Initial commit: SRDB - High-performance LSM-Tree database

- Core engine with MemTable, SST, WAL
- B+Tree indexing for SST files  
- Leveled compaction strategy
- Multi-table database management
- Schema validation and secondary indexes
- Query builder with complex conditions
- Web UI with HTMX for data visualization
- Command-line tools for diagnostics

wal/wal.go

@@ -0,0 +1,208 @@
+package wal
+
+import (
+	"encoding/binary"
+	"hash/crc32"
+	"io"
+	"os"
+	"sync"
+)
+
+const (
+	// Entry 类型
+	EntryTypePut    = 1
+	EntryTypeDelete = 2 // 预留，暂不支持
+
+	// Entry Header 大小
+	EntryHeaderSize = 17 // CRC32(4) + Length(4) + Type(1) + Seq(8)
+)
+
+// Entry WAL 条目
+type Entry struct {
+	Type  byte   // 操作类型
+	Seq   int64  // _seq
+	Data  []byte // 数据
+	CRC32 uint32 // 校验和
+}
+
+// WAL Write-Ahead Log
+type WAL struct {
+	file   *os.File
+	offset int64
+	mu     sync.Mutex
+}
+
+// Open 打开 WAL 文件
+func Open(path string) (*WAL, error) {
+	file, err := os.OpenFile(path, os.O_CREATE|os.O_RDWR|os.O_APPEND, 0644)
+	if err != nil {
+		return nil, err
+	}
+
+	// 获取当前文件大小
+	stat, err := file.Stat()
+	if err != nil {
+		file.Close()
+		return nil, err
+	}
+
+	return &WAL{
+		file:   file,
+		offset: stat.Size(),
+	}, nil
+}
+
+// Append 追加一条记录
+func (w *WAL) Append(entry *Entry) error {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+
+	// 序列化 Entry
+	data := w.marshalEntry(entry)
+
+	// 写入文件
+	_, err := w.file.Write(data)
+	if err != nil {
+		return err
+	}
+
+	w.offset += int64(len(data))
+
+	return nil
+}
+
+// Sync 同步到磁盘
+func (w *WAL) Sync() error {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+
+	return w.file.Sync()
+}
+
+// Close 关闭 WAL
+func (w *WAL) Close() error {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+
+	return w.file.Close()
+}
+
+// Truncate 清空 WAL
+func (w *WAL) Truncate() error {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+
+	err := w.file.Truncate(0)
+	if err != nil {
+		return err
+	}
+
+	_, err = w.file.Seek(0, 0)
+	if err != nil {
+		return err
+	}
+
+	w.offset = 0
+	return nil
+}
+
+// marshalEntry 序列化 Entry
+func (w *WAL) marshalEntry(entry *Entry) []byte {
+	dataLen := len(entry.Data)
+	totalLen := EntryHeaderSize + dataLen
+
+	buf := make([]byte, totalLen)
+
+	// 计算 CRC32 (不包括 CRC32 字段本身)
+	crcData := buf[4:totalLen]
+	binary.LittleEndian.PutUint32(crcData[0:4], uint32(dataLen))
+	crcData[4] = entry.Type
+	binary.LittleEndian.PutUint64(crcData[5:13], uint64(entry.Seq))
+	copy(crcData[13:], entry.Data)
+
+	crc := crc32.ChecksumIEEE(crcData)
+
+	// 写入 CRC32
+	binary.LittleEndian.PutUint32(buf[0:4], crc)
+
+	return buf
+}
+
+// Reader WAL 读取器
+type Reader struct {
+	file *os.File
+}
+
+// NewReader 创建 WAL 读取器
+func NewReader(path string) (*Reader, error) {
+	file, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+
+	return &Reader{
+		file: file,
+	}, nil
+}
+
+// Read 读取所有 Entry
+func (r *Reader) Read() ([]*Entry, error) {
+	var entries []*Entry
+
+	for {
+		entry, err := r.readEntry()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return nil, err
+		}
+		entries = append(entries, entry)
+	}
+
+	return entries, nil
+}
+
+// Close 关闭读取器
+func (r *Reader) Close() error {
+	return r.file.Close()
+}
+
+// readEntry 读取一条 Entry
+func (r *Reader) readEntry() (*Entry, error) {
+	// 读取 Header
+	header := make([]byte, EntryHeaderSize)
+	_, err := io.ReadFull(r.file, header)
+	if err != nil {
+		return nil, err
+	}
+
+	// 解析 Header
+	crc := binary.LittleEndian.Uint32(header[0:4])
+	dataLen := binary.LittleEndian.Uint32(header[4:8])
+	entryType := header[8]
+	seq := int64(binary.LittleEndian.Uint64(header[9:17]))
+
+	// 读取 Data
+	data := make([]byte, dataLen)
+	_, err = io.ReadFull(r.file, data)
+	if err != nil {
+		return nil, err
+	}
+
+	// 验证 CRC32
+	crcData := make([]byte, EntryHeaderSize-4+int(dataLen))
+	copy(crcData[0:EntryHeaderSize-4], header[4:])
+	copy(crcData[EntryHeaderSize-4:], data)
+
+	if crc32.ChecksumIEEE(crcData) != crc {
+		return nil, io.ErrUnexpectedEOF // CRC 校验失败
+	}
+
+	return &Entry{
+		Type:  entryType,
+		Seq:   seq,
+		Data:  data,
+		CRC32: crc,
+	}, nil
+}