Develop Reference

How Firebase Push Notification is send to device

I am trying to figure out how Firebase connect to specific devices and send message to it. I now how to use Firebase and send notification to registed devices from my backend server but i don't know how is it working internally. Is firebase severs using persisted connection between device and server? What kind of tehnology is it using?
For now i am mostly interested in Android devices and how firebase wake up device even with background tasks restrictions.

FCM is able to wake a device because the message is actually received by software components that come with Play services, which operates with elevated privileges. Play services can choose to wake the device and deliver the message to the target app.
The FCM software in Play services keeps a persistent socket connection open to its backend under normal circumstances. If it gets connection is dropped, it has logic to reestablish the connection without taxing the battery too much.

I tried to explain how GCM works in my answer here. The internal working principle of Firebase is similar in my opinion.
When you are installing an application which has the Firebase SDK set up in it, it gets a push registration ID from Google server. Usually, you save the push registration ID in your server as well. Hence, when there is a situation for sending a push notification, your server uses this push registration ID to generate a request to the Firebase server for sending a push notification to your device.
Now let us think of the receiver part as well (i.e. your device). In my opinion, in newer versions of Android allows a JobScheduler to check repeatedly for push messages from the Firebase server and if there is one, the device notifies the corresponding application and the application then generates the push notification.
Hope that helps!

Android client to client messaging without my own server for GCM

I am doing a prototype that involves messaging between clients.
What I want to do - from MyApp on device1, able to send message to MyApp on device2. Device2 should receive this and show a notification.
I don't have my own application server to push notifications from GCM to GCM clients.Is this possible ? How to do it ?
What I investigated - PubNub, which has a trial license that seems to answer my need to send messages on a channel without needing a server.
This discussion at SO didn't help much.
sending client to client messages without server interaction
Can anyone suggest better ways ?

You basically have to use a server in one way or another. I think Firebase would be perfect for your purposes. It has an Android plugin you can use that will basically alert your app when something changes in the database. Here is the documentation for that feature. Take a look at this example for implementation. Before you can use the plugin, you need to create an account and whatnot (basic one is free). Here are the instructions.

PubNub Realtime Messaging and Push Notifications
(server not required)
With PubNub, you do not need your own server to do the realtime messaging or the mobile push notifications. You likely have your own server for your database (MySQL or similar, traditional RDBMS, a No SQL DB like MongoDB, or a realtime DB sync, like Firebase) to authenticate users and such.
For realtime DB or non-DB type change notifications and signaling (any type of realtime messaging), PubNub makes is super simple to receive messages in realtime with a mobile push notification fallback in one publish action. So the GCM message will be sent along with the realtime message. If the app is actively running, you get it in realtime (< 1/4 on average - typically faster) and the GCM message will be received if the app is not active (background or not started at all).
And PubNub's free plan is not a trial (anymore). It is free (including all add-ons) for as long as you stay within the free plan limits.
See the PubNub Android docs for more details and contact PubNub support if you have any further questions with getting started or getting answers to any questions you have as you progress with your app implementation.

Another possibility is to use the SMS.
Android Send and Recieve Messages
"Send Binary (Data) SMS
We can send binary messages (as opposed to text based messages that we covered earlier) to specific application ports using sendDataMessage(). According to this Stack Exchange thread data sms is one which is sent over 2G/3G as well as GSM. I’ve tested it with mobile data turned off and it works fine charging me the same amount, so not very sure on whether it uses 2G/3G or not, but generally the term data is used in telephony when it’s related to network (tcp/ip). Anyway, SMS’s are generally sent to a specific port on the device (which is probably port 0 [zero]). But using sendDataMessage() we can send SMS’s to some other random port on which our app can listen for incoming SMSs and do something with that. In this case the default messaging app will not store the SMSs in their inbox for both the sender as well as the receiver.
"

Latter Delivery Ack. from GCM to App server?

I am using GCM for Chat App. If User is Offline(not Connected to App but internet is active) then i Send push notification to devices It receive perfectly.
But when Device is totally offline(neither connected to App and nor active internet) at that time GCM send me response like { id: XXXXXXXX,success: 3,failure: 2{message_id:xxxxx,ect:..}} on my App server.
two device are totally offline they don't have active internet connection..
when device will connect to internet GCM Send them message.
but how can my App server will Know that Message is delivered by GCM.
I Search a lot but can't get any satisfied answer.
I tried that on messageRecive at client device(Android device) i will send httpRequest to my App server but it not suitable for my app it makes App very slow.
So Question is how Can i know that my failure 2 message are delivered.

