Implement XEP-0184 delivery notifications

This patch provides three components required to implement XEP-0184:

 * DeliveryReceiptRequest is a PacketExtension to request a receipt
 * DeliveryReceipt is a PacketExtension that contains the receipt
 * DeliveryReceiptManager to handle sending/receiving of requests and
   receipts.

Implementation:

For requesting a receipt, just add a new DeliveryReceiptRequest() to
your message or use the helper function:

    DeliveryReceiptManager.addDeliveryReceiptRequest(packet);

Register a ReceiptReceivedListener to find out if your packet arrived:

    DeliveryReceiptManager.getInstanceFor(myConnection)
	.registerReceiptReceivedListener(new ReceiptReceivedListener() {
	    @Override public void onReceiptReceived(String fromJid,
				    String toJid, String receiptId) {
		// receipt received for packet id receiptId
	    }

To answer a receipt request, you can either check incoming packets
manually:

    if (DeliveryReceiptManager.hasDeliveryReceiptRequest(packet)) {
	// send receipt
    }

Or you can enable automatic receipt transmission with:

    DeliveryReceiptManager.getInstanceFor(myConnection)
	    .setAutoReceiptsEnabled(true);

Signed-Off-By: Georg Lukas <georg@op-co.de>

git-svn-id: http://svn.igniterealtime.org/svn/repos/smack/trunk@13431 b35dd754-fafc-0310-a699-88a17e54d16e

source/org/jivesoftware/smackx/receipts/DeliveryReceiptRequest.java

@@ -0,0 +1,54 @@
+/*
+ * All rights reserved. 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.smackx.receipts;
+
+import org.jivesoftware.smack.packet.PacketExtension;
+import org.jivesoftware.smack.provider.PacketExtensionProvider;
+import org.xmlpull.v1.XmlPullParser;
+
+/**
+ * Represents a <b>message delivery receipt request</b> entry as specified by
+ * <a href="http://xmpp.org/extensions/xep-0184.html">Message Delivery Receipts</a>.
+ *
+ * @author Georg Lukas
+ */
+public class DeliveryReceiptRequest implements PacketExtension
+{
+    public static final String ELEMENT = "request";
+
+    public String getElementName()
+    {
+        return ELEMENT;
+    }
+
+    public String getNamespace()
+    {
+        return DeliveryReceipt.NAMESPACE;
+    }
+
+    public String toXML()
+    {
+        return "<request xmlns='" + DeliveryReceipt.NAMESPACE + "'/>";
+    }
+
+    /**
+     * This Provider parses and returns DeliveryReceiptRequest packets.
+     */
+    public static class Provider implements PacketExtensionProvider {
+        @Override
+        public PacketExtension parseExtension(XmlPullParser parser) {
+            return new DeliveryReceiptRequest();
+        }
+    }
+}