Rails : Validate availablity of a distant ressource over HTTP
Sometimes you may host some ressources on a different website and you may want to validate the availability of it when creating a Rails model object (ActiveRecord::Base).
It would be dramatically unefficient to download the full media with a GET request. So, to achieve this we will use the HEAD http request that act as the GET request but return only the HTTP header without the body.
Here is a exemple of an ActiveRecord::Base object that validates the presence of the ressource among the Internet.
require 'net/http'
# the class is supposed to have a "media" attribute
# that is a relative url to a ressource hosted an a different
# website
class Article < ActiveRecord::Base
RESOURCE_HOST = "flickr.com"
RESOURCE_PORT = 80
validate :validates_presence_of_external_media
protected
def validates_presence_of_external_media
response = nil
# initiating the HTTP connection
Net::HTTP.start(RESOURCE_HOST, RESOURCE_PORT) do |http|
# doing the HEAD request
response = http.head(media)
end
# add an error if the request is not successful
errors.add :media, "ressource unavailable : #{response.code} #{response.msg}" unless
responce.kind_of?(Net::HTTPSuccess)
end
end
This is a very minimalist example, but this kind of technic may have a lot of uses.