First of all, you do not need to update your app server in case of a downstream message after it is sent to GCM Server. As explained here, GCM server stores the message in case of an offline device and delivers it once the device is online.
(Now assuming that what you want is to handle network tasks on the client)
You can use GcmNetworkManager to batch network discovery and connectivity related tasks across the system through Play Services. Go through the documentation.
You can use GCM Statistics and Diagnostics from Google Play Developer Console, too. This gives you details of messages handled by a particular app (through Registration token) down to status of specific messages (through message IDs). More explanation here.
(However I am not too clear exactly what you want)
EDIT
but how can my App server will Know that Message is delivered by GCM.
Sorry, reading through again I realised this is the real question. Answer is pretty straight forward here.
.

notification , Server to Client

I was developing an android app and a server that serve this apps. The server was coded in cakePHP. I want the app to have a notification from the server when there is an update on whatever things. Is this notification function a Server to client connection ? For example the facebook , whatapps and other social app in smart phone that could receive notification when someone send you a message, tagged you etc.
What is the proper way of doing this? I just need an idea to start. I see someone suggesting to open a long establish connection from client to check whether there is an update, but this would drain the phone battery.
If it's a Server to client connection, how would the server know where to find the client?

Google cloud messaging would seem to be the best option here; https://developer.android.com/google/gcm/index.html
As it says on the tin; "Google Cloud Messaging for Android (GCM) is a service that allows you to send data from your server to your users' Android-powered device, and also to receive messages from devices on the same connection"
xtify seems to also support what you are asking but I've no experience with it.
Although depending on your particular requirements there are other options available.
If the client only needs to get notifications when active you could have it check the server every X number of seconds for updates when it is not asleep or even when the user does a particular action. Of course this all depends on what you want to happen.
edit: Heres a good article/tutorial with code samples https://blog.serverdensity.com/android-push-notifications-tutorial/

How to achieve reliable push message service?

Since I want to build reliable communication in mobile apps, could I get push failed reports(maybe device is offline) from the third party push services (C2DM, APN, urban airship) ?
Or We need to build it by ourselves?

The intended purpose of Android C2DM is to be a battery-saving way for your server app to signal the mobile device that it wants to start reliable communications.
You can structure your message so that each new C2DM encompasses everything that has occurred since the last two-way interaction with the server (i.e., "come and get whatever I've got"). Your failed delivery report is implicit in the mobile device not responding promptly (you can do this because you know C2DM activates your app with an Intent).
Is that really any worse than guaranteed delivery of each message in a lossy medium? Okay, it's worse in that you also have to implement a primary communication method. But you had to do that anyway because C2DM is inbound-only, right?

As Vinay says, MQTT may offer you the feature you desire. When a client connects to the server, it can register a "last will and testament" message with the server. If the client disconnects unexpectedly, the server sends this message to the topic it was instructed to do.
In this scheme, your client could send a message "online" to something like client//status and register the message "offline" as a LWT for the same topic. You could then have a server local client that listened to the topic client/+/status and it would know which clients were online and which offline.
I would suggest that the tokudu demo isn't the best place to look. This blog post by Dale Lane gives insight into using MQTT on Android: http://dalelane.co.uk/blog/?p=1599 and there is a review of MQTT power usage (again on Android) at http://stephendnicholas.com/archives/219
There are client implementations to suit both IOS and Android, see http://mqtt.org/software

No one service does not provide reports about failed pushes.
Failed push report makes little sence with APN/C2DM/Helium
All services are aimed to deliver the push-message under all circumstances.
If device is offline now, then push will be delivered when device becomes online.
Moreover, for iOS push-message is just a notification for a user, not for an application!
Simple case will illustrate it:
Assume that push is received when the application is turned off. In that case, notification for the user will occur. But, application will receive data from push, only if user taps on that notification! If user will tap on application's icon, then data will not be received.
So techically, push is delivered to the iOS device and application is started, but data is not delivered.
UrbanAirhip with APN and Helium
You can consider to implement your own transport for pushes. MQTT seems to be a good option.
But in this case, you have to deal with keepalives, device sleeps and battery optimisations.
All that hard work is already done by engineers from Apple, Google and UrbanAirship.
Depending on your business needs, it can be easier to adapt your architecture for existing solutions, then reimplement push-service again.
Take a closer look to UrbanAirship. In fact, C2DM has some limitations and sometimes timings for delivery of push-message is too big. Because of that UA has implemented their own transport - Helium, it works pretty good. Helium is a paid service, but UA provides good SLA.

I am suggesting for push notification IBM MQTT protocol. This fine enough for push notification.
see the demo from https://github.com/tokudu/AndroidPushNotificationsDemo

I did something similar where I had a database keep track of push queues to known subscribers and had reporting when failed. It was very simple and went something like this...
The schema was like so:
pushMessages
messageID , GUID, PK
message , nvarchar (256),
expires , datetime
messageQueues
subscriberID , GUID, PK
messageID , GUID PK
failedPushMessages
subscriberID, GUID, PK
messageID , GUID PK
(subscriber table omitted)
Once a client received the message successfully, the client would ping back to the push server and notify it via the unique queueItems ID that it received on the push notification. There would also be a daily database process that would check for expired push messages. When found, it would do a join on the queueMessages matching the messageID then remove them from the messagesQueues table and copy them to the failedPushMessages table.
This was very easy to understand and maintain but I don't have experience doing it another way.

Push Services are an efficient and reliable way to alert your users. They allow even background applications to inform users of new information in real-time. Push Services are widely used for a variety of fields in mobile applications, such as weather updates, messaging services, mail notification, coupon services, and so on. Push Services are no longer optional but have become essential.