136 lines
4.2 KiB
Rust
136 lines
4.2 KiB
Rust
// Copyright 2019-2020 Google LLC
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//! Store specification.
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use crate::format::Format;
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use crate::{usize_to_nat, StoreError, StoreRatio, StoreResult, StoreUpdate};
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use std::collections::HashMap;
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/// Models the mutable operations of a store.
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///
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/// The model doesn't model the storage and read-only operations. This is done by the
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/// [driver](crate::StoreDriver).
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#[derive(Clone, Debug)]
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pub struct StoreModel {
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/// Represents the content of the store.
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content: HashMap<usize, Box<[u8]>>,
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/// The modeled storage configuration.
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format: Format,
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}
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/// Mutable operations on a store.
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#[derive(Clone, Debug)]
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pub enum StoreOperation {
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/// Applies a transaction.
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Transaction {
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/// The list of updates to be applied.
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updates: Vec<StoreUpdate<Vec<u8>>>,
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},
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/// Deletes all keys above a threshold.
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Clear {
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/// The minimum key to be deleted.
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min_key: usize,
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},
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/// Compacts the store until a given capacity is immediately available.
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Prepare {
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/// How much capacity should be immediately available after compaction.
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length: usize,
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},
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}
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impl StoreModel {
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/// Creates an empty model for a given storage configuration.
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pub fn new(format: Format) -> StoreModel {
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let content = HashMap::new();
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StoreModel { content, format }
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}
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/// Returns the modeled content.
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pub fn content(&self) -> &HashMap<usize, Box<[u8]>> {
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&self.content
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}
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/// Returns the storage configuration.
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pub fn format(&self) -> &Format {
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&self.format
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}
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/// Simulates a store operation.
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pub fn apply(&mut self, operation: StoreOperation) -> StoreResult<()> {
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match operation {
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StoreOperation::Transaction { updates } => self.transaction(updates),
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StoreOperation::Clear { min_key } => self.clear(min_key),
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StoreOperation::Prepare { length } => self.prepare(length),
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}
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}
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/// Returns the capacity according to the model.
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pub fn capacity(&self) -> StoreRatio {
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let total = self.format.total_capacity();
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let used = usize_to_nat(
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self.content
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.values()
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.map(|x| self.format.entry_size(x) as usize)
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.sum(),
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);
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StoreRatio { used, total }
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}
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/// Applies a transaction.
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fn transaction(&mut self, updates: Vec<StoreUpdate<Vec<u8>>>) -> StoreResult<()> {
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// Fail if the transaction is invalid.
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if self.format.transaction_valid(&updates).is_none() {
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return Err(StoreError::InvalidArgument);
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}
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// Fail if there is not enough capacity.
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let capacity = self.format.transaction_capacity(&updates) as usize;
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if self.capacity().remaining() < capacity {
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return Err(StoreError::NoCapacity);
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}
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// Apply the updates.
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for update in updates {
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match update {
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StoreUpdate::Insert { key, value } => {
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self.content.insert(key, value.into_boxed_slice());
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}
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StoreUpdate::Remove { key } => {
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self.content.remove(&key);
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}
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}
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}
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Ok(())
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}
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/// Applies a clear operation.
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fn clear(&mut self, min_key: usize) -> StoreResult<()> {
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if min_key > self.format.max_key() as usize {
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return Err(StoreError::InvalidArgument);
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}
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self.content.retain(|&k, _| k < min_key);
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Ok(())
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}
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/// Applies a prepare operation.
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fn prepare(&self, length: usize) -> StoreResult<()> {
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if self.capacity().remaining() < length {
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return Err(StoreError::NoCapacity);
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}
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Ok(())
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}
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}
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