Providing VoIP Services

冷不防 2022-08-22 11:23 23阅读 0赞

## This last one is a very powerful background mode, as it allows your app to run arbitrary code while in the background. This mode is better than the “Whatever” API because you can run the code for an indefinite amount of time. Better yet, if the app crashes or the user reboots the phone, the app is started automatically in the background. Very nice! ##

The catch is that, again, your app needs to provide the user with some sort of VoIP functionality or, you guessed it, Apple will reject you. Well, not*you*, of course, but your app.

[![worthwhileperson][]][worthwhileperson 1]

Building a VoIP app is way beyond the scope of this tutorial, but I’ll try to illustrate the principles at least. VoIP, of course, stands for Voice-over-IP or internet telephony. For the tutorial, you’ll build a simple app that connects to a server, keeps the connection open while in the background and gets callbacks when the app receives something through that connection.

To begin, open *TBFifthViewController.m* and add these property declarations to the top:

<table> 
 <tbody> 
 <tr> 
 <td> <pre><code>@property (nonatomic, strong) <a href="http://developer.apple.com/documentation/Cocoa/Reference/Foundation/Classes/NSInputStream_Class/" rel="nofollow">NSInputStream</a> *inputStream;
@property (nonatomic, strong) <a href="http://developer.apple.com/documentation/Cocoa/Reference/Foundation/Classes/NSOutputStream_Class/" rel="nofollow">NSOutputStream</a> *outputStream;
@property (nonatomic, strong) <a href="http://developer.apple.com/documentation/Cocoa/Reference/Foundation/Classes/NSMutableString_Class/" rel="nofollow">NSMutableString</a> *communicationLog;
@property (nonatomic) BOOL sentPing;</code></pre> </td> 
 </tr> 
 </tbody> 
</table>

Also define a few string constants that you’ll use as commands in your connection. Add this code right before`@implementation TBFifthViewController`:

<table> 
 <tbody> 
 <tr> 
 <td> <pre><code>const uint8_t pingString[] = "ping\n";
const uint8_t pongString[] = "pong\n";</code></pre> </td> 
 </tr> 
 </tbody> 
</table>

To start the implementation, here’s a convenience method that adds events to the text view. You’ll use this extensively to indicate when the connection is completed, if it’s broken or when something is received. Add this code anywhere in your class:

<table> 
 <tbody> 
 <tr> 
 <td> <pre><code>- (void)addEvent:(<a href="http://developer.apple.com/documentation/Cocoa/Reference/Foundation/Classes/NSString_Class/" rel="nofollow">NSString</a> *)event
{ 
 [self.communicationLog appendFormat:@"%@\n", event];
 if (UIApplication.sharedApplication.applicationState == UIApplicationStateActive)
 { 
 self.txtReceivedData.text = self.communicationLog;
 }
 else
 { 
 NSLog(@"App is backgrounded. New event: %@", event);
 }
}</code></pre> </td> 
 </tr> 
 </tbody> 
</table>

Simple enough. It appends to the string and updates the UI if the app is active, or just logs to the console if in the background.

Now add the implementation for `didTapConnect:`, which gets called when the user taps the Connect button to start things off:

<table> 
 <tbody> 
 <tr> 
 <td> <pre><code>- (IBAction)didTapConnect:(id)sender
{ 
 if (!self.inputStream)
 { 
 // 1
 CFReadStreamRef readStream;
 CFWriteStreamRef writeStream;
 CFStreamCreatePairWithSocketToHost(NULL, (__bridge CFStringRef)(self.txtIP.text), [self.txtPort.text intValue], &amp;readStream, &amp;writeStream);
&nbsp;
 // 2
 self.sentPing = NO;
 self.communicationLog = [[<a href="http://developer.apple.com/documentation/Cocoa/Reference/Foundation/Classes/NSMutableString_Class/" rel="nofollow">NSMutableString</a> alloc] init];
 self.inputStream = (__bridge_transfer <a href="http://developer.apple.com/documentation/Cocoa/Reference/Foundation/Classes/NSInputStream_Class/" rel="nofollow">NSInputStream</a> *)readStream;
 self.outputStream = (__bridge_transfer <a href="http://developer.apple.com/documentation/Cocoa/Reference/Foundation/Classes/NSOutputStream_Class/" rel="nofollow">NSOutputStream</a> *)writeStream;
 [self.inputStream setProperty:NSStreamNetworkServiceTypeVoIP forKey:NSStreamNetworkServiceType];
&nbsp;
 // 3
 [self.inputStream setDelegate:self];
 [self.outputStream setDelegate:self];
 [self.inputStream scheduleInRunLoop:[<a href="http://developer.apple.com/documentation/Cocoa/Reference/Foundation/Classes/NSRunLoop_Class/" rel="nofollow">NSRunLoop</a> currentRunLoop] forMode:NSDefaultRunLoopMode];
 [self.outputStream scheduleInRunLoop:[<a href="http://developer.apple.com/documentation/Cocoa/Reference/Foundation/Classes/NSRunLoop_Class/" rel="nofollow">NSRunLoop</a> currentRunLoop] forMode:NSDefaultRunLoopMode];
&nbsp;
 // 4
 [self.inputStream open];
 [self.outputStream open];
&nbsp;
 // 5
 [[UIApplication sharedApplication] setKeepAliveTimeout:600 handler:^{ 
 if (self.outputStream)
 { 
 [self.outputStream write:pingString maxLength:<a href="http://www.opengroup.org/onlinepubs/009695399/functions/strlen.html" rel="nofollow">strlen</a>((char*)pingString)];
 [self addEvent:@"Ping sent"];
 }
 }];
 }
}</code></pre> </td> 
 </tr> 
 </tbody> 
</table>

This looks a little complicated because you’re creating a two-way stream.

