tarfilter: add --transform option

This commit is contained in:
Johannes Schauer Marin Rodrigues 2022-08-31 05:52:28 +02:00
parent 902bc55c4d
commit 7d7d757f00
Signed by untrusted user: josch
GPG key ID: F2CBA5C78FBD83E1

View file

@ -43,17 +43,53 @@ class PaxFilterAction(argparse.Action):
setattr(namespace, "paxfilter", items)
class TransformAction(argparse.Action):
def __call__(self, parser, namespace, values, option_string=None):
items = getattr(namespace, "trans", [])
# This function mimics what src/transform.c from tar does
if not values.startswith("s"):
raise ValueError("regex must start with an 's'")
if len(values) <= 4:
# minimum regex: s/x//
raise ValueError("invalid regex (too short)")
d = values[1]
if values.startswith(f"s{d}{d}"):
raise ValueError("empty regex")
values = values.removeprefix(f"s{d}")
flags = 0
if values.endswith(f"{d}i"):
# trailing flags
flags = re.IGNORECASE
values = values.removesuffix(f"{d}i")
# This regex only finds non-empty tokens.
# Finding empty tokens would require a variable length look-behind
# or \K in order to find escaped delimiters which is not supported by
# the python re module.
tokens = re.findall(rf"(?:\\[\\{d}]|[^{d}])+", values)
match len(tokens):
case 0:
raise ValueError("invalid regex: not enough terms")
case 1:
repl = ""
case 2:
repl = tokens[1]
case _:
raise ValueError("invalid regex: too many terms: %s" % tokens)
items.append((re.compile(tokens[0], flags), repl))
setattr(namespace, "trans", items)
def main():
parser = argparse.ArgumentParser(
formatter_class=argparse.RawDescriptionHelpFormatter,
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. Since this is
meant for filtering tarballs storing a rootfs, notice that paths must be given
as /path and not as ./path even though they might be stored as such in the
tarball.
dpkg(1) for information on how these two options work in detail. To reuse the
exact same semantics as used by dpkg, paths must be given as /path and not as
./path even though they might be stored as such in the tarball.
Similarly, filter out unwanted pax extended headers. This is useful in cases
Secondly, filter out unwanted pax extended headers. This is useful in cases
where a tool only accepts certain xattr prefixes. For example tar2sqfs only
supports SCHILY.xattr.user.*, SCHILY.xattr.trusted.* and
SCHILY.xattr.security.* but not SCHILY.xattr.system.posix_acl_default.*.
@ -65,7 +101,10 @@ Both types of options use Unix shell-style wildcards:
[seq] matches any character in seq
[!seq] matches any character not in seq
Thirdly, strip leading directory components off of tar members. Just as with
Thirdly, transform the path of tar members using a sed expression just as with
GNU tar --transform.
Fourthly, strip leading directory components off of tar members. Just as with
GNU tar --strip-components, tar members that have less or equal components in
their path are not passed through.
@ -77,29 +116,41 @@ Lastly, shift user id and group id of each entry by the value given by the
"--path-exclude",
metavar="pattern",
action=PathFilterAction,
help="Exclude path matching the given shell pattern.",
help="Exclude path matching the given shell pattern. "
"This option can be specified multiple times.",
)
parser.add_argument(
"--path-include",
metavar="pattern",
action=PathFilterAction,
help="Re-include a pattern after a previous exclusion.",
help="Re-include a pattern after a previous exclusion. "
"This option can be specified multiple times.",
)
parser.add_argument(
"--pax-exclude",
metavar="pattern",
action=PaxFilterAction,
help="Exclude pax header matching the given globbing pattern.",
help="Exclude pax header matching the given globbing pattern. "
"This option can be specified multiple times.",
)
parser.add_argument(
"--pax-include",
metavar="pattern",
action=PaxFilterAction,
help="Re-include a pax header after a previous exclusion.",
help="Re-include a pax header after a previous exclusion. "
"This option can be specified multiple times.",
)
parser.add_argument(
"--transform",
"--xform",
metavar="EXPRESSION",
action=TransformAction,
help="Use sed replace EXPRESSION to transform file names. "
"This option can be specified multiple times.",
)
parser.add_argument(
"--strip-components",
metavar="number",
metavar="NUMBER",
type=int,
help="Strip NUMBER leading components from file names",
)
@ -166,6 +217,8 @@ Lastly, shift user id and group id of each entry by the value given by the
continue
if args.strip_components:
comps = member.name.split("/")
# just as with GNU tar, archive members with less or equal
# number of components are not passed through at all
if len(comps) <= args.strip_components:
continue
member.name = "/".join(comps[args.strip_components :])
@ -183,6 +236,9 @@ Lastly, shift user id and group id of each entry by the value given by the
exit(1)
member.uid += args.idshift
member.gid += args.idshift
if hasattr(args, "trans"):
for r, s in args.trans:
member.name = r.sub(s, member.name)
if member.isfile():
with in_tar.extractfile(member) as file:
out_tar.addfile(member, file)