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"""ttLib/sfnt.py -- low-level module to deal with the sfnt file format.
Defines two public classes:
SFNTReader
SFNTWriter
(Normally you don't have to use these classes explicitly; they are
used automatically by ttLib.TTFont.)
The reading and writing of sfnt files is separated in two distinct
classes, since whenever to number of tables changes or whenever
a table's length chages you need to rewrite the whole file anyway.
"""
from __future__ import print_function, division, absolute_import
from fontTools.misc.py23 import *
from fontTools.misc import sstruct
import struct
class SFNTReader(object):
def __init__(self, file, checkChecksums=1, fontNumber=-1):
self.file = file
self.checkChecksums = checkChecksums
self.flavor = None
self.flavorData = None
self.DirectoryEntry = SFNTDirectoryEntry
self.sfntVersion = self.file.read(4)
self.file.seek(0)
if self.sfntVersion == b"ttcf":
sstruct.unpack(ttcHeaderFormat, self.file.read(ttcHeaderSize), self)
assert self.Version == 0x00010000 or self.Version == 0x00020000, "unrecognized TTC version 0x%08x" % self.Version
if not 0 <= fontNumber < self.numFonts:
from fontTools import ttLib
raise ttLib.TTLibError("specify a font number between 0 and %d (inclusive)" % (self.numFonts - 1))
offsetTable = struct.unpack(">%dL" % self.numFonts, self.file.read(self.numFonts * 4))
if self.Version == 0x00020000:
pass # ignoring version 2.0 signatures
self.file.seek(offsetTable[fontNumber])
sstruct.unpack(sfntDirectoryFormat, self.file.read(sfntDirectorySize), self)
elif self.sfntVersion == b"wOFF":
self.flavor = "woff"
self.DirectoryEntry = WOFFDirectoryEntry
sstruct.unpack(woffDirectoryFormat, self.file.read(woffDirectorySize), self)
else:
sstruct.unpack(sfntDirectoryFormat, self.file.read(sfntDirectorySize), self)
self.sfntVersion = Tag(self.sfntVersion)
if self.sfntVersion not in ("\x00\x01\x00\x00", "OTTO", "true"):
from fontTools import ttLib
raise ttLib.TTLibError("Not a TrueType or OpenType font (bad sfntVersion)")
self.tables = {}
for i in range(self.numTables):
entry = self.DirectoryEntry()
entry.fromFile(self.file)
self.tables[Tag(entry.tag)] = entry
# Load flavor data if any
if self.flavor == "woff":
self.flavorData = WOFFFlavorData(self)
def has_key(self, tag):
return tag in self.tables
__contains__ = has_key
def keys(self):
return self.tables.keys()
def __getitem__(self, tag):
"""Fetch the raw table data."""
entry = self.tables[Tag(tag)]
data = entry.loadData (self.file)
if self.checkChecksums:
if tag == 'head':
# Beh: we have to special-case the 'head' table.
checksum = calcChecksum(data[:8] + b'\0\0\0\0' + data[12:])
else:
checksum = calcChecksum(data)
if self.checkChecksums > 1:
# Be obnoxious, and barf when it's wrong
assert checksum == entry.checksum, "bad checksum for '%s' table" % tag
elif checksum != entry.checkSum:
