Mini Shell

#!/usr/bin/env python3

# This implements a simple protocol to do user & group conversions between
# names & ids.  All input and output consists of simple strings with a
# terminating newline.
#
# The requests can be:
#
#   uid ID_NUM\n  ->  NAME\n
#   gid ID_NUM\n  ->  NAME\n
#   usr NAME\n    ->  ID_NUM\n
#   grp NAME\n    ->  ID_NUM\n
#
# An unknown ID_NUM or NAME results in an empty return value.
#
# This is used by an rsync daemon when configured with the "name converter" and
# (often) "use chroot = true".  While this converter uses real user & group
# lookups you could change it to use any mapping idiom you'd like.

import sys, argparse, pwd, grp

def main():
    for line in sys.stdin:
        try:
            req, arg = line.rstrip().split(' ', 1)
        except:
            req = None
        try:
            if req == 'uid':
                ans = pwd.getpwuid(int(arg)).pw_name
            elif req == 'gid':
                ans = grp.getgrgid(int(arg)).gr_name
            elif req == 'usr':
                ans = pwd.getpwnam(arg).pw_uid
            elif req == 'grp':
                ans = grp.getgrnam(arg).gr_gid
            else:
                print("Invalid request", file=sys.stderr)
                sys.exit(1)
        except KeyError:
            ans = ''
        print(ans, flush=True)


if __name__ == '__main__':
    parser = argparse.ArgumentParser(description="Convert users & groups between names & numbers for an rsync daemon.")
    args = parser.parse_args()
    main()

# vim: sw=4 et