Resource module file API migration
Moodle 2.0
Please use talk page for comments and proposals, thanks.
Current problems
Some general problems:
- plain text and html resource types separate
- embedded images and files in general are stored in course files without appropriate access control
- local course files and Internet links are mixed
- HarvestRoad Hive repository type is not maintained.
- can't move a "whole" web page properly from one course to another (eg course import).
The idea of resource types implemented as subtypes has always been a little awkward and not that helpful, incomplete list of problems follows:
- sub-plugin APIs are not as well-defined as module APIs
- refactoring inside the module is made harder
- subplugins can't uninstall
- subplugins need to bump the module version to upgrade
- universal data fields get reused for different things
- capability in subplugins not supported
- subplugin upgrade is not integrated into main module upgrade - subplugin upgrade is executed after the main module upgrade (critical)
- subplugins can not have own lang packs
- subplugins do not have own log actions
- instead of reducing code duplication advanced plugins may duplicate a lot more core
- it is not easy to move unmaintained subplugins into contrib
- unofficial subplugins not reported during upgrade
- no support for subplugins in file api
Migration of resource types in Moodle 2.0
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 and will be used for two purposes - to serve uploaded resource materials and also to redirect old URLs to the new modules. We will add a new table with backup of current resource table with all other information needed for upgrades and URL redirections.
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).
Resource types
| Resource types in Moodle 1.9 | New modules in Moodle 2.0 | ||
|---|---|---|---|
| Type | Description | Module | Description |
| directory | an arbitrary directory of files in course files | mod/folder | a collection of files in separate file area |
| html | A html page, containing absolute links to media from course files or external links | mod/page | a general text page - html markup, format FORMAT_HTML and files stored in separate file area |
| text | A plain text page in some format | mod/page | a general text page - no markup, format FORMAT_PLAIN and no files |
| file | link to file from course files of the same course, files may contain relative links to other files | mod/resource | one file or collection of files, one file is always selected as main file |
| file | link to other course or general external URL | mod/url | general URL |
| imspackage | Files extracted into moddata from an IMS content package obtained from course files or web repository | mod/imspackage | Files in separate file area extracted from an IMS content package obtained from repository |
| repository | Links to external files in repositories (ie Hive) | mod/url? | (na) |
Contrib resource types
There are other third party plugins in contrib that need to be migrated:
- 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
Resource-like contrib modules
Separate modules will use similar migration techniques:
- mod/book - displays multiple pages of HTML, print support, table of contents, etc.
- mod/lightboxgallery - http://moodle.greenhead.ac.uk/external/lightbox_gallery/
New resource modules
The new modules will be:
- mod/page - formatted text pages with embedded files (images, flashm etc.)
- mod/resource - a folder of files, with one file selected as main file
- mod/folder - a folder of files, listed for selection (view/download)
- mod/url - a URL to an external page or file
- mod/imspackage - an IMS content package
Page (mod/page)
TODO: add mockups and descriptions of functionality
Resource file (mod/resource)
General resource type with two purposes:
- display uploaded files
- redirect legacy resource links to new modules
Primary use cases:
- presentation/download of PDF files and office documents
- zip archive downloads
- presentation of general html files created in external system
TODO: add mockups and descriptions of functionality
Folder (mod/folder)
Folder resource module, replaces original directory of files resource type. Files and folders are stored in separate file area.
