source in tree for import %q: %v", name, err)
 	}
 
 	context := w.context

src/go/build/deps_test.go

@@ -351,6 +351,7 @@ var pkgDeps = map[string][]string{
 		"L4", "NET", "OS",
 		"compress/gzip", "crypto/tls", "mime/multipart", "runtime/debug",
 		"net/http/internal",
+		"golang.org/x/net/http2/hpack",
 	},
 	"net/http/internal": {"L4"},
 

src/net/http/serve_test.go

@@ -1068,6 +1068,22 @@ func TestTLSServer(t *testing.T) {
 	})
 }
 
+func TestAutomaticHTTP2(t *testing.T) {
+	ln, err := net.Listen("tcp", ":0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	ln.Close() // immediately (not a defer!)
+	var s Server
+	if err := s.Serve(ln); err == nil {
+		t.Fatal("expected an error")
+	}
+	on := s.TLSNextProto["h2"] != nil
+	if !on {
+		t.Errorf("http2 wasn't automatically enabled")
+	}
+}
+
 type serverExpectTest struct {
 	contentLength    int // of request body
 	chunked          bool

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