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refactor(store): extract compute_merkle_path_by_ordinal helper #15962

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refactor(store): extract compute_merkle_path_by_ordinal helper #15962

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148 changes: 83 additions & 65 deletions core/store/src/merkle_proof.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -42,71 +42,12 @@ pub trait MerkleProofAccess {
block_hash, head_block_hash
)));
}

let mut path = vec![];
let mut level: u64 = 0;
let mut index = leaf_index;
let mut remaining_size = tree_size;

while remaining_size > 1 {
// Walk left.
{
let cur_index = index;
let cur_level = level;
// Go up as long as we're the right child. This finds us a largest subtree for
// which our current node is the rightmost descendant of at the current level.
while remaining_size > 1 && index % 2 == 1 {
index /= 2;
remaining_size = (remaining_size + 1) / 2;
level += 1;
}
if level > cur_level {
// To prove this subtree, get the partial tree for the rightmost leaf of the
// subtree. It's OK if we can only go as far as the tree size; we'll aggregate
// whatever we can. Once we have the partial tree, we push in whatever is in
// between the levels we just traversed.
let ordinal = ((cur_index + 1) * (1 << cur_level) - 1).min(tree_size - 1);
let partial_tree_for_node = get_block_merkle_tree_from_ordinal(self, ordinal)?;
partial_tree_for_node.iter_path_from_bottom(|hash, l| {
if l >= cur_level && l < level {
path.push(MerklePathItem { hash, direction: Direction::Left });
}
});
}
}
// Walk right.
if remaining_size > 1 {
let right_sibling_index = index + 1;
let ordinal = ((right_sibling_index + 1) * (1 << level) - 1).min(tree_size - 1);
// It's possible the right sibling is actually zero, in which case we don't push
// anything to the path.
if ordinal >= right_sibling_index * (1 << level) {
// To prove a right sibling, get the partial tree for the rightmost leaf of the
// subtree, and also get the block hash of the rightmost leaf; combining these
// two will give us the root of the subtree, i.e. the right sibling.
let leaf_hash = self.get_block_hash_from_ordinal(ordinal)?;
let mut subtree_root_hash = leaf_hash;
if level > 0 {
let partial_tree_for_sibling =
get_block_merkle_tree_from_ordinal(self, ordinal)?;
partial_tree_for_sibling.iter_path_from_bottom(|hash, l| {
if l < level {
subtree_root_hash = combine_hash(&hash, &subtree_root_hash);
}
});
}
path.push(MerklePathItem {
hash: subtree_root_hash,
direction: Direction::Right,
});
}

index = (index + 1) / 2;
remaining_size = (remaining_size + 1) / 2;
level += 1;
}
}
Ok(path)
compute_merkle_path_by_ordinal(
leaf_index,
tree_size,
|ordinal| get_block_merkle_tree_from_ordinal(self, ordinal),
|ordinal| self.get_block_hash_from_ordinal(ordinal),
)
}
}

Expand All @@ -118,6 +59,83 @@ fn get_block_merkle_tree_from_ordinal(
this.get_block_merkle_tree(&block_hash)
}

/// Build the inclusion path for the leaf at `leaf_index` within a merkle tree of
/// `tree_size` leaves, given ordinal-indexed access to each leaf hash and to the
/// frontier (partial) tree as of each ordinal. Accesses no leaf below `leaf_index`
/// nor any frontier beyond `tree_size`. Errors if `leaf_index >= tree_size`.
pub fn compute_merkle_path_by_ordinal(
leaf_index: u64,
tree_size: u64,
partial_tree_at_ordinal: impl Fn(u64) -> Result<Arc<PartialMerkleTree>, Error>,
leaf_hash_at_ordinal: impl Fn(u64) -> Result<CryptoHash, Error>,
) -> Result<MerklePath, Error> {
if leaf_index >= tree_size {
return Err(Error::Other(format!(
"leaf index {leaf_index} is ahead of tree size {tree_size}"
)));
}
let mut path = vec![];
let mut level: u64 = 0;
let mut index = leaf_index;
let mut remaining_size = tree_size;

while remaining_size > 1 {
// Walk left.
{
let cur_index = index;
let cur_level = level;
// Go up as long as we're the right child. This finds us a largest subtree for
// which our current node is the rightmost descendant of at the current level.
while remaining_size > 1 && index % 2 == 1 {
index /= 2;
remaining_size = (remaining_size + 1) / 2;
level += 1;
}
if level > cur_level {
// To prove this subtree, get the partial tree for the rightmost leaf of the
// subtree. It's OK if we can only go as far as the tree size; we'll aggregate
// whatever we can. Once we have the partial tree, we push in whatever is in
// between the levels we just traversed.
let ordinal = ((cur_index + 1) * (1 << cur_level) - 1).min(tree_size - 1);
let partial_tree_for_node = partial_tree_at_ordinal(ordinal)?;
partial_tree_for_node.iter_path_from_bottom(|hash, l| {
if l >= cur_level && l < level {
path.push(MerklePathItem { hash, direction: Direction::Left });
}
});
}
}
// Walk right.
if remaining_size > 1 {
let right_sibling_index = index + 1;
let ordinal = ((right_sibling_index + 1) * (1 << level) - 1).min(tree_size - 1);
// It's possible the right sibling is actually zero, in which case we don't push
// anything to the path.
if ordinal >= right_sibling_index * (1 << level) {
// To prove a right sibling, get the partial tree for the rightmost leaf of the
// subtree, and also get the leaf hash of the rightmost leaf; combining these
// two will give us the root of the subtree, i.e. the right sibling.
let leaf_hash = leaf_hash_at_ordinal(ordinal)?;
let mut subtree_root_hash = leaf_hash;
if level > 0 {
let partial_tree_for_sibling = partial_tree_at_ordinal(ordinal)?;
partial_tree_for_sibling.iter_path_from_bottom(|hash, l| {
if l < level {
subtree_root_hash = combine_hash(&hash, &subtree_root_hash);
}
});
}
path.push(MerklePathItem { hash: subtree_root_hash, direction: Direction::Right });
}

index = (index + 1) / 2;
remaining_size = (remaining_size + 1) / 2;
level += 1;
}
}
Ok(path)
}

impl MerkleProofAccess for Store {
fn get_block_merkle_tree(
&self,
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