path: root/pysnmp/proto/mpmod/rfc3412.py

#
# This file is part of pysnmp software.
#
# Copyright (c) 2005-2019, Ilya Etingof <etingof@gmail.com>
# License: http://snmplabs.com/pysnmp/license.html
#
import sys

from pyasn1.codec.ber import decoder
from pyasn1.codec.ber import eoo
from pyasn1.type import constraint
from pyasn1.type import namedtype
from pyasn1.type import univ

from pysnmp import debug
from pysnmp.proto import api
from pysnmp.proto import errind
from pysnmp.proto import error
from pysnmp.proto import rfc1905
from pysnmp.proto import rfc3411
from pysnmp.proto.mpmod.base import AbstractMessageProcessingModel

# API to rfc1905 protocol objects
pMod = api.PROTOCOL_MODULES[api.SNMP_VERSION_2C]


# SNMPv3 message format

class ScopedPDU(univ.Sequence):
    componentType = namedtype.NamedTypes(
        namedtype.NamedType('contextEngineId', univ.OctetString()),
        namedtype.NamedType('contextName', univ.OctetString()),
        namedtype.NamedType('data', rfc1905.PDUs()))


class ScopedPduData(univ.Choice):
    componentType = namedtype.NamedTypes(
        namedtype.NamedType('plaintext', ScopedPDU()),
        namedtype.NamedType('encryptedPDU', univ.OctetString()))


class HeaderData(univ.Sequence):
    componentType = namedtype.NamedTypes(
        namedtype.NamedType(
            'msgID', univ.Integer().subtype(
                subtypeSpec=constraint.ValueRangeConstraint(0, 2147483647))),
        namedtype.NamedType(
            'msgMaxSize', univ.Integer().subtype(
                subtypeSpec=constraint.ValueRangeConstraint(484, 2147483647))),
        namedtype.NamedType(
            'msgFlags', univ.OctetString().subtype(
                subtypeSpec=constraint.ValueSizeConstraint(1, 1))),
        # NOTE (etingof): constrain SNMPv3 message to only USM+ security models
        # because SNMPv1/v2c seems incompatible in pysnmp implementation, not sure
        # if it's intended by the SNMP standard at all...
        namedtype.NamedType(
            'msgSecurityModel', univ.Integer().subtype(
                subtypeSpec=constraint.ValueRangeConstraint(3, 2147483647))))


class SNMPv3Message(univ.Sequence):
    componentType = namedtype.NamedTypes(
        namedtype.NamedType(
            'msgVersion', univ.Integer().subtype(
                subtypeSpec=constraint.ValueRangeConstraint(0, 2147483647))),
        namedtype.NamedType('msgGlobalData', HeaderData()),
        namedtype.NamedType('msgSecurityParameters', univ.OctetString()),
        namedtype.NamedType('msgData', ScopedPduData()))


# XXX move somewhere?
_snmpErrors = {
    (1, 3, 6, 1, 6, 3, 15, 1, 1, 1, 0): errind.unsupportedSecurityLevel,
    (1, 3, 6, 1, 6, 3, 15, 1, 1, 2, 0): errind.notInTimeWindow,
    (1, 3, 6, 1, 6, 3, 15, 1, 1, 3, 0): errind.unknownUserName,
    (1, 3, 6, 1, 6, 3, 15, 1, 1, 4, 0): errind.unknownEngineID,
    (1, 3, 6, 1, 6, 3, 15, 1, 1, 5, 0): errind.wrongDigest,
    (1, 3, 6, 1, 6, 3, 15, 1, 1, 6, 0): errind.decryptionError
}


class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
    MESSAGE_PROCESSING_MODEL_ID = univ.Integer(3)  # SNMPv3
    SNMP_MSG_SPEC = SNMPv3Message

