package mempool import ( "errors" "fmt" "math/bits" "sort" "sync" "github.com/holiman/uint256" "github.com/nspcc-dev/neo-go/pkg/core/mempoolevent" "github.com/nspcc-dev/neo-go/pkg/core/transaction" "github.com/nspcc-dev/neo-go/pkg/util" "go.uber.org/atomic" ) var ( // ErrInsufficientFunds is returned when the Sender is not able to pay for // the transaction being added irrespective of the other contents of the // pool. ErrInsufficientFunds = errors.New("insufficient funds") // ErrConflict is returned when the transaction being added is incompatible // with the contents of the memory pool (Sender doesn't have enough GAS // to pay for all transactions in the pool). ErrConflict = errors.New("conflicts: insufficient funds for all pooled tx") // ErrDup is returned when the transaction being added is already present // in the memory pool. ErrDup = errors.New("already in the memory pool") // ErrOOM is returned when the transaction just doesn't fit in the memory // pool because of its capacity constraints. ErrOOM = errors.New("out of memory") // ErrConflictsAttribute is returned when the transaction conflicts with other transactions // due to its (or theirs) Conflicts attributes. ErrConflictsAttribute = errors.New("conflicts with memory pool due to Conflicts attribute") // ErrOracleResponse is returned when the mempool already contains a transaction // with the same oracle response ID and higher network fee. ErrOracleResponse = errors.New("conflicts with memory pool due to OracleResponse attribute") ) // item represents a transaction in the the Memory pool. type item struct { txn *transaction.Transaction blockStamp uint32 data any } // items is a slice of an item. type items []item // utilityBalanceAndFees stores the sender's balance and overall fees of // the sender's transactions which are currently in the mempool. type utilityBalanceAndFees struct { balance uint256.Int feeSum uint256.Int } // Pool stores the unconfirmed transactions. type Pool struct { lock sync.RWMutex verifiedMap map[util.Uint256]*transaction.Transaction verifiedTxes items fees map[util.Uint160]utilityBalanceAndFees // conflicts is a map of the hashes of the transactions which are conflicting with the mempooled ones. conflicts map[util.Uint256][]util.Uint256 // oracleResp contains the ids of oracle responses for the tx in the pool. oracleResp map[uint64]util.Uint256 capacity int feePerByte int64 payerIndex int updateMetricsCb func(int) resendThreshold uint32 resendFunc func(*transaction.Transaction, any) // subscriptions for mempool events subscriptionsEnabled bool subscriptionsOn atomic.Bool stopCh chan struct{} events chan mempoolevent.Event subCh chan chan<- mempoolevent.Event // there are no other events in mempool except Event, so no need in generic subscribers type unsubCh chan chan<- mempoolevent.Event } func (p items) Len() int { return len(p) } func (p items) Swap(i, j int) { p[i], p[j] = p[j], p[i] } func (p items) Less(i, j int) bool { return p[i].CompareTo(p[j]) < 0 } // CompareTo returns the difference between two items. // difference < 0 implies p < otherP. // difference = 0 implies p = otherP. // difference > 0 implies p > otherP. func (p item) CompareTo(otherP item) int { pHigh := p.txn.HasAttribute(transaction.HighPriority) otherHigh := otherP.txn.HasAttribute(transaction.HighPriority) if pHigh && !otherHigh { return 1 } else if !pHigh && otherHigh { return -1 } // Fees sorted ascending. if ret := int(p.txn.FeePerByte() - otherP.txn.FeePerByte()); ret != 0 { return ret } return int(p.txn.NetworkFee - otherP.txn.NetworkFee) } // Count returns the total number of uncofirmed transactions. func (mp *Pool) Count() int { mp.lock.RLock() defer mp.lock.RUnlock() return mp.count() } // count is an internal unlocked version of Count. func (mp *Pool) count() int { return len(mp.verifiedTxes) } // ContainsKey checks if the transactions hash is in the