542 lines
20 KiB
Rust
542 lines
20 KiB
Rust
//! Zebra mempool.
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//!
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//! A zebrad application component that manages the active collection, reception,
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//! gossip, verification, in-memory storage, eviction, and rejection of unmined Zcash
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//! transactions (those that have not been confirmed in a mined block on the
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//! blockchain).
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//!
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//! Major parts of the mempool include:
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//! * [Mempool Service][`Mempool`]
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//! * activates when the syncer is near the chain tip
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//! * spawns [download and verify tasks][`downloads::Downloads`] for each crawled or gossiped transaction
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//! * handles in-memory [storage][`storage::Storage`] of unmined transactions
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//! * [Crawler][`crawler::Crawler`]
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//! * runs in the background to periodically poll peers for fresh unmined transactions
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//! * [Queue Checker][`queue_checker::QueueChecker`]
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//! * runs in the background, polling the mempool to store newly verified transactions
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//! * [Transaction Gossip Task][`gossip::gossip_mempool_transaction_id`]
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//! * runs in the background and gossips newly added mempool transactions
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//! to peers
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use std::{
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collections::HashSet,
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future::Future,
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iter,
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pin::Pin,
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task::{Context, Poll},
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};
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use futures::{future::FutureExt, stream::Stream};
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use tokio::sync::watch;
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use tower::{buffer::Buffer, timeout::Timeout, util::BoxService, Service};
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use zebra_chain::{
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block::Height,
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chain_tip::ChainTip,
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transaction::{UnminedTx, UnminedTxId},
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};
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use zebra_consensus::{error::TransactionError, transaction};
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use zebra_network as zn;
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use zebra_state as zs;
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use zebra_state::{ChainTipChange, TipAction};
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use crate::components::sync::SyncStatus;
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pub mod config;
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mod crawler;
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pub mod downloads;
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mod error;
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pub mod gossip;
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mod queue_checker;
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mod storage;
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#[cfg(test)]
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mod tests;
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pub use crate::BoxError;
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pub use config::Config;
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pub use crawler::Crawler;
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pub use error::MempoolError;
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pub use gossip::gossip_mempool_transaction_id;
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pub use queue_checker::QueueChecker;
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pub use storage::{
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ExactTipRejectionError, SameEffectsChainRejectionError, SameEffectsTipRejectionError,
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};
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#[cfg(test)]
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pub use storage::tests::unmined_transactions_in_blocks;
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use downloads::{
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Downloads as TxDownloads, Gossip, TRANSACTION_DOWNLOAD_TIMEOUT, TRANSACTION_VERIFY_TIMEOUT,
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};
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type Outbound = Buffer<BoxService<zn::Request, zn::Response, zn::BoxError>, zn::Request>;
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type State = Buffer<BoxService<zs::Request, zs::Response, zs::BoxError>, zs::Request>;
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type TxVerifier = Buffer<
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BoxService<transaction::Request, transaction::Response, TransactionError>,
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transaction::Request,
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>;
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type InboundTxDownloads = TxDownloads<Timeout<Outbound>, Timeout<TxVerifier>, State>;
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/// A mempool service request.
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///
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/// Requests can query the current set of mempool transactions,
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/// queue transactions to be downloaded and verified, or
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/// run the mempool to check for newly verified transactions.
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///
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/// Requests can't modify the mempool directly,
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/// because all mempool transactions must be verified.
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#[derive(Debug, Eq, PartialEq)]
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#[allow(dead_code)]
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pub enum Request {
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/// Query all transaction IDs in the mempool.
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TransactionIds,
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/// Query matching transactions in the mempool,
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/// using a unique set of [`UnminedTxId`]s.
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TransactionsById(HashSet<UnminedTxId>),
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/// Query matching cached rejected transaction IDs in the mempool,
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/// using a unique set of [`UnminedTxId`]s.
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RejectedTransactionIds(HashSet<UnminedTxId>),
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/// Queue a list of gossiped transactions or transaction IDs, or
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/// crawled transaction IDs.
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///
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/// The transaction downloader checks for duplicates across IDs and transactions.
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Queue(Vec<Gossip>),
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/// Check for newly verified transactions.
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///
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/// The transaction downloader does not push transactions into the mempool.
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/// So a task should send this request regularly (every 5-10 seconds).
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///
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/// These checks also happen for other request variants,
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/// but we can't rely on peers to send queries regularly,
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/// and crawler queue requests depend on peer responses.
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/// Also, crawler requests aren't frequent enough for transaction propagation.
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///
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/// # Correctness
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///
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/// This request is required to avoid hangs in the mempool.
