Invent "barriers" instead of nesting parsers

1 files changed, 33 insertions, 23 deletions

diff --git a/decode.go b/decode.go
index 8fab267..60b530f 100644
--- a/decode.go
+++ b/decode.go
@@ -104,7 +104,7 @@ const maxNestingDepth = 10000
 // an io.Reader.
 func NewDecoder(r io.RuneScanner) *Decoder {
 	return &Decoder{
-		io: &runeTypeScannerImpl{
+		io: runeTypeScanner{
 			inner: r,
 			parser: internal.Parser{
 				MaxDepth: maxNestingDepth,
@@ -245,6 +245,7 @@ func (dec *Decoder) Decode(ptr any) (err error) {
 	}
 
 	dec.io.Reset()
+	dec.io.PushReadBarrier()
 	defer func() {
 		if r := recover(); r != nil {
 			if de, ok := r.(decodeError); ok {
@@ -257,6 +258,7 @@ func (dec *Decoder) Decode(ptr any) (err error) {
 		}
 	}()
 	dec.decode(ptrVal.Elem(), false)
+	dec.io.PopReadBarrier()
 	return nil
 }
 
@@ -319,12 +321,21 @@ func (dec *Decoder) expectRuneType(ec rune, et internal.RuneType, gt reflect.Typ
 	}
 }
 
-type decRuneTypeScanner struct {
+type decRuneScanner struct {
 	dec *Decoder
+	eof bool
 }
 
-func (sc *decRuneTypeScanner) ReadRuneType() (rune, int, internal.RuneType, error) {
+func (sc *decRuneScanner) ReadRune() (rune, int, error) {
+	if sc.eof {
+		return 0, 0, io.EOF
+	}
 	c, s, t, e := sc.dec.io.ReadRuneType()
+	if t == internal.RuneTypeEOF {
+		sc.eof = true
+		sc.dec.io.PopReadBarrier()
+		return 0, 0, io.EOF
+	}
 	if e != nil {
 		panic(decodeError{
 			Field:       sc.dec.structStackStr(),
@@ -333,28 +344,17 @@ func (sc *decRuneTypeScanner) ReadRuneType() (rune, int, internal.RuneType, erro
 			Err:         e,
 		})
 	}
-	return c, s, t, nil
+	return c, s, nil
 }
 
-func (sc *decRuneTypeScanner) ReadRune() (rune, int, error) {
-	r, s, t, _ := sc.ReadRuneType()
-	switch t {
-	case internal.RuneTypeEOF:
-		return 0, 0, io.EOF
-	default:
-		return r, s, nil
-	}
+func (sc *decRuneScanner) UnreadRune() error {
+	return sc.dec.io.UnreadRune()
 }
 
-func (sc *decRuneTypeScanner) UnreadRune() error  { return sc.dec.io.UnreadRune() }
-func (sc *decRuneTypeScanner) InputOffset() int64 { return sc.dec.InputOffset() }
-func (sc *decRuneTypeScanner) Reset()             { sc.dec.io.Reset() }
-
-func (dec *Decoder) limitingScanner() runeTypeScanner {
-	return &elemRuneTypeScanner{
-		inner: &decRuneTypeScanner{
-			dec: dec,
-		},
+func (dec *Decoder) limitingScanner() io.RuneScanner {
+	dec.io.PushReadBarrier()
+	return &decRuneScanner{
+		dec: dec,
 	}
 }
 
@@ -867,7 +867,12 @@ func DecodeObject(r io.RuneScanner, decodeKey, decodeVal func(io.RuneScanner) er
 			}
 		}
 	}()
-	dec := NewDecoder(r)
+	var dec *Decoder
+	if dr, ok := r.(*decRuneScanner); ok {
+		dec = dr.dec
+	} else {
+		dec = NewDecoder(r)
+	}
 	dec.posStackPush()
 	defer dec.posStackPop()
 	dec.decodeObject(nil,
@@ -947,7 +952,12 @@ func DecodeArray(r io.RuneScanner, decodeMember func(r io.RuneScanner) error) (e
 			}
 		}
 	}()
-	dec := NewDecoder(r)
+	var dec *Decoder
+	if dr, ok := r.(*decRuneScanner); ok {
+		dec = dr.dec
+	} else {
+		dec = NewDecoder(r)
+	}
 	dec.posStackPush()
 	defer dec.posStackPop()
 	dec.decodeArray(nil, func() {