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//! Mempool transaction storage.
//!
//! The main struct [`Storage`] holds verified and rejected transactions.
//! [`Storage`] is effectively the data structure of the mempool. Convenient methods to
//! manage it are included.
//!
//! [`Storage`] does not expose a service so it can only be used by other code directly.
//! Only code inside the [`crate::components::mempool`] module has access to it.
use std::{
collections::{HashMap, HashSet},
mem::size_of,
sync::Arc,
time::Duration,
};
use thiserror::Error;
use zebra_chain::transaction::{
self, Hash, Transaction, UnminedTx, UnminedTxId, VerifiedUnminedTx,
};
use self::{eviction_list::EvictionList, verified_set::VerifiedSet};
use super::{config, downloads::TransactionDownloadVerifyError, MempoolError};
#[cfg(any(test, feature = "proptest-impl"))]
use proptest_derive::Arbitrary;
#[cfg(test)]
pub mod tests;
mod eviction_list;
mod verified_set;
/// The size limit for mempool transaction rejection lists per [ZIP-401].
///
/// > The size of RecentlyEvicted SHOULD never exceed `eviction_memory_entries`
/// > entries, which is the constant 40000.
///
/// We use the specified value for all lists for consistency.
///
/// [ZIP-401]: https://zips.z.cash/zip-0401#specification
pub(crate) const MAX_EVICTION_MEMORY_ENTRIES: usize = 40_000;
/// Transactions rejected based on transaction authorizing data (scripts, proofs, signatures),
/// or lock times. These rejections are only valid for the current tip.
///
/// Each committed block clears these rejections, because new blocks can supply missing inputs.
#[derive(Error, Clone, Debug, PartialEq, Eq)]
#[cfg_attr(any(test, feature = "proptest-impl"), derive(Arbitrary))]
#[allow(dead_code)]
pub enum ExactTipRejectionError {
#[error("transaction did not pass consensus validation")]
FailedVerification(#[from] zebra_consensus::error::TransactionError),
}
/// Transactions rejected based only on their effects (spends, outputs, transaction header).
/// These rejections are only valid for the current tip.
///
/// Each committed block clears these rejections, because new blocks can evict other transactions.
#[derive(Error, Clone, Debug, PartialEq, Eq)]
#[cfg_attr(any(test, feature = "proptest-impl"), derive(Arbitrary))]
#[allow(dead_code)]
pub enum SameEffectsTipRejectionError {
#[error(
"transaction rejected because another transaction in the mempool has already spent some of \
its inputs"
)]
SpendConflict,
}
/// Transactions rejected based only on their effects (spends, outputs, transaction header).
/// These rejections are valid while the current chain continues to grow.
///
/// Rollbacks and network upgrades clear these rejections, because they can lower the tip height,
/// or change the consensus rules.
#[derive(Error, Clone, Debug, PartialEq, Eq, Hash)]
#[cfg_attr(any(test, feature = "proptest-impl"), derive(Arbitrary))]
#[allow(dead_code)]
pub enum SameEffectsChainRejectionError {
#[error("best chain tip has reached transaction expiry height")]
Expired,
#[error("transaction inputs were spent, or nullifiers were revealed, in the best chain")]
DuplicateSpend,
#[error("transaction was committed to the best chain")]
Mined,
/// Otherwise valid transaction removed from mempool due to [ZIP-401] random
/// eviction.
///
/// Consensus rule:
/// > The txid (rather than the wtxid ...) is used even for version 5 transactions
///
/// [ZIP-401]: https://zips.z.cash/zip-0401#specification
#[error("transaction evicted from the mempool due to ZIP-401 denial of service limits")]
RandomlyEvicted,
}
/// Storage error that combines all other specific error types.
