json: Marshal, Unmarshal using new scanner

R=r
CC=golang-dev
https://golang.org/cl/953041

src/pkg/json/decode.go

@@ -1,4 +1,4 @@
-// Copyright 2009 The Go Authors. All rights reserved.
+// Copyright 2010 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
@@ -10,96 +10,888 @@ package json
 import (
 	"container/vector"
 	"os"
+	"reflect"
+	"runtime"
+	"strconv"
+	"strings"
+	"unicode"
+	"utf16"
+	"utf8"
 )
 
-// Decode a JSON string
-
-// Decode parses the string s as a JSON-syntax string and returns the
-// generic JSON object representation.  The object representation is a tree
-// of Go data types.  The data return value may be one of float64, string,
-// bool, nil, []interface{} or map[string]interface{}.  The array and map
-// elements may in turn contain any of the types listed above and so on.
+// Unmarshal parses the JSON-encoded data and stores the result
+// in the value pointed at by v.
 //
-// If Decode encounters a syntax error, it returns with err set to an
-// instance of ParseError.  See ParseError documentation for details.
-func Decode(s string) (data interface{}, err os.Error) {
-	jb := newDecoder(nil, nil)
-	ok, errPos, errTok := Parse(s, jb)
-	if ok {
-		data = jb.Data()
+// Unmarshal traverses the value v recursively.
+// If an encountered value implements the Unmarshaler interface,
+// Unmarshal calls its UnmarshalJSON method with a well-formed
+// JSON encoding.
+//
+// Otherwise, Unmarshal uses the inverse of the encodings that
+// Marshal uses, allocating maps, slices, and pointers as necessary,
+// with the following additional rules:
+//
+// To unmarshal a JSON value into a nil interface value, the
+// type stored in the interface value is one of:
+//
+//	bool, for JSON booleans
+//	float64, for JSON numbers
+//	string, for JSON strings
+//	[]interface{}, for JSON arrays
+//	map[string]interface{}, for JSON objects
+//	nil for JSON null
+//
+// If a JSON value is not appropriate for a given target type,
+// or if a JSON number overflows the target type, Unmarshal
+// skips that field and completes the unmarshalling as best it can.
+// If no more serious errors are encountered, Unmarshal returns
+// an UnmarshalTypeError describing the earliest such error.
+//
+func Unmarshal(data []byte, v interface{}) os.Error {
+	d := new(decodeState).init(data)
+
+	// Quick check for well-formedness.
+	// Avoids filling out half a data structure
+	// before discovering a JSON syntax error.
+	err := checkValid(data, &d.scan)
+	if err != nil {
+		return err
+	}
+
+	return d.unmarshal(v)
+}
+
+// Unmarshaler is the interface implemented by objects
+// that can unmarshal a JSON description of themselves.
+// The input can be assumed to be a valid JSON object
+// encoding.  UnmarshalJSON must copy the JSON data
+// if it wishes to retain the data after returning.
+type Unmarshaler interface {
+	UnmarshalJSON([]byte) os.Error
+}
+
+
+// An UnmarshalTypeError describes a JSON value that was
+// not appropriate for a value of a specific Go type.
+type UnmarshalTypeError struct {
+	Value string       // description of JSON value - "bool", "array", "number -5"
+	Type  reflect.Type // type of Go value it could not be assigned to
+}
+
+func (e *UnmarshalTypeError) String() string {
+	return "json: cannot unmarshal " + e.Value + " into Go value of type " + e.Type.String()
+}
+
+// An InvalidUnmarshalError describes an invalid argument passed to Unmarshal.
+// (The argument to Unmarshal must be a non-nil pointer.)
+type InvalidUnmarshalError struct {
+	Type reflect.Type
+}
+
+func (e *InvalidUnmarshalError) String() string {
+	if e.Type == nil {
+		return "json: Unmarshal(nil)"
+	}
+
+	if _, ok := e.Type.(*reflect.PtrType); !ok {
+		return "json: Unmarshal(non-pointer " + e.Type.String() + ")"
+	}
+	return "json: Unmarshal(nil " + e.Type.String() + ")"
+}
+
+func (d *decodeState) unmarshal(v interface{}) (err os.Error) {
+	defer func() {
+		if r := recover(); r != nil {
+			if _, ok := r.(runtime.Error); ok {
+				panic(r)
+			}
+			err = r.(os.Error)
+		}
+	}()
+
+	rv := reflect.NewValue(v)
+	pv, ok := rv.(*reflect.PtrValue)
+	if !ok || pv.IsNil() {
+		return &InvalidUnmarshalError{reflect.Typeof(v)}
+	}
+
+	d.scan.reset()
+	d.value(pv.Elem())
+	return d.savedError
+}
+
+// decodeState represents the state while decoding a JSON value.
+type decodeState struct {
+	data       []byte
+	off        int // read offset in data
+	scan       scanner
+	nextscan   scanner // for calls to nextValue
+	savedError os.Error
+}
+
+// errPhase is used for errors that should not happen unless
+// there is a bug in the JSON decoder or something is editing
+// the data slice while the decoder executes.
+var errPhase = os.NewError("JSON decoder out of sync - data changing underfoot?")
+
+func (d *decodeState) init(data []byte) *decodeState {
+	d.data = data
+	d.off = 0
+	d.savedError = nil
+	return d
+}
+
+// error aborts the decoding by panicking with err.
+func (d *decodeState) error(err os.Error) {
+	panic(err)
+}
+
+// saveError saves the first err it is called with,
+// for reporting at the end of the unmarshal.
+func (d *decodeState) saveError(err os.Error) {
+	if d.savedError == nil {
+		d.savedError = err
+	}
+}
+
+// next cuts off and returns the next full JSON value in d.data[d.off:].
+// The next value is known to be an object or array, not a literal.
+func (d *decodeState) next() []byte {
+	c := d.data[d.off]
+	item, rest, err := nextValue(d.data[d.off:], &d.nextscan)
+	if err != nil {
+		d.error(err)
+	}
+	d.off = len(d.data) - len(rest)
+
+	// Our scanner has seen the opening brace/bracket
+	// and thinks we're still in the middle of the object.
+	// invent a closing brace/bracket to get it out.
+	if c == '{' {
+		d.scan.step(&d.scan, '}')
 	} else {
-		err = &ParseError{Index: errPos, Token: errTok}
+		d.scan.step(&d.scan, ']')
 	}
-	return
+
+	return item
 }
 
