net/http: drop custom tls.Config cloning code.

Now that we have the Clone method on tls.Config, net/http doesn't need
any custom functions to do that any more.

Change-Id: Ib60707d37f1a7f9a7d7723045f83e59eceffd026
Reviewed-on: https://go-review.googlesource.com/31595Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/crypto/tls/common.go

@@ -455,9 +455,13 @@ func ticketKeyFromBytes(b [32]byte) (key ticketKey) {
 	return key
 }
 
-// Clone returns a shallow clone of c.
-// Only the exported fields are copied.
+// Clone returns a shallow clone of c. It is safe to clone a Config that is
+// being used concurrently by a TLS client or server.
 func (c *Config) Clone() *Config {
+	// Running serverInit ensures that it's safe to read
+	// SessionTicketsDisabled.
+	c.serverInitOnce.Do(c.serverInit)
+
 	var sessionTicketKeys []ticketKey
 	c.mutex.RLock()
 	sessionTicketKeys = c.sessionTicketKeys

src/crypto/tls/tls_test.go

@@ -508,6 +508,10 @@ func TestClone(t *testing.T) {
 	}
 
 	c2 := c1.Clone()
+	// DeepEqual also compares unexported fields, thus c2 needs to have run
+	// serverInit in order to be DeepEqual to c1. Cloning it and discarding
+	// the result is sufficient.
+	c2.Clone()
 
 	if !reflect.DeepEqual(&c1, c2) {
 		t.Errorf("clone failed to copy a field")

src/net/http/transport.go

@@ -1040,7 +1040,7 @@ func (t *Transport) dialConn(ctx context.Context, cm connectMethod) (*persistCon
 
 	if cm.targetScheme == "https" && !tlsDial {
 		// Initiate TLS and check remote host name against certificate.
-		cfg := cloneTLSClientConfig(t.TLSClientConfig)
+		cfg := cloneTLSConfig(t.TLSClientConfig)
 		if cfg.ServerName == "" {
 			cfg.ServerName = cm.tlsHost()
 		}
@@ -2099,17 +2099,9 @@ type fakeLocker struct{}
 func (fakeLocker) Lock()   {}
 func (fakeLocker) Unlock() {}
 
-// cloneTLSConfig returns a shallow clone of the exported
-// fields of cfg, ignoring the unexported sync.Once, which
-// contains a mutex and must not be copied.
-//
-// The cfg must not be in active use by tls.Server, or else
-// there can still be a race with tls.Server updating SessionTicketKey
-// and our copying it, and also a race with the server setting
-// SessionTicketsDisabled=false on failure to set the random
-// ticket key.
-//
-// If cfg is nil, a new zero tls.Config is returned.
+// clneTLSConfig returns a shallow clone of cfg, or a new zero tls.Config if
+// cfg is nil. This is safe to call even if cfg is in active use by a TLS
+// client or server.
 func cloneTLSConfig(cfg *tls.Config) *tls.Config {
 	if cfg == nil {
 		return &tls.Config{}
@@ -2117,38 +2109,6 @@ func cloneTLSConfig(cfg *tls.Config) *tls.Config {
 	return cfg.Clone()
 }
 
-// cloneTLSClientConfig is like cloneTLSConfig but omits
-// the fields SessionTicketsDisabled and SessionTicketKey.
-// This makes it safe to call cloneTLSClientConfig on a config
-// in active use by a server.
-func cloneTLSClientConfig(cfg *tls.Config) *tls.Config {
-	if cfg == nil {
-		return &tls.Config{}
-	}
-	return &tls.Config{
-		Rand:                        cfg.Rand,
-		Time:                        cfg.Time,
-		Certificates:                cfg.Certificates,
-		NameToCertificate:           cfg.NameToCertificate,
-		GetCertificate:              cfg.GetCertificate,
-		RootCAs:                     cfg.RootCAs,
-		NextProtos:                  cfg.NextProtos,
-		ServerName:                  cfg.ServerName,
-		ClientAuth:                  cfg.ClientAuth,
-		ClientCAs:                   cfg.ClientCAs,
-		InsecureSkipVerify:          cfg.InsecureSkipVerify,
-		CipherSuites:                cfg.CipherSuites,
-		PreferServerCipherSuites:    cfg.PreferServerCipherSuites,
-		ClientSessionCache:          cfg.ClientSessionCache,
-		MinVersion:                  cfg.MinVersion,
-		MaxVersion:                  cfg.MaxVersion,
-		CurvePreferences:            cfg.CurvePreferences,
-		DynamicRecordSizingDisabled: cfg.DynamicRecordSizingDisabled,
-		Renegotiation:               cfg.Renegotiation,
-		KeyLogWriter:                cfg.KeyLogWriter,
-	}
-}
-
 type connLRU struct {
 	ll *list.List // list.Element.Value type is of *persistConn
 	m  map[*persistConn]*list.Element