"""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 the number of tables changes or whenever
a table's length changes you need to rewrite the whole file anyway.
"""
from io import BytesIO
from types import SimpleNamespace
from fontTools.misc.textTools import Tag
from fontTools.misc import sstruct
from fontTools.ttLib import TTLibError, TTLibFileIsCollectionError
import struct
from collections import OrderedDict
import logging
log = logging.getLogger(__name__)
class SFNTReader(object):
def __new__(cls, *args, **kwargs):
"""Return an instance of the SFNTReader sub-class which is compatible
with the input file type.
"""
if args and cls is SFNTReader:
infile = args[0]
infile.seek(0)
sfntVersion = Tag(infile.read(4))
infile.seek(0)
if sfntVersion == "wOF2":
# return new WOFF2Reader object
from fontTools.ttLib.woff2 import WOFF2Reader
return object.__new__(WOFF2Reader)
# return default object
return object.__new__(cls)
def __init__(self, file, checkChecksums=0, fontNumber=-1):
self.file = file
self.checkChecksums = checkChecksums
self.flavor = None
self.flavorData = None
self.DirectoryEntry = SFNTDirectoryEntry
self.file.seek(0)
self.sfntVersion = self.file.read(4)
self.file.seek(0)
if self.sfntVersion == b"ttcf":
header = readTTCHeader(self.file)
numFonts = header.numFonts
if not 0 <= fontNumber < numFonts:
raise TTLibFileIsCollectionError(
"specify a font number between 0 and %d (inclusive)"
% (numFonts - 1)
)
self.numFonts = numFonts
self.file.seek(header.offsetTable[fontNumber])
data = self.file.read(sfntDirectorySize)
if len(data) != sfntDirectorySize:
raise TTLibError("Not a Font Collection (not enough data)")
sstruct.unpack(sfntDirectoryFormat, data, self)
elif self.sfntVersion == b"wOFF":
self.flavor = "woff"
self.DirectoryEntry = WOFFDirectoryEntry
data = self.file.read(woffDirectorySize)
if len(data) != woffDirectorySize:
raise TTLibError("Not a WOFF font (not enough data)")
sstruct.unpack(woffDirectoryFormat, data, self)
else:
data = self.file.read(sfntDirectorySize)
if len(data) != sfntDirectorySize:
raise TTLibError("Not a TrueType or OpenType font (not enough data)")
sstruct.unpack(sfntDirectoryFormat, data, self)
self.sfntVersion = Tag(self.sfntVersion)
if self.sfntVersion not in ("\x00\x01\x00\x00", "OTTO", "true"):
raise TTLibError("Not a TrueType or OpenType font (bad sfntVersion)")
tables = {}
for i in range(self.numTables):
entry = self.DirectoryEntry()
entry.fromFile(self.file)
tag = Tag(entry.tag)
tables[tag] = entry
self.tables = OrderedDict(sorted(tables.items(), key=lambda i: i[1].offset))
# 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 log a warning.
log.warning("bad checksum for '%s' table", tag)
return data
def __delitem__(self, tag):
del self.tables[Tag(tag)]
def close(self):
self.file.close()
# We define custom __getstate__ and __setstate__ to make SFNTReader pickle-able
# and deepcopy-able. When a TTFont is loaded as lazy=True, SFNTReader holds a
# reference to an external file object which is not pickleable. So in __getstate__
# we store the file name and current position, and in __setstate__ we reopen the
# same named file after unpickling.
def __getstate__(self):
if isinstance(self.file, BytesIO):
# BytesIO is already pickleable, return the state unmodified
return self.__dict__
# remove unpickleable file attribute, and only store its name and pos
state = self.__dict__.copy()
del state["file"]
state["_filename"] = self.file.name
state["_filepos"] = self.file.tell()
return state
def __setstate__(self, state):
if "file" not in state:
self.file = open(state.pop("_filename"), "rb")
self.file.seek(state.pop("_filepos"))
self.__dict__.update(state)
# default compression level for WOFF 1.0 tables and metadata
ZLIB_COMPRESSION_LEVEL = 6
# if set to True, use zopfli instead of zlib for compressing WOFF 1.0.
# The Python bindings are available at https://pypi.python.org/pypi/zopfli
USE_ZOPFLI = False
# mapping between zlib's compression levels and zopfli's 'numiterations'.
# Use lower values for files over several MB in size or it will be too slow
ZOPFLI_LEVELS = {
# 0: 0, # can't do 0 iterations...
1: 1,
2: 3,
3: 5,
4: 8,
5: 10,
6: 15,
7: 25,
8: 50,
9: 100,
}
def compress(data, level=ZLIB_COMPRESSION_LEVEL):
"""Compress 'data' to Zlib format. If 'USE_ZOPFLI' variable is True,
zopfli is used instead of the zlib module.
The compression 'level' must be between 0 and 9. 1 gives best speed,
9 gives best compression (0 gives no compression at all).
The default value is a compromise between speed and compression (6).