-type decoder struct {
-	// A value being constructed.
-	value interface{}
-	// Container entity to flush into.  Can be either vector.Vector or
-	// map[string]interface{}.
-	container interface{}
-	// The index into the container interface.  Either int or string.
-	index interface{}
+// scanWhile processes bytes in d.data[d.off:] until it
+// receives a scan code not equal to op.
+// It updates d.off and returns the new scan code.
+func (d *decodeState) scanWhile(op int) int {
+	var newOp int
+	for {
+		if d.off >= len(d.data) {
+			newOp = d.scan.eof()
+			d.off = len(d.data) + 1 // mark processed EOF with len+1
+		} else {
+			c := int(d.data[d.off])
+			d.off++
+			newOp = d.scan.step(&d.scan, c)
+		}
+		if newOp != op {
+			break
+		}
+	}
+	return newOp
 }
 
-func newDecoder(container interface{}, key interface{}) *decoder {
-	return &decoder{container: container, index: key}
+// value decodes a JSON value from d.data[d.off:] into the value.
+// it updates d.off to point past the decoded value.
+func (d *decodeState) value(v reflect.Value) {
+	if v == nil {
+		_, rest, err := nextValue(d.data[d.off:], &d.nextscan)
+		if err != nil {
+			d.error(err)
+		}
+		d.off = len(d.data) - len(rest)
+
+		// d.scan thinks we're still at the beginning of the item.
+		// Feed in an empty string - the shortest, simplest value -
+		// so that it knows we got to the end of the value.
+		if d.scan.step == stateRedo {
+			panic("redo")
+		}
+		d.scan.step(&d.scan, '"')
+		d.scan.step(&d.scan, '"')
+		return
+	}
+
+	switch op := d.scanWhile(scanSkipSpace); op {
+	default:
+		d.error(errPhase)
+
+	case scanBeginArray:
+		d.array(v)
+
+	case scanBeginObject:
+		d.object(v)
+
+	case scanBeginLiteral:
+		d.literal(v)
+	}
 }
 
-func (j *decoder) Int64(i int64) { j.value = float64(i) }
+// indirect walks down v allocating pointers as needed,
+// until it gets to a non-pointer.
+// if it encounters an Unmarshaler, indirect stops and returns that.
+// if wantptr is true, indirect stops at the last pointer.
+func (d *decodeState) indirect(v reflect.Value, wantptr bool) (Unmarshaler, reflect.Value) {
+	for {
+		var isUnmarshaler bool
+		if v.Type().NumMethod() > 0 {
+			// Remember that this is an unmarshaler,
+			// but wait to return it until after allocating
+			// the pointer (if necessary).
+			_, isUnmarshaler = v.Interface().(Unmarshaler)
+		}
 
