consensus: Add a mempool stub

zebra-consensus/src/lib.rs

@@ -3,7 +3,8 @@
 //! `verify::BlockVerifier` verifies blocks and their transactions, then adds them to
 //! `zebra_state::ZebraState`.
 //!
-//! `mempool::ZebraMempool` verifies transactions, and adds them to the mempool state.
+//! `mempool::MempoolTransactionVerifier` verifies transactions, and adds them to
+//! `mempool::ZebraMempoolState`.
 //!
 //! Consensus handling is provided using `tower::Service`s, to support backpressure
 //! and batch verification.
@@ -12,4 +13,5 @@
 #![doc(html_root_url = "https://doc.zebra.zfnd.org/zebra_consensus")]
 #![deny(missing_docs)]
 
+pub mod mempool;
 pub mod verify;

zebra-consensus/src/mempool.rs

@@ -0,0 +1,29 @@
+//! Mempool transaction verification and state for Zebra.
+//!
+//! Mempool updates occur in multiple stages:
+//!   - getting transactions (disk- or network-bound)
+//!   - context-free verification of signatures, proofs, and scripts (CPU-bound)
+//!   - context-dependent verification of mempool transactions against the chain state
+//!     (awaits an up-to-date chain)
+//!   - adding transactions to the mempool
+//!
+//! The mempool is provided via a `tower::Service`, to support backpressure and batch
+//! verification.
+
+/// Mempool state.
+///
+/// New transactions are verified, checked against the chain state, then added to the
+/// mempool.
+///
+/// `ZebraMempoolState` is not yet implemented.
+#[derive(Default)]
+struct ZebraMempoolState {}
+
+/// Mempool transaction verification.
+///
+/// New transactions are verified, checked against the chain state, then added to the
+/// mempool.
+///
+/// `MempoolTransactionVerifier` is not yet implemented.
+#[derive(Default)]
+struct MempoolTransactionVerifier {}