dcrd/blockchain/accept.go

// Copyright (c) 2013-2016 The btcsuite developers
// Copyright (c) 2015-2018 The Decred developers
// Use of this source code is governed by an ISC
// license that can be found in the LICENSE file.

package blockchain

import (
	"encoding/binary"
	"fmt"
	"math"
	"time"

	"github.com/decred/dcrd/blockchain/stake"
	"github.com/decred/dcrd/database"
	"github.com/decred/dcrd/dcrutil"
	"github.com/decred/dcrd/txscript"
)

// checkCoinbaseUniqueHeight checks to ensure that for all blocks height > 1 the
// coinbase contains the height encoding to make coinbase hash collisions
// impossible.
func checkCoinbaseUniqueHeight(blockHeight int64, block *dcrutil.Block) error {
	// Coinbase TxOut[0] is always tax, TxOut[1] is always
	// height + extranonce, so at least two outputs must
	// exist.
	if len(block.MsgBlock().Transactions[0].TxOut) < 2 {
		str := fmt.Sprintf("block %v is missing necessary coinbase "+
			"outputs", block.Hash())
		return ruleError(ErrFirstTxNotCoinbase, str)
	}

	// Only version 0 scripts are currently valid.
	nullDataOut := block.MsgBlock().Transactions[0].TxOut[1]
	if nullDataOut.Version != 0 {
		str := fmt.Sprintf("block %v output 1 has wrong script version",
			block.Hash())
		return ruleError(ErrFirstTxNotCoinbase, str)
	}

	// The first 4 bytes of the null data output must be the encoded height
	// of the block, so that every coinbase created has a unique transaction
	// hash.
	nullData, err := txscript.ExtractCoinbaseNullData(nullDataOut.PkScript)
	if err != nil {
		str := fmt.Sprintf("block %v output 1 has wrong script type",
			block.Hash())
		return ruleError(ErrFirstTxNotCoinbase, str)
	}
	if len(nullData) < 4 {
		str := fmt.Sprintf("block %v output 1 data push too short to "+
			"contain height", block.Hash())
		return ruleError(ErrFirstTxNotCoinbase, str)
	}

	// Check the height and ensure it is correct.
	cbHeight := binary.LittleEndian.Uint32(nullData[0:4])
	if cbHeight != uint32(blockHeight) {
		prevBlock := block.MsgBlock().Header.PrevBlock
		str := fmt.Sprintf("block %v output 1 has wrong height in "+
			"coinbase; want %v, got %v; prevBlock %v, header height %v",
			block.Hash(), blockHeight, cbHeight, prevBlock,
			block.MsgBlock().Header.Height)
		return ruleError(ErrCoinbaseHeight, str)
	}

	return nil
}

// IsFinalizedTransaction determines whether or not a transaction is finalized.
func IsFinalizedTransaction(tx *dcrutil.Tx, blockHeight int64, blockTime time.Time) bool {
	// Lock time of zero means the transaction is finalized.
	msgTx := tx.MsgTx()
	lockTime := msgTx.LockTime
	if lockTime == 0 {
		return true
	}

	// The lock time field of a transaction is either a block height at
	// which the transaction is finalized or a timestamp depending on if the
	// value is before the txscript.LockTimeThreshold.  When it is under the
	// threshold it is a block height.
	var blockTimeOrHeight int64
	if lockTime < txscript.LockTimeThreshold {
		blockTimeOrHeight = blockHeight
	} else {
		blockTimeOrHeight = blockTime.Unix()
	}
	if int64(lockTime) < blockTimeOrHeight {
		return true
	}

	// At this point, the transaction's lock time hasn't occurred yet, but
	// the transaction might still be finalized if the sequence number
	// for all transaction inputs is maxed out.
	for _, txIn := range msgTx.TxIn {
		if txIn.Sequence != math.MaxUint32 {
			return false
		}
	}
	return true
}

