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cassandra.go
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cassandra.go
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package backend
import (
"log"
"strconv"
"github.com/gocql/gocql"
)
type CassandraBackend struct {
session *gocql.Session
table string
prefix string
size int64
verbose bool
}
func NewCassandraBackend(
session *gocql.Session,
table string,
prefix string,
size int64,
verbose bool,
) *CassandraBackend {
return &CassandraBackend{
session: session,
table: table,
prefix: prefix,
size: size,
verbose: verbose,
}
}
func (b *CassandraBackend) ReadAt(p []byte, off int64) (n int, err error) {
if b.verbose {
log.Printf("ReadAt(len(p) = %v, off = %v)", len(p), off)
}
var val []byte
if err := b.session.Query(`select data from `+b.table+` where key = ? limit 1`, b.prefix+"-"+strconv.FormatInt(off, 10)).Scan(&val); err != nil {
if err == gocql.ErrNotFound {
return len(p), nil
}
return 0, err
}
return copy(p, val), nil
}
func (b *CassandraBackend) WriteAt(p []byte, off int64) (n int, err error) {
if b.verbose {
log.Printf("WriteAt(len(p) = %v, off = %v)", len(p), off)
}
if err := b.session.Query(`insert into `+b.table+` (key, data) values (?, ?)`, b.prefix+"-"+strconv.FormatInt(off, 10), p).Exec(); err != nil {
return 0, err
}
return len(p), nil
}
func (b *CassandraBackend) Size() (int64, error) {
if b.verbose {
log.Println("Size()")
}
return b.size, nil
}
func (b *CassandraBackend) Sync() error {
if b.verbose {
log.Println("Sync()")
}
return nil
}