# This file is part of Xpra.
# Copyright (C) 2018-2020 Antoine Martin <antoine@xpra.org>
# Xpra is released under the terms of the GNU GPL v2, or, at your option, any
# later version. See the file COPYING for details.

import sys
import os
import shlex
import socket
import signal
from time import sleep
from subprocess import PIPE, Popen

from xpra.scripts.main import InitException, InitExit, shellquote, host_target_string
from xpra.platform.paths import get_ssh_known_hosts_files
from xpra.platform import get_username
from xpra.scripts.config import parse_bool
from xpra.net.bytestreams import SocketConnection, SOCKET_TIMEOUT, ConnectionClosedException
from xpra.exit_codes import (
    EXIT_SSH_KEY_FAILURE, EXIT_SSH_FAILURE,
    EXIT_CONNECTION_FAILED,
    )
from xpra.os_util import (
    bytestostr, osexpand, load_binary_file, monotonic_time,
    nomodule_context, umask_context, is_main_thread,
    WIN32, OSX, POSIX,
    )
from xpra.util import envint, envbool, nonl, engs, csv, envfloat
from xpra.log import Logger, is_debug_enabled

log = Logger("network", "ssh")

INITENV_COMMAND = os.environ.get("XPRA_INITENV_COMMAND", "xpra initenv")
WINDOW_SIZE = envint("XPRA_SSH_WINDOW_SIZE", 2**27-1)
TIMEOUT = envint("XPRA_SSH_TIMEOUT", 60)
SKIP_UI = envbool("XPRA_SKIP_UI", False)

VERIFY_HOSTKEY = envbool("XPRA_SSH_VERIFY_HOSTKEY", True)
VERIFY_STRICT = envbool("XPRA_SSH_VERIFY_STRICT", False)
ADD_KEY = envbool("XPRA_SSH_ADD_KEY", True)
#which authentication mechanisms are enabled with paramiko:
NONE_AUTH = envbool("XPRA_SSH_NONE_AUTH", True)
PASSWORD_AUTH = envbool("XPRA_SSH_PASSWORD_AUTH", True)
AGENT_AUTH = envbool("XPRA_SSH_AGENT_AUTH", True)
KEY_AUTH = envbool("XPRA_SSH_KEY_AUTH", True)
PASSWORD_AUTH = envbool("XPRA_SSH_PASSWORD_AUTH", True)
PASSWORD_RETRY = envint("XPRA_SSH_PASSWORD_RETRY", 2)
assert PASSWORD_RETRY>=0
MAGIC_QUOTES = envbool("XPRA_SSH_MAGIC_QUOTES", True)
TEST_COMMAND_TIMEOUT = envint("XPRA_SSH_TEST_COMMAND_TIMEOUT", 10)
EXEC_STDOUT_TIMEOUT = envfloat("XPRA_SSH_EXEC_STDOUT_TIMEOUT", 2)
EXEC_STDERR_TIMEOUT = envfloat("XPRA_SSH_EXEC_STDERR_TIMEOUT", 0)


def keymd5(k) -> str:
    import binascii
    f = bytestostr(binascii.hexlify(k.get_fingerprint()))
    s = "MD5"
    while f:
        s += ":"+f[:2]
        f = f[2:]
    return s


def force_focus():
    from xpra.platform.gui import force_focus as _force_focus
    _force_focus()

def dialog_run(dialog) -> int:
    from gi.repository import GLib
    if is_main_thread():
        force_focus()
        dialog.show()
        try:
            return dialog.run()
        finally:
            dialog.destroy()
    #do a little dance if we're not running in the main thread:
    #block this thread and wait for the main thread to run the dialog
    from threading import Event
    e = Event()
    code = []
    def main_thread_run():
        force_focus()
        dialog.show()
        try:
            r = dialog.run()
        finally:
            dialog.destroy()
        code.append(r)
        e.set()
    GLib.idle_add(main_thread_run)
    e.wait()
    log("dialog_run(%s) code=%s", dialog, code)
    return code[0]

def dialog_pass(title="Password Input", prompt="enter password", icon="") -> str:
    from xpra.client.gtk_base.pass_dialog import PasswordInputDialogWindow
    dialog = PasswordInputDialogWindow(title, prompt, icon)
    try:
        if dialog_run(dialog)==0:
            return dialog.get_password()
        return None
    finally:
        dialog.destroy()

def dialog_confirm(title, prompt, qinfo=(), icon="", buttons=(("OK", 1),)) -> int:
    from xpra.client.gtk_base.confirm_dialog import ConfirmDialogWindow
    dialog = ConfirmDialogWindow(title, prompt, qinfo, icon, buttons)
    try:
        r = dialog_run(dialog)
    finally:
        dialog.destroy()
    return r


