path: root/core/blockchain.go

// Copyright 2019 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 (
    "bytes"
    "errors"
    "fmt"
    "sort"
    "sync"
    "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"
)

// Errors for sanity check error.
var (
    ErrBlockFromOlderPosition   = errors.New("block from older position")
    ErrNotGenesisBlock          = errors.New("not a genesis block")
    ErrIsGenesisBlock           = errors.New("is a genesis block")
    ErrIncorrectParentHash      = errors.New("incorrect parent hash")
    ErrInvalidBlockHeight       = errors.New("invalid block height")
    ErrInvalidRoundID           = errors.New("invalid round id")
    ErrInvalidTimestamp         = errors.New("invalid timestamp")
    ErrNotFollowTipPosition     = errors.New("not follow tip position")
    ErrDuplicatedPendingBlock   = errors.New("duplicated pending block")
    ErrRetrySanityCheckLater    = errors.New("retry sanity check later")
    ErrRoundNotSwitch           = errors.New("round not switch")
    ErrIncorrectAgreementResult = errors.New(
        "incorrect block randomness result")
    ErrMissingRandomness = errors.New("missing block randomness")
)

type pendingBlockRecord struct {
    position types.Position
    block    *types.Block
}

type pendingBlockRecords []pendingBlockRecord

func (pb *pendingBlockRecords) insert(p pendingBlockRecord) error {
    idx := sort.Search(len(*pb), func(i int) bool {
        return !(*pb)[i].position.Older(p.position)
    })
    switch idx {
    case len(*pb):
        *pb = append(*pb, p)
    default:
        if (*pb)[idx].position.Equal(p.position) {
            // Allow to overwrite pending block record for empty blocks, we may
            // need to pull that block from others when its parent is not found
            // locally.
            if (*pb)[idx].block == nil && p.block != nil {
                (*pb)[idx].block = p.block
                return nil
            }
            return ErrDuplicatedPendingBlock
        }
        // Insert the value to that index.
        *pb = append((*pb), pendingBlockRecord{})
        copy((*pb)[idx+1:], (*pb)[idx:])
        (*pb)[idx] = p
    }
    return nil
}

func (pb pendingBlockRecords) searchByHeight(h uint64) (
    pendingBlockRecord, bool) {
    idx := sort.Search(len(pb), func(i int) bool {
        return pb[i].position.Height >= h
    })
    if idx == len(pb) || pb[idx].position.Height != h {
        return pendingBlockRecord{}, false
    }
    return pb[idx], true
}

func (pb pendingBlockRecords) searchByPosition(p types.Position) (
    pendingBlockRecord, bool) {
    idx := sort.Search(len(pb), func(i int) bool {
        return !pb[i].block.Position.Older(p)
    })
    if idx == len(pb) || !pb[idx].position.Equal(p) {
        return pendingBlockRecord{}, false
    }
    return pb[idx], true
}

type blockChainConfig struct {
    utils.RoundBasedConfig

    minBlockInterval time.Duration
}

func (c *blockChainConfig) fromConfig(round uint64, config *types.Config) {
    c.minBlockInterval = config.MinBlockInterval
    c.SetupRoundBasedFields(round, config)
}

func newBlockChainConfig(prev blockChainConfig, config *types.Config) (
    c blockChainConfig) {
    c = blockChainConfig{}
    c.fromConfig(prev.RoundID()+1, config)
    c.AppendTo(prev.RoundBasedConfig)
    return
}

type tsigVerifierGetter interface {
    UpdateAndGet(uint64) (TSigVerifier, bool, error)
    Purge(uint64)
}

type blockChain struct {
    lock                sync.RWMutex
    ID                  types.NodeID
    lastConfirmed       *types.Block
    lastDelivered       *types.Block
    signer              *utils.Signer
    vGetter             tsigVerifierGetter
    app                 Application
    logger              common.Logger
    pendingRandomnesses map[types.Position][]byte
    configs             []blockChainConfig
    pendingBlocks       pendingBlockRecords
    confirmedBlocks     types.BlocksByPosition
    dMoment             time.Time