1.  The easiest way to do so is by using the `CFStreamCreatePairWithSocketToHost` function. That means a lot of bridging to be able to use the`NSInputStream` and `NSOutputStream` classes afterwards.
2.  After you create the stream pair with `CFStreamCreatePairWithSocketToHost`, you bridge them to the appropriate Objective-C classes. The`setProperty:forKey:` method call is really important here, as it indicates to the OS that this connection should be maintained even when the app is not the foreground app. You only need to do this for the input stream.
3.  Next, you set the controller object as the delegate and you set the run loop to be the main run loop for both streams. The OS needs to know in which run loop it should call the delegate methods, and the best run loop in this case is the one associated with the app’s main thread. You’ll want to update the UI when you get a message and you need to be in the main run loop for that.
4.  After this, the streams are configured and you only need to call `open` on both.
5.  The final thing you do in the code above is specific to VoIP apps. With the call to`setKeepAliveTimeout:handler:` you can set a handler that will be called periodically while the app is in the background. This allows your app to do anything, but it should be used to send a “ping” to your server to keep the connection alive. You’ve configured it to be called every 10 minutes – the minimum value allowed for this method, according to the documentation. All you’re doing here is sending a ping command to the server and logging the event.

Now you need to add the stream delegate that will receive updates for the connection. Add this code anywhere in your class:

<table> 
 <tbody> 
 <tr> 
 <td> <pre><code>#pragma mark - NSStreamDelegate
&nbsp;
- (void)stream:(<a href="http://developer.apple.com/documentation/Cocoa/Reference/Foundation/Classes/NSStream_Class/" rel="nofollow">NSStream</a> *)aStream handleEvent:(NSStreamEvent)eventCode
{ 
 switch (eventCode) { 
 case NSStreamEventNone:
 // do nothing.
 break;
&nbsp;
 case NSStreamEventEndEncountered:
 [self addEvent:@"Connection Closed"];
 break;
&nbsp;
 case NSStreamEventErrorOccurred:
 [self addEvent:[<a href="http://developer.apple.com/documentation/Cocoa/Reference/Foundation/Classes/NSString_Class/" rel="nofollow">NSString</a> stringWithFormat:@"Had error: %@", aStream.streamError]];
 break;
&nbsp;
 case NSStreamEventHasBytesAvailable:
 if (aStream == self.inputStream)
 { 
 uint8_t buffer[1024];
 NSInteger bytesRead = [self.inputStream read:buffer maxLength:1024];
 <a href="http://developer.apple.com/documentation/Cocoa/Reference/Foundation/Classes/NSString_Class/" rel="nofollow">NSString</a> *stringRead = [[<a href="http://developer.apple.com/documentation/Cocoa/Reference/Foundation/Classes/NSString_Class/" rel="nofollow">NSString</a> alloc] initWithBytes:buffer length:bytesRead encoding:NSUTF8StringEncoding];
 stringRead = [stringRead stringByTrimmingCharactersInSet:[<a href="http://developer.apple.com/documentation/Cocoa/Reference/Foundation/Classes/NSCharacterSet_Class/" rel="nofollow">NSCharacterSet</a> newlineCharacterSet]];
&nbsp;
 [self addEvent:[<a href="http://developer.apple.com/documentation/Cocoa/Reference/Foundation/Classes/NSString_Class/" rel="nofollow">NSString</a> stringWithFormat:@"Received: %@", stringRead]];
&nbsp;
 if ([stringRead isEqualToString:@"notify"])
 { 
 UILocalNotification *notification = [[UILocalNotification alloc] init];
 notification.alertBody = @"New VOIP call";
 notification.alertAction = @"Answer";
 [[UIApplication sharedApplication] presentLocalNotificationNow:notification];
 }
 else if ([stringRead isEqualToString:@"ping"])
 { 
 [self.outputStream write:pongString maxLength:<a href="http://www.opengroup.org/onlinepubs/009695399/functions/strlen.html" rel="nofollow">strlen</a>((char*)pongString)];
 }
 }
 break;
&nbsp;
 case NSStreamEventHasSpaceAvailable:
 if (aStream == self.outputStream &amp;&amp; !self.sentPing)
 { 
 self.sentPing = YES;
 if (aStream == self.outputStream)
 { 
 [self.outputStream write:pingString maxLength:<a href="http://www.opengroup.org/onlinepubs/009695399/functions/strlen.html" rel="nofollow">strlen</a>((char*)pingString)];
 [self addEvent:@"Ping sent"];
 }
 }
 break;
&nbsp;
 case NSStreamEventOpenCompleted:
 if (aStream == self.inputStream)
 { 
 [self addEvent:@"Connection Opened"];
 }
 break;
&nbsp;
 default:
 break;
 }
}</code></pre> </td> 
 </tr> 
 </tbody> 
</table>

This method takes care of every possible event that might happen with the connection. Most of them are simple and self-explanatory.

