cool struct access method, soon to die
This commit is contained in:
Elliot Nunn
commit
0a3d4e70ef
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import struct
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import copy
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def _split_bnode(buf, start):
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"""Slice a btree node into records, including the node descriptor"""
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ndFLink, ndBLink, ndType, ndNHeight, ndNRecs = struct.unpack_from('>LLBBH', buf, start)
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offsets = list(reversed(struct.unpack_from('>%dH'%(ndNRecs+1), buf, start+512-2*(ndNRecs+1))))
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starts = offsets[:-1]
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stops = offsets[1:]
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records = [bytes(buf[start+i_start:start+i_stop]) for (i_start, i_stop) in zip(starts, stops)]
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return ndFLink, ndBLink, ndType, ndNHeight, records
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def _join_bnode(buf, start, ndFLink, ndBLink, ndType, ndNHeight, records):
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buf[start:start+512] = bytes(512)
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next_left = 14
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next_right = 510
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for r in records:
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if next_left + len(r) > next_right - 2: raise ValueError('cannot fit these records in a B*-tree node')
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buf[start+next_left:start+next_left+len(r)] = r
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struct.pack_into('>H', buf, start+next_right, next_left)
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next_left += len(r)
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next_right -= 2
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struct.pack_into('>H', buf, start+next_right, next_left) # offset of free space
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struct.pack_into('>LLBBH', buf, start, ndFLink, ndBLink, ndType, ndNHeight, len(records))
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def _deser_btree(buf, start):
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"""Walk an HFS B*-tree, returning an iterator of (key, value) tuples.
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Only leaf nodes are used. Housekeeping data is ignored.
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"""
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# Get the header node
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ndFLink, ndBLink, ndType, ndNHeight, (header_rec, unused_rec, map_rec) = _split_bnode(buf, start)
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# Ask about the header record in the header node
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bthDepth, bthRoot, bthNRecs, bthFNode, bthLNode, bthNodeSize, bthKeyLen, bthNNodes, bthFree = \
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struct.unpack_from('>HLLLLHHLL', header_rec)
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this_leaf = bthFNode
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while True:
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ndFLink, ndBLink, ndType, ndNHeight, records = _split_bnode(buf, start+512*this_leaf)
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for rec in records:
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key = rec[1:1+rec[0]]
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val = rec[1+rec[0]:]
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yield key, val
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if this_leaf == bthLNode:
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break
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this_leaf = ndFLink
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def _ser_btree(buf, start, stop, btree_dict):
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pass
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# the above two functions should make this way easier!
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# hell... can I just read the catalog file into a dict, and then
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# dump it back when finished? With lazy back-and-forth?
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def _from_tuple(val):
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if len(val) == 1:
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return val[0]
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else:
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return val
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def _to_tuple(val):
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if isinstance(val, tuple):
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return val
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else:
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return (val,)
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def _field(offset, fmt, doc=''):
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fget = lambda self: _from_tuple(struct.unpack_from(fmt, self.buf, offset))
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fset = lambda self, val: struct.pack_into(fmt, self.buf, offset, _to_tuple(val))
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prop = property(fget, fset)
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if doc:
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prop.__doc__ = doc
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return prop
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def _mobilefield(offset, fmt, doc=''):
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fget = lambda self: _from_tuple(struct.unpack_from(fmt, self.buf, self.structoffset+offset))
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fset = lambda self, val: struct.pack_into(fmt, self.buf, self.structoffset+offset, _to_tuple(val))
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prop = property(fget, fset)
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if doc:
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prop.__doc__ = doc
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return prop
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class HFS:
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bbID = _field(0, '>H', doc='boot blocks signature')
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bbEntry = _field(2, '>L', doc='entry point to boot code')
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bbVersion = _field(6, '>H', doc='boot blocks version number')
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bbPageFlags = _field(8, '>H', doc='used internally')
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bbSysName = _field(10, '16p', doc='System filename')
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bbShellName = _field(26, '16p', doc='Finder filename')
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bbDbg1Name = _field(42, '16p', doc='debugger filename')
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bbDbg2Name = _field(58, '16p', doc='debugger filename')
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bbScreenName = _field(74, '16p', doc='name of startup screen')
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bbHelloName = _field(90, '16p', doc='name of startup program')
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bbScrapName = _field(106, '16p', doc='name of system scrap file')
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bbCntFCBs = _field(122, '>H', doc='number of FCBs to allocate')
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bbCntEvts = _field(124, '>H', doc='number of event queue elements')
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bb128KSHeap = _field(126, '>L', doc='system heap size on 128K Mac')
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bb256KSHeap = _field(130, '>L', doc='used internally')
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bbSysHeapSize = _field(134, '>L', doc='system heap size on all machines')
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bbFiller = _field(138, '>H', doc='reserved')
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bbSysHeapExtra = _field(140, '>L', doc='additional system heap space')
