Source code for sshMaxArg

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
#    Copyright (C) 2015-2017 Germar Reitze
#
#    This program is free software; you can redistribute it and/or modify
#    it under the terms of the GNU General Public License as published by
#    the Free Software Foundation; either version 2 of the License, or
#    (at your option) any later version.
#
#    This program is distributed in the hope that it will be useful,
#    but WITHOUT ANY WARRANTY; without even the implied warranty of
#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#    GNU General Public License for more details.
#
#    You should have received a copy of the GNU General Public License along
#    with this program; if not, write to the Free Software Foundation, Inc.,
#    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.

import random
import string
import subprocess
import socket
import argparse

def randomId(size=6, chars=string.ascii_uppercase + string.digits):
    return ''.join(random.choice(chars) for x in range(size))

def maxArgLength(config, mid = 1048320):
    r = round(mid / 2)
    while r > 0:
        ssh = config.sshCommand(cmd = ['printf', randomId(mid)],
                                 nice = False,
                                 ionice = False,
                                 prefix = False)
        try:
            proc = subprocess.Popen(ssh,
                                    stdout = subprocess.PIPE,
                                    stderr = subprocess.PIPE,
                                    universal_newlines = True)
            out, err = proc.communicate()
        except OSError as e:
            if e.errno == 7:
                reportTest(mid, 'python exception: %s' % e.strerror)
                mid -= r
            else:
                raise
        else:
            l = len(out)
            if l == mid:
                reportTest(mid, 'can be longer')
                mid += r
            else:
                reportTest(mid, 'is to long')
                mid -= r
        r = round(r / 2)
    return mid + 6

def reportTest(mid, msg):
    print('Check length %s:\t%s' % (mid, msg))

def reportResult(host, mid):
    print('Maximum SSH argument length between "%s" and "%s" is %s'
          % (socket.gethostname(), host, mid))

if __name__ == '__main__':
    parser = argparse.ArgumentParser(description = 'Check maximal argument length on SSH connection',
                                     formatter_class=argparse.ArgumentDefaultsHelpFormatter)
    parser.add_argument('MID',
                        type = int,
                        nargs = '?',
                        default = 1048320,
                        help = 'Start checking with MID arg length')
    args = parser.parse_args()
    import config
    cfg = config.Config()
    mid = maxArgLength(cfg, args.MID)
    reportResult(cfg.sshHost(), mid)