Add vendor dir (#16) (#4)

* Add vendor dir so builds dont require dep

* Pin specific version go-eth version

vendor/github.com/btcsuite/btcd/mining/mining.go

@@ -0,0 +1,969 @@
+// Copyright (c) 2014-2016 The btcsuite developers
+// Use of this source code is governed by an ISC
+// license that can be found in the LICENSE file.
+
+package mining
+
+import (
+	"bytes"
+	"container/heap"
+	"fmt"
+	"time"
+
+	"github.com/btcsuite/btcd/blockchain"
+	"github.com/btcsuite/btcd/chaincfg"
+	"github.com/btcsuite/btcd/chaincfg/chainhash"
+	"github.com/btcsuite/btcd/txscript"
+	"github.com/btcsuite/btcd/wire"
+	"github.com/btcsuite/btcutil"
+)
+
+const (
+	// MinHighPriority is the minimum priority value that allows a
+	// transaction to be considered high priority.
+	MinHighPriority = btcutil.SatoshiPerBitcoin * 144.0 / 250
+
+	// blockHeaderOverhead is the max number of bytes it takes to serialize
+	// a block header and max possible transaction count.
+	blockHeaderOverhead = wire.MaxBlockHeaderPayload + wire.MaxVarIntPayload
+
+	// CoinbaseFlags is added to the coinbase script of a generated block
+	// and is used to monitor BIP16 support as well as blocks that are
+	// generated via btcd.
+	CoinbaseFlags = "/P2SH/btcd/"
+)
+
+// TxDesc is a descriptor about a transaction in a transaction source along with
+// additional metadata.
+type TxDesc struct {
+	// Tx is the transaction associated with the entry.
+	Tx *btcutil.Tx
+
+	// Added is the time when the entry was added to the source pool.
+	Added time.Time
+
+	// Height is the block height when the entry was added to the the source
+	// pool.
+	Height int32
+
+	// Fee is the total fee the transaction associated with the entry pays.
+	Fee int64
+
+	// FeePerKB is the fee the transaction pays in Satoshi per 1000 bytes.
+	FeePerKB int64
+}
+
+// TxSource represents a source of transactions to consider for inclusion in
+// new blocks.
+//
+// The interface contract requires that all of these methods are safe for
+// concurrent access with respect to the source.
+type TxSource interface {
+	// LastUpdated returns the last time a transaction was added to or
+	// removed from the source pool.
+	LastUpdated() time.Time
+
+	// MiningDescs returns a slice of mining descriptors for all the
+	// transactions in the source pool.
+	MiningDescs() []*TxDesc
+
+	// HaveTransaction returns whether or not the passed transaction hash
+	// exists in the source pool.
+	HaveTransaction(hash *chainhash.Hash) bool
+}
+
+// txPrioItem houses a transaction along with extra information that allows the
+// transaction to be prioritized and track dependencies on other transactions
+// which have not been mined into a block yet.
+type txPrioItem struct {
+	tx       *btcutil.Tx
+	fee      int64
+	priority float64
+	feePerKB int64
+
+	// dependsOn holds a map of transaction hashes which this one depends
+	// on.  It will only be set when the transaction references other
+	// transactions in the source pool and hence must come after them in
+	// a block.
+	dependsOn map[chainhash.Hash]struct{}
+}
+
+// txPriorityQueueLessFunc describes a function that can be used as a compare
+// function for a transaction priority queue (txPriorityQueue).
+type txPriorityQueueLessFunc func(*txPriorityQueue, int, int) bool
+
+// txPriorityQueue implements a priority queue of txPrioItem elements that
+// supports an arbitrary compare function as defined by txPriorityQueueLessFunc.
+type txPriorityQueue struct {
+	lessFunc txPriorityQueueLessFunc
+	items    []*txPrioItem
+}
+
+// Len returns the number of items in the priority queue.  It is part of the
+// heap.Interface implementation.
