Awesome

Apple Universal Disk Image Format (UDIF/DMG)

Install via npm

$ npm install --save udif

Used by

Etcher to support Apple's disk image format (.dmg)

Related Modules

apple-partition-map – Parse / construct Apple Partition Maps
blockdevice – Read from / write to block devices
disk – Disk / image toolbox

Usage

var UDIF = require( 'udif' )

Opening a .dmg image

var dmg = new UDIF.Image( 'path/to/image.dmg' )

dmg.open( function( error ) {
  // ...
})

Closing the image

dmg.close( function( error ) {
  // ...
})

Determining the uncompressed size

Note that the image has to be opened to determine the uncompressed size, as this is read from the resource fork.

UDIF.getUncompressedSize( 'path/to/image.dmg', function( error, size ) {
  console.log( size, 'bytes' )
  // > 629145600 bytes
})

var dmg = new UDIF.Image( 'path/to/image.dmg' )

dmg.open( function( error ) {
  console.log( dmg.getUncompressedSize(), 'bytes' )
  // > 629145600 bytes
})

Creating a readable stream

var readableStream = UDIF.createReadStream( 'path/to/image.dmg' )

Or, if you already have an instance of UDIF.Image:

var readableStream = dmg.createReadStream()

Extracting the raw disk image

Extracting the uncompressed, raw disk image from a .dmg file becomes as easy as the following:

UDIF.createReadStream( 'path/to/image.dmg' )
  .pipe( fs.createWriteStream( '/path/to/destination.img' ) )

Sparse streams

var sparseStream = UDIF.createSparseReadStream( 'path/to/image.dmg' )

Sparse readstreams are in objectMode and will emit objects of the shape { buffer, position }. This means you'll need a writable stream that is also in objectMode and knows how to handle these. For the sake of brevity, the following example only demonstrates passing a chunk's properties to fs.write();

sparseStream.on( 'data', function( chunk ) {
  fs.writeSync( fd, chunk.buffer, 0, chunk.buffer.length, chunk.position )
})

Using a custom file system

var dmg = new UDIF.Image( 'https://github.com/resin-io/etcher/releases/download/v1.2.0/Etcher-1.2.0.dmg', {
  fs: new HttpFs()
})

dmg.open( function( error ) {
  // ...
})

Inspecting the UDIF footer

The footer (aka the "Koly Block") contains pointers to the XML metadata, data fork & resource fork as well as checksums.

// Once the dmg has been opened:
dmg.open( function( error ) {
  console.log( dmg.footer )
})

KolyBlock {
  signature: 1802464377,
  version: 4,
  headerSize: 512,
  flags: 1,
  runningDataForkOffset: 0,
  dataForkOffset: 0,
  dataForkLength: 6585140266,
  resourceForkOffset: 0,
  resourceForkLength: 0,
  segmentNumber: 1,
  segmentCount: 1,
  segmentId: <Buffer 18 66 9e 31 fa 6 d 4 f 7 d aa d0 f2 50 12 8 f 49 54>,
  dataChecksum: Checksum { type: 2, bits: 32, value: 'c2208200' },
  xmlOffset: 6585140266,
  xmlLength: 1752206,
  reserved1: <Buffer 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ...>,
  checksum: Checksum { type: 2, bits: 32, value: '3f40bb47' },
  imageVariant: 1,
  sectorCount: 15178432,
  reserved2: 0,
  reserved3: 0,
  reserved4: 0,
}

Inspecting the XML Metadata

The XML data is a Property List, (or plist) which contains a block map under resource-fork.blkx.

dmg.open( function( error ) {
  console.log( dmg.resourceFork )
})

