Ejemplo n.º 1
0
    def __init__(self, node: 'zeno.server.node.Node', instId: int,
                 isMaster: bool = False):
        """
        Create a new replica.

        :param node: Node on which this replica is located
        :param instId: the id of the protocol instance the replica belongs to
        :param isMaster: is this a replica of the master protocol instance
        """
        super().__init__()

        routerArgs = [(ReqDigest, self._preProcessReqDigest)]

        for r in [PrePrepare, Prepare, Commit]:
            routerArgs.append((r, self.processThreePhaseMsg))
        self.inBoxRouter = Router(*routerArgs)

        self.threePhaseRouter = Router(
                (PrePrepare, self.processPrePrepare),
                (Prepare, self.processPrepare),
                (Commit, self.processCommit)
        )

        self.node = node
        self.instId = instId

        self.name = self.generateName(node.name, self.instId)

        self.outBox = deque()
        """
        This queue is used by the replica to send messages to its node. Replica
        puts messages that are consumed by its node
        """

        self.inBox = deque()
        """
        This queue is used by the replica to receive messages from its node.
        Node puts messages that are consumed by the replica
        """

        self.inBoxStash = deque()
        """
        If messages need to go back on the queue, they go here temporarily and
        are put back on the queue on a state change
        """

        self.isMaster = isMaster

        # Do not know which node is primary or even if any node is primary yet
        # self._isPrimary = None  # type: Optional[bool]

        # Indicates name of the primary replica of this protocol instance.
        # None in case the replica does not know who the primary of the
        # instance is
        self._primaryName = None    # type: Optional[str]

        # Requests waiting to be processed once the replica is able to decide
        # whether it is primary or not
        self.postElectionMsgs = deque()

        # Requests that are stored by non primary replica for which it is
        # expecting corresponding pre prepare requests Dictionary that stores
        # a tuple of client id and request id(sequence no) as key and digest as
        # value. Not creating a set of Tuple3(clientId, reqId, digest) as such a
        # big hashable element is not good. Also this way we can look for the
        # request on the basis of (clientId, reqId) and compare the digest with
        # the received PrePrepare request's digest.
        self.reqsPendingPrePrepare = {}
        # type: Dict[Tuple[str, int], str]

        # PREPARE that are stored by non primary replica for which it has not
        #  got any PRE-PREPARE. Dictionary that stores a tuple of view no and
        #  prepare sequence number as key and a deque of PREPAREs as value.
        # This deque is attempted to be flushed on receiving every
        # PRE-PREPARE request.
        self.preparesWaitingForPrePrepare = {}
        # type: Dict[Tuple[int, int], deque]

        # Requests that are stored by primary replica which it has broadcasted
        # to all other non primary replicas
        # Key of dictionary is a 2 element tuple with elements viewNo,
        # pre-prepare seqNo and value is a Request Digest
        self.sentPrePrepares = {}
        # type: Dict[Tuple[int, int], ReqDigest]

        # Dictionary of received PrePrepare requests. Key of dictionary is a 2
        # element tuple with elements viewNo, pre-prepare seqNo and value is
        # a Request Digest
        self.prePrepares = {}
        # type: Dict[Tuple[int, int], ReqDigest]

        self.prePrepareSeqNo = 0  # type: int

        # Dictionary of received Prepare requests. Key of dictionary is a 2
        # element tuple with elements viewNo, seqNo and value is a 2 element
        # tuple containing request digest and set of sender node names(sender
        # replica names in case of multiple protocol instances)
        # (viewNo, seqNo) -> (digest, {senders})
        self.prepares = Prepares()
        # type: Dict[Tuple[int, int], Tuple[str, Set[str]]]

        self.commits = Commits()

        # Dictionary to keep track of the which replica was primary during each
        # view. Key is the view no and value is the name of the primary
        # replica during that view
        self.primaryNames = {}  # type: Dict[int, str]

        # Holds msgs that are for later views
        self.threePhaseMsgsForLaterView = deque()
Ejemplo n.º 2
0
class Replica(MessageProcessor):
    def __init__(self, node: 'zeno.server.node.Node', instId: int,
                 isMaster: bool = False):
        """
        Create a new replica.