+func (pq *txPriorityQueue) Len() int {
+	return len(pq.items)
+}
+
+// Less returns whether the item in the priority queue with index i should sort
+// before the item with index j by deferring to the assigned less function.  It
+// is part of the heap.Interface implementation.
+func (pq *txPriorityQueue) Less(i, j int) bool {
+	return pq.lessFunc(pq, i, j)
+}
+
+// Swap swaps the items at the passed indices in the priority queue.  It is
+// part of the heap.Interface implementation.
+func (pq *txPriorityQueue) Swap(i, j int) {
+	pq.items[i], pq.items[j] = pq.items[j], pq.items[i]
+}
+
+// Push pushes the passed item onto the priority queue.  It is part of the
+// heap.Interface implementation.
+func (pq *txPriorityQueue) Push(x interface{}) {
+	pq.items = append(pq.items, x.(*txPrioItem))
+}
+
+// Pop removes the highest priority item (according to Less) from the priority
+// queue and returns it.  It is part of the heap.Interface implementation.
+func (pq *txPriorityQueue) Pop() interface{} {
+	n := len(pq.items)
+	item := pq.items[n-1]
+	pq.items[n-1] = nil
+	pq.items = pq.items[0 : n-1]
+	return item
+}
+
+// SetLessFunc sets the compare function for the priority queue to the provided
+// function.  It also invokes heap.Init on the priority queue using the new
+// function so it can immediately be used with heap.Push/Pop.
+func (pq *txPriorityQueue) SetLessFunc(lessFunc txPriorityQueueLessFunc) {
+	pq.lessFunc = lessFunc
+	heap.Init(pq)
+}
+
+// txPQByPriority sorts a txPriorityQueue by transaction priority and then fees
+// per kilobyte.
+func txPQByPriority(pq *txPriorityQueue, i, j int) bool {
+	// Using > here so that pop gives the highest priority item as opposed
+	// to the lowest.  Sort by priority first, then fee.
+	if pq.items[i].priority == pq.items[j].priority {
+		return pq.items[i].feePerKB > pq.items[j].feePerKB
+	}
+	return pq.items[i].priority > pq.items[j].priority
+
+}
+
+// txPQByFee sorts a txPriorityQueue by fees per kilobyte and then transaction
+// priority.
+func txPQByFee(pq *txPriorityQueue, i, j int) bool {
+	// Using > here so that pop gives the highest fee item as opposed
+	// to the lowest.  Sort by fee first, then priority.
+	if pq.items[i].feePerKB == pq.items[j].feePerKB {
+		return pq.items[i].priority > pq.items[j].priority
+	}
+	return pq.items[i].feePerKB > pq.items[j].feePerKB
+}
+
+// newTxPriorityQueue returns a new transaction priority queue that reserves the
+// passed amount of space for the elements.  The new priority queue uses either
+// the txPQByPriority or the txPQByFee compare function depending on the
+// sortByFee parameter and is already initialized for use with heap.Push/Pop.
+// The priority queue can grow larger than the reserved space, but extra copies
+// of the underlying array can be avoided by reserving a sane value.
+func newTxPriorityQueue(reserve int, sortByFee bool) *txPriorityQueue {
+	pq := &txPriorityQueue{
+		items: make([]*txPrioItem, 0, reserve),
+	}
+	if sortByFee {
+		pq.SetLessFunc(txPQByFee)
+	} else {
+		pq.SetLessFunc(txPQByPriority)
+	}
+	return pq
+}
+
+// BlockTemplate houses a block that has yet to be solved along with additional
+// details about the fees and the number of signature operations for each
+// transaction in the block.
+type BlockTemplate struct {
+	// Block is a block that is ready to be solved by miners.  Thus, it is
+	// completely valid with the exception of satisfying the proof-of-work
+	// requirement.
+	Block *wire.MsgBlock
+
+	// Fees contains the amount of fees each transaction in the generated
+	// template pays in base units.  Since the first transaction is the
+	// coinbase, the first entry (offset 0) will contain the negative of the
+	// sum of the fees of all other transactions.
