feat(diff): Framework for change proofs #839
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Unoptimized version for reference, with some tests
Generates BatchOp operations representing the differences between two merkle tries, with an optional start key. Sub-tries with identical hashes are skipped. The two main structures are DiffMerkleKeyValueStreams which manages the dual trie iteration and holds the pending values, and DiffIteratorState which keeps track of which values are saved because they haven't been matched to the other trie yet. Algorithm: 1. Iterates through both trees simultaneously from optional start key 2. Compares keys lexicographically to determine operation type 3. Generate Put operations for additions/modifications 4. Generate Delete operations for removals 5. Saves out-of-order values in iterator state for next iteration 6. Optimizes by skipping subtrees with matching hashes (when possible) Testing: There are basic tests and a fuzz test. If the test fails, instructions on how to rerun it with the correct seed are provided in the error output. This follows the same pattern as the merkle fuzz tests.
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Took a slightly different approach, since the previous diff didn't use the optimized node iterator, and didn't even check for it. Other changes: - Renamed children_have_same_hash() to child_identical() - Added documentation around more complicated functions - Added additional tests to verify that fewer nodes are read when diffing tries with hashes already computed - Installed a test metrics recorder so metrics can be checked at runtime Note that if we add additional tests that want to use this metrics recorder, we would need to put this into a utility method and save it in case some other test initializes the metrics.
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demosdemon
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Jun 11, 2025
firewood/src/diff.rs
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| impl fmt::Debug for VisitedPairState { | ||
| fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { | ||
| f.debug_struct("VisitedPairState") | ||
| .field("children_iter_left", &"<iterator>") | ||
| .field("children_iter_right", &"<iterator>") | ||
| .finish() | ||
| } | ||
| } |
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We can use derivative to clean up these manually implemented Debugs.
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This is part 2 of 3 for change proofs, and contains the bulk of the work. The remaining changes involve calling these methods from the API to resolve #443.
Generates
BatchOpoperations representing the differences between two merkle tries, with an optional start key. Sub-tries with identical hashes are skipped.The two main structures are
DiffMerkleKeyValueStreamswhich manages the dual trie iteration and holds the pending values, andDiffIteratorStatewhich keeps track of which values are saved because they haven't been matched to the other trie yet.Algorithm: