// 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 (
"fmt"
"math/big"
"github.com/dexon-foundation/dexon-consensus-core/common"
"github.com/dexon-foundation/dexon-consensus-core/core/types"
"github.com/dexon-foundation/dexon-consensus-core/crypto"
)
// Errors for leader module.
var (
ErrIncorrectCRSSignature = fmt.Errorf("incorrect CRS signature")
)
// 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
sigToPub SigToPubFn
}
func newGenesisLeaderSelector(
crs string,
sigToPub SigToPubFn) *leaderSelector {
hash := crypto.Keccak256Hash([]byte(crs[:]))
return newLeaderSelector(hash, sigToPub)
}
func newLeaderSelector(
crs common.Hash,
sigToPub SigToPubFn) *leaderSelector {
numCRS := big.NewInt(0)
numCRS.SetBytes(crs[:])
return &leaderSelector{
numCRS: numCRS,
hashCRS: crs,
minCRSBlock: maxHash,
sigToPub: sigToPub,
}
}
func (l *leaderSelector) distance(sig crypto.Signature) *big.Int {
hash := crypto.Keccak256Hash(sig[:])
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) leaderBlockHash() common.Hash {
return l.minBlockHash
}
func (l *leaderSelector) prepareBlock(
block *types.Block, prv crypto.PrivateKey) (err error) {
block.CRSSignature, err = prv.Sign(hashCRS(block, l.hashCRS))
return
}
func (l *leaderSelector) processBlock(block *types.Block) error {
ok, err := verifyCRSSignature(block, l.hashCRS, l.sigToPub)
if err != nil {
return err
}
if !ok {
return ErrIncorrectCRSSignature
}
dist := l.distance(block.CRSSignature)
if l.minCRSBlock.Cmp(dist) == 1 {
l.minCRSBlock = dist
l.minBlockHash = block.Hash
}
return nil
}