+	Fees []int64
+
+	// SigOpCosts contains the number of signature operations each
+	// transaction in the generated template performs.
+	SigOpCosts []int64
+
+	// Height is the height at which the block template connects to the main
+	// chain.
+	Height int32
+
+	// ValidPayAddress indicates whether or not the template coinbase pays
+	// to an address or is redeemable by anyone.  See the documentation on
+	// NewBlockTemplate for details on which this can be useful to generate
+	// templates without a coinbase payment address.
+	ValidPayAddress bool
+
+	// WitnessCommitment is a commitment to the witness data (if any)
+	// within the block. This field will only be populted once segregated
+	// witness has been activated, and the block contains a transaction
+	// which has witness data.
+	WitnessCommitment []byte
+}
+
+// mergeUtxoView adds all of the entries in view to viewA.  The result is that
+// viewA will contain all of its original entries plus all of the entries
+// in viewB.  It will replace any entries in viewB which also exist in viewA
+// if the entry in viewA is fully spent.
+func mergeUtxoView(viewA *blockchain.UtxoViewpoint, viewB *blockchain.UtxoViewpoint) {
+	viewAEntries := viewA.Entries()
+	for hash, entryB := range viewB.Entries() {
+		if entryA, exists := viewAEntries[hash]; !exists ||
+			entryA == nil || entryA.IsFullySpent() {
+
+			viewAEntries[hash] = entryB
+		}
+	}
+}
+
+// standardCoinbaseScript returns a standard script suitable for use as the
+// signature script of the coinbase transaction of a new block.  In particular,
+// it starts with the block height that is required by version 2 blocks and adds
+// the extra nonce as well as additional coinbase flags.
+func standardCoinbaseScript(nextBlockHeight int32, extraNonce uint64) ([]byte, error) {
+	return txscript.NewScriptBuilder().AddInt64(int64(nextBlockHeight)).
+		AddInt64(int64(extraNonce)).AddData([]byte(CoinbaseFlags)).
+		Script()
+}
+
+// createCoinbaseTx returns a coinbase transaction paying an appropriate subsidy
+// based on the passed block height to the provided address.  When the address
+// is nil, the coinbase transaction will instead be redeemable by anyone.
+//
+// See the comment for NewBlockTemplate for more information about why the nil
+// address handling is useful.
+func createCoinbaseTx(params *chaincfg.Params, coinbaseScript []byte, nextBlockHeight int32, addr btcutil.Address) (*btcutil.Tx, error) {
+	// Create the script to pay to the provided payment address if one was
+	// specified.  Otherwise create a script that allows the coinbase to be
+	// redeemable by anyone.
+	var pkScript []byte
+	if addr != nil {
+		var err error
+		pkScript, err = txscript.PayToAddrScript(addr)
+		if err != nil {
+			return nil, err
+		}
+	} else {
+		var err error
+		scriptBuilder := txscript.NewScriptBuilder()
+		pkScript, err = scriptBuilder.AddOp(txscript.OP_TRUE).Script()
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	tx := wire.NewMsgTx(wire.TxVersion)
+	tx.AddTxIn(&wire.TxIn{
+		// Coinbase transactions have no inputs, so previous outpoint is
+		// zero hash and max index.
+		PreviousOutPoint: *wire.NewOutPoint(&chainhash.Hash{},
+			wire.MaxPrevOutIndex),
+		SignatureScript: coinbaseScript,
+		Sequence:        wire.MaxTxInSequenceNum,
+	})
+	tx.AddTxOut(&wire.TxOut{
+		Value:    blockchain.CalcBlockSubsidy(nextBlockHeight, params),
+		PkScript: pkScript,
+	})
+	return btcutil.NewTx(tx), nil
+}
+
+// spendTransaction updates the passed view by marking the inputs to the passed
+// transaction as spent.  It also adds all outputs in the passed transaction
+// which are not provably unspendable as available unspent transaction outputs.