Pool. func (mp *Pool) ContainsKey(hash util.Uint256) bool { mp.lock.RLock() defer mp.lock.RUnlock() return mp.containsKey(hash) } // containsKey is an internal unlocked version of ContainsKey. func (mp *Pool) containsKey(hash util.Uint256) bool { if _, ok := mp.verifiedMap[hash]; ok { return true } return false } // HasConflicts returns true if the transaction is already in the pool or in the Conflicts attributes // of the pooled transactions or has Conflicts attributes against the pooled transactions. func (mp *Pool) HasConflicts(t *transaction.Transaction, fee Feer) bool { mp.lock.RLock() defer mp.lock.RUnlock() if mp.containsKey(t.Hash()) { return true } // do not check sender's signature and fee if _, ok := mp.conflicts[t.Hash()]; ok { return true } for _, attr := range t.GetAttributes(transaction.ConflictsT) { if mp.containsKey(attr.Value.(*transaction.Conflicts).Hash) { return true } } return false } // tryAddSendersFee tries to add system fee and network fee to the total sender`s fee in the mempool // and returns false if both balance check is required and the sender does not have enough GAS to pay. func (mp *Pool) tryAddSendersFee(tx *transaction.Transaction, feer Feer, needCheck bool) bool { payer := tx.Signers[mp.payerIndex].Account senderFee, ok := mp.fees[payer] if !ok { _ = senderFee.balance.SetFromBig(feer.GetUtilityTokenBalance(payer)) mp.fees[payer] = senderFee } if needCheck { newFeeSum, err := checkBalance(tx, senderFee) if err != nil { return false } senderFee.feeSum = newFeeSum } else { senderFee.feeSum.AddUint64(&senderFee.feeSum, uint64(tx.SystemFee+tx.NetworkFee)) } mp.fees[payer] = senderFee return true } // checkBalance returns a new cumulative fee balance for the account or an error in // case the sender doesn't have enough GAS to pay for the transaction. func checkBalance(tx *transaction.Transaction, balance utilityBalanceAndFees) (uint256.Int, error) { var txFee uint256.Int txFee.SetUint64(uint64(tx.SystemFee + tx.NetworkFee)) if balance.balance.Cmp(&txFee) < 0 { return txFee, ErrInsufficientFunds } txFee.Add(&txFee, &balance.feeSum) if balance.balance.Cmp(&txFee) < 0 { return txFee, ErrConflict } return txFee, nil } // Add tries to add the given transaction to the Pool. func (mp *Pool) Add(t *transaction.Transaction, fee Feer, data ...any) error { var pItem = item{ txn: t, blockStamp: fee.BlockHeight(), } if data != nil { pItem.data = data[0] } mp.lock.Lock() if mp.containsKey(t.Hash()) { mp.lock.Unlock() return ErrDup } conflictsToBeRemoved, err := mp.checkTxConflicts(t, fee) if err != nil { mp.lock.Unlock() return err } if attrs := t.GetAttributes(transaction.OracleResponseT); len(attrs) != 0 { id := attrs[0].Value.(*transaction.OracleResponse).ID h, ok := mp.oracleResp[id] if ok { if mp.verifiedMap[h].NetworkFee >= t.NetworkFee { mp.lock.Unlock() return ErrOracleResponse } mp.removeInternal(h, fee) } mp.oracleResp[id] = t.Hash() } // Remove conflicting transactions. for _, conflictingTx := range conflictsToBeRemoved { mp.removeInternal(conflictingTx.Hash(), fee) } // Insert into a sorted array (from max to min, that could also be done // using sort.Sort(sort.Reverse()), but it incurs more overhead. Notice // also that we're searching for a position that is strictly more // prioritized than our new item because we do expect a lot of // transactions with the same priority and appending to the end of the // slice is always more efficient. n := sort.Search(len(mp.verifiedTxes), func(n int) bool { return pItem.CompareTo(mp.verifiedTxes[n]) > 0 }) // We've reached our capacity already. if len(mp.verifiedTxes) == mp.capacity { // Less prioritized than the least prioritized we already have, won't fit. if n == len(mp.verifiedTxes) { mp.lock.Unlock() return ErrOOM } // Ditch the last one. unlucky := mp.verifiedTxes[len(mp.verifiedTxes)-1] delete(mp.verifiedMap, unlucky.txn.Hash()) mp.removeConflictsOf(unlucky.txn) if attrs := unlucky.txn.GetAttributes(transaction.OracleResponseT); len(attrs) != 0 { delete(mp.oracleResp, attrs[0].Value.