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bbSysHeapFract = _field(144, '>L', doc='fraction of RAM for system heap')
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drSigWord = _field(1024+0, '>H', doc='volume signature')
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drCrDate = _field(1024+2, '>L', doc='date and time of volume creation')
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drLsMod = _field(1024+6, '>L', doc='date and time of last modification')
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drAtrb = _field(1024+10, '>H', doc='volume attributes')
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drNmFls = _field(1024+12, '>H', doc='number of files in root directory')
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drVBMSt = _field(1024+14, '>H', doc='first block of volume bitmap')
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drAllocPtr = _field(1024+16, '>H', doc='start of next allocation search')
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drNmAlBlks = _field(1024+18, '>H', doc='number of allocation blocks in volume')
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drAlBlkSiz = _field(1024+20, '>L', doc='size (in bytes) of allocation blocks')
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drClpSiz = _field(1024+24, '>L', doc='default clump size')
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drAlBlSt = _field(1024+28, '>H', doc='first allocation block in volume')
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drNxtCNID = _field(1024+30, '>L', doc='next unused catalog node ID')
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drFreeBks = _field(1024+34, '>H', doc='number of unused allocation blocks')
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drVN = _field(1024+36, '28p', doc='volume name Pascal string')
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drVolBkUp = _field(1024+64, '>L', doc='date and time of last backup')
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drVSeqNum = _field(1024+68, '>H', doc='volume backup sequence number')
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drWrCnt = _field(1024+70, '>L', doc='volume write count')
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drXTClpSiz = _field(1024+74, '>L', doc='clump size for extents overflow file')
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drCTClpSiz = _field(1024+78, '>L', doc='clump size for catalog file')
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drNmRtDirs = _field(1024+82, '>H', doc='number of directories in root directory')
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drFilCnt = _field(1024+84, '>L', doc='number of files in volume')
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drDirCnt = _field(1024+88, '>L', doc='number of directories in volume')
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drFndrInfo = _field(1024+92, '32s', doc='information used by the Finder')
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drVCSize = _field(1024+124, '>H', doc='size (in blocks) of volume cache')
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drVBMCSize = _field(1024+126, '>H', doc='size (in blocks) of volume bitmap cache')
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drCtlCSize = _field(1024+128, '>H', doc='size (in blocks) of common volume cache')
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drXTFlSize = _field(1024+130, '>L', doc='size of extents overflow file')
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drXTExtRec = _field(1024+134, '>6H', doc='extent record for extents overflow file')
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drCTFlSize = _field(1024+146, '>L', doc='size of catalog file')
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drCTExtRec = _field(1024+150, '>6H', doc='extent record for catalog file')
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ndFLink = _mobilefield(0, '>L', doc='forward link')
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ndBLink = _mobilefield(4, '>L', doc='backward link')
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ndType = _mobilefield(8, '>B', doc='node type')
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ndIndxNode = 0x00; ndHdrNode = 0x01; ndMapNode = 0x02; ndLeafNode = 0xFF
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ndNHeight = _mobilefield(9, '>L', doc='node level')
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ndNRecs = _mobilefield(10, '>H', doc='number of records in node')
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ndResv2 = _mobilefield(12, '>H', doc='reserved')
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bthDepth = _mobilefield(14+0, '>H', doc='current depth of tree')
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bthRoot = _mobilefield(14+2, '>L', doc='number of root node')
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bthNRecs = _mobilefield(14+6, '>L', doc='number of leaf records in tree')
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bthFNode = _mobilefield(14+10, '>L', doc='number of first leaf node')
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bthLNode = _mobilefield(14+14, '>L', doc='number of last leaf node')
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bthNodeSize = _mobilefield(14+18, '>H', doc='size of a node')
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bthKeyLen = _mobilefield(14+20, '>H', doc='maximum length of a key')
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bthNNodes = _mobilefield(14+22, '>L', doc='total number of nodes in tree')
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bthFree = _mobilefield(14+26, '>L', doc='number of free nodes')
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def _dump_attrs(self, prefix=''):
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print('Dumping %s*:' % prefix)
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for key in (k for k in dir(self) if k.startswith(prefix)):
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print('', key, hex(getattr(self, key)))
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def ablk_offset(self, ablkidx):
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"""Get byte offset from alloc block (ablk) number"""
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bits_per_pblk = 512 * 8
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ignoreblks = self.drVBMSt + (self.drNmAlBlks + bits_per_pblk - 1) // bits_per_pblk
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return ignoreblks * 512 + ablkidx * self.drAlBlkSiz
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def __init__(self, buf):
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self.structoffset = 0
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self.buf = buf
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self.cache = {}
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def __add__(self, structoffset):
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cp = copy.copy(self)
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cp.structoffset += structoffset
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return cp
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def __sub__(self, negoffset):
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return self.__add__(-negoffset)
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def clrcache(self):
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"""Clear the cache because external code has changed the buffer."""
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self.cache.clear()
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def walk_catalog(self):
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catalog_offset = self.ablk_offset(self.drCTExtRec[0])
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bt = _deser_btree(self.buf, catalog_offset)
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for key, val in bt.items():
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print(key, val)
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import sys
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if sys.argv[1:]:
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infile = sys.argv[1]
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else:
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infile = 'SourceForEmulator.dmg'
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h = HFS(bytearray(open(infile,'rb').read()))
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h.walk_catalog()
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