Heroku+jekyll deployment appends index.html to AJAX post - php

Question

I have an ajax call being made that posts to /php/rsvp.php. For some reason when this call goes through the web server, index.html is appended onto the path. The app is hosted on heroku using puma. Logs with the stacktrace are below:
2015-10-12T01:48:57.898961+00:00 heroku[router]: at=info method=POST path="/php/rsvp.php" host= request_id= fwd="" dyno=web.1 connect=1ms service=9ms status=500 bytes=168
2015-10-12T01:48:57.901579+00:00 app[web.1]: 2015-10-12 01:48:57 +0000: Rack app error: #<Errno::ENOTDIR: Not a directory # rb_sysopen - /app/_site/php/rsvp.php/index.html>
2015-10-12T01:48:57.901635+00:00 app[web.1]: /app/vendor/bundle/ruby/2.1.0/gems/rack-jekyll-0.4.1/lib/rack/jekyll/helpers.rb:14:in `initialize'
2015-10-12T01:48:57.901639+00:00 app[web.1]: /app/vendor/bundle/ruby/2.1.0/gems/rack-jekyll-0.4.1/lib/rack/jekyll/helpers.rb:14:in `open'
2015-10-12T01:48:57.901640+00:00 app[web.1]: /app/vendor/bundle/ruby/2.1.0/gems/rack-jekyll-0.4.1/lib/rack/jekyll/helpers.rb:14:in `file_info'
2015-10-12T01:48:57.901642+00:00 app[web.1]: /app/vendor/bundle/ruby/2.1.0/gems/rack-jekyll-0.4.1/lib/rack/jekyll.rb:75:in `call'
2015-10-12T01:48:57.901644+00:00 app[web.1]: /app/vendor/bundle/ruby/2.1.0/gems/puma-2.9.1/lib/puma/configuration.rb:71:in `call'
2015-10-12T01:48:57.901645+00:00 app[web.1]: /app/vendor/bundle/ruby/2.1.0/gems/puma-2.9.1/lib/puma/server.rb:490:in `handle_request'
2015-10-12T01:48:57.901647+00:00 app[web.1]: /app/vendor/bundle/ruby/2.1.0/gems/puma-2.9.1/lib/puma/server.rb:361:in `process_client'
2015-10-12T01:48:57.901649+00:00 app[web.1]: /app/vendor/bundle/ruby/2.1.0/gems/puma-2.9.1/lib/puma/server.rb:254:in `block in run'
2015-10-12T01:48:57.901652+00:00 app[web.1]: /app/vendor/bundle/ruby/2.1.0/gems/puma-2.9.1/lib/puma/thread_pool.rb:92:in `call'
2015-10-12T01:48:57.901692+00:00 app[web.1]: /app/vendor/bundle/ruby/2.1.0/gems/puma-2.9.1/lib/puma/thread_pool.rb:92:in `block in spawn_thread'
I've been looking through the puma and rack-jekyll functions to find where the append is happening, but none of the conditions are making sense. I also have yet to find any other post on this issue, which makes me think there is something simple I am overseeing. The ajax call being made is pretty straightforward:
req = $.post( '/rsvp.php', $form.serialize(), function(data, status){});
Is there some configuration I am missing to prevent this? My Gemfile, _config.yml, config.ru, etc. are identical to the ones here.

Answer 1

So we were having this problem too, and only just figured it out. The issue is that the rack-jekyll gem has a bug where it assumes that files without mime types are directories. See issue: https://github.com/adaoraul/rack-jekyll/issues/38
The bugfix is already done and it seems like it'll get released with 0.4.3, but in the meantime we managed to fix the problem by adding the following line to our config.ru file, which adds a mime type for .php extensions:
Rack::Mime::MIME_TYPES.merge!({".php" => "application/octet-stream"})