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cleanup(sync): remove obsolete zcashd trailing hash handling #11093

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cleanup(sync): remove obsolete zcashd trailing hash handling #11093

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b75539b
Remove trailing hash removal
jvff Jul 24, 2026
044a094
Update test vectors to not include trailing hash
jvff Jul 24, 2026
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37 changes: 1 addition & 36 deletions zebrad/src/components/sync.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -805,33 +805,7 @@ where
Ok(zn::Response::BlockHashes(hashes)) => {
trace!(?hashes);

// zcashd sometimes appends an unrelated hash at the start
// or end of its response.
//
// We can't discard the first hash, because it might be a
// block we want to download. So we just accept any
// out-of-order first hashes.

// We use the last hash for the tip, and we want to avoid bad
// tips from zcashd's quirk of appending an unrelated hash.
// So we discard the last hash on mainnet/testnet.
// (We don't need to worry about missed downloads, because we
// will pick them up again in ExtendTips.)
//
// In regtest we only connect to Zebra nodes, not zcashd,
// so we trust all hashes in the response and keep them all.
// This is necessary when there are only a small number of
// blocks to sync (e.g. 2 new blocks), where stripping the
// last hash leaves only 1 unknown hash and rchunks_exact(2)
// would discard the entire response.
let hashes = if self.is_regtest {
hashes.as_slice()
} else {
match hashes.as_slice() {
[] => continue,
[rest @ .., _last] => rest,
}
};
let hashes = hashes.as_slice();
if hashes.is_empty() {
continue;
}
Expand Down Expand Up @@ -995,15 +969,6 @@ where
}
};

// We use the last hash for the tip, and we want to avoid
// bad tips. So we discard the last hash. (We don't need
// to worry about missed downloads, because we will pick
// them up again in the next ExtendTips.)
let unknown_hashes = match unknown_hashes {
[] => continue,
[rest @ .., _last] => rest,
};

let new_tip = if let Some(end) = unknown_hashes.rchunks_exact(2).next() {
CheckedTip {
tip: end[0],
Expand Down
19 changes: 0 additions & 19 deletions zebrad/src/components/sync/tests/vectors.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -70,9 +70,6 @@ async fn sync_blocks_ok() -> Result<(), crate::BoxError> {
let block4: Arc<Block> = zebra_test::vectors::BLOCK_MAINNET_4_BYTES.zcash_deserialize_into()?;
let block4_hash = block4.hash();

let block5: Arc<Block> = zebra_test::vectors::BLOCK_MAINNET_5_BYTES.zcash_deserialize_into()?;
let block5_hash = block5.hash();

// Start the syncer
let chain_sync_task_handle = tokio::spawn(chain_sync_future);

Expand Down Expand Up @@ -127,7 +124,6 @@ async fn sync_blocks_ok() -> Result<(), crate::BoxError> {
.respond(zn::Response::BlockHashes(vec![
block1_hash, // tip
block2_hash, // expected_next
block3_hash, // (discarded - last hash, possibly incorrect)
]));

// State is checked for the first unknown block (block 1)
Expand Down Expand Up @@ -213,7 +209,6 @@ async fn sync_blocks_ok() -> Result<(), crate::BoxError> {
block2_hash, // tip (discarded - already fetched)
block3_hash, // expected_next
block4_hash,
block5_hash, // (discarded - last hash, possibly incorrect)
]));

// Clear remaining block locator requests
Expand Down Expand Up @@ -312,9 +307,6 @@ async fn sync_blocks_duplicate_hashes_ok() -> Result<(), crate::BoxError> {
let block4: Arc<Block> = zebra_test::vectors::BLOCK_MAINNET_4_BYTES.zcash_deserialize_into()?;
let block4_hash = block4.hash();

let block5: Arc<Block> = zebra_test::vectors::BLOCK_MAINNET_5_BYTES.zcash_deserialize_into()?;
let block5_hash = block5.hash();

// Start the syncer
let chain_sync_task_handle = tokio::spawn(chain_sync_future);

Expand Down Expand Up @@ -371,7 +363,6 @@ async fn sync_blocks_duplicate_hashes_ok() -> Result<(), crate::BoxError> {
block1_hash,
block1_hash, // tip
block2_hash, // expected_next
block3_hash, // (discarded - last hash, possibly incorrect)
]));

// State is checked for the first unknown block (block 1)
Expand Down Expand Up @@ -459,7 +450,6 @@ async fn sync_blocks_duplicate_hashes_ok() -> Result<(), crate::BoxError> {
block4_hash,
block3_hash,
block4_hash,
block5_hash, // (discarded - last hash, possibly incorrect)
]));

// Clear remaining block locator requests
Expand Down Expand Up @@ -607,9 +597,6 @@ async fn sync_block_too_high_obtain_tips() -> Result<(), crate::BoxError> {
let block2: Arc<Block> = zebra_test::vectors::BLOCK_MAINNET_2_BYTES.zcash_deserialize_into()?;
let block2_hash = block2.hash();

let block3: Arc<Block> = zebra_test::vectors::BLOCK_MAINNET_3_BYTES.zcash_deserialize_into()?;
let block3_hash = block3.hash();

// Also get a block that is a long way away from genesis
let block982k: Arc<Block> =
zebra_test::vectors::BLOCK_MAINNET_982681_BYTES.zcash_deserialize_into()?;
Expand Down Expand Up @@ -670,7 +657,6 @@ async fn sync_block_too_high_obtain_tips() -> Result<(), crate::BoxError> {
block982k_hash,
block1_hash, // tip
block2_hash, // expected_next
block3_hash, // (discarded - last hash, possibly incorrect)
]));

// State is checked for the first unknown block (block 982k)
Expand Down Expand Up @@ -780,9 +766,6 @@ async fn sync_block_too_high_extend_tips() -> Result<(), crate::BoxError> {
let block4: Arc<Block> = zebra_test::vectors::BLOCK_MAINNET_4_BYTES.zcash_deserialize_into()?;
let block4_hash = block4.hash();

let block5: Arc<Block> = zebra_test::vectors::BLOCK_MAINNET_5_BYTES.zcash_deserialize_into()?;
let block5_hash = block5.hash();

// Also get a block that is a long way away from genesis
let block982k: Arc<Block> =
zebra_test::vectors::BLOCK_MAINNET_982681_BYTES.zcash_deserialize_into()?;
Expand Down Expand Up @@ -842,7 +825,6 @@ async fn sync_block_too_high_extend_tips() -> Result<(), crate::BoxError> {
.respond(zn::Response::BlockHashes(vec![
block1_hash, // tip
block2_hash, // expected_next
block3_hash, // (discarded - last hash, possibly incorrect)
]));

// State is checked for the first unknown block (block 1)
Expand Down Expand Up @@ -929,7 +911,6 @@ async fn sync_block_too_high_extend_tips() -> Result<(), crate::BoxError> {
block3_hash, // expected_next
block4_hash,
block982k_hash,
block5_hash, // (discarded - last hash, possibly incorrect)
]));

// Clear remaining block locator requests
Expand Down
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