curses window reads are capped at 2047 and silently truncate longer lines

[serhiy-storchaka]

Bug report

window.instr(), in_wstr() and in_wchstr() clamp the count to 2047, so a longer line is cut off with no indication. A pad can be wider than that.

import curses

def check(stdscr):
    pad = curses.newpad(1, 3000)
    pad.addstr(0, 2500, 'X')
    return len(pad.instr(0, 0)), 'X' in pad.instr(0, 0).decode()

print(curses.wrapper(check))     # (2047, False), want (3000, True)

A window read is bounded by the window, so the count only needs to be capped by the columns left on the line, in the unit each method counts: cells for in_wchstr(), characters for in_wstr(), bytes for instr() -- at most CCHARW_MAX characters of MB_CUR_MAX bytes per cell.

The default could then mean the rest of the line, as n < 0 already does inside curses, instead of the arbitrary 2047.

getstr() and get_wstr() read the keyboard rather than the window, so their cap stays.

Linked PRs

• gh-156230: Bound curses window reads by the window instead of 2047 #156266