Add a cache invalidation tag and an exercise reference to the assessment interface

[raphendyr]

Currently, the assessment tool is unable to determine if the exercise has changed since the last request. Currently, the best is to inavliade the cache after a while.

However, we could add a value, which defines if the exercise configuration has changed, which would be perfect for the cache.

Few things to consider. The post_url has been the best guess for the exercise reference (even that was bad). Thus,

• [ ] Add e.g. exercise API URL to download the exercise info (name, points etc, and exercise_info).
• [ ] Add a cache invalidation tag, e.g., etag, which can be the timestamp of when the above data was changed or a checksum of it
• [ ] Add this to the aplus-assess-v1 protocol spec

Alternatively, these fields can be encoded to a single field, i.e., the cache tag could be part of the url (http://aplus/api/ex/11?c=123, where c=123 is the cache invalidation tag).

Update assessment services after this is implemented:

• [ ] MOOC-Jutut https://github.com/Aalto-LeTech/mooc-jutut/blob/master/feedback/views.py#L110

[markkuriekkinen]

Add e.g. exercise API URL to download the exercise info (name, points etc, and exercise_info).

Don't we already have this? What is missing?

[raphendyr]

Add e.g. exercise API URL to download the exercise info (name, points etc, and exercise_info).

Don't we already have this? What is missing?

Ah. Yeah. Was supposed to make clear that it would be the same for exercise and submission posts. I.e. the assessment service would be able to use it as a cache key (well, tuple of api url and etag would be the cache key).