def confirm_key(info=()) -> bool:
    if SKIP_UI:
        return False
    from xpra.platform.paths import get_icon_filename
    from xpra.os_util import use_tty
    if not use_tty():
        icon = get_icon_filename("authentication", "png") or ""
        prompt = "Are you sure you want to continue connecting?"
        code = dialog_confirm("Confirm Key", prompt, info, icon, buttons=[("yes", 200), ("NO", 201)])
        log("dialog return code=%s", code)
        r = code==200
        log.info("host key %sconfirmed", ["not ", ""][r])
        return r
    log("confirm_key(%s) will use stdin prompt", nonl(info))
    prompt = "Are you sure you want to continue connecting (yes/NO)? "
    sys.stderr.write(os.linesep.join(info)+os.linesep+prompt)
    try:
        v = sys.stdin.readline().rstrip(os.linesep)
    except KeyboardInterrupt:
        sys.exit(128+signal.SIGINT)
    return v and v.lower() in ("y", "yes")

def input_pass(prompt) -> str:
    if SKIP_UI:
        return None
    from xpra.platform.paths import get_icon_filename
    from xpra.os_util import use_tty
    if not use_tty():
        icon = get_icon_filename("authentication", "png") or ""
        return dialog_pass("Password Input", prompt, icon)
    from getpass import getpass
    try:
        return getpass(prompt)
    except KeyboardInterrupt:
        sys.exit(128+signal.SIGINT)


class SSHSocketConnection(SocketConnection):

    def __init__(self, ssh_channel, sock, sockname, peername, target, info=None):
        super().__init__(ssh_channel, sockname, peername, target, "ssh", info)
        self._raw_socket = sock

    def start_stderr_reader(self):
        from xpra.make_thread import start_thread
        start_thread(self._stderr_reader, "ssh-stderr-reader", daemon=True)

    def _stderr_reader(self):
        #stderr = self._socket.makefile_stderr(mode="rb", bufsize=1)
        chan = self._socket
        stderr = chan.makefile_stderr("rb", 1)
        errs = []
        while self.active:
            v = stderr.readline()
            if not v:
                log("SSH EOF on stderr of %s", chan.get_name())
                return
            errs.append(bytestostr(v.rstrip(b"\n\r")))
        if errs:
            log.warn("remote SSH stderr:")
            for e in errs:
                log.warn(" %s", e)

    def peek(self, n):
        if not self._raw_socket:
            return None
        return self._raw_socket.recv(n, socket.MSG_PEEK)

    def get_socket_info(self) -> dict:
        if not self._raw_socket:
            return {}
        return self.do_get_socket_info(self._raw_socket)

    def get_info(self) -> dict:
        i = SocketConnection.get_info(self)
        s = self._socket
        if s:
            i["ssh-channel"] = {
                "id"    : s.get_id(),
                "name"  : s.get_name(),
                }
        return i


class SSHProxyCommandConnection(SSHSocketConnection):
    def __init__(self, ssh_channel, peername, target, info):
        super().__init__(ssh_channel, None, None, peername, target, info)
        self.process = None

    def error_is_closed(self, e) -> bool:
        p = self.process
        if p:
            #if the process has terminated,
            #then the connection must be closed:
            if p[0].poll() is not None:
                return True
        return super().error_is_closed(e)

    def get_socket_info(self) -> dict:
        p = self.process
        if not p:
            return {}
        proc, _ssh, cmd = p
        return {
            "process" : {
                "pid"       : proc.pid,
                "returncode": proc.returncode,
                "command"   : cmd,
                }
            }

    def close(self):
        try:
            super().close()
        except Exception:
            #this can happen if the proxy command gets a SIGINT,
            #it's closed already and we don't care
            log("SSHProxyCommandConnection.close()", exc_info=True)


def ssh_paramiko_connect_to(display_desc):
    #plain socket attributes:
    dtype = display_desc["type"]
    host = display_desc["host"]
    port = display_desc.get("ssh-port", 22)
    #ssh and command attributes:
    username = display_desc.get("username") or get_username()
    if "proxy_host" in display_desc:
        display_desc.setdefault("proxy_username", get_username())
    password = display_desc.get("password")
    remote_xpra = display_desc["remote_xpra"]
    proxy_command = display_desc["proxy_command"]       #ie: "_proxy_start"
    socket_dir = display_desc.get("socket_dir")
    display = display_desc.get("display")
    display_as_args = display_desc["display_as_args"]   #ie: "--start=xterm :10"
    paramiko_config = display_desc.copy()
    paramiko_config.update(display_desc.get("paramiko-config", {}))
    socket_info = {
            "host"  : host,
            "port"  : port,
            }
    def get_keyfiles(host_config, config_name="key"):
        keyfiles = (host_config or {}).get("identityfile") or get_default_keyfiles()
        keyfile = paramiko_config.get(config_name)
        if keyfile:
            keyfiles.insert(0, keyfile)
        return keyfiles

