// getDifficultyRatio returns the proof-of-work difficulty as a multiple of the
// minimum difficulty using the passed bits field from the header of a block.
func getDifficultyRatio(bits uint32) float64 {
// The minimum difficulty is the max possible proof-of-work limit bits
// converted back to a number. Note this is not the same as the the
// proof of work limit directly because the block difficulty is encoded
// in a block with the compact form which loses precision.
max := btcchain.CompactToBig(activeNetParams.powLimitBits)
target := btcchain.CompactToBig(bits)
difficulty := new(big.Rat).SetFrac(max, target)
outString := difficulty.FloatString(2)
diff, err := strconv.ParseFloat(outString, 64)
if err != nil {
rpcsLog.Errorf("Cannot get difficulty: %v", err)
return 0
}
return diff
}
// This example demonstrates how to convert the compact "bits" in a block header
// which represent the target difficulty to a big integer and display it using
// the typical hex notation.
func ExampleCompactToBig() {
// Convert the bits from block 300000 in the main block chain.
bits := uint32(419465580)
targetDifficulty := btcchain.CompactToBig(bits)
// Display it in hex.
fmt.Printf("%064x\n", targetDifficulty.Bytes())
// Output:
// 0000000000000000896c00000000000000000000000000000000000000000000
}
func TestCompactToBig(t *testing.T) {
tests := []struct {
in uint32
out int64
}{
{10000000, 0},
}
for x, test := range tests {
n := btcchain.CompactToBig(test.in)
want := big.NewInt(test.out)
if n.Cmp(want) != 0 {
t.Errorf("TestCompactToBig test #%d failed: got %d want %d\n",
x, n.Int64(), want.Int64())
return
}
}
}
// NewBlockTemplate returns a new block template that is ready to be solved
// using the transactions from the passed transaction memory 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
// configuration options 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
// configuration option allots space for high-priority transactions.
// Transactions which spend outputs from other transactions in the memory 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 configuration option,
// the transaction will be skipped unless there is a BlockMinSize set, 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
// configuration option, 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 | | |
// |-----------------------------------| | |
// | | | | ----- cfg.BlockPrioritySize
// | High-priority Transactions | | |
// | | | |
// |-----------------------------------| | --
// | | |
// | | |
// | | |--- cfg.BlockMaxSize
// | Transactions prioritized by fee | |
// | until <= cfg.TxMinFreeFee | |
// | | |
// | | |
// | | |
// |-----------------------------------| |
// | Low-fee/Non high-priority (free) | |
// | transactions (while block size | |
// | <= cfg.BlockMinSize) | |
// ----------------------------------- --
func NewBlockTemplate(mempool *txMemPool, payToAddress btcutil.Address) (*BlockTemplate, error) {
blockManager := mempool.server.blockManager
chainState := &blockManager.chainState
chain := blockManager.blockChain
// Extend the most recently known best block.
chainState.Lock()
prevHash := chainState.newestHash
nextBlockHeight := chainState.newestHeight + 1
chainState.Unlock()
// 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 := standardCoinbaseScript(nextBlockHeight, extraNonce)
coinbaseTx, err := createCoinbaseTx(coinbaseScript, nextBlockHeight,
payToAddress)
if err != nil {
return nil, err
}
numCoinbaseSigOps := int64(btcchain.CountSigOps(coinbaseTx))
// Get the current memory pool 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 in the memory pool 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.
mempoolTxns := mempool.TxDescs()
sortedByFee := cfg.BlockPrioritySize == 0
priorityQueue := newTxPriorityQueue(len(mempoolTxns), sortedByFee)
// Create a slice to hold the transactions to be included in the
// generated block with reserved space. Also create a transaction
// store to house all of the input transactions so multiple lookups
// can be avoided.
blockTxns := make([]*btcutil.Tx, 0, len(mempoolTxns))
blockTxns = append(blockTxns, coinbaseTx)
blockTxStore := make(btcchain.TxStore)
// dependers is used to track transactions which depend on another
// transaction in the memory 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[btcwire.ShaHash]*list.List)
// 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(mempoolTxns))
txSigOpCounts := make([]int64, 0, len(mempoolTxns))
txFees = append(txFees, -1) // Updated once known
txSigOpCounts = append(txSigOpCounts, numCoinbaseSigOps)
minrLog.Debugf("Considering %d mempool transactions for inclusion to "+
"new block", len(mempoolTxns))
mempoolLoop:
for _, txDesc := range mempoolTxns {
// A block can't have more than one coinbase or contain
// non-finalized transactions.
