"""Pseudo terminal utilities."""
# Bugs: No signal handling. Doesn't set slave termios and window size.
# Only tested on Linux, FreeBSD, and macOS.
# 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
import sys
import tty
# names imported directly for test mocking purposes
from os import close, waitpid
from tty import setraw, tcgetattr, tcsetattr
__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 = os.open(slave_name, os.O_RDWR)
try:
from fcntl import ioctl, I_PUSH
except ImportError:
return master_fd, slave_fd
try:
ioctl(slave_fd, I_PUSH, "ptem")
ioctl(slave_fd, I_PUSH, "ldterm")
except OSError:
pass
return master_fd, slave_fd
def _open_terminal():
"""Open pty master and 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 OSError:
continue
return (fd, '/dev/tty' + x + y)
raise OSError('out of pty devices')
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:
os.close(master_fd)
os.login_tty(slave_fd)
else:
os.close(slave_fd)
# Parent and child process.
return pid, master_fd
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)"""
if os.get_blocking(master_fd):
# If we write more than tty/ndisc is willing to buffer, we may block
# indefinitely. So we set master_fd to non-blocking temporarily during
# the copy operation.
os.set_blocking(master_fd, False)
try:
_copy(master_fd, master_read=master_read, stdin_read=stdin_read)
finally:
# restore blocking mode for backwards compatibility
os.set_blocking(master_fd, True)
return
high_waterlevel = 4096
stdin_avail = master_fd != STDIN_FILENO
stdout_avail = master_fd != STDOUT_FILENO
i_buf = b''
o_buf = b''
while 1:
rfds = []
wfds = []
if stdin_avail and len(i_buf) < high_waterlevel:
rfds.append(STDIN_FILENO)
if stdout_avail and len(o_buf) < high_waterlevel:
rfds.append(master_fd)
if stdout_avail and len(o_buf) > 0:
wfds.append(STDOUT_FILENO)
if len(i_buf) > 0:
wfds.append(master_fd)
rfds, wfds, _xfds = select(rfds, wfds, [])
if STDOUT_FILENO in wfds:
try:
n = os.write(STDOUT_FILENO, o_buf)
o_buf = o_buf[n:]
except OSError:
stdout_avail = False
if master_fd in rfds:
# Some OSes signal EOF by returning an empty byte string,
# some throw OSErrors.
try:
data = master_read(master_fd)
except OSError:
data = b""
if not data: # Reached EOF.
return # Assume the child process has exited and is
# unreachable, so we clean up.
o_buf += data
if master_fd in wfds:
n = os.write(master_fd, i_buf)
i_buf = i_buf[n:]
if stdin_avail and STDIN_FILENO in rfds:
data = stdin_read(STDIN_FILENO)
if not data:
stdin_avail = False
else:
i_buf += data
def spawn(argv, master_read=_read, stdin_read=_read):
"""Create a spawned process."""
if isinstance(argv, str):
argv = (argv,)
sys.audit('pty.spawn', argv)
pid, master_fd = fork()
if pid == CHILD:
os.execlp(argv[0], *argv)
try:
mode = tcgetattr(STDIN_FILENO)
setraw(STDIN_FILENO)
restore = True
except tty.error: # This is the same as termios.error
restore = False
try:
_copy(master_fd, master_read, stdin_read)
finally:
if restore:
tcsetattr(STDIN_FILENO, tty.TCSAFLUSH, mode)
close(master_fd)
return waitpid(pid, 0)[1]
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