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Kenneth Reitz
82 lines
3.3 KiB
Python
82 lines
3.3 KiB
Python
# -*- coding: windows-1252 -*-
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'''
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From BIFF8 on, strings are always stored using UTF-16LE text encoding. The
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character array is a sequence of 16-bit values4. Additionally it is
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possible to use a compressed format, which omits the high bytes of all
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characters, if they are all zero.
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The following tables describe the standard format of the entire string, but
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in many records the strings differ from this format. This will be mentioned
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separately. It is possible (but not required) to store Rich-Text formatting
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information and Asian phonetic information inside a Unicode string. This
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results in four different ways to store a string. The character array
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is not zero-terminated.
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The string consists of the character count (as usual an 8-bit value or
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a 16-bit value), option flags, the character array and optional formatting
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information. If the string is empty, sometimes the option flags field will
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not occur. This is mentioned at the respective place.
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Offset Size Contents
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0 1 or 2 Length of the string (character count, ln)
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1 or 2 1 Option flags:
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Bit Mask Contents
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0 01H Character compression (ccompr):
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0 = Compressed (8-bit characters)
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1 = Uncompressed (16-bit characters)
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2 04H Asian phonetic settings (phonetic):
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0 = Does not contain Asian phonetic settings
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1 = Contains Asian phonetic settings
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3 08H Rich-Text settings (richtext):
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0 = Does not contain Rich-Text settings
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1 = Contains Rich-Text settings
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[2 or 3] 2 (optional, only if richtext=1) Number of Rich-Text formatting runs (rt)
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[var.] 4 (optional, only if phonetic=1) Size of Asian phonetic settings block (in bytes, sz)
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var. ln or
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2·ln Character array (8-bit characters or 16-bit characters, dependent on ccompr)
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[var.] 4·rt (optional, only if richtext=1) List of rt formatting runs
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[var.] sz (optional, only if phonetic=1) Asian Phonetic Settings Block
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'''
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from struct import pack
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def upack2(s, encoding='ascii'):
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# If not unicode, make it so.
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if isinstance(s, unicode):
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us = s
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else:
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us = unicode(s, encoding)
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# Limit is based on number of content characters
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# (not on number of bytes in packed result)
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len_us = len(us)
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if len_us > 65535:
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raise Exception('String longer than 65535 characters')
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try:
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encs = us.encode('latin1')
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# Success here means all chars are in U+0000 to U+00FF
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# inclusive, meaning that we can use "compressed format".
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flag = 0
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except UnicodeEncodeError:
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encs = us.encode('utf_16_le')
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flag = 1
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return pack('<HB', len_us, flag) + encs
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def upack1(s, encoding='ascii'):
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# Same as upack2(), but with a one-byte length field.
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if isinstance(s, unicode):
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us = s
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else:
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us = unicode(s, encoding)
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len_us = len(us)
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if len_us > 255:
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raise Exception('String longer than 255 characters')
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try:
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encs = us.encode('latin1')
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flag = 0
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except UnicodeEncodeError:
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encs = us.encode('utf_16_le')
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flag = 1
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return pack('<BB', len_us, flag) + encs
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