Function cbreak_already_set

invoke/terminals.py:155–174

(stream: IO)

def cbreak_already_set(stream: IO) -> bool:
    # Explicitly not docstringed to remain private, for now. Eh.
    # Checks whether tty.setcbreak appears to have already been run against
    # ``stream`` (or if it would otherwise just not do anything).
    # Used to effect idempotency for character-buffering a stream, which also
    # lets us avoid multiple capture-then-restore cycles.
    attrs = termios.tcgetattr(stream)
    lflags, cc = attrs[3], attrs[6]
    echo = bool(lflags & termios.ECHO)
    icanon = bool(lflags & termios.ICANON)
    # setcbreak sets ECHO and ICANON to 0/off, CC[VMIN] to 1-ish, and CC[VTIME]
    # to 0-ish. If any of that is not true we can reasonably assume it has not
    # yet been executed against this stream.
    sentinels = (
        not echo,
        not icanon,
        cc[termios.VMIN] in [1, b"\x01"],
        cc[termios.VTIME] in [0, b"\x00"],
    )
    return all(sentinels)


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