# Be friendly, and just print a warning.
print("bad checksum for '%s' table" % tag)
return data
def __delitem__(self, tag):
del self.tables[Tag(tag)]
def close(self):
self.file.close()
class SFNTWriter(object):
def __init__(self, file, numTables, sfntVersion="\000\001\000\000",
flavor=None, flavorData=None):
self.file = file
self.numTables = numTables
self.sfntVersion = Tag(sfntVersion)
self.flavor = flavor
self.flavorData = flavorData
if self.flavor == "woff":
self.directoryFormat = woffDirectoryFormat
self.directorySize = woffDirectorySize
self.DirectoryEntry = WOFFDirectoryEntry
self.signature = "wOFF"
else:
assert not self.flavor, "Unknown flavor '%s'" % self.flavor
self.directoryFormat = sfntDirectoryFormat
self.directorySize = sfntDirectorySize
self.DirectoryEntry = SFNTDirectoryEntry
self.searchRange, self.entrySelector, self.rangeShift = getSearchRange(numTables)
self.nextTableOffset = self.directorySize + numTables * self.DirectoryEntry.formatSize
# clear out directory area
self.file.seek(self.nextTableOffset)
# make sure we're actually where we want to be. (old cStringIO bug)
self.file.write(b'\0' * (self.nextTableOffset - self.file.tell()))
self.tables = {}
def __setitem__(self, tag, data):
"""Write raw table data to disk."""
reuse = False
if tag in self.tables:
# We've written this table to file before. If the length
# of the data is still the same, we allow overwriting it.
entry = self.tables[tag]
assert not hasattr(entry.__class__, 'encodeData')
if len(data) != entry.length:
from fontTools import ttLib
raise ttLib.TTLibError("cannot rewrite '%s' table: length does not match directory entry" % tag)
reuse = True
else:
entry = self.DirectoryEntry()
entry.tag = tag
if tag == 'head':
entry.checkSum = calcChecksum(data[:8] + b'\0\0\0\0' + data[12:])
self.headTable = data
entry.uncompressed = True
else:
entry.checkSum = calcChecksum(data)
entry.offset = self.nextTableOffset
entry.saveData (self.file, data)
if not reuse:
self.nextTableOffset = self.nextTableOffset + ((entry.length + 3) & ~3)
# Add NUL bytes to pad the table data to a 4-byte boundary.
# Don't depend on f.seek() as we need to add the padding even if no
# subsequent write follows (seek is lazy), ie. after the final table
# in the font.
self.file.write(b'\0' * (self.nextTableOffset - self.file.tell()))
assert self.nextTableOffset == self.file.tell()
self.tables[tag] = entry
def close(self):
"""All tables must have been written to disk. Now write the
directory.
"""
tables = sorted(self.tables.items())
if len(tables) != self.numTables:
from fontTools import ttLib
raise ttLib.TTLibError("wrong number of tables; expected %d, found %d" % (self.numTables, len(tables)))
if self.flavor == "woff":
self.signature = b"wOFF"
self.reserved = 0
self.totalSfntSize = 12
self.totalSfntSize += 16 * len(tables)
for tag, entry in tables:
self.totalSfntSize += (entry.origLength + 3) & ~3
data = self.flavorData if self.flavorData else WOFFFlavorData()
if data.majorVersion is not None and data.minorVersion is not None:
self.majorVersion = data.majorVersion
self.minorVersion = data.minorVersion
else:
if hasattr(self, 'headTable'):
self.majorVersion, self.minorVersion = struct.unpack(">HH", self.headTable[4:8])
else:
self.majorVersion = self.minorVersion = 0
if data.metaData:
self.metaOrigLength = len(data.metaData)
self.file.seek(0,2)
self.metaOffset = self.file.tell()
import zlib
compressedMetaData = zlib.compress(data.metaData)
self.metaLength = len(compressedMetaData)
self.file.write(compressedMetaData)
else:
self.metaOffset = self.metaLength = self.metaOrigLength = 0
if data.privData:
self.file.seek(0,2)
off = self.file.tell()
paddedOff = (off + 3) & ~3
self.file.write('\0' * (paddedOff - off))
self.privOffset = self.file.tell()
self.privLength = len(data.privData)
self.file.write(data.privData)
else:
self.privOffset = self.privLength = 0
self.file.seek(0,2)
self.length = self.file.tell()
else:
assert not self.flavor, "Unknown flavor '%s'" % self.flavor
pass
directory = sstruct.pack(self.directoryFormat, self)
self.file.seek(self.directorySize)
seenHead = 0
for tag, entry in tables:
if tag == "head":
seenHead = 1
directory = directory + entry.toString()
if seenHead:
self.writeMasterChecksum(directory)
self.file.seek(0)
self.file.write(directory)
def _calcMasterChecksum(self, directory):
# calculate checkSumAdjustment
tags = list(self.tables.keys())
checksums = []
for i in range(len(tags)):
checksums.append(self.tables[tags[i]].checkSum)
