fix: do not reference buffer for key if decoder is buffered

Subsequent reads will change buffer and so, may overwrite the key.

Author: tdakkota

dec_obj.go

@@ -25,8 +25,14 @@ func (d *Decoder) ObjBytes(f func(d *Decoder, key []byte) error) error {
 		return d.decDepth()
 	}
 	d.unread()
+	// Do not reference internal buffer for key if decoder is not buffered.
+	//
+	// Otherwise, subsequent reads may overwrite the key.
+	//
+	// See https://github.com/go-faster/jx/pull/62.
+	isBuffer := d.reader == nil
 
-	k, err := d.str(value{raw: true})
+	k, err := d.str(value{raw: isBuffer})
 	if err != nil {
 		return errors.Wrap(err, "str")
 	}
@@ -47,7 +53,7 @@ func (d *Decoder) ObjBytes(f func(d *Decoder, key []byte) error) error {
 		return errors.Wrap(err, "next")
 	}
 	for c == ',' {
-		k, err := d.str(value{raw: true})
+		k, err := d.str(value{raw: isBuffer})
 		if err != nil {
 			return errors.Wrap(err, "str")
 		}

dec_obj_iter.go

@@ -4,11 +4,12 @@ import "github.com/go-faster/errors"
 
 // ObjIter is decoding object iterator.
 type ObjIter struct {
-	d      *Decoder
-	key    []byte
-	err    error
-	closed bool
-	comma  bool
+	d        *Decoder
+	key      []byte
+	err      error
+	isBuffer bool
+	closed   bool
+	comma    bool
 }
 
 // ObjIter creates new object iterator.
@@ -23,7 +24,7 @@ func (d *Decoder) ObjIter() (ObjIter, error) {
 		return ObjIter{}, err
 	}
 	d.unread()
-	return ObjIter{d: d}, nil
+	return ObjIter{d: d, isBuffer: d.reader == nil}, nil
 }
 
 // Key returns current key.
@@ -59,7 +60,7 @@ func (i *ObjIter) Next() bool {
 		dec.unread()
 	}
 
-	k, err := dec.str(value{raw: true})
+	k, err := dec.str(value{raw: i.isBuffer})
 	if err != nil {
 		i.err = errors.Wrap(err, "str")
 		return false

dec_obj_iter_test.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"strings"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -76,3 +77,26 @@ func TestDecoder_ObjIter(t *testing.T) {
 		a.Equal([]string{"foo", "bar", "baz"}, r)
 	}))
 }
+
+func TestDecoderObjIterIssue62(t *testing.T) {
+	a := require.New(t)
+
+	const input = `{"1":1,"2":2}`
+
+	// Force decoder to read only first 4 bytes of input.
+	d := Decode(strings.NewReader(input), 4)
+
+	iter, err := d.ObjIter()
+	a.NoError(err)
+
+	actual := map[string]int{}
+	for iter.Next() {
+		val, err := d.Int()
+		a.NoError(err)
+		actual[string(iter.Key())] = val
+	}
+	a.Equal(map[string]int{
+		"1": 1,
+		"2": 2,
+	}, actual)
+}

dec_obj_test.go

@@ -2,13 +2,14 @@ package jx
 
 import (
 	"encoding/json"
+	"strings"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
-func TestDecoder_ObjectBytes(t *testing.T) {
+func TestDecoder_ObjBytes(t *testing.T) {
 	t.Run("Object", func(t *testing.T) {
 		i := DecodeStr(`{  "id" :1 ,  "randomNumber"  :  10    }`)
 		met := map[string]struct{}{}
@@ -62,3 +63,26 @@ func TestDecoder_ObjectBytes(t *testing.T) {
 		}
 	})
 }
+
+func TestDecoderObjBytesIssue62(t *testing.T) {
+	a := require.New(t)
+
+	const input = `{"1":1,"2":2}`
+
+	// Force decoder to read only first 4 bytes of input.
+	d := Decode(strings.NewReader(input), 4)
+
+	actual := map[string]int{}
+	a.NoError(d.ObjBytes(func(d *Decoder, key []byte) error {
+		val, err := d.Int()
+		if err != nil {
+			return err
+		}
+		actual[string(key)] = val
+		return nil
+	}))
+	a.Equal(map[string]int{
+		"1": 1,
+		"2": 2,
+	}, actual)
+}