if err != nil {
		t.Fatalf("%s: for URL %q, reading body: %v", testName, req.URL.String(), err)
	}
	return r, b
}

// TestLinuxSendfileChild isn't a real test. It's used as a helper process
// for TestLinuxSendfile.
func TestLinuxSendfileChild(*testing.T) {
	if os.Getenv("GO_WANT_HELPER_PROCESS") != "1" {
		return
	}
	defer os.Exit(0)
	fd3 := os.NewFile(3, "ephemeral-port-listener")