Python integration testing : Using paramiko to fake a ssh server, and log the command given to it

Question

Here is the context : I'm writing a procedure that connects to a distant server via SSH (with paramiko), execute some commands, and then returns the result of the commands to the procedure. It works fine as much as I can tell.

I'm now trying to make an "end to end" test, by faking the ssh server, in order to check if the ssh commands are sent, and that their resulkt is given back to the procedure.

I have found a fake SSH server that uses paramiko, it works well when I connect to it via a real SSH client, but I got errors when I try to connect to it with a paramiko ssh client :/

Do you have any idea of what I'm doing wrong ?

Here is my code :

Server :

#!/usr/bin/env python
"""Fake SSH Server Utilizing Paramiko"""
import threading
import socket
import sys
import traceback
import paramiko
import os

__location__ = os.path.realpath(os.path.join(os.getcwd(), os.path.dirname(__file__)))
LOG = open("log.txt", "a")
#HOST_KEY = paramiko.RSAKey(filename='keys/private.key')
HOST_KEY = paramiko.RSAKey(filename=os.path.join(__location__, 'id_rsa.new'))
PORT = 2200


def handle_cmd(cmd, chan):
    """Branching statements to handle and prepare a response for a command"""
    response = ""
    if cmd.startswith("sudo"):
        send_ascii("sudo.txt", chan)
        return
    elif cmd.startswith("ls"):
        response = "pw.txt"
    elif cmd.startswith("version"):
        response = "Super Amazing Awesome (tm) Shell v1.1"
    elif cmd.startswith("pwd"):
        response = "/home/clippy"
    elif cmd.startswith("cd"):
        send_ascii("cd.txt", chan)
        return
    elif cmd.startswith("cat"):
        send_ascii("cat.txt", chan)
        return
    elif cmd.startswith("rm"):
        send_ascii("bomb.txt", chan)
        response = "You blew up our files! How could you???"
    elif cmd.startswith("whoami"):
        send_ascii("wizard.txt", chan)
        response = "You are a wizard of the internet!"
    elif ".exe" in cmd:
        response = "Hmm, trying to access .exe files from an ssh terminal..... Your methods are unconventional"
    elif cmd.startswith("cmd"):
        response = "Command Prompt? We only use respectable shells on this machine.... Sorry"
    elif cmd == "help":
        send_ascii("help.txt", chan)
        return
    else:
        send_ascii("clippy.txt", chan)
        response = "Use the 'help' command to view available commands"

    LOG.write(response + "\n")
    LOG.flush()
    chan.send(response + "\r\n")


def send_ascii(filename, chan):
    """Print ascii from a file and send it to the channel"""
    with open('ascii/{}'.format(filename)) as text:
        chan.send("\r")
        for line in enumerate(text):
            LOG.write(line[1])
            chan.send(line[1] + "\r")
    LOG.flush()


class FakeSshServer(paramiko.ServerInterface):
    """Settings for paramiko server interface"""
    def __init__(self):
        self.event = threading.Event()

    def check_channel_request(self, kind, chanid):
        if kind == 'session':
            return paramiko.OPEN_SUCCEEDED
        return paramiko.OPEN_FAILED_ADMINISTRATIVELY_PROHIBITED

    def check_auth_password(self, username, password):
        # Accept all passwords as valid by default
        return paramiko.AUTH_SUCCESSFUL

    def get_allowed_auths(self, username):
        return 'password'

    def check_channel_shell_request(self, channel):
        self.event.set()
        return True

    def check_channel_pty_request(self, channel, term, width, height, pixelwidth, pixelheight, modes):
        return True


def start_server():
    """Init and run the ssh server"""
    try:
        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        sock.bind(('', PORT))
    except Exception as err:
        print('*** Bind failed: {}'.format(err))
        traceback.print_exc()
        sys.exit(1)

    while True:
        try:
            sock.listen(100)
            print('Listening for connection ...')
            client, addr = sock.accept()
        except Exception as err:
            print('*** Listen/accept failed: {}'.format(err))
            traceback.print_exc()

