Unconditionally importing readline causes curses resize handler to break

[Gunni]

Hey,

We had an issue in our curses application after introducing pyroute2.

What happens is as far as we can tell:

1. we import pyroute2
2. it imports readline unconditionally because the Cli module uses it
3. readline adds a SIGWINCH handler
4. we import curses
5. we start a curses wrapper
6. curses wrapper checks if a SIGWINCH handler exists
7. if it exists, it does nothing (breaking resizing)
8. if it does not exist, it installs a resize handler

Here is a fairly minimal example script I found somewhere, observe how importing pyroute2 breaks resizing the window:

import sys,os
import curses

# comment this in/out
#import pyroute2
# this one is also affected
#import pyroute2.IPRoute

def draw_menu(stdscr):
    k = 0
    cursor_x = 0
    cursor_y = 0

    # Clear and refresh the screen for a blank canvas
    stdscr.clear()
    stdscr.refresh()

    # Start colors in curses
    curses.start_color()
    curses.init_pair(1, curses.COLOR_CYAN, curses.COLOR_BLACK)
    curses.init_pair(2, curses.COLOR_RED, curses.COLOR_BLACK)
    curses.init_pair(3, curses.COLOR_BLACK, curses.COLOR_WHITE)

    # Loop where k is the last character pressed
    while (k != ord('q')):

        # Initialization
        stdscr.clear()
        height, width = stdscr.getmaxyx()

        if k == curses.KEY_DOWN:
            cursor_y = cursor_y + 1
        elif k == curses.KEY_UP:
            cursor_y = cursor_y - 1
        elif k == curses.KEY_RIGHT:
            cursor_x = cursor_x + 1
        elif k == curses.KEY_LEFT:
            cursor_x = cursor_x - 1

        cursor_x = max(0, cursor_x)
        cursor_x = min(width-1, cursor_x)

        cursor_y = max(0, cursor_y)
        cursor_y = min(height-1, cursor_y)

        # Declaration of strings
        title = "Curses example"[:width-1]
        subtitle = "Written by Clay McLeod"[:width-1]
        keystr = "Last key pressed: {}".format(k)[:width-1]
        statusbarstr = "Press 'q' to exit | STATUS BAR | Pos: {}, {}".format(cursor_x, cursor_y)
        if k == 0:
            keystr = "No key press detected..."[:width-1]

        # Centering calculations
        start_x_title = int((width // 2) - (len(title) // 2) - len(title) % 2)
        start_x_subtitle = int((width // 2) - (len(subtitle) // 2) - len(subtitle) % 2)
        start_x_keystr = int((width // 2) - (len(keystr) // 2) - len(keystr) % 2)
        start_y = int((height // 2) - 2)

        # Rendering some text
        whstr = "Width: {}, Height: {}".format(width, height)
        stdscr.addstr(0, 0, whstr, curses.color_pair(1))

        # Render status bar
        stdscr.attron(curses.color_pair(3))
        stdscr.addstr(height-1, 0, statusbarstr)
        stdscr.addstr(height-1, len(statusbarstr), " " * (width - len(statusbarstr) - 1))
        stdscr.attroff(curses.color_pair(3))

        # Turning on attributes for title
        stdscr.attron(curses.color_pair(2))
        stdscr.attron(curses.A_BOLD)

        # Rendering title
        stdscr.addstr(start_y, start_x_title, title)

        # Turning off attributes for title
        stdscr.attroff(curses.color_pair(2))
        stdscr.attroff(curses.A_BOLD)

        # Print rest of text
        stdscr.addstr(start_y + 1, start_x_subtitle, subtitle)
        stdscr.addstr(start_y + 3, (width // 2) - 2, '-' * 4)
        stdscr.addstr(start_y + 5, start_x_keystr, keystr)
        stdscr.move(cursor_y, cursor_x)

        # Refresh the screen
        stdscr.refresh()

        # Wait for next input
        k = stdscr.getch()

def main():
    curses.wrapper(draw_menu)

if __name__ == "__main__":
    main()

[svinota]

Trying to reorganize the modules so the readline will not be imported unconditionally.

[svinota]

Pls check if this solution will work for you. Now the readline module is imported in the cli script only, so it doesn't affect the rest of the library.

[svinota]

If it works, then I merge it in the main branch and tag the next release.

[svinota]

Merging, 'cause it's a good idea to move the import anyways.

[Gunni]

Hey, just tested it with the code in https://github.com/svinota/pyroute2/pull/1165.

I can confirm that it works for my use-case.

Note that I did not test the cli module.

Note that this bug may also be fixed https://github.com/svinota/pyroute2/issues/625.

Please publish a new version on PyPi when you can!

[svinota]

Will be rolled out this weekend. Thanks for the feedback!