    _emptyStr = univ.OctetString('')
    _msgFlags = {
        0: univ.OctetString('\x00'),
        1: univ.OctetString('\x01'),
        3: univ.OctetString('\x03'),
        4: univ.OctetString('\x04'),
        5: univ.OctetString('\x05'),
        7: univ.OctetString('\x07')
    }

    def __init__(self):
        AbstractMessageProcessingModel.__init__(self)
        self._scopedPDU = ScopedPDU()
        self._engineIdCache = {}
        self._engineIdCacheExpQueue = {}
        self._expirationTimer = 0

    def getPeerEngineInfo(self, transportDomain, transportAddress):
        k = transportDomain, transportAddress
        if k in self._engineIdCache:
            return (self._engineIdCache[k]['securityEngineId'],
                    self._engineIdCache[k]['contextEngineId'],
                    self._engineIdCache[k]['contextName'])
        else:
            return None, None, None

    # 7.1.1a
    def prepareOutgoingMessage(self, snmpEngine, transportDomain,
                               transportAddress, messageProcessingModel,
                               securityModel, securityName, securityLevel,
                               contextEngineId, contextName, pduVersion,
                               pdu, expectResponse, sendPduHandle):

        mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder

        snmpEngineID, = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
        snmpEngineID = snmpEngineID.syntax

        # 7.1.1b
        msgID = self._cache.newMsgID()

        debug.logger & debug.FLAG_MP and debug.logger(
            'prepareOutgoingMessage: new msgID %s' % msgID)

        k = transportDomain, transportAddress
        if k in self._engineIdCache:
            peerSnmpEngineData = self._engineIdCache[k]

        else:
            peerSnmpEngineData = None

        debug.logger & debug.FLAG_MP and debug.logger(
            'prepareOutgoingMessage: peer SNMP engine data %s '
            'for transport %s, address '
            '%s' % (peerSnmpEngineData, transportDomain, transportAddress))

        # 7.1.4
        if contextEngineId is None:
            if peerSnmpEngineData is None:
                contextEngineId = snmpEngineID

            else:
                contextEngineId = peerSnmpEngineData['contextEngineId']
                # Defaulting contextEngineID to securityEngineId should
                # probably be done on Agent side (see 7.1.3.d.2,) so this
                # is a sort of workaround.
                if not contextEngineId:
                    contextEngineId = peerSnmpEngineData['securityEngineId']
        # 7.1.5
        if not contextName:
            contextName = self._emptyStr

        debug.logger & debug.FLAG_MP and debug.logger(
            'prepareOutgoingMessage: using contextEngineId %r, contextName '
            '%r' % (contextEngineId, contextName))

        # 7.1.6
        scopedPDU = self._scopedPDU
        scopedPDU.setComponentByPosition(0, contextEngineId)
        scopedPDU.setComponentByPosition(1, contextName)
        scopedPDU.setComponentByPosition(2)
        scopedPDU.getComponentByPosition(2).setComponentByType(
            pdu.tagSet, pdu, verifyConstraints=False, matchTags=False,
            matchConstraints=False)

        # 7.1.7
        msg = self._snmpMsgSpec

        # 7.1.7a
        msg.setComponentByPosition(
            0, self.MESSAGE_PROCESSING_MODEL_ID, verifyConstraints=False,
            matchTags=False, matchConstraints=False)

        headerData = msg.setComponentByPosition(1).getComponentByPosition(1)

        # 7.1.7b
        headerData.setComponentByPosition(
            0, msgID, verifyConstraints=False, matchTags=False,
            matchConstraints=False)

        snmpEngineMaxMessageSize, = mibBuilder.importSymbols(
            '__SNMP-FRAMEWORK-MIB', 'snmpEngineMaxMessageSize')

        # 7.1.7c
        # XXX need to coerce MIB value as it has incompatible constraints set
        headerData.setComponentByPosition(
            1, snmpEngineMaxMessageSize.syntax, verifyConstraints=False,
            matchTags=False, matchConstraints=False)

        # 7.1.7d
        msgFlags = 0
        if securityLevel == 1:
            pass

        elif securityLevel == 2:
            msgFlags |= 0x01

        elif securityLevel == 3:
            msgFlags |= 0x03

        else:
            raise error.ProtocolError(
                'Unknown securityLevel %s' % securityLevel)

        if pdu.tagSet in rfc3411.CONFIRMED_CLASS_PDUS:
            msgFlags |= 0x04

        headerData.setComponentByPosition(
            2, self._msgFlags[msgFlags], verifyConstraints=False,
            matchTags=False, matchConstraints=False)

