[aerogear-dev] Sync on Android

[Summers Pittman]

TL;DR; Watch this repo over the next few days :

https://github.com/secondsun/aerogear-sync-server/tree/xmpp-diff-sync

Currently I am researching integrating the sync client technology that 
DanBev, LolQuist et al have been working on into Android all proper 
like.  Danbev wrote a POC demo a while ago* which uses the Java 
websocket client.  This seems to work "OK" but there is a lot of work 
getting websockets working right on Android.  However, Google has a two 
way messaging protocol built into Google Play Services on top of GCM.  
This is the technology I am trying to introduce to the sync systems in 
this branch.

This branch includes a fork of the server library and a fork of the 
client library which interact with GCM on the client and XMPP on the 
server side.  Right now it compiles and not much else.  However, because 
the server is decoupled from the connection handling, adding in the 
correct hooks has been rather simple.  There are going to be some issues 
to hammer out once this gets past "compiling" and makes it into "demoable".

First, the server does not receive implicit connect/disconnect messages 
from Google per device.  Google does send Ack/Nack messages however so 
with some bookkeeping connections/shadows/etc can be properly 
maintained.    There is a similar mechanism on the client side; however, 
we may need to expand the sync protocol to include some kind of heartbeat.

Second, the sync server isn't multitenant.  This means that until we 
figure out how to merge, things listening to WebSockets don't hear 
things listening to XMPP or see updates from one to the other.

Finally, Google Play Services is not FOSS by any stretch of the 
imagination.  However, having a single connection managed by the OS is 
great for usability, speed of development, battery life, etc so I feel 
like this is more getting mileage out of the chunk of my soul I tossed 
in the black Googley shredder for UPS and less of a deal breaker.

As I've said right now, today, this code is work in progress.  Soon it 
will be proof of concept and we can discuss how to work around these 
issues and merge the ideas back into mainline.


-- 
Summers Pittman
>>Phone:404 941 4698
>>Java is my crack.

PS: WebSocket's biggest problems are maintaining connections and 
performing message redelivery in a sporatic connection scenario. This is 
one of those things which is a lot of work to get right both on our end 
as service providers and on the developer's end as consumers.  
Additionally, Android L is going to include a lot more end user 
configurability which will affect when/how messages are delivered.  To 
do WebSockets right we will have to respect those settings as well.  It 
is my assumption (we all know what that means) that Google Play Services 
will correctly enforce data/power settings out of the box as well as 
correctly maintain messaging connections and delivery.