Merge pull request #100 from glyptodon/concurrent-policy

GUAC-1101: Implement concurrent use policies.

extensions/guacamole-auth-jdbc/modules/guacamole-auth-jdbc-base/src/main/java/org/glyptodon/guacamole/auth/jdbc/JDBCAuthenticationProviderModule.java

@@ -46,7 +46,6 @@ import org.glyptodon.guacamole.auth.jdbc.security.SHA256PasswordEncryptionServic
 import org.glyptodon.guacamole.auth.jdbc.security.SaltService;
 import org.glyptodon.guacamole.auth.jdbc.security.SecureRandomSaltService;
 import org.glyptodon.guacamole.auth.jdbc.permission.SystemPermissionService;
-import org.glyptodon.guacamole.auth.jdbc.socket.UnrestrictedGuacamoleSocketService;
 import org.glyptodon.guacamole.auth.jdbc.user.UserService;
 import org.apache.ibatis.transaction.jdbc.JdbcTransactionFactory;
 import org.glyptodon.guacamole.auth.jdbc.permission.ConnectionGroupPermissionMapper;
@@ -77,15 +76,27 @@ public class JDBCAuthenticationProviderModule extends MyBatisModule {
      */
     private final Environment environment;
 
+    /**
+     * The service class to use to provide GuacamoleSockets for each
+     * connection.
+     */
+    private final Class<? extends GuacamoleSocketService> socketServiceClass;
+
     /**
      * Creates a new JDBC authentication provider module that configures the
-     * various injected base classes using the given environment.
+     * various injected base classes using the given environment, and provides
+     * connections using the given socket service.
      *
      * @param environment
      *     The environment to use to configure injected classes.
+     * 
+     * @param socketServiceClass
+     *     The socket service to use to provide sockets for connections.
      */
-    public JDBCAuthenticationProviderModule(Environment environment) {
+    public JDBCAuthenticationProviderModule(Environment environment,
+            Class<? extends GuacamoleSocketService> socketServiceClass) {
         this.environment = environment;
+        this.socketServiceClass = socketServiceClass;
     }
 
     @Override
@@ -135,8 +146,8 @@ public class JDBCAuthenticationProviderModule extends MyBatisModule {
         bind(UserPermissionService.class);
         bind(UserService.class);
         
-        // Bind appropriate socket service based on policy
-        bind(GuacamoleSocketService.class).to(UnrestrictedGuacamoleSocketService.class);
+        // Bind provided socket service
+        bind(GuacamoleSocketService.class).to(socketServiceClass);
         
     }
 

extensions/guacamole-auth-jdbc/modules/guacamole-auth-jdbc-base/src/main/java/org/glyptodon/guacamole/auth/jdbc/socket/AbstractGuacamoleSocketService.java

@@ -29,6 +29,7 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.Date;
 import java.util.List;
+import java.util.concurrent.atomic.AtomicBoolean;
 import org.glyptodon.guacamole.auth.jdbc.user.AuthenticatedUser;
 import org.glyptodon.guacamole.auth.jdbc.connection.ModeledConnection;
 import org.glyptodon.guacamole.auth.jdbc.connectiongroup.ModeledConnectionGroup;
@@ -138,6 +139,109 @@ public abstract class AbstractGuacamoleSocketService implements GuacamoleSocketS
     protected abstract void release(AuthenticatedUser user,
             ModeledConnection connection);
 
