Carrierwave image extensions - ruby-on-rails

Question

I'm trying to determine whether a remote url is an image. Most url's have .jpg, .png etc...but some images, like google images, have no extension...i.e.
https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSbK2NSUILnFozlX-oCWQ0r2PS2gHPPF7c8XaxGuJFGe83KGJkhFtlLXU_u
I've tried using FastImage to determine whether a url is an image. It works when any URL is fed into it...
How could I ensure that remote urls use FastImage and uploaded files use the whitelist? Here is what have in my uploader. Avatar_remote_url isn't recognized...what do I do in the uploader to just test remote urls and not regular files.
def extension_white_list
if defined? avatar_remote_url && !FastImage.type(CGI::unescape(avatar_remote_url)).nil?
# ok to process
else # regular uploaded file should detect the following extensions
%w(jpg jpeg gif png)
end
end

Answer 1

if all you have to work with is a url like that you can send a HEAD request to the server to obtain the content type for the image. From that you can obtain the extension
require 'net/http'
require 'mime/types'
def get_extension(url)
uri = URI.parse(url)
http = Net::HTTP.new(uri.host, uri.port)
http.use_ssl = true if uri.scheme == 'https'
request = Net::HTTP::Head.new(uri.request_uri)
response = http.request(request)
content_type = response['Content-Type']
MIME::Types[content_type].first.extensions.first
end

Answer 2

I'm working with the code you provided and some of the code provided in the CarrierWave Wiki for validating remote URLs.
You can create a new validator in lib/remote_image_validator.rb.
require 'fastimage'
class RemoteImageValidator < ActiveModel::EachValidator
def validate_each(object, attribute, value)
raise(ArgumentError, "A regular expression must be supplied as the :format option of the options hash") unless options[:format].nil? || options[:format].is_a?(Regexp)
configuration = { :message => "is invalid or not responding", :format => URI::regexp(%w(http https)) }
configuration.update(options)
if value =~ configuration[:format]
begin
if FastImage.type(CGI::unescape(avatar_remote_url))
true
else
object.errors.add(attribute, configuration[:message]) and false
end
rescue
object.errors.add(attribute, configuration[:message]) and false
end
else
object.errors.add(attribute, configuration[:message]) and false
end
end
end
Then in your model
class User < ActiveRecord::Base
validates :avatar_remote_url,
:remote_image => {
:format => /(^$)|(^(http|https):\/\/[a-z0-9]+([\-\.]{1}[a-z0-9]+)*\.[a-z]{2,5}(([0-9]{1,5})?\/.*)?$)/ix,
:unless => remote_avatar_url.blank?
}
end

Answer 3

I was having a similar issue where creating the different versions from the original was failing because ImageMagick could not figure out the correct encoder to use due to the missing extension. Here is a monkey-patch I applied in Rails that fixed my problem:
module CarrierWave
module Uploader
module Download
class RemoteFile
def original_filename
value = File.basename(file.base_uri.path)
mime_type = Mime::Type.lookup(file.content_type)
unless File.extname(value).present? || mime_type.blank?
value = "#{value}.#{mime_type.symbol}"
end
value
end
end
end
end
end
I believe this will address the problem you are having as well since it ensures the existence of a file extension when the content type is set appropriately.
UPDATE:
The master branch of carrierwave has a different solution to this problem that uses the Content-Disposition header to figure out the filename. Here is the relevant pull request on github.