cpython/Lib/pty.py

"""Pseudo terminal utilities."""

# Bugs: No signal handling.  Doesn't set slave termios and window size.
#       Only tested on Linux.
# See:  W. Richard Stevens. 1992.  Advanced Programming in the
#       UNIX Environment.  Chapter 19.
# Author: Steen Lumholt -- with additions by Guido.

from select import select
import os

# Absurd:  import termios and then delete it.  This is to force an attempt
# to import pty to raise an ImportError on platforms that lack termios.
# Without this explicit import of termios here, some other module may
# import tty first, which in turn imports termios and dies with an
# ImportError then.  But since tty *does* exist across platforms, that
# leaves a damaged module object for tty in sys.modules, and the import
# of tty here then appears to work despite that the tty imported is junk.
import termios
del termios

import tty

__all__ = ["openpty","fork","spawn"]

STDIN_FILENO = 0
STDOUT_FILENO = 1
STDERR_FILENO = 2

CHILD = 0

def openpty():
    """openpty() -> (master_fd, slave_fd)
    Open a pty master/slave pair, using os.openpty() if possible."""

    try:
        return os.openpty()
    except (AttributeError, OSError):
        pass
    master_fd, slave_name = _open_terminal()
    slave_fd = slave_open(slave_name)
    return master_fd, slave_fd

def master_open():
    """master_open() -> (master_fd, slave_name)
    Open a pty master and return the fd, and the filename of the slave end.
    Deprecated, use openpty() instead."""

    try:
        master_fd, slave_fd = os.openpty()
    except (AttributeError, OSError):
        pass
    else:
        slave_name = os.ttyname(slave_fd)
        os.close(slave_fd)
        return master_fd, slave_name

    return _open_terminal()

def _open_terminal():
    """Open pty master and return (master_fd, tty_name).
    SGI and generic BSD version, for when openpty() fails."""
    try:
        import sgi
    except ImportError:
        pass
    else:
        try:
            tty_name, master_fd = sgi._getpty(os.O_RDWR, 0666, 0)
        except IOError, msg:
            raise os.error, msg
        return master_fd, tty_name
    for x in 'pqrstuvwxyzPQRST':
        for y in '0123456789abcdef':
            pty_name = '/dev/pty' + x + y
            try:
                fd = os.open(pty_name, os.O_RDWR)
            except os.error:
                continue
            return (fd, '/dev/tty' + x + y)
    raise os.error, 'out of pty devices'

def slave_open(tty_name):
    """slave_open(tty_name) -> slave_fd
    Open the pty slave and acquire the controlling terminal, returning
    opened filedescriptor.
    Deprecated, use openpty() instead."""

    return os.open(tty_name, os.O_RDWR)

def fork():
    """fork() -> (pid, master_fd)
    Fork and make the child a session leader with a controlling terminal."""

    try:
        pid, fd = os.forkpty()
    except (AttributeError, OSError):
        pass
    else:
        if pid == CHILD:
            try:
                os.setsid()
            except OSError:
                # os.forkpty() already set us session leader
                pass
        return pid, fd

    master_fd, slave_fd = openpty()
    pid = os.fork()
    if pid == CHILD:
        # Establish a new session.
        os.setsid()
        os.close(master_fd)

        # Slave becomes stdin/stdout/stderr of child.
        os.dup2(slave_fd, STDIN_FILENO)
        os.dup2(slave_fd, STDOUT_FILENO)
        os.dup2(slave_fd, STDERR_FILENO)
        if (slave_fd > STDERR_FILENO):
            os.close (slave_fd)

    # Parent and child process.
    return pid, master_fd

def _writen(fd, data):
    """Write all the data to a descriptor."""
    while data != '':
        n = os.write(fd, data)
        data = data[n:]

def _read(fd):
    """Default read function."""
    return os.read(fd, 1024)

def _copy(master_fd, master_read=_read, stdin_read=_read):
    """Parent copy loop.
    Copies
            pty master -> standard output   (master_read)
            standard input -> pty master    (stdin_read)"""
    while 1:
        rfds, wfds, xfds = select(
                [master_fd, STDIN_FILENO], [], [])
        if master_fd in rfds:
            data = master_read(master_fd)
            os.write(STDOUT_FILENO, data)
        if STDIN_FILENO in rfds:
            data = stdin_read(STDIN_FILENO)
            _writen(master_fd, data)

def spawn(argv, master_read=_read, stdin_read=_read):
    """Create a spawned process."""
    if type(argv) == type(''):
        argv = (argv,)
    pid, master_fd = fork()
    if pid == CHILD:
        apply(os.execlp, (argv[0],) + argv)
    try:
        mode = tty.tcgetattr(STDIN_FILENO)
        tty.setraw(STDIN_FILENO)
        restore = 1
    except tty.error:    # This is the same as termios.error
        restore = 0
    try:
        _copy(master_fd, master_read, stdin_read)
    except (IOError, OSError):
        if restore:
            tty.tcsetattr(STDIN_FILENO, tty.TCSAFLUSH, mode)