+    /**
+     * Returns a guacamole configuration containing the protocol and parameters
+     * from the given connection. If tokens are used in the connection
+     * parameter values, credentials from the given user will be substituted
+     * appropriately.
+     *
+     * @param user
+     *     The user whose credentials should be used if necessary.
+     *
+     * @param connection
+     *     The connection whose protocol and parameters should be added to the
+     *     returned configuration.
+     *
+     * @return
+     *     A GuacamoleConfiguration containing the protocol and parameters from
+     *     the given connection.
+     */
+    private GuacamoleConfiguration getGuacamoleConfiguration(AuthenticatedUser user,
+            ModeledConnection connection) {
+
+        // Generate configuration from available data
+        GuacamoleConfiguration config = new GuacamoleConfiguration();
+
+        // Set protocol from connection
+        ConnectionModel model = connection.getModel();
+        config.setProtocol(model.getProtocol());
+
+        // Set parameters from associated data
+        Collection<ParameterModel> parameters = parameterMapper.select(connection.getIdentifier());
+        for (ParameterModel parameter : parameters)
+            config.setParameter(parameter.getName(), parameter.getValue());
+
+        // Build token filter containing credential tokens
+        TokenFilter tokenFilter = new TokenFilter();
+        StandardTokens.addStandardTokens(tokenFilter, user.getCredentials());
+
+        // Filter the configuration
+        tokenFilter.filterValues(config.getParameters());
+
+        return config;
+        
+    }
+
+    /**
+     * Saves the given ActiveConnectionRecord to the database, associating it
+     * with the connection having the given identifier. The end date of the
+     * saved record will be populated with the current time.
+     *
+     * @param identifier
+     *     The connection to associate the new record with.
+     *
+     * @param record
+     *     The record to save.
+     */
+    private void saveConnectionRecord(String identifier,
+            ActiveConnectionRecord record) {
+
+        // Get associated models
+        AuthenticatedUser user = record.getUser();
+        UserModel userModel = user.getUser().getModel();
+        ConnectionRecordModel recordModel = new ConnectionRecordModel();
+
+        // Copy user information and timestamps into new record
+        recordModel.setUserID(userModel.getObjectID());
+        recordModel.setUsername(userModel.getIdentifier());
+        recordModel.setConnectionIdentifier(identifier);
+        recordModel.setStartDate(record.getStartDate());
+        recordModel.setEndDate(new Date());
+
+        // Insert connection record
+        connectionRecordMapper.insert(recordModel);
+
+    }
+
+    /**
+     * Returns an unconfigured GuacamoleSocket that is already connected to
+     * guacd as specified in guacamole.properties, using SSL if necessary.
+     *
+     * @return
+     *     An unconfigured GuacamoleSocket, already connected to guacd.
+     *
+     * @throws GuacamoleException 
+     *     If an error occurs while connecting to guacd, or while parsing
+     *     guacd-related properties.
+     */
+    private GuacamoleSocket getUnconfiguredGuacamoleSocket()
+        throws GuacamoleException {
+
+        // Use SSL if requested
+        if (environment.getProperty(Environment.GUACD_SSL, true))
+            return new InetGuacamoleSocket(
+                environment.getRequiredProperty(Environment.GUACD_HOSTNAME),
+                environment.getRequiredProperty(Environment.GUACD_PORT)
+            );
+
+        // Otherwise, just use straight TCP
+        return new InetGuacamoleSocket(
+            environment.getRequiredProperty(Environment.GUACD_HOSTNAME),
+            environment.getRequiredProperty(Environment.GUACD_PORT)
+        );
+
+    }
+    
     /**
      * Creates a socket for the given user which connects to the given
      * connection, which MUST already be acquired via acquire(). The given
@@ -173,28 +277,10 @@ public abstract class AbstractGuacamoleSocketService implements GuacamoleSocketS
         final ActiveConnectionRecord activeConnection = new ActiveConnectionRecord(user);
 
         // Get relevant identifiers
+        final AtomicBoolean released = new AtomicBoolean(false);
         final String identifier = connection.getIdentifier();
         final String parentIdentifier = connection.getParentIdentifier();
-        
-        // Generate configuration from available data
-        GuacamoleConfiguration config = new GuacamoleConfiguration();
-
-        // Set protocol from connection
-        ConnectionModel model = connection.getModel();
-        config.setProtocol(model.getProtocol());
-
-        // Set parameters from associated data
-        Collection<ParameterModel> parameters = parameterMapper.select(identifier);
-        for (ParameterModel parameter : parameters)
-            config.setParameter(parameter.getName(), parameter.getValue());
-
-        // Build token filter containing credential tokens
-        TokenFilter tokenFilter = new TokenFilter();
-        StandardTokens.addStandardTokens(tokenFilter, user.getCredentials());
-
-        // Filter the configuration
-        tokenFilter.filterValues(config.getParameters());
-
+    
         // Return new socket
         try {
 
@@ -204,11 +290,9 @@ public abstract class AbstractGuacamoleSocketService implements GuacamoleSocketS
 