(*transaction.OracleResponse).ID) } mp.verifiedTxes[len(mp.verifiedTxes)-1] = pItem if mp.subscriptionsOn.Load() { mp.events <- mempoolevent.Event{ Type: mempoolevent.TransactionRemoved, Tx: unlucky.txn, Data: unlucky.data, } } } else { mp.verifiedTxes = append(mp.verifiedTxes, pItem) } if n != len(mp.verifiedTxes)-1 { copy(mp.verifiedTxes[n+1:], mp.verifiedTxes[n:]) mp.verifiedTxes[n] = pItem } mp.verifiedMap[t.Hash()] = t // Add conflicting hashes to the mp.conflicts list. for _, attr := range t.GetAttributes(transaction.ConflictsT) { hash := attr.Value.(*transaction.Conflicts).Hash mp.conflicts[hash] = append(mp.conflicts[hash], t.Hash()) } // we already checked balance in checkTxConflicts, so don't need to check again mp.tryAddSendersFee(pItem.txn, fee, false) if mp.updateMetricsCb != nil { mp.updateMetricsCb(len(mp.verifiedTxes)) } mp.lock.Unlock() if mp.subscriptionsOn.Load() { mp.events <- mempoolevent.Event{ Type: mempoolevent.TransactionAdded, Tx: pItem.txn, Data: pItem.data, } } return nil } // Remove removes an item from the mempool if it exists there (and does // nothing if it doesn't). func (mp *Pool) Remove(hash util.Uint256, feer Feer) { mp.lock.Lock() mp.removeInternal(hash, feer) mp.lock.Unlock() } // removeInternal is an internal unlocked representation of Remove. func (mp *Pool) removeInternal(hash util.Uint256, feer Feer) { if tx, ok := mp.verifiedMap[hash]; ok { var num int delete(mp.verifiedMap, hash) for num = range mp.verifiedTxes { if hash.Equals(mp.verifiedTxes[num].txn.Hash()) { break } } itm := mp.verifiedTxes[num] if num < len(mp.verifiedTxes)-1 { mp.verifiedTxes = append(mp.verifiedTxes[:num], mp.verifiedTxes[num+1:]...) } else if num == len(mp.verifiedTxes)-1 { mp.verifiedTxes = mp.verifiedTxes[:num] } payer := itm.txn.Signers[mp.payerIndex].Account senderFee := mp.fees[payer] senderFee.feeSum.SubUint64(&senderFee.feeSum, uint64(tx.SystemFee+tx.NetworkFee)) mp.fees[payer] = senderFee // remove all conflicting hashes from mp.conflicts list mp.removeConflictsOf(tx) if attrs := tx.GetAttributes(transaction.OracleResponseT); len(attrs) != 0 { delete(mp.oracleResp, attrs[0].Value.(*transaction.OracleResponse).ID) } if mp.subscriptionsOn.Load() { mp.events <- mempoolevent.Event{ Type: mempoolevent.TransactionRemoved, Tx: itm.txn, Data: itm.data, } } } if mp.updateMetricsCb != nil { mp.updateMetricsCb(len(mp.verifiedTxes)) } } // RemoveStale filters verified transactions through the given function keeping // only the transactions for which it returns true result. It's used to quickly // drop a part of the mempool that is now invalid after the block acceptance. func (mp *Pool) RemoveStale(isOK func(*transaction.Transaction) bool, feer Feer) { mp.lock.Lock() policyChanged := mp.loadPolicy(feer) // We can reuse already allocated slice // because items are iterated one-by-one in increasing order. newVerifiedTxes := mp.verifiedTxes[:0] mp.fees = make(map[util.Uint160]utilityBalanceAndFees) // it'd be nice to reuse existing map, but we can't easily clear it mp.conflicts = make(map[util.Uint256][]util.Uint256) height := feer.BlockHeight() var ( staleItems []item ) for _, itm := range mp.verifiedTxes { if isOK(itm.txn) && mp.checkPolicy(itm.txn, policyChanged) && mp.tryAddSendersFee(itm.txn, feer, true) { newVerifiedTxes = append(newVerifiedTxes, itm) for _, attr := range itm.txn.GetAttributes(transaction.ConflictsT) { hash := attr.Value.(*transaction.Conflicts).Hash mp.conflicts[hash] = append(mp.conflicts[hash], itm.txn.Hash()) } if mp.resendThreshold != 0 { // item is resent at resendThreshold, 2*resendThreshold, 4*resendThreshold ... // so quotient must be a power of two. diff := (height - itm.blockStamp) if diff%mp.resendThreshold == 0 && bits.OnesCount32(diff/mp.resendThreshold) == 1 { staleItems = append(staleItems, itm) } } } else { delete(mp.verifiedMap, itm.txn.Hash()) if attrs := itm.txn.GetAttributes(transaction.OracleResponseT); len(attrs) != 0 { delete(mp.oracleResp, attrs[0].Value.