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///
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/// The queue checker task can't call `poll_ready` directly on the [`Mempool`] service,
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/// because the mempool service is wrapped in a `Buffer`.
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/// Calling [`Buffer::poll_ready`] reserves a buffer slot, which can cause hangs when
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/// too many slots are reserved but unused:
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/// <https://docs.rs/tower/0.4.10/tower/buffer/struct.Buffer.html#a-note-on-choosing-a-bound>
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CheckForVerifiedTransactions,
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}
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/// A response to a mempool service request.
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///
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/// Responses can read the current set of mempool transactions,
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/// check the queued status of transactions to be downloaded and verified, or
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/// confirm that the mempool has been checked for newly verified transactions.
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#[derive(Debug)]
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pub enum Response {
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/// Returns all transaction IDs from the mempool.
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TransactionIds(HashSet<UnminedTxId>),
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/// Returns matching transactions from the mempool.
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///
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/// Since the [`TransactionsById`] request is unique,
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/// the response transactions are also unique.
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Transactions(Vec<UnminedTx>),
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/// Returns matching cached rejected transaction IDs from the mempool,
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RejectedTransactionIds(HashSet<UnminedTxId>),
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/// Returns a list of queue results.
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///
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/// These are the results of the initial queue checks.
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/// The transaction may also fail download or verification later.
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///
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/// Each result matches the request at the corresponding vector index.
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Queued(Vec<Result<(), MempoolError>>),
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/// Confirms that the mempool has checked for recently verified transactions.
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CheckedForVerifiedTransactions,
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}
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/// The state of the mempool.
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///
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/// Indicates whether it is enabled or disabled and, if enabled, contains
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/// the necessary data to run it.
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#[allow(clippy::large_enum_variant)]
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enum ActiveState {
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/// The Mempool is disabled.
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Disabled,
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/// The Mempool is enabled.
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Enabled {
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/// The Mempool storage itself.
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///
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/// ##: Correctness: only components internal to the [`Mempool`] struct are allowed to
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/// inject transactions into `storage`, as transactions must be verified beforehand.
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storage: storage::Storage,
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/// The transaction download and verify stream.
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tx_downloads: Pin<Box<InboundTxDownloads>>,
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},
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}
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impl Default for ActiveState {
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fn default() -> Self {
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ActiveState::Disabled
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}
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}
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impl Drop for ActiveState {
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fn drop(&mut self) {
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if let ActiveState::Enabled { tx_downloads, .. } = self {
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tx_downloads.cancel_all();
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}
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}
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}
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impl ActiveState {
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/// Returns the current state, leaving a [`Disabled`] in its place.
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fn take(&mut self) -> Self {
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std::mem::take(self)
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}
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}
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/// Mempool async management and query service.
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///
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/// The mempool is the set of all verified transactions that this node is aware
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/// of that have yet to be confirmed by the Zcash network. A transaction is
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/// confirmed when it has been included in a block ('mined').
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pub struct Mempool {
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/// The configurable options for the mempool, persisted between states.
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config: Config,
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/// The state of the mempool.
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active_state: ActiveState,
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/// Allows checking if we are near the tip to enable/disable the mempool.
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sync_status: SyncStatus,
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/// If the state's best chain tip has reached this height, always enable the mempool.
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debug_enable_at_height: Option<Height>,
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/// Allow efficient access to the best tip of the blockchain.
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latest_chain_tip: zs::LatestChainTip,
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/// Allows the detection of newly added chain tip blocks,
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/// and chain tip resets.
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chain_tip_change: ChainTipChange,
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/// Handle to the outbound service.
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/// Used to construct the transaction downloader.
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outbound: Outbound,
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/// Handle to the state service.
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/// Used to construct the transaction downloader.
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state: State,
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/// Handle to the transaction verifier service.
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/// Used to construct the transaction downloader.
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tx_verifier: TxVerifier,
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/// Sender part of a gossip transactions channel.
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/// Used to broadcast transaction ids to peers.
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transaction_sender: watch::Sender<HashSet<UnminedTxId>>,
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}
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impl Mempool {
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pub(crate) fn new(
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config: &Config,
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outbound: Outbound,
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state: State,
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tx_verifier: TxVerifier,
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sync_status: SyncStatus,
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latest_chain_tip: zs::LatestChainTip,
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chain_tip_change: ChainTipChange,
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) -> (Self, watch::Receiver<HashSet<UnminedTxId>>) {
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let (transaction_sender, transaction_receiver) =
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tokio::sync::watch::channel(HashSet::new());
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let mut service = Mempool {
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config: config.clone(),
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active_state: ActiveState::Disabled,
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sync_status,
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debug_enable_at_height: config.debug_enable_at_height.map(Height),
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latest_chain_tip,
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chain_tip_change,
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outbound,
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state,
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tx_verifier,
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transaction_sender,
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};
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// Make sure `is_enabled` is accurate.
