GUAC-1517: Maintain singleton instance of AudioContext.

guacamole-common-js/src/main/webapp/modules/AudioContextFactory.js

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+/*
+ * 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.
+ */
+
+var Guacamole = Guacamole || {};
+
+/**
+ * Maintains a singleton instance of the Web Audio API AudioContext class,
+ * instantiating the AudioContext only in response to the first call to
+ * getAudioContext(), and only if no existing AudioContext instance has been
+ * provided via the singleton property. Subsequent calls to getAudioContext()
+ * will return the same instance.
+ *
+ * @namespace
+ */
+Guacamole.AudioContextFactory = {
+
+    /**
+     * A singleton instance of a Web Audio API AudioContext object, or null if
+     * no instance has yes been created. This property may be manually set if
+     * you wish to supply your own AudioContext instance, but care must be
+     * taken to do so as early as possible. Assignments to this property will
+     * not retroactively affect the value returned by previous calls to
+     * getAudioContext().
+     *
+     * @type {AudioContext}
+     */
+    'singleton' : null,
+
+    /**
+     * Returns a singleton instance of a Web Audio API AudioContext object.
+     *
+     * @return {AudioContext}
+     *     A singleton instance of a Web Audio API AudioContext object, or null
+     *     if the Web Audio API is not supported.
+     */
+    'getAudioContext' : function getAudioContext() {
+
+        // Fallback to Webkit-specific AudioContext implementation
+        var AudioContext = window.AudioContext || window.webkitAudioContext;
+
+        // Get new AudioContext instance if Web Audio API is supported
+        if (AudioContext) {
+            try {
+
+                // Create new instance if none yet exists
+                if (!Guacamole.AudioContextFactory.singleton)
+                    Guacamole.AudioContextFactory.singleton = new AudioContext();
+
+                // Return singleton instance
+                return Guacamole.AudioContextFactory.singleton;
+
+            }
+            catch (e) {
+                // Do not use Web Audio API if not allowed by browser
+            }
+        }
+
+        // Web Audio API not supported
+        return null;
+
+    }
+
+};