From my understanding you cannot socket a connection between two iPhones (correct me if I'm wrong). So what I would like to do is have one server sitting between the client application that accepts messages and redistributes them to the appropriate person(s). Essentially the application is going to allow people to have a shared map that has their locations and everyone can annotate it.
1) I have been reading and researching into the CFStream class, but I'm curious to know if it might be better to just use the C send() and recv() functions. They almost seem much easier to use. What does CFStream offer over the native C socket functions that make it a better option?
2) Since I need the phone to actively listen for updated shared user locations/new annotations from other users, my plan was to periodically have the phone poll the server for any "news" from other users (say every minute or two). Is there anyway the phone could spin off a new thread in the application that is constantly waiting for incoming traffic? It would make life easier to be able to have a user annotate the map, push that to the server which then immediately updates the appropriate users maps.
I have been using example socket code from Jonathan Zdziarski's iPhone SDK book from O'Rielly Media to just try sending messages between a server and iPhone emulator (the classic knock knock joke server/client). However, after sending 1 or 2 messages the server gets stuck "receiving." The code runs perfectly when not sent from an emulator, as I can seemly spam the client send function and get a response from the server each time. Could the server be hanging because I use send() and recv() instead of the CFRead and Write stream?
You can socket iPhone applications using bonjour, or even GameKit (which is what I use because it manages all data for you).
Related
I have an Arduino based device interfaced to a 3G modem which I use to record data from several sensors in a remote environment. I would like to be able to send commands and stream some data from the device every now and then back to my standard network connected PC. If the remote device was connected to a WIFI or other local area network this would be relatively straightforward, but as the device connects over 3G this means that it is behind the 3G carriers NAT and so establishing a connection to the device becomes difficult.
The device can, of course, open a TCP connection to my host PC any time it wishes, the problem is telling the device when i want it to do so. I need some way of getting some kind of message to the device to notify it that I would like it to initiate a connection to my PC.
I've been reading up on NAT traversal techniques that app developers use to initiate P2P comms between 2 devices both behind NATs such as UDP and TCP 'hole punching' but this method seems rather too complex for my arduino system. Another general idea is to have the device polling a web server periodically looking for a signal to initiate a connection, but I'm not sure how much traffic (and data usage costs) this would generate as the device would have to poll every 10 seconds or so in order to make sure it initiates it's connection within a reasonable time frame of the request being set on the web server that it polls.
Is there any commonly used method of achieving something like this? Any general ideas or insight would be much appreciated
Thanks,
James
I think the solution will depend largely on your particular applications and requirements.
There are several ways to achieve this type of functionality and it looks like you have covered some of them already. The most common are:
have the device poll the server. This may be ok depending on the response times you need. If you need to poll as regularly as you suggest above then I imagine power may be more important to you than data rates, especially if you are battery connected. With a typical 3G data plan the polling itself will have a negligible data overhead, I would think.
have the server send a SMS which then triggers the device to contact the server. You need to make sure the SMS variable delivery time is ok for you and you also have to be aware that SMS delivery is not guaranteed so you would have to build in some sort of check for delivery at a higher layer (or into your application).
use some low cost Android based device for your 3G connectivity and leverage the Google push notifications mechanism
It is worth noting that server polling typically gets very bad press as it is seems intuitively wasteful to have the client and the server constantly checking for messages, especially when the actual messages are fairly infrequent. However, underneath most push solutions there is still a pull mechanism in the background, albeit generally a very efficient one that may, for example, piggy back on other messages between the network and the mobile device and hence have minimal power and data overhead. Personally, I would say that if you do not have major concerns with battery/power or with the load polling might generate for your servers, then it is worth exploring if the simplicity benefits of a polling solution outweigh its other disadvantages.
How do applications know when new data is available on a server? For example, Facetime or skype knowing when a call is coming in, iMessage knowing when a new text is available, etc. I know the client is not just continually polling the server over and over again, so how is this done normally?
Such protocols send a real-time notification to the client telling it what is happening.
I have an idea of an application that involves a "chat feature", basically an ability for people to chat with each other. Since sending messages through a server would be slow (plus it would be pretty bad having to check the server every second if you have new messages) I want to use sockets to have peer to peer chat ability instead of going through a server.
My 2 questions:
1) Is socket programming the most optimal way to develop a chat program? I know there is push notification service, but I don't think it can be used for a chat program too well. Going through a server seems kind of bad if you imagine 5,000 people chatting and having to poll the server every second.
2) Will Apple have issues approving an app that has peer to peer chat program that uses sockets?
Thank you.
Sockets are indeed appropriate. But you are better off with a client/server approach rather than a P2P approach.
Having worked on a very well known instant messaging service for many years, I can tell you absolutely that going through a server is not slow - as long as your server is not slow.
Client/server has lots of advantages. Namely, it's not as difficult as any sort of P2P connectivity where such issues as NATs and Firewalls make direct socket connections difficult and unreliable. Besides, you would need a messaging service anyway for clients to exchange IP addresses.
