ncclient:NETCONF Python client

# Copyright 2009 Shikhar Bhushan

#

# Licensed under the Apache License, Version 2.0 (the "License");

# you may not use this file except in compliance with the License.

# You may obtain a copy of the License at

#

#    http://www.apache.org/licenses/LICENSE-2.0

#

# Unless required by applicable law or agreed to in writing, software

# distributed under the License is distributed on an "AS IS" BASIS,

# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

# See the License for the specific language governing permissions and

# limitations under the License.

import os

import socket

from binascii import hexlify

from cStringIO import StringIO

from select import select

import paramiko

from . import logger

from errors import AuthenticationError, SessionCloseError, SSHError, SSHUnknownHostError

from session import Session

BUF_SIZE = 4096

MSG_DELIM = ']]>]]>'

TICK = 0.1

class SSHSession(Session):

    def __init__(self):

        Session.__init__(self)

        self._host_keys = paramiko.HostKeys()

        self._system_host_keys = paramiko.HostKeys()

        self._transport = None

        self._connected = False

        self._channel = None

        self._expecting_close = False

        self._buffer = StringIO() # for incoming data

        # parsing-related, see _parse()

        self._parsing_state = 0 

        self._parsing_pos = 0

        logger.debug('[SSHSession object created]')

    def _parse(self):

        '''Messages ae delimited by MSG_DELIM. The buffer could have grown by a

        maximum of BUF_SIZE bytes everytime this method is called. Retains state

        across method calls and if a byte has been read it will not be considered

        again.

        '''

        delim = MSG_DELIM

        n = len(delim) - 1

        expect = self._parsing_state

        buf = self._buffer

        buf.seek(self._parsing_pos)

        while True:

            x = buf.read(1)

            if not x: # done reading

                break

            elif x == delim[expect]: # what we expected

                expect += 1 # expect the next delim char

            else:

                continue

            # loop till last delim char expected, break if other char encountered

            for i in range(expect, n):

                x = buf.read(1)

                if not x: # done reading

                    break

                if x == delim[expect]: # what we expected

                    expect += 1 # expect the next delim char

                else:

                    expect = 0 # reset

                    break

            else: # if we didn't break out of the loop, full delim was parsed

                msg_till = buf.tell() - n

                buf.seek(0)

                self._dispatch_received(buf.read(msg_till).strip())

                buf.seek(n+1, os.SEEK_CUR)

                rest = buf.read()

                buf = StringIO()

                buf.write(rest)

                buf.seek(0)

                expect = 0

        self._buffer = buf

        self._parsing_state = expect

        self._parsing_pos = self._buffer.tell()

    def expect_close(self):

        self._expecting_close = True

    def load_system_host_keys(self, filename=None):

        if filename is None:

            filename = os.path.expanduser('~/.ssh/known_hosts')

            try:

                self._system_host_keys.load(filename)

            except IOError:

                # for windows

                filename = os.path.expanduser('~/ssh/known_hosts')

                try:

                    self._system_host_keys.load(filename)

                except IOError:

                    pass

            return

        self._system_host_keys.load(filename)

    def load_host_keys(self, filename):

        self._host_keys.load(filename)

    def add_host_key(self, key):

        self._host_keys.add(key)

    def save_host_keys(self, filename):

        f = open(filename, 'w')

        for hostname, keys in self._host_keys.iteritems():

            for keytype, key in keys.iteritems():

                f.write('%s %s %s\n' % (hostname, keytype, key.get_base64()))

        f.close()    

    def close(self):

        if self._transport.is_active():

            self._transport.close()

        self._connected = False

    def connect(self, hostname, port=830, timeout=None,

                unknown_host_cb=None, username=None, password=None,

                key_filename=None, allow_agent=True, look_for_keys=True):

        assert(username is not None)

        for (family, socktype, proto, canonname, sockaddr) in \

        socket.getaddrinfo(hostname, port):

            if socktype==socket.SOCK_STREAM:

                af = family

                addr = sockaddr

                break

        else:

            raise SSHError('No suitable address family for %s' % hostname)

        sock = socket.socket(af, socket.SOCK_STREAM)

        sock.settimeout(timeout)

        sock.connect(addr)

        t = self._transport = paramiko.Transport(sock)

        t.set_log_channel(logger.name)

        try:

            t.start_client()

        except paramiko.SSHException:

            raise SSHError('Negotiation failed')