{
  blkx: [{
    id: -1,
    attributes: 80,
    name: 'Driver Descriptor Map (DDM : 0)',
    coreFoundationName: 'Driver Descriptor Map (DDM : 0)',
    map: BlockMap {
      signature: 1835627368,
      version: 1,
      sectorNumber: 0,
      sectorCount: 1,
      dataOffset: 0,
      buffersNeeded: 520,
      blockDescriptorCount: 0,
      reserved1: 0,
      reserved2: 0,
      reserved3: 0,
      reserved4: 0,
      reserved5: 0,
      reserved6: 0,
      checksum: Checksum { type: 2, bits: 32, value: '698a85ed' },
      blockCount: 2,
      blocks: [
        Block {
          type: 2147483653,
          description: 'UDZO (zlib-compressed)',
          comment: '',
          sectorNumber: 0,
          sectorCount: 1,
          compressedOffset: 0,
          compressedLength: 22
        },
        Block {
          type: 4294967295,
          description: 'TERMINATOR',
          comment: '',
          sectorNumber: 1,
          sectorCount: 0,
          compressedOffset: 22,
          compressedLength: 0
        }
      ]
    }
  }, {
    id: 0,
    attributes: 80,
    name: 'WINDOWSSUPPORT (Apple_ISO : 1)',
    coreFoundationName: 'WINDOWSSUPPORT (Apple_ISO : 1)',
    map: BlockMap {
      signature: 1835627368,
      version: 1,
      sectorNumber: 1,
      sectorCount: 3,
      dataOffset: 0,
      buffersNeeded: 520,
      blockDescriptorCount: 1,
      reserved1: 0,
      reserved2: 0,
      reserved3: 0,
      reserved4: 0,
      reserved5: 0,
      reserved6: 0,
      checksum: Checksum { type: 2, bits: 32, value: '6c1ce17e' },
      blockCount: 2,
      blocks: [
        Block {
          type: 2147483653,
          description: 'UDZO (zlib-compressed)',
          comment: '',
          sectorNumber: 0,
          sectorCount: 3,
          compressedOffset: 22,
          compressedLength: 24
        },
        Block {
          type: 4294967295,
          description: 'TERMINATOR',
          comment: '',
          sectorNumber: 3,
          sectorCount: 0,
          compressedOffset: 46,
          compressedLength: 0
        }
      ]
    }
  }, {
    id: 1,
    attributes: 80,
    name: 'Apple (Apple_partition_map : 2)',
    coreFoundationName: 'Apple (Apple_partition_map : 2)',
    map: BlockMap {
      signature: 1835627368,
      version: 1,
      sectorNumber: 4,
      sectorCount: 60,
      dataOffset: 0,
      buffersNeeded: 520,
      blockDescriptorCount: 2,
      reserved1: 0,
      reserved2: 0,
      reserved3: 0,
      reserved4: 0,
      reserved5: 0,
      reserved6: 0,
      checksum: Checksum { type: 2, bits: 32, value: '115fc68e' },
      blockCount: 2,
      blocks: [
        Block {
          type: 2147483653,
          description: 'UDZO (zlib-compressed)',
          comment: '',
          sectorNumber: 0,
          sectorCount: 60,
          compressedOffset: 46,
          compressedLength: 358
        },
        Block {
          type: 4294967295,
          description: 'TERMINATOR',
          comment: '',
          sectorNumber: 60,
          sectorCount: 0,
          compressedOffset: 404,
          compressedLength: 0
        }
      ]
    }
  }, {
    id: 2,
    attributes: 80,
    name: 'Macintosh (Apple_Driver_ATAPI : 3)',
    coreFoundationName: 'Macintosh (Apple_Driver_ATAPI : 3)',
    map: BlockMap {
      signature: 1835627368,
      version: 1,
      sectorNumber: 64,
      sectorCount: 2020420,
      dataOffset: 0,
      buffersNeeded: 520,
      blockDescriptorCount: 3,
      reserved1: 0,
      reserved2: 0,
      reserved3: 0,
      reserved4: 0,
      reserved5: 0,
      reserved6: 0,
      checksum: Checksum { type: 2, bits: 32, value: 'b2bb86f8' },
      blockCount: 3948,
      blocks: [
        Block {
          type: 2147483653,
          description: 'UDZO (zlib-compressed)',
          comment: '',
          sectorNumber: 0,
          sectorCount: 512,
