// Copyright 2014 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library 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 Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
// Package memorydb implements the key-value database layer based on memory maps.
package memorydb
import (
"errors"
"sort"
"strings"
"sync"
"github.com/ethereum/go-ethereum/common"
"github.com/ethereum/go-ethereum/ethdb"
)
var (
// errMemorydbClosed is returned if a memory database was already closed at the
// invocation of a data access operation.
errMemorydbClosed = errors.New("database closed")
// errMemorydbNotFound is returned if a key is requested that is not found in
// the provided memory database.
errMemorydbNotFound = errors.New("not found")
)
// Database is an ephemeral key-value store. Apart from basic data storage
// functionality it also supports batch writes and iterating over the keyspace in
// binary-alphabetical order.
type Database struct {
db map[string][]byte
lock sync.RWMutex
}
// New returns a wrapped map with all the required database interface methods
// implemented.
func New() *Database {
return &Database{
db: make(map[string][]byte),
}
}
// NewWithCap returns a wrapped map pre-allocated to the provided capcity with
// all the required database interface methods implemented.
func NewWithCap(size int) *Database {
return &Database{
db: make(map[string][]byte, size),
}
}
// Close deallocates the internal map and ensures any consecutive data access op
// failes with an error.
func (db *Database) Close() error {
db.lock.Lock()
defer db.lock.Unlock()
db.db = nil
return nil
}
// Has retrieves if a key is present in the key-value store.
func (db *Database) Has(key []byte) (bool, error) {
db.lock.RLock()
defer db.lock.RUnlock()
if db.db == nil {
return false, errMemorydbClosed
}
_, ok := db.db[string(key)]
return ok, nil
}
// Get retrieves the given key if it's present in the key-value store.
func (db *Database) Get(key []byte) ([]byte, error) {
db.lock.RLock()
defer db.lock.RUnlock()
if db.db == nil {
return nil, errMemorydbClosed
}
if entry, ok := db.db[string(key)]; ok {
return common.CopyBytes(entry), nil
}
return nil, errMemorydbNotFound
}
// Put inserts the given value into the key-value store.
func (db *Database) Put(key []byte, value []byte) error {
db.lock.Lock()
defer db.lock.Unlock()
if db.db == nil {
return errMemorydbClosed
}
db.db[string(key)] = common.CopyBytes(value)
return nil
}
// Delete removes the key from the key-value store.
func (db *Database) Delete(key []byte) error {
db.lock.Lock()
defer db.lock.Unlock()
if db.db == nil {
return errMemorydbClosed
}
delete(db.db, string(key))
return nil
}
// NewBatch creates a write-only key-value store that buffers changes to its host
// database until a final write is called.
func (db *Database) NewBatch() ethdb.Batch {
return &batch{
db: db,
}
}
// NewIterator creates a binary-alphabetical iterator over the entire keyspace
// contained within the memory database.
func (db *Database) NewIterator() ethdb.Iterator {
return db.NewIteratorWithPrefix(nil)
}
// NewIteratorWithPrefix creates a binary-alphabetical iterator over a subset
// of database content with a particular key prefix.
func (db *Database) NewIteratorWithPrefix(prefix []byte) ethdb.Iterator {
db.lock.RLock()
defer db.lock.RUnlock()
var (
pr = string(prefix)
keys = make([]string, 0, len(db.db))
values = make([][]byte, 0, len(db.db))
)
// Collect the keys from the memory database corresponding to the given prefix
for key := range db.db {
if strings.HasPrefix(key, pr) {
keys = append(keys, key)
}
}
// Sort the items and retrieve the associated values
sort.Strings(keys)
for _, key := range keys {
values = append(values, db.db[key])
}
return &iterator{
keys: keys,
values: values,
}
}
// Stat returns a particular internal stat of the database.
func (db *Database) Stat(property string) (string, error) {
return "", errors.New("unknown property")
}
// Compact is not supported on a memory database.
func (db *Database) Compact(start []byte, limit []byte) error {
return errors.New("unsupported operation")
}
// Len returns the number of entries currently present in the memory database.
//
// Note, this method is only used for testing (i.e. not public in general) and
// does not have explicit checks for closed-ness to allow simpler testing code.
func (db *Database) Len() int {
db.lock.RLock()
defer db.lock.RUnlock()
return len(db.db)
}
// keyvalue is a key-value tuple tagged with a deletion field to allow creating
// memory-database write batches.
type keyvalue struct {
key []byte
value []byte
delete bool
}
// batch is a write-only memory batch that commits changes to its host
// database when Write is called. A batch cannot be used concurrently.
type batch struct {
db *Database
writes []keyvalue
size int
}
// Put inserts the given value into the batch for later committing.
func (b *batch) Put(key, value []byte) error {
b.writes = append(b.writes, keyvalue{common.CopyBytes(key), common.CopyBytes(value), false})
b.size += len(value)
return nil
}
// Delete inserts the a key removal into the batch for later committing.
func (b *batch) Delete(key []byte) error {
b.writes = append(b.writes, keyvalue{common.CopyBytes(key), nil, true})
b.size += 1
return nil
}
// ValueSize retrieves the amount of data queued up for writing.
func (b *batch) ValueSize() int {
return b.size
}
// Write flushes any accumulated data to the memory database.
func (b *batch) Write() error {
b.db.lock.Lock()
defer b.db.lock.Unlock()
for _, keyvalue := range b.writes {
if keyvalue.delete {
delete(b.db.db, string(keyvalue.key))
continue
}
b.db.db[string(keyvalue.key)] = keyvalue.value
}
return nil
}
// Reset resets the batch for reuse.
func (b *batch) Reset() {
b.writes = b.writes[:0]
b.size = 0
}
// iterator can walk over the (potentially partial) keyspace of a memory key
// value store. Internally it is a deep copy of the entire iterated state,
// sorted by keys.
type iterator struct {
inited bool
keys []string
values [][]byte
}
// Next moves the iterator to the next key/value pair. It returns whether the
// iterator is exhausted.
func (it *iterator) Next() bool {
// If the iterator was not yet initialized, do it now
if !it.inited {
it.inited = true
return len(it.keys) > 0
}
// Iterator already initialize, advance it
if len(it.keys) > 0 {
it.keys = it.keys[1:]
it.values = it.values[1:]
}
return len(it.keys) > 0
}
// Error returns any accumulated error. Exhausting all the key/value pairs
// is not considered to be an error. A memory iterator cannot encounter errors.
func (it *iterator) Error() error {
return nil
}
// Key returns the key of the current key/value pair, or nil if done. The caller
// should not modify the contents of the returned slice, and its contents may
// change on the next call to Next.
func (it *iterator) Key() []byte {
if len(it.keys) > 0 {
return []byte(it.keys[0])
}
return nil
}
// Value returns the value of the current key/value pair, or nil if done. The
// caller should not modify the contents of the returned slice, and its contents
// may change on the next call to Next.
func (it *iterator) Value() []byte {
if len(it.values) > 0 {
return it.values[0]
}
return nil
}
// Release releases associated resources. Release should always succeed and can
// be called multiple times without causing error.
func (it *iterator) Release() {
it.keys, it.values = nil, nil
}
