Ejemplo n.º 1
0
// NewBlockTemplate returns a new block template that is ready to be solved
// using the transactions from the passed transaction source pool and a coinbase
// that either pays to the passed address if it is not nil, or a coinbase that
// is redeemable by anyone if the passed address is nil.  The nil address
// functionality is useful since there are cases such as the getblocktemplate
// RPC where external mining software is responsible for creating their own
// coinbase which will replace the one generated for the block template.  Thus
// the need to have configured address can be avoided.
//
// The transactions selected and included are prioritized according to several
// factors.  First, each transaction has a priority calculated based on its
// value, age of inputs, and size.  Transactions which consist of larger
// amounts, older inputs, and small sizes have the highest priority.  Second, a
// fee per kilobyte is calculated for each transaction.  Transactions with a
// higher fee per kilobyte are preferred.  Finally, the block generation related
// policy settings are all taken into account.
//
// Transactions which only spend outputs from other transactions already in the
// block chain are immediately added to a priority queue which either
// prioritizes based on the priority (then fee per kilobyte) or the fee per
// kilobyte (then priority) depending on whether or not the BlockPrioritySize
// policy setting allots space for high-priority transactions.  Transactions
// which spend outputs from other transactions in the source pool are added to a
// dependency map so they can be added to the priority queue once the
// transactions they depend on have been included.
//
// Once the high-priority area (if configured) has been filled with
// transactions, or the priority falls below what is considered high-priority,
// the priority queue is updated to prioritize by fees per kilobyte (then
// priority).
//
// When the fees per kilobyte drop below the TxMinFreeFee policy setting, the
// transaction will be skipped unless the BlockMinSize policy setting is
// nonzero, in which case the block will be filled with the low-fee/free
// transactions until the block size reaches that minimum size.
//
// Any transactions which would cause the block to exceed the BlockMaxSize
// policy setting, exceed the maximum allowed signature operations per block, or
// otherwise cause the block to be invalid are skipped.
//
// Given the above, a block generated by this function is of the following form:
//
//   -----------------------------------  --  --
//  |      Coinbase Transaction         |   |   |
//  |-----------------------------------|   |   |
//  |                                   |   |   | ----- policy.BlockPrioritySize
//  |   High-priority Transactions      |   |   |
//  |                                   |   |   |
//  |-----------------------------------|   | --
//  |                                   |   |
//  |                                   |   |
//  |                                   |   |--- policy.BlockMaxSize
//  |  Transactions prioritized by fee  |   |
//  |  until <= policy.TxMinFreeFee     |   |
//  |                                   |   |
//  |                                   |   |
//  |                                   |   |
//  |-----------------------------------|   |
//  |  Low-fee/Non high-priority (free) |   |
//  |  transactions (while block size   |   |
//  |  <= policy.BlockMinSize)          |   |
//   -----------------------------------  --
func (g *BlkTmplGenerator) NewBlockTemplate(payToAddress btcutil.Address) (*BlockTemplate, error) {
	// Extend the most recently known best block.
	best := g.chain.BestSnapshot()
	prevHash := best.Hash
	nextBlockHeight := best.Height + 1

	// Create a standard coinbase transaction paying to the provided
	// address.  NOTE: The coinbase value will be updated to include the
	// fees from the selected transactions later after they have actually
	// been selected.  It is created here to detect any errors early
	// before potentially doing a lot of work below.  The extra nonce helps
	// ensure the transaction is not a duplicate transaction (paying the
	// same value to the same public key address would otherwise be an
	// identical transaction for block version 1).
	extraNonce := uint64(0)
	coinbaseScript, err := standardCoinbaseScript(nextBlockHeight, extraNonce)
	if err != nil {
		return nil, err
	}
	// TODO(roasbeef): add witnesss commitment output
	coinbaseTx, err := createCoinbaseTx(g.chainParams, coinbaseScript,
		nextBlockHeight, payToAddress)
	if err != nil {
		return nil, err
	}
	coinbaseSigOpCost := int64(blockchain.CountSigOps(coinbaseTx)) * blockchain.WitnessScaleFactor

