Using a codec in a Grails unit test

This is a small issue, but I encountered it and found a solution on the mailing lists, so I thought I’d document it here.

I was demonstrating a trivial Grails application in class today and decided to unit test it. The app has a single controller, called WelcomeController:

class WelcomeController {
  def index = {
    def name = params.name ?: "Grails"
    render "Hello, $name"
  }
}

When I deploy the application and access the Welcome controller (via http://localhost:8080/hellograils/welcome/index), it displays “Hello, Grails!”. If I append “?name=Dolly” to the URL, the result is “Hello, Dolly!”. All nice and simple.

I decided I wanted to write a test case for this, and lately I’ve been learning how to favor unit tests over integration tests as much as possible, mostly for speed. I therefore wrote the following tests:

import grails.test.*

class WelcomeControllerTests extends ControllerUnitTestCase {
  void testWelcomeWithoutParameter() {
    def wc = new WelcomeController()
      wc.index()
      assertEquals "Hello, Grails!", wc.response.contentAsString
    }

  void testWelcomeWithParameter() {
    def wc = new WelcomeController()
    wc.params.name = "Dolly"
    wc.index()
    assertEquals "Hello, Dolly!", wc.response.contentAsString
  }
}

When I run the unit tests (i.e., grails test-app unit:), everything runs correctly.

One of the students pointed out that though this is a trivial example, it’s open to XSS (cross-site scripting) attacks. In the URL, replace “name=Dolly” with “name=alert('dude, you've been hacked')” and the embedded JavaScript code executes and pops up an alert box.

I knew that an easy solution to this would be to modify the index action in the controller to look like:

class WelcomeController {
  def index = {
    def name = params.name ?: "Grails"
    render "Hello, $name".encodeAsHTML()
  }
}

The “encodeAsHTML” method escapes all the HTML, so the output of the hack is just “Hello, alert(…” (i.e., the script is shown as a string, rather than executed) and the problem goes away.

The issue I encountered, though, is that my unit tests started failing, with a missing method exception that claimed that the String class doesn’t have a method called encodeAsHTML. That’s correct, of course, because that method is dynamically injected by Grails based on the org.codehaus.groovy.grails.plugin.codecs.HTMLCodec class. In a unit test, though, the injection doesn’t happen, and I get the exception.

One solution to this, as pointed out on the very valuable grails-users email list, is to add the method to the String class via its metaclass. In other words, in my test, I can add

  void setUp() {
    super.setUp()
    String.metaclass.encodeAsHTML = {
      org.codehaus.groovy.grails.plugins.codecs.HTMLCodec.encode(delegate)
    }
  }

Now the String class has the encodeAsHTML method, and everything works again.

Then I started browsing the Grails API, and found that in ControllerUnitTestCase there’s a method called loadCodec. The GroovyDocs weren’t very informative, but I found in the jira for Grails that issue GRAILS-3816 recommends the addition of the loadCodec method for just this sort of purpose.

That means that I can actually write

  void setUp() {
    super.setUp()
    loadCode(org.codehaus.groovy.grails.plugins.codecs.HTMLCodec)
  }

and everything works as it should. Since this isn’t terribly well documented, I thought I’d say something here. Hopefully this will save somebody some looking around.

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