Debugging requests can be painful, especially if you use libraries where you are not aware of every metadata that is attached to the request. With this simple one-liner you can inspect how the request arrives on the other side.  

# tested on macOS m1, be aware that nc arguments can differ on other operating systems
echo -ne "HTTP/1.1 200 OK\r\n\r\nOK\r\n" | nc -kl 1337