    // Do not access this variable besides processAgreementResult.
    lastPosition types.Position
}

func newBlockChain(nID types.NodeID, dMoment time.Time, initBlock *types.Block,
    app Application, vGetter tsigVerifierGetter, signer *utils.Signer,
    logger common.Logger) *blockChain {
    return &blockChain{
        ID:            nID,
        lastConfirmed: initBlock,
        lastDelivered: initBlock,
        signer:        signer,
        vGetter:       vGetter,
        app:           app,
        logger:        logger,
        dMoment:       dMoment,
        pendingRandomnesses: make(
            map[types.Position][]byte),
    }
}

func (bc *blockChain) notifyRoundEvents(evts []utils.RoundEventParam) error {
    bc.lock.Lock()
    defer bc.lock.Unlock()
    apply := func(e utils.RoundEventParam) error {
        if len(bc.configs) > 0 {
            lastCfg := bc.configs[len(bc.configs)-1]
            if e.BeginHeight != lastCfg.RoundEndHeight() {
                return ErrInvalidBlockHeight
            }
            if lastCfg.RoundID() == e.Round {
                bc.configs[len(bc.configs)-1].ExtendLength()
            } else if lastCfg.RoundID()+1 == e.Round {
                bc.configs = append(bc.configs, newBlockChainConfig(
                    lastCfg, e.Config))
            } else {
                return ErrInvalidRoundID
            }
        } else {
            c := blockChainConfig{}
            c.fromConfig(e.Round, e.Config)
            c.SetRoundBeginHeight(e.BeginHeight)
            if bc.lastConfirmed == nil {
                if c.RoundID() != 0 {
                    panic(fmt.Errorf(
                        "genesis config should from round 0, but %d",
                        c.RoundID()))
                }
            } else {
                if c.RoundID() != bc.lastConfirmed.Position.Round {
                    panic(fmt.Errorf("incompatible config/block round %s %d",
                        bc.lastConfirmed, c.RoundID()))
                }
                if !c.Contains(bc.lastConfirmed.Position.Height) {
                    panic(fmt.Errorf(
                        "unmatched round-event with block %s %d %d %d",
                        bc.lastConfirmed, e.Round, e.Reset, e.BeginHeight))
                }
            }
            bc.configs = append(bc.configs, c)
        }
        if e.Reset != 0 {
            bc.vGetter.Purge(e.Round + 1)
        }
        return nil
    }
    for _, e := range evts {
        if err := apply(e); err != nil {
            return err
        }
    }
    return nil
}

func (bc *blockChain) proposeBlock(position types.Position,
    proposeTime time.Time, isEmpty bool) (b *types.Block, err error) {
    bc.lock.RLock()
    defer bc.lock.RUnlock()
    return bc.prepareBlock(position, proposeTime, isEmpty)
}

func (bc *blockChain) extractBlocks() (ret []*types.Block) {
    bc.lock.Lock()
    defer bc.lock.Unlock()
    for len(bc.confirmedBlocks) > 0 {
        c := bc.confirmedBlocks[0]
        if c.Position.Round >= DKGDelayRound &&
            len(c.Randomness) == 0 &&
            !bc.setRandomnessFromPending(c) {
            break
        }
        c, bc.confirmedBlocks = bc.confirmedBlocks[0], bc.confirmedBlocks[1:]
        ret = append(ret, c)
        bc.lastDelivered = c
    }
    return
}

func (bc *blockChain) sanityCheck(b *types.Block) error {
    bc.lock.RLock()
    defer bc.lock.RUnlock()
    if bc.lastConfirmed == nil {
        // It should be a genesis block.
        if !b.IsGenesis() {
            return ErrNotGenesisBlock
        }
        if b.Timestamp.Before(bc.dMoment.Add(bc.configs[0].minBlockInterval)) {
            return ErrInvalidTimestamp
        }
        return nil
    }
    if b.IsGenesis() {
        return ErrIsGenesisBlock
    }
    if b.Position.Height != bc.lastConfirmed.Position.Height+1 {
        if b.Position.Height > bc.lastConfirmed.Position.Height {
            return ErrRetrySanityCheckLater
        }
        return ErrInvalidBlockHeight
    }
    tipConfig := bc.tipConfig()
    if tipConfig.IsLastBlock(bc.lastConfirmed) {
        if b.Position.Round != bc.lastConfirmed.Position.Round+1 {
            return ErrRoundNotSwitch
        }
    } else {
        if b.Position.Round != bc.lastConfirmed.Position.Round {
            return ErrInvalidRoundID
        }
    }
    if !b.ParentHash.Equal(bc.lastConfirmed.Hash) {
        return ErrIncorrectParentHash
    }
    if b.Timestamp.Before(bc.lastConfirmed.Timestamp.Add(
        tipConfig.minBlockInterval)) {
        return ErrInvalidTimestamp
    }
    if err := utils.VerifyBlockSignature(b); err != nil {
        return err
    }
    return nil
}