	// Get the current source transactions and create a priority queue to
	// hold the transactions which are ready for inclusion into a block
	// along with some priority related and fee metadata.  Reserve the same
	// number of items that are available for the priority queue.  Also,
	// choose the initial sort order for the priority queue based on whether
	// or not there is an area allocated for high-priority transactions.
	sourceTxns := g.txSource.MiningDescs()
	sortedByFee := g.policy.BlockPrioritySize == 0
	priorityQueue := newTxPriorityQueue(len(sourceTxns), sortedByFee)

	// Create a slice to hold the transactions to be included in the
	// generated block with reserved space.  Also create a utxo view to
	// house all of the input transactions so multiple lookups can be
	// avoided.
	blockTxns := make([]*btcutil.Tx, 0, len(sourceTxns))
	blockTxns = append(blockTxns, coinbaseTx)
	blockUtxos := blockchain.NewUtxoViewpoint()

	// dependers is used to track transactions which depend on another
	// transaction in the source pool.  This, in conjunction with the
	// dependsOn map kept with each dependent transaction helps quickly
	// determine which dependent transactions are now eligible for inclusion
	// in the block once each transaction has been included.
	dependers := make(map[chainhash.Hash]map[chainhash.Hash]*txPrioItem)

	// Create slices to hold the fees and number of signature operations
	// for each of the selected transactions and add an entry for the
	// coinbase.  This allows the code below to simply append details about
	// a transaction as it is selected for inclusion in the final block.
	// However, since the total fees aren't known yet, use a dummy value for
	// the coinbase fee which will be updated later.
	txFees := make([]int64, 0, len(sourceTxns))
	txSigOpCosts := make([]int64, 0, len(sourceTxns))
	txFees = append(txFees, -1) // Updated once known
	txSigOpCosts = append(txSigOpCosts, coinbaseSigOpCost)

	log.Debugf("Considering %d transactions for inclusion to new block",
		len(sourceTxns))

mempoolLoop:
	for _, txDesc := range sourceTxns {
		// A block can't have more than one coinbase or contain
		// non-finalized transactions.
		tx := txDesc.Tx
		if blockchain.IsCoinBase(tx) {
			log.Tracef("Skipping coinbase tx %s", tx.Hash())
			continue
		}
		if !blockchain.IsFinalizedTransaction(tx, nextBlockHeight,
			g.timeSource.AdjustedTime()) {

			log.Tracef("Skipping non-finalized tx %s", tx.Hash())
			continue
		}

		// Fetch all of the utxos referenced by the this transaction.
		// NOTE: This intentionally does not fetch inputs from the
		// mempool since a transaction which depends on other
		// transactions in the mempool must come after those
		// dependencies in the final generated block.
		utxos, err := g.chain.FetchUtxoView(tx)
		if err != nil {
			log.Warnf("Unable to fetch utxo view for tx %s: %v",
				tx.Hash(), err)
			continue
		}

		// Setup dependencies for any transactions which reference
		// other transactions in the mempool so they can be properly
		// ordered below.
		prioItem := &txPrioItem{tx: tx}
		for _, txIn := range tx.MsgTx().TxIn {
			originHash := &txIn.PreviousOutPoint.Hash
			originIndex := txIn.PreviousOutPoint.Index
			utxoEntry := utxos.LookupEntry(originHash)
			if utxoEntry == nil || utxoEntry.IsOutputSpent(originIndex) {
				if !g.txSource.HaveTransaction(originHash) {
					log.Tracef("Skipping tx %s because it "+
						"references unspent output %s "+
						"which is not available",
						tx.Hash(), txIn.PreviousOutPoint)
					continue mempoolLoop
				}

				// The transaction is referencing another
				// transaction in the source pool, so setup an
				// ordering dependency.
				deps, exists := dependers[*originHash]
				if !exists {
					deps = make(map[chainhash.Hash]*txPrioItem)
					dependers[*originHash] = deps
				}
				deps[*prioItem.tx.Hash()] = prioItem
				if prioItem.dependsOn == nil {
					prioItem.dependsOn = make(
						map[chainhash.Hash]struct{})
				}
				prioItem.dependsOn[*originHash] = struct{}{}

				// Skip the check below. We already know the
				// referenced transaction is available.
				continue
			}
		}

