From 1708f9d94679870d76cd3906b250756cbc4af07c Mon Sep 17 00:00:00 2001
From: Alfredo Garcia <oxarbitrage@gmail.com>
Date: Wed, 29 Nov 2023 21:51:32 -0300
Subject: [PATCH] change(zebra-scan): Scan only one key per backend call
 (#8034)

* scan one key per backend call

* fix docs
---
 zebra-scan/src/scan.rs  | 10 +++---
 zebra-scan/src/tests.rs | 73 ++---------------------------------------
 2 files changed, 6 insertions(+), 77 deletions(-)

diff --git a/zebra-scan/src/scan.rs b/zebra-scan/src/scan.rs
index 72577264f7a..342205680ec 100644
--- a/zebra-scan/src/scan.rs
+++ b/zebra-scan/src/scan.rs
@@ -70,7 +70,7 @@ pub async fn start(mut state: State, storage: Storage) -> Result<(), Report> {
     }
 }
 
-/// Returns transactions belonging to any of the given [`ScanningKey`]s.
+/// Returns transactions belonging to the given `ScanningKey`.
 ///
 /// TODO:
 /// - Remove the `sapling_tree_size` parameter or turn it into an `Option` once we have access to
@@ -80,7 +80,7 @@ pub fn scan_block<K: ScanningKey>(
     network: Network,
     block: Arc<Block>,
     sapling_tree_size: u32,
-    scanning_keys: &[&K],
+    scanning_key: &K,
 ) -> Result<ScannedBlock<K::Nf>, ScanError> {
     // TODO: Implement a check that returns early when the block height is below the Sapling
     // activation height.
@@ -96,10 +96,8 @@ pub fn scan_block<K: ScanningKey>(
     // Use a dummy `AccountId` as we don't use accounts yet.
     let dummy_account = AccountId::from(0);
 
-    let scanning_keys: Vec<_> = scanning_keys
-        .iter()
-        .map(|key| (&dummy_account, key))
-        .collect();
+    // We only support scanning one key and one block per function call for now.
+    let scanning_keys = vec![(&dummy_account, scanning_key)];
 
     zcash_client_backend::scanning::scan_block(
         &network,
diff --git a/zebra-scan/src/tests.rs b/zebra-scan/src/tests.rs
index 04c00335949..4434645324b 100644
--- a/zebra-scan/src/tests.rs
+++ b/zebra-scan/src/tests.rs
@@ -32,80 +32,11 @@ use zcash_primitives::{
 };
 
 use zebra_chain::{
-    block::Block, chain_tip::ChainTip, parameters::Network, serialization::ZcashDeserializeInto,
-    transaction::Hash,
+    block::Block, chain_tip::ChainTip, serialization::ZcashDeserializeInto, transaction::Hash,
 };
 
 use crate::scan::{block_to_compact, scan_block};
 
-/// Scans a continuous chain of Mainnet blocks from tip to genesis.
-///
-/// Also verifies that no relevant transaction is found in the chain when scanning for a fake
-/// account's nullifier.
-#[tokio::test]
-async fn scanning_from_populated_zebra_state() -> Result<()> {
-    let network = Network::default();
-
-    // Create a continuous chain of mainnet blocks from genesis
-    let blocks: Vec<Arc<Block>> = zebra_test::vectors::CONTINUOUS_MAINNET_BLOCKS
-        .iter()
-        .map(|(_height, block_bytes)| block_bytes.zcash_deserialize_into().unwrap())
-        .collect();
-
-    // Create a populated state service.
-    let (_state_service, read_only_state_service, latest_chain_tip, _chain_tip_change) =
-        zebra_state::populated_state(blocks.clone(), network).await;
-
-    let db = read_only_state_service.db();
-
-    // use the tip as starting height
-    let mut height = latest_chain_tip.best_tip_height().unwrap();
-
-    let mut transactions_found = 0;
-    let mut transactions_scanned = 0;
-    let mut blocks_scanned = 0;
-    // TODO: Accessing the state database directly is ok in the tests, but not in production code.
-    // Use `Request::Block` if the code is copied to production.
-    while let Some(block) = db.block(height.into()) {
-        // We use a dummy size of the Sapling note commitment tree. We can't set the size to zero
-        // because the underlying scanning function would return
-        // `zcash_client_backeng::scanning::ScanError::TreeSizeUnknown`.
-        let sapling_commitment_tree_size = 1;
-
-        let orchard_commitment_tree_size = 0;
-
-        let chain_metadata = ChainMetadata {
-            sapling_commitment_tree_size,
-            orchard_commitment_tree_size,
-        };
-
-        let compact_block = block_to_compact(block.clone(), chain_metadata);
-
-        let res =
-            scan_block::<SaplingIvk>(network, block, sapling_commitment_tree_size, &[]).unwrap();
-
-        transactions_found += res.transactions().len();
-        transactions_scanned += compact_block.vtx.len();
-        blocks_scanned += 1;
-
-        if height.is_min() {
-            break;
-        }
-
-        // scan backwards
-        height = height.previous()?;
-    }
-
-    // make sure all blocks and transactions were scanned
-    assert_eq!(blocks_scanned, 11);
-    assert_eq!(transactions_scanned, 11);
-
-    // no relevant transactions should be found
-    assert_eq!(transactions_found, 0);
-
-    Ok(())
-}
-
 /// Prove that we can create fake blocks with fake notes and scan them using the
 /// `zcash_client_backend::scanning::scan_block` function:
 /// - Function `fake_compact_block` will generate 1 block with one pre created fake nullifier in
@@ -207,7 +138,7 @@ async fn scanning_zecpages_from_populated_zebra_state() -> Result<()> {
 
         let compact_block = block_to_compact(block.clone(), chain_metadata);
 
-        let res = scan_block(network, block, sapling_commitment_tree_size, &[&ivk])
+        let res = scan_block(network, block, sapling_commitment_tree_size, &ivk)
             .expect("scanning block for the ZECpages viewing key should work");
 
         transactions_found += res.transactions().len();