        # 7.1.7e
        # XXX need to coerce MIB value as it has incompatible constraints set
        headerData.setComponentByPosition(3, int(securityModel))

        debug.logger & debug.FLAG_MP and debug.logger(
            'prepareOutgoingMessage: %s' % (msg.prettyPrint(),))

        if securityModel in snmpEngine.securityModels:
            smHandler = snmpEngine.securityModels[securityModel]

        else:
            raise error.StatusInformation(
                errorIndication=errind.unsupportedSecurityModel)

        # 7.1.9.a
        if pdu.tagSet in rfc3411.UNCONFIRMED_CLASS_PDUS:
            securityEngineId = snmpEngineID

        else:
            if peerSnmpEngineData is None:
                debug.logger & debug.FLAG_MP and debug.logger(
                    'prepareOutgoingMessage: peer SNMP engine is not known')

                securityEngineId = None

            else:
                securityEngineId = peerSnmpEngineData['securityEngineId']

        debug.logger & debug.FLAG_MP and debug.logger(
            'prepareOutgoingMessage: securityModel %r, securityEngineId %r, '
            'securityName %r, securityLevel '
            '%r' % (securityModel, securityEngineId, securityName, securityLevel))

        # 7.1.9.b
        securityParameters, wholeMsg = smHandler.generateRequestMsg(
            snmpEngine, self.MESSAGE_PROCESSING_MODEL_ID, msg,
            snmpEngineMaxMessageSize.syntax, securityModel,
            securityEngineId, securityName, securityLevel, scopedPDU
        )

        # Message size constraint verification
        if len(wholeMsg) > snmpEngineMaxMessageSize.syntax:
            raise error.StatusInformation(errorIndication=errind.tooBig)

        # 7.1.9.c
        if pdu.tagSet in rfc3411.CONFIRMED_CLASS_PDUS:
            # XXX rfc bug? why stateReference should be created?
            self._cache.pushByMsgId(
                msgID, sendPduHandle=sendPduHandle,
                msgID=msgID, snmpEngineID=snmpEngineID,
                securityModel=securityModel,
                securityName=securityName,
                securityLevel=securityLevel,
                contextEngineId=contextEngineId,
                contextName=contextName,
                transportDomain=transportDomain,
                transportAddress=transportAddress)

        snmpEngine.observer.storeExecutionContext(
            snmpEngine, 'rfc3412.prepareOutgoingMessage',
            dict(transportDomain=transportDomain,
                 transportAddress=transportAddress,
                 wholeMsg=wholeMsg,
                 securityModel=securityModel,
                 securityName=securityName,
                 securityLevel=securityLevel,
                 contextEngineId=contextEngineId,
                 contextName=contextName,
                 pdu=pdu)
        )
        snmpEngine.observer.clearExecutionContext(
            snmpEngine, 'rfc3412.prepareOutgoingMessage'
        )

        return transportDomain, transportAddress, wholeMsg

    def prepareResponseMessage(self, snmpEngine, messageProcessingModel,
                               securityModel, securityName, securityLevel,
                               contextEngineId, contextName, pduVersion,
                               pdu, maxSizeResponseScopedPDU, stateReference,
                               statusInformation):

        mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder

        snmpEngineID, = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
        snmpEngineID = snmpEngineID.syntax

        # 7.1.2.b
        cachedParams = self._cache.popByStateRef(stateReference)
        msgID = cachedParams['msgID']
        contextEngineId = cachedParams['contextEngineId']
        contextName = cachedParams['contextName']
        securityModel = cachedParams['securityModel']
        securityName = cachedParams['securityName']
        securityLevel = cachedParams['securityLevel']
        securityStateReference = cachedParams['securityStateReference']
        reportableFlag = cachedParams['reportableFlag']
        maxMessageSize = cachedParams['msgMaxSize']
        transportDomain = cachedParams['transportDomain']
        transportAddress = cachedParams['transportAddress']

        debug.logger & debug.FLAG_MP and debug.logger(
            'prepareResponseMessage: stateReference %s' % stateReference)

        # 7.1.3
        if statusInformation is not None and 'oid' in statusInformation:
            # 7.1.3a
            if pdu is None:
                pduType = None

            else:
                requestID = pdu.getComponentByPosition(0)
                pduType = pdu.tagSet