          compressedOffset: 404,
          compressedLength: 25147
        },
        Block {
          type: 2147483653,
          description: 'UDZO (zlib-compressed)',
          comment: '',
          sectorNumber: 512,
          sectorCount: 512,
          compressedOffset: 25551,
          compressedLength: 29149
        },
        ... more items
      ]
    }
  }, {
    id: 3,
    attributes: 80,
    name: ' (Apple_Free : 4)',
    coreFoundationName: ' (Apple_Free : 4)',
    map: BlockMap {
      signature: 1835627368,
      version: 1,
      sectorNumber: 2020484,
      sectorCount: 4,
      dataOffset: 0,
      buffersNeeded: 0,
      blockDescriptorCount: 4,
      reserved1: 0,
      reserved2: 0,
      reserved3: 0,
      reserved4: 0,
      reserved5: 0,
      reserved6: 0,
      checksum: Checksum { type: 2, bits: 32, value: '00000000' },
      blockCount: 2,
      blocks: [
        Block {
          type: 2,
          description: 'FREE (unallocated)',
          comment: '',
          sectorNumber: 0,
          sectorCount: 4,
          compressedOffset: 984141554,
          compressedLength: 0
        },
        Block {
          type: 4294967295,
          description: 'TERMINATOR',
          comment: '',
          sectorNumber: 4,
          sectorCount: 0,
          compressedOffset: 984141554,
          compressedLength: 0
        }
      ]
    }
  }, {
    id: 4,
    attributes: 80,
    name: 'Mac_OS_X (Apple_HFS : 5)',
    coreFoundationName: 'Mac_OS_X (Apple_HFS : 5)',
    map: BlockMap {
      signature: 1835627368,
      version: 1,
      sectorNumber: 2020488,
      sectorCount: 13157944,
      dataOffset: 0,
      buffersNeeded: 520,
      blockDescriptorCount: 5,
      reserved1: 0,
      reserved2: 0,
      reserved3: 0,
      reserved4: 0,
      reserved5: 0,
      reserved6: 0,
      checksum: Checksum { type: 2, bits: 32, value: '39ce04b6' },
      blockCount: 25387,
      blocks: [
        Block {
          type: 2147483646,
          description: 'COMMENT',
          comment: '+beg',
          sectorNumber: 0,
          sectorCount: 0,
          compressedOffset: 984141554,
          compressedLength: 0
        },
        Block {
          type: 2147483653,
          description: 'UDZO (zlib-compressed)',
          comment: '',
          sectorNumber: 0,
          sectorCount: 512,
          compressedOffset: 984141554,
          compressedLength: 1812
        },
        ... more items
      ]
    }
  }],
  cSum: [{
    Attributes: '0x0000',
    Data: <Buffer 01 00 02 00 00 00 00 00 00 00>,
    ID: '0',
    Name: null
  }, {
    Attributes: '0x0000',
    Data: <Buffer 01 00 02 00 00 00 10 fc a8 3f>,
    ID: '1',
    Name: null
  }, {
    Attributes: '0x0000',
    Data: <Buffer 01 00 02 00 00 00 10 37 71 ef>,
    ID: '2',
    Name: null
  }],
  nsiz: [{
    Attributes: '0x0000',
    Data: <Buffer 3 c 3 f 78 6 d 6 c 20 76 65 72 73 69 6 f 6e 3 d 22 31 2e 30 22 20 65 6e 63 6 f 64 69 6e 67 3 d 22 55 54 46 2 d 38 22 3 f 3e 0 a 3 c 21 44 4 f 43 54 59 50 45 20 70 ...>,
    ID: '0',
    Name: null
  }, {
    Attributes: '0x0000',
    Data: <Buffer 3 c 3 f 78 6 d 6 c 20 76 65 72 73 69 6 f 6e 3 d 22 31 2e 30 22 20 65 6e 63 6 f 64 69 6e 67 3 d 22 55 54 46 2 d 38 22 3 f 3e 0 a 3 c 21 44 4 f 43 54 59 50 45 20 70 ...>,
    ID: '1',
    Name: null
  }, {
    Attributes: '0x0000',
    Data: <Buffer 3 c 3 f 78 6 d 6 c 20 76 65 72 73 69 6 f 6e 3 d 22 31 2e 30 22 20 65 6e 63 6 f 64 69 6e 67 3 d 22 55 54 46 2 d 38 22 3 f 3e 0 a 3 c 21 44 4 f 43 54 59 50 45 20 70 ...>,
    ID: '2',
    Name: null
  }],
  plst: [{
    Attributes: '0x0050',
    Data: <Buffer 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ...>,
    ID: '0',
    Name: null
  }],
  size: [{
    Attributes: '0x0000',
    Data: <Buffer 05 00 01 00 00 00 00 60 8 c 91 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ...>,
    ID: '2',
    Name: null
  }]
}