merkledb -- encode lengths as uvarints

x/merkledb/README.md

@@ -210,7 +210,7 @@ Once this is encoded, we `sha256` hash the resulting bytes to get the node's ID.
 
 ### Encoding Varints and Bytes
 
-Varints are encoded with `binary.PutVarint` from the standard library's `binary/encoding` package.
+Varints are encoded with `binary.PutUvarint` from the standard library's `binary/encoding` package.
 Bytes are encoded by simply copying them onto the buffer.
 
 ## Design choices

x/merkledb/codec.go

@@ -42,7 +42,6 @@ var (
 	trueBytes  = []byte{trueByte}
 	falseBytes = []byte{falseByte}
 
-	errNegativeNumChildren  = errors.New("number of children is negative")
 	errTooManyChildren      = fmt.Errorf("length of children list is larger than branching factor of %d", NodeBranchFactor)
 	errChildIndexTooLarge   = fmt.Errorf("invalid child index. Must be less than branching factor of %d", NodeBranchFactor)
 	errNegativeNibbleLength = errors.New("nibble length is negative")
@@ -86,6 +85,8 @@ func newCodec() encoderDecoder {
 // Note that bytes.Buffer.Write always returns nil so we
 // can ignore its return values in [codecImpl] methods.
 type codecImpl struct {
+	// Invariant: Every byte slice returned by [varIntPool] has
+	// length [binary.MaxVarintLen64].
 	varIntPool sync.Pool
 }
 
@@ -98,12 +99,12 @@ func (c *codecImpl) encodeDBNode(n *dbNode) []byte {
 	)
 
 	c.encodeMaybeByteSlice(buf, n.value)
-	c.encodeInt(buf, numChildren)
+	c.encodeUint64(buf, uint64(numChildren))
 	// Note we insert children in order of increasing index
 	// for determinism.
 	for index := byte(0); index < NodeBranchFactor; index++ {
 		if entry, ok := n.children[index]; ok {
-			c.encodeInt(buf, int(index))
+			c.encodeUint64(buf, uint64(index))
 			path := entry.compressedPath.Serialize()
 			c.encodeSerializedPath(buf, path)
 			_, _ = buf.Write(entry.id[:])
@@ -121,12 +122,12 @@ func (c *codecImpl) encodeHashValues(hv *hashValues) []byte {
 		buf          = bytes.NewBuffer(make([]byte, 0, estimatedLen))
 	)
 
-	c.encodeInt(buf, numChildren)
+	c.encodeUint64(buf, uint64(numChildren))
 
 	// ensure that the order of entries is consistent
 	for index := byte(0); index < NodeBranchFactor; index++ {
 		if entry, ok := hv.Children[index]; ok {
-			c.encodeInt(buf, int(index))
+			c.encodeUint64(buf, uint64(index))
 			_, _ = buf.Write(entry.id[:])
 		}
 	}
@@ -149,12 +150,10 @@ func (c *codecImpl) decodeDBNode(b []byte, n *dbNode) error {
 	}
 	n.value = value
 
-	numChildren, err := c.decodeInt(src)
+	numChildren, err := c.decodeUint(src)
 	switch {
 	case err != nil:
 		return err
-	case numChildren < 0:
-		return errNegativeNumChildren
 	case numChildren > NodeBranchFactor:
 		return errTooManyChildren
 	case numChildren > src.Len()/minChildLen:
@@ -164,7 +163,7 @@ func (c *codecImpl) decodeDBNode(b []byte, n *dbNode) error {
 	n.children = make(map[byte]child, NodeBranchFactor)
 	previousChild := -1
 	for i := 0; i < numChildren; i++ {
-		index, err := c.decodeInt(src)
+		index, err := c.decodeUint(src)
 		if err != nil {
 			return err
 		}
@@ -221,18 +220,15 @@ func (*codecImpl) decodeBool(src *bytes.Reader) (bool, error) {
 	}
 }
 
-func (c *codecImpl) encodeInt(dst *bytes.Buffer, value int) {
-	c.encodeInt64(dst, int64(value))
-}
-
-func (*codecImpl) decodeInt(src *bytes.Reader) (int, error) {
+// decodeUint decodes a uvarint from [src] and returns it as an int.
+func (*codecImpl) decodeUint(src *bytes.Reader) (int, error) {
 	// To ensure encoding/decoding is canonical, we need to check for leading
 	// zeroes in the varint.
 	// The last byte of the varint we read is the most significant byte.
 	// If it's 0, then it's a leading zero, which is considered invalid in the
 	// canonical encoding.
 	startLen := src.Len()
-	val64, err := binary.ReadVarint(src)
+	val64, err := binary.ReadUvarint(src)
 	switch {
 	case err == io.EOF:
 		return 0, io.ErrUnexpectedEOF
@@ -260,9 +256,9 @@ func (*codecImpl) decodeInt(src *bytes.Reader) (int, error) {
 	return int(val64), nil
 }
 