            # 7.1.3b
            if (pdu is None and not reportableFlag or
                    pduType is not None and
                    pduType not in rfc3411.CONFIRMED_CLASS_PDUS):
                raise error.StatusInformation(
                    errorIndication=errind.loopTerminated)

            # 7.1.3c
            reportPDU = rfc1905.ReportPDU()
            pMod.apiPDU.setVarBinds(
                reportPDU, ((statusInformation['oid'], statusInformation['val']),))
            pMod.apiPDU.setErrorStatus(reportPDU, 0)
            pMod.apiPDU.setErrorIndex(reportPDU, 0)

            if pdu is None:
                pMod.apiPDU.setRequestID(reportPDU, 0)

            else:
                # noinspection PyUnboundLocalVariable
                pMod.apiPDU.setRequestID(reportPDU, requestID)

            # 7.1.3d.1
            if 'securityLevel' in statusInformation:
                securityLevel = statusInformation['securityLevel']

            else:
                securityLevel = 1

            # 7.1.3d.2
            if 'contextEngineId' in statusInformation:
                contextEngineId = statusInformation['contextEngineId']

            else:
                contextEngineId = snmpEngineID

            # 7.1.3d.3
            if 'contextName' in statusInformation:
                contextName = statusInformation['contextName']

            else:
                contextName = ""

            # 7.1.3e
            pdu = reportPDU

            debug.logger & debug.FLAG_MP and debug.logger(
                'prepareResponseMessage: prepare report PDU for '
                'statusInformation %s' % statusInformation)
        # 7.1.4
        if not contextEngineId:
            contextEngineId = snmpEngineID  # XXX impl-dep manner

        # 7.1.5
        if not contextName:
            contextName = self._emptyStr

        debug.logger & debug.FLAG_MP and debug.logger(
            'prepareResponseMessage: using contextEngineId %r, contextName '
            '%r' % (contextEngineId, contextName))

        # 7.1.6
        scopedPDU = self._scopedPDU
        scopedPDU.setComponentByPosition(0, contextEngineId)
        scopedPDU.setComponentByPosition(1, contextName)
        scopedPDU.setComponentByPosition(2)
        scopedPDU.getComponentByPosition(2).setComponentByType(
            pdu.tagSet, pdu, verifyConstraints=False, matchTags=False,
            matchConstraints=False)

        # 7.1.7
        msg = self._snmpMsgSpec

        # 7.1.7a
        msg.setComponentByPosition(
            0, self.MESSAGE_PROCESSING_MODEL_ID, verifyConstraints=False,
            matchTags=False, matchConstraints=False)

        headerData = msg.setComponentByPosition(1).getComponentByPosition(1)

        # 7.1.7b
        headerData.setComponentByPosition(
            0, msgID, verifyConstraints=False, matchTags=False,
            matchConstraints=False)

        snmpEngineMaxMessageSize, = mibBuilder.importSymbols(
            '__SNMP-FRAMEWORK-MIB', 'snmpEngineMaxMessageSize')

        # 7.1.7c
        # XXX need to coerce MIB value as it has incompatible constraints set
        headerData.setComponentByPosition(
            1, snmpEngineMaxMessageSize.syntax, verifyConstraints=False,
            matchTags=False, matchConstraints=False)

        # 7.1.7d
        msgFlags = 0

        if securityLevel == 1:
            pass

        elif securityLevel == 2:
            msgFlags |= 0x01

        elif securityLevel == 3:
            msgFlags |= 0x03

        else:
            raise error.ProtocolError('Unknown securityLevel %s' % securityLevel)

        if pdu.tagSet in rfc3411.CONFIRMED_CLASS_PDUS:  # XXX not needed?
            msgFlags |= 0x04

        headerData.setComponentByPosition(
            2, self._msgFlags[msgFlags], verifyConstraints=False, matchTags=False,
            matchConstraints=False)

