[ 
https://issues.apache.org/jira/browse/METRON-777?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16118595#comment-16118595
 ] 

ASF GitHub Bot commented on METRON-777:
---------------------------------------

Github user ottobackwards commented on a diff in the pull request:

    https://github.com/apache/metron/pull/530#discussion_r131965922
  
    --- Diff: 
bundles-lib/src/main/java/org/apache/metron/bundles/BundleClassLoaders.java ---
    @@ -0,0 +1,353 @@
    +/*
    + * Licensed to the Apache Software Foundation (ASF) under one or more
    + * contributor license agreements.  See the NOTICE file distributed with
    + * this work for additional information regarding copyright ownership.
    + * The ASF licenses this file to You under the Apache License, Version 2.0
    + * (the "License"); you may not use this file except in compliance with
    + * the License.  You may obtain a copy of the License at
    + *
    + *     http://www.apache.org/licenses/LICENSE-2.0
    + *
    + * Unless required by applicable law or agreed to in writing, software
    + * distributed under the License is distributed on an "AS IS" BASIS,
    + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    + * See the License for the specific language governing permissions and
    + * limitations under the License.
    + */
    +package org.apache.metron.bundles;
    +
    +import java.net.URISyntaxException;
    +import java.util.*;
    +
    +import org.apache.commons.collections.CollectionUtils;
    +import org.apache.commons.vfs2.FileObject;
    +import org.apache.commons.vfs2.FileSystemException;
    +import org.apache.commons.vfs2.FileSystemManager;
    +import org.apache.metron.bundles.bundle.Bundle;
    +import org.apache.metron.bundles.bundle.BundleCoordinate;
    +import org.apache.metron.bundles.bundle.BundleDetails;
    +import org.apache.metron.bundles.util.BundleProperties;
    +import org.apache.metron.bundles.util.BundleSelector;
    +import org.apache.metron.bundles.util.FileUtils;
    +import org.apache.metron.bundles.util.BundleUtil;
    +import org.slf4j.Logger;
    +import org.slf4j.LoggerFactory;
    +
    +/**
    + * A singleton class used to initialize the extension and framework 
classloaders.
    + */
    +public final class BundleClassLoaders {
    +
    +  private static volatile BundleClassLoaders bundleClassLoaders;
    +  private volatile InitContext initContext;
    +  private static final Logger logger = 
LoggerFactory.getLogger(BundleClassLoaders.class);
    +
    +  private final static class InitContext {
    +
    +    private final List<FileObject> extensionDirs;
    +    private final Map<String, Bundle> bundles;
    +
    +    private InitContext(
    +        final List<FileObject> extensionDirs,
    +        final Map<String, Bundle> bundles) {
    +      this.extensionDirs = extensionDirs;
    +      this.bundles = bundles;
    +    }
    +  }
    +
    +  private BundleClassLoaders() {
    +  }
    +
    +  /**
    +   * @return The singleton instance of the BundleClassLoaders
    +   */
    +  public static BundleClassLoaders getInstance() {
    +    BundleClassLoaders result = bundleClassLoaders;
    +    if (result == null) {
    +      synchronized (BundleClassLoaders.class) {
    +        result = bundleClassLoaders;
    +        if (result == null) {
    +          bundleClassLoaders = result = new BundleClassLoaders();
    +        }
    +      }
    +    }
    +    return result;
    +  }
    +
    +  public static void reset() {
    +    getInstance().unInit();
    +  }
    +
    +  private void unInit() {
    +    synchronized (this) {
    +      initContext = null;
    +    }
    +  }
    +
    +  /**
    +   * Initializes and loads the BundleClassLoaders. This method must be 
called before the rest of the
    +   * methods to access the classloaders are called and it can be safely 
called any number of times
    +   * provided the same framework and extension working dirs are used.
    +   *
    +   * @param fileSystemManager the FileSystemManager
    +   * @param extensionsDirs where to find extension artifacts
    +   * @param props BundleProperties
    +   * @throws FileSystemException if any issue occurs while exploding 
bundle working directories.
    +   * @throws java.lang.ClassNotFoundException if unable to load class 
definition
    +   * @throws IllegalStateException already initialized with a given pair 
of directories cannot
    +   * reinitialize or use a different pair of directories.
    +   */
    +  public void init(final FileSystemManager fileSystemManager, final 
List<FileObject> extensionsDirs,
    +      BundleProperties props)
    +      throws FileSystemException, ClassNotFoundException, 
URISyntaxException {
    +    if (extensionsDirs == null || fileSystemManager == null) {
    +      throw new NullPointerException("cannot have empty arguments");
    +    }
    +    InitContext ic = initContext;
    +    if (ic == null) {
    +      synchronized (this) {
    +        ic = initContext;
    +        if (ic == null) {
    +          initContext = ic = load(fileSystemManager, extensionsDirs, 
props);
    +        }
    +      }
    +    } else {
    +      boolean matching = CollectionUtils
    +          .isEqualCollection(initContext.extensionDirs, extensionsDirs);
    +      if (!matching) {
    +        throw new IllegalStateException(
    +            "Cannot reinitialize and extension/framework directories 
cannot change");
    +      }
    +    }
    +  }
    +
    +  /**
    +   * Should be called at most once.
    +   */
    +  private InitContext load(final FileSystemManager fileSystemManager,
    +      final List<FileObject> extensionsDirs, BundleProperties props)
    +      throws FileSystemException, ClassNotFoundException, 
URISyntaxException {
    +    // get the system classloader
    +    final ClassLoader systemClassLoader = 
ClassLoader.getSystemClassLoader();
    +
    +    // find all bundle files and create class loaders for them.
    +    final Map<String, Bundle> directoryBundleLookup = new 
LinkedHashMap<>();
    +    final Map<String, ClassLoader> coordinateClassLoaderLookup = new 
HashMap<>();
    +    final Map<String, Set<BundleCoordinate>> idBundleLookup = new 
HashMap<>();
    +
    +    for (FileObject extensionsDir : extensionsDirs) {
    +      // make sure the bundle directory is there and accessible
    +      FileUtils.ensureDirectoryExistAndCanRead(extensionsDir);
    +
    +      final List<FileObject> bundleDirContents = new ArrayList<>();
    +      FileObject[] dirFiles = extensionsDir.findFiles(new 
BundleSelector(props.getArchiveExtension()));
    +      if (dirFiles != null) {
    +        List<FileObject> fileList = Arrays.asList(dirFiles);
    +        bundleDirContents.addAll(fileList);
    +      }
    +
    +      if (!bundleDirContents.isEmpty()) {
    +        final List<BundleDetails> bundleDetails = new ArrayList<>();
    +        final Map<String, String> bundleCoordinatesToBundleFile = new 
HashMap<>();
    +
    +        // load the bundle details which includes bundle dependencies
    +        for (final FileObject bundleFile : bundleDirContents) {
    +          if(!bundleFile.exists() || !bundleFile.isFile()) {
    +            continue;
    +          }
    +          BundleDetails bundleDetail = null;
    +          try {
    +            bundleDetail = getBundleDetails(bundleFile, props);
    +          } catch (IllegalStateException e) {
    +            logger.warn("Unable to load BUNDLE {} due to {}, skipping...",
    +                new Object[]{bundleFile.getURL(), e.getMessage()});
    +          }
    +
    +          // prevent the application from starting when there are two 
BUNDLEs with same group, id, and version
    +          final String bundleCoordinate = 
bundleDetail.getCoordinate().getCoordinate();
    +          if (bundleCoordinatesToBundleFile.containsKey(bundleCoordinate)) 
{
    +            final String existingBundleWorkingDir = 
bundleCoordinatesToBundleFile
    +                .get(bundleCoordinate);
    +            throw new IllegalStateException(
    +                "Unable to load BUNDLE with coordinates " + 
bundleCoordinate
    +                    + " and working directory " + 
bundleDetail.getBundleFile()
    +                    + " because another BUNDLE with the same coordinates 
already exists at "
    +                    + existingBundleWorkingDir);
    +          }
    +
    +          bundleDetails.add(bundleDetail);
    +          bundleCoordinatesToBundleFile.put(bundleCoordinate,
    +              bundleDetail.getBundleFile().getURL().toURI().toString());
    +        }
    +
    +        // attempt to locate the jetty bundle
    +        ClassLoader jettyClassLoader = null;
    +        for (final Iterator<BundleDetails> bundleDetailsIter = 
bundleDetails.iterator();
    +            bundleDetailsIter.hasNext(); ) {
    +          final BundleDetails bundleDetail = bundleDetailsIter.next();
    +          // populate bundle lookup
    +          
idBundleLookup.computeIfAbsent(bundleDetail.getCoordinate().getId(),
    +              id -> new HashSet<>()).add(bundleDetail.getCoordinate());
    +        }
    +
    +        int bundleCount;
    +        do {
    +          // record the number of bundles to be loaded
    +          bundleCount = bundleDetails.size();
    +
    +          // attempt to create each bundle class loader
    +          for (final Iterator<BundleDetails> bundleDetailsIter = 
bundleDetails.iterator();
    +              bundleDetailsIter.hasNext(); ) {
    +            final BundleDetails bundleDetail = bundleDetailsIter.next();
    +            final BundleCoordinate bundleDependencyCoordinate = 
bundleDetail
    +                .getDependencyCoordinate();
    +
    +            // see if this class loader is eligible for loading
    +            ClassLoader potentialBundleClassLoader = null;
    +            if (bundleDependencyCoordinate == null) {
    +              potentialBundleClassLoader = 
createBundleClassLoader(fileSystemManager,
    +                  bundleDetail.getBundleFile(), 
ClassLoader.getSystemClassLoader());
    --- End diff --
    