+func spendTransaction(utxoView *blockchain.UtxoViewpoint, tx *btcutil.Tx, height int32) error {
+	for _, txIn := range tx.MsgTx().TxIn {
+		originHash := &txIn.PreviousOutPoint.Hash
+		originIndex := txIn.PreviousOutPoint.Index
+		entry := utxoView.LookupEntry(originHash)
+		if entry != nil {
+			entry.SpendOutput(originIndex)
+		}
+	}
+
+	utxoView.AddTxOuts(tx, height)
+	return nil
+}
+
+// logSkippedDeps logs any dependencies which are also skipped as a result of
+// skipping a transaction while generating a block template at the trace level.
+func logSkippedDeps(tx *btcutil.Tx, deps map[chainhash.Hash]*txPrioItem) {
+	if deps == nil {
+		return
+	}
+
+	for _, item := range deps {
+		log.Tracef("Skipping tx %s since it depends on %s\n",
+			item.tx.Hash(), tx.Hash())
+	}
+}
+
+// MinimumMedianTime returns the minimum allowed timestamp for a block building
+// on the end of the provided best chain.  In particular, it is one second after
+// the median timestamp of the last several blocks per the chain consensus
+// rules.
+func MinimumMedianTime(chainState *blockchain.BestState) time.Time {
+	return chainState.MedianTime.Add(time.Second)
+}
+
+// medianAdjustedTime returns the current time adjusted to ensure it is at least
+// one second after the median timestamp of the last several blocks per the
+// chain consensus rules.
+func medianAdjustedTime(chainState *blockchain.BestState, timeSource blockchain.MedianTimeSource) time.Time {
+	// The timestamp for the block must not be before the median timestamp
+	// of the last several blocks.  Thus, choose the maximum between the
+	// current time and one second after the past median time.  The current
+	// timestamp is truncated to a second boundary before comparison since a
+	// block timestamp does not supported a precision greater than one
+	// second.
+	newTimestamp := timeSource.AdjustedTime()
+	minTimestamp := MinimumMedianTime(chainState)
+	if newTimestamp.Before(minTimestamp) {
+		newTimestamp = minTimestamp
+	}
+
+	return newTimestamp
+}
+
+// BlkTmplGenerator provides a type that can be used to generate block templates
+// based on a given mining policy and source of transactions to choose from.
+// It also houses additional state required in order to ensure the templates
+// are built on top of the current best chain and adhere to the consensus rules.
+type BlkTmplGenerator struct {
+	policy      *Policy
+	chainParams *chaincfg.Params
+	txSource    TxSource
+	chain       *blockchain.BlockChain
+	timeSource  blockchain.MedianTimeSource
+	sigCache    *txscript.SigCache
+	hashCache   *txscript.HashCache
+}
+
+// NewBlkTmplGenerator returns a new block template generator for the given
+// policy using transactions from the provided transaction source.
+//
+// The additional state-related fields are required in order to ensure the
+// templates are built on top of the current best chain and adhere to the
+// consensus rules.
+func NewBlkTmplGenerator(policy *Policy, params *chaincfg.Params,
+	txSource TxSource, chain *blockchain.BlockChain,
+	timeSource blockchain.MedianTimeSource,
+	sigCache *txscript.SigCache,
+	hashCache *txscript.HashCache) *BlkTmplGenerator {
+
+	return &BlkTmplGenerator{
+		policy:      policy,
+		chainParams: params,
+		txSource:    txSource,
+		chain:       chain,
+		timeSource:  timeSource,
+		sigCache:    sigCache,
+		hashCache:   hashCache,
+	}
+}
+
+// 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()
+	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
+	}
+	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.
+		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 !segwitActive && tx.HasWitness():
+			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 segwitActive && !witnessIncluded && tx.HasWitness():
+			// 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 with a model coinbase tx with a
+			// witness commitment.