        # 7.1.7e
        headerData.setComponentByPosition(
            3, securityModel, verifyConstraints=False, matchTags=False,
            matchConstraints=False)

        debug.logger & debug.FLAG_MP and debug.logger(
            'prepareResponseMessage: %s' % (msg.prettyPrint(),))

        if securityModel in snmpEngine.securityModels:
            smHandler = snmpEngine.securityModels[securityModel]

        else:
            raise error.StatusInformation(
                errorIndication=errind.unsupportedSecurityModel)

        debug.logger & debug.FLAG_MP and debug.logger(
            'prepareResponseMessage: securityModel %r, securityEngineId %r, '
            'securityName %r, securityLevel %r' % (
                securityModel, snmpEngineID, securityName, securityLevel))

        # 7.1.8a
        try:
            securityParameters, wholeMsg = smHandler.generateResponseMsg(
                snmpEngine, self.MESSAGE_PROCESSING_MODEL_ID, msg,
                snmpEngineMaxMessageSize.syntax, securityModel,
                snmpEngineID, securityName, securityLevel, scopedPDU,
                securityStateReference)

        except error.StatusInformation:
            # 7.1.8.b
            raise

        debug.logger & debug.FLAG_MP and debug.logger(
            'prepareResponseMessage: SM finished')

        # Message size constraint verification
        if len(wholeMsg) > min(snmpEngineMaxMessageSize.syntax, maxMessageSize):
            raise error.StatusInformation(errorIndication=errind.tooBig)

        snmpEngine.observer.storeExecutionContext(
            snmpEngine,
            'rfc3412.prepareResponseMessage',
            dict(transportDomain=transportDomain,
                 transportAddress=transportAddress,
                 securityModel=securityModel,
                 securityName=securityName,
                 securityLevel=securityLevel,
                 contextEngineId=contextEngineId,
                 contextName=contextName,
                 securityEngineId=snmpEngineID,
                 pdu=pdu))

        snmpEngine.observer.clearExecutionContext(
            snmpEngine, 'rfc3412.prepareResponseMessage')

        return transportDomain, transportAddress, wholeMsg

    # 7.2.1

    def prepareDataElements(self, snmpEngine, transportDomain,
                            transportAddress, wholeMsg):
        # 7.2.2
        msg, restOfwholeMsg = decoder.decode(wholeMsg, asn1Spec=self._snmpMsgSpec)

        debug.logger & debug.FLAG_MP and debug.logger(
            'prepareDataElements: %s' % (msg.prettyPrint(),))

        if eoo.endOfOctets.isSameTypeWith(msg):
            raise error.StatusInformation(errorIndication=errind.parseError)

        mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder

        # 7.2.3
        headerData = msg.getComponentByPosition(1)
        msgVersion = messageProcessingModel = msg.getComponentByPosition(0)
        msgID = headerData.getComponentByPosition(0)
        msgFlags, = headerData.getComponentByPosition(2).asNumbers()
        maxMessageSize = headerData.getComponentByPosition(1)
        securityModel = headerData.getComponentByPosition(3)
        securityParameters = msg.getComponentByPosition(2)

        debug.logger & debug.FLAG_MP and debug.logger(
            'prepareDataElements: msg data msgVersion %s msgID %s '
            'securityModel %s' % (msgVersion, msgID, securityModel))

        # 7.2.4
        if securityModel not in snmpEngine.securityModels:
            snmpUnknownSecurityModels, = mibBuilder.importSymbols(
                '__SNMP-MPD-MIB', 'snmpUnknownSecurityModels')
            snmpUnknownSecurityModels.syntax += 1
            raise error.StatusInformation(errorIndication=errind.unsupportedSecurityModel)

        # 7.2.5
        if msgFlags & 0x03 == 0x00:
            securityLevel = 1

        elif (msgFlags & 0x03) == 0x01:
            securityLevel = 2

        elif (msgFlags & 0x03) == 0x03:
            securityLevel = 3

        else:
            snmpInvalidMsgs, = mibBuilder.importSymbols(
                '__SNMP-MPD-MIB', 'snmpInvalidMsgs')
            snmpInvalidMsgs.syntax += 1
            raise error.StatusInformation(errorIndication=errind.invalidMsg)

