[Freeipa-devel] [PATCH] Add plugin versioning and dependency checking

[Rob Crittenden]

Pavel Zůna wrote:
> Since there weren't any comments on my proposal about plugin versioning 
> and dependencies, I decided to make a first implementation, that shows 
> what I had in mind.

Sorry, I had looked at it and never responded. Seeing an implementation 
does help though :-)

> This patch adds two class variables to plugable.Plugin: VERSION and 
> DEPENDENCIES. VERSION is supposed to be a tuple with 2 ints specifying 
> the plugin major and minor version number. DEPENDENCIES is supposed to 
> be a tuple of tuples. The inner tuples will contain the plugin class 
> name (as a string) and a major version number.
> 
> The plugable.Registrar class has changed a bit. I decided to remove the 
> 'override' keyword argument. It wasn't used anywhere. Overriding is now 
> automatic based on the plugin class VERSION. Higher version overrides 
> lower. This way, we can have several versions of the same plugin living 
> in IPA directory (not in API!) at the same time. It allows higher 
> versions to easily build on top (extend) older ones.

So to override a plugin you need to have a higher version? What if you 
want two separate plugins to extend a plugin, there can be only one? For 
example, you have one extension that adds some Samba attributes to a 
user and another that adds some Solaris-specific attributes. Not 
everyone would want both of these but some might, I think this would 
throw a DuplicateError.

rob

> There's also a new exception:
> PluginMissingDependencyError: Plugin 'service' is missing dependency 
> plugin 'host' (version 1)
> 
> Plugin dependencies are checked when all plugin have been loaded, that 
> is when API is finalizing.
> 
> An example of what we can do with this approach:
> 
> Let's say a customer needs to extend users and groups by storing some 
> additional computed information in the entries.
> 
> indentity_ex.py:
> 
> from ipalib.plugins.user import user, user_add
> from ipalib.plugins.group import group, group_add
> 
> class user(user):
>     VERSION = (2, 0)
>     DEPENDENCIES = (('group', 2), )
>     takes_params = user.takes_params + (
>         # some new params here
>     )
> 
> api.register(user)
> 
> class user_add(user_add):
>     VERSION = (2, 0)
>     def pre_callback( # I don't feel like writing all the args :)
>          dn = super(user_add, self).pre_callback( # and again
>          # do some new stuff here
>          return dn
> 
> api.register(user_add)
> 
> # same analogous thing for groups comes here...
> 
> 
> Pavel
> 
> 
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