Merge Max's code for System 7 resource compression

macresources/GreggBits.py

@@ -0,0 +1,226 @@
+'''
+    This script implements the GreggyBits decompression algorithm
+    found in the 'dcmp' 2 resource.
+'''
+
+import struct
+
+# predefined lookup table of the most frequent words
+GreggDefLUT = (
+    0x0000, 0x0008, 0x4EBA, 0x206E, 0x4E75, 0x000C, 0x0004, 0x7000,
+    0x0010, 0x0002, 0x486E, 0xFFFC, 0x6000, 0x0001, 0x48E7, 0x2F2E,
+    0x4E56, 0x0006, 0x4E5E, 0x2F00, 0x6100, 0xFFF8, 0x2F0B, 0xFFFF,
+    0x0014, 0x000A, 0x0018, 0x205F, 0x000E, 0x2050, 0x3F3C, 0xFFF4,
+    0x4CEE, 0x302E, 0x6700, 0x4CDF, 0x266E, 0x0012, 0x001C, 0x4267,
+    0xFFF0, 0x303C, 0x2F0C, 0x0003, 0x4ED0, 0x0020, 0x7001, 0x0016,
+    0x2D40, 0x48C0, 0x2078, 0x7200, 0x588F, 0x6600, 0x4FEF, 0x42A7,
+    0x6706, 0xFFFA, 0x558F, 0x286E, 0x3F00, 0xFFFE, 0x2F3C, 0x6704,
+    0x598F, 0x206B, 0x0024, 0x201F, 0x41FA, 0x81E1, 0x6604, 0x6708,
+    0x001A, 0x4EB9, 0x508F, 0x202E, 0x0007, 0x4EB0, 0xFFF2, 0x3D40,
+    0x001E, 0x2068, 0x6606, 0xFFF6, 0x4EF9, 0x0800, 0x0C40, 0x3D7C,
+    0xFFEC, 0x0005, 0x203C, 0xFFE8, 0xDEFC, 0x4A2E, 0x0030, 0x0028,
+    0x2F08, 0x200B, 0x6002, 0x426E, 0x2D48, 0x2053, 0x2040, 0x1800,
+    0x6004, 0x41EE, 0x2F28, 0x2F01, 0x670A, 0x4840, 0x2007, 0x6608,
+    0x0118, 0x2F07, 0x3028, 0x3F2E, 0x302B, 0x226E, 0x2F2B, 0x002C,
+    0x670C, 0x225F, 0x6006, 0x00FF, 0x3007, 0xFFEE, 0x5340, 0x0040,
+    0xFFE4, 0x4A40, 0x660A, 0x000F, 0x4EAD, 0x70FF, 0x22D8, 0x486B,
+    0x0022, 0x204B, 0x670E, 0x4AAE, 0x4E90, 0xFFE0, 0xFFC0, 0x002A,
+    0x2740, 0x6702, 0x51C8, 0x02B6, 0x487A, 0x2278, 0xB06E, 0xFFE6,
+    0x0009, 0x322E, 0x3E00, 0x4841, 0xFFEA, 0x43EE, 0x4E71, 0x7400,
+    0x2F2C, 0x206C, 0x003C, 0x0026, 0x0050, 0x1880, 0x301F, 0x2200,
+    0x660C, 0xFFDA, 0x0038, 0x6602, 0x302C, 0x200C, 0x2D6E, 0x4240,
+    0xFFE2, 0xA9F0, 0xFF00, 0x377C, 0xE580, 0xFFDC, 0x4868, 0x594F,
+    0x0034, 0x3E1F, 0x6008, 0x2F06, 0xFFDE, 0x600A, 0x7002, 0x0032,
+    0xFFCC, 0x0080, 0x2251, 0x101F, 0x317C, 0xA029, 0xFFD8, 0x5240,
+    0x0100, 0x6710, 0xA023, 0xFFCE, 0xFFD4, 0x2006, 0x4878, 0x002E,
+    0x504F, 0x43FA, 0x6712, 0x7600, 0x41E8, 0x4A6E, 0x20D9, 0x005A,
+    0x7FFF, 0x51CA, 0x005C, 0x2E00, 0x0240, 0x48C7, 0x6714, 0x0C80,
+    0x2E9F, 0xFFD6, 0x8000, 0x1000, 0x4842, 0x4A6B, 0xFFD2, 0x0048,
+    0x4A47, 0x4ED1, 0x206F, 0x0041, 0x600C, 0x2A78, 0x422E, 0x3200,
+    0x6574, 0x6716, 0x0044, 0x486D, 0x2008, 0x486C, 0x0B7C, 0x2640,
+    0x0400, 0x0068, 0x206D, 0x000D, 0x2A40, 0x000B, 0x003E, 0x0220
+)
+
+
+def EncodeMaskedWords(src, dst, pos, n, tab):
+    mask = 0
+    encoded = bytearray()
+
+    for rPos in range(n):
+        mask <<= 1
+        word = src[pos+rPos]
+        compressed = 1 if word in tab else 0
+        mask |= compressed
+        if compressed: # replace word with table index
+            encoded.append(tab.index(word))
+        else: # otherwise, just copy unencoded data over
+            encoded.extend(word.to_bytes(2, 'big'))
+
+    if n < 8: # left-justify the mask for n < 8
+        mask <<= 8 - n
+
+    dst.append(mask)
+    dst.extend(encoded)
+
+    return pos+n
+
+
+def DecodeMaskedWords(src, dst, pos, n, tab, mask):
+    '''Decode n words using the specified lookup table under control of mask.
+       Return new bitstream position.
+    '''
+    if mask == 0: # all mask bits are zero?
+        nBytes = n * 2
+        dst.extend(src[pos:pos+nBytes]) # copy over n*2 bytes
+        pos += nBytes
+    else:
+        for bn in range(7, 7 - n, -1):
+            if mask & (1 << bn): # mask bit set?
+                word = tab[src[pos]] # decode next word with LUT
+                dst.extend(word.to_bytes(2, 'big')) # write it to dst
+                pos += 1
+            else: # otherwise, copy over that word
+                dst.extend(src[pos:pos+2])
+                pos += 2
+    return pos
+
+
+def GreggDecompress(src, dst, unpackSize, pos=0):
+    '''Decompress resource data from src to dst.
+
+       Parameters:
+       src          source buffer containing compressed data
+       dst          destination buffer, must be bytearray to work properly
+       unpackSize   size in bytes of the unpacked resource data
+       pos          offset to my Gregg-specific buffer in src
+    '''
+
+    _dcmp, _slop, tabSize, comprFlags = struct.unpack_from(">HHBB", src, pos)
+    pos += 6
+
+    hasDynamicTab = comprFlags & 1
+    isBitmapped   = comprFlags & 2