tx := txDesc.Tx
if btcchain.IsCoinBase(tx) {
minrLog.Tracef("Skipping coinbase tx %s", tx.Sha())
continue
}
if !btcchain.IsFinalizedTransaction(tx, nextBlockHeight, time.Now()) {
minrLog.Tracef("Skipping non-finalized tx %s", tx.Sha())
continue
}
// Fetch all of the transactions referenced by the inputs to
// 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.
txStore, err := chain.FetchTransactionStore(tx)
if err != nil {
minrLog.Warnf("Unable to fetch transaction store for "+
"tx %s: %v", tx.Sha(), err)
continue
}
// Calculate the input value age sum for the transaction. This
// is comprised of the sum all of input amounts multiplied by
// their respective age (number of confirmations since the
// referenced input transaction). While doing the above, also
// setup dependencies for any transactions which reference other
// transactions in the mempool so they can be properly ordered
// below.
prioItem := &txPrioItem{tx: txDesc.Tx}
inputValueAge := float64(0.0)
for _, txIn := range tx.MsgTx().TxIn {
originHash := &txIn.PreviousOutPoint.Hash
originIndex := txIn.PreviousOutPoint.Index
txData, exists := txStore[*originHash]
if !exists || txData.Err != nil || txData.Tx == nil {
if !mempool.HaveTransaction(originHash) {
minrLog.Tracef("Skipping tx %s because "+
"it references tx %s which is "+
"not available", tx.Sha,
originHash)
continue mempoolLoop
}
// The transaction is referencing another
// transaction in the memory pool, so setup an
// ordering dependency.
depList, exists := dependers[*originHash]
if !exists {
depList = list.New()
dependers[*originHash] = depList
}
depList.PushBack(prioItem)
if prioItem.dependsOn == nil {
prioItem.dependsOn = make(
map[btcwire.ShaHash]struct{})
}
prioItem.dependsOn[*originHash] = struct{}{}
// No need to calculate or sum input value age
// for this input since it's zero due to
// the input age multiplier of 0.
continue
}
// Ensure the output index in the referenced transaction
// is available.
msgTx := txData.Tx.MsgTx()
if originIndex > uint32(len(msgTx.TxOut)) {
minrLog.Tracef("Skipping tx %s because "+
"it references output %d of tx %s "+
"which is out of bounds", tx.Sha,
originIndex, originHash)
continue mempoolLoop
}
// Sum the input value times age.
originTxOut := txData.Tx.MsgTx().TxOut[originIndex]
inputValue := originTxOut.Value
inputAge := nextBlockHeight - txData.BlockHeight
inputValueAge += float64(inputValue * inputAge)
}
// 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
txSize := tx.MsgTx().SerializeSize()
prioItem.priority = calcPriority(tx, txSize, inputValueAge)
// Calculate the fee in Satoshi/KB.
// NOTE: This is a more precise value than the one calculated
// during calcMinRelayFee which rounds up to the nearest full
// kilobyte boundary. This is beneficial since it provides an
// incentive to create smaller transactions.
prioItem.feePerKB = float64(txDesc.Fee) / (float64(txSize) / 1000)
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 store which contains all of the input transactions
// for this transaction into the input transaction store. This
// allows the code below to avoid a second lookup.
mergeTxStore(blockTxStore, txStore)
}
minrLog.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.
blockSize := blockHeaderOverhead + uint32(coinbaseTx.MsgTx().SerializeSize())
blockSigOps := numCoinbaseSigOps
totalFees := int64(0)
// 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
// Grab the list of transactions which depend on this one (if
// any) and remove the entry for this transaction as it will
// either be included or skipped, but in either case the deps
// are no longer needed.
deps := dependers[*tx.Sha()]
delete(dependers, *tx.Sha())
// Enforce maximum block size. Also check for overflow.