+			coinbaseCopy := btcutil.NewTx(coinbaseTx.MsgTx().Copy())
+			coinbaseCopy.MsgTx().TxIn[0].Witness = [][]byte{
+				bytes.Repeat([]byte("a"),
+					blockchain.CoinbaseWitnessDataLen),
+			}
+			coinbaseCopy.MsgTx().AddTxOut(&wire.TxOut{
+				PkScript: bytes.Repeat([]byte("a"),
+					blockchain.CoinbaseWitnessPkScriptLength),
+			})
+
+			// In order to accurately account for the weight
+			// addition due to this coinbase transaction, we'll add
+			// the difference of the transaction before and after
+			// the addition of the commitment to the block weight.
+			weightDiff := blockchain.GetTransactionWeight(coinbaseCopy) -
+				blockchain.GetTransactionWeight(coinbaseTx)
+
+			blockWeight += uint32(weightDiff)
+
+			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 := 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.
+	var witnessCommitment []byte
+	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:  best.Hash,
+		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.CheckConnectBlockTemplate(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,
+		WitnessCommitment: witnessCommitment,
+	}, nil
+}
+
+// UpdateBlockTime updates the timestamp in the header of the passed block to
+// the current time while taking into account the median time of the last
+// several blocks to ensure the new time is after that time per the chain
+// consensus rules.  Finally, it will update the target difficulty if needed
+// based on the new time for the test networks since their target difficulty can
+// change based upon time.
+func (g *BlkTmplGenerator) UpdateBlockTime(msgBlock *wire.MsgBlock) error {
+	// The new timestamp is potentially adjusted to ensure it comes after
+	// the median time of the last several blocks per the chain consensus
+	// rules.
+	newTime := medianAdjustedTime(g.chain.BestSnapshot(), g.timeSource)
+	msgBlock.Header.Timestamp = newTime
+
+	// Recalculate the difficulty if running on a network that requires it.
+	if g.chainParams.ReduceMinDifficulty {
+		difficulty, err := g.chain.CalcNextRequiredDifficulty(newTime)
+		if err != nil {
+			return err
+		}
+		msgBlock.Header.Bits = difficulty
+	}
+
+	return nil
+}
+
+// UpdateExtraNonce updates the extra nonce in the coinbase script of the passed
+// block by regenerating the coinbase script with the passed value and block
+// height.  It also recalculates and updates the new merkle root that results
+// from changing the coinbase script.
+func (g *BlkTmplGenerator) UpdateExtraNonce(msgBlock *wire.MsgBlock, blockHeight int32, extraNonce uint64) error {
+	coinbaseScript, err := standardCoinbaseScript(blockHeight, extraNonce)
+	if err != nil {
+		return err
+	}
+	if len(coinbaseScript) > blockchain.MaxCoinbaseScriptLen {
+		return fmt.Errorf("coinbase transaction script length "+
+			"of %d is out of range (min: %d, max: %d)",
+			len(coinbaseScript), blockchain.MinCoinbaseScriptLen,
+			blockchain.MaxCoinbaseScriptLen)
+	}
+	msgBlock.Transactions[0].TxIn[0].SignatureScript = coinbaseScript
+
+	// TODO(davec): A btcutil.Block should use saved in the state to avoid
+	// recalculating all of the other transaction hashes.
+	// block.Transactions[0].InvalidateCache()
+
+	// Recalculate the merkle root with the updated extra nonce.
+	block := btcutil.NewBlock(msgBlock)
+	merkles := blockchain.BuildMerkleTreeStore(block.Transactions(), false)
+	msgBlock.Header.MerkleRoot = *merkles[len(merkles)-1]
+	return nil
+}
+
+// BestSnapshot returns information about the current best chain block and
+// related state as of the current point in time using the chain instance
+// associated with the block template generator.  The returned state must be
+// treated as immutable since it is shared by all callers.
+//
+// This function is safe for concurrent access.
+func (g *BlkTmplGenerator) BestSnapshot() *blockchain.BestState {
+	return g.chain.BestSnapshot()
+}
+
+// TxSource returns the associated transaction source.
+//
+// This function is safe for concurrent access.
+func (g *BlkTmplGenerator) TxSource() TxSource {
+	return g.txSource
+}