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// Copyright 2015-2018 Parity Technologies (UK) Ltd.
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// 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/>.
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//! Database of byte-slices keyed to their hash.
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extern crate elastic_array ;
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extern crate heapsize ;
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use elastic_array ::ElasticArray128 ;
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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 ;
}
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/// `HashDB` value type.
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pub type DBValue = ElasticArray128 < u8 > ;
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/// Trait modelling datastore keyed by a hash defined by the `Hasher`.
pub trait HashDB < H : Hasher > : Send + Sync + AsHashDB < H > {
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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 < DBValue > ;
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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.
fn emplace ( & mut self , key : H ::Out , value : DBValue ) ;
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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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pub trait AsHashDB < H : Hasher > {
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/// Perform upcast to HashDB for anything that derives from HashDB.
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fn as_hashdb ( & self ) -> & HashDB < H > ;
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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 > ;
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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
// 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 }
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}
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