core: add nack module (#41)

1 files changed, 211 insertions, 0 deletions

diff --git a/core/negative-ack.go b/core/negative-ack.go
new file mode 100644
index 0000000..13a4832
--- /dev/null
+++ b/core/negative-ack.go
@@ -0,0 +1,211 @@
+// Copyright 2018 The dexon-consensus-core Authors
+// This file is part of the dexon-consensus-core library.
+//
+// The dexon-consensus-core library is free software: you can redistribute it and/or
+// modify it under the terms of the GNU Lesser General Public License as
+// published by the Free Software Foundation, either version 3 of the License,
+// or (at your option) any later version.
+//
+// The dexon-consensus-core library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the dexon-consensus-core library. If not, see
+// <http://www.gnu.org/licenses/>.
+
+package core
+
+import (
+	"time"
+
+	"github.com/dexon-foundation/dexon-consensus-core/core/types"
+)
+
+type negativeAck struct {
+	// owner is the ID of proposer itself, this is used when deciding
+	// a validator to be restricted or not.
+	owner types.ValidatorID
+
+	numOfValidators int
+
+	// timeDelay and timeExpire are for nack timeout.
+	timeDelay  time.Duration
+	timeExpire time.Duration
+
+	// restricteds stores validators which has been restricted and the time it's
+	// restricted.
+	restricteds map[types.ValidatorID]time.Time
+
+	// lastVotes and lockedVotes store the votes for nack. lastVotes[vid1][vid2]
+	// and lockedVotes[vid1][vid2] both mean that vid2 votes vid1. The difference
+	// is lockedVotes works only when vid1 is restricted, so that the votes are
+	// needed to be locked.
+	lastVotes   map[types.ValidatorID]map[types.ValidatorID]struct{}
+	lockedVotes map[types.ValidatorID]map[types.ValidatorID]struct{}
+
+	// timeDiffs is the cache for last time stamps. timeDiffs[vid1][vid2] means
+	// the last updated timestamps vid1 sees vid2.
+	timeDiffs map[types.ValidatorID]map[types.ValidatorID]map[types.ValidatorID]time.Time
+}
+
+// newNegativeAck creates a new negaticeAck instance.
+func newNegativeAck(vid types.ValidatorID) *negativeAck {
+	n := &negativeAck{
+		owner:           vid,
+		numOfValidators: 0,
+		restricteds:     make(map[types.ValidatorID]time.Time),
+		lastVotes:       make(map[types.ValidatorID]map[types.ValidatorID]struct{}),
+		lockedVotes:     make(map[types.ValidatorID]map[types.ValidatorID]struct{}),
+		timeDiffs:       make(map[types.ValidatorID]map[types.ValidatorID]map[types.ValidatorID]time.Time),
+	}
+	n.addValidator(vid)
+	return n
+}
+
+// processNewVote is called when a new "vote" occurs, that is, a validator
+// sees that other 2f + 1 validators think a validator is slow. "vid" is the
+// validator which propesed the block which the timestamps votes and "h" is
+// the validator been voted to be nacked.
+func (n *negativeAck) processNewVote(
+	vid types.ValidatorID,
+	h types.ValidatorID,
+) []types.ValidatorID {
+
+	nackeds := []types.ValidatorID{}
+	if _, exist := n.restricteds[h]; exist {
+		n.lockedVotes[h][vid] = struct{}{}
+		if len(n.lockedVotes[h]) > 2*(n.numOfValidators-1)/3 {
+			nackeds = append(nackeds, h)
+			delete(n.restricteds, h)
+		}
+	} else {
+		if n.owner == vid {
+			n.restrict(h)
+		} else {
+			n.lastVotes[h][vid] = struct{}{}
+			if len(n.lastVotes[h]) > (n.numOfValidators-1)/3 {
+				n.restrict(h)
+			}
+		}
+	}
+	return nackeds
+}
+
+// processTimestamps process new timestamps of a block which is proposed by
+// validator vid, and returns the validators being nacked.
