One of our active projects is to backport Moodle 2.0 webservices to Moodle 1.9.
Because of all the differences between Moodle 2.0 and Moodle 1.9 we will have to put into practice some tricks. The following image is a diagram of the designed achitecture:
We have added to Moodle 2.0 webservices architecture a couple of components to solve some problems.
Core Layer
Core Layer has nearly the same elements that Moodle 2.0 core layer, but these elements had not been evolved. There are methods that print success messages to the screen, database libraries print error messages too, etc. This is a big problem! We don’t want to re-program all these functions, it would be a waste of time.
External Layer
We will copy external layer from Moodle 2.0 to Moodle 1.9. We want to make easier the upgrade from Moodle 1.9 to Moodle 2.0, we have to publish the same functions with the same parameters. We will have to tune their implementation a little, some published functions only exist on Moodle 2.0 or have changed a little from the previous version.
Local External REST Server is a new component that will provide a REST webservice throught localhost. It will call external functions, serialize results and return them.
Connectors Layer
We will copy all connectors from Moodle 2.0 to Moodle 1.9 and develop a proxy to the local REST server. The External Proxy will define the same functions that Moodle 2.0 Connectors are calling to the External layer. The main idea is to change all requires/includes in connectors to invoke proxy’s methods. The proxy will call external functions via local webservice and return the result.
Why are we doing this odd and tricky things?
If Moodle 1.9 core prints something to the screen, it will break all webservices response. Using this architecture, the only message that will be broken will be the response of local webservice call. If the Proxy detects an error in the local call (it can unserialize the response), it would know how to proceed in every situation.
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