Fix invalid SNI handling

SNIExtension was previously marshalling both ip addresses and empty
strings, which are not allowed. See RFC 6066, Section 3.

All of the utls specific testdata replays needed to be rebuilt to
properly accomodate this change since they had previously been including
empty server name extension values

Addresses refraction-networking#96

u_conn_test.go

@@ -196,6 +196,38 @@ func TestUTLSRemoveSNIExtension(t *testing.T) {
 	runUTLSClientTestForVersion(t, test, "TLSv12-", "-tls1_2", hello, true)
 }
 
+func TestUTLSServerNameIP(t *testing.T) {
+	hello := &helloID{HelloChrome_70}
+
+	config := getUTLSTestConfig()
+	config.ServerName = "1.1.1.1"
+
+	opensslCipherName := "ECDHE-RSA-AES128-GCM-SHA256"
+	test := &clientTest{
+		name:   "UTLS-" + opensslCipherName + "-" + hello.helloName() + "-ServerNameIP",
+		args:   []string{"-cipher", opensslCipherName},
+		config: config,
+	}
+
+	runUTLSClientTestForVersion(t, test, "TLSv12-", "-tls1_2", hello, true)
+}
+
+func TestUTLSEmptyServerName(t *testing.T) {
+	hello := &helloID{HelloChrome_70}
+
+	config := getUTLSTestConfig()
+	config.ServerName = ""
+
+	opensslCipherName := "ECDHE-RSA-AES128-GCM-SHA256"
+	test := &clientTest{
+		name:   "UTLS-" + opensslCipherName + "-" + hello.helloName() + "-EmptyServerName",
+		args:   []string{"-cipher", opensslCipherName},
+		config: config,
+	}
+
+	runUTLSClientTestForVersion(t, test, "TLSv12-", "-tls1_2", hello, true)
+}
+
 /*
 *
  HELPER FUNCTIONS BELOW
@@ -212,6 +244,7 @@ func getUTLSTestConfig() *Config {
 		MinVersion:         VersionSSL30,
 		MaxVersion:         VersionTLS13,
 		CipherSuites:       allCipherSuites(),
+		ServerName:         "foobar.com",
 	}
 	return testUTLSConfig
 }

u_tls_extensions.go

@@ -49,29 +49,43 @@ type SNIExtension struct {
 
 func (e *SNIExtension) writeToUConn(uc *UConn) error {
 	uc.config.ServerName = e.ServerName
-	uc.HandshakeState.Hello.ServerName = e.ServerName
+	hostName := hostnameInSNI(e.ServerName)
+	uc.HandshakeState.Hello.ServerName = hostName
+
 	return nil
 }
 
 func (e *SNIExtension) Len() int {
-	return 4 + 2 + 1 + 2 + len(e.ServerName)
+	// Literal IP addresses, absolute FQDNs, and empty strings are not permitted as SNI values.
+	// See RFC 6066, Section 3.
+	hostName := hostnameInSNI(e.ServerName)
+	if len(hostName) == 0 {
+		return 0
+	}
+	return 4 + 2 + 1 + 2 + len(hostName)
 }
 
 func (e *SNIExtension) Read(b []byte) (int, error) {
+	// Literal IP addresses, absolute FQDNs, and empty strings are not permitted as SNI values.
+	// See RFC 6066, Section 3.
+	hostName := hostnameInSNI(e.ServerName)
+	if len(hostName) == 0 {
+		return 0, io.EOF
+	}
 	if len(b) < e.Len() {
 		return 0, io.ErrShortBuffer
 	}
 	// RFC 3546, section 3.1
 	b[0] = byte(extensionServerName >> 8)
 	b[1] = byte(extensionServerName)
-	b[2] = byte((len(e.ServerName) + 5) >> 8)
-	b[3] = byte((len(e.ServerName) + 5))
-	b[4] = byte((len(e.ServerName) + 3) >> 8)
-	b[5] = byte(len(e.ServerName) + 3)
+	b[2] = byte((len(hostName) + 5) >> 8)
+	b[3] = byte((len(hostName) + 5))
+	b[4] = byte((len(hostName) + 3) >> 8)
+	b[5] = byte(len(hostName) + 3)
 	// b[6] Server Name Type: host_name (0)
-	b[7] = byte(len(e.ServerName) >> 8)
-	b[8] = byte(len(e.ServerName))
-	copy(b[9:], []byte(e.ServerName))
+	b[7] = byte(len(hostName) >> 8)
+	b[8] = byte(len(hostName))
+	copy(b[9:], []byte(hostName))
 	return e.Len(), io.EOF
 }