fakessh: Initial working version
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"""
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fakessh is a stream implementation that starts a local subprocess, substituting
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one of the user-supplied arguments with the name of a "fake SSH command". When
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invoked, this command passes its arguments back into the host context, and
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begins tunnelling stdio from the child back to the configured target host.
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This allows tools like rsync and scp to be invoked as subprocesses and reuse
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the connections and tunnels already established by the host program to connect
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to a target machine, without wasteful redundant SSH connection setup, 3-way
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handshakes, or firewall hopping configurations.
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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 econtext.core source code (just like any other child
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context), with a line appended to cause it to connect back to the host process
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over an FD it inherits.
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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.
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Start sequence:
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1. fakessh invoked, captures command line.
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2. _fakessh_main invoked by parent,
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a. sets up IoPump for stdio, registers stdin_handle for local context
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b. _start_slave_process invoked in target context, passing stdin_handle
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3. _start_slave_process invoked in target context,
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a. the program from the SSH command line is invoked
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b. sets up IoPump for command line's pipes
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c. returns (control_handle, stdin_handle) to fakessh_main
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4. _fakessh_main receives (control_handle, stdin_handle),
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a. registers remote's stdin_handle with local IoPump
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b. sends ("start", local_stdin_handle) to 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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5. _start_slave_process 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 econtext.core
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import econtext.master
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from econtext.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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_econtext = None
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class IoPump(econtext.core.BasicStream):
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_output_buf = ''
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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.transmit_side = econtext.core.Side(self, stdin_fd)
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self.receive_side = econtext.core.Side(self, stdout_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 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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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 not s:
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self.on_disconnect(broker)
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else:
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self.process.stdin.put(s)
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def on_disconnect(self, broker):
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super(IoPump, self).on_disconnect(broker)
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self.process.stdin.close()
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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, pid=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.pid = None
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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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def __repr__(self):
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return 'Process(%r, %r, %r)' % (
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self.stdin_fd,
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self.stdout_fd,
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self.pid,
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)
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def _on_stdin(self, msg):
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if msg == econtext.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 == econtext.core._DEAD:
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self.pump.transmit_side.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 == econtext.core._DEAD:
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return
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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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if command == 'start':
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dest = econtext.core.Context(self.router, msg.src_id)
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self.control = econtext.core.Sender(dest, arg[0])
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self.stdin = econtext.core.Sender(dest, arg[1])
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self.router.broker.start_receive(self.pump)
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elif command == 'kill':
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if self.pid is not None:
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os.kill(self.pid, signal.SIGTERM)
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else:
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LOG.warning('%r: unknown command %r', self, command)
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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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import time
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time.sleep(3)
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def _start_slave_process(econtext_, 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_process(%r, %r)', econtext_, 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(econtext_.router,
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proc.stdin.fileno(),
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proc.stdout.fileno(),
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proc.pid,
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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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_econtext.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(econtext_, 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.info('hostname: %r', hostname)
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LOG.info('opts: %r', opts)
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LOG.info('args: %r', args)
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dest = econtext.master.Context(econtext_.router, dest_context_id)
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control_handle, stdin_handle = dest.call_with_deadline(None, True,
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_start_slave_process, econtext.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(econtext_.router, 1, 0)
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process.start_master(
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stdin=econtext.core.Sender(dest, stdin_handle),
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control=econtext.core.Sender(dest, control_handle),
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)
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process.wait()
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process.control.put(('kill', None))
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#
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# Public API.
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#
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def run_with_fake_ssh(dest, router, args, deadline=None):
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context_id = router.context_id_counter.next()
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fakessh = econtext.master.Context(router, context_id)
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fakessh.name = 'fakessh'
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sock1, sock2 = socket.socketpair()
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econtext.core.set_cloexec(sock1.fileno())
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stream = econtext.core.Stream(router, context_id, fakessh.key)
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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='econtext_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(econtext.core))
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fp.write('\n')
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fp.write('ExternalContext().main%r\n' % ((
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econtext.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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