        :param node: Node on which this replica is located
        :param instId: the id of the protocol instance the replica belongs to
        :param isMaster: is this a replica of the master protocol instance
        """
        super().__init__()

        routerArgs = [(ReqDigest, self._preProcessReqDigest)]

        for r in [PrePrepare, Prepare, Commit]:
            routerArgs.append((r, self.processThreePhaseMsg))
        self.inBoxRouter = Router(*routerArgs)

        self.threePhaseRouter = Router(
                (PrePrepare, self.processPrePrepare),
                (Prepare, self.processPrepare),
                (Commit, self.processCommit)
        )

        self.node = node
        self.instId = instId

        self.name = self.generateName(node.name, self.instId)

        self.outBox = deque()
        """
        This queue is used by the replica to send messages to its node. Replica
        puts messages that are consumed by its node
        """

        self.inBox = deque()
        """
        This queue is used by the replica to receive messages from its node.
        Node puts messages that are consumed by the replica
        """

        self.inBoxStash = deque()
        """
        If messages need to go back on the queue, they go here temporarily and
        are put back on the queue on a state change
        """

        self.isMaster = isMaster

        # Do not know which node is primary or even if any node is primary yet
        # self._isPrimary = None  # type: Optional[bool]

        # Indicates name of the primary replica of this protocol instance.
        # None in case the replica does not know who the primary of the
        # instance is
        self._primaryName = None    # type: Optional[str]

        # Requests waiting to be processed once the replica is able to decide
        # whether it is primary or not
        self.postElectionMsgs = deque()

        # Requests that are stored by non primary replica for which it is
        # expecting corresponding pre prepare requests Dictionary that stores
        # a tuple of client id and request id(sequence no) as key and digest as
        # value. Not creating a set of Tuple3(clientId, reqId, digest) as such a
        # big hashable element is not good. Also this way we can look for the
        # request on the basis of (clientId, reqId) and compare the digest with
        # the received PrePrepare request's digest.
        self.reqsPendingPrePrepare = {}
        # type: Dict[Tuple[str, int], str]

        # PREPARE that are stored by non primary replica for which it has not
        #  got any PRE-PREPARE. Dictionary that stores a tuple of view no and
        #  prepare sequence number as key and a deque of PREPAREs as value.
        # This deque is attempted to be flushed on receiving every
        # PRE-PREPARE request.
        self.preparesWaitingForPrePrepare = {}
        # type: Dict[Tuple[int, int], deque]

        # Requests that are stored by primary replica which it has broadcasted
        # to all other non primary replicas
        # Key of dictionary is a 2 element tuple with elements viewNo,
        # pre-prepare seqNo and value is a Request Digest
        self.sentPrePrepares = {}
        # type: Dict[Tuple[int, int], ReqDigest]

        # Dictionary of received PrePrepare requests. Key of dictionary is a 2
        # element tuple with elements viewNo, pre-prepare seqNo and value is
        # a Request Digest
        self.prePrepares = {}
        # type: Dict[Tuple[int, int], ReqDigest]

        self.prePrepareSeqNo = 0  # type: int

        # Dictionary of received Prepare requests. Key of dictionary is a 2
        # element tuple with elements viewNo, seqNo and value is a 2 element
        # tuple containing request digest and set of sender node names(sender
        # replica names in case of multiple protocol instances)
        # (viewNo, seqNo) -> (digest, {senders})
        self.prepares = Prepares()
        # type: Dict[Tuple[int, int], Tuple[str, Set[str]]]

        self.commits = Commits()

        # Dictionary to keep track of the which replica was primary during each
        # view. Key is the view no and value is the name of the primary
        # replica during that view
        self.primaryNames = {}  # type: Dict[int, str]

        # Holds msgs that are for later views
        self.threePhaseMsgsForLaterView = deque()
        # type: deque[(ThreePhaseMsg, str)]

    @staticmethod
    def generateName(nodeName: str, instId: int):
        return "{}:{}".format(nodeName, instId)

    @staticmethod
    def getNodeName(replicaName: str):
        return replicaName.split(":")[0]

    @property
    def isPrimary(self):
        """
        Is this node primary?

