zcash_client_backend: Add `WalletRead::block_max_scanned`

Fixes #941

zcash_client_backend/CHANGELOG.md

@@ -34,8 +34,10 @@ and this library adheres to Rust's notion of
   - `ShieldedProtocol`
   - `WalletCommitmentTrees`
   - `WalletSummary`
-  - `WalletRead::{chain_height, block_metadata, block_fully_scanned, suggest_scan_ranges,
-    get_wallet_birthday, get_account_birthday, get_wallet_summary}`
+  - `WalletRead::{
+       chain_height, block_metadata, block_max_scanned, block_fully_scanned,
+       suggest_scan_ranges, get_wallet_birthday, get_account_birthday, get_wallet_summary
+     }`
   - `WalletWrite::{put_blocks, update_chain_tip}`
   - `chain::CommitmentTreeRoot`
   - `scanning` A new module containing types required for `suggest_scan_ranges`

zcash_client_backend/src/data_api.rs

@@ -233,6 +233,13 @@ pub trait WalletRead {
     /// block.
     fn block_fully_scanned(&self) -> Result<Option<BlockMetadata>, Self::Error>;
 
+    /// Returns block metadata for the maximum height that the wallet has scanned.
+    ///
+    /// If the wallet is fully synced, this will be equivalent to `block_fully_scanned`;
+    /// otherwise the maximal scanned height is likely to be greater than the fully scanned height
+    /// due to the fact that out-of-order scanning can leave gaps.
+    fn block_max_scanned(&self) -> Result<Option<BlockMetadata>, Self::Error>;
+
     /// Returns a vector of suggested scan ranges based upon the current wallet state.
     ///
     /// This method should only be used in cases where the [`CompactBlock`] data that will be made
@@ -945,6 +952,10 @@ pub mod testing {
             Ok(None)
         }
 
+        fn block_max_scanned(&self) -> Result<Option<BlockMetadata>, Self::Error> {
+            Ok(None)
+        }
+
         fn suggest_scan_ranges(&self) -> Result<Vec<ScanRange>, Self::Error> {
             Ok(vec![])
         }

zcash_client_sqlite/src/lib.rs

@@ -180,6 +180,10 @@ impl<C: Borrow<rusqlite::Connection>, P: consensus::Parameters> WalletRead for W
         wallet::block_fully_scanned(self.conn.borrow())
     }
 
+    fn block_max_scanned(&self) -> Result<Option<BlockMetadata>, Self::Error> {
+        wallet::block_max_scanned(self.conn.borrow())
+    }
+
     fn suggest_scan_ranges(&self) -> Result<Vec<ScanRange>, Self::Error> {
         wallet::scanning::suggest_scan_ranges(self.conn.borrow(), ScanPriority::Historic)
             .map_err(SqliteClientError::from)

zcash_client_sqlite/src/wallet.rs

@@ -1086,6 +1086,33 @@ pub(crate) fn block_fully_scanned(
     }
 }
 
+pub(crate) fn block_max_scanned(
+    conn: &rusqlite::Connection,
+) -> Result<Option<BlockMetadata>, SqliteClientError> {
+    conn.query_row(
+        "SELECT blocks.height, hash, sapling_commitment_tree_size, sapling_tree
+         FROM blocks
+         JOIN (SELECT MAX(height) AS height FROM blocks) blocks_max
+         ON blocks.height = blocks_max.height",
+        [],
+        |row| {
+            let height: u32 = row.get(0)?;
+            let block_hash: Vec<u8> = row.get(1)?;
+            let sapling_tree_size: Option<u32> = row.get(2)?;
+            let sapling_tree: Vec<u8> = row.get(3)?;
+            Ok((
+                BlockHeight::from(height),
+                block_hash,
+                sapling_tree_size,
+                sapling_tree,
+            ))
+        },
+    )
+    .optional()
+    .map_err(SqliteClientError::from)
+    .and_then(|meta_row| meta_row.map(parse_block_metadata).transpose())
+}
+
 /// Returns the block height at which the specified transaction was mined,
 /// if any.
 pub(crate) fn get_tx_height(
@@ -1892,8 +1919,6 @@ pub(crate) fn prune_nullifier_map(
 mod tests {
     use std::num::NonZeroU32;
 
-    use zcash_primitives::transaction::components::Amount;
-
     use zcash_client_backend::data_api::{AccountBirthday, WalletRead};
 
     use crate::{testing::TestBuilder, AccountId};
@@ -1906,7 +1931,7 @@ mod tests {
         },
         zcash_primitives::{
             consensus::BlockHeight,
-            transaction::components::{OutPoint, TxOut},
+            transaction::components::{Amount, OutPoint, TxOut},
         },
     };
 

zcash_client_sqlite/src/wallet/sapling.rs

@@ -465,7 +465,7 @@ pub(crate) mod tests {
     use crate::{
         error::SqliteClientError,
         testing::{AddressType, BlockCache, TestBuilder, TestState},
-        wallet::commitment_tree,
+        wallet::{block_max_scanned, commitment_tree},
         AccountId, NoteId, ReceivedNoteId,
     };
 
@@ -501,6 +501,13 @@ pub(crate) mod tests {
 
         // Verified balance matches total balance
         assert_eq!(st.get_total_balance(account), value);
+        assert_eq!(
+            block_max_scanned(&st.wallet().conn)
+                .unwrap()
+                .unwrap()
+                .block_height(),
+            h
+        );
 
         let to_extsk = ExtendedSpendingKey::master(&[]);
         let to: RecipientAddress = to_extsk.default_address().1.into();