Rails file uploads: Limiting a user's uploads by space available

Let's say that you want to allow people to upload files to your server. Let's also say that we want to make sure any particular user does not hog up all the space available. Let's also say you want to give each user a variable limit as to how much they can upload (i.e. for tiered services). How would you go about doing that?

Well, from a pseudo code perspective you would do the following.

1) Create a folder for each user based on the user id
2) Make sure all the user's uploads go to that folder
3) Before you do an upload, check against the user's settings to see how much space s/he is allowed
4) Check their folder to see how much space has been used
5) If they have no space left, message the user

So let's see how we do this in practice...

I guess we really want to see how much space is used, so let's start there on the User. In this example the user has a UUID as well as a space_allowed attribute which is set to a default value (and which an admin can change).

  def space_used
    space = 0
    directory = "#{Rails.root}/uploads/#{self.user.uuid}"
    
    if File.directory?(directory)
      Find.find(directory) { |f| 
        space += File.size(f); 
      }
    end
    return space
  end

So space_used first sets the directory based on the user's uuid. It then checks to see if that directory exists, and if it does, it will loop through each file and total up the space variable (unfortunately, the Directory object does not have a size variable) to see how much space has been used.

  def space_available?
    if self.space_used >= self.space_allowed
      return false
    end
    return true
  end

space_available? checks the space used and compares it to the space_allowed to the user. So in the controller you just need to call space_available? on the user and handle it appropriately

i.e.

user = User.find(params[:id])
if user.space_available?
  ... handle upload ...
else
  ... handle error ...
end