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I have developed a simple two player chess game in android to be played using Bluetooth. I want to extend it by making it possible to be played through internet. whenever a player makes a move, the move should be transferred to the other player via internet.

How to make this possible?

I have heard of C2DM mechanism.Does that suites the scenario i described and is it reliable?

Thanks:)

kannappan
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androidGuy
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  • One other possibility is port-directed SMS. I am only starting to use them, though, so I can't really talk about the caveats. – tugs Jun 16 '11 at 16:36

9 Answers9

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Yes, C2DM is ideally suited to this type of game. This is what I am using for my own game (http://www.chesspresso.net) which is a correspondence chess client for android.

Things to consider when using C2DM:

  • You don't send the info to the devices, you notify the devices that a move has been made. You don't use C2DM to transfer data, you use it to notify that something has changed.

  • Its available for 2.2+ Android, which is the majority of devices. But if you wanted to support older devices you'd have to consider an alternative. I am using polling for older devices.

  • You have to request for developer access, then once your app is ready you have to request production status. If you don't do this you'll hit the developer status quota very quickly once its released! They are very generous with production quota, but you have to explain what you're using it for and it also can take a few weeks to get accepted!

  • Your users will have to have a google account that is authorised, otherswise C2DM won't work. Most users will have an account associated with their device, but some don't so this means that you'll possibly want to validate for the presence of an account to notify the user.

  • Its reliable, but every now and again a device will have to wait for the message. Sometimes a few minutes. Usually its instant.

Hope that helps!

UPDATE: C2DM has now been deprecated, and replaced by Google's GCM.

Also, I strongly suggest looking at other options as tying yourself down to a Google specific API means you won't be able to support external marketplaces. For alternatives, I am currently evaluating Amazon SNS and I will also be looking at Urban Airship. There are possibly other alternatives I have not considered evaluating yet.

UPDATE: Evaluation update of non google based push notifications: Amazon SNS is just not a project for this task and Urban Airship for the vast majority of apps is too expensive. Unfortunately all the other alternatives are all very expensive also, especially if your app (like mine) relies heavily on push.

Eurig Jones
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  • "You don't use C2DM to transfer data, you use it to notify that something has changed.", What is the reason for this? Why not transfer data with C2DM? – Pking Feb 08 '12 at 06:22
  • Just read that "C2DM makes no guarantees about delivery or the order of messages. So, for example, while you might use this feature to tell an instant messaging application that the user has new messages, you probably would not use it to pass the actual messages.", I guess that answers my question. – Pking Feb 08 '12 at 09:59
  • I use it basically to tell the device what it needs to fetch. You only have 1KB to play with. – Eurig Jones Feb 08 '12 at 10:53
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A good way of doing that is using a simple direct TCP connection between the peers.

If you're new to socket programming on Java, try this:

All About Sockets

DallaRosa
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    Wat if one device is behind a NAT? The IP Address will not be be visible publicly?How to deal with it? – androidGuy Jun 10 '11 at 06:48
  • In that case I would recommend the user buy internet access. – vipw Jun 16 '11 at 09:25
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    @vipw:I tried to connect two device over 3G connection, the problem was IP address is changing so frequently that it is impossible to establish a connection. – androidGuy Jun 16 '11 at 09:37
  • Sorry for the late response. I had in mind a very local and point-to-point solution in my answer. An easy way to do what you want is using a server to be the middleman between the devices. You could then use polling or some push technology (like C2DM) to check for updates. Just don't forget that C2DM requires registration and is only supported by 2.2+ devices. – DallaRosa Jun 22 '11 at 00:12
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Another option is to use some sort of IM as a communication medium for app. For eg. Use Asmack to connect to XMPP Im like GTalk. Prompt user to create an account there, for your game. And use it to send and receive commands via IM. This way you won't need to setup your mediating server.

This works if user knows who he is playing with. To collect the user data and let them search for available players, you still need to setup a server. IRC chat room may be an option to avoid this also.

  • GTalk was just an example. You can use any IM or IRC also.
Aniket Awati
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  • Thanks Aniket,I have been trying smack api with openfire server for past few days.I finished setting up of openfire server and successfully sent messages between two users.The problem now is how to retrieve the list of users registered in openfire.I need this info to display it for the users playing the game so that they can add them as frnds.Iam using embedded db of openfire server.Do u now how to access this database and retrieve all the users in openfire server:) – androidGuy Jun 23 '11 at 07:42
  • sorry, no idea about openfire dude. :) – Aniket Awati Jun 23 '11 at 11:53
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C2DM it's not design to transfer informations, even if they are small like "horse in b4" or things like this. It's designed to inform the device of something, maybe a newer version of a document or more articles on a website.. Stuff like this.. It's not designed to communicate device to device. And also it may be not fast enough for a real time chess play.

