ActionDispatch::ParamsParser works for all the requests having any Content-Length (like POST). It takes raw data from the request and puts it through the parser that is picked based on Content-Type header.

In case of any error while parsing data ParamsParser::ParseError is raised.

Class Public methods
new(app, parsers = {})

Create a new ParamsParser middleware instance.

The parsers argument can take Hash of parsers where key is identifying content mime type, and value is a lambda that is going to process data.

# File actionpack/lib/action_dispatch/middleware/params_parser.rb, line 39
def, parsers = {})
  ActiveSupport::Deprecation.warn('ActionDispatch::ParamsParser is deprecated and will be removed in Rails 5.1. Configure the parameter parsing in ActionDispatch::Request.parameter_parsers.')
  parsers = parsers.transform_keys { |key| key.respond_to?(:symbol) ? key.symbol : key }
  ActionDispatch::Request.parameter_parsers = ActionDispatch::Request::DEFAULT_PARSERS.merge(parsers)