Revert "crypto/tls: don't send IP literals as SNI values."

This reverts commit a4dcc69201.

Change-Id: Ib55fd349a604d6b5220dac20327501e1ce46b962
Reviewed-on: https://go-review.googlesource.com/16770
Reviewed-by: Adam Langley <agl@golang.org>

src/crypto/tls/common.go

@@ -286,8 +286,7 @@ type Config struct {
 
 	// ServerName is used to verify the hostname on the returned
 	// certificates unless InsecureSkipVerify is given. It is also included
-	// in the client's handshake to support virtual hosting unless it is
+	// in the client's handshake to support virtual hosting.
-	// an IP address.
 	ServerName string
 
 	// ClientAuth determines the server's policy for

src/crypto/tls/handshake_client.go

@@ -49,20 +49,13 @@ func (c *Conn) clientHandshake() error {
 		return errors.New("tls: NextProtos values too large")
 	}
 
-	sni := c.config.ServerName
-	// IP address literals are not permitted as SNI values. See
-	// https://tools.ietf.org/html/rfc6066#section-3.
-	if net.ParseIP(sni) != nil {
-		sni = ""
-	}
-
 	hello := &clientHelloMsg{
 		vers:                c.config.maxVersion(),
 		compressionMethods:  []uint8{compressionNone},
 		random:              make([]byte, 32),
 		ocspStapling:        true,
 		scts:                true,
-		serverName:          sni,
+		serverName:          c.config.ServerName,
 		supportedCurves:     c.config.curvePreferences(),
 		supportedPoints:     []uint8{pointFormatUncompressed},
 		nextProtoNeg:        len(c.config.NextProtos) > 0,

src/crypto/tls/handshake_client_test.go

@@ -600,30 +600,3 @@ func TestHandshakClientSCTs(t *testing.T) {
 	}
 	runClientTestTLS12(t, test)
 }
-
-func TestNoIPAddressesInSNI(t *testing.T) {
-	for _, ipLiteral := range []string{"1.2.3.4", "::1"} {
-		c, s := net.Pipe()
-
-		go func() {
-			client := Client(c, &Config{ServerName: ipLiteral})
-			client.Handshake()
-		}()
-
-		var header [5]byte
-		if _, err := io.ReadFull(s, header[:]); err != nil {
-			t.Fatal(err)
-		}
-		recordLen := int(header[3])<<8 | int(header[4])
-
-		record := make([]byte, recordLen)
-		if _, err := io.ReadFull(s, record[:]); err != nil {
-			t.Fatal(err)
-		}
-		s.Close()
-
-		if bytes.Index(record, []byte(ipLiteral)) != -1 {
-			t.Errorf("IP literal %q found in ClientHello: %x", ipLiteral, record)
-		}
-	}
-}