support run HTTP server with specific net.Listener (gin-gonic#2023)

gin.go

@@ -338,6 +338,15 @@ func (engine *Engine) RunFd(fd int) (err error) {
 		return
 	}
 	defer listener.Close()
+	err = engine.RunListener(listener)
+	return
+}
+
+// RunListener attaches the router to a http.Server and starts listening and serving HTTP requests
+// through the specified net.Listener
+func (engine *Engine) RunListener(listener net.Listener) (err error) {
+	debugPrint("Listening and serving HTTP on listener what's bind with address@%s", listener.Addr())
+	defer func() { debugPrintError(err) }()
 	err = http.Serve(listener, engine)
 	return
 }

gin_integration_test.go

@@ -207,6 +207,42 @@ func TestBadFileDescriptor(t *testing.T) {
 	assert.Error(t, router.RunFd(0))
 }
 
+func TestListener(t *testing.T) {
+	router := New()
+	addr, err := net.ResolveTCPAddr("tcp", "localhost:0")
+	assert.NoError(t, err)
+	listener, err := net.ListenTCP("tcp", addr)
+	assert.NoError(t, err)
+	go func() {
+		router.GET("/example", func(c *Context) { c.String(http.StatusOK, "it worked") })
+		assert.NoError(t, router.RunListener(listener))
+	}()
+	// have to wait for the goroutine to start and run the server
+	// otherwise the main thread will complete
+	time.Sleep(5 * time.Millisecond)
+
+	c, err := net.Dial("tcp", listener.Addr().String())
+	assert.NoError(t, err)
+
+	fmt.Fprintf(c, "GET /example HTTP/1.0\r\n\r\n")
+	scanner := bufio.NewScanner(c)
+	var response string
+	for scanner.Scan() {
+		response += scanner.Text()
+	}
+	assert.Contains(t, response, "HTTP/1.0 200", "should get a 200")
+	assert.Contains(t, response, "it worked", "resp body should match")
+}
+
+func TestBadListener(t *testing.T) {
+	router := New()
+	addr, err := net.ResolveTCPAddr("tcp", "localhost:10086")
+	assert.NoError(t, err)
+	listener, err := net.ListenTCP("tcp", addr)
+	listener.Close()
+	assert.Error(t, router.RunListener(listener))
+}
+
 func TestWithHttptestWithAutoSelectedPort(t *testing.T) {
 	router := New()
 	router.GET("/example", func(c *Context) { c.String(http.StatusOK, "it worked") })