Regression in the Grails 4.0.6 calling response.json in Specification

[longwa]

When calling response.json in a Specification to test a RestfulController that respond with an empty list, an error occurs if you have created a default /object/_object.gson view such as:

model {
    Object object
}
json g.render(object)

Condition failed with Exception:

response.json.size() == 0
|        |
|        org.grails.web.converters.exceptions.ConverterException: Error parsing JSON
|        	at grails.converters.JSON.parse(JSON.java:260)
|        	at org.grails.plugins.testing.AbstractGrailsMockHttpServletResponse.getJson(AbstractGrailsMockHttpServletResponse.groovy:93)
|        	at example.FooControllerSpec.test something(FooControllerSpec.groovy:20)
|        Caused by: org.grails.web.json.JSONException: Missing value. at character 0 of 
|        	at org.grails.web.json.JSONTokener.syntaxError(JSONTokener.java:481)
|        	at org.grails.web.json.JSONTokener.nextValue(JSONTokener.java:358)
|        	at grails.converters.JSON.parse(JSON.java:251)
|        	... 2 more
<org.grails.plugins.testing.GrailsMockHttpServletResponse@379efd4e outputStreamAccessAllowed=true writerAccessAllowed=true characterEncoding=ISO-8859-1 charset=false content= outputStream=org.springframework.mock.web.MockHttpServletResponse$ResponseServletOutputStream@18b06b writer=null contentLength=0 contentType=application/json bufferSize=4096 committed=false locale=en_US cookies=[] headers=[Content-Type:[application/json]] status=200 errorMessage=null forwardedUrl=null includedUrls=[]>

Without the default GSON view, it works ok.

If you change the grails version to 4.0.5, the test will pass successfully, so this seems to be a regression in 4.0.6.

Task List

• Steps to reproduce provided
• Stacktrace (if present) provided
• Example that reproduces the problem uploaded to Github
• Full description of the issue provided (see below)

Steps to Reproduce

Download the sample application and run:

• git clone https://github.com/longwa/grails-gson-view-issue
• gradle test

The key is to call respond for a JSON format without an explicit GSON view to render.

Expected Behaviour

response.json should succeed and essentially return empty (size == 0) as it does in 4.0.5.

Actual Behaviour

An error occurs when JSON.parse() is called b/c the output stream has an empty string instead of empty array syntax: "" vs "[]". This seems to be a result of the _object.gson being used, which causes the renderer to follow a different path.

Environment Information

• Operating System: macOS 10.15.7
• Grails Version: 4.0.6
• JDK Version: zulu-1.8_275

Example Application

• https://github.com/longwa/grails-gson-view-issue

[xqliu]

This error happens also for our application which is on 4.0.5 currently, most of the tests depends on response.json breaks due to this issue.

Haven't had time look into this issue.

[puneetbehl]

This is happening because of the change in #235 which now correctly sets the ModelAndViews in the request attributes. But, we also removed the following line from the DefaultViewRender:

render(view, request, response) 

We removed this to avoid calling the render method from multiple places because after setting the ModelAndView request attribute, the render is also called via DispatcherServlet ( which is not the case with unit test).

Right now, I am not sure what would be the fix for this but I will spend some more time next week figure out a solution.

[amadfida]

@puneetbehl we got hit with this as well when we upgraded grails-view to 2.0.4 - any workaround available as its failing a lot of our test. In addition do you know if its only effecting unit tests?

[puneetbehl]

@amadfida Yes, it should only affect unit tests because the DispatcherServlet is not executed during the same.

[sbglasius]

I have created this trait to work around this issue:

/**
 * Due to a change in Grails DefaultViewRenderer it does no longer do the actual view rendering to the response
 * thus leading to errors in ControllerUnitTests that expect the response being fully written.
 * See https://github.com/grails/grails-views/commit/25cab090bfaf6d2264b264c7248680b4f611c806#diff-bab08f900cdc8789160b7e74825cf68433382be9d9a632842136ad2fd91dd46c
 * 
 * Calling renderGsonView() after calling the controller in the unit-test will fix this issue. Not super pretty, but it works.
 */
trait JsonControllerUnitTest implements GrailsWebUnitTest {
    void renderGsonView() {
        ModelAndView modelView =(request.getAttribute(GrailsApplicationAttributes.CONTROLLER) as Controller)?.modelAndView
        modelView?.view?.render(modelView?.model, request, response)
    }
}