             // Return newly-reserved connection
             return new ConfiguredGuacamoleSocket(
-                new InetGuacamoleSocket(
-                    environment.getRequiredProperty(Environment.GUACD_HOSTNAME),
-                    environment.getRequiredProperty(Environment.GUACD_PORT)
-                ),
-                config
+                getUnconfiguredGuacamoleSocket(),
+                getGuacamoleConfiguration(user, connection),
+                info
             ) {
 
                 @Override
@@ -217,25 +301,20 @@ public abstract class AbstractGuacamoleSocketService implements GuacamoleSocketS
                     // Attempt to close connection
                     super.close();
                     
-                    // Release connection upon close
-                    activeConnections.remove(identifier, activeConnection);
-                    activeConnectionGroups.remove(parentIdentifier, activeConnection);
-                    release(user, connection);
+                    // Release connection upon close, if not already released
+                    if (released.compareAndSet(false, true)) {
 
-                    UserModel userModel = user.getUser().getModel();
-                    ConnectionRecordModel recordModel = new ConnectionRecordModel();
+                        // Release connection
+                        activeConnections.remove(identifier, activeConnection);
+                        activeConnectionGroups.remove(parentIdentifier, activeConnection);
+                        release(user, connection);
 
-                    // Copy user information and timestamps into new record
-                    recordModel.setUserID(userModel.getObjectID());
-                    recordModel.setUsername(userModel.getIdentifier());
-                    recordModel.setConnectionIdentifier(identifier);
-                    recordModel.setStartDate(activeConnection.getStartDate());
-                    recordModel.setEndDate(new Date());
+                        // Save record to database
+                        saveConnectionRecord(identifier, activeConnection);
 
-                    // Insert connection record
-                    connectionRecordMapper.insert(recordModel);
+                    }
                     
-                }
+                } // end close()
                 
             };
 
@@ -244,10 +323,12 @@ public abstract class AbstractGuacamoleSocketService implements GuacamoleSocketS
         // Release connection in case of error
         catch (GuacamoleException e) {
 
-            // Atomically release access to connection
-            activeConnections.remove(identifier, activeConnection);
-            activeConnectionGroups.remove(parentIdentifier, activeConnection);
-            release(user, connection);
+            // Release connection if not already released
+            if (released.compareAndSet(false, true)) {
+                activeConnections.remove(identifier, activeConnection);
+                activeConnectionGroups.remove(parentIdentifier, activeConnection);
+                release(user, connection);
+            }
 
             throw e;
 

extensions/guacamole-auth-jdbc/modules/guacamole-auth-jdbc-base/src/main/java/org/glyptodon/guacamole/auth/jdbc/socket/ActiveConnectionRecord.java

@@ -60,6 +60,18 @@ public class ActiveConnectionRecord implements ConnectionRecord {
         this.user = user;
     }
 
+    /**
+     * Returns the user that connected to the connection associated with this
+     * connection record.
+     *
+     * @return
+     *     The user that connected to the connection associated with this
+     *     connection record.
+     */
+    public AuthenticatedUser getUser() {
+        return user;
+    }
+
     @Override
     public Date getStartDate() {
         return startDate;

extensions/guacamole-auth-jdbc/modules/guacamole-auth-jdbc-base/src/main/java/org/glyptodon/guacamole/auth/jdbc/socket/MultiseatGuacamoleSocketService.java

