normalize extension

lib/filename_utils.rb

@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+module FilenameUtils
+  DANGEROUS_EXTENSIONS = %w[
+    exe com bat cmd scr pif vbs vbe js jse wsf wsh msi msp
+    hta cpl jar app deb rpm dmg pkg mpkg dll so dylib sys
+    inf reg ps1 psm1 psd1 ps1xml psc1 pssc vb vba
+    sh bash zsh fish run out bin elf gadget workflow lnk scf
+    url desktop application action apk ipa xap appx
+    appxbundle msix msixbundle diagcab diagpkg msc ocx
+    drv ins isp mst paf prf shb shs slk ws wsc inf1 inf2
+  ].freeze
+
+  DANGEROUS_EXTENSIONS_REGEXP = /\.(#{Regexp.union(DANGEROUS_EXTENSIONS).source})\W*\z/i
+
+  module_function
+
+  def dangerous_extension(filename)
+    ActiveStorage::Filename.wrap(filename).sanitized[DANGEROUS_EXTENSIONS_REGEXP, 1]&.downcase
+  end
+end