Merge pull request #1427 from wpaulino/mempool-rbf
mempool: implement RBF signaling policy
This commit is contained in:
Olaoluwa Osuntokun
GitHub
commit
962a206e94
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@ -165,6 +165,7 @@ type config struct {
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DropAddrIndex bool `long:"dropaddrindex" description:"Deletes the address-based transaction index from the database on start up and then exits."`
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RelayNonStd bool `long:"relaynonstd" description:"Relay non-standard transactions regardless of the default settings for the active network."`
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RejectNonStd bool `long:"rejectnonstd" description:"Reject non-standard transactions regardless of the default settings for the active network."`
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RejectReplacement bool `long:"rejectreplacement" description:"Reject transactions that attempt to replace existing transactions within the mempool through the Replace-By-Fee (RBF) signaling policy."`
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lookup func(string) ([]net.IP, error)
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oniondial func(string, string, time.Duration) (net.Conn, error)
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dial func(string, string, time.Duration) (net.Conn, error)
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@ -38,6 +38,16 @@ const (
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// orphanExpireScanInterval is the minimum amount of time in between
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// scans of the orphan pool to evict expired transactions.
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orphanExpireScanInterval = time.Minute * 5
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// MaxRBFSequence is the maximum sequence number an input can use to
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// signal that the transaction spending it can be replaced using the
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// Replace-By-Fee (RBF) policy.
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MaxRBFSequence = 0xfffffffd
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// MaxReplacementEvictions is the maximum number of transactions that
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// can be evicted from the mempool when accepting a transaction
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// replacement.
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MaxReplacementEvictions = 100
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)
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// Tag represents an identifier to use for tagging orphan transactions. The
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@ -133,6 +143,11 @@ type Policy struct {
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// MinRelayTxFee defines the minimum transaction fee in BTC/kB to be
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// considered a non-zero fee.
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MinRelayTxFee btcutil.Amount
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// RejectReplacement, if true, rejects accepting replacement
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// transactions using the Replace-By-Fee (RBF) signaling policy into
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// the mempool.
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RejectReplacement bool
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}
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// TxDesc is a descriptor containing a transaction in the mempool along with
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@ -554,21 +569,200 @@ func (mp *TxPool) addTransaction(utxoView *blockchain.UtxoViewpoint, tx *btcutil
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// checkPoolDoubleSpend checks whether or not the passed transaction is
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// attempting to spend coins already spent by other transactions in the pool.
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// Note it does not check for double spends against transactions already in the
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// main chain.
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// If it does, we'll check whether each of those transactions are signaling for
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// replacement. If just one of them isn't, an error is returned. Otherwise, a
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// boolean is returned signaling that the transaction is a replacement. Note it
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// does not check for double spends against transactions already in the main
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// chain.
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//
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// This function MUST be called with the mempool lock held (for reads).
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func (mp *TxPool) checkPoolDoubleSpend(tx *btcutil.Tx) error {
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func (mp *TxPool) checkPoolDoubleSpend(tx *btcutil.Tx) (bool, error) {
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var isReplacement bool
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for _, txIn := range tx.MsgTx().TxIn {
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if txR, exists := mp.outpoints[txIn.PreviousOutPoint]; exists {
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conflict, ok := mp.outpoints[txIn.PreviousOutPoint]
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if !ok {
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continue
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}
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// Reject the transaction if we don't accept replacement
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// transactions or if it doesn't signal replacement.
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if mp.cfg.Policy.RejectReplacement ||
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!mp.signalsReplacement(conflict, nil) {
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str := fmt.Sprintf("output %v already spent by "+
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"transaction %v in the memory pool",
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txIn.PreviousOutPoint, txR.Hash())
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return txRuleError(wire.RejectDuplicate, str)
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txIn.PreviousOutPoint, conflict.Hash())
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return false, txRuleError(wire.RejectDuplicate, str)
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}
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isReplacement = true
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}
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return isReplacement, nil
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}
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// signalsReplacement determines if a transaction is signaling that it can be
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// replaced using the Replace-By-Fee (RBF) policy. This policy specifies two
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// ways a transaction can signal that it is replaceable:
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//
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// Explicit signaling: A transaction is considered to have opted in to allowing
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// replacement of itself if any of its inputs have a sequence number less than
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// 0xfffffffe.
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//
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// Inherited signaling: Transactions that don't explicitly signal replaceability
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// are replaceable under this policy for as long as any one of their ancestors
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// signals replaceability and remains unconfirmed.