        :return: True if this node is primary, False otherwise
        """
        return self._primaryName == self.name if self._primaryName is not None \
            else None

    @property
    def primaryName(self):
        """
        Name of the primary replica of this replica's instance

        :return: Returns name if primary is known, None otherwise
        """
        return self._primaryName

    @primaryName.setter
    def primaryName(self, value: Optional[str]) -> None:
        """
        Set the value of isPrimary.

        :param value: the value to set isPrimary to
        """
        if not value == self._primaryName:
            self._primaryName = value
            self.primaryNames[self.viewNo] = value
            logger.debug("{} setting primaryName for view no {} to: {}"
                .format(self, self.viewNo, value))
            logger.debug("{}'s primaryNames for views are: {}"
                         .format(self,self.primaryNames))
            self._stateChanged()

    def _stateChanged(self):
        """
        A series of actions to be performed when the state of this replica
        changes.

        - UnstashInBox (see _unstashInBox)
        """
        self._unstashInBox()
        if self.isPrimary is not None:
            self.process3PhaseReqsQueue()
            self.processPostElectionMsgs()

    def _stashInBox(self, msg):
        """
        Stash the specified message into the inBoxStash of this replica.

        :param msg: the message to stash
        """
        self.inBoxStash.append(msg)

    def _unstashInBox(self):
        """
        Append the inBoxStash to the right of the inBox.
        """
        self.inBox.extend(self.inBoxStash)
        self.inBoxStash.clear()

    def __repr__(self):
        return self.name

    @property
    def f(self) -> int:
        """
        Return the number of Byzantine Failures that can be tolerated by this
        system. Equal to (N - 1)/3, where N is the number of nodes in the
        system.
        """
        return self.node.f

    @property
    def viewNo(self):
        """
        Return the current view number of this replica.
        """
        return self.node.viewNo

    def isPrimaryInView(self, viewNo: int) -> Optional[bool]:
        """
        Return whether a primary has been selected for this view number.
        """
        return self.primaryNames[viewNo] == self.name

    def isMsgForLaterView(self, msg):
        """
        Return whether this request's view number is greater than the current
        view number of this replica.
        """
        # Assumes request has an attribute view no
        return msg.viewNo > self.viewNo

    def isMsgForCurrentView(self, msg):
        """
        Return whether this request's view number is equal to the current view
        number of this replica.
        """
        # Assumes request has an attribute view no
        return msg.viewNo == self.viewNo

    def isMsgForPastView(self, msg):
        """
        Return whether this request's view number is less than the current view
        number of this replica.
        """
        # Assumes request has an attribute view no
        return msg.viewNo < self.viewNo

    def isPrimaryForMsg(self, msg) -> Optional[bool]:
        """
        Return whether this replica is primary if the request's view number is
        equal this replica's view number and primary has been selected for
        the current view.
        Return None otherwise.

        :param msg: message
        """
        # Assumes request has an attribute view no
        if self.isMsgForLaterView(msg):
            RuntimeError("Cannot get primary status for a request for a later "
                         "view. Request is {}".format(msg))
        else:
            return self.isPrimary if self.isMsgForCurrentView(msg) \
                else self.isPrimaryInView(msg.viewNo)

    def isMsgFromPrimary(self, msg, sender: str) -> bool:
        """
        Return whether this message was from primary replica
        :param msg:
        :param sender:
        :return:
        """
        if self.isMsgForLaterView(msg):
            RuntimeError("Cannot get primary for a request for a later "
                         "view. Request is {}".format(msg))
        else:
            return self.primaryName == sender if self.isMsgForCurrentView(
                msg) else self.primaryNames[msg.viewNo] == sender

    def _preProcessReqDigest(self, rd: ReqDigest) -> None:
        """
        Process request digest if this replica is not a primary, otherwise stash
        the message into the inBox.

