Patch CarrierWave to test file content type using UNIX's 'file' utility

sanitized_file.rb

# lib/carrierwave_ext/sanitized_file.rb
require "carrierwave/sanitized_file"

module CarrierWave
  class SanitizedFile
    ##
    # Returns the content type of the file.
    #
    # === Returns
    #
    # [String] the content type of the file
    #
    def content_type
      @content_type ||=
        existing_content_type ||
        file_utility_content_type ||
        mime_magic_content_type ||
        mini_mime_content_type
    end

    ##
    # Uses the UNIX 'file' utility to extract the content type from
    # the file path.
    #
    # === Returns
    #
    # [String] the content type of the file, or nil if the 'file' command is not found or fails
    #          to resolve a mimetype
    def file_utility_content_type
      return unless path
      return if system("which file", out: File::NULL).blank?

      # An invalid path echos a warning to STDERR
      `file --brief --keep-going --mime-type #{path.shellescape}`
        .strip
        .downcase
        .presence
    end
  end
end