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// Otherwise, it is only updated in `poll_ready`, right before each service call.
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service.update_state();
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(service, transaction_receiver)
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}
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/// Is the mempool enabled by a debug config option?
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fn is_enabled_by_debug(&self) -> bool {
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let mut is_debug_enabled = false;
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// optimise non-debug performance
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if self.debug_enable_at_height.is_none() {
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return is_debug_enabled;
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}
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let enable_at_height = self
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.debug_enable_at_height
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.expect("unexpected debug_enable_at_height: just checked for None");
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if let Some(best_tip_height) = self.latest_chain_tip.best_tip_height() {
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is_debug_enabled = best_tip_height >= enable_at_height;
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if is_debug_enabled && !self.is_enabled() {
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info!(
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?best_tip_height,
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?enable_at_height,
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"enabling mempool for debugging"
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);
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}
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}
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is_debug_enabled
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}
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/// Update the mempool state (enabled / disabled) depending on how close to
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/// the tip is the synchronization, including side effects to state changes.
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///
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/// Returns `true` if the state changed.
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fn update_state(&mut self) -> bool {
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let is_close_to_tip = self.sync_status.is_close_to_tip() || self.is_enabled_by_debug();
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if self.is_enabled() == is_close_to_tip {
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// the active state is up to date
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return false;
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}
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// Update enabled / disabled state
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if is_close_to_tip {
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info!(
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tip_height = ?self.latest_chain_tip.best_tip_height(),
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"activating mempool: Zebra is close to the tip"
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);
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let tx_downloads = Box::pin(TxDownloads::new(
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Timeout::new(self.outbound.clone(), TRANSACTION_DOWNLOAD_TIMEOUT),
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Timeout::new(self.tx_verifier.clone(), TRANSACTION_VERIFY_TIMEOUT),
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self.state.clone(),
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));
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self.active_state = ActiveState::Enabled {
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storage: storage::Storage::new(&self.config),
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tx_downloads,
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};
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} else {
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info!(
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tip_height = ?self.latest_chain_tip.best_tip_height(),
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"deactivating mempool: Zebra is syncing lots of blocks"
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);
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// This drops the previous ActiveState::Enabled,
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// cancelling its download tasks.
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self.active_state = ActiveState::Disabled
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}
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true
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}
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/// Return whether the mempool is enabled or not.
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pub fn is_enabled(&self) -> bool {
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match self.active_state {
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ActiveState::Disabled => false,
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ActiveState::Enabled { .. } => true,
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}
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}
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/// Remove expired transaction ids from a given list of inserted ones.
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fn remove_expired_from_peer_list(
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send_to_peers_ids: &HashSet<UnminedTxId>,
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expired_transactions: &HashSet<UnminedTxId>,
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) -> HashSet<UnminedTxId> {
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send_to_peers_ids
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.difference(expired_transactions)
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.copied()
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.collect()
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}
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}
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impl Service<Request> for Mempool {
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type Response = Response;
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type Error = BoxError;
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type Future =
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Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>> + Send + 'static>>;
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fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
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let is_state_changed = self.update_state();
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// When the mempool is disabled we still return that the service is ready.
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// Otherwise, callers could block waiting for the mempool to be enabled.
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if !self.is_enabled() {
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return Poll::Ready(Ok(()));
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}
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let tip_action = self.chain_tip_change.last_tip_change();
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// If the mempool was just freshly enabled,
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// skip resetting and removing mined transactions for this tip.
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if is_state_changed {
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return Poll::Ready(Ok(()));
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}
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// Clear the mempool and cancel downloads if there has been a chain tip reset.
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if matches!(tip_action, Some(TipAction::Reset { .. })) {
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info!(
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tip_height = ?tip_action.as_ref().unwrap().best_tip_height(),
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"resetting mempool: switched best chain, skipped blocks, or activated network upgrade"
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);
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// Use the same code for dropping and resetting the mempool,
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// to avoid subtle bugs.
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// Drop the current contents of the state,
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// cancelling any pending download tasks,
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// and dropping completed verification results.
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std::mem::drop(self.active_state.take());
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// Re-initialise an empty state.
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self.update_state();
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return Poll::Ready(Ok(()));
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}
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if let ActiveState::Enabled {
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storage,
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tx_downloads,
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} = &mut self.active_state
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{
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// Collect inserted transaction ids.
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let mut send_to_peers_ids = HashSet::<_>::new();
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// Clean up completed download tasks and add to mempool if successful.
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while let Poll::Ready(Some(r)) = tx_downloads.as_mut().poll_next(cx) {
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match r {
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Ok(tx) => {
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if let Ok(inserted_id) = storage.insert(tx.clone()) {
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// Save transaction ids that we will send to peers
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send_to_peers_ids.insert(inserted_id);
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}
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}
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Err((txid, e)) => {
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metrics::counter!("mempool.failed.verify.tasks.total", 1, "reason" => e.to_string());
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storage.reject_if_needed(txid, e);
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// TODO: should we also log the result?
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}
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};
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}
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// Handle best chain tip changes
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if let Some(TipAction::Grow { block }) = tip_action {
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// Cancel downloads/verifications/storage of transactions
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// with the same mined IDs as recently mined transactions.
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let mined_ids = block.transaction_hashes.iter().cloned().collect();
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tx_downloads.cancel(&mined_ids);
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storage.remove_same_effects(&mined_ids);
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storage.clear_tip_rejections();
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}
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// Remove expired transactions from the mempool.
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if let Some(tip_height) = self.latest_chain_tip.best_tip_height() {
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let expired_transactions = storage.remove_expired_transactions(tip_height);
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// Remove transactions that are expired from the peers list
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send_to_peers_ids =
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Self::remove_expired_from_peer_list(&send_to_peers_ids, &expired_transactions);
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}
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// Send transactions that were not rejected nor expired to peers
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if !send_to_peers_ids.is_empty() {
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let _ = self.transaction_sender.send(send_to_peers_ids)?;
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}
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}
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Poll::Ready(Ok(()))
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}
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/// Call the mempool service.
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///
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/// Errors indicate that the peer has done something wrong or unexpected,
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/// and will cause callers to disconnect from the remote peer.
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#[instrument(name = "mempool", skip(self, req))]
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fn call(&mut self, req: Request) -> Self::Future {
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match &mut self.active_state {
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ActiveState::Enabled {
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storage,
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tx_downloads,
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} => match req {
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// Queries
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Request::TransactionIds => {
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let res = storage.tx_ids().collect();
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async move { Ok(Response::TransactionIds(res)) }.boxed()
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}
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Request::TransactionsById(ids) => {
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let res = storage.transactions_exact(ids).cloned().collect();
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async move { Ok(Response::Transactions(res)) }.boxed()
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}
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Request::RejectedTransactionIds(ids) => {
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let res = storage.rejected_transactions(ids).collect();
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async move { Ok(Response::RejectedTransactionIds(res)) }.boxed()
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}
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// Queue mempool candidates
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Request::Queue(gossiped_txs) => {
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let rsp: Vec<Result<(), MempoolError>> = gossiped_txs
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.into_iter()
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.map(|gossiped_tx| {
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storage.should_download_or_verify(gossiped_tx.id())?;
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tx_downloads.download_if_needed_and_verify(gossiped_tx)?;
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Ok(())
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})
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.collect();
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async move { Ok(Response::Queued(rsp)) }.boxed()
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}
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// Store successfully downloaded and verified transactions in the mempool
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Request::CheckForVerifiedTransactions => {
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// all the work for this request is done in poll_ready
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async move { Ok(Response::CheckedForVerifiedTransactions) }.boxed()
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}
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},
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ActiveState::Disabled => {
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// We can't return an error since that will cause a disconnection
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// by the peer connection handler. Therefore, return successful
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// empty responses.
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let resp = match req {
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// Empty Queries
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Request::TransactionIds => Response::TransactionIds(Default::default()),
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Request::TransactionsById(_) => Response::Transactions(Default::default()),
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Request::RejectedTransactionIds(_) => {
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Response::RejectedTransactionIds(Default::default())
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}
|
|
|
|
// Don't queue mempool candidates
|
|
Request::Queue(gossiped_txs) => Response::Queued(
|
|
// Special case; we can signal the error inside the response,
|
|
// because the inbound service ignores inner errors.
|
|
iter::repeat(Err(MempoolError::Disabled))
|
|
.take(gossiped_txs.len())
|
|
.collect(),
|
|
),
|
|
|
|
// Check if the mempool should be enabled.
|
|
// This request makes sure mempools are debug-enabled in the acceptance tests.
|
|
Request::CheckForVerifiedTransactions => {
|
|
// all the work for this request is done in poll_ready
|
|
Response::CheckedForVerifiedTransactions
|
|
}
|
|
};
|
|
async move { Ok(resp) }.boxed()
|
|
}
|
|
}
|
|
}
|
|
}
|