Plugins block does not handle classpath correctly under certain circumstances

Schalk_Cronje · June 24, 2016, 1:02am

As mentioned to you at GradleSummit, here is the sample project that does not work correctly with the plugins {} closure.

https://github.com/ysb33r/SampleProjects/tree/GradleNewModel/PluginsBlockDoesNotHandleClasspath

old-style.gradle is the one that works, and new-style.gradle, which contains the plugins block, fails. The error that is reported is directly related to the plugin not seeing the appropriate JARs on the classpath when it is applied.

eljobe · June 24, 2016, 6:08pm

I can confirm that I can reproduce this problem with Gradle 3.0-M2.

We are pretty busy right now, but we will be looking into this.

Schalk_Cronje · June 24, 2016, 6:23pm

No problem. There is a workaround.

st_oehme · July 4, 2016, 12:42pm

Can you tell us a bit more about how the plugin decides which URI schemes to activate? I debugged and can see that the http-client jar is on the classpath and the classloader of your plugin can see the HttpClient class. So I’m a little lost as to why it would not work.

Schalk_Cronje · July 5, 2016, 9:41am

When the plugin is applied the VFS object is initialised at

github.com

ysb33r/groovy-vfs/blob/master/gradle-plugin/src/main/groovy/org/ysb33r/gradle/vfs/VfsPlugin.groovy#L47


void apply(Project project) {


//        project.extensions.create('vfsOptions',)
    addProjectExtension(project)
}


void addProjectExtension(Project project) {
    if(!project.metaClass.respondsTo(project,'vfs',Closure)) {


        if(!project.ext.hasProperty(VfsProxy.PROJECT_PROPERTY_NAME)) {
            project.ext."${VfsProxy.PROJECT_PROPERTY_NAME}" = VfsProxy.request(project)
        }
        project.ext.vfs = { Closure c -> project."${VfsProxy.PROJECT_PROPERTY_NAME}".script(c) }
        project.logger.debug 'Added project.vfs'
    }


    if(!project.metaClass.respondsTo(project,'vfsCopySpec',Closure)) {


        project.ext.vfsCopySpec = { Closure c->
            DefaultVfsCopySpec.create(VfsProxy.request(project),c)
        }

which in turn instantiates it via

github.com

ysb33r/groovy-vfs/blob/master/gradle-plugin/src/main/groovy/org/ysb33r/gradle/vfs/VfsProxy.groovy#L46


* @author Schalk W. Cronjé
* @since 1.0
*/
class VfsProxy {
   static final String PROJECT_PROPERTY_NAME = '__vfs'


   static VFS request(Project project) {
       if(project.ext.hasProperty(PROJECT_PROPERTY_NAME)) {
           project.ext."${PROJECT_PROPERTY_NAME}"
       } else {
           new VFS(
               logger: LogFactory.getLog('vfs'),
               temporaryFileStore: "${project.gradle.gradleUserHomeDir}/vfs/${UUID.randomUUID()}".toString()
           )
       }
   }
}

Drilling down into the Groovy VFS library the key to loading lies within the specification for ZIP

github.com

ysb33r/groovy-vfs/blob/master/dsl/src/main/groovy/org/ysb33r/groovy/dsl/vfs/impl/ProviderSpecification.groovy#L53


List<Extension> extensions = []




static final ProviderSpecification DEFAULT_PROVIDERS = new ProviderSpecification (
    defaultProvider : new Provider( className : 'org.apache.commons.vfs2.provider.url.UrlFileProvider' ),
    providers : [
        new Provider(
            className : 'org.apache.commons.vfs2.provider.local.DefaultLocalFileProvider',
            schemes : [ 'file']
        ),
        new Provider(
                className : 'org.apache.commons.vfs2.provider.zip.ZipFileProvider',
                schemes : [ 'zip']
        ),
        new Provider(
                className : 'org.apache.commons.vfs2.provider.tar.TarFileProvider',
                schemes : [ 'tar'],
// 2.0                    dependsOnClasses : [ 'org.apache.commons.vfs2.provider.tar.TarInputStream' ]
                dependsOnClasses : [ 'org.apache.commons.compress.archivers.tar.TarArchiveOutputStream' ]


        ),

and for http

github.com

ysb33r/groovy-vfs/blob/master/dsl/src/main/groovy/org/ysb33r/groovy/dsl/vfs/impl/ProviderSpecification.groovy#L92


new Provider(
        className : 'org.apache.commons.vfs2.provider.ftp.FtpFileProvider',
        schemes : [ 'ftp'],
        dependsOnClasses : [ 'org.apache.commons.net.ftp.FTPFile' ]
),
new Provider(
        className : 'org.apache.commons.vfs2.provider.ftps.FtpsFileProvider',
        schemes : [ 'ftps'],
        dependsOnClasses : [ 'org.apache.commons.net.ftp.FTPFile' ]
),
new Provider(
        className : 'org.apache.commons.vfs2.provider.http.HttpFileProvider',
        schemes : [ 'http'],
        dependsOnClasses : [ 'org.apache.commons.httpclient.HttpClient' ]
),
new Provider(
        className : 'org.apache.commons.vfs2.provider.https.HttpsFileProvider',
        schemes : [ 'https'],
        dependsOnClasses : [ 'org.apache.commons.httpclient.HttpClient' ]
),
new Provider(

Evautally the loading occurs by checking first whether the dependsOnClasses are on the classpath

github.com

ysb33r/groovy-vfs/blob/master/dsl/src/main/groovy/org/ysb33r/groovy/dsl/vfs/impl/StandardFileSystemManager.groovy#L163


        loggerInstance().debug "Skipping ${provider.className} due to missing scheme '${it}'"
        true
    } else {
        false
    }
} ) {
    return false
}


ClassLoader cl = _classLoader()
if( provider.dependsOnClasses?.any { String it ->
    try {
        cl.loadClass(it)
        false
    }
    catch(final ClassNotFoundException e) {
        loggerInstance().debug "Skipping ${provider.className} due to missing class '${it}'"
        true
    }
} ) { return false }

and then by whether the className itself is on the classpath.

github.com

ysb33r/groovy-vfs/blob/master/dsl/src/main/groovy/org/ysb33r/groovy/dsl/vfs/impl/StandardFileSystemManager.groovy#L176


        false
    }
    catch(final ClassNotFoundException e) {
        loggerInstance().debug "Skipping ${provider.className} due to missing class '${it}'"
        true
    }
} ) { return false }




// Create and register the provider
FileProvider fp
try {
    fp = createFileProvider(provider.className)
    if(provider.schemes?.size() > 0) {
        addProvider(provider.schemes as String[],fp)
    }
} catch(final FileSystemException e) {
    loggerInstance().debug "Skipping ${provider.className} due to missing class: `${e}`"
    return false
}

If any of the required classes are not on the classpath at the given initialisation then the specific scheme providers are not loaded.

Schalk_Cronje · July 5, 2016, 9:44am

VFS allows for double-barrel scheme names i.e. zip:http://foo/path/file.zip which allows for file.zip to be downloaded to a temporary file store, and then be interpreted as a ZIP in a way that is transparent to the used

st_oehme · July 5, 2016, 4:34pm

I think I found the problem: The StandardFileSystemManager uses the current Thread’s context classloader. That classloader is different for the logic running inside the plugins block. If the plugin used getClass().getClassLoader() instead, it would work.

I’m going to bring this up for internal discussion, as other plugin authors might trip over this slight change in the environment that the plugin runs in. Thanks for taking the time to walk me through your plugin

Schalk_Cronje · July 5, 2016, 9:31pm

Wow, that makes sense.

I definitely would be interested in what the outcome of that discussion would be. If need be I can craft up a version of the plugin on a branch that uses a different classloader to test any ideas forthcoming.

st_oehme · July 15, 2016, 7:29am

I’ve raised GRADLE-3503, which we will fix for 3.0.