Updated Whisper Push Notifications (markdown)

Whisper-Push-Notifications.md

@@ -62,6 +62,9 @@ var newChatSessionTopic = '0x509579a2'; // NEW_CHAT_SESSION
 var ackNewChatSessionTopic = '0xd012aae8'; // ACK_NEW_CHAT_SESSION
 var newDeviceRegistrationTopic = '0x14621a51'; // NEW_DEVICE_REGISTRATION
 var ackDeviceRegistrationTopic = '0x424358d6'; // ACK_DEVICE_REGISTRATION
+var checkClientSessionTopic = '0x8745d931'; // CHECK_CLIENT_SESSION
+var confirmClientSessionTopic  = '0xd3202c5f'; // CONFIRM_CLIENT_SESSION
+var dropClientSessionTopic = '0x3a6656bb'; // DROP_CLIENT_SESSION
 ```
 
 Finally, in order to test everything out, you'd better use two different clients not one. So, assume that we have two nodes (`Device A` and `Device B`) which have different underlying Status daemons:
@@ -390,6 +393,65 @@ We provide all the code for `Device B` in a single chunk. Basically, all that `D
 
 ### 4. Checking subscription status and unsubscribing
 
+```js
+var checkClientSessionTopic = '0x8745d931'; // CHECK_CLIENT_SESSION
+var confirmClientSessionTopic  = '0xd3202c5f'; // CONFIRM_CLIENT_SESSION
+var dropClientSessionTopic = '0x3a6656bb'; // DROP_CLIENT_SESSION
+var removeClientSession = function () {
+    var checkClientSession = function (callback) {
+        // before sending request, let's start waiting for response
+        var filter = web3.shh.filter({
+            to: identity,
+            topics: [confirmClientSessionTopic]
+        });
+        filter.watch(function (error, result) {
+            if (!error) {
+                // response will be in JSON, e.g. {"server": "0xdeadbeef", "key": "0xdeadbeef"}
+                var payload = JSON.parse(web3.toAscii(result.payload));
+                console.log("Client session confirmation received: ", result, payload);
+
+                // no need to watch for the filter any more
+                filter.stopWatching();
+
+                callback(payload)
+            }
+        });
+
+        // send enquiry to all servers, to learn whether we have a client session with any of them
+        var err = web3.shh.post({
+            from: identity,
+            to: protocolKey,
+            topics: [checkClientSessionTopic],
+            ttl: 20
+        });
+        if (err !== null) {
+            console.log("message NOT sent")
+        } else {
+            console.log("message sent OK")
+        }
+    };
+
+    checkClientSession(function (payload) {
+        console.log("time to cleanup: ", payload.server);
+        console.log("session key: ", payload.key);
+
+        setTimeout(function () {
+            // notify server that you want to unsubscribe
+            var err = web3.shh.post({
+                from: identity,
+                to: protocolKey,
+                topics: [dropClientSessionTopic],
+                ttl: 20
+            });
+            if (err !== null) {
+                console.log("message NOT sent")
+            } else {
+                console.log("message sent OK")
+            }
+        }, 5000); // let's all other concurrent tasks to wrap up
+    });
+};
+```
 
 # Complete Sample