Standalone page encoding/decoding (#66)

Author: benbjohnson

decoder.go

@@ -83,7 +83,7 @@ func (dec *Decoder) Close() error {
 	dec.writeToHash(remainingBytes[:len(remainingBytes)-ChecksumSize])
 
 	// Read page index.
-	if err := dec.decodePageIndex(remaining); err != nil {
+	if dec.pageIndex, err = DecodePageIndex(remaining, 0, dec.header.MinTXID, dec.header.MaxTXID); err != nil {
 		return fmt.Errorf("read page index: %w", err)
 	}
 
@@ -115,42 +115,6 @@ func (dec *Decoder) Close() error {
 	return nil
 }
 
-func (dec *Decoder) decodePageIndex(r io.ByteReader) error {
-	pageIndex := make(map[uint32]PageIndexElem)
-
-	for {
-		pgno, err := binary.ReadUvarint(r)
-		if err != nil {
-			return fmt.Errorf("read page index pgno: %w", err)
-		} else if pgno == 0 {
-			break // End when we hit the end marker.
-		}
-
-		offset, err := binary.ReadUvarint(r)
-		if err != nil {
-			return fmt.Errorf("read page index offset: %w", err)
-		}
-		size, err := binary.ReadUvarint(r)
-		if err != nil {
-			return fmt.Errorf("read page index size: %w", err)
-		}
-
-		pageIndex[uint32(pgno)] = PageIndexElem{
-			Offset: int64(offset),
-			Size:   int64(size),
-		}
-	}
-
-	// Read size of page index.
-	var size uint64
-	if err := binary.Read(r.(io.Reader), binary.BigEndian, &size); err != nil {
-		return fmt.Errorf("read page index size: %w", err)
-	}
-
-	dec.pageIndex = pageIndex
-	return nil
-}
-
 // DecodeHeader reads the LTX file header frame and stores it internally.
 // Call Header() to retrieve the header after this is successfully called.
 func (dec *Decoder) DecodeHeader() error {
@@ -341,3 +305,42 @@ func DecodePageData(b []byte) (hdr PageHeader, data []byte, err error) {
 	data, err = io.ReadAll(zr)
 	return hdr, data, err
 }
+
+// DecodePageIndex decodes the page index from r.
+func DecodePageIndex(r io.ByteReader, level int, minTXID, maxTXID TXID) (map[uint32]PageIndexElem, error) {
+	pageIndex := make(map[uint32]PageIndexElem)
+
+	for {
+		pgno, err := binary.ReadUvarint(r)
+		if err != nil {
+			return nil, fmt.Errorf("read page index pgno: %w", err)
+		} else if pgno == 0 {
+			break // End when we hit the end marker.
+		}
+
+		offset, err := binary.ReadUvarint(r)
+		if err != nil {
+			return nil, fmt.Errorf("read page index offset: %w", err)
+		}
+		size, err := binary.ReadUvarint(r)
+		if err != nil {
+			return nil, fmt.Errorf("read page index size: %w", err)
+		}
+
+		pageIndex[uint32(pgno)] = PageIndexElem{
+			Level:   level,
+			MinTXID: minTXID,
+			MaxTXID: maxTXID,
+			Offset:  int64(offset),
+			Size:    int64(size),
+		}
+	}
+
+	// Read size of page index.
+	var size uint64
+	if err := binary.Read(r.(io.Reader), binary.BigEndian, &size); err != nil {
+		return nil, fmt.Errorf("read page index size: %w", err)
+	}
+
+	return pageIndex, nil
+}

decoder_test.go

@@ -66,8 +66,8 @@ func TestDecoder(t *testing.T) {
 	// Verify page index.
 	index := dec.PageIndex()
 	if got, want := index, map[uint32]ltx.PageIndexElem{
-		1: {Offset: 100, Size: 49},
-		2: {Offset: 149, Size: 49},
+		1: {MinTXID: 1, MaxTXID: 1, Offset: 100, Size: 49},
+		2: {MinTXID: 1, MaxTXID: 1, Offset: 149, Size: 49},
 	}; !reflect.DeepEqual(got, want) {
 		t.Fatalf("page index mismatch:\ngot=%#v\nwant=%#v", got, want)
 	}

encoder.go

@@ -307,6 +307,10 @@ func (enc *Encoder) writeToHash(b []byte) {
 }
 
 type PageIndexElem struct {
+	Level   int
+	MinTXID TXID
+	MaxTXID TXID
+
 	Offset int64
 	Size   int64
 }