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Rack middleware to validate content
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Even Rails can't be trusted not to produce malformed xml sometimes. Add this Rack middleware to the stack while you run your tests and it will monitor the responses you send, infer the appropriate validations based on content type, and raise if they fail.


Add this line to your application's Gemfile:

gem 'probity', git: ''

And then execute:

$ bundle

Or install it yourself as:

$ gem install probity


Probity should only be included in your middleware stack when running in test/development mode. If you're using a conventional Rails app, for example, you could include it like so:

# in config/environments/test.rb

Now, run your test scripts! If your app produces malformed responses, Probity will turn a passing test into a failing one by raising a parsing error in your server. Depending on your particular test setup, this might manifest in different ways, but as long as your tests are at all meaningful they at least shouldn't pass.


By default, Probity will validate the application/xml and application/json content types, and raise if it sees anything else. If you're serving something other than those two, such as html, you'll probably want to do

middleware.use(Probity::ResponseValidatorMiddleware, missing_validator: :warn)
middleware.use(Probity::ResponseValidatorMiddleware, missing_validator: :ignore)

A blank body is not valid JSON or XML. If you would like to special-case this as an allowable response, use

middleware.use(Probity::ResponseValidatorMiddleware, blank_body: :ignore)

You can add validators for your content types with code like this:

Probity.validators['application/hal+json'] = do |body|
	raise unless

You can also override the default validators the same way:

Probity.validators['application/xml'] = # Object that responds to .call(str)


The XML validator uses Nokogiri in Strict Mode, while the JSON validator uses Ruby's built-in JSON.parse. Pull requests are welcome for more content types.


  1. Fork it ([my-github-username]/probity/fork )
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create a new Pull Request
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