Exception for incorrect format in rails - ruby-on-rails

Question

Im trying to test if the format send through the request url is json or not?
so in link_to I sent the format like this
<%= link_to "Embed", {:controller=>'api/oembed' ,:action => 'show',:url => catalog_url, format: 'xml'} %>
In the relevant controller I catch the param and raise the exception like this
format_request = params[:format]
if format_request != "json"
raise DRI::Exceptions::NotImplemented
end
but the exception wont display instead the server simply ran into internal error but if I changed the param inside the controller then exception displayed so if the url is like this
<%= link_to "Embed", {:controller=>'api/oembed' ,:action => 'show',:url => catalog_url, format: 'json'} %>
format_request = "xml"
if format_request != "json"
raise DRI::Exceptions::NotImplemented
end
why 501 exception does not triggered if I send the format as xml in url? Im doing it for the testing purpose that in case if someone send the request with wrong format 501 expetion show up

Answer 1

Use ActionController::MimeResponds instead of badly reinventing the wheel:
# or whatever your base controller class is
class ApplicationController < ActionController::API
# MimeResponds is not included in ActionController::API
include ActionController::MimeResponds
# Defining this in your parent class avoids repeating the same error handling code
rescue_from ActionController::UnknownFormat do
raise DRI::Exceptions::NotImplemented # do you really need to add another layer of complexity?
end
end
module Api
class OembedController < ApplicationController
def oembed
respond_to :json
end
end
end
If you don't use respond_to Rails will implicitly assume that the controller responds to all response formats. But if you explicitly list the formats you respond to with a list of symbols (or the more common block syntax) Rails will raise ActionController::UnknownFormat if the request format is not listed. You can rescue exceptions with rescue_from which lets you use inheritance instead of repeating yourself with the same error handling.

Answer 2

As #max mentions, sending the format: 'xml' is unnecessary because Rails already knows the format of the request.
<%= link_to "Embed", {:controller=>'api/oembed' ,:action => 'show',:url => catalog_url } %>
In the controller:
def oembed
respond_to do |format|
format.json { # do the thing you want }
format.any(:xml, :html) { # render your DRI::Exceptions::NotImplemented }
end
end
Or if you want more control you could throw to a custom action:
def oembed
respond_to do |format|
format.json { # do the thing you want }
format.any(:xml, :html) { render not_implemented }
end
end
def not_implemented
# just suggestions here
flash[:notice] = 'No support for non-JSON requests at this time'
redirect_to return_path
# or if you really want to throw an error
raise DRI::Exceptions::NotImplemented
end
If you really want to reinvent the wheel (it's your wheel, reinvent if you want to):
I'd rename format to something else, it's probably reserved and might give you problems
<%= link_to "Embed", {:controller=>'api/oembed' ,:action => 'show',:url => catalog_url, custom_format: 'xml'} %>
Then, in your controller, you need to explicitly allow this parameter:
def oembed
raise DRI::Exceptions::NotImplemented unless format_params[:custom_format] == 'json'
end
private
def format_params
params.permit(:custom_format)
end