        :param rd: the client Request Digest
        """
        if self.isPrimary is not None:
            self.processReqDigest(rd)
        else:
            self._stashInBox(rd)

    async def serviceQueues(self, limit=None):
        """
        Process `limit` number of messages in the inBox.

        :param limit: the maximum number of messages to process
        :return: the number of messages successfully processed
        """
        return await self.inBoxRouter.handleAll(self.inBox, limit)
        # Messages that can be processed right now needs to be added back to the
        # queue. They might be able to be processed later

    def processPostElectionMsgs(self):
        """
        Process messages waiting for the election of a primary replica to
        complete.
        """
        while self.postElectionMsgs:
            req = self.postElectionMsgs.popleft()
            logger.debug("{} processing pended request {}".format(self, req))
            self.dispatchThreePhaseMsg(*req)

    def process3PhaseReqsQueue(self):
        """
        Process the 3 phase requests from the queue whose view number is equal
        to the current view number of this replica.
        """
        unprocessed = deque()
        while self.threePhaseMsgsForLaterView:
            request, sender = self.threePhaseMsgsForLaterView.popleft()
            logger.debug("{} processing pended 3 phase request: {}"
                         .format(self, request))
            # If the request is for a later view dont try to process it but add
            # it back to the queue.
            # Sacrificing brevity for efficiency.
            if self.isMsgForLaterView(request):
                unprocessed.append((request, sender))
            else:
                self.processThreePhaseMsg(request, sender)
        self.threePhaseMsgsForLaterView = unprocessed

    @property
    def quorum(self) -> int:
        r"""
        Return the quorum of this RBFT system. Equal to :math:`2f + 1`.
        Return None if `f` is not yet determined.
        """
        return self.node.quorum

    def dispatchThreePhaseMsg(self, request: ThreePhaseMsg,
                              sender: str) -> Any:
        """
        Create a three phase request to be handled by the threePhaseRouter.

        :param request: the ThreePhaseRequest to dispatch
        :param senderRep: the name of the node that sent this request
        """
        senderRep = self.generateName(sender, self.instId)
        self.threePhaseRouter.handleSync((request, senderRep))

    def processReqDigest(self, rd: ReqDigest):
        """
        Process a request digest. Works only if this replica has decided its
        primary status.

        :param rd: the client request digest to process
        """
        if self.isPrimary is False:
            logger.debug("Non primary replica {} pended request for Pre "
                         "Prepare {}".format(self, (rd.clientId, rd.reqId)))
            self.reqsPendingPrePrepare[(rd.clientId, rd.reqId)] = rd.digest
        else:
            self.sendPrePrepare(rd)

    def processThreePhaseMsg(self, msg: ThreePhaseMsg, sender: str):
        """
        Process a 3-phase (pre-prepare, prepare and commit) request.
        Dispatch the request only if primary has already been decided, otherwise
        stash it.

        :param msg: the Three Phase message, one of PRE-PREPARE, PREPARE,
            COMMIT
        :param sender: name of the node that sent this message
        """
        # Can only proceed further if it knows whether its primary or not
        if self.isMsgForLaterView(msg):
            self.threePhaseMsgsForLaterView.append((msg, sender))
            logger.debug("{} pended received 3 phase request for a later view: "
                         "{}".format(self, msg))
        else:
            if self.isPrimary is None:
                self.postElectionMsgs.append((msg, sender))
                logger.debug("Replica {} pended request {} from {}".
                             format(self, msg, sender))
            else:
                self.dispatchThreePhaseMsg(msg, sender)

    def processPrePrepare(self, pp: PrePrepare, sender: str):
        """
        Validate and process the PRE-PREPARE specified.
        If validation is successful, create a PREPARE and broadcast it.

