Documentation

Make sure every error is converted to a suitable application-level error.

There are many cases where Servant will handle errors itself and reply to a client without even disturbing the application. This is both handy and clunky since our application return errors in a specific format (e.g. JSON, XML ...).

This is the case for instance if the client hits a non-exiting endpoint of the API, or if the client requests an invalid content-type, etc ...

Ideally, we would like clients to be able to expect one and only one format, so this middleware allows for manipulating the response returned by a Wai application (what servant boils down to) and adjust the response when necessary. So, any response with or without payload but no content-type will trigger the convert function and offer the caller to adjust the response as needed.