// addEmptyBlock is called when an empty block is confirmed by BA.
func (bc *blockChain) addEmptyBlock(position types.Position) (
    *types.Block, error) {
    bc.lock.Lock()
    defer bc.lock.Unlock()
    add := func() *types.Block {
        emptyB, err := bc.prepareBlock(position, time.Time{}, true)
        if err != nil || emptyB == nil {
            // This helper is expected to be called when an empty block is ready
            // to be confirmed.
            panic(err)
        }
        bc.confirmBlock(emptyB)
        bc.checkIfBlocksConfirmed()
        return emptyB
    }
    if bc.lastConfirmed != nil {
        if !position.Newer(bc.lastConfirmed.Position) {
            bc.logger.Warn("Dropping empty block: older than tip",
                "position", &position,
                "last-confirmed", bc.lastConfirmed)
            return nil, ErrBlockFromOlderPosition
        }
        if bc.lastConfirmed.Position.Height+1 == position.Height {
            return add(), nil
        }
    } else if position.Height == types.GenesisHeight && position.Round == 0 {
        return add(), nil
    } else {
        return nil, ErrInvalidBlockHeight
    }
    return nil, bc.addPendingBlockRecord(pendingBlockRecord{position, nil})
}

// addBlock should be called when the block is confirmed by BA, we won't perform
// sanity check against this block, it's ok to add block with skipping height.
func (bc *blockChain) addBlock(b *types.Block) error {
    if b.Position.Round >= DKGDelayRound &&
        len(b.Randomness) == 0 &&
        !bc.setRandomnessFromPending(b) {
        return ErrMissingRandomness
    }
    bc.lock.Lock()
    defer bc.lock.Unlock()
    confirmed := false
    if bc.lastConfirmed != nil {
        if !b.Position.Newer(bc.lastConfirmed.Position) {
            bc.logger.Warn("Dropping block: older than tip",
                "block", b, "last-confirmed", bc.lastConfirmed)
            return nil
        }
        if bc.lastConfirmed.Position.Height+1 == b.Position.Height {
            confirmed = true
        }
    } else if b.IsGenesis() {
        confirmed = true
    }
    delete(bc.pendingRandomnesses, b.Position)
    if !confirmed {
        return bc.addPendingBlockRecord(pendingBlockRecord{b.Position, b})
    }
    bc.confirmBlock(b)
    bc.checkIfBlocksConfirmed()
    return nil
}

func (bc *blockChain) tipRound() uint64 {
    bc.lock.RLock()
    defer bc.lock.RUnlock()
    if bc.lastConfirmed == nil {
        return 0
    }
    offset, tipConfig := uint64(0), bc.tipConfig()
    if tipConfig.IsLastBlock(bc.lastConfirmed) {
        offset++
    }
    return bc.lastConfirmed.Position.Round + offset
}

func (bc *blockChain) confirmed(h uint64) bool {
    bc.lock.RLock()
    defer bc.lock.RUnlock()
    if bc.lastConfirmed != nil && bc.lastConfirmed.Position.Height >= h {
        return true
    }
    r, found := bc.pendingBlocks.searchByHeight(h)
    if !found {
        return false
    }
    return r.block != nil
}

func (bc *blockChain) nextBlock() (uint64, time.Time) {
    bc.lock.RLock()
    defer bc.lock.RUnlock()
    // It's ok to access tip config directly without checking the existence of
    // lastConfirmed block in the scenario of "nextBlock" method.
    tip, config := bc.lastConfirmed, bc.configs[0]
    if tip == nil {
        return types.GenesisHeight, bc.dMoment
    }
    return tip.Position.Height + 1, tip.Timestamp.Add(config.minBlockInterval)
}

func (bc *blockChain) pendingBlocksWithoutRandomness() []*types.Block {
    bc.lock.RLock()
    defer bc.lock.RUnlock()
    blocks := make([]*types.Block, 0)
    for _, b := range bc.confirmedBlocks {
        if b.Position.Round < DKGDelayRound ||
            len(b.Randomness) > 0 ||
            bc.setRandomnessFromPending(b) {
            continue
        }
        blocks = append(blocks, b)
    }
    for _, r := range bc.pendingBlocks {
        if r.position.Round < DKGDelayRound {
            continue
        }
        if r.block != nil &&
            len(r.block.Randomness) == 0 &&
            !bc.setRandomnessFromPending(r.block) {
            blocks = append(blocks, r.block)
        }
    }
    return blocks
}

func (bc *blockChain) lastDeliveredBlock() *types.Block {
    bc.lock.RLock()
    defer bc.lock.RUnlock()
    return bc.lastDelivered
}

func (bc *blockChain) lastPendingBlock() *types.Block {
    bc.lock.RLock()
    defer bc.lock.RUnlock()
    if len(bc.confirmedBlocks) == 0 {
        return nil
    }
    return bc.confirmedBlocks[0]
}

