port: add ChildIP

allow users to override the IP to use for the connection inside the
network namespace.

It is useful e.g. with slirp4netns to override the IP to "10.0.2.100".

Signed-off-by: Giuseppe Scrivano <[email protected]>

pkg/port/builtin/child/child.go

@@ -106,7 +106,11 @@ func (d *childDriver) handleConnectRequest(c *net.UnixConn, req *msg.Request) er
 		return errors.Errorf("unknown proto: %q", req.Proto)
 	}
 	var dialer net.Dialer
-	targetConn, err := dialer.Dial(req.Proto, fmt.Sprintf("127.0.0.1:%d", req.Port))
+	ip := req.IP
+	if ip == "" {
+		ip = "127.0.0.1"
+	}
+	targetConn, err := dialer.Dial(req.Proto, fmt.Sprintf("%s:%d", ip, req.Port))
 	if err != nil {
 		return err
 	}

pkg/port/builtin/msg/msg.go

@@ -20,6 +20,7 @@ const (
 type Request struct {
 	Type  string // "init" or "connect"
 	Proto string // "tcp" or "udp"
+	IP    string
 	Port  int
 }
 
@@ -53,6 +54,7 @@ func ConnectToChild(c *net.UnixConn, spec port.Spec) (int, error) {
 		Type:  RequestTypeConnect,
 		Proto: spec.Proto,
 		Port:  spec.ChildPort,
+		IP:    spec.ChildIP,
 	}
 	if _, err := msgutil.MarshalToWriter(c, &req); err != nil {
 		return 0, err

pkg/port/port.go

@@ -10,6 +10,7 @@ type Spec struct {
 	ParentIP   string `json:"parentIP,omitempty"` // IPv4 address. can be empty (0.0.0.0).
 	ParentPort int    `json:"parentPort,omitempty"`
 	ChildPort  int    `json:"childPort,omitempty"`
+	ChildIP    string `json:"childIP,omitempty"`
 }
 
 type Status struct {