A way to register preferred TLS config

Signed-off-by: lance6716 <lance6716@gmail.com>

dsn.go

@@ -47,6 +47,7 @@ type Config struct {
 	pubKey           *rsa.PublicKey    // Server public key
 	TLSConfig        string            // TLS configuration name
 	tls              *tls.Config       // TLS configuration
+	tlsIsPreferred   bool              // TLS is preferred, not a must
 	Timeout          time.Duration     // Dial timeout
 	ReadTimeout      time.Duration     // I/O read timeout
 	WriteTimeout     time.Duration     // I/O write timeout
@@ -124,10 +125,13 @@ func (cfg *Config) normalize() error {
 		// don't set anything
 	case "true":
 		cfg.tls = &tls.Config{}
-	case "skip-verify", "preferred":
+	case "skip-verify":
 		cfg.tls = &tls.Config{InsecureSkipVerify: true}
+	case "preferred":
+		cfg.tls = &tls.Config{InsecureSkipVerify: true}
+		cfg.tlsIsPreferred = true
 	default:
-		cfg.tls = getTLSConfigClone(cfg.TLSConfig)
+		cfg.tls, cfg.tlsIsPreferred = getTLSConfigCloneAndPreferred(cfg.TLSConfig)
 		if cfg.tls == nil {
 			return errors.New("invalid value / unknown config name: " + cfg.TLSConfig)
 		}

dsn_test.go

@@ -221,6 +221,66 @@ func TestDSNWithCustomTLS(t *testing.T) {
 	}
 }
 
+func TestRegisterPreferredTLSConfig(t *testing.T) {
+	tlsMust := "tls-must"
+	tlsPreferred := "tls-preferred"
+	tlsCfg := tls.Config{ServerName: tlsMust}
+	tlsCfg2 := tls.Config{ServerName: tlsPreferred}
+
+	err := RegisterTLSConfig(tlsMust, &tlsCfg)
+	if err != nil {
+		t.Error(err.Error())
+	}
+	defer DeregisterTLSConfig(tlsMust)
+	err = RegisterPreferredTLSConfig(tlsPreferred, &tlsCfg2)
+	if err != nil {
+		t.Error(err.Error())
+	}
+	defer DeregisterTLSConfig(tlsPreferred)
+
+	checkCfgAndPreferred := func(key, expectedName string, expectedPreferred bool) {
+		cfg, preferred := getTLSConfigCloneAndPreferred(key)
+		if cfg.ServerName != expectedName {
+			t.Errorf("did not get the correct TLS ServerName (%s): %s.", expectedName, cfg.ServerName)
+		}
+		if expectedPreferred && !preferred {
+			t.Errorf("this should not be a preferred TLS config: %s", key)
+		}
+		if !expectedPreferred && preferred {
+			t.Errorf("this should be a preferred TLS config: %s", key)
+		}
+	}
+
+	checkCfgAndPreferred(tlsMust, tlsMust, false)
+	checkCfgAndPreferred(tlsPreferred, tlsPreferred, true)
+
+	// test RegisterTLSConfig overwrites existing config and preferred
+	tlsAnother := "tls-another"
+	tlsCfg3 := tls.Config{ServerName: tlsAnother}
+	// register the name tlsPreferred in non-preferred mode!
+	err = RegisterTLSConfig(tlsPreferred, &tlsCfg3)
+	if err != nil {
+		t.Error(err.Error())
+	}
+	checkCfgAndPreferred(tlsPreferred, tlsAnother, false)
+
+	// overwrite it back to preferred
+	err = RegisterPreferredTLSConfig(tlsPreferred, &tlsCfg3)
+	if err != nil {
+		t.Error(err.Error())
+	}
+	checkCfgAndPreferred(tlsPreferred, tlsAnother, true)
+
+	DeregisterTLSConfig(tlsPreferred)
+	cfg, preferred := getTLSConfigCloneAndPreferred(tlsPreferred)
+	if cfg != nil {
+		t.Error("found TLS config after deregister")
+	}
+	if preferred {
+		t.Error("preferred should be false after deregister")
+	}
+}
+
 func TestDSNTLSConfig(t *testing.T) {
 	expectedServerName := "example.com"
 	dsn := "tcp(example.com:1234)/?tls=true"

packets.go

@@ -223,7 +223,7 @@ func (mc *mysqlConn) readHandshakePacket() (data []byte, plugin string, err erro
 		return nil, "", ErrOldProtocol
 	}
 	if mc.flags&clientSSL == 0 && mc.cfg.tls != nil {
-		if mc.cfg.TLSConfig == "preferred" {
+		if mc.cfg.tlsIsPreferred {
 			mc.cfg.tls = nil
 		} else {
 			return nil, "", ErrNoTLS

utils.go

@@ -25,8 +25,9 @@ import (
 
 // Registry for custom tls.Configs
 var (
-	tlsConfigLock     sync.RWMutex
-	tlsConfigRegistry map[string]*tls.Config
+	tlsConfigLock      sync.RWMutex
+	tlsConfigRegistry  map[string]*tls.Config
+	tlsConfigPreferred map[string]struct{}
 )
 
 // RegisterTLSConfig registers a custom tls.Config to be used with sql.Open.
@@ -55,6 +56,17 @@ var (
 //	})
 //	db, err := sql.Open("mysql", "user@tcp(localhost:3306)/test?tls=custom")
 func RegisterTLSConfig(key string, config *tls.Config) error {
+	return registerTLSConfig(key, config, false)
+}
+
+// RegisterPreferredTLSConfig is like a RegisterTLSConfig, but when the MySQL
+// server does not support TLS the driver will try to connect without TLS.
+// It can be used as a customized "preferred" TLS configuration in the DSN.
+func RegisterPreferredTLSConfig(key string, config *tls.Config) error {
+	return registerTLSConfig(key, config, true)
+}
+
+func registerTLSConfig(key string, config *tls.Config, preferred bool) error {
 	if _, isBool := readBool(key); isBool || strings.ToLower(key) == "skip-verify" || strings.ToLower(key) == "preferred" {
 		return fmt.Errorf("key '%s' is reserved", key)
 	}
@@ -63,8 +75,16 @@ func RegisterTLSConfig(key string, config *tls.Config) error {
 	if tlsConfigRegistry == nil {
 		tlsConfigRegistry = make(map[string]*tls.Config)
 	}
-
 	tlsConfigRegistry[key] = config
+
+	if preferred {
+		if tlsConfigPreferred == nil {
+			tlsConfigPreferred = make(map[string]struct{})
+		}
+		tlsConfigPreferred[key] = struct{}{}
+	} else {
+		delete(tlsConfigPreferred, key)
+	}
 	tlsConfigLock.Unlock()
 	return nil
 }
@@ -75,14 +95,18 @@ func DeregisterTLSConfig(key string) {
 	if tlsConfigRegistry != nil {
 		delete(tlsConfigRegistry, key)
 	}
+	if tlsConfigPreferred != nil {
+		delete(tlsConfigPreferred, key)
+	}
 	tlsConfigLock.Unlock()
 }
 
-func getTLSConfigClone(key string) (config *tls.Config) {
+func getTLSConfigCloneAndPreferred(key string) (config *tls.Config, preferred bool) {
 	tlsConfigLock.RLock()
 	if v, ok := tlsConfigRegistry[key]; ok {
 		config = v.Clone()
 	}
+	_, preferred = tlsConfigPreferred[key]
 	tlsConfigLock.RUnlock()
 	return
 }