consensus: fix same-block utxo lookups

The UTXO query system assumes that a transaction will only request
information about UTXOs created in prior blocks.  But transactions are
allowed to spend UTXOs created by prior transactions in the same block.

This doesn't fit with the existing query model, so instead of trying to
change it, allow the script verifier to take an additional set of known
UTXOs, and propagate this set from the block.

Cargo.lock

@@ -2744,7 +2744,7 @@ dependencies = [
 [[package]]
 name = "tower"
 version = "0.4.0"
-source = "git+https://github.com/tower-rs/tower?rev=5e1e07744820028877654c336a3b9fe057bf46f1#5e1e07744820028877654c336a3b9fe057bf46f1"
+source = "git+https://github.com/tower-rs/tower?rev=d4d1c67c6a0e4213a52abcc2b9df6cc58276ee39#d4d1c67c6a0e4213a52abcc2b9df6cc58276ee39"
 dependencies = [
  "futures-core",
  "futures-util",
@@ -2789,7 +2789,7 @@ dependencies = [
 [[package]]
 name = "tower-layer"
 version = "0.3.0"
-source = "git+https://github.com/tower-rs/tower?rev=5e1e07744820028877654c336a3b9fe057bf46f1#5e1e07744820028877654c336a3b9fe057bf46f1"
+source = "git+https://github.com/tower-rs/tower?rev=d4d1c67c6a0e4213a52abcc2b9df6cc58276ee39#d4d1c67c6a0e4213a52abcc2b9df6cc58276ee39"
 
 [[package]]
 name = "tower-service"

zebra-consensus/src/block.rs

@@ -8,6 +8,7 @@
 //! verification, where it may be accepted or rejected.
 
 use std::{
+    collections::HashMap,
     future::Future,
     pin::Pin,
     sync::Arc,
@@ -25,6 +26,7 @@ use zebra_chain::{
     block::{self, Block},
     parameters::Network,
     parameters::NetworkUpgrade,
+    transparent,
     work::equihash,
 };
 use zebra_state as zs;
@@ -165,13 +167,16 @@ where
 
             let mut async_checks = FuturesUnordered::new();
 
+            let known_utxos = known_utxos(&block);
             for transaction in &block.transactions {
-                let req = transaction::Request::Block(transaction.clone());
                 let rsp = transaction_verifier
                     .ready_and()
                     .await
                     .expect("transaction verifier is always ready")
-                    .call(req);
+                    .call(transaction::Request::Block {
+                        transaction: transaction.clone(),
+                        known_utxos: known_utxos.clone(),
+                    });
                 async_checks.push(rsp);
             }
             tracing::trace!(len = async_checks.len(), "built async tx checks");
@@ -207,3 +212,16 @@ where
         .boxed()
     }
 }
+
+fn known_utxos(block: &Block) -> Arc<HashMap<transparent::OutPoint, transparent::Output>> {
+    let mut map = HashMap::default();
+    for transaction in &block.transactions {
+        let hash = transaction.hash();
+        for (index, output) in transaction.outputs().iter().cloned().enumerate() {
+            let index = index as u32;
+            map.insert(transparent::OutPoint { hash, index }, output);
+        }
+    }
+
+    Arc::new(map)
+}

zebra-consensus/src/script.rs

@@ -1,4 +1,4 @@
-use std::{future::Future, pin::Pin, sync::Arc};
+use std::{collections::HashMap, future::Future, pin::Pin, sync::Arc};
 
 use tracing::Instrument;
 
@@ -40,6 +40,7 @@ impl<ZS> Verifier<ZS> {
 pub struct Request {
     pub transaction: Arc<Transaction>,
     pub input_index: usize,
+    pub known_utxos: Arc<HashMap<transparent::OutPoint, transparent::Output>>,
 }
 
 impl<ZS> tower::Service<Request> for Verifier<ZS>
@@ -62,32 +63,35 @@ where
     fn call(&mut self, req: Request) -> Self::Future {
         use futures_util::FutureExt;
 
-        let input = &req.transaction.inputs()[req.input_index];
+        let Request {
+            transaction,
+            input_index,
+            known_utxos,
+        } = req;
+        let input = &transaction.inputs()[input_index];
 
         match input {
             transparent::Input::PrevOut { outpoint, .. } => {
                 let outpoint = *outpoint;
-                let transaction = req.transaction;
                 let branch_id = self.branch;
-                let input_index = req.input_index;
 
                 let span = tracing::trace_span!("script", ?outpoint);
-                let output =
+                let query =
                     span.in_scope(|| self.state.call(zebra_state::Request::AwaitUtxo(outpoint)));
 
                 async move {
                     tracing::trace!("awaiting outpoint lookup");
-                    let previous_output = match output.await? {
+                    let output = if let Some(output) = known_utxos.get(&outpoint) {
-                        zebra_state::Response::Utxo(output) => output,
+                        tracing::trace!("UXTO in known_utxos, discarding query");
-                        _ => unreachable!("AwaitUtxo always responds with Utxo"),
+                        output.clone()
+                    } else if let zebra_state::Response::Utxo(output) = query.await? {
+                        output
+                    } else {
+                        unreachable!("AwaitUtxo always responds with Utxo")
                     };
-                    tracing::trace!(?previous_output, "got UTXO");
+                    tracing::trace!(?output, "got UTXO");
 
-                    zebra_script::is_valid(
+                    zebra_script::is_valid(transaction, branch_id, (input_index as u32, output))?;
-                        transaction,
-                        branch_id,
-                        (input_index as u32, previous_output),
-                    )?;
                     tracing::trace!("script verification succeeded");
 
                     Ok(())

zebra-consensus/src/transaction.rs

@@ -1,4 +1,5 @@
 use std::{
+    collections::HashMap,
     future::Future,
     pin::Pin,
     sync::Arc,
@@ -15,6 +16,7 @@ use tracing::Instrument;
 use zebra_chain::{
     parameters::NetworkUpgrade,
     transaction::{self, HashType, Transaction},
+    transparent,
 };
 
 use zebra_state as zs;
@@ -51,9 +53,17 @@ where
 #[allow(dead_code)]
 pub enum Request {
     /// Verify the supplied transaction as part of a block.
-    Block(Arc<Transaction>),
+    Block {
+        transaction: Arc<Transaction>,
+        /// Additional UTXOs which are known at the time of verification.
+        known_utxos: Arc<HashMap<transparent::OutPoint, transparent::Output>>,
+    },
     /// Verify the supplied transaction as part of the mempool.
-    Mempool(Arc<Transaction>),
+    Mempool {
+        transaction: Arc<Transaction>,
+        /// Additional UTXOs which are known at the time of verification.
+        known_utxos: Arc<HashMap<transparent::OutPoint, transparent::Output>>,
+    },
 }
 
 impl<ZS> Service<Request> for Verifier<ZS>
@@ -73,17 +83,23 @@ where
     // TODO: break up each chunk into its own method
     fn call(&mut self, req: Request) -> Self::Future {
         let is_mempool = match req {
-            Request::Block(_) => false,
+            Request::Block { .. } => false,
-            Request::Mempool(_) => true,
+            Request::Mempool { .. } => true,
         };
         if is_mempool {
             // XXX determine exactly which rules apply to mempool transactions
             unimplemented!();
         }
 
-        let tx = match req {
+        let (tx, known_utxos) = match req {
-            Request::Block(tx) => tx,
+            Request::Block {
-            Request::Mempool(tx) => tx,
+                transaction,
+                known_utxos,
+            } => (transaction, known_utxos),
+            Request::Mempool {
+                transaction,
+                known_utxos,
+            } => (transaction, known_utxos),
         };
 
         let mut redjubjub_verifier = crate::primitives::redjubjub::VERIFIER.clone();
@@ -119,6 +135,7 @@ where
                         // feed all of the inputs to the script verifier
                         for input_index in 0..inputs.len() {
                             let rsp = script_verifier.ready_and().await?.call(script::Request {
+                                known_utxos: known_utxos.clone(),
                                 transaction: tx.clone(),
                                 input_index,
                             });