MozLz4a compression/decompression utility

mozlz4a.py

#!/usr/bin/env python3
# vim: sw=4 ts=4 et tw=100 cc=+1
#
####################################################################################################
#                                           DESCRIPTION                                            #
####################################################################################################
#
# Decompressor/compressor for files in Mozilla's "mozLz4" format. Firefox uses this file format to
# compress e. g. bookmark backups (*.jsonlz4).
#
# This file format is in fact just plain LZ4 data with a custom header (magic number [8 bytes] and
# uncompressed file size [4 bytes, little endian]).
#
####################################################################################################
#                                           DEPENDENCIES                                           #
####################################################################################################
#
# - Tested with Python 3.10
# - LZ4 bindings for Python, version 4.x: https://pypi.python.org/pypi/lz4
#
####################################################################################################
#                                             LICENSE                                              #
####################################################################################################
#
# Copyright (c) 2015-2022, Tilman Blumenbach
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without modification, are permitted
# provided that the following conditions are met:
#
# 1. Redistributions of source code must retain the above copyright notice, this list of conditions
#    and the following disclaimer.
# 2. Redistributions in binary form must reproduce the above copyright notice, this list of
#    conditions and the following disclaimer in the documentation and/or other materials provided
#    with the distribution.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
# IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
# FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
# IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
# OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

import argparse
import sys

import lz4.block


class BinFileArg:
    def __init__(self, mode):
        self._mode = mode

    def __call__(self, arg):
        objs = {
            "r": sys.stdin.buffer,
            "w": sys.stdout.buffer,
        }

        if arg == "-":
            return objs[self._mode]

        try:
            return open(arg, self._mode + "b")
        except OSError as e:
            raise argparse.ArgumentTypeError(
                "failed to open file for %s: %s" % (
                    "reading" if self._mode == "r" else "writing",
                    e
                )
            )


def decompress(file_obj):
    if file_obj.read(8) != b"mozLz40\0":
        raise ValueError("Invalid magic number")

    return lz4.block.decompress(file_obj.read())


def compress(file_obj):
    compressed = lz4.block.compress(file_obj.read())
    return b"mozLz40\0" + compressed


def get_argparser():
    p = argparse.ArgumentParser(
        description="MozLz4a compression/decompression utility"
    )

    p.add_argument(
        "-d", "--decompress", "--uncompress",
        action="store_true",
        help="Decompress the input file instead of compressing it."
    )

    p.add_argument(
        "in_file",
        type=BinFileArg("r"),
        help="Path to input file. `-' means standard input."
    )
    p.add_argument(
        "out_file",
        type=BinFileArg("w"),
        nargs="?",
        default="-",
        help="Path to output file. `-' means standard output (and is the default)."
    )

    return p


def main():
    args = get_argparser().parse_args()

    try:
        with args.in_file as fh:
            if args.decompress:
                data = decompress(fh)
            else:
                data = compress(fh)
    except Exception as e:
        print(
            "Could not compress/decompress file `%s': %s" % (
                args.in_file.name,
                e
            ),
            file=sys.stderr
        )
        sys.exit(4)

    try:
        with args.out_file as fh:
            fh.write(data)
    except Exception as e:
        print(
            "Could not write to output file `%s': %s" % (
                args.out_file.name,
                e
            ),
            file=sys.stderr
        )
        sys.exit(5)


if __name__ == "__main__":
    sys.exit(main())

They also use lz4 for the session file containing tabs and history, which can be much larger. Getting access to the contents of that file is why I'm interested in lz4 at all. Although I find your conspiracy theory interesting, and it may be true, I'm not really interested about default search engines.

Not sure what you mean by, "are you a courtroom?" Yes I am. Or no I'm not. Who cares.

Also, you need to chill out.