mmdebstrap/tarfilter

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#!/usr/bin/env python3
#
# This script is in the public domain
#
# This script accepts a tarball on standard input and filters it according to
# the same rules used by dpkg --path-exclude and --path-include, using command
# line options of the same name. The result is then printed on standard output.
#
# A tool like this should be written in C but libarchive has issues:
# https://github.com/libarchive/libarchive/issues/587
# https://github.com/libarchive/libarchive/pull/1288/ (needs 3.4.1)
# Should these issues get fixed, then a good template is tarfilter.c in the
# examples directory of libarchive.
#
# We are not using Perl either, because Archive::Tar slurps the whole tarball
# into memory.
#
# We could also use Go but meh...
# https://stackoverflow.com/a/59542307/784669
import tarfile
import sys
import argparse
import fnmatch
import re
class FilterAction(argparse.Action):
def __call__(self, parser, namespace, values, option_string=None):
items = getattr(namespace, "filter", [])
regex = re.compile(fnmatch.translate(values))
items.append((self.dest, regex))
setattr(namespace, "filter", items)
def main():
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parser = argparse.ArgumentParser(
description="""\
Filters a tarball on standard input by the same rules as the dpkg --path-exclude
and --path-include options and writes resulting tarball to standard output. See
dpkg(1) for information on how these two options work in detail.
"""
)
parser.add_argument(
"--path-exclude",
metavar="pattern",
action=FilterAction,
help="Exclude path matching the given shell pattern.",
)
parser.add_argument(
"--path-include",
metavar="pattern",
action=FilterAction,
help="Re-include a pattern after a previous exclusion.",
)
args = parser.parse_args()
if not hasattr(args, "filter"):
from shutil import copyfileobj
copyfileobj(sys.stdin.buffer, sys.stdout.buffer)
exit()
# same logic as in dpkg/src/filters.c/filter_should_skip()
def filter_should_skip(member):
skip = False
if not args.filter:
return False
for (t, r) in args.filter:
if r.match(member.name[1:]) is not None:
if t == "path_include":
skip = False
else:
skip = True
if skip and (member.isdir() or member.issym()):
for (t, r) in args.filter:
if t != "path_include":
continue
prefix = re.sub(r"^([^*?[\\]*).*", r"\1", r.pattern)
prefix = prefix.rstrip("/")
if member.name[1:].startswith(prefix):
if member.name == "./usr/share/doc/doc-debian":
print("foo", prefix, "bar", file=sys.stderr)
return False
return skip
# starting with Python 3.8, the default format became PAX_FORMAT, so this
# is only for compatibility with older versions of Python 3
with tarfile.open(fileobj=sys.stdin.buffer, mode="r|*") as in_tar, tarfile.open(
fileobj=sys.stdout.buffer, mode="w|", format=tarfile.PAX_FORMAT
) as out_tar:
for member in in_tar:
if filter_should_skip(member):
continue
if member.isfile():
with in_tar.extractfile(member) as file:
out_tar.addfile(member, file)
else:
out_tar.addfile(member)
if __name__ == "__main__":
main()