add taridshift.py

taridshift.py

@@ -0,0 +1,55 @@
+#!/usr/bin/env python3
+#
+# This script is in the public domain
+#
+# This script accepts a tarball on standard input and prints a tarball on
+# standard output with the same contents but all uid and gid ownership
+# information shifted by the value given as first command line argument.
+#
+# 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
+
+
+def main():
+    if len(sys.argv) < 2:
+        print("usage: %s idshift" % sys.argv[0], file=sys.stderr)
+        exit(1)
+
+    idshift = int(sys.argv[1])
+
+    # 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 idshift < 0 and -idshift > member.uid:
+                print("uid cannot be negative", file=sys.stderr)
+                exit(1)
+            if idshift < 0 and -idshift > member.gid:
+                print("gid cannot be negative", file=sys.stderr)
+                exit(1)
+
+            member.uid += idshift
+            member.gid += idshift
+            if member.isfile():
+                with in_tar.extractfile(member) as file:
+                    out_tar.addfile(member, file)
+            else:
+                out_tar.addfile(member)
+
+
+if __name__ == "__main__":
+    main()