Paramiko example with proper stderr/stdout behaviour

para.py

import contextlib
import functools
import paramiko
import select
import sys
import os


if __name__ == '__main__':

    host = '172.28.10.2'
    username = 'adisbladis'

    shell_script = f'''
    set -euxo pipefail
    echo COOL
    '''

    client = paramiko.SSHClient()

    # Contextlib can be "abused" to implement
    # defer-like behaviour
    with contextlib.ExitStack() as stack:

        def defer(fn, *args, **kwargs):
            partial = functools.partial(fn, *args, **kwargs)
            stack.callback(partial)

        client.set_missing_host_key_policy(paramiko.AutoAddPolicy())
        client.connect(host, username=username)
        defer(client.close)

        session = client.get_transport().open_session()
        forward = paramiko.agent.AgentRequestHandler(session)

        stdin, stdout, stderr = client.exec_command('exec bash')
        defer(stdin.close)
        defer(stdout.close)
        defer(stderr.close)

        stdin.write(shell_script)
        stdin.close()

        # Stdout/stderr are multiplexed over the same channel
        chan = stdout.channel

        # Close channel in outgoing direction
        # Cannot write any more data after this
        chan.shutdown_write()

        # Flush fds before exit
        defer(sys.stdout.buffer.flush)
        defer(sys.stderr.buffer.flush)

        # Emulate select() over stdout/stderr
        read_size = 1024
        while not chan.exit_status_ready():

            if chan.recv_ready():
                b = chan.recv(read_size)
                while b:
                    sys.stdout.buffer.write(b)
                    b = chan.recv(read_size)

            if chan.recv_stderr_ready():
                b = chan.recv_stderr(read_size)
                while b:
                    sys.stderr.buffer.write(b)
                    b = chan.recv_stderr(read_size)

        exit(chan.recv_exit_status())