1 files changed, 73 insertions, 9 deletions

diff --git a/compat/json/compat.go b/compat/json/compat.go
index 3a9bd6c..695c1a8 100644
--- a/compat/json/compat.go
+++ b/compat/json/compat.go
@@ -237,14 +237,14 @@ func Valid(data []byte) bool {
 
 // Decode wrappers ///////////////////////////////////////////////////
 
-func convertDecodeError(err error) error {
+func convertDecodeError(err error, isUnmarshal bool) error {
 	if derr, ok := err.(*lowmemjson.DecodeError); ok {
 		switch terr := derr.Err.(type) {
 		case *lowmemjson.DecodeSyntaxError:
 			switch {
 			case errors.Is(terr.Err, io.EOF):
 				err = io.EOF
-			case errors.Is(terr.Err, io.ErrUnexpectedEOF):
+			case errors.Is(terr.Err, io.ErrUnexpectedEOF) && isUnmarshal:
 				err = &SyntaxError{
 					msg:    "unexpected end of JSON input",
 					Offset: terr.Offset,
@@ -284,13 +284,66 @@ func convertDecodeError(err error) error {
 	return err
 }
 
+type decodeValidator struct{}
+
+func (*decodeValidator) DecodeJSON(r io.RuneScanner) error {
+	for {
+		if _, _, err := r.ReadRune(); err != nil {
+
+			if err == io.EOF {
+				return nil
+			}
+			return err
+		}
+	}
+}
+
+var _ lowmemjson.Decodable = (*decodeValidator)(nil)
+
 func Unmarshal(data []byte, ptr any) error {
-	return convertDecodeError(lowmemjson.NewDecoder(bytes.NewReader(data)).DecodeThenEOF(ptr))
+	if err := convertDecodeError(lowmemjson.NewDecoder(bytes.NewReader(data)).DecodeThenEOF(&decodeValidator{}), true); err != nil {
+		return err
+	}
+	if err := convertDecodeError(lowmemjson.NewDecoder(bytes.NewReader(data)).DecodeThenEOF(ptr), true); err != nil {
+		return err
+	}
+	return nil
+}
+
+type teeRuneScanner struct {
+	src      io.RuneScanner
+	dst      *bytes.Buffer
+	lastSize int
+}
+
+func (tee *teeRuneScanner) ReadRune() (r rune, size int, err error) {
+	r, size, err = tee.src.ReadRune()
+	if err == nil {
+		if _, err := tee.dst.WriteRune(r); err != nil {
+			return 0, 0, err
+		}
+	}
+
+	tee.lastSize = size
+	return
+}
+
+func (tee *teeRuneScanner) UnreadRune() error {
+	if tee.lastSize == 0 {
+		return lowmemjson.ErrInvalidUnreadRune
+	}
+	_ = tee.src.UnreadRune()
+	tee.dst.Truncate(tee.dst.Len() - tee.lastSize)
+	tee.lastSize = 0
+	return nil
 }
 
 type Decoder struct {
+	validatorBuf *bufio.Reader
+	validator    *lowmemjson.Decoder
+
+	decoderBuf bytes.Buffer
 	*lowmemjson.Decoder
-	buf *bufio.Reader
 }
 
 func NewDecoder(r io.Reader) *Decoder {
@@ -298,18 +351,29 @@ func NewDecoder(r io.Reader) *Decoder {
 	if !ok {
 		br = bufio.NewReader(r)
 	}
-	return &Decoder{
-		Decoder: lowmemjson.NewDecoder(br),
-		buf:     br,
+	ret := &Decoder{
+		validatorBuf: br,
 	}
+	ret.validator = lowmemjson.NewDecoder(&teeRuneScanner{
+		src: ret.validatorBuf,
+		dst: &ret.decoderBuf,
+	})
+	ret.Decoder = lowmemjson.NewDecoder(&ret.decoderBuf)
+	return ret
 }
 
 func (dec *Decoder) Decode(ptr any) error {
-	return convertDecodeError(dec.Decoder.Decode(ptr))
+	if err := convertDecodeError(dec.validator.Decode(&decodeValidator{}), false); err != nil {
+		return err
+	}
+	if err := convertDecodeError(dec.Decoder.Decode(ptr), false); err != nil {
+		return err
+	}
+	return nil
 }
 
 func (dec *Decoder) Buffered() io.Reader {
-	dat, _ := dec.buf.Peek(dec.buf.Buffered())
+	dat, _ := dec.validatorBuf.Peek(dec.validatorBuf.Buffered())
 	return bytes.NewReader(dat)
 }