    with nogssapi_context():
        from paramiko import SSHConfig, ProxyCommand
        ssh_config = SSHConfig()
        user_config_file = os.path.expanduser("~/.ssh/config")
        sock = None
        host_config = None
        if os.path.exists(user_config_file):
            with open(user_config_file) as f:
                ssh_config.parse(f)
            log("parsed user config '%s': %i hosts found", user_config_file, len(ssh_config.get_hostnames()))
            host_config = ssh_config.lookup(host)
            if host_config:
                log("got host config for '%s': %s", host, host_config)
                chost = host_config.get("hostname", host)
                cusername = host_config.get("user", username)
                cport = host_config.get("port", port)
                try:
                    port = int(cport)
                except ValueError:
                    raise InitExit(EXIT_SSH_FAILURE, "invalid ssh port specified: '%s'" % cport)
                proxycommand = host_config.get("proxycommand")
                if proxycommand:
                    log("found proxycommand='%s' for host '%s'", proxycommand, chost)
                    sock = ProxyCommand(proxycommand)
                    log("ProxyCommand(%s)=%s", proxycommand, sock)
                    from xpra.child_reaper import getChildReaper
                    cmd = getattr(sock, "cmd", [])
                    def proxycommand_ended(proc):
                        log("proxycommand_ended(%s) exit code=%s", proc, proc.poll())
                    getChildReaper().add_process(sock.process, "paramiko-ssh-client", cmd, True, True,
                                                 callback=proxycommand_ended)
                    proxy_keys = get_keyfiles(host_config, "proxy_key")
                    log("proxy keys=%s", proxy_keys)
                    from paramiko.client import SSHClient
                    ssh_client = SSHClient()
                    ssh_client.load_system_host_keys()
                    log("ssh proxy command connect to %s", (chost, cport, sock))
                    ssh_client.connect(chost, cport, sock=sock)
                    transport = ssh_client.get_transport()
                    do_ssh_paramiko_connect_to(transport, chost,
                                               cusername, password,
                                               host_config or ssh_config.lookup("*"),
                                               proxy_keys,
                                               paramiko_config)
                    chan = paramiko_run_remote_xpra(transport, proxy_command, remote_xpra, socket_dir, display_as_args)
                    peername = (chost, cport)
                    conn = SSHProxyCommandConnection(chan, peername, peername, socket_info)
                    conn.target = host_target_string("ssh", cusername, chost, port, display)
                    conn.timeout = SOCKET_TIMEOUT
                    conn.start_stderr_reader()
                    conn.process = (sock.process, "ssh", cmd)
                    from xpra.net import bytestreams
                    from paramiko.ssh_exception import ProxyCommandFailure
                    bytestreams.CLOSED_EXCEPTIONS = tuple(list(bytestreams.CLOSED_EXCEPTIONS)+[ProxyCommandFailure])
                    return conn

        keys = get_keyfiles(host_config)
        from xpra.scripts.main import socket_connect
        from paramiko.transport import Transport
        from paramiko import SSHException
        if "proxy_host" in display_desc:
            proxy_host = display_desc["proxy_host"]
            proxy_port = display_desc.get("proxy_port", 22)
            proxy_username = display_desc.get("proxy_username", username)
            proxy_password = display_desc.get("proxy_password", password)
            proxy_keys = get_keyfiles(host_config, "proxy_key")
            sock = socket_connect(dtype, proxy_host, proxy_port)
            middle_transport = Transport(sock)
            middle_transport.use_compression(False)
            try:
                middle_transport.start_client()
            except SSHException as e:
                log("start_client()", exc_info=True)
                raise InitExit(EXIT_SSH_FAILURE, "SSH negotiation failed: %s" % e) from None
            proxy_host_config = ssh_config.lookup(host)
            do_ssh_paramiko_connect_to(middle_transport, proxy_host,
                                       proxy_username, proxy_password,
                                       proxy_host_config or ssh_config.lookup("*"),
                                       proxy_keys,
                                       paramiko_config)
            log("Opening proxy channel")
            chan_to_middle = middle_transport.open_channel("direct-tcpip", (host, port), ('localhost', 0))

            transport = Transport(chan_to_middle)
            transport.use_compression(False)
            try:
                transport.start_client()
            except SSHException as e:
                log("start_client()", exc_info=True)
                raise InitExit(EXIT_SSH_FAILURE, "SSH negotiation failed: %s" % e)
            do_ssh_paramiko_connect_to(transport, host,
                                       username, password,
                                       host_config or ssh_config.lookup("*"),
                                       keys,
                                       paramiko_config)
            chan = paramiko_run_remote_xpra(transport, proxy_command, remote_xpra, socket_dir, display_as_args)
            peername = (host, port)
            conn = SSHProxyCommandConnection(chan, peername, peername, socket_info)
            conn.target = "%s via %s" % (
                host_target_string("ssh", username, host, port, display),
                host_target_string("ssh", proxy_username, proxy_host, proxy_port, None),
                )
            conn.timeout = SOCKET_TIMEOUT
            conn.start_stderr_reader()
            return conn

