net/http: support disabling built-in HTTP/2 with a new build tag

Fixes #35082
Updates #6853

Change-Id: I4eeb0e15f534cff57fefb6039cd33fadf15b946e
Reviewed-on: https://go-review.googlesource.com/c/go/+/205139Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Reviewed-by: David Crawshaw <crawshaw@golang.org>

src/net/http/clientserver_test.go

@@ -83,6 +83,9 @@ func optWithServerLog(lg *log.Logger) func(*httptest.Server) {
 }
 
 func newClientServerTest(t *testing.T, h2 bool, h Handler, opts ...interface{}) *clientServerTest {
+	if h2 {
+		CondSkipHTTP2(t)
+	}
 	cst := &clientServerTest{
 		t:  t,
 		h2: h2,

src/net/http/export_test.go

@@ -60,6 +60,12 @@ func init() {
 	}
 }
 
+func CondSkipHTTP2(t *testing.T) {
+	if omitBundledHTTP2 {
+		t.Skip("skipping HTTP/2 test when nethttpomithttp2 build tag in use")
+	}
+}
+
 var (
 	SetEnterRoundTripHook = hookSetter(&testHookEnterRoundTrip)
 	SetRoundTripRetried   = hookSetter(&testHookRoundTripRetried)

src/net/http/h2_bundle.go

+// +build !nethttpomithttp2
+
 // Code generated by golang.org/x/tools/cmd/bundle. DO NOT EDIT.
-//go:generate bundle -o h2_bundle.go -prefix http2 golang.org/x/net/http2
+//   $ bundle -o=h2_bundle.go -prefix=http2 -tags=!nethttpomithttp2 golang.org/x/net/http2
 
 // Package http2 implements the HTTP/2 protocol.
 //

src/net/http/http.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:generate bundle -o=h2_bundle.go -prefix=http2 -tags=!nethttpomithttp2 golang.org/x/net/http2
+
 package http
 
 import (
@@ -22,6 +24,11 @@ const maxInt64 = 1<<63 - 1
 // immediate cancellation of network operations.
 var aLongTimeAgo = time.Unix(1, 0)
 
+// omitBundledHTTP2 is set by omithttp2.go when the nethttpomithttp2
+// build tag is set. That means h2_bundle.go isn't compiled in and we
+// shouldn't try to use it.
+var omitBundledHTTP2 bool
+
 // TODO(bradfitz): move common stuff here. The other files have accumulated
 // generic http stuff in random places.
 

src/net/http/http_test.go

@@ -111,6 +111,32 @@ func TestCmdGoNoHTTPServer(t *testing.T) {
 	}
 }
 
+// Tests that the nethttpomithttp2 build tag doesn't rot too much,
+// even if there's not a regular builder on it.
+func TestOmitHTTP2(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping in short mode")
+	}
+	t.Parallel()
+	goTool := testenv.GoToolPath(t)
+	out, err := exec.Command(goTool, "test", "-short", "-tags=nethttpomithttp2", "net/http").CombinedOutput()
+	if err != nil {
+		t.Fatalf("go test -short failed: %v, %s", err, out)
+	}
+}
+
+// Tests that the nethttpomithttp2 build tag at least type checks
+// in short mode.
+// The TestOmitHTTP2 test above actually runs tests (in long mode).
+func TestOmitHTTP2Vet(t *testing.T) {
+	t.Parallel()
+	goTool := testenv.GoToolPath(t)
+	out, err := exec.Command(goTool, "vet", "-tags=nethttpomithttp2", "net/http").CombinedOutput()
+	if err != nil {
+		t.Fatalf("go vet failed: %v, %s", err, out)
+	}
+}
+
 var valuesCount int
 
 func BenchmarkCopyValues(b *testing.B) {

src/net/http/main_test.go

@@ -90,6 +90,9 @@ func goroutineLeaked() bool {
 // (all.bash), but as a serial test otherwise. Using t.Parallel isn't
 // compatible with the afterTest func in non-short mode.
 func setParallel(t *testing.T) {
+	if strings.Contains(t.Name(), "HTTP2") {
+		http.CondSkipHTTP2(t)
+	}
 	if testing.Short() {
 		t.Parallel()
 	}