        if msgFlags & 0x04:
            reportableFlag = 1

        else:
            reportableFlag = 0

        # 7.2.6
        smHandler = snmpEngine.securityModels[securityModel]

        try:
            (securityEngineId,
             securityName,
             scopedPDU,
             maxSizeResponseScopedPDU,
             securityStateReference) = smHandler.processIncomingMsg(
                snmpEngine, messageProcessingModel, maxMessageSize,
                securityParameters, securityModel, securityLevel,
                wholeMsg, msg)

            debug.logger & debug.FLAG_MP and debug.logger(
                'prepareDataElements: SM succeeded')

        except error.StatusInformation as exc:
            statusInformation = exc

            debug.logger & debug.FLAG_MP and debug.logger(
                'prepareDataElements: SM failed, statusInformation '
                '%s' % statusInformation)

            snmpEngine.observer.storeExecutionContext(
                snmpEngine, 'rfc3412.prepareDataElements:sm-failure',
                dict(transportDomain=transportDomain,
                     transportAddress=transportAddress,
                     securityModel=securityModel,
                     securityLevel=securityLevel,
                     securityParameters=securityParameters,
                     statusInformation=statusInformation))

            snmpEngine.observer.clearExecutionContext(
                snmpEngine, 'rfc3412.prepareDataElements:sm-failure')

            if 'errorIndication' in statusInformation:
                # 7.2.6a
                if 'oid' in statusInformation:
                    # 7.2.6a1
                    securityStateReference = statusInformation['securityStateReference']
                    contextEngineId = statusInformation['contextEngineId']
                    contextName = statusInformation['contextName']

                    if 'scopedPDU' in statusInformation:
                        scopedPDU = statusInformation['scopedPDU']
                        pdu = scopedPDU.getComponentByPosition(2).getComponent()

                    else:
                        pdu = None

                    maxSizeResponseScopedPDU = statusInformation['maxSizeResponseScopedPDU']
                    securityName = None  # XXX secmod cache used

                    # 7.2.6a2
                    stateReference = self._cache.newStateReference()

                    self._cache.pushByStateRef(
                        stateReference, msgVersion=messageProcessingModel,
                        msgID=msgID, contextEngineId=contextEngineId,
                        contextName=contextName, securityModel=securityModel,
                        securityName=securityName, securityLevel=securityLevel,
                        securityStateReference=securityStateReference,
                        reportableFlag=reportableFlag,
                        msgMaxSize=maxMessageSize,
                        maxSizeResponseScopedPDU=maxSizeResponseScopedPDU,
                        transportDomain=transportDomain,
                        transportAddress=transportAddress)

                    # 7.2.6a3
                    try:
                        snmpEngine.msgAndPduDsp.returnResponsePdu(
                            snmpEngine, 3, securityModel, securityName,
                            securityLevel, contextEngineId, contextName,
                            1, pdu, maxSizeResponseScopedPDU, stateReference,
                            statusInformation)

                    except error.StatusInformation:
                        pass

                    debug.logger & debug.FLAG_MP and debug.logger(
                        'prepareDataElements: error reported')

            # 7.2.6b
            if sys.version_info[0] <= 2:
                raise statusInformation

            else:
                origTraceback = sys.exc_info()[2]

                try:
                    raise statusInformation.with_traceback(origTraceback)

                finally:
                    # Break cycle between locals and traceback object
                    # (seems to be irrelevant on Py3 but just in case)
                    del origTraceback
        else:
            # Sniff for engineIdCache
            k = transportDomain, transportAddress
            if k not in self._engineIdCache:
                contextEngineId = scopedPDU[0]
                contextName = scopedPDU[1]

                pdus = scopedPDU[2]
                pdu = pdus.getComponent()

                # Here we assume that authentic/default EngineIDs
                # come only in the course of engine-to-engine communication.
                if pdu.tagSet in rfc3411.INTERNAL_CLASS_PDUS:
                    self._engineIdCache[k] = {
                        'securityEngineId': securityEngineId,
                        'contextEngineId': contextEngineId,
                        'contextName': contextName
                    }

                    timerResolution = snmpEngine.transportDispatcher.getTimerResolution()
                    expireAt = int(self._expirationTimer + 300 / timerResolution)

                    if expireAt not in self._engineIdCacheExpQueue:
                        self._engineIdCacheExpQueue[expireAt] = []

                    self._engineIdCacheExpQueue[expireAt].append(k)

                    debug.logger & debug.FLAG_MP and debug.logger(
                        'prepareDataElements: cache securityEngineId %r for %r %r' % (
                            securityEngineId, transportDomain, transportAddress))

        snmpEngineID, = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
        snmpEngineID = snmpEngineID.syntax