        :param pp: a prePrepareRequest
        :param sender: name of the node that sent this message
        """
        logger.debug("{} Receiving PRE-PREPARE at {}".
                     format(self, time.perf_counter()))
        try:
            if self.canProcessPrePrepare(pp, sender):
                self.addToPrePrepares(pp)
                if self.canSendPrepare(pp):
                    self.sendPrepare(pp)
                else:
                    logger.debug("{} cannot send PREPARE".format(self))
        except SuspiciousNode as ex:
            logger.warning(
                    "{} cannot process incoming PRE-PREPARE".format(self))
            self.discard(pp, ex.reason, logger.debug)

    def processPrepare(self, prepare: Prepare, sender: str) -> None:
        """
        Validate and process the PREPARE specified.
        If validation is successful, create a COMMIT and broadcast it.

        :param prepare: a PREPARE msg
        :param sender: name of the node that sent the PREPARE
        """
        if self.isValidPrepare(prepare, sender):
            self.addToPrepares(prepare, sender)
            if self.canSendCommit(prepare):
                self.sendCommit(prepare)
            else:
                logger.debug("{} not yet able to send COMMIT".format(self))
        else:
            logger.warning("{} cannot process incoming PREPARE".format(self))

    def processCommit(self, commit: Commit, sender: str) -> None:
        """
        Validate and process the COMMIT specified.
        If validation is successful, return the message to the node.

        :param commit: an incoming COMMIT message
        :param sender: name of the node that sent the COMMIT
        """
        try:
            if self.isValidCommit(commit, sender):
                self.addToCommits(commit, sender)
            if self.canOrder(commit):
                logging.debug("{} returning request to node".format(self))
                self.order(commit)
            else:
                logger.trace("{} cannot return request to node".format(self))
        except SuspiciousNode as ex:
            logger.warning("{} cannot process incoming COMMIT".format(self))
            self.discard(commit, ex.reason, logger.debug)

    def sendPrePrepare(self, reqDigest: ReqDigest) -> None:
        """
        Broadcast a PRE-PREPARE to all the replicas.

        :param reqDigest: a tuple with elements clientId, reqId, and digest
        """
        logger.debug("{} Sending PRE-PREPARE at {}".
                     format(self, time.perf_counter()))
        self.prePrepareSeqNo += 1
        prePrepareReq = PrePrepare(self.instId,
                                   self.viewNo,
                                   self.prePrepareSeqNo,
                                   *reqDigest)
        self.sentPrePrepares[self.viewNo, self.prePrepareSeqNo] = reqDigest
        self.send(prePrepareReq)

    def sendPrepare(self, pp: PrePrepare):
        logger.debug("{} Sending PREPARE at {}".
                     format(self, time.perf_counter()))
        prepare = Prepare(self.instId,
                          pp.viewNo,
                          pp.ppSeqNo,
                          pp.digest)
        self.addToPrepares(prepare, self.name)
        self.send(prepare)

    def sendCommit(self, p: Prepare):
        commit = Commit(self.instId,
                        p.viewNo,
                        p.ppSeqNo,
                        p.digest)
        self.addToCommits(commit, self.name)
        self.send(commit)

    def canProcessPrePrepare(self, pp: PrePrepare, sender: str):
        """
        Decide whether this replica is eligible to process a PRE-PREPARE,
        based on the following criteria:

        - this replica is non-primary replica
        - the request isn't in its list of received PRE-PREPAREs
        - the request is waiting to for PRE-PREPARE and the digest value matches

        :param pp: a PRE-PREPARE msg to process
        :param sender: the name of the node that sent the PRE-PREPARE msg
        :return: True if processing is allowed, False otherwise
        """
        # PRE-PREPARE should not be sent from non primary
        if not self.isMsgFromPrimary(pp, sender):
            self.raiseSuspicion(sender, Suspicions.PPR_FRM_NON_PRIMARY)

        # A PRE-PREPARE is being sent to primary
        if self.isPrimaryForMsg(pp) is True:
            self.raiseSuspicion(sender, Suspicions.PPR_TO_PRIMARY)

        if (pp.viewNo, pp.ppSeqNo) in self.prePrepares:
            self.raiseSuspicion(sender, Suspicions.DUPLICATE_PPR_SENT)

        key = (pp.clientId, pp.reqId)

        if key in self.reqsPendingPrePrepare and \
                        self.reqsPendingPrePrepare[key] != pp.digest:
            self.raiseSuspicion(sender, Suspicions.PPR_DIGEST_WRONG)

        return True

    def addToPrePrepares(self, pp: PrePrepare) -> None:
        """
        Add the specified PRE-PREPARE to this replica's list of received
        PRE-PREPAREs.

