Bonjour Programming on the iPhone, Part I

Bonjour is Apple's implementation of the Zeroconf protocol, which enables the automatic discovery of computers, devices and services on an IP network. In this article, you will learn how to implement Bonjour on the iPhone by using the NSNetService class to publish a service. You will also use the NSNetServiceBrowser class to discover services that have been published. In the next article, you will learn how to communicate with another device that you have discovered using TCP/IP.

Creating the Project

Using Xcode, create a View-based Application project and name it as Bonjour.

Double-click on the BonjourViewController.xib file and populate the View window with the following views (see Figure 1):

* Text Field
* Round Rect Button
* Label
* Table View
* Text View

Figure 1: Populating the View window with the various views.

In the BonjourViewController.h file, add the following statements in bold:

#import <UIKit/UIKit.h>

@interface BonjourViewController : UIViewController {
    //---outlets---
    IBOutlet UITableView *tbView;
    IBOutlet UITextField *message;
    IBOutlet UITextView *debug;
}

//---expose the outlets as properties---
@property (nonatomic, retain) UITableView *tbView;
@property (nonatomic, retain) UITextField *message;
@property (nonatomic, retain) UITextView *debug;

//---actions---
-(IBAction) btnConnect:(id)sender;
-(IBAction) btnSend:(id)sender;
-(IBAction) doneEditing;

@end

In the BonjourViewController.xib window, perform the following connections:

* Control-click the File's Owner item and drag and drop it over the Text Field view. Select message.
* Control-click the File's Owner item and drag and drop it over the Table View. Select tbView.
* Control-click the File's Owner item and drag and drop it over the Text View. Select debug.
* Control-click the Send button and drag and drop it over the File's Owner item. Select btnSend:.
* Control-click the Connect button and drag and drop it over the File's Owner item. Select btnConnect:.
* Right-click on the Text Field view and connect the Did End on Exit event to the File's Owner item. Select doneEditing:.
* Right-click on the Table View and connect the dataSource outlet to the File's Owner item.
* Right-click on the Table View and connect the delegate outlet to the File's Owner item.

To verify that all the connections are made correctly, right-click on the File's Owner item and view its connections (see Figure 2).

Figure 2: Verifying that all the connections are made correctly.

Publishing a Service

With all the views and actions wired up, let's start by seeing how you can publish a service.

In the BonjourAppDelegate.h file, add the following statements in bold:

#import <UIKit/UIKit.h>

@class BonjourViewController;

@interface BonjourAppDelegate : NSObject <UIApplicationDelegate> {
    UIWindow *window;
    BonjourViewController *viewController;

    //---use this to publish a service---    
    NSNetService *netService;
}

@property (nonatomic, retain) IBOutlet UIWindow *window;
@property (nonatomic, retain) IBOutlet 
    BonjourViewController *viewController;

@end

Basically, you will use the NSNetService class to publish your presence on the network.

In the BonjourAppDelegate.m file, add the following statements in bold:

#import "BonjourAppDelegate.h"
#import "BonjourViewController.h"

@implementation BonjourAppDelegate

@synthesize window;
@synthesize viewController;

- (void)applicationDidFinishLaunching:(UIApplication *)application {    
    [window addSubview:viewController.view];
    [window makeKeyAndVisible];    
    
    //---publish the service---
    netService = [[NSNetService alloc] 
 

                

;    initWithDomain:@"" 
 

                

;              type:@"_My

Service._tcp." 
 

                

;              name:@"" 
 

                

;              port:9876]

;
    netService.delegate = self;
    [netService publish];    
}

-(void)netService:(NSNetService *)aNetService 
    didNotPublish:(NSDictionary *)dict {
    NSLog(@"Service did not publish: %@", dict);
}

- (void)applicationWillTerminate:(UIApplication *)application {
    //---stop the service when the application is terminated---
    [netService stop];
}

- (void)dealloc {
    [netService release]; 
    [viewController release];
    [window release];
    [super dealloc];
}

@end

Here, you advertise your presence on the network by publishing a network service when your application has finished launching (applicationDidFinishLaunching:). You publish a network service by passing several parameters to the NSNetService class:

    netService = [[NSNetService alloc] 
 

                

;    initWithDomain:@"" 
 

                

;              type:@"_My

Service._tcp." 
 

                

;              name:@"" 
 

                

;              port:9876]

;

The first argument specifies the domain for the service. You use @"" to denote the default domain. The second argument indicates the service type and transport layer. In this example, I named the service as MyService and it uses TCP. Note that you need to prefix the service name and protocol with a "_" and end the protocol with a ".". The third argument specifies the name of the service, which must be a unique name (I have used an empty string in this case). Finally, specify the port number on which the service is published via the fourth argument.

You also implemented the netService:didNotPublish: method so that in the event the service is not published successfully, you will write a message to the debugger console.

When the application exits (applicationWillTerminate:) you will stop publishing the service.

Browsing for Services

Now that you have seen how to publish a service, let's see how you can browse for services that have been published on the network.

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