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378 lines
12 KiB
Python
378 lines
12 KiB
Python
"""
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fakessh is a stream implementation that starts a local subprocess with its
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environment modified such that ``PATH`` searches for `ssh` return an mitogen
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implementation of the SSH command. When invoked, this tool arranges for the
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command line supplied by the calling program to be executed in a context
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already established by the master process, reusing the master's (possibly
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proxied) connection to that context.
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This allows tools like `rsync` and `scp` to transparently reuse the connections
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and tunnels already established by the host program to connect to a target
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machine, without wasteful redundant SSH connection setup, 3-way handshakes,
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or firewall hopping configurations, and enables these tools to be used in
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impossible scenarios, such as over `sudo` with ``requiretty`` enabled.
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The fake `ssh` command source is written to a temporary file on disk, and
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consists of a copy of the :py:mod:`mitogen.core` source code (just like any
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other child context), with a line appended to cause it to connect back to the
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host process over an FD it inherits. As there is no reliance on an existing
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filesystem file, it is possible for child contexts to use fakessh.
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As a consequence of connecting back through an inherited FD, only one SSH
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invocation is possible, which is fine for tools like `rsync`, however in future
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this restriction will be lifted.
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Sequence:
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1. ``fakessh`` Context and Stream created by parent context. The stream's
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buffer has a `_fakessh_main()` ``CALL_FUNCTION`` enqueued.
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2. Target program (`rsync/scp/sftp`) invoked, which internally executes
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`ssh` from ``PATH``.
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3. :py:mod:`mitogen.core` bootstrap begins, recovers the stream FD
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inherited via the target program, established itself as the fakessh
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context.
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4. `_fakessh_main()` ``CALL_FUNCTION`` is read by fakessh context,
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a. sets up :py:class:`mitogen.fakessh.IoPump` for stdio, registers
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stdin_handle for local context.
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b. Enqueues ``CALL_FUNCTION`` for `_start_slave()` invoked in target context,
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i. the program from the `ssh` command line is started
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ii. sets up :py:class:`mitogen.fakessh.IoPump` for `ssh` command
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line process's stdio pipes
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iii. returns `(control_handle, stdin_handle)` to `_fakessh_main()`
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5. `_fakessh_main()` receives control/stdin handles from from `_start_slave()`,
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a. registers remote's stdin_handle with local IoPump
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b. sends `("start", local_stdin_handle)` to remote's control_handle
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c. registers local IoPump with Broker
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d. loops waiting for 'local stdout closed && remote stdout closed'
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6. `_start_slave()` control channel receives `("start", stdin_handle)`,
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a. registers remote's stdin_handle with local IoPump
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b. registers local IoPump with Broker
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c. loops waiting for 'local stdout closed && remote stdout closed'
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"""
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import getopt
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import inspect
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import logging
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import os
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import shutil
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import signal
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import socket
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import subprocess
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import sys
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import tempfile
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import threading
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import mitogen.core
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import mitogen.master
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from mitogen.core import LOG, IOLOG
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SSH_GETOPTS = (
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"1246ab:c:e:fgi:kl:m:no:p:qstvx"
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"ACD:E:F:I:KL:MNO:PQ:R:S:TVw:W:XYy"
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)
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_mitogen = None
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class IoPump(mitogen.core.BasicStream):
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_output_buf = ''
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_closed = False
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def __init__(self, process, broker, stdin_fd, stdout_fd):
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self.process = process
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self._broker = broker
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self.receive_side = mitogen.core.Side(self, stdout_fd)
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self.transmit_side = mitogen.core.Side(self, stdin_fd)
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def write(self, s):
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self._output_buf += s
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self._broker.start_transmit(self)
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def close(self):
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self._closed = True
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# If local process hasn't exitted yet, ensure its write buffer is
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# drained before lazily triggering disconnect in on_transmit.
