scripts/make_data_cpp.py

#!/usr/bin/env python

# Copyright 2022 Google LLC.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

'''
Generate a source file containing the given binary data.

Output type is C++.

This is required for a WASM build because the Emscripten toolchain cannot
load data files using file I/O, nor can it consume assembly files.

This is in use by the Flutter web engine and Skia CanvasKit. See
[this](https://github.com/google/skia/blob/main/modules/canvaskit/README.md)
for an example of a build using this.
'''

from __future__ import print_function

import os
import struct
import sys
import mmap

def get_version_number(path):
    input_data = open(path, 'rb').read()
    n = input_data.find(b'icudt')
    if n == -1:
        exit("Cannot find a version number in %s." % path)

    return input_data[n + 5:n + 7].decode("ascii")

def iterate_as_uint32(path):
    with open(path, 'rb') as f:
        s = struct.Struct('@I')
        assert s.size == 4
        mm = mmap.mmap(f.fileno(), 0, access=mmap.ACCESS_READ)
        assert (len(mm) % s.size) == 0
        for offset in range(0, len(mm), s.size):
            yield s.unpack_from(mm, offset)[0]
        mm.close()


def convert(fmt, src_path, dst_path):
    header, line_begin, line_end, footer = fmt
    assert os.path.exists(src_path)
    version_number = get_version_number(src_path)
    name = 'icudt%s_dat' % version_number
    src = iterate_as_uint32(src_path)
    with open(dst_path, 'w') as o:
        o.write(header.format(name))
        while True:
            line = ','.join('%d' % v for _, v in zip(range(8), src))
            if not line:
                break
            o.write('%s%s%s\n' % (line_begin, line, line_end))
        o.write(footer.format(name))


cpp = ('#include <cstdint>\nextern "C" uint32_t {0}[] __attribute__((aligned(16))) = {{\n',
       '', ',', '}};\n')

if __name__ == '__main__':
    convert(cpp, sys.argv[1], sys.argv[2])