mastodon/app/models/concerns/attachmentable.rb

# frozen_string_literal: true

require 'mime/types/columnar'

module Attachmentable
  extend ActiveSupport::Concern

  MAX_MATRIX_LIMIT = 16_777_216 # 4096x4096px or approx. 16MB
  GIF_MATRIX_LIMIT = 921_600    # 1280x720px

  included do
    before_post_process :obfuscate_file_name
    before_post_process :set_file_extensions
    before_post_process :check_image_dimensions
    before_post_process :set_file_content_type
  end

  private

  def set_file_content_type
    self.class.attachment_definitions.each_key do |attachment_name|
      attachment = send(attachment_name)

      next if attachment.blank? || attachment.queued_for_write[:original].blank?

      attachment.instance_write :content_type, calculated_content_type(attachment)
    end
  end

  def set_file_extensions
    self.class.attachment_definitions.each_key do |attachment_name|
      attachment = send(attachment_name)

      next if attachment.blank?

      attachment.instance_write :file_name, [Paperclip::Interpolations.basename(attachment, :original), appropriate_extension(attachment)].delete_if(&:blank?).join('.')
    end
  end

  def check_image_dimensions
    self.class.attachment_definitions.each_key do |attachment_name|
      attachment = send(attachment_name)

      next if attachment.blank? || !/image.*/.match?(attachment.content_type) || attachment.queued_for_write[:original].blank?

      width, height = FastImage.size(attachment.queued_for_write[:original].path)
      matrix_limit  = attachment.content_type == 'image/gif' ? GIF_MATRIX_LIMIT : MAX_MATRIX_LIMIT

      raise Mastodon::DimensionsValidationError, "#{width}x#{height} images are not supported" if width.present? && height.present? && (width * height > matrix_limit)
    end
  end

  def appropriate_extension(attachment)
    mime_type = MIME::Types[attachment.content_type]

    extensions_for_mime_type = mime_type.empty? ? [] : mime_type.first.extensions
    original_extension       = Paperclip::Interpolations.extension(attachment, :original)
    proper_extension         = extensions_for_mime_type.first.to_s
    extension                = extensions_for_mime_type.include?(original_extension) ? original_extension : proper_extension
    extension                = 'jpeg' if extension == 'jpe'

    extension
  end

  def calculated_content_type(attachment)
    content_type = Paperclip.run('file', '-b --mime :file', file: attachment.queued_for_write[:original].path).split(/[:;\s]+/).first.chomp
    content_type = 'video/mp4' if content_type == 'video/x-m4v'
    content_type
  rescue Terrapin::CommandLineError
    ''
  end

  def obfuscate_file_name
    self.class.attachment_definitions.each_key do |attachment_name|
      attachment = send(attachment_name)

      next if attachment.blank?

      attachment.instance_write :file_name, SecureRandom.hex(8) + File.extname(attachment.instance_read(:file_name))
    end
  end
end