change(rpc): Avoid re-verifying transactions in blocks if those transactions are in the mempool

zebra-consensus/src/block.rs

@@ -8,6 +8,7 @@
 //! verification, where it may be accepted or rejected.
 
 use std::{
+    collections::HashSet,
     future::Future,
     pin::Pin,
     sync::Arc,
@@ -25,7 +26,7 @@ use zebra_chain::{
     amount::Amount,
     block,
     parameters::{subsidy::FundingStreamReceiver, Network},
-    transparent,
+    transaction, transparent,
     work::equihash,
 };
 use zebra_state as zs;
@@ -232,13 +233,21 @@ where
                 &block,
                 &transaction_hashes,
             ));
-            for transaction in &block.transactions {
+
+            let known_outpoint_hashes: Arc<HashSet<transaction::Hash>> =
+                Arc::new(known_utxos.keys().map(|outpoint| outpoint.hash).collect());
+
+            for (&transaction_hash, transaction) in
+                transaction_hashes.iter().zip(block.transactions.iter())
+            {
                 let rsp = transaction_verifier
                     .ready()
                     .await
                     .expect("transaction verifier is always ready")
                     .call(tx::Request::Block {
+                        transaction_hash,
                         transaction: transaction.clone(),
+                        known_outpoint_hashes: known_outpoint_hashes.clone(),
                         known_utxos: known_utxos.clone(),
                         height,
                         time: block.header.time,

zebra-consensus/src/transaction.rs

@@ -1,7 +1,7 @@
 //! Asynchronous verification of transactions.
 
 use std::{
-    collections::HashMap,
+    collections::{HashMap, HashSet},
     future::Future,
     pin::Pin,
     sync::Arc,
@@ -146,8 +146,12 @@ where
 pub enum Request {
     /// Verify the supplied transaction as part of a block.
     Block {
+        /// The transaction hash.
+        transaction_hash: transaction::Hash,
         /// The transaction itself.
         transaction: Arc<Transaction>,
+        /// Set of transaction hashes that create new transparent outputs.
+        known_outpoint_hashes: Arc<HashSet<transaction::Hash>>,
         /// Additional UTXOs which are known at the time of verification.
         known_utxos: Arc<HashMap<transparent::OutPoint, transparent::OrderedUtxo>>,
         /// The height of the block containing this transaction.
@@ -259,6 +263,16 @@ impl Request {
         }
     }
 
+    /// The mined transaction ID for the transaction in this request.
+    pub fn tx_mined_id(&self) -> transaction::Hash {
+        match self {
+            Request::Block {
+                transaction_hash, ..
+            } => *transaction_hash,
+            Request::Mempool { transaction, .. } => transaction.id.mined_id(),
+        }
+    }
+
     /// The set of additional known unspent transaction outputs that's in this request.
     pub fn known_utxos(&self) -> Arc<HashMap<transparent::OutPoint, transparent::OrderedUtxo>> {
         match self {
@@ -267,6 +281,17 @@ impl Request {
         }
     }
 
+    /// The set of additional known [`transparent::OutPoint`]s of unspent transaction outputs that's in this request.
+    pub fn known_outpoint_hashes(&self) -> Arc<HashSet<transaction::Hash>> {
+        match self {
+            Request::Block {
+                known_outpoint_hashes,
+                ..
+            } => known_outpoint_hashes.clone(),
+            Request::Mempool { .. } => HashSet::new().into(),
+        }
+    }
+
     /// The height used to select the consensus rules for verifying this transaction.
     pub fn height(&self) -> block::Height {
         match self {
@@ -377,6 +402,16 @@ where
         async move {
             tracing::trace!(?tx_id, ?req, "got tx verify request");
 
+            if let Some(result) = Self::try_find_verified_unmined_tx(&req, mempool.clone()).await {
+                let verified_tx = result?;
+
+                return Ok(Response::Block {
+                    tx_id: verified_tx.transaction.id,
+                    miner_fee: Some(verified_tx.miner_fee),
+                    legacy_sigop_count: verified_tx.legacy_sigop_count
+                });
+            }
+
             // Do quick checks first
             check::has_inputs_and_outputs(&tx)?;
             check::has_enough_orchard_flags(&tx)?;
@@ -608,6 +643,51 @@ where
         }
     }
 
+    /// Attempts to find a transaction in the mempool by its transaction hash and checks
+    /// that all of its dependencies are available in the block.
+    ///
+    /// Returns [`Some(Ok(VerifiedUnminedTx))`](VerifiedUnminedTx) if successful,
+    /// None if the transaction id was not found in the mempool,
+    /// or `Some(Err(TransparentInputNotFound))` if the transaction was found, but some of its
+    /// dependencies are missing in the block.
+    async fn try_find_verified_unmined_tx(
+        req: &Request,
+        mempool: Option<Timeout<Mempool>>,
+    ) -> Option<Result<VerifiedUnminedTx, TransactionError>> {
+        if req.is_mempool() {
+            return None;
+        }
+
+        let mempool = mempool?;
+        let known_outpoint_hashes = req.known_outpoint_hashes();
+        let tx_id = req.tx_mined_id();
+
+        let mempool::Response::TransactionWithDeps {
+            transaction,
+            dependencies,
+        } = mempool
+            .oneshot(mempool::Request::TransactionWithDepsByMinedId(tx_id))
+            .await
+            .ok()?
+        else {
+            panic!("unexpected response to TransactionWithDepsByMinedId request");
+        };
+
+        // Note: This does not verify that the spends are in order, this should be
+        //       done during contextual validation in zebra-state.
+        let has_all_tx_deps = dependencies
+            .into_iter()
+            .all(|dependency_id| known_outpoint_hashes.contains(&dependency_id));
+
+        let result = if has_all_tx_deps {
+            Ok(transaction)
+        } else {
+            Err(TransactionError::TransparentInputNotFound)
+        };
+
+        Some(result)
+    }
+
     /// Wait for the UTXOs that are being spent by the given transaction.
     ///
     /// `known_utxos` are additional UTXOs known at the time of validation (i.e.