Allowing :controller and :action values to be specified via the path
in config/routes.rb has been an underlying cause of a number of issues
in Rails that have resulted in security releases. In light of this it's
better that controllers and actions are explicitly whitelisted rather
than trying to blacklist or sanitize 'bad' values.
Controllers should always have a request and response when responding.
Since we make this The Rule(tm), then controllers don't need to be
somewhere in limbo between "asking a response object for a rack
response" or "I, myself contain a rack response". This duality leads to
conditionals spread through the codebase that we can delete:
* 85a78d9358/actionpack/lib/action_controller/metal.rb (L221-L223)
`render nothing: true` or rendering a `nil` body no longer add a single
space to the response body.
The old behavior was added as a workaround for a bug in an early version of
Safari, where the HTTP headers are not returned correctly if the response
body has a 0-length. This is been fixed since and the workaround is no
longer necessary.
Use `render body: ' '` if the old behavior is desired.
This is as an option to render content with a content type of
`text/plain`. This is the preferred option if you are planning to render
a plain text content.
Please see #12374 for more detail.
