Fix those now-failing error checks

3 files changed, 71 insertions, 9 deletions

diff --git a/compat/json/compat.go b/compat/json/compat.go
index 8d6ec35..59eff6c 100644
--- a/compat/json/compat.go
+++ b/compat/json/compat.go
@@ -78,6 +78,9 @@ func convertReEncodeError(err error) error {
 			msg:    se.Err.Error(),
 			Offset: se.Offset + 1,
 		}
+		if errors.Is(se.Err, io.ErrUnexpectedEOF) {
+			err.(*SyntaxError).msg = "unexpected end of JSON input"
+		}
 	}
 	return err
 }
@@ -91,6 +94,9 @@ func HTMLEscape(dst *bytes.Buffer, src []byte) {
 
 func reencode(src []byte, formatter *lowmemjson.ReEncoder) error {
 	_, err := formatter.Write(src)
+	if err == nil {
+		err = formatter.Close()
+	}
 	return convertReEncodeError(err)
 }
 
@@ -130,6 +136,9 @@ func convertDecodeError(err error) error {
 				msg:    terr.Err.Error(),
 				Offset: terr.Offset,
 			}
+			if errors.Is(terr.Err, io.ErrUnexpectedEOF) {
+				err.(*SyntaxError).msg = "unexpected end of JSON input"
+			}
 		case *lowmemjson.DecodeTypeError:
 			if typeErr, ok := terr.Err.(*json.UnmarshalTypeError); ok {
 				err = &UnmarshalTypeError{
@@ -160,7 +169,7 @@ func convertDecodeError(err error) error {
 }
 
 func Unmarshal(data []byte, ptr any) error {
-	return convertDecodeError(lowmemjson.Decode(bytes.NewReader(data), ptr))
+	return convertDecodeError(lowmemjson.DecodeThenEOF(bytes.NewReader(data), ptr))
 }
 
 type Decoder struct {
diff --git a/decode.go b/decode.go
index a17a572..52fcb5e 100644
--- a/decode.go
+++ b/decode.go
@@ -121,6 +121,26 @@ func Decode(r interface {
 	return NewDecoder(r).Decode(ptr)
 }
 
+// DecodeThenEOF is like decode, but emits an error if there is extra data after the JSON.
+func DecodeThenEOF(r interface {
+	io.Reader
+	io.RuneScanner
+}, ptr any) error {
+	dec := NewDecoder(r)
+	if err := dec.Decode(ptr); err != nil {
+		return err
+	}
+	if c, _, err := r.ReadRune(); err == nil {
+		return &DecodeError{
+			Err: &DecodeSyntaxError{
+				Err:    fmt.Errorf("invalid character %q after top-level value", c),
+				Offset: dec.InputOffset(),
+			},
+		}
+	}
+	return nil
+}
+
 func (dec *Decoder) Decode(ptr any) (err error) {
 	ptrVal := reflect.ValueOf(ptr)
 	if ptrVal.Kind() != reflect.Pointer || ptrVal.IsNil() || !ptrVal.Elem().CanSet() {
@@ -147,6 +167,15 @@ func (dec *Decoder) Decode(ptr any) (err error) {
 		}
 	}()
 	dec.decode(ptrVal.Elem(), false)
+	for {
+		_, s, t, _ := dec.io.ReadRuneType()
+		if t == RuneTypeEOF || t == RuneTypeError {
+			if s > 0 {
+				dec.io.UnreadRune()
+			}
+			break
+		}
+	}
 	return nil
 }
 
diff --git a/reencode.go b/reencode.go
index 1e5f5aa..7c5ce52 100644
--- a/reencode.go
+++ b/reencode.go
@@ -5,7 +5,6 @@
 package lowmemjson
 
 import (
-	"errors"
 	"fmt"
 	"io"
 	"unicode/utf8"
@@ -16,6 +15,8 @@ type reencodeState func(rune) error
 type ReEncoder struct {
 	Out io.Writer
 
+	AllowMultipleValues bool
+
 	// Whether to minify the JSON.
 	Compact bool
 	// String to use to indent; ignored if Compact is true.
@@ -83,13 +84,22 @@ func (enc *ReEncoder) Close() error {
 		}
 	}
 	if _, err := enc.par.HandleEOF(); err != nil {
-		enc.err = err
+		enc.err = &ReEncodeSyntaxError{
+			Err:    err,
+			Offset: enc.inputPos,
+		}
 		return enc.err
 	}
 	if err := enc.handleRune(0, 0); err != nil {
-		enc.err = err
+		enc.err = &ReEncodeSyntaxError{
+			Err:    err,
+			Offset: enc.inputPos,
+		}
 		return enc.err
 	}
+	if enc.AllowMultipleValues {
+		enc.par.Reset()
+	}
 	return nil
 }
 
@@ -97,22 +107,36 @@ func (enc *ReEncoder) WriteRune(c rune) (n int, err error) {
 	if enc.err != nil {
 		return 0, enc.err
 	}
-	if enc.bufLen != 0 {
-		enc.err = errors.New("lowmemjson.ReEncoder: cannot .WriteRune() when there is a partial rune that has been .Write()n")
+	if enc.bufLen > 0 {
+		enc.err = fmt.Errorf("lowmemjson.ReEncoder: cannot .WriteRune() when there is a partial rune that has been .Write()en: %q", enc.buf[:enc.bufLen])
 		return 0, enc.err
 	}
 
+	enc.written = 0
+
+rehandle:
 	t, err := enc.par.HandleRune(c)
 	if err != nil {
 		enc.err = &ReEncodeSyntaxError{
 			Err:    err,
 			Offset: enc.inputPos,
 		}
-		return 0, enc.err
+		return enc.written, enc.err
 	}
-
-	enc.written = 0
 	enc.err = enc.handleRune(c, t)
+	if enc.err == nil && t == RuneTypeEOF {
+		if enc.AllowMultipleValues {
+			enc.par.Reset()
+			goto rehandle
+		} else {
+			enc.err = &ReEncodeSyntaxError{
+				Err:    fmt.Errorf("invalid character %q after top-level value", c),
+				Offset: enc.inputPos,
+			}
+			return enc.written, enc.err
+		}
+	}
+
 	enc.inputPos += int64(utf8.RuneLen(c))
 	return enc.written, enc.err
 }