added UseLibHeaders option to allow disabling of lib headers

[yuchunc]

#529 I am not familiar with erlang, and I can't, for the life of me, seem to figure out how to get erlang test suite to run. I fiddle with the code under my /deps, and this is working for me.

Please let me know if anything need to be updated.

Thank you!

[hazardfn]

@yuchunc I can't speak for @benoitc and this is his project, I personally see a potential problem regarding multi-part-streams partially because I don't know what the code you are bypassing does, here are a list of things I see:

• You have bypassed handle_body for multi part streams, which sounds like a massive side-effect for just disabling standard headers. It may not be important but I suspect it is without looking deeper.
• I would have the proplist value be a boolean and be called disable_default_headers (true/false)
• I would use proplist:get_value/3 and explicitly write a default of false
• I would use a function guard instead of having maybe_add_host like below
• A big one: lack of tests.

add_host(Headers, Netloc, DisableHeaders) when DisableHeaders ->
  Headers;
add_host(Headers0, Netloc, _DisableHeaders) ->
  {_, Headers1} = hackney_headers_new:store_new(<<"Host">>, Netloc, Headers0),
  Headers1.

[hazardfn]

@benoitc for some context, here is the original post and reasoning behind why this may be a requirement (despite my personal belief the person who wrote this third-party API should have their computer(s) revoked): https://elixirforum.com/t/options-for-httpoison-and-hackney-to-not-append-library-headers/16519/4

[benoitc]

@hazardfn it would have been interesting which headers are triggering an error als.

@yuchunc Patch looks good but I think I would prefer to have it named skip_default_headers (false by default). Also I think that in such case the request should probably be validated before being sent. to make sure it comply to http 1.1, this would fix possible errors when sending a body or else as spotted by @hazardfn . Can you make such changes?

[hazardfn]

@benoitc that's up to @yuchunc, I just offered to give it a general review as he requested some input due to him being more comfortable with Elixir than Erlang 👍

[yuchunc]

@benoitc, @hazardfn Thank you both for reviewing this PR. To be perfectly honest, I am not familiar with http 1.1 compliant, but I can send sometime looking in to it. I'll find sometime to make the changes.

I also do agree with @hazardfn, this api is pretty stupid . ☹️