@@ -0,0 +1,138 @@
+/*
+ * Copyright (C) 2015 Glyptodon LLC
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package org.glyptodon.guacamole.auth.jdbc.socket;
+
+import com.google.inject.Singleton;
+import java.util.Collections;
+import java.util.List;
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+import org.glyptodon.guacamole.auth.jdbc.user.AuthenticatedUser;
+import org.glyptodon.guacamole.auth.jdbc.connection.ModeledConnection;
+import org.glyptodon.guacamole.GuacamoleException;
+import org.glyptodon.guacamole.GuacamoleResourceConflictException;
+
+
+/**
+ * GuacamoleSocketService implementation which restricts concurrency only on a
+ * per-user basis. Each connection may be used concurrently any number of
+ * times, but each concurrent use must be associated with a different user.
+ *
+ * @author Michael Jumper
+ */
+@Singleton
+public class MultiseatGuacamoleSocketService
+    extends AbstractGuacamoleSocketService {
+
+    /**
+     * A unique pairing of user and connection.
+     */
+    private static class Seat {
+
+        /**
+         * The user using this seat.
+         */
+        private final String username;
+
+        /**
+         * The connection associated with this seat.
+         */
+        private final String connectionIdentifier;
+
+        /**
+         * Creates a new seat which associated the given user with the given
+         * connection.
+         *
+         * @param username
+         *     The username of the user using this seat.
+         *
+         * @param connectionIdentifier
+         *     The identifier of the connection associated with this seat.
+         */
+        public Seat(String username, String connectionIdentifier) {
+            this.username = username;
+            this.connectionIdentifier = connectionIdentifier;
+        }
+
+        @Override
+        public int hashCode() {
+
+            // The various properties will never be null
+            assert(username != null);
+            assert(connectionIdentifier != null);
+
+            // Derive hashcode from username and connection identifier
+            int hash = 5;
+            hash = 37 * hash + username.hashCode();
+            hash = 37 * hash + connectionIdentifier.hashCode();
+            return hash;
+
+        }
+
+        @Override
+        public boolean equals(Object object) {
+
+            // We are only comparing against other seats here
+            assert(object instanceof Seat);
+            Seat seat = (Seat) object;
+
+            // The various properties will never be null
+            assert(seat.username != null);
+            assert(seat.connectionIdentifier != null);
+
+            return username.equals(seat.username)
+                && connectionIdentifier.equals(seat.connectionIdentifier);
+
+        }
+
+    }
+    
+    /**
+     * The set of all active user/connection pairs.
+     */
+    private final Set<Seat> activeSeats =
+            Collections.newSetFromMap(new ConcurrentHashMap<Seat, Boolean>());
+   
+    @Override
+    protected ModeledConnection acquire(AuthenticatedUser user,
+            List<ModeledConnection> connections) throws GuacamoleException {
+
+        String username = user.getUser().getIdentifier();
+        
+        // Return the first unreserved connection
+        for (ModeledConnection connection : connections) {
+            if (activeSeats.add(new Seat(username, connection.getIdentifier())))
+                return connection;
+        }
+
+        // Already in use
+        throw new GuacamoleResourceConflictException("Cannot connect. This connection is in use.");
+
+    }
+
+    @Override
+    protected void release(AuthenticatedUser user, ModeledConnection connection) {
+        activeSeats.remove(new Seat(user.getUser().getIdentifier(), connection.getIdentifier()));
+    }
+
+}

extensions/guacamole-auth-jdbc/modules/guacamole-auth-jdbc-base/src/main/java/org/glyptodon/guacamole/auth/jdbc/socket/ReservedGuacamoleSocketService.java