/////////////////////////////////////////////
//
// internal helpers
//
/////////////////////////////////////////////

// findPendingBlock is a helper to find a block in either pending or confirmed
// state by position.
func (bc *blockChain) findPendingBlock(p types.Position) *types.Block {
    if idx := sort.Search(len(bc.confirmedBlocks), func(i int) bool {
        return !bc.confirmedBlocks[i].Position.Older(p)
    }); idx != len(bc.confirmedBlocks) &&
        bc.confirmedBlocks[idx].Position.Equal(p) {
        return bc.confirmedBlocks[idx]
    }
    pendingRec, _ := bc.pendingBlocks.searchByPosition(p)
    return pendingRec.block
}

func (bc *blockChain) addPendingBlockRecord(p pendingBlockRecord) error {
    if err := bc.pendingBlocks.insert(p); err != nil {
        if err == ErrDuplicatedPendingBlock {
            // We need to ignore this error because BA might confirm duplicated
            // blocks in position.
            err = nil
        }
        return err
    }
    return nil
}

func (bc *blockChain) checkIfBlocksConfirmed() {
    var err error
    for len(bc.pendingBlocks) > 0 {
        if bc.pendingBlocks[0].position.Height <
            bc.lastConfirmed.Position.Height+1 {
            panic(fmt.Errorf("unexpected case %s %s", bc.lastConfirmed,
                bc.pendingBlocks[0].position))
        }
        if bc.pendingBlocks[0].position.Height >
            bc.lastConfirmed.Position.Height+1 {
            break
        }
        var pending pendingBlockRecord
        pending, bc.pendingBlocks = bc.pendingBlocks[0], bc.pendingBlocks[1:]
        nextTip := pending.block
        if nextTip == nil {
            if nextTip, err = bc.prepareBlock(
                pending.position, time.Time{}, true); err != nil {
                // It should not be error when prepare empty block for correct
                // position.
                panic(err)
            }
        }
        bc.confirmBlock(nextTip)
    }
}

func (bc *blockChain) purgeConfig() {
    for bc.configs[0].RoundID() < bc.lastConfirmed.Position.Round {
        bc.configs = bc.configs[1:]
    }
    if bc.configs[0].RoundID() != bc.lastConfirmed.Position.Round {
        panic(fmt.Errorf("mismatched tip config: %d %d",
            bc.configs[0].RoundID(), bc.lastConfirmed.Position.Round))
    }
}

func (bc *blockChain) verifyRandomness(
    blockHash common.Hash, round uint64, randomness []byte) (bool, error) {
    if round < DKGDelayRound {
        return bytes.Compare(randomness, NoRand) == 0, nil
    }
    v, ok, err := bc.vGetter.UpdateAndGet(round)
    if err != nil {
        return false, err
    }
    if !ok {
        return false, ErrTSigNotReady
    }
    return v.VerifySignature(blockHash, crypto.Signature{
        Type:      "bls",
        Signature: randomness}), nil
}