    It depends if the parent classloader has what is required, and any of the 
'extraneous' bundles are accessed and they are not satisfied with the current 
parent.
    
    Our bundle host is currently the metron-parser shaded jar.  Any of our 
shaded jars ( topologies ) should be fine for this, given that they would only 
try to load extensions of types they know about.
    
    NiFi seems to want every bundle to have access to a Jetty Server.


> Create a plugin system for Metron based on 'NAR'
> ------------------------------------------------
>
>                 Key: METRON-777
>                 URL: https://issues.apache.org/jira/browse/METRON-777
>             Project: Metron
>          Issue Type: New Feature
>            Reporter: Otto Fowler
>            Assignee: Otto Fowler
>
> The success of the Metron project will be greatly dependent on community 
> participation, and with that the ability to adapt and extend Metron without 
> having to maintain a fork of the project.
> As organizations and individuals look to extend the Metron system with custom 
> parsers, enrichments, and stellar functions that may be proprietary in 
> nature, the ability to develop and deploy these extensions outside the Metron 
> code base is critically important.
> To that end, and after community discussion and proposal we create or 
> formalize the 'plugin' development story in Metron.  
> The proposal is to adapt the Apache Nifi NAR system for use in Metron.  This 
> will provide the system with:
> * archetype(s) for developer projects and independent development
> * defined packaging and metadata for 'plugin' products
> * loading and instantiation with classloader isolation capabilities
> * removing the necessity for shading plugin jars
> These capabilities will also enable other features, such as plugin lifecycle, 
> plugin configuration+redeployment, and other things.
> The plugin archetypes and their installation will be a followon



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