#[derive(Error, Clone, Debug, PartialEq, Eq)]
#[cfg_attr(any(test, feature = "proptest-impl"), derive(Arbitrary))]
#[allow(dead_code)]
pub enum RejectionError {
#[error(transparent)]
ExactTip(#[from] ExactTipRejectionError),
#[error(transparent)]
SameEffectsTip(#[from] SameEffectsTipRejectionError),
#[error(transparent)]
SameEffectsChain(#[from] SameEffectsChainRejectionError),
}
/// Hold mempool verified and rejected mempool transactions.
pub struct Storage {
/// The set of verified transactions in the mempool.
verified: VerifiedSet,
/// The set of transactions rejected due to bad authorizations, or for other
/// reasons, and their rejection reasons. These rejections only apply to the
/// current tip.
///
/// Only transactions with the exact [`UnminedTxId`] are invalid.
tip_rejected_exact: HashMap<UnminedTxId, ExactTipRejectionError>,
/// A set of transactions rejected for their effects, and their rejection
/// reasons. These rejections only apply to the current tip.
///
/// Any transaction with the same [`transaction::Hash`] is invalid.
tip_rejected_same_effects: HashMap<transaction::Hash, SameEffectsTipRejectionError>,
/// Sets of transactions rejected for their effects, keyed by rejection reason.
/// These rejections apply until a rollback or network upgrade.
///
/// Any transaction with the same [`transaction::Hash`] is invalid.
///
/// An [`EvictionList`] is used for both randomly evicted and expired
/// transactions, even if it is only needed for the evicted ones. This was
/// done just to simplify the existing code; there is no harm in having a
/// timeout for expired transactions too since re-checking expired
/// transactions is cheap.
// If this code is ever refactored and the lists are split in different
// fields, then we can use an `EvictionList` just for the evicted list.
chain_rejected_same_effects: HashMap<SameEffectsChainRejectionError, EvictionList>,
/// The mempool transaction eviction age limit.
/// Same as [`config::Config::eviction_memory_time`].
eviction_memory_time: Duration,
/// Max total cost of the verified mempool set, beyond which transactions
/// are evicted to make room.
tx_cost_limit: u64,
}
impl Drop for Storage {
fn drop(&mut self) {
self.clear();
}
}
impl Storage {
#[allow(clippy::field_reassign_with_default)]
pub(crate) fn new(config: &config::Config) -> Self {
Self {
tx_cost_limit: config.tx_cost_limit,
eviction_memory_time: config.eviction_memory_time,
verified: Default::default(),
tip_rejected_exact: Default::default(),
tip_rejected_same_effects: Default::default(),
chain_rejected_same_effects: Default::default(),
}
}
/// Insert a [`VerifiedUnminedTx`] into the mempool, caching any rejections.
///
/// Returns an error if the mempool's verified transactions or rejection caches
/// prevent this transaction from being inserted.
/// These errors should not be propagated to peers, because the transactions are valid.
///
/// If inserting this transaction evicts other transactions, they will be tracked
/// as [`SameEffectsChainRejectionError::RandomlyEvicted`].
#[allow(clippy::unwrap_in_result)]
pub fn insert(&mut self, tx: VerifiedUnminedTx) -> Result<UnminedTxId, MempoolError> {
// # Security
//
// This method must call `reject`, rather than modifying the rejection lists directly.
let tx_id = tx.transaction.id;
// First, check if we have a cached rejection for this transaction.
if let Some(error) = self.rejection_error(&tx_id) {
tracing::trace!(
?tx_id,
?error,
stored_transaction_count = ?self.verified.transaction_count(),
"returning cached error for transaction",
);
return Err(error);
}
// If `tx` is already in the mempool, we don't change anything.
