Override method/variable in a gem rails - ruby

Question

I am trying to find a way to override a variable in a rails gem actionpack/http/parameters.rb. I have to process an ndjson stream and the rails middleware cannot process ndjson. It uses ActiveSupport::JSON.decode
This is the source of the code below
DEFAULT_PARSERS = {
Mime[:json].symbol => -> (raw_post) {
data = ActiveSupport::JSON.decode(raw_post)
data.is_a?(Hash) ? data : { _json: data }
}
}
I get this error when it tries to parse ndjson
ActionDispatch::Http::Parameters::ParseError in MyController#activity
My objective is to override the parser to allow it to decode the ndjson... Potentially using split(\n) as opposed to the current ActiveSupport::JSON.decode.
So far i have tried creating a file in lib/ folder and using the following code but it doesn't seem to do the override. How do i do this without Monkey patching
require 'lib/action_dispatch/http/parameters'
module MyParser
module Overrides
extend ActiveSupport::Concern
DEFAULT_PARSERS = {
Mime[:json].symbol => -> (raw_post) {
data = raw_post.split("\n")
data = ActiveSupport::JSON.decode(data)
data.is_a?(Hash) ? data : { _json: data }
}
}
end
end
ActionDispatch::Http::Parameters.include(MyParser::Overrides)
UPDATE:
The second approach i tried:
ActionDispatch::Http::Parameters.const_set(:DEFAULT_PARSERS, {
Mime[:json].symbol => -> (raw_post) {
data = raw_post.split("\n")
data = ActiveSupport::JSON.decode(data)
data.is_a?(Hash) ? data : { _json: data }
},
})
Unfortunately it keeps warning me that the constant is already defined.

Answer 1

I took another approach. Instead of reinitializing the constant, i created a file in config/initializers/custom_params.rb to override the method parse_formatted_parameters (here) that was using the DEFAULT_PARSERS variable. From within i was able to change the Proc value for the json data type.
This conveniently overrides the method and allows the ActionDispatch::Http::Parameters module to pass the ndjson to my controller without any parsing errors.
module ActionDispatch
module Http
module Parameters
extend ActiveSupport::Concern
private
def parse_formatted_parameters(parsers)
parsers[Mime[:json].symbol] = Proc.new { |raw_post|
data = ActiveSupport::JSON.decode(raw_post) rescue nil
if !data
data = raw_post
end
data.is_a?(Hash) ? data : { _json: data }
}
return yield if content_length.zero? || content_mime_type.nil?
# rubocop:enable all
strategy = parsers.fetch(content_mime_type.symbol) { return yield }
begin
strategy.call(raw_post)
rescue # JSON or Ruby code block errors.
my_logger = logger || ActiveSupport::Logger.new($stderr)
my_logger.debug "Error occurred while parsing request parameters.\nContents:\n\n#{raw_post}"
raise ParseError
end
end
end
end
end