@@ -0,0 +1,183 @@
+/*
+ * Copyright (C) 2015 Glyptodon LLC
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package org.glyptodon.guacamole.auth.jdbc.socket;
+
+import com.google.inject.Singleton;
+import java.util.List;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
+import org.glyptodon.guacamole.auth.jdbc.user.AuthenticatedUser;
+import org.glyptodon.guacamole.auth.jdbc.connection.ModeledConnection;
+import org.glyptodon.guacamole.GuacamoleException;
+import org.glyptodon.guacamole.GuacamoleResourceConflictException;
+
+
+/**
+ * GuacamoleSocketService implementation which allows only one user per
+ * connection at any time, but does not disallow concurrent use. Once
+ * connected, a user has effectively reserved that connection, and may
+ * continue to concurrently use that connection any number of times. The
+ * connection will remain reserved until all associated connections are closed.
+ * Other users will be denied access to that connection while it is reserved.
+ *
+ * @author Michael Jumper
+ */
+@Singleton
+public class ReservedGuacamoleSocketService
+    extends AbstractGuacamoleSocketService {
+
+    /**
+     * An arbitrary number of reservations associated with a specific user.
+     * Initially, each Reservation instance represents exactly one reservation,
+     * but future calls to acquire() may increase this value. Once the
+     * reservation count is reduced to zero by calls to release(), a
+     * Reservation instance is empty and cannot be reused. It must be discarded
+     * and replaced with a fresh Reservation.
+     * 
+     * This is necessary as each Reservation will be stored within a Map, and
+     * the effect of acquire() must be deterministic. If Reservations could be
+     * reused, the internal count could potentially increase after being
+     * removed from the map, resulting in a successful acquire() that really
+     * should have failed.
+     */
+    private static class Reservation {
+
+        /**
+         * The username of the user associated with this reservation.
+         */
+        private final String username;
+
+        /**
+         * The number of reservations effectively present under the associated
+         * username.
+         */
+        private int count = 1;
+
+        /**
+         * Creates a new reservation which tracks the overall number of
+         * reservations for a given user.
+         * @param username 
+         */
+        public Reservation(String username) {
+            this.username = username;
+        }
+
+        /**
+         * Attempts to acquire a new reservation under the given username. If
+         * this reservation is for a different user, or the reservation has
+         * expired, this will fail.
+         *
+         * @param username
+         *     The username of the user to acquire the reservation for.
+         *
+         * @return
+         *     true if the reservation was successful, false otherwise.
+         */
+        public boolean acquire(String username) {
+
+            // Acquire always fails if for the wrong user
+            if (!this.username.equals(username))
+                return false;
+
+            // Determine success/failure based on count
+            synchronized (this) {
+
+                // If already expired, no further reservations are allowed
+                if (count == 0)
+                    return false;
+
+                // Otherwise, add another reservation, report success
+                count++;
+                return true;
+                
+            }
+            
+        }
+
+        /**
+         * Releases a previous reservation. The result of calling this function
+         * without a previous matching call to acquire is undefined.
+         *
+         * @return
+         *     true if the last reservation has been released and this
+         *     reservation is now empty, false otherwise.
+         */
+        public boolean release() {
+            synchronized (this) {
+
+                // Reduce reservation count
+                count--;
+
+                // Empty if no reservations remain
+                return count == 0;
+                
+            }
+        }
+        
+    }
+
+    /**
+     * Map of connection identifier to associated reservations.
+     */
+    private final ConcurrentMap<String, Reservation> reservations =
+            new ConcurrentHashMap<String, Reservation>();
+    
+    @Override
+    protected ModeledConnection acquire(AuthenticatedUser user,
+            List<ModeledConnection> connections) throws GuacamoleException {
+
+        String username = user.getUser().getIdentifier();
+        
+        // Return the first successfully-reserved connection
+        for (ModeledConnection connection : connections) {
+
+            String identifier = connection.getIdentifier();
+
+            // Attempt to reserve connection, return if successful
+            Reservation reservation = reservations.putIfAbsent(identifier, new Reservation(username));
+            if (reservation == null || reservation.acquire(username))
+                return connection;
+
+        }
+
+        // Already in use
+        throw new GuacamoleResourceConflictException("Cannot connect. This connection is in use.");
+
+    }
+
+    @Override
+    protected void release(AuthenticatedUser user, ModeledConnection connection) {
+
+        String identifier = connection.getIdentifier();
+        
+        // Retrieve active reservation (which must exist)
+        Reservation reservation = reservations.get(identifier);
+        assert(reservation != null);
+
+        // Release reservation, remove from map if empty
+        if (reservation.release())
+            reservations.remove(identifier);
+        
+    }
+
+}

extensions/guacamole-auth-jdbc/modules/guacamole-auth-jdbc-base/src/main/java/org/glyptodon/guacamole/auth/jdbc/socket/SingleSeatGuacamoleSocketService.java

@@ -0,0 +1,72 @@
+/*
+ * Copyright (C) 2015 Glyptodon LLC
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package org.glyptodon.guacamole.auth.jdbc.socket;
+
+import com.google.inject.Singleton;
+import java.util.Collections;
+import java.util.List;
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+import org.glyptodon.guacamole.auth.jdbc.user.AuthenticatedUser;
+import org.glyptodon.guacamole.auth.jdbc.connection.ModeledConnection;
+import org.glyptodon.guacamole.GuacamoleException;
+import org.glyptodon.guacamole.GuacamoleResourceConflictException;
+
+
+/**
+ * GuacamoleSocketService implementation which allows exactly one use
+ * of any connection at any time. Concurrent usage of any kind is not allowed.
+ *
+ * @author Michael Jumper
+ */
+@Singleton
+public class SingleSeatGuacamoleSocketService
+    extends AbstractGuacamoleSocketService {
+
+    /**
+     * The set of all active connection identifiers.
+     */
+    private final Set<String> activeConnections =
+            Collections.newSetFromMap(new ConcurrentHashMap<String, Boolean>());
+    
+    @Override
+    protected ModeledConnection acquire(AuthenticatedUser user,
+            List<ModeledConnection> connections) throws GuacamoleException {
+
+        // Return the first unused connection
+        for (ModeledConnection connection : connections) {
+            if (activeConnections.add(connection.getIdentifier()))
+                return connection;
+        }
+
+        // Already in use
+        throw new GuacamoleResourceConflictException("Cannot connect. This connection is in use.");
+
+    }
+
+    @Override
+    protected void release(AuthenticatedUser user, ModeledConnection connection) {
+        activeConnections.remove(connection.getIdentifier());
+    }
+
+}