//
// Security: transactions must not get refreshed by new queries,
// because that allows malicious peers to keep transactions live forever.
if self.verified.contains(&tx_id) {
tracing::trace!(
?tx_id,
stored_transaction_count = ?self.verified.transaction_count(),
"returning InMempool error for transaction that is already in the mempool",
);
return Err(MempoolError::InMempool);
}
// Then, we try to insert into the pool. If this fails the transaction is rejected.
let mut result = Ok(tx_id);
if let Err(rejection_error) = self.verified.insert(tx) {
tracing::debug!(
?tx_id,
?rejection_error,
stored_transaction_count = ?self.verified.transaction_count(),
"insertion error for transaction",
);
// We could return here, but we still want to check the mempool size
self.reject(tx_id, rejection_error.clone().into());
result = Err(rejection_error.into());
}
// Once inserted, we evict transactions over the pool size limit per [ZIP-401];
//
// > On receiving a transaction: (...)
// > Calculate its cost. If the total cost of transactions in the mempool including this
// > one would `exceed mempooltxcostlimit`, then the node MUST repeatedly call
// > EvictTransaction (with the new transaction included as a candidate to evict) until the
// > total cost does not exceed `mempooltxcostlimit`.
//
// 'EvictTransaction' is equivalent to [`VerifiedSet::evict_one()`] in
// our implementation.
//
// [ZIP-401]: https://zips.z.cash/zip-0401
while self.verified.total_cost() > self.tx_cost_limit {
// > EvictTransaction MUST do the following:
// > Select a random transaction to evict, with probability in direct proportion to
// > eviction weight. (...) Remove it from the mempool.
let victim_tx = self
.verified
.evict_one()
.expect("mempool is empty, but was expected to be full");
// > Add the txid and the current time to RecentlyEvicted, dropping the oldest entry in
// > RecentlyEvicted if necessary to keep it to at most `eviction_memory_entries entries`.
self.reject(
victim_tx.transaction.id,
SameEffectsChainRejectionError::RandomlyEvicted.into(),
);
// If this transaction gets evicted, set its result to the same error
// (we could return here, but we still want to check the mempool size)
if victim_tx.transaction.id == tx_id {
result = Err(SameEffectsChainRejectionError::RandomlyEvicted.into());
}
}
result
}
/// Remove transactions from the mempool via exact [`UnminedTxId`].
///
/// For v5 transactions, transactions are matched by WTXID, using both the:
/// - non-malleable transaction ID, and
/// - authorizing data hash.
///
/// This matches the exact transaction, with identical blockchain effects, signatures, and proofs.
///
/// Returns the number of transactions which were removed.
///
/// Removes from the 'verified' set, if present.
/// Maintains the order in which the other unmined transactions have been inserted into the mempool.
///
/// Does not add or remove from the 'rejected' tracking set.
#[allow(dead_code)]
pub fn remove_exact(&mut self, exact_wtxids: &HashSet<UnminedTxId>) -> usize {
self.verified
.remove_all_that(|tx| exact_wtxids.contains(&tx.transaction.id))
}
/// Reject and remove transactions from the mempool via non-malleable [`transaction::Hash`].
/// - For v5 transactions, transactions are matched by TXID,
/// using only the non-malleable transaction ID.
/// This matches any transaction with the same effect on the blockchain state,
/// even if its signatures and proofs are different.
/// - Returns the number of transactions which were removed.
/// - Removes from the 'verified' set, if present.
/// Maintains the order in which the other unmined transactions have been inserted into the mempool.
///
/// Reject and remove transactions from the mempool that contain any spent outpoints or revealed
/// nullifiers from the passed in `transactions`.
///
/// Returns the number of transactions that were removed.