func (bc *blockChain) prepareBlock(position types.Position,
    proposeTime time.Time, empty bool) (b *types.Block, err error) {
    b = &types.Block{Position: position, Timestamp: proposeTime}
    tip := bc.lastConfirmed
    // Make sure we can propose a block at expected position for callers.
    if tip == nil {
        if bc.configs[0].RoundID() != uint64(0) {
            panic(fmt.Errorf(
                "Genesis config should be ready when preparing genesis: %d",
                bc.configs[0].RoundID()))
        }
        // It should be the case for genesis block.
        if !position.Equal(types.Position{Height: types.GenesisHeight}) {
            b, err = nil, ErrNotGenesisBlock
            return
        }
        minExpectedTime := bc.dMoment.Add(bc.configs[0].minBlockInterval)
        if empty {
            b.Timestamp = minExpectedTime
        } else {
            bc.logger.Debug("Calling genesis Application.PreparePayload")
            if b.Payload, err = bc.app.PreparePayload(b.Position); err != nil {
                b = nil
                return
            }
            bc.logger.Debug("Calling genesis Application.PrepareWitness")
            if b.Witness, err = bc.app.PrepareWitness(0); err != nil {
                b = nil
                return
            }
            if proposeTime.Before(minExpectedTime) {
                b.Timestamp = minExpectedTime
            }
        }
    } else {
        tipConfig := bc.tipConfig()
        if tip.Position.Height+1 != position.Height {
            b, err = nil, ErrNotFollowTipPosition
            return
        }
        if tipConfig.IsLastBlock(tip) {
            if tip.Position.Round+1 != position.Round {
                b, err = nil, ErrRoundNotSwitch
                return
            }
        } else {
            if tip.Position.Round != position.Round {
                b, err = nil, ErrInvalidRoundID
                return
            }
        }
        minExpectedTime := tip.Timestamp.Add(bc.configs[0].minBlockInterval)
        b.ParentHash = tip.Hash
        if !empty {
            bc.logger.Debug("Calling Application.PreparePayload",
                "position", b.Position)
            if b.Payload, err = bc.app.PreparePayload(b.Position); err != nil {
                b = nil
                return
            }
            bc.logger.Debug("Calling Application.PrepareWitness",
                "height", tip.Witness.Height)
            if b.Witness, err = bc.app.PrepareWitness(
                tip.Witness.Height); err != nil {
                b = nil
                return
            }
            if b.Timestamp.Before(minExpectedTime) {
                b.Timestamp = minExpectedTime
            }
        } else {
            b.Witness.Height = tip.Witness.Height
            b.Witness.Data = make([]byte, len(tip.Witness.Data))
            copy(b.Witness.Data, tip.Witness.Data)
            b.Timestamp = minExpectedTime
        }
    }
    if empty {
        if b.Hash, err = utils.HashBlock(b); err != nil {
            b = nil
            return
        }
    } else {
        if err = bc.signer.SignBlock(b); err != nil {
            b = nil
            return
        }
    }
    return
}

func (bc *blockChain) tipConfig() blockChainConfig {
    if bc.lastConfirmed == nil {
        panic(fmt.Errorf("attempting to access config without tip"))
    }
    if bc.lastConfirmed.Position.Round != bc.configs[0].RoundID() {
        panic(fmt.Errorf("inconsist config and tip: %d %d",
            bc.lastConfirmed.Position.Round, bc.configs[0].RoundID()))
    }
    return bc.configs[0]
}

func (bc *blockChain) confirmBlock(b *types.Block) {
    if bc.lastConfirmed != nil &&
        bc.lastConfirmed.Position.Height+1 != b.Position.Height {
        panic(fmt.Errorf("confirmed blocks not continuous in height: %s %s",
            bc.lastConfirmed, b))
    }
    bc.logger.Debug("Calling Application.BlockConfirmed", "block", b)
    bc.app.BlockConfirmed(*b)
    bc.lastConfirmed = b
    bc.confirmedBlocks = append(bc.confirmedBlocks, b)
    bc.purgeConfig()
}

func (bc *blockChain) setRandomnessFromPending(b *types.Block) bool {
    if r, exist := bc.pendingRandomnesses[b.Position]; exist {
        b.Randomness = r
        delete(bc.pendingRandomnesses, b.Position)
        return true
    }
    return false
}

func (bc *blockChain) processAgreementResult(result *types.AgreementResult) error {
    if result.Position.Round < DKGDelayRound {
        return nil
    }
    if !result.Position.Newer(bc.lastPosition) {
        return ErrSkipButNoError
    }
    ok, err := bc.verifyRandomness(
        result.BlockHash, result.Position.Round, result.Randomness)
    if err != nil {
        return err
    }
    if !ok {
        return ErrIncorrectAgreementResult
    }
    bc.lock.Lock()
    defer bc.lock.Unlock()
    if !result.Position.Newer(bc.lastDelivered.Position) {
        return nil
    }
    bc.pendingRandomnesses[result.Position] = result.Randomness
    bc.lastPosition = bc.lastDelivered.Position
    return nil
}

func (bc *blockChain) addBlockRandomness(pos types.Position, rand []byte) {
    if pos.Round < DKGDelayRound {
        return
    }
    bc.lock.Lock()
    defer bc.lock.Unlock()
    if !pos.Newer(bc.lastDelivered.Position) {
        return
    }
    bc.pendingRandomnesses[pos] = rand
}