        # host key verification

        server_key = t.get_remote_server_key()

        known_host = self._host_keys.check(hostname, server_key) or \

                        self._system_host_keys.check(hostname, server_key)

        if unknown_host_cb is None:

            unknown_host_cb = lambda *args: False

        if not known_host and not unknown_host_cb(hostname, server_key):

                raise SSHUnknownHostError(hostname, server_key)

        if key_filename is None:

            key_filenames = []

        elif isinstance(key_filename, basestring):

            key_filenames = [ key_filename ]

        else:

            key_filenames = key_filename

        self._auth(username, password, key_filenames, allow_agent, look_for_keys)

        self._connected = True # there was no error authenticating

        c = self._channel = self._transport.open_session()

        c.invoke_subsystem('netconf')

        c.set_name('netconf')

        self._post_connect()

    # on the lines of paramiko.SSHClient._auth()

    def _auth(self, username, password, key_filenames, allow_agent,

              look_for_keys):

        saved_exception = None

        for key_filename in key_filenames:

            for cls in (paramiko.RSAKey, paramiko.DSSKey):

                try:

                    key = cls.from_private_key_file(key_filename, password)

                    logger.debug('Trying key %s from %s' %

                              (hexlify(key.get_fingerprint()), key_filename))

                    self._transport.auth_publickey(username, key)

                    return

                except Exception as e:

                    saved_exception = e

                    logger.debug(e)

        if allow_agent:

            for key in paramiko.Agent().get_keys():

                try:

                    logger.debug('Trying SSH agent key %s' %

                                 hexlify(key.get_fingerprint()))

                    self._transport.auth_publickey(username, key)

                    return

                except Exception as e:

                    saved_exception = e

                    logger.debug(e)

        keyfiles = []

        if look_for_keys:

            rsa_key = os.path.expanduser('~/.ssh/id_rsa')

            dsa_key = os.path.expanduser('~/.ssh/id_dsa')

            if os.path.isfile(rsa_key):

                keyfiles.append((paramiko.RSAKey, rsa_key))

            if os.path.isfile(dsa_key):

                keyfiles.append((paramiko.DSSKey, dsa_key))

            # look in ~/ssh/ for windows users:

            rsa_key = os.path.expanduser('~/ssh/id_rsa')

            dsa_key = os.path.expanduser('~/ssh/id_dsa')

            if os.path.isfile(rsa_key):

                keyfiles.append((paramiko.RSAKey, rsa_key))

            if os.path.isfile(dsa_key):

                keyfiles.append((paramiko.DSSKey, dsa_key))

        for cls, filename in keyfiles:

            try:

                key = cls.from_private_key_file(filename, password)

                logger.debug('Trying discovered key %s in %s' %

                          (hexlify(key.get_fingerprint()), filename))

                self._transport.auth_publickey(username, key)

                return

            except Exception as e:

                saved_exception = e

                logger.debug(e)

        if password is not None:

            try:

                self._transport.auth_password(username, password)

                return

            except Exception as e:

                saved_exception = e

                logger.debug(e)

        if saved_exception is not None:

            raise SSHAuthenticationError(repr(saved_exception))

        raise SSHAuthenticationError('No authentication methods available')

    def run(self):

        chan = self._channel

        chan.setblocking(0)

        q = self._q

        try:

            while True:

                # select on a paramiko ssh channel object does not ever return

                # it in the writable list, so it channel's don't exactly emulate 

                # the socket api

                r, w, e = select([chan], [], [], TICK)

                # will wakeup evey TICK seconds to check if something

                # to send, more if something to read (due to select returning

                # chan in readable list)

                if r:

                    data = chan.recv(BUF_SIZE)

                    if data:

                        self._buffer.write(data)

                        self._parse()

                    else:

                        raise SessionCloseError(self._buffer.getvalue())

                if not q.empty() and chan.send_ready():

                    data = q.get() + MSG_DELIM

                    while data:

                        n = chan.send(data)

                        if n <= 0:

                            raise SessionCloseError(self._buffer.getvalue(), data)

                        data = data[n:]

        except Exception as e:

            logger.debug('*** broke out of main loop ***')

            self.close()

            if not (isinstance(e, SessionCloseError) and self._expecting_close):

                self._dispatch_error(e)

    @property

    def transport(self):

        '''Get underlying paramiko transport object; this is provided so methods

        like set_keepalive can be called on it. See paramiko.Transport

        documentation for details.

        '''

        return self._transport