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