XQueue defines an interface for the LMS to communicate with external grader services.
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README.rst

Part of edX code.

xqueue

XQueue defines an interface for the LMS to communicate with external grader services. For example, when a student submits a problem in the LMS, it gets sent to the XQueue. The XQueue then has the problem graded by an external service and sends the response back to the LMS.

How the LMS Interacts with the XQueue

1. The LMS pushes student submissions to the XQueue with an HTTP POST request to the URL /xqueue/submit. The submission contains a callback URL indicating where the graded response should be sent.

2. When the submission has been graded, the XQueue pushes a response back to the LMS with an HTTP POST request to the callback URL.

How External Graders Interact with the XQueue

There are two ways kinds of grading services: passive and active. These interact with the XQueue in different ways.

Passive Graders

Passive graders wait for the XQueue to send them submissions. They then respond synchronously with a graded response.

  1. The LMS sends messages to a particular queue.

2. XQueue checks its settings and finds that the queue has a URL associated with it. XQueue forwards the message to that URL.

3. The passive grader receives a POST request from the XQueue and responds synchronously with the graded response.

4. XQueue forwards the graded response to the callback URL the LMS provided in its original message.

Active Graders

Active graders pull messages off the XQueue and push responses back to the XQueue.

  1. The test client sends messages to a particular queue.

2. The active grader polls the XQueue using a REST-like interface. When it receives a submission, it pushes a response back to the XQueue, also using a REST-like interface.

  1. XQueue pushes the response back to the LMS.

Tests

You can run the unit/integration test suite using:

rake test

from the base xqueue directory.

Note: If you do not have RabbitMQ installed and running, some tests will produce errors. See test_framework/README.md for more information.

License

The code in this repository is licensed under version 3 of the AGPL unless otherwise noted.

Please see LICENSE.txt for details.

How to Contribute

Contributions are very welcome. The easiest way is to fork this repo, and then make a pull request from your fork. The first time you make a pull request, you may be asked to sign a Contributor Agreement.

Reporting Security Issues

Please do not report security issues in public. Please email security@edx.org

Mailing List and IRC Channel

You can discuss this code on the edx-code Google Group or in the edx-code IRC channel on Freenode.