Template engine
From LimeSurvey Manual
Since Louis factored out all HTML from qanda and added a configuration file to the templates, it's a small task to add a template engine, replace the PHP views with e.g. Twig templates.
Use case
- Template providers don't have to worry about core changes in the question view files
- Template providers can apply any CSS framework specific HTML they want, like Foundation, Bootstrap etc.
- User can show some question the way they want (with some html ability)
- User can show all questions as a table
Requirements
Must have
- Template files in template zip packages can override question view files
- Template zip package can upload template files in template editor
- Actual views used in public part must use the template engine
Should have
- Possible to edit Twig/Mustache templates in template editor
- Use same tags as Backbone template engine (e.g. Underscore) (both Mustache and Twig can configure this, and Underscore too, for that matter (instructions))
Could have
- Include another file : the actual view use different files (see Talk)
- Add Twig filter to process EM
Will not have
- No additional templates will be added to the template engine (like token form)
Ways of working with Twig
Function | Twig |
---|---|
Echo variable | {{var}} |
Echo field in variable | {{var.field}} or {{var['field']}} |
Loop variable | {% for user in users %} ... {% endfor %} |
Branch on boolean | {% if trueOrFalse %} ... {% endif %} |
Translate | Add a filter, like {{"Translate me"|eT}} |
Include another template file | Include tag TODO |
Sandbox | Yes |
Security
Longer article about template injection: http://blog.portswigger.net/2015/08/server-side-template-injection.html
The lowest risk approach is to simply use a trivial template engine such as Mustache
About CPU load: It wold be easy for a template designer to make a loop within a loop within a loop etc, to exhaust the CPU power of the server. This vulnerability is in all template engines where you can loop an array (Mustache, Twig). To protect against this, the server should have a max script runtime set.
- BUT: Rendering PDF takes a long time, how to know the right limit?
Test instructions
How to write good bug reports and feature requests:
https://www.limesurvey.org/community-services/bug-tracker
https://www.limesurvey.org/community-services/feature-requests