        LOG.write("\n\nConnection from: " + addr[0] + "\n")
        print('Got a connection!')
        try:
            transport = paramiko.Transport(client)
            transport.add_server_key(HOST_KEY)
            # Change banner to appear legit on nmap (or other network) scans
            transport.local_version = "SSH-2.0-OpenSSH_7.6p1 Ubuntu-4ubuntu0.3"
            server = FakeSshServer()
            try:
                transport.start_server(server=server)
            except paramiko.SSHException:
                print('*** SSH negotiation failed.')
                raise Exception("SSH negotiation failed")
            # wait for auth
            chan = transport.accept(20)
            if chan is None:
                print('*** No channel.')
                raise Exception("No channel")

            server.event.wait(10)
            if not server.event.is_set():
                print('*** Client never asked for a shell.')
                raise Exception("No shell request")

            try:
                chan.send("Welcome to the my control server\r\n\r\n")
                run = True
                while run:
                    chan.send("$ ")
                    command = ""
                    while not command.endswith("\r"):
                        transport = chan.recv(1024)
                        # Echo input to psuedo-simulate a basic terminal
                        chan.send(transport)
                        command += transport.decode("utf-8")

                    chan.send("\r\n")
                    command = command.rstrip()
                    LOG.write("$ " + command + "\n")
                    print(command)
                    if command == "exit":
                        run = False
                    else:
                        handle_cmd(command, chan)

            except Exception as err:
                print('!!! Exception: {}: {}'.format(err.__class__, err))
                traceback.print_exc()
                try:
                    transport.close()
                except Exception:
                    pass

            chan.close()

        except Exception as err:
            print('!!! Exception: {}: {}'.format(err.__class__, err))
            traceback.print_exc()
            try:
                transport.close()
            except Exception:
                pass


if __name__ == "__main__":
    start_server()

Here is the code I have tried to connect to it with paramiko :

    sshClient = paramiko.SSHClient()
    sshClient.set_missing_host_key_policy(paramiko.AutoAddPolicy())
    sshClient.connect('127.0.0.1', username='bnc', password='pass', port=2200)

    sshClient.exec_command('ls')

and also

    sshClient = paramiko.SSHClient()
    sshClient.set_missing_host_key_policy(paramiko.AutoAddPolicy())
    sshClient.connect('127.0.0.1', username='bnc', password='pass', port=2200)

    channel = sshClient.get_transport().open_session()
    channel.get_pty()
    channel.invoke_shell()
    channel.send('ls\r\n')

with both tests, I got the same error :

Listening for connection ...
Got a connection!
!!! Exception: <class 'socket.error'>: Socket is closed
Traceback (most recent call last):
Listening for connection ...
  File "/home/cbrunain/Projects/daa/Python/test/ssh_mock_server.py", line 152, in start_server
    chan.send(transport)
  File "/home/cbrunain/.local/share/virtualenvs/daa-hnBs4Nn2/lib/python2.7/site-packages/paramiko/channel.py", line 801, in send
    return self._send(s, m)
  File "/home/cbrunain/.local/share/virtualenvs/daa-hnBs4Nn2/lib/python2.7/site-packages/paramiko/channel.py", line 1198, in _send
    raise socket.error("Socket is closed")
error: Socket is closed
No handlers could be found for logger "paramiko.transport"

Answer 1

I finally found something that is working : https://gist.github.com/cschwede/3e2c025408ab4af531651098331cce45

import logging
import socket
import sys
import threading

import paramiko

logging.basicConfig()
logger = logging.getLogger()

running = True
host_key = paramiko.RSAKey(filename='id_rsa')


def ssh_command_handler(command):
    print('default : ', command)


class Server(paramiko.ServerInterface):
    def __init__(self):
        self.event = threading.Event()

    def check_channel_request(self, kind, chanid):
        if kind == 'session':
            return paramiko.OPEN_SUCCEEDED

    def check_auth_publickey(self, username, key):
        return paramiko.AUTH_SUCCESSFUL

    def get_allowed_auths(self, username):
        return 'publickey'

    def check_channel_exec_request(self, channel, command):
        global running
        # This is the command we need to parse
        if command == 'exit':
            running = False
        ssh_command_handler(command)
        self.event.set()
        return True


def listener():
    print('listener')
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    sock.bind(('', 2222))

    sock.listen(100)
    client, addr = sock.accept()

    t = paramiko.Transport(client)
    t.set_gss_host(socket.getfqdn(""))
    t.load_server_moduli()
    t.add_server_key(host_key)
    server = Server()
    t.start_server(server=server)

    # Wait 30 seconds for a command
    server.event.wait(30)
    t.close()
    print('end listener')


def run_server(command_handler):
    global running
    global ssh_command_handler
    ssh_command_handler = command_handler
    while running:
        try:
            listener()
        except KeyboardInterrupt:
            sys.exit(0)
        except Exception as exc:
            logger.error(exc)


def run_in_thread(command_handler):
    thread = threading.Thread(target=run_server, args=(command_handler,))
    thread.start()


if __name__ == '__main__':
    run_in_thread(ssh_command_handler)