discourse/app/models/user_avatar.rb

require_dependency 'letter_avatar'

class UserAvatar < ActiveRecord::Base
  belongs_to :user
  belongs_to :gravatar_upload, class_name: 'Upload', dependent: :destroy
  belongs_to :custom_upload, class_name: 'Upload', dependent: :destroy

  def contains_upload?(id)
    gravatar_upload_id == id || custom_upload_id == id
  end

  def update_gravatar!
    DistributedMutex.synchronize("update_gravatar_#{user.id}") do
      begin
        # special logic for our system user
        email_hash = user.id == Discourse::SYSTEM_USER_ID ? User.email_hash("info@discourse.org") : user.email_hash

        self.last_gravatar_download_attempt = Time.new

        gravatar_url = "http://www.gravatar.com/avatar/#{email_hash}.png?s=500&d=404"
        tempfile = FileHelper.download(gravatar_url, SiteSetting.max_image_size_kb.kilobytes, "gravatar")
        upload = Upload.create_for(user.id, tempfile, 'gravatar.png', tempfile.size, { origin: gravatar_url })

        if gravatar_upload_id != upload.id
          gravatar_upload.try(:destroy!)
          self.gravatar_upload = upload
          save!
        end
      rescue OpenURI::HTTPError
        save!
      rescue SocketError
        # skip saving, we are not connected to the net
        Rails.logger.warn "Failed to download gravatar, socket error - user id #{user.id}"
      ensure
        tempfile.try(:close!)
      end
    end
  end

end

# == Schema Information
#
# Table name: user_avatars
#
#  id                             :integer          not null, primary key
#  user_id                        :integer          not null
#  custom_upload_id               :integer
#  gravatar_upload_id             :integer
#  last_gravatar_download_attempt :datetime
#  created_at                     :datetime         not null
#  updated_at                     :datetime         not null
#
# Indexes
#
#  index_user_avatars_on_user_id  (user_id)
#