        #plain TCP connection to the server,
        #we open it then give the socket to paramiko:
        sock = socket_connect(dtype, host, port)
        sockname = sock.getsockname()
        peername = sock.getpeername()
        log("paramiko socket_connect: sockname=%s, peername=%s", sockname, peername)
        transport = Transport(sock)
        transport.use_compression(False)
        try:
            transport.start_client()
        except SSHException as e:
            log("start_client()", exc_info=True)
            raise InitExit(EXIT_SSH_FAILURE, "SSH negotiation failed: %s" % e) from None
        do_ssh_paramiko_connect_to(transport, host, username, password,
                                   host_config or ssh_config.lookup("*"),
                                   keys,
                                   paramiko_config)
        chan = paramiko_run_remote_xpra(transport, proxy_command, remote_xpra, socket_dir, display_as_args)
        conn = SSHSocketConnection(chan, sock, sockname, peername, (host, port), socket_info)
        conn.target = host_target_string("ssh", username, host, port, display)
        conn.timeout = SOCKET_TIMEOUT
        conn.start_stderr_reader()
        return conn


#workaround incompatibility between paramiko and gssapi:
class nogssapi_context(nomodule_context):

    def __init__(self):
        super().__init__("gssapi")


def get_default_keyfiles():
    dkf = os.environ.get("XPRA_SSH_DEFAULT_KEYFILES", None)
    if dkf is not None:
        return [x for x in dkf.split(":") if x]
    return [osexpand(os.path.join("~/", ".ssh", keyfile)) for keyfile in ("id_ed25519", "id_ecdsa", "id_rsa", "id_dsa")]


def do_ssh_paramiko_connect_to(transport, host, username, password, host_config=None, keyfiles=None, paramiko_config=None):
    from paramiko import SSHException, PasswordRequiredException
    from paramiko.agent import Agent
    from paramiko.hostkeys import HostKeys
    log("do_ssh_paramiko_connect_to%s", (transport, host, username, password, host_config, keyfiles, paramiko_config))
    log("SSH transport %s", transport)

    def configvalue(key):
        #if the paramiko config has a setting, honour it:
        if paramiko_config and key in paramiko_config:
            return paramiko_config.get(key)
        #fallback to the value from the host config:
        return (host_config or {}).get(key)
    def configbool(key, default_value=True):
        return parse_bool(key, configvalue(key), default_value)
    def configint(key, default_value=0):
        v = configvalue(key)
        if v is None:
            return default_value
        return int(v)

    host_key = transport.get_remote_server_key()
    assert host_key, "no remote server key"
    log("remote_server_key=%s", keymd5(host_key))
    if configbool("verify-hostkey", VERIFY_HOSTKEY):
        host_keys = HostKeys()
        host_keys_filename = None
        KNOWN_HOSTS = get_ssh_known_hosts_files()
        for known_hosts in KNOWN_HOSTS:
            host_keys.clear()
            try:
                path = os.path.expanduser(known_hosts)
                if os.path.exists(path):
                    host_keys.load(path)
                    log("HostKeys.load(%s) successful", path)
                    host_keys_filename = path
                    break
            except IOError:
                log("HostKeys.load(%s)", known_hosts, exc_info=True)

        log("host keys=%s", host_keys)
        keys = host_keys.lookup(host)
        known_host_key = (keys or {}).get(host_key.get_name())
        def keyname():
            return host_key.get_name().replace("ssh-", "")
        if host_key==known_host_key:
            assert host_key
            log("%s host key '%s' OK for host '%s'", keyname(), keymd5(host_key), host)
        else:
            dnscheck = ""
            if configbool("verifyhostkeydns"):
                try:
                    from xpra.net.sshfp import check_host_key
                    dnscheck = check_host_key(host, host_key)
                except ImportError as e:
                    log("verifyhostkeydns failed", exc_info=True)
                    log.warn("Warning: cannot check SSHFP DNS records")
                    log.warn(" %s", e)
            log("dnscheck=%s", dnscheck)
            def adddnscheckinfo(q):
                if dnscheck is not True:
                    if dnscheck:
                        q += [
                            "SSHFP validation failed:",
                            dnscheck
                            ]
                    else:
                        q += [
                            "SSHFP validation failed"
                            ]
            if dnscheck is True:
                #DNSSEC provided a matching record
                log.info("found a valid SSHFP record for host %s", host)
            elif known_host_key:
                log.warn("Warning: SSH server key mismatch")
                qinfo = [
"WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!",
"IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!",
"Someone could be eavesdropping on you right now (man-in-the-middle attack)!",
"It is also possible that a host key has just been changed.",
"The fingerprint for the %s key sent by the remote host is" % keyname(),
keymd5(host_key),
]
                adddnscheckinfo(qinfo)
                if configbool("stricthostkeychecking", VERIFY_STRICT):
                    log.warn("Host key verification failed.")
                    #TODO: show alert with no option to accept key
                    qinfo += [
                        "Please contact your system administrator.",
                        "Add correct host key in %s to get rid of this message.",
                        "Offending %s key in %s" % (keyname(), host_keys_filename),
                        "ECDSA host key for %s has changed and you have requested strict checking." % keyname(),
                        ]
                    sys.stderr.write(os.linesep.join(qinfo))
                    transport.close()
                    raise InitExit(EXIT_SSH_KEY_FAILURE, "SSH Host key has changed")
                if not confirm_key(qinfo):
                    transport.close()
                    raise InitExit(EXIT_SSH_KEY_FAILURE, "SSH Host key has changed")

