Help needed closing NSPipe

Scripting Forums AppleScriptObjC and Xcode
#1

I’m working on an app that creates compressed disk images using dd and gzip. I have set up a working pipe between dd and gzip NSTask’s but I cannot figure out how to close the pipe. When the dd process completes, the pipe stays open and gzip continues to wait for more data. How can I close the pipe or the pipe’s fileHandleForWriting so that gzip receives the EOF it needs to terminate successfully?

Here’s a working abridged copy of the app code:

script AppDelegate
	property parent : class "NSObject"
    property NSPipe : class "NSPipe"
    property NSNotificationCenter : class "NSNotificationCenter"
    
    property ddTask : missing value
    property gzipTask :missing value
    property applicationPipe : missing value
    property pipeHandle : missing value
    property appTargetFileForWriting : missing value
    
    property theButton : missing value
	
	-- IBOutlets
	property theWindow : missing value
	
	on applicationWillFinishLaunching_(aNotification)
		-- Insert code here to initialize your application before any files are opened 
	end applicationWillFinishLaunching_
	
    on buttonClicked_(sender)
        log "button click registered"
        theButton's setEnabled_(0)
        
        set fileManager to current application's NSFileManager's defaultManager()
        try
            fileManager's createFileAtPath_contents_attributes_("/tmp/test.img.gz", missing value, missing value)
            log "target file created"
        on error
            log "file creation error"
        end try
        
        try
            set appTargetFileForWriting to current application's NSFileHandle's fileHandleForWritingAtPath_("/tmp/test.img.gz")
            log "target file handle set"
        on error
            log "error creating file handle"
        end try
        
        set ddTask to current application's NSTask's alloc()'s init()
        set applicationPipe to NSPipe's pipe()
        ddTask's setLaunchPath_("/bin/dd")
        ddTask's setArguments_({"bs=4k","count=1000","if=/dev/random"})
        ddTask's setStandardOutput_(applicationPipe)
        NSNotificationCenter's defaultCenter()'s addObserver_selector_name_object_(me, "ddTerminationHandler:", "NSTaskDidTerminateNotification", ddTask)
        
        set gzipTask to current application's NSTask's alloc()'s init()
        gzipTask's setLaunchPath_("/usr/bin/gzip")
        gzipTask's setArguments_({"--verbose"})
        gzipTask's setStandardInput_(applicationPipe)
        gzipTask's setStandardOutput_(appTargetFileForWriting)
        NSNotificationCenter's defaultCenter()'s addObserver_selector_name_object_(me, "gzipTaskTerminationHandler:", "NSTaskDidTerminateNotification", gzipTask)
        
        ddTask's |launch|()
        gzipTask's |launch|()
        
    end buttonClicked_
    
    on ddTerminationHandler_(aNotification)
        log "DD task completed"
        --Close pipe here?
        NSNotificationCenter's defaultCenter()'s removeObserver_name_object_(me, "NSTaskDidTerminateNotification", missing value)
    end ddTerminationHandler_
    
    on gzipTaskTerminationHandler_(aNotification)
        log "gzip task completed"
        appTargetFileForWriting's closeFile()
        theButton's setEnabled_(1)
        NSNotificationCenter's defaultCenter()'s removeObserver_name_object_(me, "NSTaskDidTerminateNotification", missing value)
    end gzipTaskTerminationHandler_
    
    on applicationShouldTerminateAfterLastWindowClosed_(sender)
        return true
    end applicationShouldTerminateAfterLastWindowClosed_
    
	on applicationShouldTerminate_(sender)
        return current application's NSTerminateNow
	end applicationShouldTerminate_
	
end script

Sorry for the multiple posts. Was having network issues and must have created them trying to refresh the submission page.

#2

The first thing you need to do is fix how you’re using properties. If you declare a property x, you set its value using “set my x…”. If you leave out the my, you just create a local variable of the same name.

And I can’t fathom what this line is trying to do:

set applicationPipe to current application's NSFileHandle's fileHandleForWriting()'s closeFile()

Apart from the above problem, fileHandleForWriting is a pipe method, not a file handle method.

#3

And where you say “Close pipe here?”, you probably want:

my applicationPipe's fileHandleForWriting()'s closeFile()
#4

Whoops. That was something I was testing. I’ve removed it from the code above.

EDIT:
Found the problem.

The following code in ddTask’s termination handler kills the all the termination handlers so “on gzipTaskTerminationHandler_(aNotification)” never runs.

NSNotificationCenter's defaultCenter()'s removeObserver_name_object_(me, "NSTaskDidTerminateNotification", missing value)

Should probably use something like this instead:

NSNotificationCenter's defaultCenter()'s removeObserver_name_object_(me, "NSTaskDidTerminateNotification", my ddtask)