GUACAMOLE-641: Allow extensions to add arbitrary sources of Guacamole properties.

guacamole-ext/src/main/java/org/apache/guacamole/environment/Environment.java

@@ -19,9 +19,11 @@
 
 package org.apache.guacamole.environment;
 
+import org.apache.guacamole.properties.GuacamoleProperties;
 import java.io.File;
 import java.util.Map;
 import org.apache.guacamole.GuacamoleException;
+import org.apache.guacamole.GuacamoleUnsupportedException;
 import org.apache.guacamole.net.auth.GuacamoleProxyConfiguration;
 import org.apache.guacamole.properties.BooleanGuacamoleProperty;
 import org.apache.guacamole.properties.GuacamoleProperty;
@@ -162,4 +164,24 @@ public interface Environment {
     public GuacamoleProxyConfiguration getDefaultGuacamoleProxyConfiguration()
             throws GuacamoleException;
 
+    /**
+     * Adds another possible source of Guacamole configuration properties to
+     * this Environment. Properties not already defined by other sources of
+     * Guacamole configuration properties will alternatively be read from the
+     * given {@link GuacamoleProperties}.
+     *
+     * @param properties
+     *     The GuacamoleProperties to add to this Environment.
+     *
+     * @throws GuacamoleException
+     *     If the given GuacamoleProperties cannot be added, or if this
+     *     Environment does not support this operation.
+     */
+    public default void addGuacamoleProperties(GuacamoleProperties properties)
+            throws GuacamoleException {
+        throw new GuacamoleUnsupportedException(String.format("%s does not "
+                + "support dynamic definition of Guacamole properties.",
+                getClass()));
+    }
+
 }

guacamole-ext/src/main/java/org/apache/guacamole/properties/FileGuacamoleProperties.java

@@ -0,0 +1,85 @@
+/*
+ * 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.properties;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.Properties;
+import org.apache.guacamole.GuacamoleException;
+import org.apache.guacamole.GuacamoleServerException;
+
+/**
+ * GuacamoleProperties implementation which reads all properties from a
+ * standard Java properties file.
+ */
+public class FileGuacamoleProperties extends PropertiesGuacamoleProperties {
+
+    /**
+     * Reads the given Java properties file, storing all property name/value
+     * pairs in a new {@link Properties} object.
+     *
+     * @param propertiesFile
+     *     The Java properties file to read.
+     *
+     * @return
+     *     A new Properties containing all property name/value pairs defined in
+     *     the given file.
+     *
+     * @throws GuacamoleException
+     *     If an error prevents reading the given Java properties file.
+     */
+    private static Properties read(File propertiesFile) throws GuacamoleException {
+
+        // Fail early if file simply does not exist
+        if (!propertiesFile.exists())
+            throw new GuacamoleServerException(String.format("\"%s\" does not "
+                    + "exist.", propertiesFile));
+
+        // Load properties from stream, if any, always closing stream when done
+        Properties properties = new Properties();
+        try (InputStream stream = new FileInputStream(propertiesFile)) {
+            properties.load(stream);
+        }
+        catch (IOException e) {
+            throw new GuacamoleServerException(String.format("\"%s\" cannot "
+                    + "be read: %s", propertiesFile, e.getMessage()), e);
+        }
+
+        return properties;
+        
+    }
+
+    /**
+     * Creates a new FileGuacamoleProperties which reads all properties from
+     * the given standard Java properties file.
+     *
+     * @param propertiesFile
+     *     The Java properties file to read.
+     *
+     * @throws GuacamoleException
+     *     If an error prevents reading the given Java properties file.
+     */
+    public FileGuacamoleProperties(File propertiesFile) throws GuacamoleException {
+        super(read(propertiesFile));
+    }
+
+}

guacamole-ext/src/main/java/org/apache/guacamole/properties/GuacamoleProperties.java

@@ -0,0 +1,49 @@
+/*
+ * 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.properties;
+
+import java.util.Properties;
+import org.apache.guacamole.GuacamoleException;
+
+/**
+ * An arbitrary set of Guacamole configuration property name/value pairs. This
+ * interface is similar in concept to {@link Properties} except that
+ * implementations are not required to allow properties to be enumerated or
+ * iterated. Properties may simply be retrieved by their names, if known.
+ */
+public interface GuacamoleProperties {
+
+    /**
+     * Returns the value of the property having the given name, if defined. If
+     * no such property exists, null is returned.
+     *
+     * @param name
+     *     The name of the property to retrieve.
+     *
+     * @return
+     *     The value of the given property, or null if no such property is
+     *     defined.
+     *
+     * @throws GuacamoleException
+     *     If an error prevents the given property from being read.
+     */
+    String getProperty(String name) throws GuacamoleException;
+
+}

guacamole-ext/src/main/java/org/apache/guacamole/properties/PropertiesGuacamoleProperties.java

@@ -0,0 +1,54 @@
+/*
+ * 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.properties;
+
+import java.util.Properties;
+import org.apache.guacamole.GuacamoleException;
+
+/**
+ * GuacamoleProperties implementation which reads all properties from a
+ * {@link Properties} object.
+ */
+public class PropertiesGuacamoleProperties implements GuacamoleProperties {
+
+    /**
+     * The Properties from which all property values should be read.
+     */
+    private final Properties properties;
+
+    /**
+     * Creates a new PropertiesGuacamoleProperties which wraps the given
+     * {@link Properties}, providing access to the values of any properties
+     * defined therein.
+     *
+     * @param properties
+     *     The Properties that should be used as the source of all property
+     *     values exposed by this instance of PropertiesGuacamoleProperties.
+     */
+    public PropertiesGuacamoleProperties(Properties properties) {
+        this.properties = properties;
+    }
+
+    @Override
+    public String getProperty(String name) throws GuacamoleException {
+        return properties.getProperty(name);
+    }
+
+}