// maybeAcceptBlock potentially accepts a block into the block chain and, if
// accepted, returns the length of the fork the block extended.  It performs
// several validation checks which depend on its position within the block chain
// before adding it.  The block is expected to have already gone through
// ProcessBlock before calling this function with it.  In the case the block
// extends the best chain or is now the tip of the best chain due to causing a
// reorganize, the fork length will be 0.
//
// The flags are also passed to checkBlockContext and connectBestChain.  See
// their documentation for how the flags modify their behavior.
//
// This function MUST be called with the chain state lock held (for writes).
func (b *BlockChain) maybeAcceptBlock(block *dcrutil.Block, flags BehaviorFlags) (int64, error) {
	// This function should never be called with orphan blocks or the
	// genesis block.
	prevHash := &block.MsgBlock().Header.PrevBlock
	prevNode := b.index.LookupNode(prevHash)
	if prevNode == nil {
		str := fmt.Sprintf("previous block %s is not known", prevHash)
		return 0, ruleError(ErrMissingParent, str)
	}

	// There is no need to validate the block if an ancestor is already
	// known to be invalid.
	if b.index.NodeStatus(prevNode).KnownInvalid() {
		str := fmt.Sprintf("previous block %s is known to be invalid",
			prevHash)
		return 0, ruleError(ErrInvalidAncestorBlock, str)
	}

	// The block must pass all of the validation rules which depend on the
	// position of the block within the block chain.
	err := b.checkBlockContext(block, prevNode, flags)
	if err != nil {
		return 0, err
	}

	// Prune stake nodes which are no longer needed before creating a new
	// node.
	b.pruner.pruneChainIfNeeded()

	// Insert the block into the database if it's not already there.  Even
	// though it is possible the block will ultimately fail to connect, it
	// has already passed all proof-of-work and validity tests which means
	// it would be prohibitively expensive for an attacker to fill up the
	// disk with a bunch of blocks that fail to connect.  This is necessary
	// since it allows block download to be decoupled from the much more
	// expensive connection logic.  It also has some other nice properties
	// such as making blocks that never become part of the main chain or
	// blocks that fail to connect available for further analysis.
	err = b.db.Update(func(dbTx database.Tx) error {
		return dbMaybeStoreBlock(dbTx, block)
	})
	if err != nil {
		return 0, err
	}

	// Create a new block node for the block and add it to the block index.
	// The block could either be on a side chain or the main chain, but it
	// starts off as a side chain regardless.
	blockHeader := &block.MsgBlock().Header
	newNode := newBlockNode(blockHeader, prevNode)
	newNode.populateTicketInfo(stake.FindSpentTicketsInBlock(block.MsgBlock()))
	newNode.status = statusDataStored
	b.index.AddNode(newNode)

	// Ensure the new block index entry is written to the database.
	err = b.index.flush()
	if err != nil {
		return 0, err
	}

	// Fetching a stake node could enable a new DoS vector, so restrict
	// this only to blocks that are recent in history.
	if newNode.height < b.bestChain.Tip().height-minMemoryNodes {
		newNode.stakeNode, err = b.fetchStakeNode(newNode)
		if err != nil {
			return 0, err
		}
		newNode.stakeUndoData = newNode.stakeNode.UndoData()
	}

	// Grab the parent block since it is required throughout the block
	// connection process.
	parent, err := b.fetchBlockByNode(newNode.parent)
	if err != nil {
		return 0, err
	}

	// Connect the passed block to the chain while respecting proper chain
	// selection according to the chain with the most proof of work.  This
	// also handles validation of the transaction scripts.
	forkLen, err := b.connectBestChain(newNode, block, parent, flags)
	if err != nil {
		return 0, err
	}

	// Notify the caller that the new block was accepted into the block
	// chain.  The caller would typically want to react by relaying the
	// inventory to other peers.
	bestHeight := b.bestChain.Tip().height
	b.chainLock.Unlock()
	b.sendNotification(NTBlockAccepted, &BlockAcceptedNtfnsData{
		BestHeight: bestHeight,
		ForkLen:    forkLen,
		Block:      block,
	})
	b.chainLock.Lock()

	return forkLen, nil
}