+    # print("tabSize: %d" % tabSize)
+    # print("comprFlags: 0x%X, dynamic table: %s, bitmap data: %s" % (comprFlags,
+    #       "yes" if hasDynamicTab else "no", "yes" if isBitmapped else "no"))
+
+    if hasDynamicTab:
+        nEntries = tabSize + 1
+        dynamicLUT = struct.unpack_from(">" + str(nEntries) + "H", src, pos)
+        pos += nEntries * 2
+        # dump dynamic LUT
+        if 0:
+            for idx, elem in enumerate(dynamicLUT):
+                if idx and not idx & 3:
+                    print(",")
+                else:
+                    print(", ", end="")
+                print("0x%04X" % elem, end="")
+            print("")
+
+    LUT = dynamicLUT if hasDynamicTab else GreggDefLUT
+    nWords = unpackSize >> 1
+    hasExtraByte = unpackSize & 1
+
+    if isBitmapped:
+        nRuns = nWords >> 3
+        for idx in range(nRuns):
+            mask = src[pos]
+            pos += 1
+            #print("Mask for run #%d: 0x%X" % (idx, bitmap))
+
+            pos = DecodeMaskedWords(src, dst, pos, 8, LUT, mask)
+
+        if nWords & 7:
+            trailingWords = nWords & 7
+            lastMask = src[pos]
+            pos += 1
+            #print("Last mask: 0x%X, trailing words: %d" % (lastMask, trailingWords))
+            pos = DecodeMaskedWords(src, dst, pos, trailingWords, LUT, lastMask)
+    else:
+        for i in range(nWords):
+            word = LUT[src[pos]] # decode next word with LUT
+            dst.extend(word.to_bytes(2, 'big')) # write it to dst
+            pos += 1
+
+    if hasExtraByte: # have a got an extra byte at the end?
+        dst.append(src[pos]) # copy it over
+        pos += 1
+
+    #print("Last input position: %d" % pos)
+
+
+def GreggCompress(src, dst, customTab='auto', isBitmapped='auto'):
+    # future addition 
+    customTab = True # so the big code path gets tested!
+    isBitmapped = True # required for now
+
+    if customTab: # calculate, and if necessary, resolve 'auto'
+        # convert input bytes into an array of words
+        nWords = len(src) >> 1
+        inWords = struct.unpack(">" + str(nWords) + "H", src[:nWords*2])
+
+        # count occurence of each word
+        from collections import Counter
+        wordsCounts = Counter(inWords)
+
+        # grab word counts in descending order (most frequent comes first)
+        sortedCounts = list(set(wordsCounts.values()))
+        sortedCounts.sort(reverse=True)
+
+        # now we're ready to construct a table of 256 most common words
+        embeddedTab = list()
+        nElems = 0
+
+        for cnt in sortedCounts:
+            # pick all words for a specific count and sort them in descending order
+            words = [key for (key, value) in wordsCounts.items() if value == cnt]
+            words.sort(reverse=True)
+
+            # append them to the table, stop when tableMax is reached
+            if nElems + len(words) < 256:
+                embeddedTab.extend(words)
+                nElems += len(words)
+            else:
+                remainedElems = 256 - nElems
+                embeddedTab.extend(words[:remainedElems])
+                nElems += remainedElems
+
+            if nElems >= 256:
+                break
+
+        if 0: # dump the resulting table
+            for idx, elem in enumerate(embeddedTab):
+                if idx and not idx & 3:
+                    print(",")
+                else:
+                    print(", ", end="")
+                print("0x%04X" % elem, end="")
+            print("")
+
+        # here, decide whether 'auto' customTab should be on or off!
+
+    # write out the header
+    isBitmapped = True # will need to resolve this later
+    flags = customTab * 1 + isBitmapped * 2
+    dst.extend(struct.pack(">HHBB", 2, 0, len(embeddedTab)-1, flags))
+
+    if customTab:
+        # write the constructed table into output
+        for word in embeddedTab:
+            dst.extend(word.to_bytes(2, 'big'))
+
+    if isBitmapped:
+        pos = 0
+        nRuns = nWords >> 3
+
+        for idx in range(nRuns):
+            pos = EncodeMaskedWords(inWords, dst, pos, 8, embeddedTab)
+
+        if nWords & 7:
+            pos = EncodeMaskedWords(inWords, dst, pos, nWords & 7, embeddedTab)
+
+        if len(src) & 1: # copy over last byte in the case of odd length
+            dst.append(src[-1])
+    else:
+        raise ValueError("Non-bitmapped compression not yet implemented")

