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titleContent pre downloading

Content pre downloading

This part is about how user will receive a content for a specific course on their device to be able to work while offline. This requires to download:

  • course info

  • dates

  • discussions

  • XBlocks

  • updates

  • handouts

Solution

Create an endpoint that generates For JSON based data it is going to be cached for future offline use. No extra work on the backend.

For XBlocks a compressed file with all data for the course. Data is compressed and structured by the main course componentsstatic files is generated presumably only on course publish event.

Implementation assumptions

  • provide all the text based data into JSON format

  • content for a course can be potentially big. Therefore it is needed to be compressed

  • media file is going to be created for downloading on demand

  • static content (course info image, handouts etc) is transferred using links. On the mobile device it can be pre downloaded

  • each XBlock is separate HTML file (assumption for now)

Pre downloaded XBlocks

XBlocks are assumed to be a single HTML file for now. But there are different types and different complexities. This means one xblock can load something else which makes things complicated.

The idea is to separate XBlocks into offline-friendly and non-offline-friendly and incrementally work with each type.

  • which path/filename will be based on the XBlock path. This allow to omit extra backend endpoint for media file path

  • media file should be using storage classes to be configurable in production

  • static content will be put near the main XBlock’s HTML file and all the links are changed to forward to local static directory

  • each XBlock is separate compressed archive

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titleOffline-to-online sync

Offline-to-online sync

This part involves batch data transfer when a user goes online after being offline. It requires to take care of:

  • XBlocks submissions

  • Events

  • Course XBlocks updates

Solution

Create:

  • endpoint that accepts user’s submissions in a batch

  • endpoint that accepts user’s events in a batch

XBlock submissions assumptions

  • it is required to insert a JS bridge for mobile application to intercept XBlocks requests. For now we can assume that submit answer and sending events should be intercepted.

  • Requests are grouped by XBlock

  • For the same XBlock requests are processed in the order of timestamp

  • Changes to XBlocks should reflect on the downloaded course XBlocks state. This means default state of the XBlock when user sees it for the first time changes to the state after user submitted a response and obtained a feedback.

  • When state of XBlock is changed (default state of the XBlock when user sees it for the first time changes to the state after when user submitted a response and obtained a feedback), in the offline mode XBlock is displayed with a feedback.

  • If server returns 4xx or 5xx it is required to store their requests and not loose a progress. Process this case intelligently.

  • Handle conflicts and make a comprehensive response.
    Assuming there can be situations:

    • where user did some actions in both offline mobile and online web

    • user did some actions before a deadline and went online after the deadline

    • [here can be more cases later]

  • bad internet connection == offline? Assuming that there can be large data to send and user can have poor experience with online in that moment. We can propose to use offline mode in this case or automatically use it.

  • processed based on the server timestamp or mobile timestamp?

Events assumptions

  • should be processed in order of timestamps

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titleCourse XBlocks updates

Course XBlocks updates

This part is partially touched in the section above when state changes are mentioned. There are different scenarios when the XBlock stored on the mobile device for offline mode is required to be updated.

  • course XBlock was changed after user had downloaded the course

  • user obtained a feedback in the XBlock. Consequently user should see feedback in offline

Solution

Implement an endpoint to download a part of the course (presumably course section/subsection) to replace outdated parts in the mobile store. It should consider efficiency, because downloading the whole course again is not appropriateEndpoint for XBlock can be extended with query parameters to be able to download default state of the XBlock and state with a feedback. If user would want to reset his feedback in the offline mode there will be 2 XBlocks states already stored.

Potentially it would be good to know which XBlocks are outdated before sending batch data to the server. By this potential conflicts can be avoided. Validating all XBlocks can require to have a separate endpoint with last updates dates. Mobile application can compare each XBlock update date and react in different ways like show some information for user or skip submissions for outdated XBlock.

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