            else:
                assert (not keys) or (host_key.get_name() not in keys)
                if not keys:
                    log.warn("Warning: unknown SSH host")
                else:
                    log.warn("Warning: unknown %s SSH host key", keyname())
                qinfo = [
                    "The authenticity of host '%s' can't be established." % (host,),
                    "%s key fingerprint is" % keyname(),
                    keymd5(host_key),
                    ]
                adddnscheckinfo(qinfo)
                if not confirm_key(qinfo):
                    transport.close()
                    raise InitExit(EXIT_SSH_KEY_FAILURE, "Unknown SSH host '%s'" % host)

            if configbool("addkey", ADD_KEY):
                try:
                    if not host_keys_filename:
                        #the first one is the default,
                        #ie: ~/.ssh/known_hosts on posix
                        host_keys_filename = os.path.expanduser(KNOWN_HOSTS[0])
                    log("adding %s key for host '%s' to '%s'", keyname(), host, host_keys_filename)
                    if not os.path.exists(host_keys_filename):
                        keys_dir = os.path.dirname(host_keys_filename)
                        if not os.path.exists(keys_dir):
                            log("creating keys directory '%s'", keys_dir)
                            os.mkdir(keys_dir, 0o700)
                        elif not os.path.isdir(keys_dir):
                            log.warn("Warning: '%s' is not a directory")
                            log.warn(" key not saved")
                        if os.path.exists(keys_dir) and os.path.isdir(keys_dir):
                            log("creating known host file '%s'", host_keys_filename)
                            with umask_context(0o133):
                                with open(host_keys_filename, 'a+'):
                                    pass
                    host_keys.add(host, host_key.get_name(), host_key)
                    host_keys.save(host_keys_filename)
                except OSError as e:
                    log("failed to add key to '%s'", host_keys_filename)
                    log.error("Error adding key to '%s'", host_keys_filename)
                    log.error(" %s", e)
                except Exception as e:
                    log.error("cannot add key", exc_info=True)
    else:
        log("ssh host key verification skipped")


    def auth_agent():
        agent = Agent()
        agent_keys = agent.get_keys()
        log("agent keys: %s", agent_keys)
        if agent_keys:
            for agent_key in agent_keys:
                log("trying ssh-agent key '%s'", keymd5(agent_key))
                try:
                    transport.auth_publickey(username, agent_key)
                    if transport.is_authenticated():
                        log("authenticated using agent and key '%s'", keymd5(agent_key))
                        break
                except SSHException:
                    log("agent key '%s' rejected", keymd5(agent_key), exc_info=True)
            if not transport.is_authenticated():
                log.info("agent authentication failed, tried %i key%s", len(agent_keys), engs(agent_keys))

    def auth_publickey():
        log("trying public key authentication using %s", keyfiles)
        for keyfile_path in keyfiles:
            if not os.path.exists(keyfile_path):
                log("no keyfile at '%s'", keyfile_path)
                continue
            log("trying '%s'", keyfile_path)
            key = None
            import paramiko
            for pkey_classname in ("RSA", "DSS", "ECDSA", "Ed25519"):
                pkey_class = getattr(paramiko, "%sKey" % pkey_classname, None)
                if pkey_class is None:
                    log("no %s key type", pkey_classname)
                    continue
                log("trying to load as %s", pkey_classname)
                try:
                    key = pkey_class.from_private_key_file(keyfile_path)
                    log.info("loaded %s private key from '%s'", pkey_classname, keyfile_path)
                    break
                except PasswordRequiredException as e:
                    log("%s keyfile requires a passphrase; %s", keyfile_path, e)
                    passphrase = input_pass("please enter the passphrase for %s:" % (keyfile_path,))
                    if passphrase:
                        try:
                            key = pkey_class.from_private_key_file(keyfile_path, passphrase)
                            log.info("loaded %s private key from '%s'", pkey_classname, keyfile_path)
                        except SSHException as e:
                            log("from_private_key_file", exc_info=True)
                            log.info("cannot load key from file '%s':", keyfile_path)
                            log.info(" %s", e)
                    break
                except Exception as e:
                    log("auth_publickey() loading as %s", pkey_classname, exc_info=True)
                    key_data = load_binary_file(keyfile_path)
                    if key_data and key_data.find(b"BEGIN OPENSSH PRIVATE KEY")>=0 and paramiko.__version__<"2.7":
                        log.warn("Warning: private key '%s'", keyfile_path)
                        log.warn(" this file seems to be using OpenSSH's own format")
                        log.warn(" please convert it to something more standard (ie: PEM)")
                        log.warn(" so it can be used with the paramiko backend")
                        log.warn(" or switch to the OpenSSH backend with '--ssh=ssh'")
            if key:
                log("auth_publickey using %s as %s: %s", keyfile_path, pkey_classname, keymd5(key))
                try:
                    transport.auth_publickey(username, key)
                except SSHException as e:
                    log("key '%s' rejected", keyfile_path, exc_info=True)
                    log.info("SSH authentication using key '%s' failed:", keyfile_path)
                    log.info(" %s", e)
                else:
                    if transport.is_authenticated():
                        break
            else:
                log.error("Error: cannot load private key '%s'", keyfile_path)