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//
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// The cache is optional and serves as an optimization to avoid visiting
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// transactions we've already determined don't signal replacement.
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//
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// This function MUST be called with the mempool lock held (for reads).
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func (mp *TxPool) signalsReplacement(tx *btcutil.Tx,
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cache map[chainhash.Hash]struct{}) bool {
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// If a cache was not provided, we'll initialize one now to use for the
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// recursive calls.
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if cache == nil {
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cache = make(map[chainhash.Hash]struct{})
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}
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for _, txIn := range tx.MsgTx().TxIn {
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if txIn.Sequence <= MaxRBFSequence {
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return true
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}
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hash := txIn.PreviousOutPoint.Hash
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unconfirmedAncestor, ok := mp.pool[hash]
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if !ok {
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continue
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}
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// If we've already determined the transaction doesn't signal
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// replacement, we can avoid visiting it again.
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if _, ok := cache[hash]; ok {
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continue
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}
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if mp.signalsReplacement(unconfirmedAncestor.Tx, cache) {
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return true
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}
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// Since the transaction doesn't signal replacement, we'll cache
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// its result to ensure we don't attempt to determine so again.
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cache[hash] = struct{}{}
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}
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return false
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}
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// txAncestors returns all of the unconfirmed ancestors of the given
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// transaction. Given transactions A, B, and C where C spends B and B spends A,
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// A and B are considered ancestors of C.
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//
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// The cache is optional and serves as an optimization to avoid visiting
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// transactions we've already determined ancestors of.
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//
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// This function MUST be called with the mempool lock held (for reads).
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func (mp *TxPool) txAncestors(tx *btcutil.Tx,
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cache map[chainhash.Hash]map[chainhash.Hash]*btcutil.Tx) map[chainhash.Hash]*btcutil.Tx {
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// If a cache was not provided, we'll initialize one now to use for the
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// recursive calls.
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if cache == nil {
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cache = make(map[chainhash.Hash]map[chainhash.Hash]*btcutil.Tx)
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}
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ancestors := make(map[chainhash.Hash]*btcutil.Tx)
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for _, txIn := range tx.MsgTx().TxIn {
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parent, ok := mp.pool[txIn.PreviousOutPoint.Hash]
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if !ok {
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continue
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}
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ancestors[*parent.Tx.Hash()] = parent.Tx
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// Determine if the ancestors of this ancestor have already been
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// computed. If they haven't, we'll do so now and cache them to
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// use them later on if necessary.
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moreAncestors, ok := cache[*parent.Tx.Hash()]
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if !ok {
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moreAncestors = mp.txAncestors(parent.Tx, cache)
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cache[*parent.Tx.Hash()] = moreAncestors
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}
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for hash, ancestor := range moreAncestors {
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ancestors[hash] = ancestor
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}
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}
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return nil
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return ancestors
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}
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// txDescendants returns all of the unconfirmed descendants of the given
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// transaction. Given transactions A, B, and C where C spends B and B spends A,
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// B and C are considered descendants of A. A cache can be provided in order to
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// easily retrieve the descendants of transactions we've already determined the
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// descendants of.
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//
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// This function MUST be called with the mempool lock held (for reads).
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func (mp *TxPool) txDescendants(tx *btcutil.Tx,
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cache map[chainhash.Hash]map[chainhash.Hash]*btcutil.Tx) map[chainhash.Hash]*btcutil.Tx {
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// If a cache was not provided, we'll initialize one now to use for the
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// recursive calls.
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if cache == nil {
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cache = make(map[chainhash.Hash]map[chainhash.Hash]*btcutil.Tx)
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}
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// We'll go through all of the outputs of the transaction to determine
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// if they are spent by any other mempool transactions.
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descendants := make(map[chainhash.Hash]*btcutil.Tx)
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op := wire.OutPoint{Hash: *tx.Hash()}
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for i := range tx.MsgTx().TxOut {
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op.Index = uint32(i)
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descendant, ok := mp.outpoints[op]
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if !ok {
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continue
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}
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descendants[*descendant.Hash()] = descendant
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// Determine if the descendants of this descendant have already
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// been computed. If they haven't, we'll do so now and cache
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// them to use them later on if necessary.