pub fn reject_and_remove_same_effects(
&mut self,
mined_ids: &HashSet<transaction::Hash>,
transactions: Vec<Arc<Transaction>>,
) -> usize {
let num_removed_mined = self
.verified
.remove_all_that(|tx| mined_ids.contains(&tx.transaction.id.mined_id()));
let spent_outpoints: HashSet<_> = transactions
.iter()
.flat_map(|tx| tx.spent_outpoints())
.collect();
let sprout_nullifiers: HashSet<_> = transactions
.iter()
.flat_map(|transaction| transaction.sprout_nullifiers())
.collect();
let sapling_nullifiers: HashSet<_> = transactions
.iter()
.flat_map(|transaction| transaction.sapling_nullifiers())
.collect();
let orchard_nullifiers: HashSet<_> = transactions
.iter()
.flat_map(|transaction| transaction.orchard_nullifiers())
.collect();
let duplicate_spend_ids: HashSet<_> = self
.verified
.transactions()
.filter_map(|tx| {
(tx.transaction
.spent_outpoints()
.any(|outpoint| spent_outpoints.contains(&outpoint))
|| tx
.transaction
.sprout_nullifiers()
.any(|nullifier| sprout_nullifiers.contains(nullifier))
|| tx
.transaction
.sapling_nullifiers()
.any(|nullifier| sapling_nullifiers.contains(nullifier))
|| tx
.transaction
.orchard_nullifiers()
.any(|nullifier| orchard_nullifiers.contains(nullifier)))
.then_some(tx.id)
})
.collect();
let num_removed_duplicate_spend = self
.verified
.remove_all_that(|tx| duplicate_spend_ids.contains(&tx.transaction.id));
for &mined_id in mined_ids {
self.reject(
// the reject and rejection_error fns that store and check `SameEffectsChainRejectionError`s
// only use the mined id, so using `Legacy` ids will apply to v5 transactions as well.
UnminedTxId::Legacy(mined_id),
SameEffectsChainRejectionError::Mined.into(),
);
}
for duplicate_spend_id in duplicate_spend_ids {
self.reject(
duplicate_spend_id,
SameEffectsChainRejectionError::DuplicateSpend.into(),
);
}
num_removed_mined + num_removed_duplicate_spend
}
/// Clears the whole mempool storage.
#[allow(dead_code)]
pub fn clear(&mut self) {
self.verified.clear();
self.tip_rejected_exact.clear();
self.tip_rejected_same_effects.clear();
self.chain_rejected_same_effects.clear();
self.update_rejected_metrics();
}
/// Clears rejections that only apply to the current tip.
pub fn clear_tip_rejections(&mut self) {
self.tip_rejected_exact.clear();
self.tip_rejected_same_effects.clear();
self.update_rejected_metrics();
}
/// Clears rejections that only apply to the current tip.
///
/// # Security
///
/// This method must be called at the end of every method that adds rejections.
/// Otherwise, peers could make our reject lists use a lot of RAM.
fn limit_rejection_list_memory(&mut self) {
// These lists are an optimisation - it's ok to totally clear them as needed.
if self.tip_rejected_exact.len() > MAX_EVICTION_MEMORY_ENTRIES {
self.tip_rejected_exact.clear();
}
if self.tip_rejected_same_effects.len() > MAX_EVICTION_MEMORY_ENTRIES {
self.tip_rejected_same_effects.clear();
}
// `chain_rejected_same_effects` limits its size by itself
self.update_rejected_metrics();
}
/// Returns the set of [`UnminedTxId`]s in the mempool.
pub fn tx_ids(&self) -> impl Iterator<Item = UnminedTxId> + '_ {
self.verified.transactions().map(|tx| tx.id)
}
/// Returns an iterator over the [`UnminedTx`]s in the mempool.
//
// TODO: make the transactions() method return VerifiedUnminedTx,
// and remove the full_transactions() method
pub fn transactions(&self) -> impl Iterator<Item = &UnminedTx> {
self.verified.transactions()
}
/// Returns an iterator over the [`VerifiedUnminedTx`] in the set.
///
/// Each [`VerifiedUnminedTx`] contains an [`UnminedTx`],
/// and adds extra fields from the transaction verifier result.
#[allow(dead_code)]
pub fn full_transactions(&self) -> impl Iterator<Item = &VerifiedUnminedTx> + '_ {
self.verified.full_transactions()
}
/// Returns the number of transactions in the mempool.
#[allow(dead_code)]
pub fn transaction_count(&self) -> usize {
self.verified.transaction_count()
}
/// Returns the cost of the transactions in the mempool, according to ZIP-401.
