Fix "happy eyeballs" not being disabled since Golang 1.12 upgrade

* The Dialer.DualStack setting is now ignored and deprecated; RFC 6555 Fast Fallback ("Happy Eyeballs") is now enabled by default. To disable, set Dialer.FallbackDelay to a negative value.

cmd/cloudflared/tunnel/configuration.go

@@ -203,11 +203,14 @@ func prepareTunnelConfig(
 		TLSClientConfig:       &tls.Config{RootCAs: originCertPool, InsecureSkipVerify: c.IsSet("no-tls-verify")},
 	}
 
-	dialContext := (&net.Dialer{
+	dialer := &net.Dialer{
 		Timeout:   c.Duration("proxy-connect-timeout"),
 		KeepAlive: c.Duration("proxy-tcp-keepalive"),
-		DualStack: !c.Bool("proxy-no-happy-eyeballs"),
-	}).DialContext
+	}
+	if c.Bool("proxy-no-happy-eyeballs") {
+		dialer.FallbackDelay = -1 // As of Golang 1.12, a negative delay disables "happy eyeballs"
+	}
+	dialContext := dialer.DialContext
 
 	if c.IsSet("unix-socket") {
 		unixSocket, err := config.ValidateUnixSocket(c)

connection/manager.go

@@ -202,7 +202,7 @@ func (em *EdgeManager) dialEdge(ctx context.Context, edgeIP *net.TCPAddr) (*tls.
 	dialCtx, dialCancel := context.WithTimeout(ctx, timeout)
 	defer dialCancel()
 
-	dialer := net.Dialer{DualStack: true}
+	dialer := net.Dialer{}
 	edgeConn, err := dialer.DialContext(dialCtx, "tcp", edgeIP.String())
 	if err != nil {
 		return nil, dialError{cause: errors.Wrap(err, "DialContext error")}

origin/tunnel.go

@@ -465,7 +465,7 @@ type TunnelHandler struct {
 	noChunkedEncoding bool
 }
 
-var dialer = net.Dialer{DualStack: true}
+var dialer = net.Dialer{}
 
 // NewTunnelHandler returns a TunnelHandler, origin LAN IP and error
 func NewTunnelHandler(ctx context.Context,

tunnelrpc/pogs/config.go

@@ -197,11 +197,14 @@ func (hc *HTTPOriginConfig) Service() (originservice.OriginService, error) {
 		return nil, err
 	}
 
-	dialContext := (&net.Dialer{
+	dialer := &net.Dialer{
 		Timeout:   hc.ProxyConnectionTimeout,
 		KeepAlive: hc.TCPKeepAlive,
-		DualStack: hc.DialDualStack,
-	}).DialContext
+	}
+	if !hc.DialDualStack {
+		dialer.FallbackDelay = -1
+	}
+	dialContext := dialer.DialContext
 	transport := &http.Transport{
 		Proxy:       http.ProxyFromEnvironment,
 		DialContext: dialContext,
@@ -270,7 +273,6 @@ func (*HelloWorldOriginConfig) Service() (originservice.OriginService, error) {
 		DialContext: (&net.Dialer{
 			Timeout:   30 * time.Second,
 			KeepAlive: 30 * time.Second,
-			DualStack: true,
 		}).DialContext,
 		TLSClientConfig: &tls.Config{
 			RootCAs: rootCAs,