		// Calculate the final transaction priority using the input
		// value age sum as well as the adjusted transaction size.  The
		// formula is: sum(inputValue * inputAge) / adjustedTxSize
		prioItem.priority = CalcPriority(tx.MsgTx(), utxos,
			nextBlockHeight)

		// Calculate the fee in Satoshi/kB.
		// TODO(roasbeef): cost accounting by weight
		prioItem.feePerKB = txDesc.FeePerKB
		prioItem.fee = txDesc.Fee

		// Add the transaction to the priority queue to mark it ready
		// for inclusion in the block unless it has dependencies.
		if prioItem.dependsOn == nil {
			heap.Push(priorityQueue, prioItem)
		}

		// Merge the referenced outputs from the input transactions to
		// this transaction into the block utxo view.  This allows the
		// code below to avoid a second lookup.
		mergeUtxoView(blockUtxos, utxos)
	}

	log.Tracef("Priority queue len %d, dependers len %d",
		priorityQueue.Len(), len(dependers))

	// The starting block size is the size of the block header plus the max
	// possible transaction count size, plus the size of the coinbase
	// transaction.
	blockWeight := uint32((blockHeaderOverhead * blockchain.WitnessScaleFactor) +
		blockchain.GetTransactionWeight(coinbaseTx))
	blockSigOpCost := coinbaseSigOpCost
	totalFees := int64(0)

	// Query the version bits state to see if segwit has been activated, if
	// so then this means that we'll include any transactions with witness
	// data in the mempool, and also add the witness commitment as an
	// OP_RETURN output in the coinbase transaction.
	segwitState, err := g.chain.ThresholdState(chaincfg.DeploymentSegwit)
	if err != nil {
		return nil, err
	}
	segwitActive := segwitState == blockchain.ThresholdActive

	witnessIncluded := false

	// Choose which transactions make it into the block.
	for priorityQueue.Len() > 0 {
		// Grab the highest priority (or highest fee per kilobyte
		// depending on the sort order) transaction.
		prioItem := heap.Pop(priorityQueue).(*txPrioItem)
		tx := prioItem.tx

		switch {
		// If segregated witness has not been activated yet, then we
		// shouldn't include any witness transactions in the block.
		case tx.MsgTx().HasWitness() && !segwitActive:
			continue

		// Otherwise, Keep track of if we've included a transaction
		// with witness data or not. If so, then we'll need to include
		// the witness commitment as the last output in the coinbase
		// transaction.
		case tx.MsgTx().HasWitness() && segwitActive:
			// If we're about to include a transaction bearing
			// witness data, then we'll also need to include a
			// witness commitment in the coinbase transaction.
			// Therefore, we account for the additional weight
			// within the block.
			if !witnessIncluded {
				// First we account for the additional witness
				// data in the witness nonce of the coinbaes
				// transaction: 32-bytes of zeroes.
				blockWeight += 2 + 32

				// Next we account for the additional flag and
				// marker bytes in the transaction
				// serialization.
				blockWeight += (1 + 1) * blockchain.WitnessScaleFactor

				// Finally we account for the weight of the
				// additional OP_RETURN output: 8-bytes (value)
				// + 1-byte (var-int) + 38-bytes (pkScript),
				// scaling up the weight as it's non-witness
				// data.
				blockWeight += (8 + 1 + 38) * blockchain.WitnessScaleFactor
			}

			witnessIncluded = true
		}

		// Grab any transactions which depend on this one.
		deps := dependers[*tx.Hash()]

		// Enforce maximum block size.  Also check for overflow.
		txWeight := uint32(blockchain.GetTransactionWeight(tx))
		blockPlusTxWeight := uint32(blockWeight + txWeight)
		if blockPlusTxWeight < blockWeight ||
			blockPlusTxWeight >= g.policy.BlockMaxWeight {

			log.Tracef("Skipping tx %s because it would exceed "+
				"the max block weight", tx.Hash())
			logSkippedDeps(tx, deps)
			continue
		}