-func (c *codecImpl) encodeInt64(dst *bytes.Buffer, value int64) {
+func (c *codecImpl) encodeUint64(dst *bytes.Buffer, value uint64) {
 	buf := c.varIntPool.Get().([]byte)
-	size := binary.PutVarint(buf, value)
+	size := binary.PutUvarint(buf, value)
 	_, _ = dst.Write(buf[:size])
 	c.varIntPool.Put(buf)
 }
@@ -297,7 +293,7 @@ func (c *codecImpl) decodeByteSlice(src *bytes.Reader) ([]byte, error) {
 		return nil, io.ErrUnexpectedEOF
 	}
 
-	length, err := c.decodeInt(src)
+	length, err := c.decodeUint(src)
 	switch {
 	case err == io.EOF:
 		return nil, io.ErrUnexpectedEOF
@@ -320,7 +316,7 @@ func (c *codecImpl) decodeByteSlice(src *bytes.Reader) ([]byte, error) {
 }
 
 func (c *codecImpl) encodeByteSlice(dst *bytes.Buffer, value []byte) {
-	c.encodeInt(dst, len(value))
+	c.encodeUint64(dst, uint64(len(value)))
 	if value != nil {
 		_, _ = dst.Write(value)
 	}
@@ -340,7 +336,7 @@ func (*codecImpl) decodeID(src *bytes.Reader) (ids.ID, error) {
 }
 
 func (c *codecImpl) encodeSerializedPath(dst *bytes.Buffer, s SerializedPath) {
-	c.encodeInt(dst, s.NibbleLength)
+	c.encodeUint64(dst, uint64(s.NibbleLength))
 	_, _ = dst.Write(s.Value)
 }
 
@@ -353,7 +349,7 @@ func (c *codecImpl) decodeSerializedPath(src *bytes.Reader) (SerializedPath, err
 		result SerializedPath
 		err    error
 	)
-	if result.NibbleLength, err = c.decodeInt(src); err != nil {
+	if result.NibbleLength, err = c.decodeUint(src); err != nil {
 		return SerializedPath{}, err
 	}
 	if result.NibbleLength < 0 {

x/merkledb/codec_test.go

@@ -54,7 +54,7 @@ func FuzzCodecInt(f *testing.F) {
 			codec := codec.(*codecImpl)
 			reader := bytes.NewReader(b)
 			startLen := reader.Len()
-			got, err := codec.decodeInt(reader)
+			got, err := codec.decodeUint(reader)
 			if err != nil {
 				t.SkipNow()
 			}
@@ -63,7 +63,7 @@ func FuzzCodecInt(f *testing.F) {
 
 			// Encoding [got] should be the same as [b].
 			var buf bytes.Buffer
-			codec.encodeInt(&buf, got)
+			codec.encodeUint64(&buf, uint64(got))
 			bufBytes := buf.Bytes()
 			require.Len(bufBytes, numRead)
 			require.Equal(b[:numRead], bufBytes)
@@ -195,22 +195,12 @@ func TestCodecDecodeDBNode(t *testing.T) {
 	}
 
 	nodeBytes := codec.encodeDBNode(&proof)
-
 	// Remove num children (0) from end
 	nodeBytes = nodeBytes[:len(nodeBytes)-minVarIntLen]
 	proofBytesBuf := bytes.NewBuffer(nodeBytes)
-	// Put num children -1 at end
-	codec.(*codecImpl).encodeInt(proofBytesBuf, -1)
-
-	err = codec.decodeDBNode(proofBytesBuf.Bytes(), &parsedDBNode)
-	require.ErrorIs(err, errNegativeNumChildren)
 
-	// Remove num children from end
-	nodeBytes = proofBytesBuf.Bytes()
-	nodeBytes = nodeBytes[:len(nodeBytes)-minVarIntLen]
-	proofBytesBuf = bytes.NewBuffer(nodeBytes)
 	// Put num children NodeBranchFactor+1 at end
-	codec.(*codecImpl).encodeInt(proofBytesBuf, NodeBranchFactor+1)
+	codec.(*codecImpl).encodeUint64(proofBytesBuf, NodeBranchFactor+1)
 
 	err = codec.decodeDBNode(proofBytesBuf.Bytes(), &parsedDBNode)
 	require.ErrorIs(err, errTooManyChildren)