Implement Checksum()

cmd/litestream/main.go

@@ -11,7 +11,7 @@ import (
 
 	"bazil.org/fuse"
 	"bazil.org/fuse/fs"
-	"github.com/middlemost/litestream"
+	"github.com/benbjohnson/litestream"
 )
 
 func main() {

handle.go

@@ -53,7 +53,7 @@ func (h *Handle) Read(ctx context.Context, req *fuse.ReadRequest, resp *fuse.Rea
 
 // Write writes data at a given offset to the underlying file.
 func (h *Handle) Write(ctx context.Context, req *fuse.WriteRequest, resp *fuse.WriteResponse) (err error) {
-	log.Printf("write: name=%s offset=%d", h.f.Name(), req.Offset)
+	log.Printf("write: name=%s offset=%d n=%d", h.f.Name(), req.Offset, len(req.Data))
 	println(hex.Dump(req.Data))
 
 	resp.Size, err = h.f.WriteAt(req.Data, req.Offset)

litestream.go

@@ -1,9 +1,16 @@
 package litestream
 
 import (
+	"encoding/binary"
 	"io"
 )
 
+// Magic number specified at the beginning of WAL files.
+const (
+	MagicLittleEndian = 0x377f0682
+	MagicBigEndian    = 0x377f0683
+)
+
 const (
 	WriteVersionOffset = 18
 	ReadVersionOffset  = 19
@@ -17,3 +24,19 @@ func ReadVersion(b []byte) (writeVersion, readVersion uint8, err error) {
 	}
 	return b[WriteVersionOffset], b[ReadVersionOffset], nil
 }
+
+// Checksum computes a running checksum over a byte slice.
+func Checksum(bo binary.ByteOrder, s uint64, b []byte) (_ uint64, err error) {
+	// Ensure byte slice length is divisible by 8.
+	if len(b)%8 != 0 {
+		return 0, ErrChecksumMisaligned
+	}
+
+	// Iterate over 8-byte units and compute checksum.
+	s0, s1 := uint32(s>>32), uint32(s&0xFFFFFFFF)
+	for i := 0; i < len(b); i += 8 {
+		s0 += bo.Uint32(b[i:]) + s1
+		s1 += bo.Uint32(b[i+4:]) + s0
+	}
+	return uint64(s0)<<32 | uint64(s1), nil
+}

wal.go

@@ -2,10 +2,24 @@ package litestream
 
 import (
 	"encoding/binary"
+	"errors"
+	"fmt"
 	"io"
 	"os"
 )
 
+var (
+	// ErrWALHeaderEmpty is returned when writing an empty header.
+	ErrWALHeaderEmpty = errors.New("wal header empty")
+
+	// ErrWALFileInitialized is returned when writing a header to a
+	// WAL file that has already has its header written.
+	ErrWALFileInitialized = errors.New("wal file already initialized")
+
+	// ErrChecksumMisaligned is returned when input byte length is not divisible by 8.
+	ErrChecksumMisaligned = errors.New("checksum input misaligned")
+)
+
 // WALFile represents a write-ahead log file.
 type WALFile struct {
 	path string
@@ -19,17 +33,54 @@ func NewWALFile(path string) *WALFile {
 	return &WALFile{path: path}
 }
 
-func (s *WALFile) Open() error {
+// WALHeader returns the WAL header. The return is the zero value if unset.
-	panic("TODO")
+func (s *WALFile) Header() WALHeader {
+	return s.hdr
 }
 
+// Open initializes the WAL file descriptor. Creates the file if it doesn't exist.
+func (s *WALFile) Open() (err error) {
+	// TODO: Validate file contents if non-zero. Return ErrWALFileInvalidHeader if header invalid.
+	// TODO: Truncate transaction if commit record is invalid.
+
+	if s.f, err = os.OpenFile(s.path, os.O_RDWR|os.O_CREATE, 0666); err != nil {
+		return err
+	}
+	return nil
+}
+
+// Close syncs the WAL file and closes the file descriptor.
 func (s *WALFile) Close() error {
-	panic("TODO")
+	if err := s.f.Sync(); err != nil {
+		return fmt.Errorf("wal sync: %w", err)
+	}
+	return s.f.Close()
 }
 