		// Enforce maximum signature operation cost per block.  Also
		// check for overflow.
		sigOpCost, err := blockchain.GetSigOpCost(tx, false,
			blockUtxos, true, segwitActive)
		if err != nil {
			log.Tracef("Skipping tx %s due to error in "+
				"GetSigOpCost: %v", tx.Hash(), err)
			logSkippedDeps(tx, deps)
			continue
		}
		if blockSigOpCost+int64(sigOpCost) < blockSigOpCost ||
			blockSigOpCost+int64(sigOpCost) > blockchain.MaxBlockSigOpsCost {
			log.Tracef("Skipping tx %s because it would "+
				"exceed the maximum sigops per block", tx.Hash())
			logSkippedDeps(tx, deps)
			continue
		}

		// Skip free transactions once the block is larger than the
		// minimum block size.
		if sortedByFee &&
			prioItem.feePerKB < int64(g.policy.TxMinFreeFee) &&
			blockPlusTxWeight >= g.policy.BlockMinWeight {

			log.Tracef("Skipping tx %s with feePerKB %d "+
				"< TxMinFreeFee %d and block weight %d >= "+
				"minBlockWeight %d", tx.Hash(), prioItem.feePerKB,
				g.policy.TxMinFreeFee, blockPlusTxWeight,
				g.policy.BlockMinWeight)
			logSkippedDeps(tx, deps)
			continue
		}

		// Prioritize by fee per kilobyte once the block is larger than
		// the priority size or there are no more high-priority
		// transactions.
		if !sortedByFee && (blockPlusTxWeight >= g.policy.BlockPrioritySize ||
			prioItem.priority <= MinHighPriority) {

			log.Tracef("Switching to sort by fees per "+
				"kilobyte blockSize %d >= BlockPrioritySize "+
				"%d || priority %.2f <= minHighPriority %.2f",
				blockPlusTxWeight, g.policy.BlockPrioritySize,
				prioItem.priority, MinHighPriority)

			sortedByFee = true
			priorityQueue.SetLessFunc(txPQByFee)

			// Put the transaction back into the priority queue and
			// skip it so it is re-priortized by fees if it won't
			// fit into the high-priority section or the priority
			// is too low.  Otherwise this transaction will be the
			// final one in the high-priority section, so just fall
			// though to the code below so it is added now.
			if blockPlusTxWeight > g.policy.BlockPrioritySize ||
				prioItem.priority < MinHighPriority {

				heap.Push(priorityQueue, prioItem)
				continue
			}
		}

		// Ensure the transaction inputs pass all of the necessary
		// preconditions before allowing it to be added to the block.
		_, err = blockchain.CheckTransactionInputs(tx, nextBlockHeight,
			blockUtxos, g.chainParams)
		if err != nil {
			log.Tracef("Skipping tx %s due to error in "+
				"CheckTransactionInputs: %v", tx.Hash(), err)
			logSkippedDeps(tx, deps)
			continue
		}
		err = blockchain.ValidateTransactionScripts(tx, blockUtxos,
			txscript.StandardVerifyFlags, g.sigCache,
			g.hashCache)
		if err != nil {
			log.Tracef("Skipping tx %s due to error in "+
				"ValidateTransactionScripts: %v", tx.Hash(), err)
			logSkippedDeps(tx, deps)
			continue
		}

		// Spend the transaction inputs in the block utxo view and add
		// an entry for it to ensure any transactions which reference
		// this one have it available as an input and can ensure they
		// aren't double spending.
		spendTransaction(blockUtxos, tx, nextBlockHeight)

		// Add the transaction to the block, increment counters, and
		// save the fees and signature operation counts to the block
		// template.
		blockTxns = append(blockTxns, tx)
		blockWeight += txWeight
		blockSigOpCost += int64(sigOpCost)
		totalFees += prioItem.fee
		txFees = append(txFees, prioItem.fee)
		txSigOpCosts = append(txSigOpCosts, int64(sigOpCost))

		log.Tracef("Adding tx %s (priority %.2f, feePerKB %.2f)",
			prioItem.tx.Hash(), prioItem.priority, prioItem.feePerKB)

		// Add transactions which depend on this one (and also do not
		// have any other unsatisified dependencies) to the priority
		// queue.
		for _, item := range deps {
			// Add the transaction to the priority queue if there
			// are no more dependencies after this one.
			delete(item.dependsOn, *tx.Hash())
			if len(item.dependsOn) == 0 {
				heap.Push(priorityQueue, item)
			}
		}
	}