# TODO(behdad) I'm fairly sure the checksum for woff is not working correctly.
# Haven't debugged.
if self.DirectoryEntry != SFNTDirectoryEntry:
# Create a SFNT directory for checksum calculation purposes
self.searchRange, self.entrySelector, self.rangeShift = getSearchRange(self.numTables)
directory = sstruct.pack(sfntDirectoryFormat, self)
tables = sorted(self.tables.items())
for tag, entry in tables:
sfntEntry = SFNTDirectoryEntry()
for item in ['tag', 'checkSum', 'offset', 'length']:
setattr(sfntEntry, item, getattr(entry, item))
directory = directory + sfntEntry.toString()
directory_end = sfntDirectorySize + len(self.tables) * sfntDirectoryEntrySize
assert directory_end == len(directory)
checksums.append(calcChecksum(directory))
checksum = sum(checksums) & 0xffffffff
# BiboAfba!
checksumadjustment = (0xB1B0AFBA - checksum) & 0xffffffff
return checksumadjustment
def writeMasterChecksum(self, directory):
checksumadjustment = self._calcMasterChecksum(directory)
# write the checksum to the file
self.file.seek(self.tables['head'].offset + 8)
self.file.write(struct.pack(">L", checksumadjustment))
# -- sfnt directory helpers and cruft
ttcHeaderFormat = """
> # big endian
TTCTag: 4s # "ttcf"
Version: L # 0x00010000 or 0x00020000
numFonts: L # number of fonts
# OffsetTable[numFonts]: L # array with offsets from beginning of file
# ulDsigTag: L # version 2.0 only
# ulDsigLength: L # version 2.0 only
# ulDsigOffset: L # version 2.0 only
"""
ttcHeaderSize = sstruct.calcsize(ttcHeaderFormat)
sfntDirectoryFormat = """
> # big endian
sfntVersion: 4s
numTables: H # number of tables
searchRange: H # (max2 <= numTables)*16
entrySelector: H # log2(max2 <= numTables)
rangeShift: H # numTables*16-searchRange
"""
sfntDirectorySize = sstruct.calcsize(sfntDirectoryFormat)
sfntDirectoryEntryFormat = """
> # big endian
tag: 4s
checkSum: L
offset: L
length: L
"""
sfntDirectoryEntrySize = sstruct.calcsize(sfntDirectoryEntryFormat)
woffDirectoryFormat = """
> # big endian
signature: 4s # "wOFF"
sfntVersion: 4s
length: L # total woff file size
numTables: H # number of tables
reserved: H # set to 0
totalSfntSize: L # uncompressed size
majorVersion: H # major version of WOFF file
minorVersion: H # minor version of WOFF file
metaOffset: L # offset to metadata block
metaLength: L # length of compressed metadata
metaOrigLength: L # length of uncompressed metadata
privOffset: L # offset to private data block
privLength: L # length of private data block
"""
woffDirectorySize = sstruct.calcsize(woffDirectoryFormat)
woffDirectoryEntryFormat = """
> # big endian
tag: 4s
offset: L
length: L # compressed length
origLength: L # original length
checkSum: L # original checksum
"""
woffDirectoryEntrySize = sstruct.calcsize(woffDirectoryEntryFormat)
class DirectoryEntry(object):
def __init__(self):
self.uncompressed = False # if True, always embed entry raw
def fromFile(self, file):
sstruct.unpack(self.format, file.read(self.formatSize), self)
def fromString(self, str):
sstruct.unpack(self.format, str, self)
def toString(self):
return sstruct.pack(self.format, self)
def __repr__(self):
if hasattr(self, "tag"):
return "<%s '%s' at %x>" % (self.__class__.__name__, self.tag, id(self))
else:
return "<%s at %x>" % (self.__class__.__name__, id(self))