#[allow(dead_code)]
pub fn total_cost(&self) -> u64 {
self.verified.total_cost()
}
/// Returns the total serialized size of the verified transactions in the set.
///
/// See [`VerifiedSet::total_serialized_size()`] for details.
pub fn total_serialized_size(&self) -> usize {
self.verified.total_serialized_size()
}
/// Returns the set of [`UnminedTx`]es with exactly matching `tx_ids` in the
/// mempool.
///
/// This matches the exact transaction, with identical blockchain effects,
/// signatures, and proofs.
pub fn transactions_exact(
&self,
tx_ids: HashSet<UnminedTxId>,
) -> impl Iterator<Item = &UnminedTx> {
self.verified
.transactions()
.filter(move |tx| tx_ids.contains(&tx.id))
}
/// Returns the set of [`UnminedTx`]es with matching [`transaction::Hash`]es
/// in the mempool.
///
/// This matches transactions with the same effects, regardless of
/// [`transaction::AuthDigest`].
pub fn transactions_same_effects(
&self,
tx_ids: HashSet<Hash>,
) -> impl Iterator<Item = &UnminedTx> {
self.verified
.transactions()
.filter(move |tx| tx_ids.contains(&tx.id.mined_id()))
}
/// Returns `true` if a transaction exactly matching an [`UnminedTxId`] is in
/// the mempool.
///
/// This matches the exact transaction, with identical blockchain effects,
/// signatures, and proofs.
pub fn contains_transaction_exact(&self, txid: &UnminedTxId) -> bool {
self.verified.transactions().any(|tx| &tx.id == txid)
}
/// Returns the number of rejected [`UnminedTxId`]s or [`transaction::Hash`]es.
///
/// Transactions on multiple rejected lists are counted multiple times.
#[allow(dead_code)]
pub fn rejected_transaction_count(&mut self) -> usize {
self.tip_rejected_exact.len()
+ self.tip_rejected_same_effects.len()
+ self
.chain_rejected_same_effects
.iter_mut()
.map(|(_, map)| map.len())
.sum::<usize>()
}
/// Add a transaction to the rejected list for the given reason.
pub fn reject(&mut self, txid: UnminedTxId, reason: RejectionError) {
match reason {
RejectionError::ExactTip(e) => {
self.tip_rejected_exact.insert(txid, e);
}
RejectionError::SameEffectsTip(e) => {
self.tip_rejected_same_effects.insert(txid.mined_id(), e);
}
RejectionError::SameEffectsChain(e) => {
let eviction_memory_time = self.eviction_memory_time;
self.chain_rejected_same_effects
.entry(e)
.or_insert_with(|| {
EvictionList::new(MAX_EVICTION_MEMORY_ENTRIES, eviction_memory_time)
})
.insert(txid.mined_id());
}
}
self.limit_rejection_list_memory();
}
/// Returns the rejection error if a transaction matching an [`UnminedTxId`]
/// is in any mempool rejected list.
///
/// This matches transactions based on each rejection list's matching rule.
///
/// Returns an arbitrary error if the transaction is in multiple lists.
pub fn rejection_error(&self, txid: &UnminedTxId) -> Option<MempoolError> {
if let Some(error) = self.tip_rejected_exact.get(txid) {
return Some(error.clone().into());
}
if let Some(error) = self.tip_rejected_same_effects.get(&txid.mined_id()) {
return Some(error.clone().into());
}
for (error, set) in self.chain_rejected_same_effects.iter() {
if set.contains_key(&txid.mined_id()) {
return Some(error.clone().into());
}
}
None
}
/// Returns the set of [`UnminedTxId`]s matching `tx_ids` in the rejected list.
///
/// This matches transactions based on each rejection list's matching rule.
pub fn rejected_transactions(
&self,
tx_ids: HashSet<UnminedTxId>,
) -> impl Iterator<Item = UnminedTxId> + '_ {
tx_ids
.into_iter()
.filter(move |txid| self.contains_rejected(txid))
}
/// Returns `true` if a transaction matching the supplied [`UnminedTxId`] is in
/// the mempool rejected list.
