Development:Resource module file API migration

Please use talk page for comments and proposals, thanks.

Current problems

• plain text and html resource types separate
• embedded images and files in general are stored in course files without appropriate access control
• local files and Internet links mixed
• HarvestRoad Hive repository type is not maintained.
• embedded images are lost during backup & restore which moves the course to a new site. -- Matt Gibson 08:53, 18 May 2009 (UTC)
• can't move a "whole" web page properly from one course to another (eg course import).

Types of resources

Plugin	Moodle 1.9	Moodle 2.0
directory	a directory of files on disk	a collection of files in database
html	A html page, containing media from course files or external	A html page, containing associated media or external
text	A plain text page in some format	?
file	A single file, from course files or external URL	A single file, associated file or external URL
ims	An IMS resource package from course file or repository web root	An IMS resource package from associated files
repository	Links to external files in repositories (ie Hive)	(na)

There are other third party plugins in contrib that need to be migrated:

• mod/book - displays multiple pages of HTML etc
• mod/resource/type/digitalnz - browser and add items listed in http://www.digitalnz.org/
• mod/resource/type/globe - browser and add items in Ariadne repositories
• mod/resource/type/jmol - display chemistry structures from a jmol format file
• mod/resource/type/rss - display one RSS feed on a page
• mod/resource/type/slideshow - display a directory of images as a slideshow

Automatic upgrade

Each resource type requires different upgrade code because the files are stored in different places that require special handling. They also have different settings and options with different text encoding in the table fields: reference, alltext and options.

Resources that can not be completely migrated during upgrade time will be flagged using a new field called legacyfiles:

• 0 = new resource created in Moodle 2
• 1 = upgraded resource that has completed migration
• 2 = upgraded resource that has not started migration yet
• timestamp = last date of a migrated file within this resource

Directory

Recursively copy the chosen course directory to the resource area. No other upgrade steps are required.

A full filemanager will be required to manage the tree of files.

File

Files in the course directory

1. Copy the linked file (image, sound, pdf, HTML, etc.) from course area to resource file area
2. If the file is HTML or SWF then flag this resource for post-upgrade processing with legacyfiles = 2 (see next section), otherwise flag with legacyfiles = 1

Files referenced by URL

(This includes links to other courses and site files)

This does not require any upgrade. The url is stored in reference field and will continue working.

Page (Web and Text)

1. Convert to one plug-in called 'page' (editable via the new editor forms element)
2. Flag this resource for post-upgrade processing with legacyfiles = 2 (see next section).

IMS

1. Copy files from moddata to new resource file area
2. Copy original backup of package file to another new resource area

No other special upgrade steps required.

Repository

Work out the URL of the resource and convert it to a simple URL.

Others

(TODO: Add some docs here for each type)

Post-upgrade processing

After the Moodle 2.0 upgrade has completed we take the admin to a special page that:

1. explains the issue of resources that contain links to other files
2. explains how it can be fixed by on-demand migration (see below)
3. presents an option for "automatic parsing" which tries to automatically migrate simpler resources such as HTML files with links to HTML files, images, CSS
4. presents a list of remaining flagged resources as links that need to be visited manually in the browser to be fixed

I imagine this interface might have a small frame on the left with the main pages being loaded in the larger frame on the right. The left frame has controls and info like:

• total number of pages to process
• next and previous buttons
• some button to say "I have completely viewed this resource"

So the admin will have to sit there and go through all these resources and check them off to complete the upgrade. Until this process is finished none of these operations can be guaranteed to work so we might even think about disabling those operations:

• Backup
• Restore
• Import of a course

Normal viewing of resources WILL work fine for teachers and students, because it will just trigger the normal on-demand migration of files.

On-demand migration of files

After the upgraded process we will have resources flagged with legacyfiles = 2 that need migrating, including:

• html files possibly containing images, applets and javascript
• flash applets containing relative links to media (eg sounds or images)
• java applets containing relative links to media
• javascript that loads media via relative links (eg imagine an auto-generated slideshow)

We still want to move all these legacy files into the correct resource filearea, so we do it like this:

1. When a browser requests to view one of these "legacyfile" HTML files, it will load all the JS and Java and Flash it contains.
2. These programs run, and make relative requests to media if they want to.
3. These requests to Moodle will hit the pluginfile.php script
4. The pluginfile.php script checks that the file doesn't exist yet in the resource file area, and if so:
   1. pluginfile.php uses the relative path to copy the original file from the courses area to the resource file area
   2. pluginfile.php updates legacyfile field for the resource to be the current timestamp, indicating that some processing has happened.

Problem: we don't really know when the resource is completely "finished" (ie every single associated file has been checked), so we can't automatically reset legacyfiles = 1 after this process. That's why the manual post-upgrade script described above is necessary.

Since we have a timestamp in there we COULD consider a cron job to reset the value to 1 once the timestamp has reached some old age (and it's unlikely that any more files need to be migrated for that resource) to prevent too much parsing. Alternatively we could contact the admin or teacher and ask them to confirm migration using the postupgrade script.

Resource types

Problems with the existing subtypes

The idea of resource types implemented as subtypes has always been a little awkward and not that helpful.

Some of the problems:

1. sub-plugin APIs are not as well-defined as module APIs
2. refactoring inside the module is made harder
3. subplugins can't uninstall
4. subplugins need to bump the module version to upgrade
5. universal data fields get reused for different things
6. capability in subplugins not supported
7. subplugin upgrade is not integrated into main module upgrade - subplugin upgrade is executed after the main module upgrade (critical)
8. subplugins can not have own lang packs
9. subplugins do not have own log actions
10. instead of reducing code duplication advanced plugins may duplicate a lot more core
11.  it is not easy to move unmaintained subplugins into contrib
12. unofficial subplugins not reported during upgrade
13. no support for subplugins in file api

Splitting resource into multiple modules

After some discussion, we've decided to split resource into normal modules, simplifying the structure at the same time. The benefits are cleaner, more maintainable code and a simpler Moodle.

mod/resource will still remain, to redirect old URLs to the right places, but it won't be used as an actual activity module any more.

In order to still be able to group the new modules together in the user interface as "resource" plugins, we can mark these as "resource" plugins in the modules table in core, in a field called "archetypes" (later there might be "assignment" in here too).

New resource modules

The new modules will be:

• mod/page - formatted text pages (combines text and html subtypes)
• mod/file - a folder of files, with one file picked as default
• mod/folder - a folder of files, listed for selection (view/download)
• mod/url - a URL to an external page or file

mod/page

TODO: add mockups and descriptions of functionality

mod/file

TODO: add mockups and descriptions of functionality

mod/folder

TODO: add mockups and descriptions of functionality

mod/url

TODO: add mockups and descriptions of functionality

Moving to contrib

•  New module/type for special mod/resource/type/file/localfile.php (win32 only tweak) - originally intended for large files stored on local networks or CDs
• (No idea what to do with hive repositories, we should also remove the obsoleted auth hive SSO support)

Other ideas

Dealing with caching issues

To have more control over the caching of files, we could use the same mechanism already implemented in the SCORM module, by changing the URL:

1. Internally store all files as itemid=0
2. Add new revision db field into resource table
3. When serving files always construct links with itemid==revision
4. Ignore itemid for resource files in pluginfile.php

See also

• Development:Using the file API
• Development:Repository API
• Development:Portfolio API
• Development:File API
• MDL-14589 - File API Meta issue
• MDL-16089 - Resource module conversion