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1import errno
2import os
3import pty
4import select
5import signal
6import sys
7import termios
8
9STDIN = 0
10STDOUT = 1
11STDERR = 2
12
13
14def pipe(sfd, dfd):
15  try:
16    data = os.read(sfd, 256)
17  except OSError as e:
18    if e.errno != errno.EIO:
19      raise
20    return True  # EOF
21
22  if not data:
23    return True  # EOF
24
25  if dfd == STDOUT:
26    # Work around platform quirks. Some platforms echo ^D as \x04
27    # (AIX, BSDs) and some don't (Linux).
28    #
29    # The comparison against b' '[0] is because |data| is
30    # a string in python2 but a bytes object in python3.
31    filt = lambda c: c >= b' '[0] or c in b'\t\n\r\f'
32    data = filter(filt, data)
33    data = bytes(data)
34
35  while data:
36    try:
37      n = os.write(dfd, data)
38    except OSError as e:
39      if e.errno != errno.EIO:
40        raise
41      return True  # EOF
42    data = data[n:]
43
44
45if __name__ == '__main__':
46  argv = sys.argv[1:]
47
48  # Make select() interruptable by SIGCHLD.
49  signal.signal(signal.SIGCHLD, lambda nr, _: None)
50
51  parent_fd, child_fd = pty.openpty()
52  assert parent_fd > STDIN
53
54  mode = termios.tcgetattr(child_fd)
55  # Don't translate \n to \r\n.
56  mode[1] = mode[1] & ~termios.ONLCR  # oflag
57  # Disable ECHOCTL. It's a BSD-ism that echoes e.g. \x04 as ^D but it
58  # doesn't work on platforms like AIX and Linux. I checked Linux's tty
59  # driver and it's a no-op, the driver is just oblivious to the flag.
60  mode[3] = mode[3] & ~termios.ECHOCTL  # lflag
61  termios.tcsetattr(child_fd, termios.TCSANOW, mode)
62
63  pid = os.fork()
64  if not pid:
65    os.setsid()
66    os.close(parent_fd)
67
68    # Ensure the pty is a controlling tty.
69    name = os.ttyname(child_fd)
70    fd = os.open(name, os.O_RDWR)
71    os.dup2(fd, child_fd)
72    os.close(fd)
73
74    os.dup2(child_fd, STDIN)
75    os.dup2(child_fd, STDOUT)
76    os.dup2(child_fd, STDERR)
77
78    if child_fd > STDERR:
79      os.close(child_fd)
80
81    os.execve(argv[0], argv, os.environ)
82    raise Exception('unreachable')
83
84  os.close(child_fd)
85
86  fds = [STDIN, parent_fd]
87  while fds:
88    try:
89      rfds, _, _ = select.select(fds, [], [])
90    except select.error as e:
91      if e[0] != errno.EINTR:
92        raise
93      if pid == os.waitpid(pid, os.WNOHANG)[0]:
94        break
95
96    if STDIN in rfds:
97      if pipe(STDIN, parent_fd):
98        fds.remove(STDIN)
99
100    if parent_fd in rfds:
101      if pipe(parent_fd, STDOUT):
102        break
103