    def auth_none():
        log("trying none authentication")
        try:
            transport.auth_none(username)
        except SSHException:
            log("auth_none()", exc_info=True)

    def auth_password():
        log("trying password authentication")
        try:
            transport.auth_password(username, password)
        except SSHException as e:
            log("auth_password(..)", exc_info=True)
            log.info("SSH password authentication failed:")
            log.info(" %s", getattr(e, "message", e))

    def auth_interactive():
        log("trying interactive authentication")
        class iauthhandler:
            def __init__(self):
                self.authcount = 0
            def handlestuff(self, _title, _instructions, prompt_list):
                p = []
                for pent in prompt_list:
                    if self.authcount==0 and password:
                        p.append(password)
                    else:
                        p.append(input_pass(pent[0]))
                    self.authcount += 1
                return p
        try:
            myiauthhandler = iauthhandler()
            transport.auth_interactive(username, myiauthhandler.handlestuff, "")
        except SSHException as e:
            log("auth_interactive(..)", exc_info=True)
            log.info("SSH password authentication failed:")
            log.info(" %s", getattr(e, "message", e))

    banner = transport.get_banner()
    if banner:
        log.info("SSH server banner:")
        for x in banner.splitlines():
            log.info(" %s", x)

    if paramiko_config and "auth" in paramiko_config:
        auth = paramiko_config.get("auth", "").split("+")
        AUTH_OPTIONS = ("none", "agent", "key", "password")
        if any(a for a in auth if a not in AUTH_OPTIONS):
            raise InitExit(EXIT_SSH_FAILURE, "invalid ssh authentication module specified: %s" %
                           csv(a for a in auth if a not in AUTH_OPTIONS))
    else:
        auth = []
        if configbool("noneauthentication", NONE_AUTH):
            auth.append("none")
        if password and configbool("passwordauthentication", PASSWORD_AUTH):
            auth.append("password")
        if configbool("agentauthentication", AGENT_AUTH):
            auth.append("agent")
        # Some people do two-factor using KEY_AUTH to kick things off, so this happens first
        if configbool("keyauthentication", KEY_AUTH):
            auth.append("key")
        if not password and configbool("passwordauthentication", PASSWORD_AUTH):
            auth.append("password")
    #def doauth(authtype):
    #    return authtype in auth and not transport.is_authenticated()

    log("starting authentication, authentication methods: %s", auth)
    # per the RFC we probably should do none first always and read off the supported
    # methods, however, the current code seems to work fine with OpenSSH
    while not transport.is_authenticated() and auth:
        a = auth.pop(0)
        log("auth=%s", a)
        if a=="none":
            auth_none()
        elif a=="agent":
            auth_agent()
        elif a=="key":
            auth_publickey()
        elif a=="password":
            auth_interactive()
            if not transport.is_authenticated():
                if password:
                    auth_password()
                else:
                    tries = configint("numberofpasswordprompts", PASSWORD_RETRY)
                    for _ in range(tries):
                        password = input_pass("please enter the SSH password for %s@%s:" % (username, host))
                        if not password:
                            break
                        auth_password()
                        if transport.is_authenticated():
                            break
    if not transport.is_authenticated():
        transport.close()
        raise InitExit(EXIT_CONNECTION_FAILED, "SSH Authentication on %s failed" % host)


def paramiko_run_test_command(transport, cmd):
    from paramiko import SSHException
    log("paramiko_run_test_command(transport, %r)", cmd)
    try:
        chan = transport.open_session(window_size=None, max_packet_size=0, timeout=60)
        chan.set_name("find %s" % cmd)
    except SSHException as e:
        log("open_session", exc_info=True)
        raise InitExit(EXIT_SSH_FAILURE, "failed to open SSH session: %s" % e) from None
    chan.exec_command(cmd)
    log("exec_command returned")
    start = monotonic_time()
    while not chan.exit_status_ready():
        if monotonic_time()-start>TEST_COMMAND_TIMEOUT:
            chan.close()
            raise InitException("SSH test command '%s' timed out" % cmd)
        log("exit status is not ready yet, sleeping")
        sleep(0.01)
    code = chan.recv_exit_status()
    log("exec_command('%s')=%s", cmd, code)
    def chan_read(read_fn):
        try:
            return read_fn()
        except socket.error:
            log("chan_read(%s)", read_fn, exc_info=True)
            return b""
    #don't wait too long for the data:
    chan.settimeout(EXEC_STDOUT_TIMEOUT)
    out = chan_read(chan.makefile().readline)
    log("exec_command out=%r", out)
    chan.settimeout(EXEC_STDERR_TIMEOUT)
    err = chan_read(chan.makefile_stderr().readline)
    log("exec_command err=%r", err)
    chan.close()
    return out, err, code