(*transaction.OracleResponse).ID) } if mp.subscriptionsOn.Load() { mp.events <- mempoolevent.Event{ Type: mempoolevent.TransactionRemoved, Tx: itm.txn, Data: itm.data, } } } } if len(staleItems) != 0 { go mp.resendStaleItems(staleItems) } mp.verifiedTxes = newVerifiedTxes mp.lock.Unlock() } // loadPolicy updates feePerByte field and returns whether the policy has been // changed. func (mp *Pool) loadPolicy(feer Feer) bool { newFeePerByte := feer.FeePerByte() if newFeePerByte > mp.feePerByte { mp.feePerByte = newFeePerByte return true } return false } // checkPolicy checks whether the transaction fits the policy. func (mp *Pool) checkPolicy(tx *transaction.Transaction, policyChanged bool) bool { if !policyChanged || tx.FeePerByte() >= mp.feePerByte { return true } return false } // New returns a new Pool struct. func New(capacity int, payerIndex int, enableSubscriptions bool, updateMetricsCb func(int)) *Pool { mp := &Pool{ verifiedMap: make(map[util.Uint256]*transaction.Transaction, capacity), verifiedTxes: make([]item, 0, capacity), capacity: capacity, payerIndex: payerIndex, fees: make(map[util.Uint160]utilityBalanceAndFees), conflicts: make(map[util.Uint256][]util.Uint256), oracleResp: make(map[uint64]util.Uint256), subscriptionsEnabled: enableSubscriptions, stopCh: make(chan struct{}), events: make(chan mempoolevent.Event), subCh: make(chan chan<- mempoolevent.Event), unsubCh: make(chan chan<- mempoolevent.Event), updateMetricsCb: updateMetricsCb, } mp.subscriptionsOn.Store(false) return mp } // SetResendThreshold sets a threshold after which the transaction will be considered stale // and returned for retransmission by `GetStaleTransactions`. func (mp *Pool) SetResendThreshold(h uint32, f func(*transaction.Transaction, any)) { mp.lock.Lock() defer mp.lock.Unlock() mp.resendThreshold = h mp.resendFunc = f } func (mp *Pool) resendStaleItems(items []item) { for i := range items { mp.resendFunc(items[i].txn, items[i].data) } } // TryGetValue returns a transaction and its fee if it exists in the memory pool. func (mp *Pool) TryGetValue(hash util.Uint256) (*transaction.Transaction, bool) { mp.lock.RLock() defer mp.lock.RUnlock() if tx, ok := mp.verifiedMap[hash]; ok { return tx, ok } return nil, false } // TryGetData returns data associated with the specified transaction if it exists in the memory pool. func (mp *Pool) TryGetData(hash util.Uint256) (any, bool) { mp.lock.RLock() defer mp.lock.RUnlock() if tx, ok := mp.verifiedMap[hash]; ok { itm := item{txn: tx} n := sort.Search(len(mp.verifiedTxes), func(n int) bool { return itm.CompareTo(mp.verifiedTxes[n]) >= 0 }) if n < len(mp.verifiedTxes) { for i := n; i < len(mp.verifiedTxes); i++ { // items may have equal priority, so `n` is the left bound of the items which are as prioritized as the desired `itm`. if mp.verifiedTxes[i].txn.Hash() == hash { return mp.verifiedTxes[i].data, ok } if itm.CompareTo(mp.verifiedTxes[i]) != 0 { break } } } } return nil, false } // GetVerifiedTransactions returns a slice of transactions with their fees. func (mp *Pool) GetVerifiedTransactions() []*transaction.Transaction { mp.lock.RLock() defer mp.lock.RUnlock() var t = make([]*transaction.Transaction, len(mp.verifiedTxes)) for i := range mp.verifiedTxes { t[i] = mp.verifiedTxes[i].txn } return t } // checkTxConflicts is an internal unprotected version of Verify. It takes into // consideration conflicting transactions which are about to be removed from mempool. func (mp *Pool) checkTxConflicts(tx *transaction.Transaction, fee Feer) ([]*transaction.Transaction, error) { payer := tx.Signers[mp.payerIndex].Account actualSenderFee, ok := mp.fees[payer] if !ok { actualSenderFee.balance.SetFromBig(fee.GetUtilityTokenBalance(payer)) } var expectedSenderFee utilityBalanceAndFees // Check Conflicts attributes. var ( conflictsToBeRemoved []*transaction.Transaction conflictingFee int64 ) // Step 1: check if `tx` was in attributes of mempooled transactions. if conflictingHashes, ok := mp.conflicts[tx.Hash()]; ok { for _, hash := range conflictingHashes { existingTx := mp.verifiedMap[hash] if existingTx.HasSigner(payer) { conflictingFee += existingTx.NetworkFee } conflictsToBeRemoved = append(conflictsToBeRemoved, existingTx) } } // Step 2: check if mempooled transactions were in `tx`'s attributes. conflictsAttrs := tx.GetAttributes(transaction.ConflictsT) if len(conflictsAttrs) != 0 { txSigners := make(map[util.Uint160]struct{}, len(tx.Signers)) for _, s := range tx.Signers { txSigners[s.Account] = struct{}{} } for _, attr := range conflictsAttrs { hash := attr.Value.(*transaction.Conflicts).Hash existingTx, ok := mp.verifiedMap[hash] if !ok { continue } var signerOK bool for _, s := range existingTx.Signers { if _, ok := txSigners[s.Account]; ok { signerOK = true break } } if !signerOK { return nil, fmt.Errorf("%w: not signed by a signer of conflicting transaction %s", ErrConflictsAttribute, existingTx.Hash().StringBE()) } conflictingFee += existingTx.NetworkFee conflictsToBeRemoved = append(conflictsToBeRemoved, existingTx) } } if conflictingFee != 0 && tx.NetworkFee <= conflictingFee { return nil, fmt.Errorf("%w: conflicting transactions have bigger or equal network fee: %d vs %d", ErrConflictsAttribute, tx.NetworkFee, conflictingFee) } // Step 3: take into account sender's conflicting transactions before balance check. expectedSenderFee = actualSenderFee for _, conflictingTx := range conflictsToBeRemoved { if conflictingTx.Signers[mp.payerIndex].Account.Equals(payer) { expectedSenderFee.feeSum.SubUint64(&expectedSenderFee.feeSum, uint64(conflictingTx.SystemFee+conflictingTx.NetworkFee)) } } _, err := checkBalance(tx, expectedSenderFee) return conflictsToBeRemoved, err } // Verify checks if the Sender of the tx is able to pay for it (and all the other // transactions in the pool). If yes, the transaction tx is a valid // transaction and the function returns true. If no, the transaction tx is // considered to be invalid, the function returns false. func (mp *Pool) Verify(tx *transaction.Transaction, feer Feer) bool { mp.lock.RLock() defer mp.lock.RUnlock() _, err := mp.checkTxConflicts(tx, feer) return err == nil } // removeConflictsOf removes the hash of the given transaction from the conflicts list // for each Conflicts attribute. func (mp *Pool) removeConflictsOf(tx *transaction.Transaction) { // remove all conflicting hashes from mp.conflicts list for _, attr := range tx.GetAttributes(transaction.ConflictsT) { conflictsHash := attr.Value.(*transaction.Conflicts).Hash if len(mp.conflicts[conflictsHash]) == 1 { delete(mp.conflicts, conflictsHash) continue } for i, existingHash := range mp.conflicts[conflictsHash] { if existingHash == tx.Hash() { // tx.Hash can occur in the conflicting hashes array only once, because we can't add the same transaction to the mempol twice mp.conflicts[conflictsHash] = append(mp.conflicts[conflictsHash][:i], mp.conflicts[conflictsHash][i+1:]...) break } } } } // IterateVerifiedTransactions iterates through verified transactions and invokes // function `cont`. Iterations continue while the function `cont` returns true. // Function `cont` is executed within a read-locked memory pool, // thus IterateVerifiedTransactions will block any write mempool operation, // use it with care. Do not modify transaction or data via `cont`. func (mp *Pool) IterateVerifiedTransactions(cont func(tx *transaction.Transaction, data any) bool) { mp.lock.RLock() defer mp.lock.RUnlock() for i := range mp.verifiedTxes { if !cont(mp.verifiedTxes[i].txn, mp.verifiedTxes[i].data) { return } } }