[docker] Helper function to get exposed host ports for -P flag (#807)

* Add GetExposedHostPort function

* Update modules/docker/inspect.go

Co-authored-by: Yoriyasu Yano <[email protected]>

Co-authored-by: Yoriyasu Yano <[email protected]>

modules/docker/inspect.go

@@ -230,6 +230,16 @@ func transformContainerPorts(container inspectOutput) ([]Port, error) {
 	return ports, nil
 }
 
+// GetExposedHostPort returns an exposed host port according to requested container port. Returns 0 if the requested port is not exposed.
+func (inspectOutput ContainerInspect) GetExposedHostPort(containerPort uint16) uint16 {
+	for _, port := range inspectOutput.Ports {
+		if port.ContainerPort == containerPort {
+			return port.HostPort
+		}
+	}
+	return uint16(0)
+}
+
 // transformContainerVolumes converts Docker's volume bindings from the
 // format "/foo/bar:/foo/baz" into a more testable one
 func transformContainerVolumes(container inspectOutput) []VolumeBind {

modules/docker/inspect_test.go

@@ -56,6 +56,26 @@ func TestInspectWithExposedPort(t *testing.T) {
 	require.EqualValues(t, port, c.Ports[0].HostPort)
 }
 
+func TestInspectWithRandomExposedPort(t *testing.T) {
+	t.Parallel()
+
+	var expectedPort uint16 = 80
+	var unexpectedPort uint16 = 1234
+	options := &RunOptions{
+		Detach:       true,
+		OtherOptions: []string{fmt.Sprintf("-P")},
+	}
+
+	id := RunAndGetID(t, dockerInspectTestImage, options)
+	defer removeContainer(t, id)
+
+	c := Inspect(t, id)
+
+	require.NotEmptyf(t, c.Ports, "Container's exposed ports should not be empty")
+	require.NotEqualf(t, uint16(0), c.GetExposedHostPort(expectedPort), fmt.Sprintf("There are no exposed port %d!", expectedPort))
+	require.Equalf(t, uint16(0), c.GetExposedHostPort(unexpectedPort), fmt.Sprintf("There is an unexpected exposed port %d!", unexpectedPort))
+}
+
 func TestInspectWithHostVolume(t *testing.T) {
 	t.Parallel()