+func (n *negativeAck) processTimestamps(
+	vid types.ValidatorID,
+	ts map[types.ValidatorID]time.Time,
+) []types.ValidatorID {
+
+	n.checkRestrictExpire()
+
+	nackeds := []types.ValidatorID{}
+	for h := range n.timeDiffs {
+		if n.timeDiffs[vid][h][h].Equal(ts[h]) {
+			votes := 0
+			for hh := range n.timeDiffs {
+				if ts[hh].Sub(n.timeDiffs[vid][h][hh]) >= n.timeDelay {
+					votes++
+				}
+			}
+			if votes > 2*((n.numOfValidators-1)/3) {
+				n.lastVotes[h][vid] = struct{}{}
+				nack := n.processNewVote(vid, h)
+				for _, i := range nack {
+					nackeds = append(nackeds, i)
+				}
+			} else {
+				delete(n.lastVotes[h], vid)
+			}
+		} else {
+			for hh := range n.timeDiffs {
+				n.timeDiffs[vid][h][hh] = ts[hh]
+			}
+			delete(n.lastVotes[h], vid)
+		}
+	}
+	return nackeds
+}
+
+func (n *negativeAck) checkRestrictExpire() {
+	expired := []types.ValidatorID{}
+	now := time.Now()
+	for h, t := range n.restricteds {
+		if now.Sub(t) >= n.timeExpire {
+			expired = append(expired, h)
+		}
+	}
+	for _, h := range expired {
+		delete(n.restricteds, h)
+	}
+}
+
+func (n *negativeAck) restrict(vid types.ValidatorID) {
+	if _, exist := n.restricteds[vid]; !exist {
+		n.restricteds[vid] = time.Now().UTC()
+		n.lockedVotes[vid] = map[types.ValidatorID]struct{}{}
+		for h := range n.lastVotes[vid] {
+			n.lockedVotes[vid][h] = struct{}{}
+		}
+	}
+}
+
+func (n *negativeAck) getRestrictedValidators() map[types.ValidatorID]struct{} {
+	n.checkRestrictExpire()
+	ret := map[types.ValidatorID]struct{}{}
+	for h := range n.restricteds {
+		ret[h] = struct{}{}
+	}
+	return ret
+}
+
+func (n *negativeAck) setTimeDelay(t time.Duration) {
+	n.timeDelay = t
+}
+
+func (n *negativeAck) setTimeExpire(t time.Duration) {
+	n.timeExpire = t
+}
+
+func (n *negativeAck) addValidator(vid types.ValidatorID) {
+	n.numOfValidators++
+	n.lastVotes[vid] = make(map[types.ValidatorID]struct{})
+	n.lockedVotes[vid] = make(map[types.ValidatorID]struct{})
+
+	newTimeDiff := make(map[types.ValidatorID]map[types.ValidatorID]time.Time)
+	for h := range n.timeDiffs {
+		newTimeDiff2 := make(map[types.ValidatorID]time.Time)
+		for hh := range n.timeDiffs {
+			newTimeDiff2[hh] = time.Time{}
+		}
+		newTimeDiff[h] = newTimeDiff2
+	}
+	n.timeDiffs[vid] = newTimeDiff
+	for h := range n.timeDiffs {
+		n.timeDiffs[h][vid] = make(map[types.ValidatorID]time.Time)
+	}
+}
+
+func (n *negativeAck) deleteValidator(vid types.ValidatorID) {
+	n.numOfValidators--
+
+	delete(n.timeDiffs, vid)
+
+	for h := range n.lastVotes {
+		delete(n.lastVotes[h], vid)
+	}
+	delete(n.lastVotes, vid)
+	delete(n.lockedVotes, vid)
+
+	for h := range n.timeDiffs {
+		delete(n.timeDiffs[h], vid)
+		for hh := range n.timeDiffs[h] {
+			delete(n.timeDiffs[h][hh], vid)
+		}
+	}
+
+	delete(n.restricteds, vid)
+}