path: root/core/consensus-timestamp.go

// 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 (
    "errors"

    "github.com/dexon-foundation/dexon-consensus-core/core/types"
)

// consensusTimestamp is for Concensus Timestamp Algorithm.
type consensusTimestamp struct {
    lastMainChainBlock   *types.Block
    blocksNotInMainChain []*types.Block
}

var (
    // ErrInvalidMainChain would be reported if the invalid result from
    // main chain selection algorithm is detected.
    ErrInvalidMainChain = errors.New("invalid main chain")
)

// newConsensusTimestamp create timestamper object.
func newConsensusTimestamp() *consensusTimestamp {
    return &consensusTimestamp{}
}

// ProcessBlocks is the entry function.
func (ct *consensusTimestamp) processBlocks(blocks []*types.Block) (
    blocksWithTimestamp []*types.Block, mainChain []*types.Block, err error) {
    if len(blocks) == 0 {
        // TODO (jimmy-dexon): Remove this panic before release.
        panic("Unexpected empty block list.")
    }
    outputFirstBlock := true
    blocks = append(ct.blocksNotInMainChain, blocks...)
    if ct.lastMainChainBlock != nil {
        // TODO (jimmy-dexon): The performance here can be optimized.
        blocks = append([]*types.Block{ct.lastMainChainBlock}, blocks...)
        outputFirstBlock = false
    }
    mainChain, nonMainChain := ct.selectMainChain(blocks)
    ct.blocksNotInMainChain = nonMainChain
    ct.lastMainChainBlock = mainChain[len(mainChain)-1]
    blocksWithTimestamp = blocks[:len(blocks)-len(nonMainChain)]
    leftMainChainIdx := 0
    rightMainChainIdx := 0
    idxMainChain := 0
    for idx, block := range blocksWithTimestamp {
        if idxMainChain >= len(mainChain) {
            err = ErrInvalidMainChain
            return
        } else if block.Hash == mainChain[idxMainChain].Hash {
            rightMainChainIdx = idx
            blocksWithTimestamp[idx].Notary.Timestamp, err =
                getMedianTime(block)
            if err != nil {
                return
            }
            // Process Non-MainChain blocks.
            if rightMainChainIdx > leftMainChainIdx {
                for idx, timestamp := range interpoTime(
                    blocksWithTimestamp[leftMainChainIdx].Notary.Timestamp,
                    blocksWithTimestamp[rightMainChainIdx].Notary.Timestamp,
                    rightMainChainIdx-leftMainChainIdx-1) {
                    blocksWithTimestamp[leftMainChainIdx+idx+1].Notary.Timestamp =
                        timestamp
                }
            }
            leftMainChainIdx = idx
            idxMainChain++
        }
    }
    if !outputFirstBlock {
        blocksWithTimestamp = blocksWithTimestamp[1:]
    }
    return
}

func (ct *consensusTimestamp) selectMainChain(blocks []*types.Block) (
    mainChain []*types.Block, nonMainChain []*types.Block) {
    for _, block := range blocks {
        if len(mainChain) != 0 {
            if _, exists := block.Acks[mainChain[len(mainChain)-1].Hash]; !exists {
                nonMainChain = append(nonMainChain, block)
                continue
            }
        }
        nonMainChain = []*types.Block{}
        mainChain = append(mainChain, block)
    }
    return
}