Improvement suggestions to the ResourceTransformerChain [SPR-13806]

[spring-projects-issues]

Felix Kurth opened SPR-13806 and commented

This is a follow up from #18300.

The customization possibilities for the resource chain should be improved.
Right now, if one adds a <resource-chain> tag to the xml, a complete default Resource chain is wired up according to ResourceChainRegistration.java.

<mvc:resources mapping="/resources/**" location="/"   >
        <mvc:resource-chain  >
            <mvc:resolvers >
                <mvc:version-resolver >
                    <mvc:fixed-version-strategy patterns="/**" version="1234" />
                </mvc:version-resolver>
            </mvc:resolvers>
        </mvc:resource-chain>
    </mvc:resources>

including a CssLinkResourceTransformer, AppCacheManifestTransformer, CachingResourceTransformer, CachingResourceResolver, WebJarsResourceResolver, PathResourceResolver,
depending whether the user has supplied a VersionResourceResolver or not.
\
\

• Please give the developer a chance to disable the default transformers and resolvers without wiring up the complete chain itself.
  i tried to disable auto registration

<mvc:resource-chain resource-cache="false" auto-registration="false" >

But i was not able to wire up the chain myself. There seems to be no docs on that. Please add the possibility to configure the transformers:
I would expect that an empty element:

<mvc:transformers >
</mvc:transformers>

means no transformers, and no "default" implicit ones. Another option would be a property like

<mvc:transformers default-transformers="false" />

For all spring supplied transformers, there should then be an xml tag (or a property) available

<mvc:transformers default-transformers="false" >
	<mvc:css-link-resourcetransformer />
<mvc:transformers>

The same applies to the resolvers, have the possibility to disable the default ones.

• For the version strategies, please add a NoVersionStrategy with its xml counterpart:

<mvc:no-version-strategy patterns="/images/*.png" />

• Right now its not possible to use the FixedVersionStrategy with an empty or null version. I don't see a reason for that and would be convenient for a development profile etc. This would solve the NoVersionStrategy case as well.

• The CssLinkResourceTransformer is not able to handle relative paths with a fixed version strategy, if the path is relative and does not start with an ".".
  For example from
  An example from jquery-ui.css

url("images/ui-bg_flat_100_ffffff_40x100.png")

will not work. If both, the css file and the url within it are are under a fixed version strategy, it may end up with a double version-ed path like

/resources/VERSION/styles/VERSION/images/abc.png

My suggestion to this problem: Do no chain up PrefixVersionPathStrategy's. So if

• the css file the CssLinkResourceTransformer is currently parsing itself is version-ed with PrefixVersionPathStrategy,
• AND
• the url within the css currently under processing would lead to another PrefixVersionPathStrategy (for the png for example) then do not touch the url itself.

---

Affects: 4.2.4

Issue Links:

• CssLinkResourceTransformer is incompatible with FixedVersionStrategy VersionResourceResolver [SPR-13727] #18300 CssLinkResourceTransformer is incompatible with FixedVersionStrategy VersionResourceResolver

Referenced from: commits spring-attic/spring-framework-issues@139ad04

[spring-projects-issues]

Brian Clozel commented

Hi Felix Kurth

Thanks for this report! Could you check out this comment and help me refine the refinements you're looking for?

There is already a way to disable auto-registration of resolvers and transformers, and you've found it; that's the auto-registration="false" flag. I've created a repro test to demonstrate that: in that case, a single PathResourceResolver is registered by default.

With the sample configuration you're showing, the resolvers and transformers you've listed aren't all registered. Only the PathResourceResolver, CssLinkResourceTransformer and VersionResourceResolver are registered (see this repro test).

Now could you explain a bit more why a NoVersionStrategy would be interesting? I thought briefly about it and it seems that:

• since you probably want to change the resource locations, the cache flag, and other configuration properties, a separate (per profile) mvc:resource tag would be a better fit
• not requiring a version string for the FixedVersionStrategy might sound like a good idea until your configuration value is not properly expanded and it silently "fails" in production with no version string at all

Now about CssLinkResourceTransformer and relative paths, I've explained why version strings aren't inserted there in that comment.

Feel free to check out the repro project and submit PRs to make it more relevant to our discussion.

Thanks!

[spring-projects-issues]

Brian Clozel commented

I'm resolving this for now.
Feel free to reopen this issue with a working repro case.

Thanks!