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store.go
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305 lines (247 loc) · 5.97 KB
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package minkv
import (
"encoding/binary"
"fmt"
"io"
"os"
"sync"
"time"
)
// timestamp (4 bytes) + key len (4 bytes) + value len (4 bytes) + tombstone (1 byte)
const headerSize = 13
const tombstoneOffset = -1
type Record struct {
Key []byte
Value []byte
Timestamp uint32
Tombstone bool
}
type Store struct {
filename string
mu sync.RWMutex
file *os.File
index map[string]int64
}
func Open(filename string) (*Store, error) {
file, err := os.OpenFile(filename, os.O_RDWR|os.O_CREATE, 0666)
if err != nil {
return nil, fmt.Errorf("failed to open file: %w", err)
}
store := &Store{
filename: filename,
file: file,
index: make(map[string]int64),
}
if err := store.buildIndex(); err != nil {
file.Close()
return nil, fmt.Errorf("failed to rebuild index: %w", err)
}
return store, nil
}
func (s *Store) buildIndex() error {
s.mu.Lock()
defer s.mu.Unlock()
var offset int64
for {
record, err := s.readRecord(offset)
if err == io.EOF {
break
}
if err != nil {
return fmt.Errorf("failed to read record: %v", err)
}
// mark tombstoned records as deleted
if record.Tombstone {
s.index[string(record.Key)] = tombstoneOffset
} else {
s.index[string(record.Key)] = offset
}
offset += int64(headerSize + len(record.Key) + len(record.Value))
}
return nil
}
func (s *Store) Close() error {
s.mu.Lock()
defer s.mu.Unlock()
if s.file != nil {
return s.file.Close()
}
return nil
}
func (s *Store) writeRecord(record *Record) (int64, error) {
totalSize := headerSize + len(record.Key) + len(record.Value)
buf := make([]byte, totalSize)
// serialize timestamp (4 bytes)
binary.BigEndian.PutUint32(buf[0:4], record.Timestamp)
// serialize key len (4 bytes)
binary.BigEndian.PutUint32(buf[4:8], uint32(len(record.Key)))
// serialize value len (4 bytes)
binary.BigEndian.PutUint32(buf[8:12], uint32(len(record.Value)))
// serialize tombstone (1 byte)
if record.Tombstone {
buf[12] = 1
} else {
buf[12] = 0
}
// copy key data
copy(buf[headerSize:headerSize+len(record.Key)], record.Key)
// copy value data
copy(buf[headerSize+len(record.Key):], record.Value)
// write record to file
offset, err := s.file.Seek(0, io.SeekEnd)
if err != nil {
return 0, err
}
if _, err := s.file.Write(buf); err != nil {
return 0, err
}
return offset, nil
}
func (s *Store) Put(key, value []byte) error {
if len(key) == 0 {
return fmt.Errorf("key cannot be empty")
}
s.mu.Lock()
defer s.mu.Unlock()
record := &Record{
Key: key,
Value: value,
Timestamp: uint32(time.Now().Unix()),
}
offset, err := s.writeRecord(record)
if err != nil {
return fmt.Errorf("failed to write record: %w", err)
}
s.index[string(key)] = offset
return nil
}
func (s *Store) readRecord(offset int64) (*Record, error) {
if _, err := s.file.Seek(offset, io.SeekStart); err != nil {
return nil, fmt.Errorf("failed to seek: %w", err)
}
record := &Record{}
// read timestamp (4 bytes)
timestampBuf := make([]byte, 4)
if _, err := s.file.Read(timestampBuf); err != nil {
return nil, err
}
record.Timestamp = binary.BigEndian.Uint32(timestampBuf)
// read key len (4 bytes)
keyLenBuf := make([]byte, 4)
if _, err := s.file.Read(keyLenBuf); err != nil {
return nil, err
}
keyLen := binary.BigEndian.Uint32(keyLenBuf)
// read value len (4 bytes)
valueLenBuf := make([]byte, 4)
if _, err := s.file.Read(valueLenBuf); err != nil {
return nil, err
}
valueLen := binary.BigEndian.Uint32(valueLenBuf)
// read tombstone (1 byte)
tombstoneBuf := make([]byte, 1)
if _, err := s.file.Read(tombstoneBuf); err != nil {
return nil, err
}
record.Tombstone = tombstoneBuf[0] == 1
// read key data
key := make([]byte, keyLen)
if _, err := s.file.Read(key); err != nil {
return nil, err
}
record.Key = key
// read value data
value := make([]byte, valueLen)
if _, err := s.file.Read(value); err != nil {
return nil, err
}
record.Value = value
return record, nil
}
func (s *Store) Get(key []byte) ([]byte, error) {
if len(key) == 0 {
return nil, fmt.Errorf("key cannot be empty")
}
s.mu.RLock()
defer s.mu.RUnlock()
offset, exists := s.index[string(key)]
if !exists || offset == tombstoneOffset {
return nil, fmt.Errorf("key not found: %s", key)
}
record, err := s.readRecord(offset)
if err != nil {
return nil, fmt.Errorf("failed to read record: %w", err)
}
return record.Value, nil
}
func (s *Store) Delete(key []byte) error {
if len(key) == 0 {
return fmt.Errorf("key cannot be empty")
}
s.mu.Lock()
defer s.mu.Unlock()
record := &Record{
Key: key,
Tombstone: true,
Timestamp: uint32(time.Now().Unix()),
}
if _, err := s.writeRecord(record); err != nil {
return fmt.Errorf("failed to write record: %w", err)
}
s.index[string(key)] = tombstoneOffset
return nil
}
type Iterator interface {
Next() bool
Record() (*Record, error)
}
type storeIterator struct {
store *Store
record *Record
offset int64
fileSize int64
err error
}
func (s *Store) Iterator() (Iterator, error) {
s.mu.RLock()
defer s.mu.RUnlock()
fileInfo, err := s.file.Stat()
if err != nil {
return nil, fmt.Errorf("failed to get file info: %w", err)
}
return &storeIterator{
store: s,
offset: 0,
fileSize: fileInfo.Size(),
}, nil
}
func (it *storeIterator) Next() bool {
for it.offset < it.fileSize {
record, err := it.store.readRecord(it.offset)
if err != nil {
it.err = fmt.Errorf("failed to read record at offset %d: %w", it.offset, err)
return false
}
recordSize := headerSize + len(record.Key) + len(record.Value)
// skip tombstoned record
if record.Tombstone {
it.offset += int64(recordSize)
continue
}
off, exists := it.store.index[string(record.Key)]
if exists && off == it.offset {
it.record = record
it.offset += int64(recordSize)
return true
}
it.offset += int64(recordSize)
}
it.record = nil
return false
}
func (it *storeIterator) Record() (*Record, error) {
if it.err != nil {
return nil, it.err
}
return it.record, nil
}