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.

from threading import Event, Lock

from uuid import uuid1

from ncclient.xml_ import *

from ncclient.transport import SessionListener

from errors import OperationError, TimeoutExpiredError, MissingCapabilityError

import logging

logger = logging.getLogger("ncclient.operations.rpc")

class RPCError(OperationError):

    "Represents an `rpc-error`. It is a type of :exc:`OperationError` and can be raised as such."

    tag_to_attr = {

        qualify("error-type"): "_type",

        qualify("error-tag"): "_tag",

        qualify("error-severity"): "_severity",

        qualify("error-info"): "_info",

        qualify("error-path"): "_path",

        qualify("error-message"): "_message"

    }

    def __init__(self, raw):

        self._raw = raw

        for attr in RPCError.tag_to_attr.values():

            setattr(self, attr, None)

        for subele in raw:

            attr = RPCError.tag_to_attr.get(subele.tag, None)

            if attr is not None:

                setattr(self, attr, subele.text if attr != "_info" else to_xml(subele) )

        if self.message is not None:

            OperationError.__init__(self, self.message)

        else:

            OperationError.__init__(self, self.to_dict())

    def to_dict(self):

        return dict([ (attr[1:], getattr(self, attr)) for attr in RPCError.tag_to_attr.values() ])

    @property

    def xml(self):

        "The `rpc-error` element as returned in XML."

        return self._raw

    @property

    def type(self):

        "The contents of the `error-type` element."

        return self._type

    @property

    def tag(self):

        "The contents of the `error-tag` element."

        return self._tag

    @property

    def severity(self):

        "The contents of the `error-severity` element."

        return self._severity

    @property

    def path(self):

        "The contents of the `error-path` element if present or `None`."

        return self._path

    @property

    def message(self):

        "The contents of the `error-message` element if present or `None`."

        return self._message

    @property

    def info(self):

        "XML string or `None`; representing the `error-info` element."

        return self._info

class RPCReply:

    """Represents an *rpc-reply*. Only concerns itself with whether the operation was successful.

    .. note::

        If the reply has not yet been parsed there is an implicit, one-time parsing overhead to

        accessing some of the attributes defined by this class.

    """

    ERROR_CLS = RPCError

    "Subclasses can specify a different error class, but it should be a subclass of `RPCError`."

    def __init__(self, raw):

        self._raw = raw

        self._parsed = False

        self._root = None

        self._errors = []

    def __repr__(self):

        return self._raw

    def parse(self):

        "Parses the *rpc-reply*."

        if self._parsed: return

        root = self._root = to_ele(self._raw) # The <rpc-reply> element

        # Per RFC 4741 an <ok/> tag is sent when there are no errors or warnings

        ok = root.find(qualify("ok"))

        if ok is None:

            # Create RPCError objects from <rpc-error> elements

            error = root.find(qualify("rpc-error"))

            if error is not None:

                for err in root.getiterator(error.tag):

                    # Process a particular <rpc-error>

                    self._errors.append(self.ERROR_CLS(err))

        self._parsing_hook(root)

        self._parsed = True

    def _parsing_hook(self, root):

        "No-op by default. Gets passed the *root* element for the reply."

        pass

    @property

    def xml(self):

        "*rpc-reply* element as returned."

        return self._raw

    @property

    def ok(self):

        "Boolean value indicating if there were no errors."

        return not self.errors # empty list => false

    @property

    def error(self):

        "Returns the first :class:`RPCError` and `None` if there were no errors."

        self.parse()

        if self._errors:

            return self._errors[0]

        else:

            return None

    @property

    def errors(self):

        "List of `RPCError` objects. Will be empty if there were no *rpc-error* elements in reply."

        self.parse()

        return self._errors

class RPCReplyListener(SessionListener): # internal use

    creation_lock = Lock()

    # one instance per session -- maybe there is a better way??

    def __new__(cls, session):

        with RPCReplyListener.creation_lock:

            instance = session.get_listener_instance(cls)

            if instance is None:

                instance = object.__new__(cls)

                instance._lock = Lock()

                instance._id2rpc = {}

                #instance._pipelined = session.can_pipeline

                session.add_listener(instance)

            return instance

    def register(self, id, rpc):

        with self._lock:

            self._id2rpc[id] = rpc

    def callback(self, root, raw):

        tag, attrs = root

        if tag != qualify("rpc-reply"):

            return

        for key in attrs: # in the <rpc-reply> attributes

            if key == "message-id": # if we found msgid attr

                id = attrs[key] # get the msgid

                with self._lock:

                    try:

                        rpc = self._id2rpc[id] # the corresponding rpc

                        logger.debug("Delivering to %r" % rpc)

                        rpc.deliver_reply(raw)

                    except KeyError:

                        raise OperationError("Unknown 'message-id': %s", id)

                    # no catching other exceptions, fail loudly if must

                    else:

                        # if no error delivering, can del the reference to the RPC

                        del self._id2rpc[id]

                        break

        else:

            raise OperationError("Could not find 'message-id' attribute in <rpc-reply>")

    def errback(self, err):

        try:

            for rpc in self._id2rpc.values():

                rpc.deliver_error(err)

        finally:

            self._id2rpc.clear()

class RaiseMode(object):

    NONE = 0

    "Don't attempt to raise any type of `rpc-error` as :exc:`RPCError`."

    ERRORS = 1

    "Raise only when the `error-type` indicates it is an honest-to-god error."

