Spring MVC raises MissingPathVariableException resulting in 500 instead of 400 error when path segment is u001F or u00D and cannot be converted to target type UUID

[ltsallas]

This is an corner case, discovered while performing some property-based testing for my API.

Affects spring-web:6.0.12

Here is a minimal code sample that reproduces the issue

https://gist.github.com/ltsallas/9903343b6b7a90013cdd155bfcd670ce

I think the the last two tests in the DemoControllerTest should return a 400(MethodArgumentTypeMismatchException) and not a 500(MissingPathVariableException) response.

[rstoyanchev]

This case where a value is present, but becomes null after conversion (StringToUUIDConverter calls UUID.fromString) was addressed in #26679. We now detect it and raise MissingPathVariableException, which is what we do generally with missing path variables since that could be an incorrectly defined URI template.

That said in this case a value is present, but not valid and indeed should be treated as a 400. As part of #26679 we did add a missingAfterConversion flag to MissingRequestValueException and could use that to differentiate this case from the more general case of a missing path variable.

[ltsallas]

Thanks for taking a look into this one @rstoyanchev
Are you suggesting this change in the getStatusCode() of the MissingPathVariableException ?

@Override
   public HttpStatusCode getStatusCode() {
       return isMissingAfterConversion() ? super.getStatusCode() : HttpStatus.INTERNAL_SERVER_ERROR;
   }