def paramiko_run_remote_xpra(transport, xpra_proxy_command=None, remote_xpra=None, socket_dir=None, display_as_args=None):
    from paramiko import SSHException
    assert remote_xpra
    log("will try to run xpra from: %s", remote_xpra)
    def rtc(cmd):
        return paramiko_run_test_command(transport, cmd)
    tried = set()
    for xpra_cmd in remote_xpra:
        if xpra_cmd.lower() in ("xpra.exe", "xpra_cmd.exe"):
            #win32 mode, quick and dirty platform test first:
            r = rtc("ver")
            if r[2]!=0:
                continue
            #let's find where xpra is installed:
            r = rtc("FOR /F \"usebackq tokens=3*\" %A IN (`REG QUERY \"HKEY_LOCAL_MACHINE\Software\Xpra\" /v InstallPath`) DO (echo %A %B)")
            if r[2]==0:
                #found in registry:
                lines = r[0].splitlines()
                installpath = bytestostr(lines[-1])
                xpra_cmd = "%s\\%s" % (installpath, xpra_cmd)
                xpra_cmd = xpra_cmd.replace("\\", "\\\\")
                log("using '%s'", xpra_cmd)
        elif xpra_cmd.endswith(".exe"):
            #assume this path exists
            pass
        else:
            #assume Posix and find that command:
            r = rtc("which %s" % xpra_cmd)
            if r[2]!=0:
                continue
        if xpra_cmd in tried:
            continue
        tried.add(xpra_cmd)
        cmd = '"' + xpra_cmd + '" ' + ' '.join(shellquote(x) for x in xpra_proxy_command)
        if socket_dir:
            cmd += " \"--socket-dir=%s\"" % socket_dir
        if display_as_args:
            cmd += " "
            cmd += " ".join(shellquote(x) for x in display_as_args)
        log("cmd(%s, %s)=%s", xpra_proxy_command, display_as_args, cmd)

        #see https://github.com/paramiko/paramiko/issues/175
        #WINDOW_SIZE = 2097152
        log("trying to open SSH session, window-size=%i, timeout=%i", WINDOW_SIZE, TIMEOUT)
        try:
            chan = transport.open_session(window_size=WINDOW_SIZE, max_packet_size=0, timeout=TIMEOUT)
            chan.set_name("run-xpra")
        except SSHException as e:
            log("open_session", exc_info=True)
            raise InitExit(EXIT_SSH_FAILURE, "failed to open SSH session: %s" % e) from None
        else:
            log("channel exec_command(%s)" % cmd)
            chan.exec_command(cmd)
            return chan
    raise Exception("all SSH remote proxy commands have failed")


def ssh_connect_failed(_message):
    #by the time ssh fails, we may have entered the gtk main loop
    #(and more than once thanks to the clipboard code..)
    if "gtk" in sys.modules or "gi.repository.Gtk" in sys.modules:
        from xpra.gtk_common.quit import gtk_main_quit_really
        gtk_main_quit_really()


