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64 bytes from 69.39.89.150: icmp_seq=4 ttl=50 time=35.685 ms

64 bytes from 69.39.89.150: icmp_seq=5 ttl=50 time=35.667 ms

64 bytes from 69.39.89.150: icmp_seq=6 ttl=50 time=36.435 ms

64 bytes from 69.39.89.150: icmp_seq=7 ttl=50 time=52.296 ms

64 bytes from 69.39.89.150: icmp_seq=8 ttl=50 time=36.142 ms

64 bytes from 69.39.89.150: icmp_seq=9 ttl=50 time=36.188 ms

--- www.bignerdranch.com ping statistics ---

10 packets transmitted, 10 packets received, 0% packet loss

round-trip min/avg/max/stddev = 34.546/37.313/52.296/5.021 ms

If you want to end the program prematurely, press Control-C to send it a sigint signal. This will cause it to write out the stats and terminate.

iPing

Now you are going to write a Cocoa app that uses NSTask to run ping (Figure 36.6).

Figure 36.6. Completed Application

In Xcode, create a new project, iPing, of type Cocoa Application. Set the Class Prefix to iPing. Uncheck Create Document-Based Application. In iPingAppDelegate, add two outlets, pointers to the NSTask and the NSPipe, and an action:

@interface iPingAppDelegate : NSObject {

IBOutlet NSTextView *outputView;

IBOutlet NSTextField *hostField;

IBOutlet NSButton *startButton;

NSTask *task;

NSPipe *pipe;

}

@property (assign) IBOutlet NSWindow *window;

- (IBAction)startStopPing:(id)sender;

@end

Open MainMenu.xib and drop a text view, a text field, and a button onto the window. The button should be put in Toggle mode. The title should be Start Ping (Figure 36.7), and the alternate title should be Stop Ping. Set the state to Off.

Figure 36.7. Button Attributes

Make the iPingAppDelegate the target of the button; its action should be startStopPing:. Set the outputView, hostField, and startButton outlets to point to the text view, the text field, and the button, respectively (Figure 36.8).

Figure 36.8. Object Diagram

In iPingAppDelegate.m, implement startStopPing:

- (IBAction)startStopPing:(id)sender

{

// Is the task running?

if (task) {

[task interrupt];

} else {

task = [[NSTask alloc] init];

[task setLaunchPath:@"/sbin/ping"];

NSArray *args = [NSArray arrayWithObjects:@"-c10",

[hostField stringValue], nil];

[task setArguments:args];

// Create a new pipe

pipe = [[NSPipe alloc] init];

[task setStandardOutput:pipe];

NSFileHandle *fh = [pipe fileHandleForReading];

NSNotificationCenter *nc;

nc = [NSNotificationCenter defaultCenter];

[nc removeObserver:self];

[nc addObserver:self

selector:@selector(dataReady:)

name:NSFileHandleReadCompletionNotification

object:fh];

[nc addObserver:self

selector:@selector(taskTerminated:)

name:NSTaskDidTerminateNotification

object:task];

[task launch];

[outputView setString:@""];

[fh readInBackgroundAndNotify];

}

}

While the task is running, the file handle will be posting notifications when data is ready. Implement the method that will get called:

- (void)appendData:(NSData *)d

{

NSString *s = [[NSString alloc] initWithData:d

encoding:NSUTF8StringEncoding];

NSTextStorage *ts = [outputView textStorage];

[ts replaceCharactersInRange:NSMakeRange([ts length], 0)

withString:s];

}

- (void)dataReady:(NSNotification *)n

{

NSData *d;

d = [[n userInfo] valueForKey:NSFileHandleNotificationDataItem];

NSLog(@"dataReady:%ld bytes", [d length]);

if ([d length]) {

[self appendData:d];

}

// If the task is running, start reading again

if (task)

[[pipe fileHandleForReading] readInBackgroundAndNotify];

}

When the process is done, we should do some cleanup:

- (void)taskTerminated:(NSNotification *)note

{

NSLog(@"taskTerminated:");

task = nil;

[startButton setState:0];

}

Build and run the application.

Challenge: .tar and .tgz files

A listing of files in a zip file is given by zipinfo. You can get a similar listing for tar files by using the command-line tool tar:

# /usr/bin/tar tf MyFiles.tar

If the tar file is also compressed, just add a z to the flags:

# /usr/bin/tar tzf MyFiles.tgz

Extend ZIPspector to deal