Provide a data directory to plugins on demand

If a plugin requests a data directory with a @PluginData File
dependency, a data directory will be created automatically by the
server in $site_path/data/$plugin_name and passed to the plugin.

Plugins can use this to store any data they want.

Change-Id: I98de44a033889740cafc8a3d72c582c0e99b7ffd

gerrit-server/src/main/java/com/google/gerrit/server/plugins/Plugin.java

@@ -16,6 +16,7 @@ package com.google.gerrit.server.plugins;
 
 import com.google.common.base.Strings;
 import com.google.common.collect.Lists;
+import com.google.gerrit.extensions.annotations.PluginData;
 import com.google.gerrit.extensions.annotations.PluginName;
 import com.google.gerrit.extensions.registration.RegistrationHandle;
 import com.google.gerrit.extensions.registration.ReloadableRegistrationHandle;
@@ -26,6 +27,8 @@ import com.google.inject.AbstractModule;
 import com.google.inject.Guice;
 import com.google.inject.Injector;
 import com.google.inject.Module;
+import com.google.inject.Provider;
+import com.google.inject.ProvisionException;
 
 import org.eclipse.jgit.storage.file.FileSnapshot;
 
@@ -51,6 +54,7 @@ public class Plugin {
   private final FileSnapshot snapshot;
   private final JarFile jarFile;
   private final Manifest manifest;
+  private final File dataDir;
   private final ClassLoader classLoader;
   private Class<? extends Module> sysModule;
   private Class<? extends Module> sshModule;
@@ -67,6 +71,7 @@ public class Plugin {
       FileSnapshot snapshot,
       JarFile jarFile,
       Manifest manifest,
+      File dataDir,
       ClassLoader classLoader,
       @Nullable Class<? extends Module> sysModule,
       @Nullable Class<? extends Module> sshModule,
@@ -76,6 +81,7 @@ public class Plugin {
     this.snapshot = snapshot;
     this.jarFile = jarFile;
     this.manifest = manifest;
+    this.dataDir = dataDir;
     this.classLoader = classLoader;
     this.sysModule = sysModule;
     this.sshModule = sshModule;
@@ -181,6 +187,27 @@ public class Plugin {
         bind(String.class)
           .annotatedWith(PluginName.class)
           .toInstance(name);
+
+        bind(File.class)
+          .annotatedWith(PluginData.class)
+          .toProvider(new Provider<File>() {
+            private volatile boolean ready;
+
+            @Override
+            public File get() {
+              if (!ready) {
+                synchronized (dataDir) {
+                  if (!dataDir.exists() && !dataDir.mkdirs()) {
+                    throw new ProvisionException(String.format(
+                        "Cannot create %s for plugin %s",
+                        dataDir.getAbsolutePath(), name));
+                  }
+                  ready = true;
+                }
+              }
+              return dataDir;
+            }
+          });
       }
     });
     return Guice.createInjector(modules);

gerrit-server/src/main/java/com/google/gerrit/server/plugins/PluginLoader.java

@@ -58,6 +58,7 @@ public class PluginLoader implements LifecycleListener {
   static final Logger log = LoggerFactory.getLogger(PluginLoader.class);
 
   private final File pluginsDir;
+  private final File dataDir;
   private final File tmpDir;
   private final PluginGuiceEnvironment env;
   private final ServerInformationImpl srvInfoImpl;
@@ -73,6 +74,7 @@ public class PluginLoader implements LifecycleListener {
       ServerInformationImpl sii,
       @GerritServerConfig Config cfg) {
     pluginsDir = sitePaths.plugins_dir;
+    dataDir = sitePaths.data_dir;
     tmpDir = sitePaths.tmp_dir;
     env = pe;
     srvInfoImpl = sii;
@@ -343,7 +345,7 @@ public class PluginLoader implements LifecycleListener {
       return new Plugin(name,
           srcJar, snapshot,
           jarFile, manifest,
-          pluginLoader,
+          new File(dataDir, name), pluginLoader,
           sysModule, sshModule, httpModule);
     } finally {
       if (!keep) {