Add WALHeader & WALFrameHeader

wal.go

@@ -0,0 +1,121 @@
+package litestream
+
+import (
+	"encoding/binary"
+	"io"
+	"os"
+)
+
+// WALFile represents a write-ahead log file.
+type WALFile struct {
+	path string
+	hdr  WALHeader
+
+	f *os.File
+}
+
+// NewWALFile returns a new instance of WALFile.
+func NewWALFile(path string) *WALFile {
+	return &WALFile{path: path}
+}
+
+func (s *WALFile) Open() error {
+	panic("TODO")
+}
+
+func (s *WALFile) Close() error {
+	panic("TODO")
+}
+
+func (s *WALFile) WriteHeader(hdr WALHeader) error {
+	s.hdr = hdr
+	panic("TODO")
+}
+
+func (s *WALFile) WriteFrame(hdr WALFrameHeader, buf []byte) error {
+	panic("TODO")
+}
+
+// WALHeaderSize is the size of the WAL header, in bytes.
+const WALHeaderSize = 32
+
+type WALHeader struct {
+	Magic             uint32
+	FileFormatVersion uint32
+	PageSize          uint32
+	CheckpointSeqNo   uint32
+	Salt              uint64
+	Checksum          uint64
+}
+
+// MarshalTo encodes the header to b.
+// Returns io.ErrShortWrite if len(b) is less than WALHeaderSize.
+func (hdr *WALHeader) MarshalTo(b []byte) error {
+	if len(b) < WALHeaderSize {
+		return io.ErrShortWrite
+	}
+	binary.BigEndian.PutUint32(b[0:], hdr.Magic)
+	binary.BigEndian.PutUint32(b[4:], hdr.FileFormatVersion)
+	binary.BigEndian.PutUint32(b[8:], hdr.PageSize)
+	binary.BigEndian.PutUint32(b[12:], hdr.CheckpointSeqNo)
+	binary.BigEndian.PutUint64(b[16:], hdr.Salt)
+	binary.BigEndian.PutUint64(b[24:], hdr.Checksum)
+	return nil
+}
+
+// Unmarshal decodes the header from b.
+// Returns io.ErrUnexpectedEOF if len(b) is less than WALHeaderSize.
+func (hdr *WALHeader) Unmarshal(b []byte) error {
+	if len(b) < WALHeaderSize {
+		return io.ErrUnexpectedEOF
+	}
+	hdr.Magic = binary.BigEndian.Uint32(b[0:])
+	hdr.FileFormatVersion = binary.BigEndian.Uint32(b[4:])
+	hdr.PageSize = binary.BigEndian.Uint32(b[8:])
+	hdr.CheckpointSeqNo = binary.BigEndian.Uint32(b[12:])
+	hdr.Salt = binary.BigEndian.Uint64(b[16:])
+	hdr.Checksum = binary.BigEndian.Uint64(b[24:])
+	return nil
+}
+
+// WALFrameHeaderSize is the size of the WAL frame header, in bytes.
+const WALFrameHeaderSize = 24
+
+// WALFrameHeader represents a SQLite WAL frame header.
+type WALFrameHeader struct {
+	Pgno     uint32
+	PageN    uint32 // only set for commit records
+	Salt     uint64
+	Checksum uint64
+}
+
+// IsCommit returns true if the frame represents a commit header.
+func (hdr *WALFrameHeader) IsCommit() bool {
+	return hdr.PageN != 0
+}
+
+// MarshalTo encodes the frame header to b.
+// Returns io.ErrShortWrite if len(b) is less than WALHeaderSize.
+func (hdr *WALFrameHeader) MarshalTo(b []byte) error {
+	if len(b) < WALFrameHeaderSize {
+		return io.ErrShortWrite
+	}
+	binary.BigEndian.PutUint32(b[0:], hdr.Pgno)
+	binary.BigEndian.PutUint32(b[4:], hdr.PageN)
+	binary.BigEndian.PutUint64(b[8:], hdr.Salt)
+	binary.BigEndian.PutUint64(b[16:], hdr.Checksum)
+	return nil
+}
+
+// Unmarshal decodes the frame header from b.
+// Returns io.ErrUnexpectedEOF if len(b) is less than WALHeaderSize.
+func (hdr *WALFrameHeader) Unmarshal(b []byte) error {
+	if len(b) < WALFrameHeaderSize {
+		return io.ErrUnexpectedEOF
+	}
+	hdr.Pgno = binary.BigEndian.Uint32(b[0:])
+	hdr.PageN = binary.BigEndian.Uint32(b[4:])
+	hdr.Salt = binary.BigEndian.Uint64(b[8:])
+	hdr.Checksum = binary.BigEndian.Uint64(b[16:])
+	return nil
+}