	// Now that the actual transactions have been selected, update the
	// block weight for the real transaction count and coinbase value with
	// the total fees accordingly.
	blockWeight -= wire.MaxVarIntPayload -
		(uint32(wire.VarIntSerializeSize(uint64(len(blockTxns)))) *
			blockchain.WitnessScaleFactor)
	coinbaseTx.MsgTx().TxOut[0].Value += totalFees
	txFees[0] = -totalFees

	// If segwit is active and we included transactions with witness data,
	// then we'll need to include a commitment to the witness data in an
	// OP_RETURN output within the coinbase transaction.
	if witnessIncluded {
		// The witness of the coinbase transaction MUST be exactly 32-bytes
		// of all zeroes.
		var witnessNonce [blockchain.CoinbaseWitnessDataLen]byte
		coinbaseTx.MsgTx().TxIn[0].Witness = wire.TxWitness{witnessNonce[:]}

		// Next, obtain the merkle root of a tree which consists of the
		// wtxid of all transactions in the block. The coinbase
		// transaction will have a special wtxid of all zeroes.
		witnessMerkleTree := blockchain.BuildMerkleTreeStore(blockTxns,
			true)
		witnessMerkleRoot := witnessMerkleTree[len(witnessMerkleTree)-1]

		// The preimage to the witness commitment is:
		// witnessRoot || coinbaseWitness
		var witnessPreimage [64]byte
		copy(witnessPreimage[:32], witnessMerkleRoot[:])
		copy(witnessPreimage[32:], witnessNonce[:])

		// The witness commitment itself is the double-sha256 of the
		// witness preimage generated above. With the commitment
		// generated, the witness script for the output is: OP_RETURN
		// OP_DATA_36 {0xaa21a9ed || witnessCommitment}. The leading
		// prefix is refered to as the "witness magic bytes".
		witnessCommitment := chainhash.DoubleHashB(witnessPreimage[:])
		witnessScript := append(blockchain.WitnessMagicBytes, witnessCommitment...)

		// Finally, create the OP_RETURN carrying witness commitment
		// output as an additional output within the coinbase.
		commitmentOutput := &wire.TxOut{
			Value:    0,
			PkScript: witnessScript,
		}
		coinbaseTx.MsgTx().TxOut = append(coinbaseTx.MsgTx().TxOut,
			commitmentOutput)
	}

	// Calculate the required difficulty for the block.  The timestamp
	// is potentially adjusted to ensure it comes after the median time of
	// the last several blocks per the chain consensus rules.
	ts := medianAdjustedTime(best, g.timeSource)
	reqDifficulty, err := g.chain.CalcNextRequiredDifficulty(ts)
	if err != nil {
		return nil, err
	}

	// Calculate the next expected block version based on the state of the
	// rule change deployments.
	nextBlockVersion, err := g.chain.CalcNextBlockVersion()
	if err != nil {
		return nil, err
	}

	// Create a new block ready to be solved.
	merkles := blockchain.BuildMerkleTreeStore(blockTxns, false)
	var msgBlock wire.MsgBlock
	msgBlock.Header = wire.BlockHeader{
		Version:    nextBlockVersion,
		PrevBlock:  *prevHash,
		MerkleRoot: *merkles[len(merkles)-1],
		Timestamp:  ts,
		Bits:       reqDifficulty,
	}
	for _, tx := range blockTxns {
		if err := msgBlock.AddTransaction(tx.MsgTx()); err != nil {
			return nil, err
		}
	}

	// Finally, perform a full check on the created block against the chain
	// consensus rules to ensure it properly connects to the current best
	// chain with no issues.
	block := btcutil.NewBlock(&msgBlock)
	block.SetHeight(nextBlockHeight)
	if err := g.chain.CheckConnectBlock(block); err != nil {
		return nil, err
	}

	log.Debugf("Created new block template (%d transactions, %d in "+
		"fees, %d signature operations cost, %d weight, target difficulty "+
		"%064x)", len(msgBlock.Transactions), totalFees, blockSigOpCost,
		blockWeight, blockchain.CompactToBig(msgBlock.Header.Bits))