        :param pp: the PRE-PREPARE to add to the list
        """
        self.prePrepares[(pp.viewNo, pp.ppSeqNo)] = \
            (pp.clientId, pp.reqId, pp.digest)
        self.dequeuePrepares(pp.viewNo, pp.ppSeqNo)

    def canSendPrepare(self, request) -> None:
        """
        Return whether the request identified by (clientId, requestId) can
        proceed to the Prepare step.

        :param request: any object with clientId and requestId attributes
        """
        return self.node.requests.canPrepare(request, self.f + 1)

    def isValidPrepare(self, prepare: Prepare, sender: str):
        """
        Return whether the PREPARE specified is valid.

        :param prepare: the PREPARE to validate
        :param sender: the name of the node that sent the PREPARE
        :return: True if PREPARE is valid, False otherwise
        """
        key = (prepare.viewNo, prepare.ppSeqNo)
        primaryStatus = self.isPrimaryForMsg(prepare)

        ppReqs = self.sentPrePrepares if primaryStatus else self.prePrepares

        # If a non primary replica and receiving a PREPARE request before a
        # PRE-PREPARE request, then proceed

        # PREPARE should not be sent from primary
        if self.isMsgFromPrimary(prepare, sender):
            self.raiseSuspicion(sender, Suspicions.PR_FRM_PRIMARY)

        # If non primary replica
        try:
            if primaryStatus is False:
                if self.prepares.hasVoteFromSender(prepare, sender):
                    self.raiseSuspicion(sender, Suspicions.DUPLICATE_PR_SENT)
                # If PRE-PREPARE not received for the PREPARE, might be slow network
                elif key not in ppReqs:
                    self.enqueuePrepare(prepare, sender)
                elif prepare.digest != ppReqs[key][2]:
                    self.raiseSuspicion(sender, Suspicions.PR_DIGEST_WRONG)
                else:
                    return True
        # If primary replica
            else:
                if self.prepares.hasVoteFromSender(prepare, sender):
                    self.raiseSuspicion(sender, Suspicions.DUPLICATE_PR_SENT)
                # If PRE-PREPARE was not sent for this PREPARE, certainly
                # malicious behavior
                elif key not in ppReqs:
                    self.raiseSuspicion(sender, Suspicions.UNKNOWN_PR_SENT)
                elif prepare.digest != ppReqs[key][2]:
                    self.raiseSuspicion(sender, Suspicions.PR_DIGEST_WRONG)
                else:
                    return True
        except SuspiciousNode as ex:
            logger.warn("Invalid prepare message received: {}".format(prepare))
            self.discard(prepare, ex.reason, logger.debug)

    def addToPrepares(self, prepare: Prepare, sender: str):
        self.prepares.addVote(prepare, sender)

    def canSendCommit(self, request: Prepare) -> bool:
        """
        Return whether the specified PREPARE can proceed to the Commit
        step.

        Decision criteria:

        - If this replica has got just 2f PREPARE requests then commit request.
        - If less than 2f PREPARE requests then probably there's no consensus on
            the request; don't commit
        - If more than 2f then already sent COMMIT; don't commit

        :param request: the PREPARE
        """
        return self.prepares.hasQuorum(request, self.f)

    def isValidCommit(self, request: Commit, sender: str):
        """
        Return whether the COMMIT specified is valid.

