[wildfly-dev] JBoss Modules - "advanced" PathFilter for ResourceLoaderSpec?

[David M. Lloyd]

Hi Jaikiran!

On 12/08/2016 05:59 AM, Jaikiran Pai wrote:
> (Using this list since I couldn't find a place to ask JBoss Modules
> question anywhere else, feel free to direct me there if there's one)
>
> Hello everyone :)
>
> I have been using JBoss Modules for one of the projects I'm involved in.
> The usage there is pretty much similar to how we use it for setting up
> classloaders in WildFly server for deployments. A new module M1 gets
> dynamically created and assigned to a component and this module is added
> with dependencies to some pre-defined static modules A, B, C and such.
> M1 also gets N number of resource roots (backed by ResourceLoaderSpec),
> each pointing to a jar file within some well known directory. So to put
> in some sort of a code, it looks like:
>
> // add each jar as a resource root for the module
> for (final File jar : jars) {
>     final ResourceLoader jarResourceLoader;
>     try {
>         jarResourceLoader =
> ResourceLoaders.createJarResourceLoader(jar.getName(), new JarFile(jar));
>     } catch (IOException e) {
>         // log and continue
>         logger.warn("....", e);
>         continue;
>     }
>
> moduleSpecBuilder.addResourceRoot(ResourceLoaderSpec.createResourceLoaderSpec(jarResourceLoader));
> }
>
>
>
> All works fine without any issues and the module M1 has access to the
> resources in these jars. Now there are times where the components for
> which I've created this module M1 and attach these jars, "accidentally"
> ship/package jars which have resources (classes to be precise) which are
> also exposed/present in one of the dependency modules (remember A, B,
> C...). So this then leads to the same old thing where I have go back and
> tell my users not to package such jars.
>
> I want to try and make this a bit more robust and get away with having
> to tell users not to package xyz jars. I had a look at the
> ResourceLoaderSpec interface and it takes a PathFilter
> https://github.com/jboss-modules/jboss-modules/blob/1.x/src/main/java/org/jboss/modules/ResourceLoaderSpec.java#L48
> which gets me one step closer to what I want to achieve. So if I know
> that static module A, B, C etc... expose classes belonging to package
> foo.bar.blah, I can setup a PathFilter on these jar resource loader to
> skip/decline the path in the accept() method. I think that should work
> out fine (I need to test it out tonight) and I wouldn't have to worry
> that some jar packaged within that component will introduce these
> classes belonging to the foo.bar.blah package.
>
> However, although it might work, I then have to keep a very close vigil
> or rather keep inspecting what packages (or resources in general) the
> modules A, B and C provide. Instead what I'm thinking of is a "smart"
> PathFilter or anything along those lines whose semantics would be to
> "skip/don't accept/filter out all those resources, from a resource root,
> if the resource is provided by any of the specified modules". So
> something like:
>
> ResourceLoaderSpec.createResourceLoaderSpec(jarResourceLoader,
> *PathFilters.excludeResourcesExposedByModules("A**:slot", "B:slot",
> "C:slot" ...)*);
>
>
> Having looked at the JBoss Modules code, I don't think this is possible
> currently. But that's OK. What I really want to check is, is this
> something that would be feasible to implement (doesn't have to be in
> JBoss Modules itself) and is there any obvious issues with the approach?
> Also, is this something that would be useful to have in JBoss Modules
> itself?

A smart filter is a pretty good idea!  I think that it might make more 
sense as part of a dependency specification though, from a user's 
perspective: if I say "I depend on module org.foo.bar:main" I should 
also be able to say "...and use their packages" which would exclude all 
paths in the source module's resource roots (other than META-INF and the 
root path).

In fact, maybe that ought to be the default setting, with the user 
having to opt in to override packages.  So a user might say:

    <dependencies>
        ...
        <module name="org.foo.bar">
            <override-paths/> <!-- now my paths take precedence -->
        </module>
        ...
    </dependencies>

In the programmatic API it'd be fairly straightforward as well.  We 
could add an overridePaths path filter to the dependency specification 
(which ought to be builder-based at this point, I now realize, what with 
the parameter explosion).  Any dependency paths that are not matched by 
that filter would be subtracted from all resource roots.

As far as XML compatibility goes, the default for 1.5 and earlier can be 
to override all paths, whereas the default for 1.6 and later can be to 
only override META-INF and the root path.

We'd have to have logic to allow for dependency recalculation when a 
module is relinked, but that shouldn't be too hard.

What do you think?
-- 
- DML