Duplicate pwntools process output to stdout with tee(2) syscall

tee.py

import sys
import os
from pwn import *

def tee_process(p):
    import threading
    import ctypes
    libc = ctypes.CDLL(None)
    splice = libc.splice
    tee = libc.tee

    read_fd, write_fd = os.pipe2(os.O_NONBLOCK)
    saved_stdout_fd = os.dup(p.stdout.fileno())
    os.dup2(read_fd, p.stdout.fileno())
    p.proc.stdout = os.fdopen(p.stdout.fileno(), 'rb', 0) # force reopen

    def do_tee_splice():
        while not p.poll():
            n = tee(saved_stdout_fd, write_fd, 0x7ffffff, 0)
            if n < 0:
                continue
            if n == 0:
                break
            splice(saved_stdout_fd, 0, sys.stdout.fileno(), 0, n, 0)
        os.close(saved_stdout_fd)
        os.close(read_fd)
        os.close(write_fd)

    threading.Thread(target=do_tee_splice, daemon=True).start()

# There may be issues with input buffering of the subprocess. If thats the case run python with -u so the entire process tree is unbuffered
p = process('/bin/cat', stdout=PIPE) # IMPORTANT: stdout=PIPE is required
tee_process(p)

p.sendline(b'1234')
p.sendline(b'12345')
p.sendline(b'123456')
p.sendline(b'1234567')
p.sendline(b'12345678')
p.stdin.close()
p.stream()

print('Bye')