Add decoder for Array or Slice type

decode.go

@@ -1,6 +1,7 @@
 package json
 
 import (
+	"bytes"
 	"io"
 	"reflect"
 	"strings"
@@ -8,25 +9,26 @@ import (
 	"unsafe"
 )
 
+// A Token holds a value of one of these types:
+//
+//	Delim, for the four JSON delimiters [ ] { }
+//	bool, for JSON booleans
+//	float64, for JSON numbers
+//	Number, for JSON numbers
+//	string, for JSON string literals
+//	nil, for JSON null
+//
 type Token interface{}
 
 type Delim rune
 
-const (
-	stateNone int = iota
-	stateLiteral
-	stateObject
-	stateArray
-)
-
 type decoder interface {
 	decode(*context, uintptr) error
 }
 
 type Decoder struct {
-	r     io.Reader
-	state int
-	value []byte
+	r        io.Reader
+	buffered func() io.Reader
 }
 
 var (
@@ -43,14 +45,18 @@ func init() {
 	}
 }
 
+// NewDecoder returns a new decoder that reads from r.
+//
+// The decoder introduces its own buffering and may
+// read data from r beyond the JSON values requested.
 func NewDecoder(r io.Reader) *Decoder {
-	return &Decoder{
-		r: r,
-	}
+	return &Decoder{r: r}
 }
 
+// Buffered returns a reader of the data remaining in the Decoder's
+// buffer. The reader is valid until the next call to Decode.
 func (d *Decoder) Buffered() io.Reader {
-	return d.r
+	return d.buffered()
 }
 
 func (d *Decoder) decode(src []byte, header *interfaceHeader) error {
@@ -92,6 +98,11 @@ func (d *Decoder) decodeForUnmarshalNoEscape(src []byte, v interface{}) error {
 	return d.decode(src, header)
 }
 
+// Decode reads the next JSON-encoded value from its
+// input and stores it in the value pointed to by v.
+//
+// See the documentation for Unmarshal for details about
+// the conversion of JSON into a Go value.
 func (d *Decoder) Decode(v interface{}) error {
 	header := (*interfaceHeader)(unsafe.Pointer(&v))
 	typ := header.typ
@@ -113,6 +124,9 @@ func (d *Decoder) Decode(v interface{}) error {
 	ptr := uintptr(header.ptr)
 	ctx := ctxPool.Get().(*context)
 	defer ctxPool.Put(ctx)
+	d.buffered = func() io.Reader {
+		return bytes.NewReader(ctx.buf[ctx.cursor:])
+	}
 	for {
 		buf := make([]byte, 1024)
 		n, err := d.r.Read(buf)
@@ -136,6 +150,10 @@ func (d *Decoder) compile(typ *rtype) (decoder, error) {
 		return d.compilePtr(typ)
 	case reflect.Struct:
 		return d.compileStruct(typ)
+	case reflect.Slice:
+		return d.compileSlice(typ)
+	case reflect.Array:
+		return d.compileArray(typ)
 	case reflect.Int:
 		return d.compileInt()
 	case reflect.Int8:
@@ -256,6 +274,24 @@ func (d *Decoder) compileBool() (decoder, error) {
 	return newBoolDecoder(), nil
 }
 
+func (d *Decoder) compileSlice(typ *rtype) (decoder, error) {
+	elem := typ.Elem()
+	decoder, err := d.compile(elem)
+	if err != nil {
+		return nil, err
+	}
+	return newSliceDecoder(decoder, elem, elem.Size()), nil
+}
+
+func (d *Decoder) compileArray(typ *rtype) (decoder, error) {
+	elem := typ.Elem()
+	decoder, err := d.compile(elem)
+	if err != nil {
+		return nil, err
+	}
+	return newArrayDecoder(decoder, elem, typ.Len()), nil
+}
+
 func (d *Decoder) getTag(field reflect.StructField) string {
 	return field.Tag.Get("json")
 }
@@ -300,6 +336,9 @@ func (d *Decoder) compileStruct(typ *rtype) (decoder, error) {
 	return newStructDecoder(fieldMap), nil
 }
 
+// DisallowUnknownFields causes the Decoder to return an error when the destination
+// is a struct and the input contains object keys which do not match any
+// non-ignored, exported fields in the destination.
 func (d *Decoder) DisallowUnknownFields() {
 
 }
@@ -316,6 +355,8 @@ func (d *Decoder) Token() (Token, error) {
 	return nil, nil
 }
 
+// UseNumber causes the Decoder to unmarshal a number into an interface{} as a
+// Number instead of as a float64.
 func (d *Decoder) UseNumber() {
 
