Add CustomDialer option for LeafNodes

server/leafnode.go

@@ -539,7 +539,11 @@ func (s *Server) connectToRemoteLeafNode(remote *leafNodeCfg, firstConnect bool)
 				err = ErrLeafNodeDisabled
 			} else {
 				s.Debugf("Trying to connect as leafnode to remote server on %q%s", rURL.Host, ipStr)
-				conn, err = natsDialTimeout("tcp", url, dialTimeout)
+				if opts.LeafNode.CustomDialer != nil {
+					conn, err = opts.LeafNode.CustomDialer.Dial("tcp", url)
+				} else {
+					conn, err = natsDialTimeout("tcp", url, dialTimeout)
+				}
 			}
 		}
 		if err != nil {

server/opts.go

@@ -143,6 +143,10 @@ type RemoteGatewayOpts struct {
 	tlsConfigOpts *TLSConfigOpts
 }
 
+type CustomDialer interface {
+	Dial(network, address string) (net.Conn, error)
+}
+
 // LeafNodeOpts are options for a given server to accept leaf node connections and/or connect to a remote cluster.
 type LeafNodeOpts struct {
 	Host           string        `json:"addr,omitempty"`
@@ -193,6 +197,9 @@ type LeafNodeOpts struct {
 
 	// Snapshot of configured TLS options.
 	tlsConfigOpts *TLSConfigOpts
+
+	// CustomDialer is used to override the default dialer.
+	CustomDialer CustomDialer
 }
 
 // SignatureHandler is used to sign a nonce from the server while

test/leafnode_test.go

@@ -76,6 +76,18 @@
 	return RunServer(&o), &o
 }
 
+func runSolicitLeafServerCustomDialer(lso *server.Options, dialer server.CustomDialer) (*server.Server, *server.Options) {
+	surl := fmt.Sprintf("nats-leaf://%s:%d", lso.LeafNode.Host, lso.LeafNode.Port)
+	o := DefaultTestOptions
+	o.Port = -1
+	o.NoSystemAccount = true
+	rurl, _ := url.Parse(surl)
+	o.LeafNode.Remotes = []*server.RemoteLeafOpts{{URLs: []*url.URL{rurl}}}
+	o.LeafNode.ReconnectInterval = 100 * time.Millisecond
+	o.LeafNode.CustomDialer = dialer
+	return RunServer(&o), &o
+}
+
 func TestLeafNodeInfo(t *testing.T) {
 	s, opts := runLeafServer()
 	defer s.Shutdown()
@@ -526,6 +538,34 @@
 	checkLeafNodeConnected(t, s)
 }
 
+type TestDialer struct{
+}
+
+func (td TestDialer) Dial(network, address string) (net.Conn, error) {
+	d := net.Dialer{
+		Timeout:   1 * time.Second,
+		KeepAlive: -1,
+	}
+	return d.Dial(network, address)
+}
+
+func TestLeafNodeSolicitCustomDialer(t *testing.T) {
+	s, opts := runLeafServer()
+	defer s.Shutdown()
+
+	sl, _ := runSolicitLeafServerCustomDialer(opts,&TestDialer{})
+	defer sl.Shutdown()
+
+	checkLeafNodeConnected(t, s)
+
+	// Now test reconnect.
+	s.Shutdown()
+	// Need to restart it on the same port.
+	s, _ = runLeafServerOnPort(opts.LeafNode.Port)
+	defer s.Shutdown()
+	checkLeafNodeConnected(t, s)
+}
+
 func TestLeafNodeNoEcho(t *testing.T) {
 	s, opts := runLeafServer()
 	defer s.Shutdown()