Your stated assumption that a client or server would have to "poll" is not how scalable systems work. You should use a persistent TCP socket and look at scaling a socket service up though any of the available async methods that exist today. select(), poll(), epoll on Linux, and IO Completion Ports on Windows are all techniques for having thousands of sockets simultaneously connected without periodic polling.
My suggestion - just deploy an XMPP/Jabber server. Most implementations scale up nicely to the thousands of clients. Then your chat program is just an XMPP client socket. Some of the Jabber servers even support HTTP connectivity for situations where a user's only access is via an http or http proxy server. I played around with Openfire a while back and was reasonably impresseed.
I'm fairly certain that iOS has sockets, and that it's allowed by Apple. I only know via second hand from folks that have worked on iOS products. You probably shouldn't use the push notification service for anything more than notifications to wake up your app that there is something it needs to do.
Hope this helps.
I want to write an iOS app that can act as a client and a server to other iPhones over the cellular data network (i.e., without a typical centralized server). The goal is to share series of about 200 short event messages, one at a time, from the iPhone server to multiple iPhone clients by some means of notification. Apple Push Notification service would be fine for such notifications, but there is no need to use it specifically.
I think sending push notifications from one iPhone to another is possible by connecting to gateway.push.apple.com from the serving iPhone as described in the Local and Push Notification Programming Guide, but I can't find anyone else discussing this approach (maybe it's too obvious?).
The reason for all this is an attempt to avoid the overhead of infrastructure. If this isn't feasible, alternatives which minimize or avoid additional hardware are welcome.
Requirements:
Communication must be [strictly] over cellular data network
Wi-Fi isn't available
Bluetooth doesn't have enough range
Unidirectional communication with an iPhone server multicasting to many iPhone clients
No jailbreaking
Ideally the serving phone's battery will be able to handle this without a recharge
Update 5/4/11 2:12 AM EST: Just to be clear, I don't have any particular requirement to use APNs; I thought it may have been feasible in this setup, but from the discussion below, it sounds like that's not the case. However, I'm still interested in any other system that could help me achieve the same end result with some type of message passing or similar form of communication.
Theoretically you should be able to write a iOS app that can connect to the APNS and send notifications to other devices running your applications. However, your main problem will be to actually acquire the 'tokens' of other devices. When you have a centralized server doing the job, its always online and thus, the clients can 'talk' to it via http and register them self (giving their tokens to the server in the process). Thus the server knows the client token and it can use them to send notifications to the clients via APNS.
However this is not possible in the scenario you are talking about. But this is not to say its impossible. May be you could use an email account X, to store all client tokens. Every client will send a email to this account with their token in it. So when a another 'client' want to send a notification to another client, it can find out the token by reffering to the inbox of the email account (you can cache this stuff and optimize it in a zillion ways of course).
But the point is some how a (third party(ex: email service provider)/your own) server that is online 24/7 will be involved in the process.
Let us know how you progress with this. It would be interesting to know.
I'm looking for a best-practice for the following scenario:
A Mobile Device (iOS) sends its (Sensor-)Data to another device (iPad, Laptop, PC, whatever) over the Internet in realtime.
Sure, I need a web service but as far as my understanding is, a webservice gets "called" and returns Data or takes Data. But I require a constant exchange of sensor data between two devices in nearly realtime. I'm looking to implement something like a Multiplayer Online Game, how do they do such a thing? Or the Glympse service?
"Just because it's called GameKit doesn't mean its uses are limited to games. Any data you want to pump through that connection is fair game"
How true. The name GameKit is such a terrible misnomer, which very unfortunately diminishes it's significance, there are so much in this kit that you can do to develop serious apps.
The way I'd approach it is to create a "server" out there on the net, that would run some application (like a CGI script) to collect the data (store it, in maybe a database) - then allow the remote device to query it.
This means that every device has a "well-known service" which they are connecting to - potentially "logging into" - and selecting the data from.
For example, each "client" could push their "vessel name" and GPS location. The CGI script on the server would just put these in a MySQL database - as simple table containing "Vessel name" and "Location".
Alternativiley, clients could query and "pull" GPS locations for a specific vessel name. As simple CGI script that would take "Vesel Name" as a value, and send a MySQL query to the database to return the "Location". It could send the location (and vessel name) back in XML format.
The iPhone client could user NSXMLParser - or even a JavaScript "AJAX" client could use it's own inherent XML parsing capabilites to send a request for one (or more) vessels, and receive the results.
What you don't want to do is to have each client have to speak directly to each other client. This will get you into trouble with firewall rules, and mess up when you try to scale many-to-many communications.
If your devices are both running iOS, you can use the peer-to-peer connectivity functions in GameKit for this. There's a pretty good question and answer about that here.
Just because it's called GameKit doesn't mean its uses are limited to games. Any data you want to pump through that connection is fair game (so to speak).
You may use XMPP protocol to send/receive any xml data in almost realtime.
You will need to create chat room and every XMPP client (your app) will just need to login to that room. Message that is sent to the room will be delivered to every XMPP client.
Info on protocol and public servers can be found here: http://xmpp.org/
Good book on XMPP: http://download.cnet.com/XMPP-The-Definitive-Guide/3000-20412_4-75114351.html
Link to free iOS XMPP library can be found here: iOS messenger SDK