Question

Is there a sample project showing how to use APNS on the IPhone and how to set up things? I’m currently looking at the documentation but it would be nice to have some working code to pick apart and see how it all works together?

I can’t seem to find anything using google or in the iphone dev center.

Answer 1

The worst part about setting up the push notification service is the provisioning. The major stumbling block that I came across was that there is a certificate and a key in the .cer file you download from Apple’s site, I wrote a system service in C# that sent out notifications and the connections kept failing because I had exported the certificate and not the key.

I don’t recall who originally wrote this, here is a little bit of code in python that helped me out when I was first testing the notification service. I like it because it is very simple and works well during testing.

import socket, ssl, json, struct

# device token returned when the iPhone application
# registers to receive alerts

deviceToken = 'XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX' 

thePayLoad = {
     'aps': {
          'alert':'Oh no! Server\'s Down!',
          'sound':'k1DiveAlarm.caf',
          'badge':42,
          },
     'test_data': { 'foo': 'bar' },
     }

# Certificate issued by apple and converted to .pem format with openSSL
# Per Apple's Push Notification Guide (end of chapter 3), first export the cert in p12 format
# openssl pkcs12 -in cert.p12 -out cert.pem -nodes 
#   when prompted "Enter Import Password:" hit return
#
theCertfile = 'cert.pem'
# 
theHost = ( 'gateway.sandbox.push.apple.com', 2195 )

# 
data = json.dumps( thePayLoad )

# Clear out spaces in the device token and convert to hex
deviceToken = deviceToken.replace(' ','')
byteToken = bytes.fromhex( deviceToken ) # Python 3
# byteToken = deviceToken.decode('hex') # Python 2

theFormat = '!BH32sH%ds' % len(data)
theNotification = struct.pack( theFormat, 0, 32, byteToken, len(data), data )

# Create our connection using the certfile saved locally
ssl_sock = ssl.wrap_socket( socket.socket( socket.AF_INET, socket.SOCK_STREAM ), certfile = theCertfile )
ssl_sock.connect( theHost )

# Write out our data
ssl_sock.write( theNotification )

# Close the connection -- apple would prefer that we keep
# a connection open and push data as needed.
ssl_sock.close()

There’s also a rails gem called apn_on_rails that seems to work pretty well if you’re developing a rails application, I just saw it today and was able to send out notifications from the console.

On the iPhone side you’ll just need to call the following to register for all types of notifications:

[[UIApplication sharedApplication] registerForRemoteNotificationTypes: UIRemoteNotificationTypeBadge | UIRemoteNotificationTypeSound | UIRemoteNotificationTypeAlert];

To receive the device token you’ll need to implement the following delegate methods:

- (void)application:(UIApplication *)application didRegisterForRemoteNotificationsWithDeviceToken:(NSData *)deviceToken

- (void)application:(UIApplication *)application didFailToRegisterForRemoteNotificationsWithError:(NSError *)error

During testing you can just kick the deviceToken to the console with NSLog, then paste it into the python script above, in production you’ll obviously need to set up some method to get the token to your servers.

Also, in production you’ll need to query Apple’s feedback service and remove device tokens from users who removed your app.