        # 7.2.7 XXX PDU would be parsed here?
        contextEngineId = scopedPDU[0]
        contextName = scopedPDU[1]
        pdu = scopedPDU[2]

        pdu = pdu.getComponent()  # PDUs

        # 7.2.8
        pduVersion = api.SNMP_VERSION_2C

        # 7.2.9
        pduType = pdu.tagSet

        # 7.2.10
        if (pduType in rfc3411.RESPONSE_CLASS_PDUS or
                pduType in rfc3411.INTERNAL_CLASS_PDUS):
            # 7.2.10a
            try:
                cachedReqParams = self._cache.popByMsgId(msgID)

            except error.ProtocolError:
                smHandler.releaseStateInformation(securityStateReference)
                raise error.StatusInformation(errorIndication=errind.dataMismatch)

            # 7.2.10b
            sendPduHandle = cachedReqParams['sendPduHandle']

        else:
            sendPduHandle = None

        debug.logger & debug.FLAG_MP and debug.logger(
            'prepareDataElements: using sendPduHandle %s for msgID '
            '%s' % (sendPduHandle, msgID))

        # 7.2.11
        if pduType in rfc3411.INTERNAL_CLASS_PDUS:
            # 7.2.11a
            varBinds = pMod.apiPDU.getVarBinds(pdu)

            if varBinds:
                errorIndication = _snmpErrors.get(
                    varBinds[0][0],
                    errind.ReportPduReceived(varBinds[0][0].prettyPrint()))

                statusInformation = error.StatusInformation(
                    errorIndication=errorIndication,
                    oid=varBinds[0][0], val=varBinds[0][1],
                    sendPduHandle=sendPduHandle)

            else:
                statusInformation = error.StatusInformation(
                    sendPduHandle=sendPduHandle)

            # 7.2.11b (incomplete implementation)

            snmpEngine.observer.storeExecutionContext(
                snmpEngine, 'rfc3412.prepareDataElements:internal',
                dict(transportDomain=transportDomain,
                     transportAddress=transportAddress,
                     securityModel=securityModel,
                     securityName=securityName,
                     securityLevel=securityLevel,
                     contextEngineId=contextEngineId,
                     contextName=contextName,
                     securityEngineId=securityEngineId,
                     pdu=pdu))

            snmpEngine.observer.clearExecutionContext(
                snmpEngine, 'rfc3412.prepareDataElements:internal')

            # 7.2.11c
            smHandler.releaseStateInformation(securityStateReference)

            # 7.2.11d
            # no-op

            # 7.2.11e XXX may need to pass Reports up to app in some cases...
            raise statusInformation

        statusInformation = None  # no errors ahead

        # 7.2.12
        if pduType in rfc3411.RESPONSE_CLASS_PDUS:
            # 7.2.12a -> no-op

            # 7.2.12b
            # noinspection PyUnboundLocalVariable
            if (securityModel != cachedReqParams['securityModel'] or
                    securityName != cachedReqParams['securityName'] or
                    securityLevel != cachedReqParams['securityLevel'] or
                    contextEngineId != cachedReqParams['contextEngineId'] or
                    contextName != cachedReqParams['contextName']):

                smHandler.releaseStateInformation(securityStateReference)

                raise error.StatusInformation(errorIndication=errind.dataMismatch)

            snmpEngine.observer.storeExecutionContext(
                snmpEngine, 'rfc3412.prepareDataElements:response',
                dict(transportDomain=transportDomain,
                     transportAddress=transportAddress,
                     securityModel=securityModel,
                     securityName=securityName,
                     securityLevel=securityLevel,
                     contextEngineId=contextEngineId,
                     contextName=contextName,
                     securityEngineId=securityEngineId,
                     pdu=pdu))

            snmpEngine.observer.clearExecutionContext(
                snmpEngine, 'rfc3412.prepareDataElements:response')