Primary use cases:
- easy distribution of multiple files
Edit UI mockup
View UI mockup
URL (mod/url)
TODO: add mockups and descriptions of functionality
IMS Content Package (mod/imspackage)
IMS Content Package module, designed for easy presentation of standard compliant content packages. This is the recommended format for import of materials created in external systems. See http://www.imsglobal.org/content/packaging/
Primary use cases:
- import of study materials from other systems
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
lib/db/upgrade.php
Create new table resource_historic and copy all current records from resource table. Add new fields:
- oldid - original id from resource table
- cmid - original course module id
- newmodule - null means not converted, string value is name of new module
- newid - new instance id referencing id in newmodule table
Switching resource types to full modules
Implemented in lib/upgradelib.php function switch_resource_type($resource_historic)
- $resource_historic must already contain new module info (newmodule and newid fields)
- links course_module to newid instead of old resource id
- deletes old record instance
- updates log table
- no need to upgrade gradebook - no grades or outcomes in current resources
- no need to change permissions - the same cmid means the same context
- no need for capability migration - resource does not define any capabilities, only mod/resource:exportresource added in 2.0dev
- old section placement retained, because it is specified in course_modules table
- no need to migrate files, no files in areas yet
Module upgrade steps
mod/resource/db/upgrade.php
- change resource table structure - we do not need to keep any data because copy of everything is kept in resource_historic table
- mark all records in resource table as not migrated
- search for migration candidates in resource_historic table - original type file, link pointing to course file from the same course
- find out old setting from historic record
- update resource table record, marks the instance as active too
- copy linked course file to new file area, mark this file as main file
- enable automatic migration of files if file may contain relative links (whitelist image types and some other binary types)
mod/url/db/install.php
- search for migration candidates in resource_historic table - type file with URLs outside of current course files
- find out all new settings from existing historic record
- create new instance in url table
- update resource_historic
- call switch_resource_type($resource_historic)
mod/folder/db/install.php
- search for migration candidates in resource_historic table - type directory
- create new instance in folder table
- update resource_historic
- call switch_resource_type($resource_historic)
- recursively copy the chosen course directory to the folder file area
mod/page/db/install.php
- search for migration candidates in resource_historic table - type html and text
- find out all new settings from existing historic record
- create new instance in page table
- search for any absolute links in case of html text and copy them to new page file area keeping the same path relative to course files root
- enable automatic migration of files if any copied file above may contain relative links
mod/imspackage/db/install.php
- search for migration candidates in resource_historic table - type ims
- find instance setting
- create new instance in ims table
- update resource_historic
- call switch_resource_type($resource_historic)
- recursively copy moddata files into ims file area
- copy original backup of package file to another new ims file area
Others
- local files - type file with link starting with #
- Hive repositories - work out the URL of the resource and convert it to a simple URL?
- TODO: add detailed contrib migration info
Post-upgrade processing
After the Moodle 2.0 upgrade has completed we take the admin to a special page that:
- explains the issue of resources that contain links to other files
- explains how it can be fixed by on-demand migration (see below)
- presents an option for "automatic parsing" which tries to automatically migrate simpler resources such as HTML files with links to HTML files, images, CSS
- 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:
- When a browser requests to view one of these "legacyfile" HTML files, it will load all the JS and Java and Flash it contains.
- These programs run, and make relative requests to media if they want to.
- These requests to Moodle will hit the pluginfile.php script
- The pluginfile.php script checks that the file doesn't exist yet in the resource file area, and if so:
- pluginfile.php uses the relative path to copy the original file from the courses area to the resource file area
- 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.
Candidates for removal
List of obsoleted or unmaintained features proposed for removal from core:
- hive SSO
- hive repositories
- IMS repository
- special mod/resource/type/file/localfile.php (win32 only tweak)
- weblinkauth hook from login/index.php
- opening of resources in new windows
hive sso
Located in /sso/hive/*. Unmaintained and obsoleted by auth SSO plugins and Moodle networking. It should be possible to implement new auth/hivesso and maintain it in contrib. Any volunteers?
hive repositories
Unmaintained. Any volunteers?
IMS repository
Obsoleted by regular repositories. Maybe a new core IMS repo plugin.
file/localfile.php
No maintainer. Intended for large files stored on local networks or CDs, obsoleted by faster Internet connections and various offline Moodle projects. Volunteers may create new plugin and maintained it in contrib.
weblinkauth hook
Obsoleted during the auth refactoring in 1.8dev. Volunteers may continue maintaining it as new contrib auth plugin.
Opening resources in customized new windows
This is going to be controversial, not really sure if this is a good idea, please post in the page comments ;-)
Cons:
- teachers are used to it
- enlarges browser screen area
Pros:
- no support in xhtml strict
- not recommended by accessibility experts
- browsers allow users to easily open links in new tabs/windows manually when needed
- removing browser UI elements such as address/menu/status via javascript is considered evil - browser interfaces are not cluttered with useless dead space anymore, screens are larger, general F11 full-screen support
- chrome-less windows give false sense of copy-protection
- new window support was never implemented in directory type
Possible solution:
- keep support for opening of files in normal new windows for local files and external links - prevents loss of navigation
- remove new window detailed options completely - no more browser tricks such as window resize, chrome removal, etc.
- remove new window support from mod/page - more consistency with other modules, improves accessibility compliance
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:
- Internally store all files as itemid=0
- Add new revision db field into resource table
- When serving files always construct links with itemid==revision
- Ignore itemid for resource files in pluginfile.php
See also
- Using the file API
- Repository API
- Portfolio API
- File API
- MDL-14589 - File API Meta issue
- MDL-16089 - Resource module conversion
