path: root/core/utils.go

// 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 (
    "errors"
    "fmt"
    "math/rand"
    "os"
    "sort"
    "time"

    "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"
)

// NodeSetCache is type alias to avoid fullnode compile error when moving
// it to core/utils package.
type NodeSetCache = utils.NodeSetCache

// NewNodeSetCache is function alias to avoid fullnode compile error when moving
// it to core/utils package.
var NewNodeSetCache = utils.NewNodeSetCache

var (
    debug = false
    // ErrEmptyTimestamps would be reported if Block.timestamps is empty.
    ErrEmptyTimestamps = errors.New("timestamp vector should not be empty")
)

func init() {
    if os.Getenv("DEBUG") != "" {
        debug = true
    }
}

// Debugf is like fmt.Printf, but only output when we are in debug mode.
func Debugf(format string, args ...interface{}) {
    if debug {
        fmt.Printf(format, args...)
    }
}

// Debugln is like fmt.Println, but only output when we are in debug mode.
func Debugln(args ...interface{}) {
    if debug {
        fmt.Println(args)
    }
}

func interpoTime(t1 time.Time, t2 time.Time, sep int) []time.Time {
    if sep == 0 {
        return []time.Time{}
    }
    if t1.After(t2) {
        return interpoTime(t2, t1, sep)
    }
    timestamps := make([]time.Time, sep)
    duration := t2.Sub(t1)
    period := time.Duration(
        (duration.Nanoseconds() / int64(sep+1))) * time.Nanosecond
    prevTime := t1
    for idx := range timestamps {
        prevTime = prevTime.Add(period)
        timestamps[idx] = prevTime
    }
    return timestamps
}

func getMedianTime(timestamps []time.Time) (t time.Time, err error) {
    if len(timestamps) == 0 {
        err = ErrEmptyTimestamps
        return
    }
    tscopy := make([]time.Time, 0, len(timestamps))
    for _, ts := range timestamps {
        tscopy = append(tscopy, ts)
    }
    sort.Sort(common.ByTime(tscopy))
    if len(tscopy)%2 == 0 {
        t1 := tscopy[len(tscopy)/2-1]
        t2 := tscopy[len(tscopy)/2]
        t = interpoTime(t1, t2, 1)[0]
    } else {
        t = tscopy[len(tscopy)/2]
    }
    return
}

func removeFromSortedUint32Slice(xs []uint32, x uint32) []uint32 {
    indexToRemove := sort.Search(len(xs), func(idx int) bool {
        return xs[idx] >= x
    })
    if indexToRemove == len(xs) || xs[indexToRemove] != x {
        // This value is not found.
        return xs
    }
    return append(xs[:indexToRemove], xs[indexToRemove+1:]...)
}

// pickBiasedTime returns a biased time based on a given range.
func pickBiasedTime(base time.Time, biasedRange time.Duration) time.Time {
    return base.Add(time.Duration(rand.Intn(int(biasedRange))))
}

// HashConfigurationBlock returns the hash value of configuration block.
func HashConfigurationBlock(
    notarySet map[types.NodeID]struct{},
    config *types.Config,
    snapshotHash common.Hash,
    prevHash common.Hash,
) common.Hash {
    notaryIDs := make(types.NodeIDs, 0, len(notarySet))
    for nID := range notarySet {
        notaryIDs = append(notaryIDs, nID)
    }
    sort.Sort(notaryIDs)
    notarySetBytes := make([]byte, 0, len(notarySet)*len(common.Hash{}))
    for _, nID := range notaryIDs {
        notarySetBytes = append(notarySetBytes, nID.Hash[:]...)
    }
    configBytes := config.Bytes()

    return crypto.Keccak256Hash(
        notarySetBytes[:],
        configBytes[:],
        snapshotHash[:],
        prevHash[:],
    )
}

// VerifyBlock verifies the signature of types.Block.
func VerifyBlock(b *types.Block) (err error) {
    hash, err := hashBlock(b)
    if err != nil {
        return
    }
    if hash != b.Hash {
        err = ErrIncorrectHash
        return
    }
    pubKey, err := crypto.SigToPub(b.Hash, b.Signature)
    if err != nil {
        return
    }
    if !b.ProposerID.Equal(types.NewNodeID(pubKey)) {
        err = ErrIncorrectSignature
        return
    }
    return
}

// DiffUint64 calculates difference between two uint64.
func DiffUint64(a, b uint64) uint64 {
    if a > b {
        return a - b
    }
    return b - a
}