    ALL = 2

    "Don't look at the `error-type`, always raise."

class RPC(object):

    """Base class for all operations, directly corresponding to *rpc* requests. Handles making the request, and taking delivery of the reply."""

    DEPENDS = []

    """Subclasses can specify their dependencies on capabilities as a list of URI's or abbreviated names, e.g. ':writable-running'. These are verified at the time of instantiation. If the capability is not available, :exc:`MissingCapabilityError` is raised."""

    REPLY_CLS = RPCReply

    "By default :class:`RPCReply`. Subclasses can specify a :class:`RPCReply` subclass."

    def __init__(self, session, async=False, timeout=30, raise_mode=RaiseMode.NONE):

        """

        *session* is the :class:`~ncclient.transport.Session` instance

        *async* specifies whether the request is to be made asynchronously, see :attr:`is_async`

        *timeout* is the timeout for a synchronous request, see :attr:`timeout`

        *raise_mode* specifies the exception raising mode, see :attr:`raise_mode`

        """

        self._session = session

        try:

            for cap in self.DEPENDS:

                self._assert(cap)

        except AttributeError:

            pass

        self._async = async

        self._timeout = timeout

        self._raise_mode = raise_mode

        self._id = uuid1().urn # Keeps things simple instead of having a class attr with running ID that has to be locked

        self._listener = RPCReplyListener(session)

        self._listener.register(self._id, self)

        self._reply = None

        self._error = None

        self._event = Event()

    def _wrap(self, subele):

        # internal use

        ele = new_ele("rpc", {"message-id": self._id})

        ele.append(subele)

        return to_xml(ele)

    def _request(self, op):

        """Implementations of :meth:`request` call this method to send the request and process the reply.

        In synchronous mode, blocks until the reply is received and returns :class:`RPCReply`. Depending on the :attr:`raise_mode` a `rpc-error` element in the reply may lead to an :exc:`RPCError` exception.

        In asynchronous mode, returns immediately, returning `self`. The :attr:`event` attribute will be set when the reply has been received (see :attr:`reply`) or an error occured (see :attr:`error`).

        *op* is the operation to be requested as an :class:`~xml.etree.ElementTree.Element`

        """

        logger.info('Requesting %r' % self.__class__.__name__)

        req = self._wrap(op)

        self._session.send(req)

        if self._async:

            logger.debug('Async request, returning %r', self)

            return self

        else:

            logger.debug('Sync request, will wait for timeout=%r' % self._timeout)

            self._event.wait(self._timeout)

            if self._event.isSet():

                if self._error:

                    # Error that prevented reply delivery

                    raise self._error

                self._reply.parse()

                if self._reply.error is not None:

                    # <rpc-error>'s [ RPCError ]

                    if self._raise_mode == RaiseMode.ALL:

                        raise self._reply.error

                    elif (self._raise_mode == RaiseMode.ERRORS and self._reply.error.type == "error"):

                        raise self._reply.error

                return self._reply

            else:

                raise TimeoutExpiredError

    def request(self):

        """Subclasses must implement this method. Typically only the request needs to be built as an

        :class:`~xml.etree.ElementTree.Element` and everything else can be handed off to

        :meth:`_request`."""

        pass

    def _assert(self, capability):

        """Subclasses can use this method to verify that a capability is available with the NETCONF

        server, before making a request that requires it. A :exc:`MissingCapabilityError` will be

        raised if the capability is not available."""

        if capability not in self._session.server_capabilities:

            raise MissingCapabilityError('Server does not support [%s]' % capability)

    def deliver_reply(self, raw):

        # internal use

        self._reply = self.REPLY_CLS(raw)

        self._event.set()

    def deliver_error(self, err):

        # internal use

        self._error = err

        self._event.set()

    @property

    def reply(self):

        ":class:`RPCReply` element if reply has been received or `None`"

        return self._reply

    @property

    def error(self):

        """:exc:`Exception` type if an error occured or `None`.

        .. note::

            This represents an error which prevented a reply from being received. An *rpc-error*

            does not fall in that category -- see `RPCReply` for that.

        """

        return self._error

    @property

    def id(self):

        "The *message-id* for this RPC."

        return self._id

    @property

    def session(self):

        "The `~ncclient.transport.Session` object associated with this RPC."

        return self._session

    @property

    def event(self):

        """:class:`~threading.Event` that is set when reply has been received or when an error preventing

        delivery of the reply occurs.

        """

        return self._event

    def __set_async(self, async=True):

        self._async = async

        if async and not session.can_pipeline:

            raise UserWarning('Asynchronous mode not supported for this device/session')

    def __set_raise_mode(self, mode):

        assert(choice in ("all", "errors", "none"))

        self._raise_mode = mode

    def __set_timeout(self, timeout):

        self._timeout = timeout

    raise_mode = property(fget=lambda self: self._raise_mode, fset=__set_raise_mode)

    """Depending on this exception raising mode, an `rpc-error` in the reply may be raised as an :exc:`RPCError` exception. Valid values are the constants defined in :class:`RaiseMode`. """

    is_async = property(fget=lambda self: self._async, fset=__set_async)

    """Specifies whether this RPC will be / was requested asynchronously. By default RPC's are synchronous."""

    timeout = property(fget=lambda self: self._timeout, fset=__set_timeout)

    """Timeout in seconds for synchronous waiting defining how long the RPC request will block on a reply before raising :exc:`TimeoutExpiredError`.

    Irrelevant for asynchronous usage.

    """