core: Add ExtensionElementFilter

smack-core/src/main/java/org/jivesoftware/smack/filter/ExtensionElementFilter.java

@@ -0,0 +1,53 @@
+/**
+ *
+ * Copyright 2020 Florian Schmaus
+ *
+ * Licensed 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.jivesoftware.smack.filter;
+
+import javax.xml.namespace.QName;
+
+import org.jivesoftware.smack.packet.ExtensionElement;
+import org.jivesoftware.smack.packet.Stanza;
+import org.jivesoftware.smack.util.XmppElementUtil;
+
+public class ExtensionElementFilter<E extends ExtensionElement> implements StanzaFilter {
+
+    private final Class<E> extensionElementClass;
+    private final QName extensionElementQName;
+
+    protected ExtensionElementFilter(Class<E> extensionElementClass) {
+        this.extensionElementClass = extensionElementClass;
+        extensionElementQName = XmppElementUtil.getQNameFor(extensionElementClass);
+    }
+
+    @Override
+    public final boolean accept(Stanza stanza) {
+        ExtensionElement extensionElement = stanza.getExtension(extensionElementQName);
+        if (extensionElement == null) {
+            return false;
+        }
+
+        if (!extensionElementClass.isInstance(extensionElement)) {
+            return false;
+        }
+
+        E specificExtensionElement = extensionElementClass.cast(extensionElement);
+        return accept(specificExtensionElement);
+    }
+
+    public boolean accept(E extensionElement) {
+        return true;
+    }
+}