Why is reading response body after calling http.Get(..) causing resource leaks even though I am closing the response body?

func getRespBody(link string) (string, error) {

	res, err := http.Get(link)
	if err != nil {
		return "", err
	}
	defer res.Body.Close()
	resBody, err := ioutil.ReadAll(res.Body)
	if err != nil {
		return "", err
	}
	return string(resBody), nil
}

and I have a test -

func TestRespBody(t *testing.T) {
	defer goleak.VerifyNone(t)
	getRespBody("https://google.com")
}

Why does this cause resource leaks?

I was hoping that defer res.Body.Close() would take care of closing the resp body and there wouldn't be resource leak(s). What should be done in here to prevent resource leaks?

The underlying TCP connections used within the HTTP calls, are not closed by default when you close the response body, because it is advantageous to reuse them. This is normal, but that's also the cause of your false positive leak.

You can modify the default http client behavior if you set DisableKeepAlives true.

If you refactor your function to receive an HTTP client as an argument, you can craft an http client which explicitly closes the connection rather than saving it in the connection pool, just in the scope of that test.

func getResBody(c http.Client, url string) (string, error) {
	res, err := c.Get(url)
	if err != nil {
		return "", err
	}
	defer res.Body.Close()
	resBody, err := ioutil.ReadAll(res.Body)
	if err != nil {
		return "", err
	}
	return string(resBody), nil
}


func Test_getResBody(t *testing.T) {
	defer goleak.VerifyNone(t)

	client := http.Client{
		Transport: &http.Transport{
			DisableKeepAlives: true,
		},
	}

	getResBody(client, "https://google.com")
}