151 lines
4.9 KiB
Rust
151 lines
4.9 KiB
Rust
//! Performs cached merkle-hashing adhering to the Ethereum 2.0 specification defined
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//! [here](https://github.com/ethereum/eth2.0-specs/blob/v0.5.1/specs/simple-serialize.md#merkleization).
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//!
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//! Caching allows for reduced hashing when some object has only been partially modified. This
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//! allows for significant CPU-time savings (at the cost of additional storage). For example,
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//! determining the root of a list of 1024 items with a single modification has been observed to
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//! run in 1/25th of the time of a full merkle hash.
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//!
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//!
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//! # Example:
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//!
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//! ```
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//! use cached_tree_hash::TreeHashCache;
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//! use tree_hash_derive::{TreeHash, CachedTreeHash};
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//!
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//! #[derive(TreeHash, CachedTreeHash)]
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//! struct Foo {
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//! bar: u64,
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//! baz: Vec<u64>
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//! }
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//!
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//! let mut foo = Foo {
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//! bar: 1,
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//! baz: vec![0, 1, 2]
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//! };
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//!
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//! let mut cache = TreeHashCache::new(&foo).unwrap();
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//!
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//! foo.baz[1] = 0;
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//!
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//! cache.update(&foo).unwrap();
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//!
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//! println!("Root is: {:?}", cache.tree_hash_root().unwrap());
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//! ```
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use hashing::hash;
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use std::ops::Range;
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use tree_hash::{TreeHash, TreeHashType, BYTES_PER_CHUNK, HASHSIZE};
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mod btree_overlay;
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mod errors;
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mod impls;
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pub mod merkleize;
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mod resize;
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mod tree_hash_cache;
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pub use btree_overlay::{BTreeOverlay, BTreeSchema};
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pub use errors::Error;
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pub use impls::vec;
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pub use tree_hash_cache::TreeHashCache;
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pub trait CachedTreeHash: TreeHash {
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fn tree_hash_cache_schema(&self, depth: usize) -> BTreeSchema;
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fn num_tree_hash_cache_chunks(&self) -> usize {
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self.tree_hash_cache_schema(0).into_overlay(0).num_chunks()
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}
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fn new_tree_hash_cache(&self, depth: usize) -> Result<TreeHashCache, Error>;
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fn update_tree_hash_cache(&self, cache: &mut TreeHashCache) -> Result<(), Error>;
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}
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/// Implements `CachedTreeHash` on `$type` as a fixed-length tree-hash vector of the ssz encoding
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/// of `$type`.
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#[macro_export]
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macro_rules! cached_tree_hash_ssz_encoding_as_vector {
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($type: ident, $num_bytes: expr) => {
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impl cached_tree_hash::CachedTreeHash for $type {
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fn new_tree_hash_cache(
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&self,
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depth: usize,
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) -> Result<cached_tree_hash::TreeHashCache, cached_tree_hash::Error> {
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let (cache, _schema) =
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cached_tree_hash::vec::new_tree_hash_cache(&ssz::ssz_encode(self), depth)?;
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Ok(cache)
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}
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fn tree_hash_cache_schema(&self, depth: usize) -> cached_tree_hash::BTreeSchema {
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let lengths =
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vec![1; cached_tree_hash::merkleize::num_unsanitized_leaves($num_bytes)];
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cached_tree_hash::BTreeSchema::from_lengths(depth, lengths)
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}
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fn update_tree_hash_cache(
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&self,
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cache: &mut cached_tree_hash::TreeHashCache,
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) -> Result<(), cached_tree_hash::Error> {
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cached_tree_hash::vec::update_tree_hash_cache(&ssz::ssz_encode(self), cache)?;
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Ok(())
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}
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}
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};
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}
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/// Implements `CachedTreeHash` on `$type` as a variable-length tree-hash list of the result of
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/// calling `.as_bytes()` on `$type`.
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#[macro_export]
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macro_rules! cached_tree_hash_bytes_as_list {
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($type: ident) => {
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impl cached_tree_hash::CachedTreeHash for $type {
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fn new_tree_hash_cache(
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&self,
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depth: usize,
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) -> Result<cached_tree_hash::TreeHashCache, cached_tree_hash::Error> {
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let bytes = self.to_bytes();
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let (mut cache, schema) =
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cached_tree_hash::vec::new_tree_hash_cache(&bytes, depth)?;
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cache.add_length_nodes(schema.into_overlay(0).chunk_range(), bytes.len())?;
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Ok(cache)
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}
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fn num_tree_hash_cache_chunks(&self) -> usize {
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// Add two extra nodes to cater for the node before and after to allow mixing-in length.
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cached_tree_hash::BTreeOverlay::new(self, 0, 0).num_chunks() + 2
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}
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fn tree_hash_cache_schema(&self, depth: usize) -> cached_tree_hash::BTreeSchema {
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let bytes = self.to_bytes();
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cached_tree_hash::vec::produce_schema(&bytes, depth)
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}
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fn update_tree_hash_cache(
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&self,
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cache: &mut cached_tree_hash::TreeHashCache,
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) -> Result<(), cached_tree_hash::Error> {
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let bytes = self.to_bytes();
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// Skip the length-mixed-in root node.
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cache.chunk_index += 1;
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// Update the cache, returning the new overlay.
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let new_overlay = cached_tree_hash::vec::update_tree_hash_cache(&bytes, cache)?;
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// Mix in length
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cache.mix_in_length(new_overlay.chunk_range(), bytes.len())?;
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// Skip an extra node to clear the length node.
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cache.chunk_index += 1;
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Ok(())
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}
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}
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};
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}
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