1 files changed, 43 insertions, 0 deletions
diff --git a/lib/gitlab/untrusted_regexp/ruby_syntax.rb b/lib/gitlab/untrusted_regexp/ruby_syntax.rb
new file mode 100644
index 00000000000..91f300f97d0
--- /dev/null
+++ b/lib/gitlab/untrusted_regexp/ruby_syntax.rb
@@ -0,0 +1,43 @@
+# frozen_string_literal: true
+
+module Gitlab
+  class UntrustedRegexp
+    # This class implements support for Ruby syntax of regexps
+    # and converts that to RE2 representation:
+    # /<regexp>/<flags>
+    class RubySyntax
+      PATTERN = %r{^/(?<regexp>.+)/(?<flags>[ismU]*)$}.freeze
+
+      # Checks if pattern matches a regexp pattern
+      # but does not enforce it's validity
+      def self.matches_syntax?(pattern)
+        pattern.is_a?(String) && pattern.match(PATTERN).present?
+      end
+
+      # The regexp can match the pattern `/.../`, but may not be fabricatable:
+      # it can be invalid or incomplete: `/match ( string/`
+      def self.valid?(pattern)
+        !!self.fabricate(pattern)
+      end
+
+      def self.fabricate(pattern)
+        self.fabricate!(pattern)
+      rescue RegexpError
+        nil
+      end
+
+      def self.fabricate!(pattern)
+        raise RegexpError, 'Pattern is not string!' unless pattern.is_a?(String)
+
+        matches = pattern.match(PATTERN)
+        raise RegexpError, 'Invalid regular expression!' if matches.nil?
+
+        expression = matches[:regexp]
+        flags = matches[:flags]
+        expression.prepend("(?#{flags})") if flags.present?
+
+        UntrustedRegexp.new(expression, multiline: false)
+      end
+    end
+  end
+end