            # 7.2.12c
            smHandler.releaseStateInformation(securityStateReference)
            stateReference = None

            # 7.2.12d
            return (messageProcessingModel, securityModel, securityName,
                    securityLevel, contextEngineId, contextName,
                    pduVersion, pdu, pduType, sendPduHandle,
                    maxSizeResponseScopedPDU, statusInformation,
                    stateReference)

        # 7.2.13
        if pduType in rfc3411.CONFIRMED_CLASS_PDUS:
            # 7.2.13a
            if securityEngineId != snmpEngineID:
                smHandler.releaseStateInformation(securityStateReference)
                raise error.StatusInformation(
                    errorIndication=errind.engineIDMismatch)

            # 7.2.13b
            stateReference = self._cache.newStateReference()

            self._cache.pushByStateRef(
                stateReference, msgVersion=messageProcessingModel,
                msgID=msgID, contextEngineId=contextEngineId,
                contextName=contextName, securityModel=securityModel,
                securityName=securityName, securityLevel=securityLevel,
                securityStateReference=securityStateReference,
                reportableFlag=reportableFlag, msgMaxSize=maxMessageSize,
                maxSizeResponseScopedPDU=maxSizeResponseScopedPDU,
                transportDomain=transportDomain,
                transportAddress=transportAddress)

            debug.logger & debug.FLAG_MP and debug.logger(
                'prepareDataElements: new stateReference %s' % stateReference)

            snmpEngine.observer.storeExecutionContext(
                snmpEngine, 'rfc3412.prepareDataElements:confirmed',
                dict(transportDomain=transportDomain,
                     transportAddress=transportAddress,
                     securityModel=securityModel,
                     securityName=securityName,
                     securityLevel=securityLevel,
                     contextEngineId=contextEngineId,
                     contextName=contextName,
                     securityEngineId=securityEngineId,
                     pdu=pdu))

            snmpEngine.observer.clearExecutionContext(
                snmpEngine, 'rfc3412.prepareDataElements:confirmed')

            # 7.2.13c
            return (messageProcessingModel, securityModel, securityName,
                    securityLevel, contextEngineId, contextName,
                    pduVersion, pdu, pduType, sendPduHandle,
                    maxSizeResponseScopedPDU, statusInformation,
                    stateReference)

        # 7.2.14
        if pduType in rfc3411.UNCONFIRMED_CLASS_PDUS:

            # Pass new stateReference to let app browse request details
            stateReference = self._cache.newStateReference()

            snmpEngine.observer.storeExecutionContext(
                snmpEngine, 'rfc3412.prepareDataElements:unconfirmed',
                dict(transportDomain=transportDomain,
                     transportAddress=transportAddress,
                     securityModel=securityModel,
                     securityName=securityName,
                     securityLevel=securityLevel,
                     contextEngineId=contextEngineId,
                     contextName=contextName,
                     securityEngineId=securityEngineId,
                     pdu=pdu))

            snmpEngine.observer.clearExecutionContext(
                snmpEngine, 'rfc3412.prepareDataElements:unconfirmed')

            # This is not specified explicitly in RFC
            smHandler.releaseStateInformation(securityStateReference)

            return (messageProcessingModel, securityModel, securityName,
                    securityLevel, contextEngineId, contextName,
                    pduVersion, pdu, pduType, sendPduHandle,
                    maxSizeResponseScopedPDU, statusInformation,
                    stateReference)

        smHandler.releaseStateInformation(securityStateReference)

        raise error.StatusInformation(errorIndication=errind.unsupportedPDUtype)

    def _expireEnginesInfo(self):
        if self._expirationTimer in self._engineIdCacheExpQueue:

            for engineKey in self._engineIdCacheExpQueue[self._expirationTimer]:
                del self._engineIdCache[engineKey]

                debug.logger & debug.FLAG_MP and debug.logger(
                    '__expireEnginesInfo: expiring %r' % (engineKey,))

            del self._engineIdCacheExpQueue[self._expirationTimer]

        self._expirationTimer += 1

    def receiveTimerTick(self, snmpEngine, timeNow):
        self._expireEnginesInfo()
        AbstractMessageProcessingModel.receiveTimerTick(self, snmpEngine, timeNow)