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if self.transmit_side.fd is not None:
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self._broker.start_transmit(self)
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def on_shutdown(self, broker):
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self.close()
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def on_transmit(self, broker):
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written = self.transmit_side.write(self._output_buf)
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IOLOG.debug('%r.on_transmit() -> len %r', self, written)
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if written is None:
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self.on_disconnect(broker)
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else:
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self._output_buf = self._output_buf[written:]
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if not self._output_buf:
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broker.stop_transmit(self)
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if self._closed:
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self.on_disconnect(broker)
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def on_receive(self, broker):
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s = self.receive_side.read()
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IOLOG.debug('%r.on_receive() -> len %r', self, len(s))
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if s:
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mitogen.core.fire(self, 'receive', s)
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else:
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self.on_disconnect(broker)
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def __repr__(self):
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return 'IoPump(%r)' % (
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self.process,
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)
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class Process(object):
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"""
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Manages the lifetime and pipe connections of the SSH command running in the
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slave.
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"""
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def __init__(self, router, stdin_fd, stdout_fd, proc=None):
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self.router = router
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self.stdin_fd = stdin_fd
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self.stdout_fd = stdout_fd
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self.proc = proc
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self.control_handle = router.add_handler(self._on_control)
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self.stdin_handle = router.add_handler(self._on_stdin)
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self.pump = IoPump(self, router.broker, stdin_fd, stdout_fd)
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self.stdin = None
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self.control = None
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self.wake_event = threading.Event()
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mitogen.core.listen(self.pump, 'disconnect', self._on_pump_disconnect)
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mitogen.core.listen(self.pump, 'receive', self._on_pump_receive)
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if proc:
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pmon = mitogen.master.ProcessMonitor.instance()
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pmon.add(proc.pid, self._on_proc_exit)
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def __repr__(self):
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return 'Process(%r, %r)' % (self.stdin_fd, self.stdout_fd)
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def _on_proc_exit(self, status):
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LOG.debug('%r._on_proc_exit(%r)', self, status)
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self.control.put(('exit', status))
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def _on_stdin(self, msg):
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if msg == mitogen.core._DEAD:
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return
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data = msg.unpickle()
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IOLOG.debug('%r._on_stdin(%r)', self, data)
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if data == mitogen.core._DEAD:
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self.pump.close()
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else:
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self.pump.write(data)
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def _on_control(self, msg):
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if msg != mitogen.core._DEAD:
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command, arg = msg.unpickle()
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LOG.debug('%r._on_control(%r, %s)', self, command, arg)
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func = getattr(self, '_on_%s' % (command,), None)
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if func:
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return func(msg, arg)
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LOG.warning('%r: unknown command %r', self, command)
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def _on_start(self, msg, arg):
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dest = mitogen.core.Context(self.router, msg.src_id)
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self.control = mitogen.core.Sender(dest, arg[0])
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self.stdin = mitogen.core.Sender(dest, arg[1])
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self.router.broker.start_receive(self.pump)
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def _on_exit(self, msg, arg):
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LOG.debug('on_exit: proc = %r', self.proc)
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if self.proc:
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self.proc.terminate()
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else:
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self.router.broker.shutdown()
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def _on_pump_receive(self, s):
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IOLOG.info('%r._on_pump_receive()', self)
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self.stdin.put(s)
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def _on_pump_disconnect(self):
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LOG.debug('%r._on_pump_disconnect()', self)
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mitogen.core.fire(self, 'disconnect')
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self.stdin.close()
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self.wake_event.set()
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def start_master(self, stdin, control):
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self.stdin = stdin
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self.control = control
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control.put(('start', (self.control_handle, self.stdin_handle)))
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self.router.broker.start_receive(self.pump)
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def wait(self):
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while not self.wake_event.wait(0.1):
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pass
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def _start_slave(mitogen_, src_id, args):
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"""
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This runs in the target context, it is invoked by _fakessh_main running in
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the fakessh context immediately after startup. It starts the slave process
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(the the point where it has a stdin_handle to target but not stdout_chan to
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write to), and waits for main to.
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"""
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LOG.debug('_start_slave(%r, %r)', mitogen_, args)
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proc = subprocess.Popen(args,
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stdin=subprocess.PIPE,
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stdout=subprocess.PIPE,
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)
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process = Process(mitogen_.router,
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proc.stdin.fileno(),
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proc.stdout.fileno(),
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proc,
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)
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return process.control_handle, process.stdin_handle
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#
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# SSH client interface.
