Android GCM : understanding XMPP

问题

I'm trying to implement a XMPP protocol in my GCM using app, but even after searching extensively, I don't understand the concepts behind it.

Also, maybe I don't really need XMPP for what I want to do with my app, but I like to learn things.

Let's take this example of what I could do with HTTP :

1. my app send "hello word" and the regId to my little personnal server : url.openConnection(""), then OutputStream for sending POST data and InputStream for getting the response

2. the server, at this url, put the "hello word" message in a database with the regId, and then use the curl library of php to send data to GCM servers as a json string like {"myResponse":"I'm not world I'm Dan"} (using a test destinator id, in an emulator)

3. GCM server do his business

4. my app (maybe on another phone) use an IntentService in a WakefulBroadcastReceiver that get the message as intent.getExtras().getString("myResponse")

This works well and I could send messages from one phone to another using my app, and collecting data on my server the way through.

Very little Question

Is this way of handling HTTP ok theorically ? (I saw a lot of posts and tutorials, especially Google ones, but still not sure)

Big real Question

What are the steps to do the same with XMPP ?

I don't want a tutorial or pieces of codes, I want to understand the way the info goes through this protocol I don't know well (I managed to install ejabberd on my server and use pidgin on my PC and Xabber on my phone).

回答1:

Official definition:

The Google Cloud Messaging (GCM) Cloud Connection Server (CCS) is an XMPP endpoint that provides a persistent, asynchronous, bidirectional connection to Google servers.

Establishing a connection with CCS is the first and most important step here. Once you are done with this and maintain a long-lived connection, other parts are not that tricky.

Some differences between the two:
1) Unlike HTTP, with XMPP messages you do not need to include Authentication headers with every payload since server is authenticated at the time of connecting and we are maintaining the same connection.
2) CCS uses XMPP as a Transport Layer and therefore after you have successfully established connection you can exchange stanzas.
3) You could keep using HTTP for downstream though and use XMPP only for upstream if you wish.
4) Instead of registration_ids param use to: in XMPP and we can only send to one RegID through one stanza.

So if I were to explain how your example would work with XMPP:
- Establish a connection with CCS
- Send an upstream message to your server from the client "Hello, World!"
- Acknowledge once your server receives this message by sending ACK to GCM
- For downstream message you have choice of using either of HTTP or XMPP
- But if XMPP: receive, save in database and when sending response ({"myResponse":"I'm not world I'm Dan"}) back to the client (same or different RegID) send a downstream stanza to CCS; CCS will send ACK/NACK to acknowledge that it has received the message
- You will also receive delivery_receipt (if requested) once the client app has received the message.

Other than this, you can understand more in depth by reading the official documentation which I have linked throughout the post.

Hope this helps!

来源：https://stackoverflow.com/questions/33826148/android-gcm-understanding-xmpp