def ssh_exec_connect_to(display_desc, opts=None, debug_cb=None, ssh_fail_cb=ssh_connect_failed):
    if not ssh_fail_cb:
        ssh_fail_cb = ssh_connect_failed
    sshpass_command = None
    try:
        cmd = list(display_desc["full_ssh"])
        kwargs = {}
        env = display_desc.get("env")
        kwargs["stderr"] = sys.stderr
        if WIN32:
            from subprocess import CREATE_NEW_PROCESS_GROUP, CREATE_NEW_CONSOLE, STARTUPINFO, STARTF_USESHOWWINDOW
            startupinfo = STARTUPINFO()
            startupinfo.dwFlags |= STARTF_USESHOWWINDOW
            startupinfo.wShowWindow = 0     #aka win32.con.SW_HIDE
            kwargs["startupinfo"] = startupinfo
            flags = CREATE_NEW_PROCESS_GROUP | CREATE_NEW_CONSOLE
            kwargs["creationflags"] = flags
            kwargs["stderr"] = PIPE
        elif not display_desc.get("exit_ssh", False) and not OSX:
            kwargs["start_new_session"] = True
        remote_xpra = display_desc["remote_xpra"]
        assert remote_xpra
        socket_dir = display_desc.get("socket_dir")
        proxy_command = display_desc["proxy_command"]       #ie: "_proxy_start"
        display_as_args = display_desc["display_as_args"]   #ie: "--start=xterm :10"
        remote_cmd = ""
        for x in remote_xpra:
            if not remote_cmd:
                check = "if"
            else:
                check = "elif"
            if x=="xpra":
                #no absolute path, so use "which" to check that the command exists:
                pc = ['%s which "%s" > /dev/null 2>&1; then' % (check, x)]
            else:
                pc = ['%s [ -x %s ]; then' % (check, x)]
            pc += [x] + proxy_command + [shellquote(x) for x in display_as_args]
            if socket_dir:
                pc.append("--socket-dir=%s" % socket_dir)
            remote_cmd += " ".join(pc)+";"
        remote_cmd += "else echo \"no run-xpra command found\"; exit 1; fi"
        if INITENV_COMMAND:
            remote_cmd = INITENV_COMMAND + ";" + remote_cmd
        #how many times we need to escape the remote command string
        #depends on how many times the ssh command is parsed
        if MAGIC_QUOTES:
            nssh = sum(int(x=="ssh") for x in cmd)
            for _ in range(nssh):
                remote_cmd = shlex.quote(remote_cmd)
        else:
            remote_cmd = "'%s'" % remote_cmd
        cmd.append("sh -c %s" % remote_cmd)
        if debug_cb:
            debug_cb("starting %s tunnel" % str(cmd[0]))
        #non-string arguments can make Popen choke,
        #instead of lazily converting everything to a string, we validate the command:
        for x in cmd:
            if not isinstance(x, str):
                raise InitException("argument is not a string: %s (%s), found in command: %s" % (x, type(x), cmd))
        password = display_desc.get("password")
        if password and not display_desc.get("is_putty", False):
            from xpra.platform.paths import get_sshpass_command
            sshpass_command = get_sshpass_command()
            if sshpass_command:
                #sshpass -e ssh ...
                cmd.insert(0, sshpass_command)
                cmd.insert(1, "-e")
                if env is None:
                    env = os.environ.copy()
                env["SSHPASS"] = password
                #the password will be used by ssh via sshpass,
                #don't try to authenticate again over the ssh-proxy connection,
                #which would trigger warnings if the server does not require
                #authentication over unix-domain-sockets:
                opts.password = None
                del display_desc["password"]
        if env:
            kwargs["env"] = env
        if is_debug_enabled("ssh"):
            log.info("executing ssh command: %s" % (" ".join("\"%s\"" % x for x in cmd)))
        child = Popen(cmd, stdin=PIPE, stdout=PIPE, **kwargs)
    except OSError as e:
        raise InitExit(EXIT_SSH_FAILURE,
                       "Error running ssh command '%s': %s" % (" ".join("\"%s\"" % x for x in cmd), e))
    def abort_test(action):
        """ if ssh dies, we don't need to try to read/write from its sockets """
        e = child.poll()
        if e is not None:
            had_connected = conn.input_bytecount>0 or conn.output_bytecount>0
            if had_connected:
                error_message = "cannot %s using SSH" % action
            else:
                error_message = "SSH connection failure"
            sshpass_error = None
            if sshpass_command:
                sshpass_error = {
                                 1  : "Invalid command line argument",
                                 2  : "Conflicting arguments given",
                                 3  : "General runtime error",
                                 4  : "Unrecognized response from ssh (parse error)",
                                 5  : "Invalid/incorrect password",
                                 6  : "Host public key is unknown. sshpass exits without confirming the new key.",
                                 }.get(e)
                if sshpass_error:
                    error_message += ": %s" % sshpass_error
            if debug_cb:
                debug_cb(error_message)
            if ssh_fail_cb:
                ssh_fail_cb(error_message)
            if "ssh_abort" not in display_desc:
                display_desc["ssh_abort"] = True
                if not had_connected:
                    log.error("Error: SSH connection to the xpra server failed")
                    if sshpass_error:
                        log.error(" %s", sshpass_error)
                    else:
                        log.error(" check your username, hostname, display number, firewall, etc")
                    display_name = display_desc["display_name"]
                    log.error(" for server: %s", display_name)
                else:
                    log.error("The SSH process has terminated with exit code %s", e)
                cmd_info = " ".join(display_desc["full_ssh"])
                log.error(" the command line used was:")
                log.error(" %s", cmd_info)
            raise ConnectionClosedException(error_message) from None
    def stop_tunnel():
        if POSIX:
            #on posix, the tunnel may be shared with other processes
            #so don't kill it... which may leave it behind after use.
            #but at least make sure we close all the pipes:
            for name,fd in {
                            "stdin" : child.stdin,
                            "stdout" : child.stdout,
                            "stderr" : child.stderr,
                            }.items():
                try:
                    if fd:
                        fd.close()
                except Exception as e:
                    print("error closing ssh tunnel %s: %s" % (name, e))
            if not display_desc.get("exit_ssh", False):
                #leave it running
                return
        try:
            if child.poll() is None:
                child.terminate()
        except Exception as e:
            print("error trying to stop ssh tunnel process: %s" % e)
    host = display_desc["host"]
    port = display_desc.get("ssh-port", 22)
    username = display_desc.get("username")
    display = display_desc.get("display")
    info = {
        "host"  : host,
        "port"  : port,
        }
    from xpra.net.bytestreams import TwoFileConnection
    conn = TwoFileConnection(child.stdin, child.stdout,
                             abort_test, target=(host, port),
                             socktype="ssh", close_cb=stop_tunnel, info=info)
    conn.endpoint = host_target_string("ssh", username, host, port, display)
    conn.timeout = 0            #taken care of by abort_test
    conn.process = (child, "ssh", cmd)
    return conn