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#
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def exit():
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_mitogen.broker.shutdown()
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def die(msg, *args):
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if args:
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msg %= args
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print msg
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exit()
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def parse_args():
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hostname = None
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remain = sys.argv[1:]
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allopts = []
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restarted = 0
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while remain and restarted < 2:
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opts, args = getopt.getopt(remain, SSH_GETOPTS)
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remain = remain[:] # getopt bug!
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allopts += opts
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if not args:
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break
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if not hostname:
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hostname = args.pop(0)
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remain = remain[remain.index(hostname) + 1:]
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restarted += 1
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return hostname, allopts, args
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def _fakessh_main(mitogen_, dest_context_id):
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hostname, opts, args = parse_args()
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if not hostname:
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die('Missing hostname')
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for opt, optarg in opts:
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if 0 and opt == '-s':
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subsystem = True
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else:
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LOG.debug('Warning option %s %s is ignored.', opt, optarg)
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LOG.debug('hostname: %r', hostname)
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LOG.debug('opts: %r', opts)
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LOG.debug('args: %r', args)
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dest = mitogen.master.Context(mitogen_.router, dest_context_id)
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control_handle, stdin_handle = dest.call_with_deadline(None, True,
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_start_slave, mitogen.context_id, args)
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LOG.debug('_fakessh_main: received control_handle=%r, stdin_handle=%r',
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control_handle, stdin_handle)
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process = Process(mitogen_.router, 1, 0)
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process.start_master(
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stdin=mitogen.core.Sender(dest, stdin_handle),
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control=mitogen.core.Sender(dest, control_handle),
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)
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process.wait()
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process.control.put(('exit', None))
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#
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# Public API.
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#
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def run(dest, router, args, deadline=None):
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"""
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Run the command specified by the argument vector `args` such that ``PATH``
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searches for SSH by the command will cause its attempt to use SSH to
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execute a remote program to be redirected to use mitogen to execute that
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program using the context `dest` instead.
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:param mitogen.core.Context dest:
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The destination context to execute the SSH command line in.
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:param mitogen.core.Router router:
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:param list[str] args:
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Command line arguments for local program, e.g. ``['rsync', '/tmp', 'remote:/tmp']``
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"""
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context_id = router.context_id_counter.next()
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fakessh = mitogen.master.Context(router, context_id)
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fakessh.name = 'fakessh'
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sock1, sock2 = socket.socketpair()
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mitogen.core.set_cloexec(sock1.fileno())
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stream = mitogen.core.Stream(router, context_id, fakessh.key)
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stream.name = 'fakessh'
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stream.accept(sock1.fileno(), sock1.fileno())
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router.register(fakessh, stream)
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# Held in socket buffer until process is booted.
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fakessh.call_async(True, _fakessh_main, dest.context_id)
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tmp_path = tempfile.mkdtemp(prefix='mitogen_fakessh')
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try:
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ssh_path = os.path.join(tmp_path, 'ssh')
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fp = file(ssh_path, 'w')
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try:
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fp.write('#!/usr/bin/env python\n')
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fp.write(inspect.getsource(mitogen.core))
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fp.write('\n')
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fp.write('ExternalContext().main%r\n' % ((
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mitogen.context_id, # parent_id
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context_id, # context_id
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fakessh.key, # key
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router.debug, # debug
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logging.getLogger().level, # log_level
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sock2.fileno(), # in_fd
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sock2.fileno(), # out_fd
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None, # core_src_fd
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False, # setup_stdio
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),))
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finally:
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fp.close()
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os.chmod(ssh_path, 0755)
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env = os.environ.copy()
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env.update({
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'PATH': '%s:%s' % (tmp_path, env.get('PATH', '')),
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'ARGV0': `[sys.executable]`,
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'SSH_PATH': ssh_path,
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})
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proc = subprocess.Popen(args, env=env)
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proc.wait()
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finally:
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shutil.rmtree(tmp_path)
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