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KF8 Input: When decompressing fonts, rely on zlib to handle the header and checksum instead of trying to do it ourselves

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This commit is contained in:
Kovid Goyal 2012-04-16 11:05:13 +05:30
parent 22a6b2200c
commit 46c45be7ef
1 changed files with 35 additions and 42 deletions
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77
src/calibre/ebooks/mobi/utils.py
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@ -7,7 +7,7 @@ __license__ = 'GPL v3'
__copyright__ = '2011, Kovid Goyal <kovid@kovidgoyal.net>'
__docformat__ = 'restructuredtext en'
import struct, string, imghdr, zlib
import struct, string, imghdr, zlib, os
from collections import OrderedDict
from calibre.utils.magick.draw import Image, save_cover_data_to, thumbnail
@ -388,27 +388,8 @@ def mobify_image(data):
data = im.export('gif')
return data
def read_zlib_header(header):
header = bytearray(header)
# See sec 2.2 of RFC 1950 for the zlib stream format
# http://www.ietf.org/rfc/rfc1950.txt
if (header[0]*256 + header[1])%31 != 0:
return None, 'Bad zlib header, FCHECK failed'
cmf = header[0] & 0b1111
cinfo = header[0] >> 4
if cmf != 8:
return None, 'Unknown zlib compression method: %d'%cmf
if cinfo > 7:
return None, 'Invalid CINFO field in zlib header: %d'%cinfo
fdict = (header[1]&0b10000)>>5
if fdict != 0:
return None, 'FDICT based zlib compression not supported'
wbits = cinfo + 8
return wbits, None
def read_font_record(data, extent=1040): # {{{
# Font records {{{
def read_font_record(data, extent=1040):
'''
Return the font encoded in the MOBI FONT record represented by data.
The return value in a dict with fields raw_data, font_data, err, ext,
@ -466,15 +447,8 @@ def read_font_record(data, extent=1040): # {{{
if flags & 0b1:
# ZLIB compressed data
wbits, err = read_zlib_header(font_data[:2])
if err is not None:
ans['err'] = err
return ans
adler32, = struct.unpack_from(b'>I', font_data, len(font_data) - 4)
try:
# remove two bytes of zlib header and 4 bytes of trailing checksum
# negative wbits indicates no standard gzip header
font_data = zlib.decompress(font_data[2:-4], -wbits, usize)
font_data = zlib.decompress(font_data)
except Exception as e:
ans['err'] = 'Failed to zlib decompress font data (%s)'%e
return ans
@ -483,23 +457,42 @@ def read_font_record(data, extent=1040): # {{{
ans['err'] = 'Uncompressed font size mismatch'
return ans
if False:
# For some reason these almost never match, probably Amazon has a
# buggy Adler32 implementation
sig = (zlib.adler32(font_data) & 0xffffffff)
if sig != adler32:
ans['err'] = ('Adler checksum did not match. Stored: %d '
'Calculated: %d')%(adler32, sig)
return ans
ans['font_data'] = font_data
sig = font_data[:4]
ans['ext'] = ('ttf' if sig in {b'\0\1\0\0', b'true', b'ttcf'}
else 'otf' if sig == b'OTTO' else 'dat')
return ans
def write_font_record(data, obfuscate=True, compress=True):
'''
Write the ttf/otf font represented by data into a font record. See
read_font_record() for details on the format of the record.
'''
flags = 0
key_len = 20
usize = len(data)
xor_key = b''
if compress:
flags |= 0b1
data = zlib.compress(data, 9)
if obfuscate:
flags |= 0b10
xor_key = os.urandom(key_len)
key = bytearray(xor_key)
data = bytearray(data)
for i in xrange(1040):
data[i] ^= key[i%key_len]
data = bytes(data)
key_start = struct.calcsize(b'>5L') + 4
data_start = key_start + len(xor_key)
header = b'FONT' + struct.pack(b'>5L', usize, flags, data_start,
len(xor_key), key_start)
return header + xor_key + data
# }}}