"""
if not (0 <= level <= 9):
raise ValueError("Bad compression level: %s" % level)
if not USE_ZOPFLI or level == 0:
from zlib import compress
return compress(data, level)
else:
from zopfli.zlib import compress
return compress(data, numiterations=ZOPFLI_LEVELS[level])
class SFNTWriter(object):
def __new__(cls, *args, **kwargs):
"""Return an instance of the SFNTWriter sub-class which is compatible
with the specified 'flavor'.
"""
flavor = None
if kwargs and "flavor" in kwargs:
flavor = kwargs["flavor"]
elif args and len(args) > 3:
flavor = args[3]
if cls is SFNTWriter:
if flavor == "woff2":
# return new WOFF2Writer object
from fontTools.ttLib.woff2 import WOFF2Writer
return object.__new__(WOFF2Writer)
# return default object
return object.__new__(cls)
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"
# to calculate WOFF checksum adjustment, we also need the original SFNT offsets
self.origNextTableOffset = (
sfntDirectorySize + numTables * sfntDirectoryEntrySize
)
else:
assert not self.flavor, "Unknown flavor '%s'" % self.flavor
self.directoryFormat = sfntDirectoryFormat
self.directorySize = sfntDirectorySize
self.DirectoryEntry = SFNTDirectoryEntry
from fontTools.ttLib import getSearchRange
self.searchRange, self.entrySelector, self.rangeShift = getSearchRange(
numTables, 16
)
self.directoryOffset = self.file.tell()
self.nextTableOffset = (
self.directoryOffset
+ 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 = OrderedDict()
def setEntry(self, tag, entry):
if tag in self.tables:
raise TTLibError("cannot rewrite '%s' table" % tag)
self.tables[tag] = entry
def __setitem__(self, tag, data):
"""Write raw table data to disk."""
if tag in self.tables:
raise TTLibError("cannot rewrite '%s' table" % tag)
entry = self.DirectoryEntry()
entry.tag = tag
entry.offset = self.nextTableOffset
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.saveData(self.file, data)
if self.flavor == "woff":
entry.origOffset = self.origNextTableOffset
self.origNextTableOffset += (entry.origLength + 3) & ~3
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.setEntry(tag, entry)
def __getitem__(self, tag):
return self.tables[tag]
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:
raise 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()
compressedMetaData = 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(b"\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.directoryOffset + 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(self.directoryOffset)
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)
if self.DirectoryEntry != SFNTDirectoryEntry:
# Create a SFNT directory for checksum calculation purposes
from fontTools.ttLib import getSearchRange
self.searchRange, self.entrySelector, self.rangeShift = getSearchRange(
self.numTables, 16
)
directory = sstruct.pack(sfntDirectoryFormat, self)
tables = sorted(self.tables.items())
for tag, entry in tables:
sfntEntry = SFNTDirectoryEntry()
sfntEntry.tag = entry.tag
sfntEntry.checkSum = entry.checkSum
sfntEntry.offset = entry.origOffset
sfntEntry.length = entry.origLength
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))
def reordersTables(self):
return False
# -- 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
def __init__(self):
super(WOFFDirectoryEntry, self).__init__()
# With fonttools<=3.1.2, the only way to set a different zlib
# compression level for WOFF directory entries was to set the class
# attribute 'zlibCompressionLevel'. This is now replaced by a globally
# defined `ZLIB_COMPRESSION_LEVEL`, which is also applied when
# compressing the metadata. For backward compatibility, we still
# use the class attribute if it was already set.
if not hasattr(WOFFDirectoryEntry, "zlibCompressionLevel"):
self.zlibCompressionLevel = ZLIB_COMPRESSION_LEVEL
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):
self.origLength = len(data)
if not self.uncompressed:
compressedData = 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
data = self._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 _decompress(self, rawData):
import zlib
return zlib.decompress(rawData)
def calcChecksum(data):
"""Calculate the checksum for an arbitrary block of data.
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 readTTCHeader(file):
file.seek(0)
data = file.read(ttcHeaderSize)
if len(data) != ttcHeaderSize:
raise TTLibError("Not a Font Collection (not enough data)")
self = SimpleNamespace()
sstruct.unpack(ttcHeaderFormat, data, self)
if self.TTCTag != "ttcf":
raise TTLibError("Not a Font Collection")
assert self.Version == 0x00010000 or self.Version == 0x00020000, (
"unrecognized TTC version 0x%08x" % self.Version
)
self.offsetTable = struct.unpack(
">%dL" % self.numFonts, file.read(self.numFonts * 4)
)
if self.Version == 0x00020000:
pass # ignoring version 2.0 signatures
return self
def writeTTCHeader(file, numFonts):
self = SimpleNamespace()
self.TTCTag = "ttcf"
self.Version = 0x00010000
self.numFonts = numFonts
file.seek(0)
file.write(sstruct.pack(ttcHeaderFormat, self))
offset = file.tell()
file.write(struct.pack(">%dL" % self.numFonts, *([0] * self.numFonts)))
return offset
if __name__ == "__main__":
import sys
import doctest
sys.exit(doctest.testmod().failed)