OSX Receipt validation in Swift, part 5: The Device GUID

During receipt verification there is a point where we need the device GUID, a unique identifier for the Mac.On OS-X this is the MAC address of the primary network card. You can read about this here: https://developer.apple.com/library/ios/releasenotes/General/ValidateAppStoreReceipt/Chapters/ValidateLocally.html#//apple_ref/doc/uid/TP40010573-CH1-SW14
If that link is stale, try searching for "validating receipts locally" that should get you to the necessary article.

In that article there is a code example that shows you how to read the GUID. There is IMO little sense in translating it to Swift, so I suggest that you grab the code from Apple and create an Objective-C header/implementation pair of files as follows:

The Objective-C header file:

//

//  deviceGuid.h

//

#ifndef MyGreatApp_deviceGuid_h

#define MyGreatApp_deviceGuid_h

#import <Foundation/Foundation.h>

CFDataRef copy_mac_address(void);

#endif

The Objective-C implementation file:

//

//  deviceGuid.m

//

#import "deviceGuid.h"

#import <IOKit/IOKitLib.h>

// Returns a CFData object, containing the computer's GUID.

CFDataRef copy_mac_address(void)

{

    kern_return_t             kernResult;

    mach_port_t               master_port;

    CFMutableDictionaryRef    matchingDict;

    io_iterator_t             iterator;

    io_object_t               service;

    CFDataRef                 macAddress = nil;

    

    kernResult = IOMasterPort(MACH_PORT_NULL, &master_port);

    if (kernResult != KERN_SUCCESS) {

        // printf("IOMasterPort returned %d\n", kernResult);

        return nil;

    }

    

    matchingDict = IOBSDNameMatching(master_port, 0, "en0");

    if (!matchingDict) {

        // printf("IOBSDNameMatching returned empty dictionary\n");

        return nil;

    }

    

    kernResult = IOServiceGetMatchingServices(master_port, matchingDict, &iterator);

    if (kernResult != KERN_SUCCESS) {

        // printf("IOServiceGetMatchingServices returned %d\n", kernResult);

        return nil;

    }

    

    while((service = IOIteratorNext(iterator)) != 0) {

        io_object_t parentService;

        

        kernResult = IORegistryEntryGetParentEntry(service, kIOServicePlane,

                                                   &parentService);

        if (kernResult == KERN_SUCCESS) {

            if (macAddress) CFRelease(macAddress);

            

            macAddress = (CFDataRef) IORegistryEntryCreateCFProperty(parentService,

                                                                     CFSTR("IOMACAddress"), kCFAllocatorDefault, 0);

            IOObjectRelease(parentService);

        } /* else {

            printf("IORegistryEntryGetParentEntry returned %d\n", kernResult);

        }*/

        

        IOObjectRelease(service);

    }

    IOObjectRelease(iterator);

    

    return macAddress;

}

As you can see, I removed the printing parts as I don't want that.

Since the Foundation headers are needed, the above code must be placed in Objective-C files and not as C files. If C files are used, the compiler will complain about "Could not build module Foundation".

The above operation returns either 'nil' or a pointer to the appropriate CFData object. In Swift this can be used as follows:

let guidDataOrNil = copy_mac_address()

if guidDataOrNil == nil {

    println("Could not retrieve the device GUID")

    exit(errorCode)

}

let guidData: NSData = guidDataOrNil.takeRetainedValue()

log.atLevelDebug(id: 0, source: "Main", message: "Device GUID retrieved OK")

Note the "takeRetainedValue". In Xcode the editor shows that the function returns the type "Unmanaged<CFData>" (in accordance with the Apple approach that an object returned by a "Create" API has a retain count of 0). The CFData is toll-free bridged to a NSData, but we need to retain the object so that ARC can delete it when it is no longer needed.

Next up, part 6: Example Swift code for receipt validation & verification

Happy Coding...

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