macresources/compression.py

@@ -0,0 +1,65 @@
+'''
+    Handling of compressed MacOS resources.
+    Author: Max Poliakovski 2018
+'''
+import struct
+
+from .GreggBits import GreggDecompress, GreggCompress
+
+
+def GetEncoding(dat):
+    sig, hdrlen, vers, attrs, biglen = struct.unpack_from(">IHBBI", dat)
+    if sig != 0xA89F6572:
+        # print("Invalid extended resource header sig: 0x%X" % sig)
+        return 'UnknownCompression'
+    if vers not in (8, 9):
+        # print("Unknown ext res header format: %d" % vers)
+        return 'UnknownCompression'
+    if attrs & 1 == 0:
+        # print("extAttributes,bit0 isn't set. Treat this res as uncompressed.")
+        return 'UnknownCompression'
+
+    # print("Uncompressed length: %d" % biglen)
+
+    if vers == 8:
+        return 'UnknownCompression' # return 'DonnBits'
+    elif vers == 9:
+        if dat[12:14] == b'\x00\x02':
+            return 'GreggyBits'
+        else:
+            return 'UnknownCompression'
+    else:
+        return 'UnknownCompression'
+
+
+def DecompressResource(dat):
+    encoding = GetEncoding(dat)
+    sig, hdrlen, vers, attrs, biglen = struct.unpack_from(">IHBBI", dat)
+
+    if encoding == 'DonnBits':
+        raise NotImplementedError('DonnBits')
+
+    elif encoding == 'GreggyBits':
+        dst = bytearray()
+        GreggDecompress(dat, dst, unpackSize=biglen, pos=12)
+        return bytes(dst)
+
+    elif encoding == 'UnknownCompression':
+        return dat # passthru
+
+
+def CompressResource(dat, encoding):
+    if encoding == 'UnknownCompression':
+        return dat
+
+    elif encoding == 'GreggyBits':
+        dst = bytearray()
+
+        # re-create extended resource header
+        dst.extend([0xA8, 0x9F, 0x65, 0x72, 0x00, 0x12, 0x09, 0x01])
+        dst.extend(len(dat).to_bytes(4, 'big'))
+
+        # leave Gregg-specific header to the compressor
+        GreggCompress(dat, dst)
+
+        return bytes(dst)

macresources/main.py

@@ -2,7 +2,7 @@ import collections
 import struct
 import enum
 import re
-from ResDecompress import DecompressResource, CompressResource, GetEncoding
+from .compression import DecompressResource, CompressResource, GetEncoding
 
 
 FAKE_HEADER_RSRC_TYPE = b'header' # obviously invalid

setup.py

@@ -17,6 +17,6 @@ setup(
         'Topic :: System :: Filesystems',
         'Development Status :: 3 - Alpha',
     ],
-    packages=['macresources', 'ResDecompress'],
+    packages=['macresources'],
     scripts=['bin/SimpleRez', 'bin/SimpleDeRez'],
 )

test_compress.py

@@ -0,0 +1,13 @@
+from .macresources.compression import GetEncoding, DecompressResource, CompressResource
+
+def compress_then_extract(dat, encoding):
+    a = CompressResource(dat, encoding);
+    if encoding != 'UnknownCompression': assert a.startswith(b'\xA8\x9F\x65\x72')
+    assert GetEncoding(a) == encoding
+    b = DecompressResource(a)
+    assert b == dat
+
+def test_all():
+    for enc in ['GreggyBits', 'UnknownCompression']:
+        compress_then_extract(bytes(100), encoding=enc)
+        compress_then_extract(b'The quick brown fox jumps over the lazy dog', encoding=enc)