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// Copyright 2017, 2018 Parity Technologies // // Licensed under the Apache License, Version 2.0 (the "License"); // you may not use this file except in compliance with the License. // You may obtain a copy of the License at // // http://www.apache.org/licenses/LICENSE-2.0 // // Unless required by applicable law or agreed to in writing, software // distributed under the License is distributed on an "AS IS" BASIS, // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. // See the License for the specific language governing permissions and // limitations under the License. //! Database of byte-slices keyed to their hash. #![cfg_attr(not(feature = "std"), no_std)] #![cfg_attr(not(feature = "std"), feature(core_intrinsics))] #[cfg(feature = "std")] use std::fmt::Debug; #[cfg(feature = "std")] use std::hash; #[cfg(feature = "std")] pub trait MaybeDebug: Debug {} #[cfg(feature = "std")] impl<T: Debug> MaybeDebug for T {} #[cfg(not(feature = "std"))] use core::hash; #[cfg(not(feature = "std"))] pub trait MaybeDebug {} #[cfg(not(feature = "std"))] impl<T> MaybeDebug for T {} /// 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 + MaybeDebug + PartialEq + Eq + hash::Hash + Send + Sync + Clone + Copy; /// What to use to build `HashMap`s with this `Hasher` type StdHasher: Sync + Send + Default + 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; } /// Trait modelling a plain datastore whose key is a fixed type. /// The caller should ensure that a key only corresponds to /// one value. pub trait PlainDB<K, V>: Send + Sync + AsPlainDB<K, V> { /// Look up a given hash into the bytes that hash to it, returning None if the /// hash is not known. fn get(&self, key: &K) -> Option<V>; /// Check for the existance of a hash-key. fn contains(&self, key: &K) -> bool; /// Insert a datum item into the DB. Insertions are counted and the equivalent /// number of `remove()`s must be performed before the data is considered dead. /// The caller should ensure that a key only corresponds to one value. fn emplace(&mut self, key: K, value: V); /// 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. /// The caller should ensure that a key only corresponds to one value. fn remove(&mut self, key: &K); } /// Trait for immutable reference of PlainDB. pub trait PlainDBRef<K, V> { /// Look up a given hash into the bytes that hash to it, returning None if the /// hash is not known. fn get(&self, key: &K) -> Option<V>; /// Check for the existance of a hash-key. fn contains(&self, key: &K) -> bool; } impl<'a, K, V> PlainDBRef<K, V> for &'a PlainDB<K, V> { fn get(&self, key: &K) -> Option<V> { PlainDB::get(*self, key) } fn contains(&self, key: &K) -> bool { PlainDB::contains(*self, key) } } impl<'a, K, V> PlainDBRef<K, V> for &'a mut PlainDB<K, V> { fn get(&self, key: &K) -> Option<V> { PlainDB::get(*self, key) } fn contains(&self, key: &K) -> bool { PlainDB::contains(*self, key) } } /// Trait modelling datastore keyed by a hash defined by the `Hasher`. pub trait HashDB<H: Hasher, T>: Send + Sync + AsHashDB<H, T> { /// 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, prefix: &[u8]) -> Option<T>; /// Check for the existance of a hash-key. fn contains(&self, key: &H::Out, prefix: &[u8]) -> 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, prefix: &[u8], value: &[u8]) -> H::Out; /// Like `insert()`, except you provide the key and the data is all moved. fn emplace(&mut self, key: H::Out, prefix: &[u8], value: T); /// 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, prefix: &[u8]); } /// Trait for immutable reference of HashDB. pub trait HashDBRef<H: Hasher, T> { /// 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, prefix: &[u8]) -> Option<T>; /// Check for the existance of a hash-key. fn contains(&self, key: &H::Out, prefix: &[u8]) -> bool; } impl<'a, H: Hasher, T> HashDBRef<H, T> for &'a HashDB<H, T> { fn get(&self, key: &H::Out, prefix: &[u8]) -> Option<T> { HashDB::get(*self, key, prefix) } fn contains(&self, key: &H::Out, prefix: &[u8]) -> bool { HashDB::contains(*self, key, prefix) } } impl<'a, H: Hasher, T> HashDBRef<H, T> for &'a mut HashDB<H, T> { fn get(&self, key: &H::Out, prefix: &[u8]) -> Option<T> { HashDB::get(*self, key, prefix) } fn contains(&self, key: &H::Out, prefix: &[u8]) -> bool { HashDB::contains(*self, key, prefix) } } /// Upcast trait for HashDB. pub trait AsHashDB<H: Hasher, T> { /// Perform upcast to HashDB for anything that derives from HashDB. fn as_hash_db(&self) -> &HashDB<H, T>; /// Perform mutable upcast to HashDB for anything that derives from HashDB. fn as_hash_db_mut<'a>(&'a mut self) -> &'a mut (HashDB<H, T> + 'a); } /// Upcast trait for PlainDB. pub trait AsPlainDB<K, V> { /// Perform upcast to PlainDB for anything that derives from PlainDB. fn as_plain_db(&self) -> &PlainDB<K, V>; /// Perform mutable upcast to PlainDB for anything that derives from PlainDB. fn as_plain_db_mut<'a>(&'a mut self) -> &'a mut (PlainDB<K, V> + 'a); } // 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, T> AsHashDB<H, T> for &'a mut HashDB<H, T> { fn as_hash_db(&self) -> &HashDB<H, T> { &**self } fn as_hash_db_mut<'b>(&'b mut self) -> &'b mut (HashDB<H, T> + 'b) { &mut **self } } #[cfg(feature = "std")] impl<'a, K, V> AsPlainDB<K, V> for &'a mut PlainDB<K, V> { fn as_plain_db(&self) -> &PlainDB<K, V> { &**self } fn as_plain_db_mut<'b>(&'b mut self) -> &'b mut (PlainDB<K, V> + 'b) { &mut **self } }