[jira] [Commented] (NUTCH-2429) Fix Plugin System to allow protocol plugins to bundle their URLStreamHandlers

[ASF GitHub Bot (JIRA)]

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https://issues.apache.org/jira/browse/NUTCH-2429?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16193260#comment-16193260
 ] 

ASF GitHub Bot commented on NUTCH-2429:
---------------------------------------

lewismc commented on a change in pull request #222: NUTCH-2429 Fix Plugin 
System to allow protocol plugins to bundle their URLStreamHandlers
URL: https://github.com/apache/nutch/pull/222#discussion_r143002246
 
 

 ##########
 File path: src/java/org/apache/nutch/plugin/PluginRepository.java
 ##########
 @@ -521,4 +532,105 @@ public static void main(String[] args) throws Exception {
     System.arraycopy(args, 2, subargs, 0, subargs.length);
     m.invoke(null, new Object[] { subargs });
   }
+
+  /**
+   * Registers this PluginRepository to be invoked whenever URLs have to be
+   * parsed. This allows to check the registered protocol plugins for uncommon
+   * protocols.
+   */
+  private void registerURLStreamHandlerFactory() {
+    
org.apache.nutch.plugin.URLStreamHandlerFactory.getInstance().registerPluginRepository(this);
+  }
+
+  /**
+   * Invoked whenever a java.net.URL needs to be instantiated. Tries to find a
+   * suitable extension and allow it to provide a URLStreamHandler. This is 
done
+   * by several attempts:
+   * <ul>
+   * <li>Find a protocol plugin that implements the desired protocol. If found,
+   * instantiate it so eventually the plugin can install a URLStreamHandler
+   * through a static hook.</li>
+   * <li>If the plugin specifies a URLStreamHandler in its <tt>plugin.xml</tt>,
+   * return an instance of this URLStreamHandler. Example:
+   * 
+   * <pre>
+   *  ...
+   *  &lt;implementation id="org.apache.nutch.protocol.foo.Foo" 
class="my.foo.Foo"&gt;
+   *      &lt;parameter name="protocolName" value="foo"/&gt;
+   *      &lt;parameter name="urlStreamHandler" value="my.foo.Handler"/&gt;
+   *  &lt;/implementation&gt;
+   *  ...
+   * </pre>
+   * 
+   * </li>
+   * <li>if all else fails, return null. This will fallback to the JVM's method
+   * of evaluating the system property 
<tt>java.protocol.handler.pkgs</tt>.</li>
+   * </ul>
+   * 
+   * @return the URLStreamHandler found, or null.
+   * @see java.net.URL
+   */
+  public URLStreamHandler createURLStreamHandler(String protocol) {
+    LOG.debug("createURLStreamHandler(" + protocol + ")");
+
+    if (fExtensionPoints != null) {
+      ExtensionPoint ep = fExtensionPoints
+          .get("org.apache.nutch.protocol.Protocol");
+      if (ep != null) {
+        Extension[] extensions = ep.getExtensions();
+        for (Extension extension : extensions) {
+          String p = extension.getAttribute("protocolName");
+          LOG.trace("Found " + p);
+          if (p.equals(protocol)) {
+            LOG.debug("suitable " + p);
+
+            // instantiate the plugin. This allows it to execute a static hook,
+            // if present
+            // TODO: only do this if not done already
 
 Review comment:
   What does the TODO mean?
 
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> Fix Plugin System to allow protocol plugins to bundle their URLStreamHandlers
> -----------------------------------------------------------------------------
>
>                 Key: NUTCH-2429
>                 URL: https://issues.apache.org/jira/browse/NUTCH-2429
>             Project: Nutch
>          Issue Type: Improvement
>          Components: commoncrawl
>    Affects Versions: 1.14
>         Environment: Tested on both Nutch 1.13 and 1.14 in Ubuntu Linux with 
> OpenJDK 1.8.
>            Reporter: Hiran Chaudhuri
>             Fix For: 1.14
>
>
> While trying to use the protocol-smb plugin (which is not part of the Nutch 
> distribution) I realized there are four steps to successfully make use of a 
> protocol plugin:
> 1 - put the artifact into the plugins directory
> 2 - modify Nutch configuration files to allow smb:// urls plus include the 
> plugin to the loaded list
> 3 - extract jcifs.jar and place it on the system classpath
> 4 - run nutch with the correct system property
> While steps 1 and 2 seem obvious, 3 and 4 require knowledge of plugin 
> internals which does not feel right for nutch and plugin users. Even more, 
> the jcifs.jar would exist twice on the classpath and could even cause further 
> problems during runtime.



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