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// Copyright 2018 The dexon-consensus Authors
// This file is part of the dexon-consensus library.
//
// The dexon-consensus 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 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 library. If not, see
// <http://www.gnu.org/licenses/>.
package core
import (
"fmt"
"math/big"
"sync"
"github.com/dexon-foundation/dexon-consensus/common"
"github.com/dexon-foundation/dexon-consensus/core/crypto"
"github.com/dexon-foundation/dexon-consensus/core/types"
"github.com/dexon-foundation/dexon-consensus/core/utils"
)
// Errors for leader module.
var (
ErrIncorrectCRSSignature = fmt.Errorf("incorrect CRS signature")
)
type validLeaderFn func(*types.Block) (bool, error)
// Some constant value.
var (
maxHash *big.Int
one *big.Rat
)
func init() {
hash := make([]byte, common.HashLength)
for i := range hash {
hash[i] = 0xff
}
maxHash = big.NewInt(0).SetBytes(hash)
one = big.NewRat(1, 1)
}
type leaderSelector struct {
hashCRS common.Hash
numCRS *big.Int
minCRSBlock *big.Int
minBlockHash common.Hash
pendingBlocks map[common.Hash]*types.Block
validLeader validLeaderFn
lock sync.Mutex
logger common.Logger
}
func newLeaderSelector(
validLeader validLeaderFn, logger common.Logger) *leaderSelector {
return &leaderSelector{
minCRSBlock: maxHash,
validLeader: validLeader,
logger: logger,
}
}
func (l *leaderSelector) distance(sig crypto.Signature) *big.Int {
hash := crypto.Keccak256Hash(sig.Signature[:])
num := big.NewInt(0)
num.SetBytes(hash[:])
num.Abs(num.Sub(l.numCRS, num))
return num
}
func (l *leaderSelector) probability(sig crypto.Signature) float64 {
dis := l.distance(sig)
prob := big.NewRat(1, 1).SetFrac(dis, maxHash)
p, _ := prob.Sub(one, prob).Float64()
return p
}
func (l *leaderSelector) restart(crs common.Hash) {
numCRS := big.NewInt(0)
numCRS.SetBytes(crs[:])
l.lock.Lock()
defer l.lock.Unlock()
l.numCRS = numCRS
l.hashCRS = crs
l.minCRSBlock = maxHash
l.minBlockHash = common.Hash{}
l.pendingBlocks = make(map[common.Hash]*types.Block)
}
func (l *leaderSelector) leaderBlockHash() common.Hash {
l.lock.Lock()
defer l.lock.Unlock()
for _, b := range l.pendingBlocks {
ok, dist := l.potentialLeader(b)
if !ok {
continue
}
ok, err := l.validLeader(b)
if err != nil {
l.logger.Error("Error checking validLeader", "error", err, "block", b)
delete(l.pendingBlocks, b.Hash)
continue
}
if ok {
l.updateLeader(b, dist)
delete(l.pendingBlocks, b.Hash)
}
}
return l.minBlockHash
}
func (l *leaderSelector) processBlock(block *types.Block) error {
ok, err := utils.VerifyCRSSignature(block, l.hashCRS)
if err != nil {
return err
}
if !ok {
return ErrIncorrectCRSSignature
}
l.lock.Lock()
defer l.lock.Unlock()
ok, dist := l.potentialLeader(block)
if !ok {
return nil
}
ok, err = l.validLeader(block)
if err != nil {
return err
}
if !ok {
l.pendingBlocks[block.Hash] = block
return nil
}
l.updateLeader(block, dist)
return nil
}
func (l *leaderSelector) potentialLeader(block *types.Block) (bool, *big.Int) {
dist := l.distance(block.CRSSignature)
cmp := l.minCRSBlock.Cmp(dist)
return (cmp > 0 || (cmp == 0 && block.Hash.Less(l.minBlockHash))), dist
}
func (l *leaderSelector) updateLeader(block *types.Block, dist *big.Int) {
l.minCRSBlock = dist
l.minBlockHash = block.Hash
}
func (l *leaderSelector) findPendingBlock(
hash common.Hash) (*types.Block, bool) {
b, e := l.pendingBlocks[hash]
return b, e
}
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