Add simple key-value storage package

storage/storage.go

@@ -0,0 +1,125 @@
+/*
+ * Copyright 2018 The ThunderDB Authors.
+ *
+ * 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.
+ */
+
+// Package storage implements simple key-value storage interfaces based on sqlite3
+// Although DB should be safe for concurrent use according to
+// https://golang.org/pkg/database/sql/#OpenDB, there are some issue with go-sqlite3 implementation.
+// See https://github.com/mattn/go-sqlite3/issues/148 for details.
+// As a result, concurrent use in this package is not recommended for now.
+package storage
+
+import (
+	"database/sql"
+	"fmt"
+	"sync"
+
+	// Register go-sqlite3 engine
+	_ "github.com/mattn/go-sqlite3"
+)
+
+var (
+	index = struct {
+		mu *sync.Mutex
+		db map[string]*sql.DB
+	}{
+		&sync.Mutex{},
+		make(map[string]*sql.DB),
+	}
+)
+
+func openDB(dsn string) (db *sql.DB, err error) {
+	index.mu.Lock()
+	defer index.mu.Unlock()
+
+	db = index.db[dsn]
+	if db == nil {
+		db, err = sql.Open("sqlite3", dsn)
+
+		if err != nil {
+			return nil, err
+		}
+
+		index.db[dsn] = db
+	}
+
+	return db, err
+}
+
+// Storage represents a key-value storage
+type Storage struct {
+	dsn   string
+	table string
+	db    *sql.DB
+}
+
+// OpenStorage opens a database using the specified DSN and ensures that the specified table exists.
+func OpenStorage(dsn string, table string) (st *Storage, err error) {
+	// Open database
+	var db *sql.DB
+	db, err = openDB(dsn)
+
+	if err != nil {
+		return st, err
+	}
+
+	// Ensure table
+	stmt := fmt.Sprintf("CREATE TABLE IF NOT EXISTS `%s` (`key` TEXT PRIMARY KEY, `value` BLOB)",
+		table)
+	_, err = db.Exec(stmt)
+
+	if err != nil {
+		return st, err
+	}
+
+	st = &Storage{dsn, table, db}
+	return st, err
+}
+
+// SetValue sets or replace the value to key
+func (s *Storage) SetValue(key string, value []byte) (err error) {
+	stmt := fmt.Sprintf("INSERT OR REPLACE INTO `%s` (`key`, `value`) VALUES (?, ?)", s.table)
+	_, err = s.db.Exec(stmt, key, value)
+
+	return err
+}
+
+// SetValueIfNotExist sets the value to key if it doesn't exist
+func (s *Storage) SetValueIfNotExist(key string, value []byte) (err error) {
+	stmt := fmt.Sprintf("INSERT OR IGNORE INTO `%s` (`key`, `value`) VALUES (?, ?)", s.table)
+	_, err = s.db.Exec(stmt, key, value)
+
+	return err
+}
+
+// DelValue deletes the value of key
+func (s *Storage) DelValue(key string) (err error) {
+	stmt := fmt.Sprintf("DELETE FROM `%s` WHERE key = ?", s.table)
+	_, err = s.db.Exec(stmt, key)
+
+	return err
+}
+
+// GetValue fetches the value of key
+func (s *Storage) GetValue(key string) (value []byte, err error) {
+	stmt := fmt.Sprintf("SELECT `value` FROM `%s` WHERE key = ?", s.table)
+	err = s.db.QueryRow(stmt, key).Scan(&value)
+
+	if err == sql.ErrNoRows {
+		err = nil
+	}
+
+	return value, err
+}