class ActiveStorage::Download # Sending .ai files as application/postscript to Safari opens them in a blank, grey screen. # Downloading .ai as application/postscript files in Safari appends .ps to the extension. # Sending HTML, SVG, XML and SWF files as binary closes XSS vulnerabilities. # Sending JS files as binary avoids InvalidCrossOriginRequest without compromising security. CONTENT_TYPES_TO_RENDER_AS_BINARY = %w( text/html text/javascript image/svg+xml application/postscript application/x-shockwave-flash text/xml application/xml application/xhtml+xml ) BINARY_CONTENT_TYPE = "application/octet-stream" def initialize(stored_file) @stored_file = stored_file end def headers(force_attachment: false) { x_accel_redirect: "/reproxy", x_reproxy_url: reproxy_url, content_type: content_type, content_disposition: content_disposition(force_attachment), x_frame_options: "SAMEORIGIN" } end private def reproxy_url @stored_file.depot_location.paths.first end def content_type if @stored_file.content_type.in? CONTENT_TYPES_TO_RENDER_AS_BINARY BINARY_CONTENT_TYPE else @stored_file.content_type end end def content_disposition(force_attachment = false) if force_attachment || content_type == BINARY_CONTENT_TYPE "attachment; #{escaped_filename}" else "inline; #{escaped_filename}" end end # RFC2231 encoding for UTF-8 filenames, with an ASCII fallback # first for unsupported browsers (IE < 9, perhaps others?). # http://greenbytes.de/tech/tc2231/#encoding-2231-fb def escaped_filename filename = @stored_file.filename.sanitized ascii_filename = encode_ascii_filename(filename) utf8_filename = encode_utf8_filename(filename) "#{ascii_filename}; #{utf8_filename}" end TRADITIONAL_PARAMETER_ESCAPED_CHAR = /[^ A-Za-z0-9!#$+.^_`|~-]/ def encode_ascii_filename(filename) # There is no reliable way to escape special or non-Latin characters # in a traditionally quoted Content-Disposition filename parameter. # Settle for transliterating to ASCII, then percent-escaping special # characters, excluding spaces. filename = I18n.transliterate(filename) filename = percent_escape(filename, TRADITIONAL_PARAMETER_ESCAPED_CHAR) %(filename="#{filename}") end RFC5987_PARAMETER_ESCAPED_CHAR = /[^A-Za-z0-9!#$&+.^_`|~-]/ def encode_utf8_filename(filename) # RFC2231 filename parameters can simply be percent-escaped according # to RFC5987. filename = percent_escape(filename, RFC5987_PARAMETER_ESCAPED_CHAR) %(filename*=UTF-8''#{filename}) end def percent_escape(string, pattern) string.gsub(pattern) do |char| char.bytes.map { |byte| "%%%02X" % byte }.join("") end end end