/
cache.go
118 lines (99 loc) · 2.34 KB
/
cache.go
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// Copyright 2013, Amahi. All rights reserved.
// Use of this source code is governed by the
// license that can be found in the LICENSE file.
// Functions for implementing cache
package metadata
import (
"database/sql"
"errors"
_ "github.com/mattn/go-sqlite3"
"os"
"time"
)
//performs cache lookup and return error if data not found in cache
func (l *Library) cache_lookup(MediaName string) (result string, mediatype string, err error) {
db, err := sql.Open("sqlite3", l.dbpath)
if err != nil {
return "", "", err
}
defer db.Close()
_, err = os.Open(l.dbpath)
if err != nil {
return "", "", err
}
rows, err := db.Query("SELECT data,type FROM metadata WHERE filename=?", MediaName)
if err != nil {
return "", "", err
}
defer rows.Close()
for rows.Next() {
var data string
var mediatype string
err = rows.Scan(&data, &mediatype)
return data, mediatype, nil
}
return "", "", errors.New("No Data found in cache")
}
//adds data to cache
func (l *Library) add_to_cache(MediaName string, content string, mediatype string) error {
if l.current_size > l.max_size {
return errors.New("size exceeded")
}
db, err := sql.Open("sqlite3", l.dbpath)
if err != nil {
return err
}
defer db.Close()
_, err = os.Open(l.dbpath)
if err != nil {
sql := `
create table metadata (filename text not null primary key, data text not null, type text, timestamp integer not null);
`
_, err = db.Exec(sql)
if err != nil {
return err
}
}
tx, err := db.Begin()
if err != nil {
return err
}
stmt, err := tx.Prepare("insert into metadata(filename, data, type, timestamp) values(?, ?, ?, ?)")
if err != nil {
return err
}
defer stmt.Close()
_, err = stmt.Exec(MediaName, content, mediatype, int(time.Now().Unix()))
err = tx.Commit()
if err != nil {
return err
}
l.current_size++
if l.current_size > l.max_size {
err = l.removeDB_LeastRecentlyUsed(db)
if err != nil {
return err
}
}
return nil
}
// LRU policy implemented here
func (l *Library) removeDB_LeastRecentlyUsed(db *sql.DB) error {
rows, err := db.Query("SELECT MIN(timestamp) FROM metadata;")
if err != nil {
return err
}
defer rows.Close()
var ts int
for rows.Next() {
err = rows.Scan(&ts)
if err != nil {
return err
}
}
_, err = db.Exec("DELETE from metadata where timestamp=?", ts)
if err != nil {
return err
}
return nil
}