crypto/tls: add server-side OCSP stapling support.

We already had support on the client side. I also changed the name of
the flag in the ServerHello structure to match the name of the same
flag in the ClientHello (ocspStapling).

R=bradfitzgo
CC=golang-dev
https://golang.org/cl/4408044

src/pkg/crypto/tls/common.go

@@ -178,6 +178,9 @@ func (c *Config) cipherSuites() []uint16 {
 type Certificate struct {
 	Certificate [][]byte
 	PrivateKey  *rsa.PrivateKey
+	// OCSPStaple contains an optional OCSP response which will be served
+	// to clients that request it.
+	OCSPStaple []byte
 }
 
 // A TLS record.

src/pkg/crypto/tls/handshake_client.go

@@ -145,7 +145,7 @@ func (c *Conn) clientHandshake() os.Error {
 
 	c.peerCertificates = certs
 
-	if serverHello.certStatus {
+	if serverHello.ocspStapling {
 		msg, err = c.readHandshake()
 		if err != nil {
 			return err

src/pkg/crypto/tls/handshake_messages.go

@@ -306,7 +306,7 @@ type serverHelloMsg struct {
 	compressionMethod uint8
 	nextProtoNeg      bool
 	nextProtos        []string
-	certStatus        bool
+	ocspStapling      bool
 }
 
 func (m *serverHelloMsg) marshal() []byte {
@@ -327,7 +327,7 @@ func (m *serverHelloMsg) marshal() []byte {
 		nextProtoLen += len(m.nextProtos)
 		extensionsLength += nextProtoLen
 	}
-	if m.certStatus {
+	if m.ocspStapling {
 		numExtensions++
 	}
 	if numExtensions > 0 {
@@ -373,7 +373,7 @@ func (m *serverHelloMsg) marshal() []byte {
 			z = z[1+l:]
 		}
 	}
-	if m.certStatus {
+	if m.ocspStapling {
 		z[0] = byte(extensionStatusRequest >> 8)
 		z[1] = byte(extensionStatusRequest)
 		z = z[4:]
@@ -406,7 +406,7 @@ func (m *serverHelloMsg) unmarshal(data []byte) bool {
 
 	m.nextProtoNeg = false
 	m.nextProtos = nil
-	m.certStatus = false
+	m.ocspStapling = false
 
 	if len(data) == 0 {
 		// ServerHello is optionally followed by extension data
@@ -450,7 +450,7 @@ func (m *serverHelloMsg) unmarshal(data []byte) bool {
 			if length > 0 {
 				return false
 			}
-			m.certStatus = true
+			m.ocspStapling = true
 		}
 		data = data[length:]
 	}

src/pkg/crypto/tls/handshake_server.go

@@ -103,6 +103,9 @@ FindCipherSuite:
 		hello.nextProtoNeg = true
 		hello.nextProtos = config.NextProtos
 	}
+	if clientHello.ocspStapling && len(config.Certificates[0].OCSPStaple) > 0 {
+		hello.ocspStapling = true
+	}
 
 	finishedHash.Write(hello.marshal())
 	c.writeRecord(recordTypeHandshake, hello.marshal())
@@ -116,6 +119,14 @@ FindCipherSuite:
 	finishedHash.Write(certMsg.marshal())
 	c.writeRecord(recordTypeHandshake, certMsg.marshal())
 
+	if hello.ocspStapling {
+		certStatus := new(certificateStatusMsg)
+		certStatus.statusType = statusTypeOCSP
+		certStatus.response = config.Certificates[0].OCSPStaple
+		finishedHash.Write(certStatus.marshal())
+		c.writeRecord(recordTypeHandshake, certStatus.marshal())
+	}
+
 	keyAgreement := suite.ka()
 
 	skx, err := keyAgreement.generateServerKeyExchange(config, clientHello, hello)