GUACAMOLE-5: Use singleton Guice Injector via common base class.

extensions/guacamole-auth-jdbc/modules/guacamole-auth-jdbc-base/src/main/java/org/apache/guacamole/auth/jdbc/JDBCAuthenticationProvider.java

@@ -0,0 +1,101 @@
+/*
+ * 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.guacamole.auth.jdbc;
+
+import com.google.inject.Injector;
+import org.apache.guacamole.GuacamoleException;
+import org.apache.guacamole.net.auth.AuthenticationProvider;
+import org.apache.guacamole.net.auth.Credentials;
+import org.apache.guacamole.net.auth.UserContext;
+import org.apache.guacamole.auth.jdbc.user.AuthenticationProviderService;
+import org.apache.guacamole.net.auth.AuthenticatedUser;
+
+/**
+ * Provides a base implementation of an AuthenticationProvider which is backed
+ * by an arbitrary underlying database. It is up to the subclass implementation
+ * to configure the underlying database appropriately via Guice.
+ *
+ * @author James Muehlner
+ * @author Michael Jumper
+ */
+public abstract class JDBCAuthenticationProvider implements AuthenticationProvider {
+
+    /**
+     * Provider of the singleton Injector instance which will manage the object
+     * graph of this authentication provider.
+     */
+    private final JDBCInjectorProvider injectorProvider;
+
+    /**
+     * Creates a new AuthenticationProvider that is backed by an arbitrary
+     * underlying database.
+     *
+     * @param injectorProvider
+     *     A JDBCInjectorProvider instance which provides singleton instances
+     *     of a Guice Injector, pre-configured to set up all injections and
+     *     access to the underlying database via MyBatis.
+     */
+    public JDBCAuthenticationProvider(JDBCInjectorProvider injectorProvider) {
+        this.injectorProvider = injectorProvider;
+    }
+
+    @Override
+    public AuthenticatedUser authenticateUser(Credentials credentials)
+            throws GuacamoleException {
+
+        Injector injector = injectorProvider.get();
+
+        // Create AuthenticatedUser based on credentials, if valid
+        AuthenticationProviderService authProviderService = injector.getInstance(AuthenticationProviderService.class);
+        return authProviderService.authenticateUser(this, credentials);
+
+    }
+
+    @Override
+    public AuthenticatedUser updateAuthenticatedUser(AuthenticatedUser authenticatedUser,
+            Credentials credentials) throws GuacamoleException {
+
+        // No need to update authenticated users
+        return authenticatedUser;
+
+    }
+
+    @Override
+    public UserContext getUserContext(AuthenticatedUser authenticatedUser)
+            throws GuacamoleException {
+
+        Injector injector = injectorProvider.get();
+
+        // Create UserContext based on credentials, if valid
+        AuthenticationProviderService authProviderService = injector.getInstance(AuthenticationProviderService.class);
+        return authProviderService.getUserContext(authenticatedUser);
+
+    }
+
+    @Override
+    public UserContext updateUserContext(UserContext context,
+            AuthenticatedUser authenticatedUser) throws GuacamoleException {
+
+        // No need to update the context
+        return context;
+
+    }
+
+}

extensions/guacamole-auth-jdbc/modules/guacamole-auth-jdbc-base/src/main/java/org/apache/guacamole/auth/jdbc/JDBCInjectorProvider.java

@@ -0,0 +1,90 @@
+/*
+ * 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.guacamole.auth.jdbc;
+
+import com.google.inject.Injector;
+import java.util.concurrent.atomic.AtomicReference;
+import org.apache.guacamole.GuacamoleException;
+
+/**
+ * A caching provider of singleton Guice Injector instances. The first call to
+ * get() will return a new instance of the Guice Injector, while all subsequent
+ * calls will return that same instance. It is up to implementations of this
+ * class to define how the Guice Injector will be created through defining the
+ * create() function.
+ *
+ * IMPORTANT: Because the Injector returned by get() is cached statically, only
+ * ONE implementation of this class may be used within any individual
+ * classloader. Within the context of the JDBC extension, as long as each built
+ * extension only provides one subclass of this class, things should work
+ * properly, as each extension is given its own classloader by Guacamole.
+ *
+ * @author Michael Jumper
+ */
+public abstract class JDBCInjectorProvider {
+
+    /**
+     * An AtomicReference wrapping the cached Guice Injector. If the Injector
+     * has not yet been created, null will be wrapped instead.
+     */
+    private static final AtomicReference<Injector> injector = new AtomicReference<Injector>(null);
+
+    /**
+     * Creates a new instance of the Guice Injector which should be used
+     * across the entire JDBC authentication extension. This function will
+     * generally only be called once, but multiple invocations are possible if
+     * get() is invoked several times concurrently prior to the Injector being
+     * cached.
+     *
+     * @return
+     * @throws GuacamoleException
+     */
+    protected abstract Injector create() throws GuacamoleException;
+
+    /**
+     * Returns a common, singleton instance of a Guice Injector, configured for
+     * the injections required by the JDBC authentication extension. The result
+     * of the first call to this function will be cached statically within this
+     * class, and will be returned for all subsequent calls.
+     *
+     * @return
+     *     A singleton instance of the Guice Injector used across the entire
+     *     JDBC authentication extension.
+     *
+     * @throws GuacamoleException
+     *     If the Injector cannot be created due to an error.
+     */
+    public Injector get() throws GuacamoleException {
+
+        // Return existing Injector if already created
+        Injector value = injector.get();
+        if (value != null)
+            return value;
+
+        // Explicitly create and store new Injector only if necessary
+        injector.compareAndSet(null, create());
+
+        // Consistently return the same Injector, even if two create operations
+        // happen concurrently
+        return injector.get();
+
+    }
+
+}