woff2otf.py

#!/usr/bin/env python3
#
# Copyright 2012, Steffen Hanikel (https://github.com/hanikesn)
#
#   Licensed under the Apache License, Version 2.0 (the "License");
#   you may not use this file except in compliance with the License.
#   You may obtain a copy of the License at
#
#       http://www.apache.org/licenses/LICENSE-2.0
#
#   Unless required by applicable law or agreed to in writing, software
#   distributed under the License is distributed on an "AS IS" BASIS,
#   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
#   See the License for the specific language governing permissions and
#   limitations under the License.
#
# A tool to convert a WOFF back to a TTF/OTF font file, in pure Python

import struct
import sys
import zlib


def convert_streams(infile, outfile):
    WOFFHeader = {'signature': struct.unpack(">I", infile.read(4))[0],
                  'flavor': struct.unpack(">I", infile.read(4))[0],
                  'length': struct.unpack(">I", infile.read(4))[0],
                  'numTables': struct.unpack(">H", infile.read(2))[0],
                  'reserved': struct.unpack(">H", infile.read(2))[0],
                  'totalSfntSize': struct.unpack(">I", infile.read(4))[0],
                  'majorVersion': struct.unpack(">H", infile.read(2))[0],
                  'minorVersion': struct.unpack(">H", infile.read(2))[0],
                  'metaOffset': struct.unpack(">I", infile.read(4))[0],
                  'metaLength': struct.unpack(">I", infile.read(4))[0],
                  'metaOrigLength': struct.unpack(">I", infile.read(4))[0],
                  'privOffset': struct.unpack(">I", infile.read(4))[0],
                  'privLength': struct.unpack(">I", infile.read(4))[0]}

    outfile.write(struct.pack(">I", WOFFHeader['flavor']));
    outfile.write(struct.pack(">H", WOFFHeader['numTables']));
    maximum = list(filter(lambda x: x[1] <= WOFFHeader['numTables'], [(n, 2**n) for n in range(64)]))[-1]; 
    searchRange = maximum[1] * 16
    outfile.write(struct.pack(">H", searchRange));
    entrySelector = maximum[0]
    outfile.write(struct.pack(">H", entrySelector));
    rangeShift = WOFFHeader['numTables'] * 16 -  searchRange;
    outfile.write(struct.pack(">H", rangeShift));

    offset = outfile.tell()

    TableDirectoryEntries = []
    for i in range(0, WOFFHeader['numTables']):
        TableDirectoryEntries.append({'tag': struct.unpack(">I", infile.read(4))[0],
                               'offset': struct.unpack(">I", infile.read(4))[0],
                               'compLength': struct.unpack(">I", infile.read(4))[0],
                               'origLength': struct.unpack(">I", infile.read(4))[0],
                               'origChecksum': struct.unpack(">I", infile.read(4))[0]})
        offset += 4*4
        
    for TableDirectoryEntry in TableDirectoryEntries:   
        outfile.write(struct.pack(">I", TableDirectoryEntry['tag']))
        outfile.write(struct.pack(">I", TableDirectoryEntry['origChecksum']))
        outfile.write(struct.pack(">I", offset))
        outfile.write(struct.pack(">I", TableDirectoryEntry['origLength']))
        TableDirectoryEntry['outOffset'] = offset
        offset += TableDirectoryEntry['origLength']
        if (offset % 4) != 0:
            offset += 4 - (offset % 4)
            
    for TableDirectoryEntry in TableDirectoryEntries:
        infile.seek(TableDirectoryEntry['offset'])
        compressedData = infile.read(TableDirectoryEntry['compLength'])
        if TableDirectoryEntry['compLength'] != TableDirectoryEntry['origLength']:
            uncompressedData = zlib.decompress(compressedData)
        else:
            uncompressedData = compressedData
        outfile.seek(TableDirectoryEntry['outOffset'])
        outfile.write(uncompressedData)
        offset = TableDirectoryEntry['outOffset'] + TableDirectoryEntry['origLength'];
        padding = 0
        if (offset % 4) != 0:
            padding = 4 - (offset % 4)
        outfile.write(bytearray(padding));


def convert(infilename, outfilename):
    with open(infilename , mode='rb') as infile:
        with open(outfilename, mode='wb') as outfile:
            convert_streams(infile, outfile)


def main(argv):
    if len(argv) == 1 or len(argv) > 3:
        print('I convert *.woff files to *.otf files. (one at a time :)\n'
              'Usage: woff2otf.py web_font.woff [converted_filename.otf]\n'
              'If the target file name is omitted, it will be guessed. Have fun!\n')
        return

    source_file_name  = argv[1]
    if len(argv) == 3:
        target_file_name = argv[2]
    else:
        target_file_name = source_file_name.rsplit('.', 1)[0] + '.otf'

    convert(source_file_name, target_file_name)
    return 0


if __name__ == '__main__':
    sys.exit(main(sys.argv))