You should look for a more traditional way of communicate via internet or to search for some libraries (I'm pretty sure that something exists..) that will help you.

Marco Grassi
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IMHO, C2DM is exactly the kind of thing you would want for a chess game; to be notified when the oppo has made his turn (which may be minutes /hours / days later ?). I have discussed my game with a few google android devs and they've stated that C2DM is ideal for this. You'll need to go via a centralised server though (well, not essential but very advisable) as there may be issues with resync'ing game state etc. Worried about "hitting the limit" ? Well, for a start my c2dm acct is restricted to "just" 100,000 messages per day. I guess you're buying the drinks if you hit that !!

Richard Green
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  • Thanks,the reliability of C2DM is my concern.What kind of game did u develop, was that turn based game like chess?what was the delay in C2DM? – androidGuy Jun 16 '11 at 09:54
  • The game is called "Barcode Beasties". I currently use a god-awful "http link through google talk" to do in game messaging... It was an absolute pain to get working on 1.x AND 2.x devices (don't talk to me about intent filters!!!) but I finally got it going and ... that week.. Google announced C2DM. GAAAAAAHHHHH!!!!! Anyway .. the delay is measurable in MICROSECONDS.. If the c2dm message doesn't get to the phone in under a second, that's slow ! I don't know the exact figure but I would guess around 0.5 - 0.7 seconds is average. The c2dm version is in testing and will be released vvv soon btw. – Richard Green Jun 16 '11 at 13:04
  • Oh and reliability... I have never lost a correctly sent c2dm message to date *however* for a chess game I would (just for belt and braces) offer a user prompted sync option as well - I would imagine you would need something like that for <2.2 phones anyway. – Richard Green Jun 16 '11 at 13:07
  • Last post from me : If you want to see c2dm in action, the download an app I've written called "Vera Alert" - market.android.com/details?id=com.fawepark.veralert - and then fire off an http request like this : vera-alert.appspot.com/stat?msg=Hello&recipient=XXXXX where XXXXX is the code presented to you when you start the app. I have written this app so people can link their home automation system with their phone for near-immediate alerting if a pre-determined event occurs in their home, but you can use it to see c2dm in action if you need to. – Richard Green Jun 16 '11 at 15:36
  • +1 I agree that C2DM is the right way to go in this situation. If you want to test its speed before you implement it, try out Chrome 2 Phone on your Android device. I use it in my app for messaging purposes, and it is incredibly fast. Also, the connection is always alive anyway, so it does not use any extra battery power to have it active. – Glendon Trullinger Jun 16 '11 at 21:48
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Chess is often played by email. You could do that.

Of course, any centralized/federated messaging system will work.

What might be better for your use is to add a jabber client to the application and have the program generate an account name that is used for automated messaging. You could host the jabber server or generate the accounts on a free provider.

vipw
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    Thanks,can u give me some useful links on jabber client and server? – androidGuy Jun 16 '11 at 09:51
  • http://stackoverflow.com/questions/3092534/good-tutorials-on-xmpp and http://stackoverflow.com/questions/177514/good-xmpp-java-libraries-for-server-side – Hussain Jun 16 '11 at 12:07
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Google App Engine if you know Python or Java.

Alternatively there are two web app API styles in wide use today: SOAP XML and RESTful web services.

If you know RoR I would recommend using JSON/REST, because you can just use Phusion Passenger with Apache to deploy your app. Free, extremely easy, and makes your server very reliable.

You could, and I only mention this because my friends do this all the time, use twitter as a server between the games.

I also found a lib called mages which looks quite promising.

Good luck.

expelledboy
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I did this for my online 2D rpg: http://developingthedream.blogspot.com

Basically, use a middle-man server to co-ordinate data between all your clients. You simply open a socket and communicate with the middle server and it takes care of passing on the information to any other connected clients.

I wouldn't recommend C2DM because of the message limit, and because the latency is still to big. Using your own server you can optimize it, plus you'll be the only one using the service so your data will be delivered faster.

Miguel Morales
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I think that C2DM is not right way for playing chess because there is no warranty that messages will be delivered. You need more reliable way for data transfer

mobiledev Alex
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