"""Loopback-only SSH/SFTP fixture; password arrives through stdin, never logs."""
import io
import socket
import sys
import threading
import time
import paramiko

password = sys.stdin.readline().rstrip('\n')
key = paramiko.RSAKey.generate(2048)

class Server(paramiko.ServerInterface):
    def __init__(self):
        self.direct = set()

    def check_auth_password(self, username, supplied):
        return paramiko.AUTH_SUCCESSFUL if supplied == password else paramiko.AUTH_FAILED

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

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

    def check_channel_direct_tcpip_request(self, chanid, origin, destination):
        self.direct.add(chanid)
        return paramiko.OPEN_SUCCEEDED

    def check_channel_exec_request(self, channel, command):
        def finish():
            time.sleep(0.1)
            channel.send_exit_status(0)
            channel.close()
        threading.Thread(target=finish, daemon=True).start()
        return True

class SFTP(paramiko.SFTPServerInterface):
    def stat(self, path):
        return paramiko.SFTP_NO_SUCH_FILE

    def open(self, path, flags, attr):
        class Handle(paramiko.SFTPHandle):
            def chattr(self, attr):
                return paramiko.SFTP_OK
        handle = Handle(flags)
        handle.writefile = io.BytesIO()
        return handle

def connection(client):
    transport = paramiko.Transport(client)
    transport.add_server_key(key)
    class SFTPSubsystem(paramiko.SFTPServer):
        def start_subsystem(self, name, transport, channel):
            super().start_subsystem(name, transport, channel)
            channel.send_exit_status(0)
    transport.set_subsystem_handler('sftp', SFTPSubsystem, SFTP)
    try:
        server = Server()
        channels = []
        transport.start_server(server=server)
        while transport.is_active():
            channel = transport.accept(0.5)
            if channel:
                channels.append(channel)
                if channel.chanid not in server.direct:
                    continue
                def echo(c):
                    while not c.closed:
                        if c.recv_ready():
                            data = c.recv(1024)
                            if data:
                                c.sendall(data)
                        time.sleep(0.01)
                threading.Thread(target=echo, args=(channel,), daemon=True).start()
    except (EOFError, OSError, paramiko.SSHException):
        pass
    finally:
        transport.close()

listener = socket.socket()
listener.bind(('127.0.0.1', 0))
listener.listen(10)
print(listener.getsockname()[1], flush=True)
while True:
    client, _ = listener.accept()
    threading.Thread(target=connection, args=(client,), daemon=True).start()