txSize := uint32(tx.MsgTx().SerializeSize())
blockPlusTxSize := blockSize + txSize
if blockPlusTxSize < blockSize || blockPlusTxSize >= cfg.BlockMaxSize {
minrLog.Tracef("Skipping tx %s because it would exceed "+
"the max block size", tx.Sha())
logSkippedDeps(tx, deps)
continue
}
// Enforce maximum signature operations per block. Also check
// for overflow.
numSigOps := int64(btcchain.CountSigOps(tx))
if blockSigOps+numSigOps < blockSigOps ||
blockSigOps+numSigOps > btcchain.MaxSigOpsPerBlock {
minrLog.Tracef("Skipping tx %s because it would "+
"exceed the maximum sigops per block", tx.Sha())
logSkippedDeps(tx, deps)
continue
}
numP2SHSigOps, err := btcchain.CountP2SHSigOps(tx, false,
blockTxStore)
if err != nil {
minrLog.Tracef("Skipping tx %s due to error in "+
"CountP2SHSigOps: %v", tx.Sha(), err)
logSkippedDeps(tx, deps)
continue
}
numSigOps += int64(numP2SHSigOps)
if blockSigOps+numSigOps < blockSigOps ||
blockSigOps+numSigOps > btcchain.MaxSigOpsPerBlock {
minrLog.Tracef("Skipping tx %s because it would "+
"exceed the maximum sigops per block (p2sh)",
tx.Sha())
logSkippedDeps(tx, deps)
continue
}
// Skip free transactions once the block is larger than the
// minimum block size.
if sortedByFee && prioItem.feePerKB < minTxRelayFee &&
blockPlusTxSize >= cfg.BlockMinSize {
minrLog.Tracef("Skipping tx %s with feePerKB %.2f "+
"< minTxRelayFee %d and block size %d >= "+
"minBlockSize %d", tx.Sha(), prioItem.feePerKB,
minTxRelayFee, blockPlusTxSize,
cfg.BlockMinSize)
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 && (blockPlusTxSize >= cfg.BlockPrioritySize ||
prioItem.priority <= minHighPriority) {
minrLog.Tracef("Switching to sort by fees per "+
"kilobyte blockSize %d >= BlockPrioritySize "+
"%d || priority %.2f <= minHighPriority %.2f",
blockPlusTxSize, cfg.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 blockPlusTxSize > cfg.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 = btcchain.CheckTransactionInputs(tx, nextBlockHeight,
blockTxStore)
if err != nil {
minrLog.Tracef("Skipping tx %s due to error in "+
"CheckTransactionInputs: %v", tx.Sha(), err)
logSkippedDeps(tx, deps)
continue
}
err = btcchain.ValidateTransactionScripts(tx, blockTxStore,
standardScriptVerifyFlags)
if err != nil {
minrLog.Tracef("Skipping tx %s due to error in "+
"ValidateTransactionScripts: %v", tx.Sha(), err)
logSkippedDeps(tx, deps)
continue
}
// Spend the transaction inputs in the block transaction store
// 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(blockTxStore, 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)
blockSize += txSize
blockSigOps += numSigOps
totalFees += prioItem.fee
txFees = append(txFees, prioItem.fee)
txSigOpCounts = append(txSigOpCounts, numSigOps)
minrLog.Tracef("Adding tx %s (priority %.2f, feePerKB %.2f)",
prioItem.tx.Sha(), prioItem.priority, prioItem.feePerKB)
// Add transactions which depend on this one (and also do not
// have any other unsatisified dependencies) to the priority
// queue.
if deps != nil {
for e := deps.Front(); e != nil; e = e.Next() {
// Add the transaction to the priority queue if
// there are no more dependencies after this
// one.
item := e.Value.(*txPrioItem)
delete(item.dependsOn, *tx.Sha())
if len(item.dependsOn) == 0 {
heap.Push(priorityQueue, item)
}
}
}
}
// Now that the actual transactions have been selected, update the
// block size for the real transaction count and coinbase value with
// the total fees accordingly.
