change(scan): Store scanned TXIDs in "display order" (#8057)

* Store scanned TXIDs in "display order"

* Unrelated: Remove a redundant `Arc`

---------

Co-authored-by: teor <teor@riseup.net>

zebra-scan/src/scan.rs

@@ -22,12 +22,8 @@ use zcash_primitives::{
 };
 
 use zebra_chain::{
-    block::Block,
-    chain_tip::ChainTip,
-    diagnostic::task::WaitForPanics,
-    parameters::Network,
-    serialization::ZcashSerialize,
-    transaction::{self, Transaction},
+    block::Block, chain_tip::ChainTip, diagnostic::task::WaitForPanics, parameters::Network,
+    serialization::ZcashSerialize, transaction::Transaction,
 };
 use zebra_state::{ChainTipChange, SaplingScannedResult};
 
@@ -191,7 +187,7 @@ pub async fn start(
 /// - Add prior block metadata once we have access to Zebra's state.
 pub fn scan_block<K: ScanningKey>(
     network: Network,
-    block: &Arc<Block>,
+    block: &Block,
     sapling_tree_size: u32,
     scanning_keys: &[K],
 ) -> Result<ScannedBlock<K::Nf>, ScanError> {
@@ -255,7 +251,7 @@ pub fn sapling_key_to_scan_block_keys(
 }
 
 /// Converts a zebra block and meta data into a compact block.
-pub fn block_to_compact(block: &Arc<Block>, chain_metadata: ChainMetadata) -> CompactBlock {
+pub fn block_to_compact(block: &Block, chain_metadata: ChainMetadata) -> CompactBlock {
     CompactBlock {
         height: block
             .coinbase_height()
@@ -344,6 +340,6 @@ fn scanned_block_to_db_result<Nf>(scanned_block: ScannedBlock<Nf>) -> Vec<Saplin
     scanned_block
         .transactions()
         .iter()
-        .map(|tx| transaction::Hash::from_bytes_in_display_order(tx.txid.as_ref()))
+        .map(|tx| SaplingScannedResult::from(tx.txid.as_ref()))
         .collect()
 }

zebra-scan/src/tests.rs

@@ -36,8 +36,8 @@ use zebra_chain::{
     chain_tip::ChainTip,
     parameters::Network,
     serialization::ZcashDeserializeInto,
-    transaction::Hash,
 };
+use zebra_state::SaplingScannedResult;
 
 use crate::{
     config::Config,
@@ -211,8 +211,7 @@ fn scanning_fake_blocks_store_key_and_results() -> Result<()> {
         Some(0),
     );
 
-    // Scan with our key
-    let res = zcash_client_backend::scanning::scan_block(
+    let result = zcash_client_backend::scanning::scan_block(
         &zcash_primitives::consensus::MainNetwork,
         cb.clone(),
         &vks[..],
@@ -221,21 +220,18 @@ fn scanning_fake_blocks_store_key_and_results() -> Result<()> {
     )
     .unwrap();
 
-    // Get transaction hash
-    let found_transaction = res.transactions()[0].txid.as_ref();
-    let found_transaction_hash = Hash::from_bytes_in_display_order(found_transaction);
+    // The response should have one transaction relevant to the key we provided.
+    assert_eq!(result.transactions().len(), 1);
+
+    let result = SaplingScannedResult::from(result.transactions()[0].txid.as_ref());
 
     // Add result to database
-    s.add_sapling_result(
-        key_to_be_stored.clone(),
-        Height(1),
-        vec![found_transaction_hash],
-    );
+    s.add_sapling_result(key_to_be_stored.clone(), Height(1), vec![result]);
 
     // Check the result was added
     assert_eq!(
         s.sapling_results(&key_to_be_stored).get(&Height(1)),
-        Some(&vec![found_transaction_hash])
+        Some(&vec![result])
     );
 
     Ok(())

zebra-state/src/service/finalized_state/disk_format/scan.rs

@@ -26,8 +26,24 @@ pub const SAPLING_SCANNING_RESULT_LENGTH: usize = 32;
 /// It can represent a full viewing key or an individual viewing key.
 pub type SaplingScanningKey = String;
 
-/// The type used in Zebra to store Sapling scanning results.
-pub type SaplingScannedResult = transaction::Hash;
+/// Stores a scanning result.
+///
+/// Currently contains a TXID in "display order", which is big-endian byte order following the u256
+/// convention set by Bitcoin and zcashd.
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+pub struct SaplingScannedResult([u8; 32]);
+
+impl From<SaplingScannedResult> for transaction::Hash {
+    fn from(scanned_result: SaplingScannedResult) -> Self {
+        transaction::Hash::from_bytes_in_display_order(&scanned_result.0)
+    }
+}
+
+impl From<&[u8; 32]> for SaplingScannedResult {
+    fn from(bytes: &[u8; 32]) -> Self {
+        Self(*bytes)
+    }
+}
 
 /// A database column family entry for a block scanned with a Sapling vieweing key.
 #[derive(Clone, Debug, Eq, PartialEq)]
@@ -123,6 +139,20 @@ impl FromDisk for SaplingScannedDatabaseIndex {
     }
 }
 
+impl IntoDisk for SaplingScannedResult {
+    type Bytes = [u8; 32];
+
+    fn as_bytes(&self) -> Self::Bytes {
+        self.0
+    }
+}
+
+impl FromDisk for SaplingScannedResult {
+    fn from_bytes(bytes: impl AsRef<[u8]>) -> Self {
+        SaplingScannedResult(bytes.as_ref().try_into().unwrap())
+    }
+}
+
 impl IntoDisk for Vec<SaplingScannedResult> {
     type Bytes = Vec<u8>;