///
/// This matches transactions based on each rejection list's matching rule.
pub fn contains_rejected(&self, txid: &UnminedTxId) -> bool {
self.rejection_error(txid).is_some()
}
/// Add a transaction that failed download and verification to the rejected list
/// if needed, depending on the reason for the failure.
pub fn reject_if_needed(&mut self, txid: UnminedTxId, e: TransactionDownloadVerifyError) {
match e {
// Rejecting a transaction already in state would speed up further
// download attempts without checking the state. However it would
// make the reject list grow forever.
//
// TODO: revisit after reviewing the rejected list cleanup criteria?
// TODO: if we decide to reject it, then we need to pass the block hash
// to State::Confirmed. This would require the zs::Response::Transaction
// to include the hash, which would need to be implemented.
TransactionDownloadVerifyError::InState |
// An unknown error in the state service, better do nothing
TransactionDownloadVerifyError::StateError(_) |
// If download failed, do nothing; the crawler will end up trying to
// download it again.
TransactionDownloadVerifyError::DownloadFailed(_) |
// If it was cancelled then a block was mined, or there was a network
// upgrade, etc. No reason to reject it.
TransactionDownloadVerifyError::Cancelled => {}
// Consensus verification failed. Reject transaction to avoid
// having to download and verify it again just for it to fail again.
TransactionDownloadVerifyError::Invalid(e) => {
self.reject(txid, ExactTipRejectionError::FailedVerification(e).into())
}
}
}
/// Remove transactions from the mempool if they have not been mined after a
/// specified height, per [ZIP-203].
///
/// > Transactions will have a new field, nExpiryHeight, which will set the
/// > block height after which transactions will be removed from the mempool
/// > if they have not been mined.
///
///
/// [ZIP-203]: https://zips.z.cash/zip-0203#specification
pub fn remove_expired_transactions(
&mut self,
tip_height: zebra_chain::block::Height,
) -> HashSet<UnminedTxId> {
let mut txid_set = HashSet::new();
// we need a separate set, since reject() takes the original unmined ID,
// then extracts the mined ID out of it
let mut unmined_id_set = HashSet::new();
for t in self.transactions() {
if let Some(expiry_height) = t.transaction.expiry_height() {
if tip_height >= expiry_height {
txid_set.insert(t.id.mined_id());
unmined_id_set.insert(t.id);
}
}
}
// expiry height is effecting data, so we match by non-malleable TXID
self.verified
.remove_all_that(|tx| txid_set.contains(&tx.transaction.id.mined_id()));
// also reject it
for id in unmined_id_set.iter() {
self.reject(*id, SameEffectsChainRejectionError::Expired.into());
}
unmined_id_set
}
/// Check if transaction should be downloaded and/or verified.
///
/// If it is already in the mempool (or in its rejected list)
/// then it shouldn't be downloaded/verified.
pub fn should_download_or_verify(&mut self, txid: UnminedTxId) -> Result<(), MempoolError> {
// Check if the transaction is already in the mempool.
if self.contains_transaction_exact(&txid) {
return Err(MempoolError::InMempool);
}
if let Some(error) = self.rejection_error(&txid) {
return Err(error);
}
Ok(())
}
/// Update metrics related to the rejected lists.
///
/// Must be called every time the rejected lists change.
fn update_rejected_metrics(&mut self) {
metrics::gauge!("mempool.rejected.transaction.ids",)
.set(self.rejected_transaction_count() as f64);
// This is just an approximation.
// TODO: make it more accurate #2869
let item_size = size_of::<(transaction::Hash, SameEffectsTipRejectionError)>();
metrics::gauge!("mempool.rejected.transaction.ids.bytes",)
.set((self.rejected_transaction_count() * item_size) as f64);
}
}