[sph]

I had to write a piece of logic that sends a GET when HEAD fails, because of a non-HTTP compliant servers. HEAD should in theory return the same status as a GET, but without any body. In practice, many web servers return 404, sometimes 500. HN itself returns 405 Method Not Allowed, which makes some sense, I guess.

The code in question, simplified:

    defp try_get_request?(%Link{method: :head}, %StatusResponse{} = response) do
      # Per HTTP specification, the HEAD response should be functionally equivalent to a
      # GET, but shall not contain any body.
      # Not all servers respect this, so might have a different status response on HEAD than on GET.
      #
      # We assume that some HTTP status codes are suspicious and worth retrying.
      #
      # HTTP 520 is seen with Cloudflare to mean "Web Server Returned an Unknown Error", possibly
      # in response to a HEAD request.
   
      response.code in [403, 404, 405, 520]
   end