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"""CLI utility to compute crc32c on an input file."""
import argparse
import functools
import mmap
import os
import sys
import time
import typing
from ._crc32c import crc32c
DEFAULT_BLOCK_SIZE_FREAD = 64 * 1024
DEFAULT_BLOCK_SIZE_MMAP = 10 * 1024 * 1024
class _ChecksumingResult(typing.NamedTuple):
filename: str
file_size: int
checksum: int
duration: float
class _FormattingOptions(typing.NamedTuple):
show_filename: bool
show_speed: bool
def _mmap_iterator(
fileno: int, file_size: int, block_size: int
) -> typing.Generator[mmap.mmap, None, None]:
for offset in range(0, file_size, block_size):
length = min(block_size, file_size - offset)
with mmap.mmap(
fileno, length=length, offset=offset, access=mmap.ACCESS_READ
) as mm:
yield mm
def _get_checksum(filename: str, block_size: int, use_mmap: bool) -> _ChecksumingResult:
with open(filename, "rb") as input_file:
fileno = input_file.fileno()
file_size = os.stat(fileno).st_size
data_iterator: typing.Iterator[mmap.mmap | bytes]
if use_mmap:
data_iterator = _mmap_iterator(fileno, file_size, block_size)
else:
read = functools.partial(input_file.read, block_size)
data_iterator = iter(read, b"")
checksum = 0
start = time.monotonic()
for data in data_iterator:
checksum = crc32c(data, checksum)
end = time.monotonic()
return _ChecksumingResult(filename, file_size, checksum, (end - start))
def _format_result(
result: _ChecksumingResult, formatting_opts: _FormattingOptions
) -> str:
report = f"{result.checksum:08x}"
if formatting_opts.show_filename:
report += f" {result.filename}"
if formatting_opts.show_speed:
speed = result.file_size / result.duration
report += f" ({speed / 1024 / 1024:.2f} MB/s)"
return report
def main(name: str = sys.argv[0], args: typing.List[str] = sys.argv[1:]) -> None:
"""Main application entry-point."""
parser = argparse.ArgumentParser(
sys.argv[0], description="Calculates and prints crc32c on input file(s)"
)
parser.add_argument("filenames", nargs="+", help="input file(s)")
io_group = parser.add_argument_group("I/O options")
io_group.add_argument(
"-M", "--disable-mmap", help="Avoid reading file with mmap", action="store_true"
)
io_group.add_argument(
"-b",
"--block-size",
type=int,
help=f"Block size for iterative reading",
)
formatting_group = parser.add_argument_group("Formatting options")
formatting_group.add_argument(
"-s",
"--show-speed",
help="Report checksumming speed on each file",
action="store_true",
)
formatting_group.add_argument(
"-N",
"--hide-filename",
help="Do not print filename in result",
action="store_true",
)
opts = parser.parse_args(args)
use_mmap = not opts.disable_mmap
block_size = DEFAULT_BLOCK_SIZE_MMAP if use_mmap else DEFAULT_BLOCK_SIZE_FREAD
get_checksum = functools.partial(
_get_checksum, block_size=block_size, use_mmap=use_mmap
)
formatting_opts = _FormattingOptions(not opts.hide_filename, opts.show_speed)
for result in map(get_checksum, opts.filenames):
print(_format_result(result, formatting_opts))
if __name__ == "__main__":
main()