blockSize -= btcwire.MaxVarIntPayload -
uint32(btcwire.VarIntSerializeSize(uint64(len(blockTxns))))
coinbaseTx.MsgTx().TxOut[0].Value += totalFees
txFees[0] = -totalFees
// 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, err := medianAdjustedTime(chainState)
if err != nil {
return nil, err
}
requiredDifficulty, err := blockManager.CalcNextRequiredDifficulty(ts)
if err != nil {
return nil, err
}
// Create a new block ready to be solved.
merkles := btcchain.BuildMerkleTreeStore(blockTxns)
var msgBlock btcwire.MsgBlock
msgBlock.Header = btcwire.BlockHeader{
Version: generatedBlockVersion,
PrevBlock: *prevHash,
MerkleRoot: *merkles[len(merkles)-1],
Timestamp: ts,
Bits: requiredDifficulty,
}
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 := blockManager.CheckConnectBlock(block); err != nil {
return nil, err
}
minrLog.Debugf("Created new block template (%d transactions, %d in "+
"fees, %d signature operations, %d bytes, target difficulty "+
"%064x)", len(msgBlock.Transactions), totalFees, blockSigOps,
blockSize, btcchain.CompactToBig(msgBlock.Header.Bits))
return &BlockTemplate{
block: &msgBlock,
fees: txFees,
sigOpCounts: txSigOpCounts,
height: nextBlockHeight,
validPayAddress: payToAddress != nil,
}, nil
}
// solveBlock attempts to find some combination of a nonce, extra nonce, and
// current timestamp which makes the passed block hash to a value less than the
// target difficulty. The timestamp is updated periodically and the passed
// block is modified with all tweaks during this process. This means that
// when the function returns true, the block is ready for submission.
//
// This function will return early with false when conditions that trigger a
// stale block such as a new block showing up or periodically when there are
// new transactions and enough time has elapsed without finding a solution.
func (m *CPUMiner) solveBlock(msgBlock *btcwire.MsgBlock, blockHeight int64,
ticker *time.Ticker, quit chan struct{}) bool {
// Choose a random extra nonce offset for this block template and
// worker.
enOffset, err := btcwire.RandomUint64()
if err != nil {
minrLog.Errorf("Unexpected error while generating random "+
"extra nonce offset: %v", err)
enOffset = 0
}
// Create a couple of convenience variables.
header := &msgBlock.Header
targetDifficulty := btcchain.CompactToBig(header.Bits)
// Initial state.
lastGenerated := time.Now()
lastTxUpdate := m.server.txMemPool.LastUpdated()
hashesCompleted := uint64(0)
// Note that the entire extra nonce range is iterated and the offset is
// added relying on the fact that overflow will wrap around 0 as
// provided by the Go spec.
for extraNonce := uint64(0); extraNonce < maxExtraNonce; extraNonce++ {
// Update the extra nonce in the block template with the
// new value by regenerating the coinbase script and
// setting the merkle root to the new value. The
UpdateExtraNonce(msgBlock, blockHeight, extraNonce+enOffset)
// Search through the entire nonce range for a solution while
// periodically checking for early quit and stale block
// conditions along with updates to the speed monitor.
for i := uint32(0); i <= maxNonce; i++ {
select {
case <-quit:
return false
case <-ticker.C:
m.updateHashes <- hashesCompleted
hashesCompleted = 0
// The current block is stale if the best block
// has changed.
bestHash, _ := m.server.blockManager.chainState.Best()
if !header.PrevBlock.IsEqual(bestHash) {
return false
}
// The current block is stale if the memory pool
// has been updated since the block template was
// generated and it has been at least one
// minute.
if lastTxUpdate != m.server.txMemPool.LastUpdated() &&
time.Now().After(lastGenerated.Add(time.Minute)) {
return false
}
UpdateBlockTime(msgBlock, m.server.blockManager)
default:
// Non-blocking select to fall through
}
// Update the nonce and hash the block header. Each
// hash is actually a double sha256 (two hashes), so
// increment the number of hashes completed for each
// attempt accordingly.
header.Nonce = i
hash, _ := header.BlockSha()
hashesCompleted += 2
// The block is solved when the new block hash is less
// than the target difficulty. Yay!
if btcchain.ShaHashToBig(&hash).Cmp(targetDifficulty) <= 0 {
m.updateHashes <- hashesCompleted
return true
}
}
}
return false
}