Fix issue with conflicting ports when starting multiple Dev sessions …

…on Podman

Due to regression on 6.1+ kernels [1], binding on 127.0.0.1:$port after some process
listens on 0.0.0.0:$port does pass, which is not expected.
Until this issue is fixed [2], a possible workaround is to try to bind on 0.0.0.0:$port.
This works correctly on Podman, and also on Kubernetes
(because we do port-forwarding on Kubernetes on 127.0.0.1:$port).

The unit test added should allow us to detect similar issues faster in the future,
should it happen again.

[1] https://lore.kernel.org/stable/e21bf153-80b0-9ec0-15ba-e04a4ad42c34@redhat.com/T/
[2] https://lore.kernel.org/netdev/20230312031904.4674-3-kuniyu@amazon.com/T/

pkg/util/util.go

@@ -782,12 +782,11 @@ func SafeGetBool(b *bool) bool {
 
 // IsPortFree checks if the port on localhost is free to use
 func IsPortFree(port int) bool {
-	address := fmt.Sprintf("localhost:%d", port)
+	address := fmt.Sprintf("0.0.0.0:%d", port)
 	listener, err := net.Listen("tcp", address)
 	if err != nil {
 		return false
 	}
-	_ = listener.Addr().(*net.TCPAddr).Port
 	err = listener.Close()
 	return err == nil
 }

pkg/util/util_test.go

@@ -2735,3 +2735,129 @@ bar
 		})
 	}
 }
+
+func TestIsPortFree(t *testing.T) {
+	type serverCloser interface {
+		Close()
+	}
+	type args struct {
+		port         int
+		portProvider func() (int, serverCloser, error)
+	}
+	type test struct {
+		name string
+		args args
+		want bool
+	}
+	tests := []test{
+		{
+			name: "negative port should return an error, handles as false",
+			args: args{port: -10},
+			want: false,
+		},
+		{
+			name: "0 should always be free",
+			args: args{port: 0},
+			want: true,
+		},
+		{
+			name: "random port bound on 127.0.0.1",
+			args: args{
+				portProvider: func() (int, serverCloser, error) {
+					s := httptest.NewServer(nil)
+					_, p, err := net.SplitHostPort(strings.TrimPrefix(s.URL, "http://"))
+					if err != nil {
+						return 0, s, err
+					}
+					port, err := strconv.Atoi(p)
+					if err != nil {
+						return 0, s, err
+					}
+					return port, s, nil
+				},
+			},
+			want: false,
+		},
+		{
+			name: "random port bound on 127.0.0.1 and checking 0 as input",
+			args: args{
+				portProvider: func() (int, serverCloser, error) {
+					s := httptest.NewServer(nil)
+					return 0, s, nil
+				},
+			},
+			want: true,
+		},
+		{
+			name: "random port bound on 0.0.0.0 and checking 0 as input",
+			args: args{
+				portProvider: func() (int, serverCloser, error) {
+					// Intentionally not using httptest.Server, which listens to 127.0.0.1
+					l, err := net.Listen("tcp", "0.0.0.0:0")
+					if err != nil {
+						return 0, nil, err
+					}
+					s := &httptest.Server{
+						Listener: l,
+						Config:   &http.Server{},
+					}
+					s.Start()
+
+					return 0, s, nil
+				},
+			},
+			want: true,
+		},
+		{
+			name: "random port bound on 0.0.0.0",
+			args: args{
+				portProvider: func() (int, serverCloser, error) {
+					// Intentionally not using httptest.Server, which listens to 127.0.0.1
+					l, err := net.Listen("tcp", "0.0.0.0:0")
+					if err != nil {
+						return 0, nil, err
+					}
+					s := &httptest.Server{
+						Listener: l,
+						Config:   &http.Server{},
+					}
+					s.Start()
+
+					_, p, err := net.SplitHostPort(strings.TrimPrefix(s.URL, "http://"))
+					if err != nil {
+						return 0, s, err
+					}
+					port, err := strconv.Atoi(p)
+					if err != nil {
+						return 0, s, err
+					}
+					return port, s, nil
+				},
+			},
+			want: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			port := tt.args.port
+			var s serverCloser
+			var err error
+			if tt.args.portProvider != nil {
+				port, s, err = tt.args.portProvider()
+				if s != nil {
+					defer s.Close()
+				}
+				if err != nil {
+					t.Errorf("error while computing port: %v", err)
+					return
+				}
+			}
+
+			if got := IsPortFree(port); got != tt.want {
+				t.Errorf("IsPortFree() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+
+}