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Code Issues Projects Releases Packages Wiki Activity Actions 18

bpo-26228: Fix pty EOF handling (GH-12049)

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On non-Linux POSIX platforms, like FreeBSD or macOS,
the FD used to read a forked PTY may signal its exit not
by raising an error but by sending empty data to the read
syscall. This case wasn't handled, leading to hanging
`pty.spawn` calls.

Co-authored-by: Reilly Tucker Siemens <reilly@tuckersiemens.com>
Co-authored-by: Łukasz Langa <lukasz@langa.pl>
This commit is contained in:
Zephyr Shannon 2021-08-11 15:21:46 -07:00 • committed by GitHub
parent 64a7812c17
commit 81ab8db235
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GPG key ID: 4AEE18F83AFDEB23
5 changed files with 85 additions and 37 deletions
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45
Lib/pty.py
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@ -11,7 +11,11 @@ import os
import sys
import tty
__all__ = ["openpty","fork","spawn"]
# 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
@ -105,8 +109,8 @@ def fork():
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)
if slave_fd > STDERR_FILENO:
os.close(slave_fd)
# Explicitly open the tty to make it become a controlling tty.
tmp_fd = os.open(os.ttyname(STDOUT_FILENO), os.O_RDWR)
@ -133,14 +137,22 @@ def _copy(master_fd, master_read=_read, stdin_read=_read):
pty master -> standard output (master_read)
standard input -> pty master (stdin_read)"""
fds = [master_fd, STDIN_FILENO]
while True:
rfds, wfds, xfds = select(fds, [], [])
while fds:
rfds, _wfds, _xfds = select(fds, [], [])
if master_fd in rfds:
data = master_read(master_fd)
# 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.
fds.remove(master_fd)
return # Assume the child process has exited and is
# unreachable, so we clean up.
else:
os.write(STDOUT_FILENO, data)
if STDIN_FILENO in rfds:
data = stdin_read(STDIN_FILENO)
if not data:
@ -153,20 +165,23 @@ def spawn(argv, master_read=_read, stdin_read=_read):
if type(argv) == type(''):
argv = (argv,)
sys.audit('pty.spawn', argv)
pid, master_fd = fork()
if pid == CHILD:
os.execlp(argv[0], *argv)
try:
mode = tty.tcgetattr(STDIN_FILENO)
tty.setraw(STDIN_FILENO)
restore = 1
mode = tcgetattr(STDIN_FILENO)
setraw(STDIN_FILENO)
restore = True
except tty.error: # This is the same as termios.error
restore = 0
restore = False
try:
_copy(master_fd, master_read, stdin_read)
except OSError:
finally:
if restore:
tty.tcsetattr(STDIN_FILENO, tty.TCSAFLUSH, mode)
tcsetattr(STDIN_FILENO, tty.TCSAFLUSH, mode)
os.close(master_fd)
return os.waitpid(pid, 0)[1]
close(master_fd)
return waitpid(pid, 0)[1]