def loadData(self, file):
file.seek(self.offset)
data = file.read(self.length)
assert len(data) == self.length
if hasattr(self.__class__, 'decodeData'):
data = self.decodeData(data)
return data
def saveData(self, file, data):
if hasattr(self.__class__, 'encodeData'):
data = self.encodeData(data)
self.length = len(data)
file.seek(self.offset)
file.write(data)
def decodeData(self, rawData):
return rawData
def encodeData(self, data):
return data
class SFNTDirectoryEntry(DirectoryEntry):
format = sfntDirectoryEntryFormat
formatSize = sfntDirectoryEntrySize
class WOFFDirectoryEntry(DirectoryEntry):
format = woffDirectoryEntryFormat
formatSize = woffDirectoryEntrySize
zlibCompressionLevel = 6
def decodeData(self, rawData):
import zlib
if self.length == self.origLength:
data = rawData
else:
assert self.length < self.origLength
data = zlib.decompress(rawData)
assert len (data) == self.origLength
return data
def encodeData(self, data):
import zlib
self.origLength = len(data)
if not self.uncompressed:
compressedData = zlib.compress(data, self.zlibCompressionLevel)
if self.uncompressed or len(compressedData) >= self.origLength:
# Encode uncompressed
rawData = data
self.length = self.origLength
else:
rawData = compressedData
self.length = len(rawData)
return rawData
class WOFFFlavorData():
Flavor = 'woff'
def __init__(self, reader=None):
self.majorVersion = None
self.minorVersion = None
self.metaData = None
self.privData = None
if reader:
self.majorVersion = reader.majorVersion
self.minorVersion = reader.minorVersion
if reader.metaLength:
reader.file.seek(reader.metaOffset)
rawData = reader.file.read(reader.metaLength)
assert len(rawData) == reader.metaLength
import zlib
data = zlib.decompress(rawData)
assert len(data) == reader.metaOrigLength
self.metaData = data
if reader.privLength:
reader.file.seek(reader.privOffset)
data = reader.file.read(reader.privLength)
assert len(data) == reader.privLength
self.privData = data
def calcChecksum(data):
"""Calculate the checksum for an arbitrary block of data.
Optionally takes a 'start' argument, which allows you to
calculate a checksum in chunks by feeding it a previous
result.
If the data length is not a multiple of four, it assumes
it is to be padded with null byte.
>>> print calcChecksum(b"abcd")
1633837924
>>> print calcChecksum(b"abcdxyz")
3655064932
"""
remainder = len(data) % 4
if remainder:
data += b"\0" * (4 - remainder)
value = 0
blockSize = 4096
assert blockSize % 4 == 0
for i in range(0, len(data), blockSize):
block = data[i:i+blockSize]
longs = struct.unpack(">%dL" % (len(block) // 4), block)
value = (value + sum(longs)) & 0xffffffff
return value
def maxPowerOfTwo(x):
"""Return the highest exponent of two, so that
(2 ** exponent) <= x
"""
exponent = 0
while x:
x = x >> 1
exponent = exponent + 1
return max(exponent - 1, 0)
def getSearchRange(n):
"""Calculate searchRange, entrySelector, rangeShift for the
sfnt directory. 'n' is the number of tables.
"""
# This stuff needs to be stored in the file, because?
exponent = maxPowerOfTwo(n)
searchRange = (2 ** exponent) * 16
entrySelector = exponent
rangeShift = n * 16 - searchRange
return searchRange, entrySelector, rangeShift
if __name__ == "__main__":
import doctest
doctest.testmod()
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