How to fix invalid byte sequence in UTF-8 rack in Rails

README.md

Add the utf8_sanitizer.rb to your Rails 3.2 project in app/middleware. Instead of removing the invalid request characters and continuing the request (as some gems do) it returns a 400 error.

Add the following line to your config/application.rb:

config.middleware.use 'Utf8Sanitizer'

If you only need it in production add to config/environments/production.rb. This can be without quotes:

config.middleware.use Utf8Sanitizer

Check if it works by adding ?%28t%B3odei%29 to a request to your app. Instead of a HTTP 500 error you should get a error 400 returned saying Bad request.

Sources:

• http://dev.mensfeld.pl/2014/03/rack-argument-error-invalid-byte-sequence-in-utf-8/
• http://stackoverflow.com/questions/3428343/where-do-you-put-your-rack-middleware-files-and-requires

Gems that do something similar:

• https://github.com/singlebrook/utf8-cleaner
• https://github.com/whitequark/rack-utf8_sanitizer

utf8_sanitizer.rb

# Put in /app/middleware/utf8_sanitizer.rb and add
#     config.middleware.use 'Utf8Sanitizer'
# to config/application.rb.
# See: https://gist.github.com/joost/ca4eda8f31655cf6095a
class Utf8Sanitizer
  SANITIZE_ENV_KEYS = %w(
    HTTP_REFERER
    PATH_INFO
    REQUEST_URI
    REQUEST_PATH
    QUERY_STRING
  )

  def initialize(app)
    @app = app
  end

  def call(env)
    SANITIZE_ENV_KEYS.each do |key|
      string = env[key].to_s
      valid = URI.decode(string).force_encoding('UTF-8').valid_encoding?
      # Don't accept requests with invalid byte sequence
      return [ 400, { }, [ 'Bad request' ] ] unless valid
    end

    @app.call(env)
  end
end

Nice work. Thanks!