+// Sync calls Sync() on the underlying file descriptor.
+func (s *WALFile) Sync() error {
+	return s.f.Sync()
+}
+
+// WriteHeader writes hdr to the WAL file.
+// Returns an error if hdr is empty or if the file already has a header.
 func (s *WALFile) WriteHeader(hdr WALHeader) error {
+	if hdr.IsZero() {
+		return ErrWALHeaderEmpty
+	} else if !s.hdr.IsZero() {
+		return ErrWALFileInitialized
+	}
 	s.hdr = hdr
-	panic("TODO")
+
+	// Marshal header & write to file.
+	b := make([]byte, WALHeaderSize)
+	if err := s.hdr.MarshalTo(b); err != nil {
+		return fmt.Errorf("marshal wal header: %w", err)
+	} else if _, err := s.f.Write(b); err != nil {
+		return err
+	}
+
+	return nil
 }
 
 func (s *WALFile) WriteFrame(hdr WALFrameHeader, buf []byte) error {
@@ -48,6 +99,23 @@ type WALHeader struct {
 	Checksum          uint64
 }
 
+// IsZero returns true if hdr is the zero value.
+func (hdr WALHeader) IsZero() bool {
+	return hdr == (WALHeader{})
+}
+
+// ByteOrder returns the byte order based on the hdr magic.
+func (hdr WALHeader) ByteOrder() binary.ByteOrder {
+	switch hdr.Magic {
+	case MagicLittleEndian:
+		return binary.LittleEndian
+	case MagicBigEndian:
+		return binary.BigEndian
+	default:
+		return nil
+	}
+}
+
 // MarshalTo encodes the header to b.
 // Returns io.ErrShortWrite if len(b) is less than WALHeaderSize.
 func (hdr *WALHeader) MarshalTo(b []byte) error {
@@ -89,6 +157,11 @@ type WALFrameHeader struct {
 	Checksum uint64
 }
 
+// IsZero returns true if hdr is the zero value.
+func (hdr WALFrameHeader) IsZero() bool {
+	return hdr == (WALFrameHeader{})
+}
+
 // IsCommit returns true if the frame represents a commit header.
 func (hdr *WALFrameHeader) IsCommit() bool {
 	return hdr.PageN != 0

wal_test.go

@@ -2,11 +2,30 @@ package litestream_test
 
 import (
 	"io"
+	"path/filepath"
 	"testing"
 
 	"github.com/benbjohnson/litestream"
 )
 
+func TestWALFile_WriteHeader(t *testing.T) {
+	t.Run("OK", func(t *testing.T) {
+		f := MustOpenWALFile(t, "0000")
+		defer MustCloseWALFile(t, f)
+
+		if err := f.WriteHeader(litestream.WALHeader{
+			Magic:             litestream.MagicLittleEndian,
+			FileFormatVersion: 1001,
+			PageSize:          4096,
+			CheckpointSeqNo:   1003,
+		}); err != nil {
+			t.Fatal(err)
+		}
+
+		t.Fatal("TODO: Ensure header written correctly")
+	})
+}
+
 func TestWALHeader_MarshalTo(t *testing.T) {
 	// Ensure the WAL header can be marshaled and unmarshaled correctly.
 	t.Run("OK", func(t *testing.T) {
@@ -90,3 +109,22 @@ func TestWALFrameHeader_Unmarshal(t *testing.T) {
 		}
 	})
 }
+
+// MustOpenWALFile returns a new, open instance of WALFile written to a temp dir.
+func MustOpenWALFile(tb testing.TB, name string) *litestream.WALFile {
+	tb.Helper()
+
+	f := litestream.NewWALFile(filepath.Join(tb.TempDir(), name))
+	if err := f.Open(); err != nil {
+		tb.Fatal(err)
+	}
+	return f
+}
+
+// MustCloseWALFile closes an instance of WALFile.
+func MustCloseWALFile(tb testing.TB, f *litestream.WALFile) {
+	tb.Helper()
+	if err := f.Close(); err != nil {
+		tb.Fatal(err)
+	}
+}