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// Copyright 2015-2018 Parity Technologies (UK) Ltd. // This file is part of Parity. // Parity is free software: you can redistribute it and/or modify // it under the terms of the GNU General Public License as published by // the Free Software Foundation, either version 3 of the License, or // (at your option) any later version. // Parity is distributed in the hope that it will be useful, // but WITHOUT ANY WARRANTY; without even the implied warranty of // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the // GNU General Public License for more details. // You should have received a copy of the GNU General Public License // along with Parity. If not, see <http://www.gnu.org/licenses/>. //! Database of byte-slices keyed to their hash. extern crate elastic_array; extern crate heapsize; use elastic_array::ElasticArray128; use heapsize::HeapSizeOf; use std::collections::HashMap; use std::{fmt::Debug, hash::Hash}; /// Trait describing an object that can hash a slice of bytes. Used to abstract /// other types over the hashing algorithm. Defines a single `hash` method and an /// `Out` associated type with the necessary bounds. pub trait Hasher: Sync + Send { /// The output type of the `Hasher` type Out: AsRef<[u8]> + AsMut<[u8]> + Default + HeapSizeOf + Debug + PartialEq + Eq + Hash + Send + Sync + Clone + Copy; /// What to use to build `HashMap`s with this `Hasher` type StdHasher: Sync + Send + Default + std::hash::Hasher; /// The length in bytes of the `Hasher` output const LENGTH: usize; /// Compute the hash of the provided slice of bytes returning the `Out` type of the `Hasher` fn hash(x: &[u8]) -> Self::Out; } /// `HashDB` value type. pub type DBValue = ElasticArray128<u8>; /// Trait modelling datastore keyed by a hash defined by the `Hasher`. pub trait HashDB<H: Hasher>: Send + Sync + AsHashDB<H> { /// Get the keys in the database together with number of underlying references. fn keys(&self) -> HashMap<H::Out, i32>; /// Look up a given hash into the bytes that hash to it, returning None if the /// hash is not known. fn get(&self, key: &H::Out) -> Option<DBValue>; /// Check for the existance of a hash-key. fn contains(&self, key: &H::Out) -> bool; /// Insert a datum item into the DB and return the datum's hash for a later lookup. Insertions /// are counted and the equivalent number of `remove()`s must be performed before the data /// is considered dead. fn insert(&mut self, value: &[u8]) -> H::Out; /// Like `insert()`, except you provide the key and the data is all moved. fn emplace(&mut self, key: H::Out, value: DBValue); /// Remove a datum previously inserted. Insertions can be "owed" such that the same number of `insert()`s may /// happen without the data being eventually being inserted into the DB. It can be "owed" more than once. fn remove(&mut self, key: &H::Out); } /// Upcast trait. pub trait AsHashDB<H: Hasher> { /// Perform upcast to HashDB for anything that derives from HashDB. fn as_hashdb(&self) -> &HashDB<H>; /// Perform mutable upcast to HashDB for anything that derives from HashDB. fn as_hashdb_mut(&mut self) -> &mut HashDB<H>; } // NOTE: There used to be a `impl<T> AsHashDB for T` but that does not work with generics. See https://stackoverflow.com/questions/48432842/implementing-a-trait-for-reference-and-non-reference-types-causes-conflicting-im // This means we need concrete impls of AsHashDB in several places, which somewhat defeats the point of the trait. impl<'a, H: Hasher> AsHashDB<H> for &'a mut HashDB<H> { fn as_hashdb(&self) -> &HashDB<H> { &**self } fn as_hashdb_mut(&mut self) -> &mut HashDB<H> { &mut **self } }