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moreDescendants, ok := cache[*descendant.Hash()]
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if !ok {
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moreDescendants = mp.txDescendants(descendant, cache)
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cache[*descendant.Hash()] = moreDescendants
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}
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for _, moreDescendant := range moreDescendants {
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descendants[*moreDescendant.Hash()] = moreDescendant
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}
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}
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return descendants
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}
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// txConflicts returns all of the unconfirmed transactions that would become
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// conflicts if we were to accept the given transaction into the mempool. An
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// unconfirmed conflict is known as a transaction that spends an output already
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// spent by a different transaction within the mempool. Any descendants of these
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// transactions are also considered conflicts as they would no longer exist.
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// These are generally not allowed except for transactions that signal RBF
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// support.
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//
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// This function MUST be called with the mempool lock held (for reads).
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func (mp *TxPool) txConflicts(tx *btcutil.Tx) map[chainhash.Hash]*btcutil.Tx {
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conflicts := make(map[chainhash.Hash]*btcutil.Tx)
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for _, txIn := range tx.MsgTx().TxIn {
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conflict, ok := mp.outpoints[txIn.PreviousOutPoint]
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if !ok {
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continue
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}
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conflicts[*conflict.Hash()] = conflict
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for hash, descendant := range mp.txDescendants(conflict, nil) {
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conflicts[hash] = descendant
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}
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}
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return conflicts
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}
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// CheckSpend checks whether the passed outpoint is already spent by a
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@ -631,6 +825,100 @@ func (mp *TxPool) FetchTransaction(txHash *chainhash.Hash) (*btcutil.Tx, error)
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return nil, fmt.Errorf("transaction is not in the pool")
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}
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// validateReplacement determines whether a transaction is deemed as a valid
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// replacement of all of its conflicts according to the RBF policy. If it is
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// valid, no error is returned. Otherwise, an error is returned indicating what
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// went wrong.
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//
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// This function MUST be called with the mempool lock held (for reads).
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func (mp *TxPool) validateReplacement(tx *btcutil.Tx,
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txFee int64) (map[chainhash.Hash]*btcutil.Tx, error) {
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// First, we'll make sure the set of conflicting transactions doesn't
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// exceed the maximum allowed.
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conflicts := mp.txConflicts(tx)
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if len(conflicts) > MaxReplacementEvictions {
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str := fmt.Sprintf("replacement transaction %v evicts more "+
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"transactions than permitted: max is %v, evicts %v",
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tx.Hash(), MaxReplacementEvictions, len(conflicts))
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return nil, txRuleError(wire.RejectNonstandard, str)
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}
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// The set of conflicts (transactions we'll replace) and ancestors
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// should not overlap, otherwise the replacement would be spending an
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// output that no longer exists.
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for ancestorHash := range mp.txAncestors(tx, nil) {
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if _, ok := conflicts[ancestorHash]; !ok {
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continue
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}
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str := fmt.Sprintf("replacement transaction %v spends parent "+
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"transaction %v", tx.Hash(), ancestorHash)
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return nil, txRuleError(wire.RejectInvalid, str)
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}
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// The replacement should have a higher fee rate than each of the
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// conflicting transactions and a higher absolute fee than the fee sum
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// of all the conflicting transactions.
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//
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// We usually don't want to accept replacements with lower fee rates
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// than what they replaced as that would lower the fee rate of the next
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// block. Requiring that the fee rate always be increased is also an
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// easy-to-reason about way to prevent DoS attacks via replacements.
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var (
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txSize = GetTxVirtualSize(tx)
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txFeeRate = txFee * 1000 / txSize
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conflictsFee int64
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conflictsParents = make(map[chainhash.Hash]struct{})
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)
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for hash, conflict := range conflicts {
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if txFeeRate <= mp.pool[hash].FeePerKB {
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str := fmt.Sprintf("replacement transaction %v has an "+
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"insufficient fee rate: needs more than %v, "+
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"has %v", tx.Hash(), mp.pool[hash].FeePerKB,
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txFeeRate)
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return nil, txRuleError(wire.RejectInsufficientFee, str)
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}
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conflictsFee += mp.pool[hash].Fee
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// We'll track each conflict's parents to ensure the replacement
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// isn't spending any new unconfirmed inputs.
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for _, txIn := range conflict.MsgTx().TxIn {
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conflictsParents[txIn.PreviousOutPoint.Hash] = struct{}{}
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}
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}
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// It should also have an absolute fee greater than all of the
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// transactions it intends to replace and pay for its own bandwidth,
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// which is determined by our minimum relay fee.
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minFee := calcMinRequiredTxRelayFee(txSize, mp.cfg.Policy.MinRelayTxFee)
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if txFee < conflictsFee+minFee {
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str := fmt.Sprintf("replacement transaction %v has an "+
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"insufficient absolute fee: needs %v, has %v",
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tx.Hash(), conflictsFee+minFee, txFee)
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return nil, txRuleError(wire.RejectInsufficientFee, str)
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}
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// Finally, it should not spend any new unconfirmed outputs, other than
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// the ones already included in the parents of the conflicting
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// transactions it'll replace.
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for _, txIn := range tx.MsgTx().TxIn {
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if _, ok := conflictsParents[txIn.PreviousOutPoint.Hash]; ok {
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continue
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}
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// Confirmed outputs are valid to spend in the replacement.
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if _, ok := mp.pool[txIn.PreviousOutPoint.Hash]; !ok {
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continue
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}
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str := fmt.Sprintf("replacement transaction spends new "+
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"unconfirmed input %v not found in conflicting "+
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"transactions", txIn.PreviousOutPoint)
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return nil, txRuleError(wire.RejectInvalid, str)
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}
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return conflicts, nil
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}
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// maybeAcceptTransaction is the internal function which implements the public
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// MaybeAcceptTransaction. See the comment for MaybeAcceptTransaction for
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// more details.
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@ -714,13 +1002,14 @@ func (mp *TxPool) maybeAcceptTransaction(tx *btcutil.Tx, isNew, rateLimit, rejec
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// The transaction may not use any of the same outputs as other
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// transactions already in the pool as that would ultimately result in a
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// double spend. This check is intended to be quick and therefore only
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// detects double spends within the transaction pool itself. The
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// transaction could still be double spending coins from the main chain
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// at this point. There is a more in-depth check that happens later
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// after fetching the referenced transaction inputs from the main chain
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// which examines the actual spend data and prevents double spends.
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err = mp.checkPoolDoubleSpend(tx)
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// double spend, unless those transactions signal for RBF. This check is
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// intended to be quick and therefore only detects double spends within
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// the transaction pool itself. The transaction could still be double
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// spending coins from the main chain at this point. There is a more
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// in-depth check that happens later after fetching the referenced
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// transaction inputs from the main chain which examines the actual
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// spend data and prevents double spends.
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isReplacement, err := mp.checkPoolDoubleSpend(tx)
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if err != nil {
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return nil, nil, err
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}
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@ -899,6 +1188,16 @@ func (mp *TxPool) maybeAcceptTransaction(tx *btcutil.Tx, isNew, rateLimit, rejec
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mp.cfg.Policy.FreeTxRelayLimit*10*1000)
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}
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// If the transaction has any conflicts and we've made it this far, then
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// we're processing a potential replacement.
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var conflicts map[chainhash.Hash]*btcutil.Tx
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if isReplacement {
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conflicts, err = mp.validateReplacement(tx, txFee)
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if err != nil {
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return nil, nil, err
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}
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}
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// Verify crypto signatures for each input and reject the transaction if
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// any don't verify.
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err = blockchain.ValidateTransactionScripts(tx, utxoView,
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@ -911,7 +1210,20 @@ func (mp *TxPool) maybeAcceptTransaction(tx *btcutil.Tx, isNew, rateLimit, rejec
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return nil, nil, err
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}
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// Add to transaction pool.
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// Now that we've deemed the transaction as valid, we can add it to the
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// mempool. If it ended up replacing any transactions, we'll remove them
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// first.
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for _, conflict := range conflicts {
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log.Debugf("Replacing transaction %v (fee_rate=%v sat/kb) "+
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"with %v (fee_rate=%v sat/kb)\n", conflict.Hash(),
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mp.pool[*conflict.Hash()].FeePerKB, tx.Hash(),
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txFee*1000/serializedSize)
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// The conflict set should already include the descendants for
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// each one, so we don't need to remove the redeemers within
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// this call as they'll be removed eventually.
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mp.removeTransaction(conflict, false)
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}
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txD := mp.addTransaction(utxoView, tx, bestHeight, txFee)
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log.Debugf("Accepted transaction %v (pool size: %v)", txHash,
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File diff suppressed because it is too large
Load diff
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@ -2709,6 +2709,7 @@ func newServer(listenAddrs, agentBlacklist, agentWhitelist []string,
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MaxSigOpCostPerTx: blockchain.MaxBlockSigOpsCost / 4,
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MinRelayTxFee: cfg.minRelayTxFee,
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MaxTxVersion: 2,
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RejectReplacement: cfg.RejectReplacement,
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},
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ChainParams: chainParams,
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FetchUtxoView: s.chain.FetchUtxoView,
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