root / ncclient / transport / ssh.py @ bb700ea5
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# Copyright 2009 Shikhar Bhushan
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import os |
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import socket |
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from binascii import hexlify |
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from cStringIO import StringIO |
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from select import select |
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import paramiko |
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from errors import AuthenticationError, SessionCloseError, SSHError, SSHUnknownHostError |
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from session import Session |
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import logging |
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logger = logging.getLogger('ncclient.transport.ssh')
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BUF_SIZE = 4096
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MSG_DELIM = ']]>]]>'
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TICK = 0.1
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def default_unknown_host_cb(host, key): |
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"""An `unknown host callback` returns :const:`True` if it finds the key
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acceptable, and :const:`False` if not.
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This default callback always returns :const:`False`, which would lead to
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:meth:`connect` raising a :exc:`SSHUnknownHost` exception.
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Supply another valid callback if you need to verify the host key
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programatically.
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:arg host: the host for whom key needs to be verified
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:type host: string
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:arg key: a hex string representing the host key fingerprint
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:type key: string
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"""
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return False |
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class SSHSession(Session): |
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"Implements a :rfc:`4742` NETCONF session over SSH."
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def __init__(self, capabilities): |
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Session.__init__(self, capabilities)
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self._host_keys = paramiko.HostKeys()
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self._transport = None |
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self._connected = False |
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self._channel = None |
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self._expecting_close = False |
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self._buffer = StringIO() # for incoming data |
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# parsing-related, see _parse()
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self._parsing_state = 0 |
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self._parsing_pos = 0 |
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def _parse(self): |
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'''Messages ae delimited by MSG_DELIM. The buffer could have grown by a
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maximum of BUF_SIZE bytes everytime this method is called. Retains state
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across method calls and if a byte has been read it will not be
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considered again. '''
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delim = MSG_DELIM |
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n = len(delim) - 1 |
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expect = self._parsing_state
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buf = self._buffer
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buf.seek(self._parsing_pos)
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while True: |
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x = buf.read(1)
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if not x: # done reading |
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break
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elif x == delim[expect]: # what we expected |
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expect += 1 # expect the next delim char |
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else:
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continue
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# loop till last delim char expected, break if other char encountered
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for i in range(expect, n): |
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x = buf.read(1)
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if not x: # done reading |
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break
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if x == delim[expect]: # what we expected |
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expect += 1 # expect the next delim char |
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else:
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expect = 0 # reset |
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break
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else: # if we didn't break out of the loop, full delim was parsed |
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msg_till = buf.tell() - n |
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buf.seek(0)
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logger.debug('parsed new message')
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self._dispatch_message(buf.read(msg_till).strip())
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buf.seek(n+1, os.SEEK_CUR)
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rest = buf.read() |
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buf = StringIO() |
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buf.write(rest) |
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buf.seek(0)
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expect = 0
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self._buffer = buf
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self._parsing_state = expect
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self._parsing_pos = self._buffer.tell() |
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def load_known_hosts(self, filename=None): |
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"""Load host keys from a :file:`known_hosts`-style file. Can be called multiple
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times.
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If *filename* is not specified, looks in the default locations i.e.
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:file:`~/.ssh/known_hosts` and :file:`~/ssh/known_hosts` for Windows.
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"""
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if filename is None: |
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filename = os.path.expanduser('~/.ssh/known_hosts')
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try:
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self._host_keys.load(filename)
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except IOError: |
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# for windows
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filename = os.path.expanduser('~/ssh/known_hosts')
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try:
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self._host_keys.load(filename)
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except IOError: |
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pass
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else:
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self._host_keys.load(filename)
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def close(self): |
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self._expecting_close = True |
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if self._transport.is_active(): |
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self._transport.close()
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self._connected = False |
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def connect(self, host, port=830, timeout=None, |
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unknown_host_cb=default_unknown_host_cb, |
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username=None, password=None, |
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key_filename=None, allow_agent=True, look_for_keys=True): |
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"""Connect via SSH and initialize the NETCONF session. First attempts
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the publickey authentication method and then password authentication.
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To disable attemting publickey authentication altogether, call with
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*allow_agent* and *look_for_keys* as :const:`False`. This may be needed
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for Cisco devices which immediately disconnect on an incorrect
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authentication attempt.