The `NSStreamEventHasBytesAvailable` condition usually occurs in the input stream, but it should be checked anyway. You read the buffer into a string, trim the newline and then log the whole thing.

Then comes the fun part: if the event is “notify”, you schedule a local notification. In a real VoIP app, this would correspond to an incoming call so that the notification gets shown even if the app is running in the background.

If the command is “ping”, you send a “pong” response to the server.

You call `NSStreamEventHasSpaceAvailable` when there’s space in the output buffer to send data. When you get this for the first time and only for the first time, you send a ping command to the server.

To get this running, of course you need to add the *App provides Voice over IP services* background mode to Info.plist:

![Screenshot\_20\_1\_13\_8\_56\_PM][Screenshot_20_1_13_8_56_PM]

Before you run the app, you need a server with which to test it. You can use a handy little utility every Mac already has called*netcat* that, among other things, allows you to easily create simple text-based servers. Open a Terminal session (from the*Applications/Utilities/Terminal.app* app) and type this command:

This starts a server on port 10000 and starts listening for a connection. Now go back to Xcode and run the app:

![Screenshot\_4\_29\_13\_2\_32\_PM][Screenshot_4_29_13_2_32_PM]

If you’re running on the Simulator, you can leave the address as 127.0.0.1. If you’re testing on a device, you might need to find out the address of your Mac on your network and change the value of the*Address* field to your Mac’s IP.

Now click *Connect*. You should see a ping come up in your console when the connection is established.

In your Terminal console, type *ping* and hit return. You should see a pong being sent back from the app. If you send something other than “ping”, for example*xxxxx*, then the app does not send a response.

![Screenshot\_1\_28\_13\_2\_46\_AM][Screenshot_1_28_13_2_46_AM]

Also try the *notify* command. You’ll need to run on a device, as notifications don’t work on the Simulator.

If you hit the home button and send a ping command on the Terminal, you should still see a pong response. And if running on the device, trying sending it the notify command when the app is in the background and you should see the notification:

![photo][]

That’s the fifth, most powerful background mode calling. Use it wisely!

The GitHub repository tag for this point in the tutorial is [ BackgroundVoIP][BackgroundVoIP].

## Where to Go From Here? ##

You can [ download the full project][download the full project] with all of the source code from the above tutorial here.

If you want to read Apple’s documentation on what we covered here, the best place to start is in[Background Execution and Multitasking][]. This documentation explains every background mode and has links to the appropriate section of the documentation for every mode.

A particularly interesting section of this document is the one that talks about[being a responsible background app][]. There are some details that might or might not relate to your app here that you should know before releasing an app that runs in the background.

I hope you enjoyed the tutorial. You’re now ready to go off on your own and create wonderful things with whichever of the background modes are useful for your purposes.

Remember the whole project is in [ my GitHub][my GitHub] so download it, fork it, fix any bugs and have fun!

[worthwhileperson]: /images/20220722/627783ade80d435f93bcd4c66b7cacb7.png
[worthwhileperson 1]: http://www.raywenderlich.com/wp-content/uploads/2013/04/worthwhileperson.png
[Screenshot_20_1_13_8_56_PM]: /images/20220722/9ef708afde89452b9b4d2b625117945b.png
[Screenshot_4_29_13_2_32_PM]: /images/20220722/410c22073d924c0c9bf96d6eb17fbcc1.png
[Screenshot_1_28_13_2_46_AM]: /images/20220722/3ef0d5a405374dd28afd534845203f26.png
[photo]: /images/20220722/ca77b20500804dab9906de99c76b7272.png
[BackgroundVoIP]: https://github.com/gpambrozio/TheBackgrounder/tree/BackgroundVoIP
[download the full project]: http://www.raywenderlich.com/wp-content/uploads/2013/04/TheBackgrounder-final.zip
[Background Execution and Multitasking]: http://developer.apple.com/library/ios/documentation/iPhone/Conceptual/iPhoneOSProgrammingGuide/ManagingYourApplicationsFlow/ManagingYourApplicationsFlow.html#//apple_ref/doc/uid/TP40007072-CH4-SW20
[being a responsible background app]: http://developer.apple.com/library/ios/documentation/iPhone/Conceptual/iPhoneOSProgrammingGuide/ManagingYourApplicationsFlow/ManagingYourApplicationsFlow.html#//apple_ref/doc/uid/TP40007072-CH4-SW47
[my GitHub]: https://github.com/gpambrozio/TheBackgrounder