 }

decode_array.go

@@ -0,0 +1,52 @@
+package json
+
+import (
+	"errors"
+)
+
+type arrayDecoder struct {
+	elemType     *rtype
+	size         uintptr
+	valueDecoder decoder
+	alen         int
+}
+
+func newArrayDecoder(dec decoder, elemType *rtype, alen int) *arrayDecoder {
+	return &arrayDecoder{
+		valueDecoder: dec,
+		elemType:     elemType,
+		size:         elemType.Size(),
+		alen:         alen,
+	}
+}
+
+func (d *arrayDecoder) decode(ctx *context, p uintptr) error {
+	buf := ctx.buf
+	buflen := ctx.buflen
+	cursor := ctx.cursor
+	for ; cursor < buflen; cursor++ {
+		switch buf[cursor] {
+		case ' ', '\n', '\t', '\r':
+			continue
+		case '[':
+			idx := 0
+			for {
+				ctx.cursor = cursor + 1
+				if err := d.valueDecoder.decode(ctx, p+uintptr(idx)*d.size); err != nil {
+					return err
+				}
+				cursor = ctx.skipWhiteSpace()
+				switch buf[cursor] {
+				case ']':
+					return nil
+				case ',':
+					idx++
+					continue
+				default:
+					return errors.New("syntax error array")
+				}
+			}
+		}
+	}
+	return errors.New("unexpected error array")
+}

decode_slice.go

@@ -0,0 +1,72 @@
+package json
+
+import (
+	"errors"
+	"reflect"
+	"unsafe"
+)
+
+type sliceDecoder struct {
+	elemType     *rtype
+	valueDecoder decoder
+	size         uintptr
+}
+
+func newSliceDecoder(dec decoder, elemType *rtype, size uintptr) *sliceDecoder {
+	return &sliceDecoder{
+		valueDecoder: dec,
+		elemType:     elemType,
+		size:         size,
+	}
+}
+
+//go:linkname copySlice reflect.typedslicecopy
+func copySlice(elemType *rtype, dst, src reflect.SliceHeader) int
+
+//go:linkname newArray reflect.unsafe_NewArray
+func newArray(*rtype, int) unsafe.Pointer
+
+func (d *sliceDecoder) decode(ctx *context, p uintptr) error {
+	buf := ctx.buf
+	buflen := ctx.buflen
+	cursor := ctx.cursor
+	for ; cursor < buflen; cursor++ {
+		switch buf[cursor] {
+		case ' ', '\n', '\t', '\r':
+			continue
+		case '[':
+			idx := 0
+			cap := 2
+			data := uintptr(newArray(d.elemType, cap))
+			for {
+				ctx.cursor = cursor + 1
+				if cap <= idx {
+					src := reflect.SliceHeader{Data: data, Len: idx, Cap: cap}
+					cap *= 2
+					data = uintptr(newArray(d.elemType, cap))
+					dst := reflect.SliceHeader{Data: data, Len: idx, Cap: cap}
+					copySlice(d.elemType, dst, src)
+				}
+				if err := d.valueDecoder.decode(ctx, data+uintptr(idx)*d.size); err != nil {
+					return err
+				}
+				cursor = ctx.skipWhiteSpace()
+				switch buf[cursor] {
+				case ']':
+					*(*reflect.SliceHeader)(unsafe.Pointer(p)) = reflect.SliceHeader{
+						Data: data,
+						Len:  idx + 1,
+						Cap:  cap,
+					}
+					return nil
+				case ',':
+					idx++
+					continue
+				default:
+					return errors.New("syntax error slice")
+				}
+			}
+		}
+	}
+	return errors.New("unexpected error slice")
+}

decode_test.go

@@ -1,6 +1,7 @@
 package json_test
 
 import (
+	"fmt"
 	"testing"
 
 	"github.com/goccy/go-json"
@@ -75,17 +76,25 @@ func Test_Decoder(t *testing.T) {
 		assertEq(t, "string", "hello", v)
 	})
 	t.Run("float32", func(t *testing.T) {
-		var v struct {
-			F float32
-		}
-		assertErr(t, json.Unmarshal([]byte(`{"f": 3.14}`), &v))
-		assertEq(t, "float32", float32(3.14), v.F)
+		var v float32
+		assertErr(t, json.Unmarshal([]byte(`3.14`), &v))
+		assertEq(t, "float32", float32(3.14), v)
 	})
 	t.Run("float64", func(t *testing.T) {
 		var v float64
 		assertErr(t, json.Unmarshal([]byte(`3.14`), &v))
 		assertEq(t, "float64", float64(3.14), v)
 	})
+	t.Run("slice", func(t *testing.T) {
+		var v []int
+		assertErr(t, json.Unmarshal([]byte(` [ 1 , 2 , 3 , 4 ] `), &v))
+		assertEq(t, "slice", fmt.Sprint([]int{1, 2, 3, 4}), fmt.Sprint(v))
+	})
+	t.Run("array", func(t *testing.T) {
+		var v [4]int
+		assertErr(t, json.Unmarshal([]byte(` [ 1 , 2 , 3 , 4 ] `), &v))
+		assertEq(t, "array", fmt.Sprint([4]int{1, 2, 3, 4}), fmt.Sprint(v))
+	})
 	t.Run("struct", func(t *testing.T) {
 		type T struct {
 			AA int    `json:"aa"`