Template engine

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
• A custom template should be possible to be completely independent of core, but not required to
• 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 templates in template editor
• Use same tags as Backbone template engine (Twig can configure this)

Could have

• Include another file : the actual view use different files (see Talk)
• Add Twig filter to process EM
• Idea :
  • User can only add some css/update template.css
  • User choose another 'theme' for his template : in 3.0 replace boostrap.css : a GUI and a theme system ? Need some pstpl too i think
  • User choose another framework
  • USer want to completely use his own views

Will not have

• No additional templates will be added to the template engine (like token form)
  • See discussion

Twig

http://twig.sensiolabs.org/

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