Shrine validation of file extension does not allow Facebook image

Question

I'm using Srhine for images in my project and Omniauth gems for logging via Google and Facebook.

My method of getting data from Omniauth provider is the standard one:

  def self.from_omniauth(auth)
    where(provider: auth.provider, uid: auth.uid).first_or_create do |user|
      user.email = auth.info.email
      user.name = [auth.info.first_name, auth.info.last_name].join(" ")
      user.password = Devise.friendly_token[0, 20]
      user.avatar_remote_url = auth.info.image
    end
  end

It allows me to login via Google and Facebook and get user data, name and image. I also have standard registration and possibility to update user.avatar so I wanted to validate the image so that it has a limited size and so that the extensions are also limited. I wrote the following validation in my Uploader class:

  Attacher.validate do
    validate_max_size 2*1024*1024
    # validate_extension %w[jpg jpeg png webp]
  end

The problem is that the validation of extension doesn't allow for registering new user via Facebook. In case of FB auth.info.image doesn't really return a link to an image like 'https://blabla/image.jpg' but rather it creates a link which, when you paste it into the browser, results in direct download of the image to the hard drive. How can I write this validation so that it allows for the FB way of providing image to be saved? Or maybe how can I skip this validation in the Omniauth method?

Answer 1

You can set a custom flag in Shrine::Attacher context hash before attaching the file:

def self.from_omniauth(auth)
  where(provider: auth.provider, uid: auth.uid).first_or_create do |user|
    user.email = auth.info.email
    user.name = [auth.info.first_name, auth.info.last_name].join(" ")
    user.password = Devise.friendly_token[0, 20]
    user.avatar_attacher.context[:omniauth] = true # <=== set the flag
    user.avatar_remote_url = auth.info.image
  end
end

Then in the validate block you can access it and skip extension validation if the flag is present:

Attacher.validate do
  validate_max_size 2*1024*1024
  validate_extension %w[jpg jpeg png webp] unless context[:omniauth]
end