extensions/guacamole-auth-jdbc/modules/guacamole-auth-jdbc-mysql/src/main/java/net/sourceforge/guacamole/net/auth/mysql/MySQLAuthenticationProvider.java

@@ -29,9 +29,15 @@ import org.glyptodon.guacamole.net.auth.AuthenticationProvider;
 import org.glyptodon.guacamole.net.auth.Credentials;
 import org.glyptodon.guacamole.net.auth.UserContext;
 import org.glyptodon.guacamole.auth.jdbc.JDBCAuthenticationProviderModule;
+import org.glyptodon.guacamole.auth.jdbc.socket.GuacamoleSocketService;
+import org.glyptodon.guacamole.auth.jdbc.socket.MultiseatGuacamoleSocketService;
+import org.glyptodon.guacamole.auth.jdbc.socket.ReservedGuacamoleSocketService;
+import org.glyptodon.guacamole.auth.jdbc.socket.SingleSeatGuacamoleSocketService;
+import org.glyptodon.guacamole.auth.jdbc.socket.UnrestrictedGuacamoleSocketService;
 import org.glyptodon.guacamole.auth.jdbc.user.UserContextService;
 import org.glyptodon.guacamole.environment.Environment;
 import org.glyptodon.guacamole.environment.LocalEnvironment;
+import org.glyptodon.guacamole.properties.GuacamoleProperties;
 
 /**
  * Provides a MySQL based implementation of the AuthenticationProvider
@@ -48,6 +54,55 @@ public class MySQLAuthenticationProvider implements AuthenticationProvider {
      */
     private final Injector injector;
 
+    /**
+     * Returns the appropriate socket service class given the Guacamole
+     * environment. The class is chosen based on configuration options that
+     * dictate concurrent usage policy.
+     *
+     * @param environment
+     *     The environment of the Guacamole server.
+     *
+     * @return
+     *     The socket service class that matches the concurrent usage policy
+     *     options set in the Guacamole environment.
+     *
+     * @throws GuacamoleException
+     *     If an error occurs while reading the configuration options.
+     */
+    private Class<? extends GuacamoleSocketService>
+        getSocketServiceClass(Environment environment)
+                throws GuacamoleException {
+
+        // Read concurrency-related properties
+        boolean disallowSimultaneous = environment.getProperty(MySQLGuacamoleProperties.MYSQL_DISALLOW_SIMULTANEOUS_CONNECTIONS, false);
+        boolean disallowDuplicate    = environment.getProperty(MySQLGuacamoleProperties.MYSQL_DISALLOW_DUPLICATE_CONNECTIONS, true);
+
+        if (disallowSimultaneous) {
+
+            // Connections may not be used concurrently
+            if (disallowDuplicate)
+                return SingleSeatGuacamoleSocketService.class;
+
+            // Connections are reserved for a single user when in use
+            else
+                return ReservedGuacamoleSocketService.class;
+
+        }
+
+        else {
+
+            // Connections may be used concurrently, but only once per user
+            if (disallowDuplicate)
+                return MultiseatGuacamoleSocketService.class;
+
+            // Connection use is not restricted
+            else
+                return UnrestrictedGuacamoleSocketService.class;
+
+        }
+         
+    }
+    
     /**
      * Creates a new MySQLAuthenticationProvider that reads and writes
      * authentication data to a MySQL database defined by properties in
@@ -69,7 +124,7 @@ public class MySQLAuthenticationProvider implements AuthenticationProvider {
             new MySQLAuthenticationProviderModule(environment),
 
             // Configure JDBC authentication core
-            new JDBCAuthenticationProviderModule(environment)
+            new JDBCAuthenticationProviderModule(environment, getSocketServiceClass(environment))
 
         );