src/net/http/omithttp2.go

+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build nethttpomithttp2
+
+package http
+
+import (
+	"errors"
+	"sync"
+	"time"
+)
+
+func init() {
+	omitBundledHTTP2 = true
+}
+
+const noHTTP2 = "no bundled HTTP/2" // should never see this
+
+var http2errRequestCanceled = errors.New("net/http: request canceled")
+
+var http2goAwayTimeout = 1 * time.Second
+
+const http2NextProtoTLS = "h2"
+
+type http2Transport struct {
+	MaxHeaderListSize uint32
+	ConnPool          interface{}
+}
+
+func (*http2Transport) RoundTrip(*Request) (*Response, error) { panic(noHTTP2) }
+func (*http2Transport) CloseIdleConnections()                 {}
+
+type http2erringRoundTripper struct{}
+
+func (http2erringRoundTripper) RoundTrip(*Request) (*Response, error) { panic(noHTTP2) }
+
+type http2noDialClientConnPool struct {
+	http2clientConnPool http2clientConnPool
+}
+
+type http2clientConnPool struct {
+	mu    *sync.Mutex
+	conns map[string][]struct{}
+}
+
+func http2configureTransport(*Transport) (*http2Transport, error) { panic(noHTTP2) }
+
+func http2isNoCachedConnError(err error) bool {
+	_, ok := err.(interface{ IsHTTP2NoCachedConnError() })
+	return ok
+}
+
+type http2Server struct {
+	NewWriteScheduler func() http2WriteScheduler
+}
+
+type http2WriteScheduler interface{}
+
+func http2NewPriorityWriteScheduler(interface{}) http2WriteScheduler { panic(noHTTP2) }
+
+func http2ConfigureServer(s *Server, conf *http2Server) error { panic(noHTTP2) }
+
+var http2ErrNoCachedConn = http2noCachedConnError{}
+
+type http2noCachedConnError struct{}
+
+func (http2noCachedConnError) IsHTTP2NoCachedConnError() {}
+
+func (http2noCachedConnError) Error() string { return "http2: no cached connection was available" }

src/net/http/serve_test.go

@@ -1507,6 +1507,7 @@ func TestTLSServer(t *testing.T) {
 }
 
 func TestServeTLS(t *testing.T) {
+	CondSkipHTTP2(t)
 	// Not parallel: uses global test hooks.
 	defer afterTest(t)
 	defer SetTestHookServerServe(nil)
@@ -1657,6 +1658,7 @@ func TestAutomaticHTTP2_ListenAndServe_GetCertificate(t *testing.T) {
 }
 
 func testAutomaticHTTP2_ListenAndServe(t *testing.T, tlsConf *tls.Config) {
+	CondSkipHTTP2(t)
 	// Not parallel: uses global test hooks.
 	defer afterTest(t)
 	defer SetTestHookServerServe(nil)

src/net/http/server.go

@@ -3160,7 +3160,7 @@ func (srv *Server) onceSetNextProtoDefaults_Serve() {
 // configured otherwise. (by setting srv.TLSNextProto non-nil)
 // It must only be called via srv.nextProtoOnce (use srv.setupHTTP2_*).
 func (srv *Server) onceSetNextProtoDefaults() {
-	if strings.Contains(os.Getenv("GODEBUG"), "http2server=0") {
+	if omitBundledHTTP2 || strings.Contains(os.Getenv("GODEBUG"), "http2server=0") {
 		return
 	}
 	// Enable HTTP/2 by default if the user hasn't otherwise

src/net/http/transport.go

@@ -286,7 +286,6 @@ func (t *Transport) Clone() *Transport {
 		DialContext:            t.DialContext,
 		Dial:                   t.Dial,
 		DialTLS:                t.DialTLS,
-		TLSClientConfig:        t.TLSClientConfig.Clone(),
 		TLSHandshakeTimeout:    t.TLSHandshakeTimeout,
 		DisableKeepAlives:      t.DisableKeepAlives,
 		DisableCompression:     t.DisableCompression,
@@ -302,6 +301,9 @@ func (t *Transport) Clone() *Transport {
 		WriteBufferSize:        t.WriteBufferSize,
 		ReadBufferSize:         t.ReadBufferSize,
 	}
+	if t.TLSClientConfig != nil {
+		t2.TLSClientConfig = t.TLSClientConfig.Clone()
+	}
 	if !t.tlsNextProtoWasNil {
 		npm := map[string]func(authority string, c *tls.Conn) RoundTripper{}
 		for k, v := range t.TLSNextProto {
@@ -359,6 +361,9 @@ func (t *Transport) onceSetNextProtoDefaults() {
 		// However, if ForceAttemptHTTP2 is true, it overrides the above checks.
 		return
 	}
+	if omitBundledHTTP2 {
+		return
+	}
 	t2, err := http2configureTransport(t)
 	if err != nil {
 		log.Printf("Error enabling Transport HTTP/2 support: %v", err)

src/net/http/transport_test.go

@@ -591,6 +591,7 @@ func TestTransportMaxConnsPerHostIncludeDialInProgress(t *testing.T) {
 
 func TestTransportMaxConnsPerHost(t *testing.T) {
 	defer afterTest(t)
+	CondSkipHTTP2(t)
 
 	h := HandlerFunc(func(w ResponseWriter, r *Request) {
 		_, err := w.Write([]byte("foo"))
@@ -3994,6 +3995,7 @@ func TestTransportAutomaticHTTP2_DialTLS(t *testing.T) {
 }
 
 func testTransportAutoHTTP(t *testing.T, tr *Transport, wantH2 bool) {
+	CondSkipHTTP2(t)
 	_, err := tr.RoundTrip(new(Request))
 	if err == nil {
 		t.Error("expected error from RoundTrip")
@@ -5896,6 +5898,7 @@ func TestDontCacheBrokenHTTP2Conn(t *testing.T) {
 // only be one decrement regardless of the number of failures.
 func TestTransportDecrementConnWhenIdleConnRemoved(t *testing.T) {
 	defer afterTest(t)
+	CondSkipHTTP2(t)
 
 	h := HandlerFunc(func(w ResponseWriter, r *Request) {
 		_, err := w.Write([]byte("foo"))