Optimize PMMR segments to only include hashes at pruning boundaries #3820
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
|
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@@ -307,10 +307,11 @@ where | |
| T: Readable + Writeable + Debug, | ||
| { | ||
| /// Generate a segment from a PMMR | ||
| /// If bitmap is provided, only hashes at pruning boundaries are included. | ||
| pub fn from_pmmr<U, B>( | ||
| segment_id: SegmentIdentifier, | ||
| pmmr: &ReadonlyPMMR<'_, U, B>, | ||
| bitmap: Option<&Bitmap>, | ||
| ) -> Result<Self, SegmentError> | ||
| where | ||
| U: PMMRable<E = T>, | ||
|
|
@@ -331,15 +332,40 @@ where | |
| segment.leaf_data.push(data); | ||
| segment.leaf_pos.push(pos0); | ||
| continue; | ||
| } else if bitmap.is_none() { | ||
| return Err(SegmentError::MissingLeaf(pos0)); | ||
| } | ||
| } | ||
| if let Some(bm) = bitmap { | ||
| // Only include hash if this subtree is fully pruned | ||
| // AND the sibling subtree is NOT fully pruned (pruning boundary) | ||
| if subtree_fully_pruned(pos0, bm, mmr_size) { | ||
| // Find sibling position | ||
| let height = pmmr::bintree_postorder_height(pos0); | ||
| let subtree_size = (1u64 << (height + 1)) - 1; | ||
| let sibling_pos0 = if pmmr::is_left_sibling(pos0) { | ||
| // Right sibling is at pos0 + size of this subtree | ||
| Some(pos0 + subtree_size) | ||
| } else { | ||
| // Left sibling: go back by sibling's subtree size | ||
| pos0.checked_sub(subtree_size) | ||
| }; | ||
| // Need hash if sibling exists in segment and is not fully pruned | ||
| let need_hash = match sibling_pos0 { | ||
| Some(sib) if sib >= segment_first_pos && sib <= segment_last_pos => { | ||
| !subtree_fully_pruned(sib, bm, mmr_size) | ||
| } | ||
| _ => { | ||
| // Sibling outside segment or underflow - may need hash for proof | ||
| true | ||
| } | ||
| }; | ||
| if need_hash { | ||
|
Contributor
There was a problem hiding this comment. If need_hash is true, silently skipping a missing hash can produce a segment that later fails validation with MissingHash or Invalid Root. Should this return an error instead? like:
Contributor
There was a problem hiding this comment. This also matches the failure pattern you observed, @ardocrat. |
||
| if let Some(hash) = pmmr.get_from_file(pos0) { | ||
| segment.hashes.push(hash); | ||
| segment.hash_pos.push(pos0); | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
|
@@ -842,3 +868,14 @@ impl Writeable for SegmentProof { | |
| Ok(()) | ||
| } | ||
| } | ||
|
|
||
| /// Check if a subtree rooted at pos0 is fully pruned (no unspent leaves in bitmap) | ||
| fn subtree_fully_pruned(pos0: u64, bitmap: &Bitmap, mmr_size: u64) -> bool { | ||
| let leftmost = pmmr::bintree_leftmost(pos0); | ||
| let rightmost = pmmr::bintree_rightmost(pos0); | ||
| let n_leaves = pmmr::n_leaves(mmr_size); | ||
| let start_leaf = pmmr::n_leaves(leftmost + 1).saturating_sub(1); | ||
| let end_leaf = min(pmmr::n_leaves(rightmost + 1), n_leaves); | ||
| // If any leaf in range is in bitmap (unspent), subtree is not fully pruned | ||
| bitmap.range_cardinality(start_leaf as u32..end_leaf as u32) == 0 | ||
| } | ||
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Can we avoid .ok() here? If building the bitmap fails, I think this should return an error