Determine if a Volume is a Disk Image (DMG) from code

Question

From Objective C (or Swift), I need to determine if a mounted volume is a Disk Image (mounted from a .dmg file).

Similar questions led me to NSURL Volume Property Keys, but none of them seem to give the type/protocol of the volume.

However, I can see this information with the terminal diskutil function under Protocol:

~/Temp$ diskutil info /dev/disk8
   Device Identifier:        disk8
   Device Node:              /dev/disk8
   Part of Whole:            disk8
   Device / Media Name:      Apple UDIF read-only Media

   Volume Name:              Not applicable (no file system)

   Mounted:                  Not applicable (no file system)

   File System:              None

   Content (IOContent):      GUID_partition_scheme
   OS Can Be Installed:      No
   Media Type:               Generic
   Protocol:                 Disk Image <=== THIS IS WHAT I WANT
   SMART Status:             Not Supported

   Total Size:               5.2 MB (5242880 Bytes) (exactly 10240 512-Byte-Units)
   Volume Free Space:        Not applicable (no file system)
   Device Block Size:        512 Bytes

   Read-Only Media:          Yes
   Read-Only Volume:         Not applicable (no file system)
   Ejectable:                Yes

   Whole:                    Yes
   Internal:                 No
   OS 9 Drivers:             No
   Low Level Format:         Not supported

EDIT: Found some code that at least used to do this, by means of this included category extension to NSWorkspace. However, it is pre-ARC and I'm not sure if it would still work.

Found it via this partial answer on other question..

Mimosaceous

I did not try it, but what about NSURLVolumeIsEjectableKey, perhaps in combination with NSURLVolumeIsRemovableKey ? Just an idea. – Celebration

@MartinR Thanks! However, I think this would also catch removable HD and SSD drives, which are the drives I want to detect. (And right now I'm getting false positives on every dmg installer that I open.) – Mimosaceous

Answer 1

You can obtain this information using the DiskArbitration framework. To use the example below, you must link against and #import it.

#import <DiskArbitration/DiskArbitration.h>

...

- (BOOL)isDMGVolumeAtURL:(NSURL *)url
{

  BOOL isDMG = NO;

  if (url.isFileURL) {

    DASessionRef session = DASessionCreate(kCFAllocatorDefault);
    if (session != nil) {

      DADiskRef disk = DADiskCreateFromVolumePath(kCFAllocatorDefault, session, (__bridge CFURLRef)url);
      if (disk != nil) {

        NSDictionary * desc = CFBridgingRelease(DADiskCopyDescription(disk));
        NSString * model = desc[(NSString *)kDADiskDescriptionDeviceModelKey];
        isDMG = ([model isEqualToString:@"Disk Image"]);

        CFRelease(disk);

      }

      CFRelease(session);

    }

  }

  return isDMG;

}

Usage:

BOOL isDMG = [someObject isDMGVolumeAtURL:[NSURL fileURLWithPath:@"/Volumes/Some Volume"]];

I hope this helps.

Noctiluca

Amazing. The most perfect answer one could hope for on SO: a working function, the needed #import, and an example call. It's up and running in my project now. – Mimosaceous