        :param request: the COMMIT to validate
        :return: True if `request` is valid, False otherwise
        """
        key = (request.viewNo, request.ppSeqNo)
        if key not in self.prepares and \
                        key not in self.preparesWaitingForPrePrepare:
            self.raiseSuspicion(sender, Suspicions.UNKNOWN_CM_SENT)
        elif self.commits.hasVoteFromSender(request, sender):
            self.raiseSuspicion(sender, Suspicions.DUPLICATE_CM_SENT)
        else:
            if request.digest != self.getDigestFromPrepare(*key):
                self.raiseSuspicion(sender, Suspicions.CM_DIGEST_WRONG)
            else:
                return True

    def addToCommits(self, commit: Commit, sender: str):
        """
        Add the specified COMMIT to this replica's list of received
        commit requests.

        :param commit: the COMMIT to add to the list
        :param sender: the name of the node that sent the COMMIT
        """
        self.commits.addVote(commit, sender)

    def canOrder(self, commit: Commit) -> bool:
        """
        Return whether the specified commitRequest can be returned to the node.

        Decision criteria:

        - If have got just 2f+1 Commit requests then return request to node
        - If less than 2f+1 of commit requests then probably don't have
            consensus on the request; don't return request to node
        - If more than 2f+1 then already returned to node; don't return request
            to node

        :param commit: the COMMIT
        """
        return self.commits.hasQuorum(commit, self.f)

    def order(self, commit: Commit) -> None:
        """
        Attempt to send an ORDERED request for the specified COMMIT to the
        node.

        :param commit: the COMMIT message
        """
        key = (commit.viewNo, commit.ppSeqNo)
        primaryStatus = self.isPrimaryForMsg(commit)

        if primaryStatus is True:
            clientId, reqId, digest = self.sentPrePrepares[key]
        elif primaryStatus is False:
            # When the node received PREPARE requests and PRE-PREPARE request
            if key in self.prePrepares:
                clientId, reqId, digest = self.prePrepares[key]
            else:
                digest = self.getDigestFromPrepare(*key)
                for (cid, rid), dgst \
                        in self.reqsPendingPrePrepare.items():
                    if digest == dgst:
                        clientId, reqId = cid, rid
                        break
        else:
            self.discard(commit,
                         "{}'s primary status found None while returning "
                         "request {} to node".format(self, commit),
                         logger.warning)

        self.send(Ordered(self.instId,
                          commit.viewNo,
                          clientId,
                          reqId,
                          digest))

    def enqueuePrepare(self, request: Prepare, sender: str):
        logging.debug("Queueing prepares due to unavailability of "
                      "pre-prepare. request {} from {}".format(request, sender))
        key = (request.viewNo, request.ppSeqNo)
        if key not in self.preparesWaitingForPrePrepare:
            self.preparesWaitingForPrePrepare[key] = deque()
        self.preparesWaitingForPrePrepare[key].append((request, sender))

    def dequeuePrepares(self, viewNo: int, ppSeqNo: int):
        key = (viewNo, ppSeqNo)
        if key in self.preparesWaitingForPrePrepare:
            logging.debug("Processing prepares waiting for pre-prepare for "
                          "view no {} and seq no {}".format(viewNo, ppSeqNo))
            while self.preparesWaitingForPrePrepare[key]:
                prepare, sender = self.preparesWaitingForPrePrepare[
                    key].popleft()
                self.processPrePrepare(prepare, sender)

    def getDigestFromPrepare(self, viewNo: int, ppSeqNo: int) -> Optional[str]:
        key = (viewNo, ppSeqNo)
        if key in self.prepares:
            return self.prepares[key].digest
        elif key in self.preparesWaitingForPrePrepare:
            prepare, _ = self.preparesWaitingForPrePrepare[key][0]
            return prepare.digest
        else:
            return None

    def send(self, msg) -> None:
        """
        Send a message to the node on which this replica resides.

        :param msg: the message to send
        """
        logger.debug("{} sending {}".format(self, msg.__class__.__name__),
                     extra={"cli": True})
        logger.trace("{} sending {}".format(self, msg))
        self.outBox.append(msg)

    def raiseSuspicion(self, on: str, suspicion: Suspicion):
        nodeName = self.getNodeName(on)
        self.node.reportSuspiciousNode(nodeName, suspicion.reason, suspicion.code)
        raise SuspiciousNode(suspicion)