feat(agent): expose Addr and Port functions for listening agent

agent/agent.go

@@ -114,6 +114,31 @@ func Listen(opts Options) error {
 	return nil
 }
 
+// Addr returns the network address the agent is listening on, or nil if not listening.
+func Addr() net.Addr {
+	mu.Lock()
+	defer mu.Unlock()
+	if listener == nil {
+		return nil
+	}
+	return listener.Addr()
+}
+
+// Port returns the TCP port number the agent is listening on.
+// It returns an error if the agent is not listening or the address is not a TCP address.
+func Port() (int, error) {
+	mu.Lock()
+	defer mu.Unlock()
+	if listener == nil {
+		return 0, errors.New("gops: agent is not listening")
+	}
+	tcpAddr, ok := listener.Addr().(*net.TCPAddr)
+	if !ok {
+		return 0, fmt.Errorf("gops: listener address is not TCP: %T", listener.Addr())
+	}
+	return tcpAddr.Port, nil
+}
+
 func listen(l net.Listener) {
 	buf := make([]byte, 1)
 	for {

agent/agent_test.go

@@ -65,6 +65,42 @@ func TestAgentListenReuseAddrAndPort(t *testing.T) {
 	Close()
 }
 
+func TestAgentAddrAndPort(t *testing.T) {
+	if Addr() != nil {
+		t.Fatalf("Addr() = %v; want nil before Listen", Addr())
+	}
+	if _, err := Port(); err == nil {
+		t.Fatal("Port() expected error before Listen, got nil")
+	}
+
+	err := Listen(Options{Addr: "127.0.0.1:0"})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	addr := Addr()
+	if addr == nil {
+		t.Fatal("Addr() = nil; want non-nil after Listen")
+	}
+
+	port, err := Port()
+	if err != nil {
+		t.Fatalf("Port() unexpected error: %v", err)
+	}
+	if port <= 0 {
+		t.Fatalf("Port() = %d; want > 0", port)
+	}
+
+	Close()
+
+	if Addr() != nil {
+		t.Fatalf("Addr() = %v; want nil after Close", Addr())
+	}
+	if _, err := Port(); err == nil {
+		t.Fatal("Port() expected error after Close, got nil")
+	}
+}
+
 func TestFormatBytes(t *testing.T) {
 	tests := []struct {
 		val  uint64