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:arg host: the hostname or IP address to connect to
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:type host: `string`
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:arg port: by default 830, but some devices use the default SSH port of 22 so this may need to be specified
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:type port: `int`
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:arg timeout: an optional timeout for the TCP handshake
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:type timeout: `int`
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:arg unknown_host_cb: called when a host key is not recognized
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:type unknown_host_cb: see :meth:`signature <ssh.default_unknown_host_cb>`
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:arg username: the username to use for SSH authentication
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:type username: `string`
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:arg password: the password used if using password authentication, or the passphrase to use for unlocking keys that require it
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:type password: `string`
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:arg key_filename: a filename where a the private key to be used can be found
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:type key_filename: `string`
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:arg allow_agent: enables querying SSH agent (if found) for keys
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:type allow_agent: `bool`
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:arg look_for_keys: enables looking in the usual locations for ssh keys (e.g. :file:`~/.ssh/id_*`)
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:type look_for_keys: `bool`
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"""
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if username is None: |
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raise SSHError("No username specified") |
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sock = None
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for res in socket.getaddrinfo(host, port, socket.AF_UNSPEC, socket.SOCK_STREAM): |
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af, socktype, proto, canonname, sa = res |
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try:
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sock = socket.socket(af, socktype, proto) |
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sock.settimeout(timeout) |
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except socket.error:
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continue
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try:
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sock.connect(sa) |
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except socket.error:
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sock.close() |
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continue
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break
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else:
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raise SSHError("Could not open socket") |
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t = self._transport = paramiko.Transport(sock)
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t.set_log_channel(logger.name) |
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try:
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t.start_client() |
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except paramiko.SSHException:
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raise SSHError('Negotiation failed') |
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# host key verification
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server_key = t.get_remote_server_key() |
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known_host = self._host_keys.check(host, server_key)
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fingerprint = hexlify(server_key.get_fingerprint()) |
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if not known_host and not unknown_host_cb(host, fingerprint): |
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raise SSHUnknownHostError(host, fingerprint)
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if key_filename is None: |
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key_filenames = [] |
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elif isinstance(key_filename, basestring): |
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key_filenames = [ key_filename ] |
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else:
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key_filenames = key_filename |
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self._auth(username, password, key_filenames, allow_agent, look_for_keys)
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self._connected = True # there was no error authenticating |
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c = self._channel = self._transport.open_session() |
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c.set_name('netconf')
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c.invoke_subsystem('netconf')
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self._post_connect()
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# on the lines of paramiko.SSHClient._auth()
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def _auth(self, username, password, key_filenames, allow_agent, |
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look_for_keys): |
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saved_exception = None
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for key_filename in key_filenames: |
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for cls in (paramiko.RSAKey, paramiko.DSSKey): |
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try:
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key = cls.from_private_key_file(key_filename, password) |
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logger.debug('Trying key %s from %s' %
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(hexlify(key.get_fingerprint()), key_filename)) |
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self._transport.auth_publickey(username, key)
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return
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except Exception as e: |
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saved_exception = e |
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logger.debug(e) |
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if allow_agent:
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for key in paramiko.Agent().get_keys(): |
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try:
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logger.debug('Trying SSH agent key %s' %
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hexlify(key.get_fingerprint())) |
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self._transport.auth_publickey(username, key)
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return
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except Exception as e: |
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saved_exception = e |
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logger.debug(e) |
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keyfiles = [] |
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if look_for_keys:
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rsa_key = os.path.expanduser('~/.ssh/id_rsa')
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dsa_key = os.path.expanduser('~/.ssh/id_dsa')
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if os.path.isfile(rsa_key):
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keyfiles.append((paramiko.RSAKey, rsa_key)) |
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if os.path.isfile(dsa_key):
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keyfiles.append((paramiko.DSSKey, dsa_key)) |
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# look in ~/ssh/ for windows users:
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rsa_key = os.path.expanduser('~/ssh/id_rsa')
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dsa_key = os.path.expanduser('~/ssh/id_dsa')
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if os.path.isfile(rsa_key):
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keyfiles.append((paramiko.RSAKey, rsa_key)) |
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if os.path.isfile(dsa_key):
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keyfiles.append((paramiko.DSSKey, dsa_key)) |
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for cls, filename in keyfiles: |
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try:
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key = cls.from_private_key_file(filename, password) |
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logger.debug('Trying discovered key %s in %s' %
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(hexlify(key.get_fingerprint()), filename)) |
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self._transport.auth_publickey(username, key)
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return
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except Exception as e: |
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saved_exception = e |
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logger.debug(e) |
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if password is not None: |
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try:
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self._transport.auth_password(username, password)
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return
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except Exception as e: |
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saved_exception = e |
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logger.debug(e) |
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if saved_exception is not None: |
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# need pep-3134 to do this right
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raise AuthenticationError(repr(saved_exception)) |
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raise AuthenticationError('No authentication methods available') |
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def run(self): |
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chan = self._channel
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chan.setblocking(0)
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q = self._q
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try:
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while True: |
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# select on a paramiko ssh channel object does not ever return
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# it in the writable list, so it channel's don't exactly emulate
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# the socket api
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r, w, e = select([chan], [], [], TICK) |
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# will wakeup evey TICK seconds to check if something
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# to send, more if something to read (due to select returning
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# chan in readable list)
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if r:
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data = chan.recv(BUF_SIZE) |
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if data:
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self._buffer.write(data)
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self._parse()
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else:
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raise SessionCloseError(self._buffer.getvalue()) |
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if not q.empty() and chan.send_ready(): |
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logger.debug('sending message')
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data = q.get() + MSG_DELIM |
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while data:
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n = chan.send(data) |
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if n <= 0: |
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raise SessionCloseError(self._buffer.getvalue(), data) |
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data = data[n:] |
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except Exception as e: |
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logger.debug('broke out of main loop')
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expecting = self._expecting_close
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self.close()
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logger.debug('error=%r' % e)
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logger.debug('expecting_close=%r' % expecting)
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if not (isinstance(e, SessionCloseError) and expecting): |
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self._dispatch_error(e)
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@property
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def transport(self): |
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"""Underlying `paramiko.Transport
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<http://www.lag.net/paramiko/docs/paramiko.Transport-class.html>`_
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object. This makes it possible to call methods like set_keepalive on it.
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"""
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return self._transport |
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@property
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def can_pipeline(self): |
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if 'Cisco' in self._transport.remote_version: |
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return False |
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# elif ..
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return True |