refactor(pkg/trie/triedb): implement generics, refactor nibbles, revise iterator

[timwu20]

Changes

• Introduces and integrates a new hash.Hash and hash.Hasher interface constraints into triedb package.
  • This is a local interface that is similar to runtime.Hash and runtime.Hasher already on development.
  • Updates all the tests to use hash.H256 for the hash and runtime.BlakeTwo256 as the hasher.
• Refactors how we handle nibbles in triedb. Introduces NibbleSlice, Nibbles, and LeftNibbles. Each of these introduced types has their own distinct public interface and are used in different components within triedb.
  • Nibbles is analogous to trie_db::nibble::NibbleSlice. Primarily used to avoid costly slice manipulation and unnecessary copying of underlying bytes. Able to represent different nibble starting points, but not mutable to be able to reconstruct full keys.
  • NibbleSlice is analogous to trie_db::nibble::NibbleVec. Mutable in the sense you can push and pop nibbles as well as truncate. Used to reconstruct full keys.
  • LeftNibbles is analogous to trie_db::nibble::LeftNibbleSlice. Used in proof generation and verification. Since NibbleSlice and Nibbles are right aligned it makes it more expensive to truncate. LeftNibbles left aligns the nibbles which facilitates faster truncation.
• Revises the iterator to mirror TrieDBRawIterator which is imported by the state machine primitives in substrate. This is embedded in other types to be able to iterate and return expected types. The rawItem introduced that is returned by rawIterator.nextRawItem includes the partial key as NibbleSlice, hash of the node, and an in-memory type that fulfills the codec.EncodedNode interface (Branch or Leaf).

Notes

• Removes caching and introduces a temporary Cache interface to avoid too many code changes to how we construct TrieDBs and the options we provide it.
• Future PR will introduce the new caching interface as required from future client db work. The implementation of the cache is actually in substrate and will not be included as part triedb package.
• Backwards compatibility is now broken given we have revised how we store the nodes in underlying k/v store. We are now inline with the rust trie impl on how we store keys for nodes.
  • We were using an "expanded" view of the nibbles as part of the storage keys for the nodes. An expanded view is essentially where each nibble occupies an entire byte. So keys were 2x longer than we actually needed.
  • We also now prefix hash values based on child to avoid any key collisions. It was highly unlikely we would retrieve the wrong value, but I think it's a prudent decision to prefix it in our impl.

Tests

go test -tags integration github.com/ChainSafe/gossamer

Issues

contributes to #4157

[dimartiro]

A few comments but overall ok!
Thanks for spending time working on this changes Tim! I tried to keep the TrieDB as simple as possible but it seems that it wasn't enough 💔

[timwu20]

A few comments but overall ok! Thanks for spending time working on this changes Tim! I tried to keep the TrieDB as simple as possible but it seems that it wasn't enough 💔

You did all the heavy lifting @dimartiro! The fact that I have something to integrate with and contribute to is a testament to your hard work. 💪