102 lines
3.8 KiB
Rust
102 lines
3.8 KiB
Rust
//! The Zebra mempool.
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//!
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//! A service that manages known unmined Zcash transactions.
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use std::collections::HashSet;
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use zebra_chain::transaction::{Hash, UnminedTx, UnminedTxId};
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use crate::BoxError;
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mod gossip;
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pub use self::gossip::Gossip;
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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 transactions in the mempool,
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/// using a unique set of [`struct@Hash`]s. Pre-V5 transactions are matched
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/// directly; V5 transaction are matched just by the Hash, disregarding
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/// the [`AuthDigest`](zebra_chain::transaction::AuthDigest).
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TransactionsByMinedId(HashSet<Hash>),
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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
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/// service, because the service is wrapped in a `Buffer`. Calling
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/// `Buffer::poll_ready` reserves a buffer slot, which can cause hangs
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/// when 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 [`Request::TransactionsById`] request is unique,
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/// the response transactions are also unique. The same applies to
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/// [`Request::TransactionsByMinedId`] requests, since the mempool does not allow
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/// different transactions with different mined IDs.
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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<(), BoxError>>),
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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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