	return &BlockTemplate{
		Block:           &msgBlock,
		Fees:            txFees,
		SigOpCosts:      txSigOpCosts,
		Height:          nextBlockHeight,
		ValidPayAddress: payToAddress != nil,
	}, nil
}
Ejemplo n.º 2
0
// checkTransactionStandard performs a series of checks on a transaction to
// ensure it is a "standard" transaction.  A standard transaction is one that
// conforms to several additional limiting cases over what is considered a
// "sane" transaction such as having a version in the supported range, being
// finalized, conforming to more stringent size constraints, having scripts
// of recognized forms, and not containing "dust" outputs (those that are
// so small it costs more to process them than they are worth).
func checkTransactionStandard(tx *btcutil.Tx, height int32,
	medianTimePast time.Time, minRelayTxFee btcutil.Amount,
	maxTxVersion int32) error {

	// The transaction must be a currently supported version.
	msgTx := tx.MsgTx()
	if msgTx.Version > maxTxVersion || msgTx.Version < 1 {
		str := fmt.Sprintf("transaction version %d is not in the "+
			"valid range of %d-%d", msgTx.Version, 1,
			maxTxVersion)
		return txRuleError(wire.RejectNonstandard, str)
	}

	// The transaction must be finalized to be standard and therefore
	// considered for inclusion in a block.
	if !blockchain.IsFinalizedTransaction(tx, height, medianTimePast) {
		return txRuleError(wire.RejectNonstandard,
			"transaction is not finalized")
	}

	// Since extremely large transactions with a lot of inputs can cost
	// almost as much to process as the sender fees, limit the maximum
	// size of a transaction.  This also helps mitigate CPU exhaustion
	// attacks.
	txWeight := blockchain.GetTransactionWeight(tx)
	if txWeight > maxStandardTxWeight {
		str := fmt.Sprintf("weight of transaction %v is larger than max "+
			"allowed weight of %v", txWeight, maxStandardTxWeight)
		return txRuleError(wire.RejectNonstandard, str)
	}

	for i, txIn := range msgTx.TxIn {
		// Each transaction input signature script must not exceed the
		// maximum size allowed for a standard transaction.  See
		// the comment on maxStandardSigScriptSize for more details.
		sigScriptLen := len(txIn.SignatureScript)
		if sigScriptLen > maxStandardSigScriptSize {
			str := fmt.Sprintf("transaction input %d: signature "+
				"script size of %d bytes is large than max "+
				"allowed size of %d bytes", i, sigScriptLen,
				maxStandardSigScriptSize)
			return txRuleError(wire.RejectNonstandard, str)
		}

		// Each transaction input signature script must only contain
		// opcodes which push data onto the stack.
		if !txscript.IsPushOnlyScript(txIn.SignatureScript) {
			str := fmt.Sprintf("transaction input %d: signature "+
				"script is not push only", i)
			return txRuleError(wire.RejectNonstandard, str)
		}
	}

	// None of the output public key scripts can be a non-standard script or
	// be "dust" (except when the script is a null data script).
	numNullDataOutputs := 0
	for i, txOut := range msgTx.TxOut {
		scriptClass := txscript.GetScriptClass(txOut.PkScript)
		err := checkPkScriptStandard(txOut.PkScript, scriptClass)
		if err != nil {
			// Attempt to extract a reject code from the error so
			// it can be retained.  When not possible, fall back to
			// a non standard error.
			rejectCode := wire.RejectNonstandard
			if rejCode, found := extractRejectCode(err); found {
				rejectCode = rejCode
			}
			str := fmt.Sprintf("transaction output %d: %v", i, err)
			return txRuleError(rejectCode, str)
		}

		// Accumulate the number of outputs which only carry data.  For
		// all other script types, ensure the output value is not
		// "dust".
		if scriptClass == txscript.NullDataTy {
			numNullDataOutputs++
		} else if isDust(txOut, minRelayTxFee) {
			str := fmt.Sprintf("transaction output %d: payment "+
				"of %d is dust", i, txOut.Value)
			return txRuleError(wire.RejectDust, str)
		}
	}

	// A standard transaction must not have more than one output script that
	// only carries data.
	if numNullDataOutputs > 1 {
		str := "more than one transaction output in a nulldata script"
		return txRuleError(wire.RejectNonstandard, str)
	}

	return nil
}