resize3.py

# Resize ExtremeXOS (EXOS) CLI to current terminal dimensions.

# Copyright (C) 2016,2021 Erik Auerswald <auerswal@unix-ag.uni-kl.de>

# 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, version 3.
#
# 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, see <https://www.gnu.org/licenses/>.

# -----------------------------------------------------------------------------
# source for code inside terminal_size_ioctl() function taken from a Stack
# Overflow answer by "pascal" and modified by "mic_e":
# http://stackoverflow.com/questions/566746/how-to-get-console-window-width-in-python/3010495#3010495
# (short link: https://stackoverflow.com/a/3010495)
# answer is from 2010, thus licensed under CC BY-SA 2.5 by Stack Exchange Inc.
def terminal_size_ioctl():
    import fcntl, termios, struct
    print 'attempting TTY IOCTL "TIOCGWINSZ"...'
    h, w, hp, wp = struct.unpack('HHHH',
        fcntl.ioctl(1, termios.TIOCGWINSZ,
        struct.pack('HHHH', 0, 0, 0, 0)))
    return w, h
# -----------------------------------------------------------------------------

# -----------------------------------------------------------------------------
# This method works via serial console, but only if the terminal (emulator)
# supports it and has it enabled.  GNOME Terminal supports it by default,
# XTerm needs enabling of the "Allow Window Ops" configuration option.
def terminal_size_cs():
    import os
    import signal
    import time

    print 'attempting terminal control sequence...'

    # send a command to the connected terminal(s)
    fd = os.open('/dev/tty', os.O_WRONLY)
    os.write(fd, b"\033[18t")
    os.close(fd)

    # overwrite echoed terminal answer(s)
    time.sleep(0.15)
    print '\rpress ENTER or CTRL-D to continue...'

    # Python needs to be kicked to read the data, the script will block
    # until the user does something useful...

    # read the first arriving answer, or time out
    signal.alarm(15)
    reply_list = []
    fd = os.open('/dev/tty', os.O_RDONLY)
    try:
        c = os.read(fd, 1)
        while c != 't':
            reply_list.append(c)
            c = os.read(fd, 1)
    except:
        print 'no terminal size information received before timeout'
        return 0, 0

    # read and discard whatever was sent after the first answer
    fd = os.open('/dev/tty', os.O_RDONLY | os.O_NONBLOCK)
    try:
        while os.read(fd, 1):
            pass
    except:
        pass

    # try to parse the reply
    reply = ''.join(reply_list)
    parts = reply.split(';')
    try:
        if len(parts) >= 3:
            lines = int(parts[1])
            columns = int(parts[2])
        else:
            lines, columns = 24, 80
    except:
        lines, columns = 24, 80

    return columns, lines
# -----------------------------------------------------------------------------

# this only works in remote sessions (SSH, Telnet), not via serial console
columns, lines = terminal_size_ioctl()

# if TIOCGWINSZ did not work, try a terminal control sequence
if (columns <= 0) or (lines <= 0):
    columns, lines = terminal_size_cs()

# exit with error message if nothing worked
if (columns <= 0) or (lines <= 0):
    print 'Error: could not determine terminal size'
    exit(1)

# columns must be in the range [80, 256]
if columns < 80:
    columns = 80
elif columns > 256:
    columns = 256

# lines must be in the range [24, 128]
if lines < 24:
    lines = 24
elif lines > 128:
    lines = 128

# tell the user what we are going to do
print 'setting terminal size to {0}x{1}'.format(columns, lines)

# the exsh module is available on ExtremeXOS switches that provide Python
import exsh
exsh.clicmd("configure cli columns {0}".format(columns))
exsh.clicmd("configure cli lines {0}".format(lines))