-func (j *decoder) Uint64(i uint64) { j.value = float64(i) }
+		pv, ok := v.(*reflect.PtrValue)
+		if !ok {
+			break
+		}
+		_, isptrptr := pv.Elem().(*reflect.PtrValue)
+		if !isptrptr && wantptr && !isUnmarshaler {
+			return nil, pv
+		}
+		pv.PointTo(reflect.MakeZero(pv.Type().(*reflect.PtrType).Elem()))
+		if isUnmarshaler {
+			// Using v.Interface().(Unmarshaler)
+			// here means that we have to use a pointer
+			// as the struct field.  We cannot use a value inside
+			// a pointer to a struct, because in that case
+			// v.Interface() is the value (x.f) not the pointer (&x.f).
+			// This is an unfortunate consequence of reflect.
+			// An alternative would be to look up the
+			// UnmarshalJSON method and return a FuncValue.
+			return v.Interface().(Unmarshaler), nil
+		}
+		v = pv.Elem()
+	}
+	return nil, v
+}
 
-func (j *decoder) Float64(f float64) { j.value = float64(f) }
+// array consumes an array from d.data[d.off-1:], decoding into the value v.
+// the first byte of the array ('[') has been read already.
+func (d *decodeState) array(v reflect.Value) {
+	// Check for unmarshaler.
+	unmarshaler, pv := d.indirect(v, false)
+	if unmarshaler != nil {
+		d.off--
+		err := unmarshaler.UnmarshalJSON(d.next())
+		if err != nil {
+			d.error(err)
+		}
+		return
+	}
+	v = pv
 
-func (j *decoder) String(s string) { j.value = s }
+	// Decoding into nil interface?  Switch to non-reflect code.
+	iv, ok := v.(*reflect.InterfaceValue)
+	if ok {
+		iv.Set(reflect.NewValue(d.arrayInterface()))
+		return
+	}
 
-func (j *decoder) Bool(b bool) { j.value = b }
-
-func (j *decoder) Null() { j.value = nil }
-
-func (j *decoder) Array() { j.value = new(vector.Vector) }
-
-func (j *decoder) Map() { j.value = make(map[string]interface{}) }
-
-func (j *decoder) Elem(i int) Builder {
-	v, ok := j.value.(*vector.Vector)
+	// Check type of target.
+	av, ok := v.(reflect.ArrayOrSliceValue)
 	if !ok {
-		v = new(vector.Vector)
-		j.value = v
+		d.saveError(&UnmarshalTypeError{"array", v.Type()})
 	}
-	if v.Len() <= i {
-		v.Resize(i+1, (i+1)*2)
-	}
-	return newDecoder(v, i)
-}
 
-func (j *decoder) Key(s string) Builder {
-	m, ok := j.value.(map[string]interface{})
-	if !ok {
-		m = make(map[string]interface{})
-		j.value = m
-	}
-	return newDecoder(m, s)
-}
+	sv, _ := v.(*reflect.SliceValue)
 
-func (j *decoder) Flush() {
-	switch c := j.container.(type) {
-	case *vector.Vector:
-		index := j.index.(int)
-		c.Set(index, j.Data())
-	case map[string]interface{}:
-		index := j.index.(string)
-		c[index] = j.Data()
+	i := 0
+	for {
+		// Look ahead for ] - can only happen on first iteration.
+		op := d.scanWhile(scanSkipSpace)
+		if op == scanEndArray {
+			break
+		}
+
+		// Back up so d.value can have the byte we just read.
+		d.off--
+		d.scan.undo(op)
+
+		// Get element of array, growing if necessary.
+		if i >= av.Cap() && sv != nil {
+			newcap := sv.Cap() + sv.Cap()/2
+			if newcap < 4 {
+				newcap = 4
+			}
+			newv := reflect.MakeSlice(sv.Type().(*reflect.SliceType), sv.Len(), newcap)
+			reflect.ArrayCopy(newv, sv)
+			sv.Set(newv)
+		}
+		if i >= av.Len() && sv != nil {
+			// Must be slice; gave up on array during i >= av.Cap().
+			sv.SetLen(i + 1)
+		}
+
+		// Decode into element.
+		if i < av.Len() {
+			d.value(av.Elem(i))
+		} else {
+			// Ran out of fixed array: skip.
+			d.value(nil)
+		}
+		i++
+
+		// Next token must be , or ].
+		op = d.scanWhile(scanSkipSpace)
+		if op == scanEndArray {
+			break
+		}
+		if op != scanArrayValue {
+			d.error(errPhase)
+		}
+	}
+	if i < av.Len() {
+		if sv == nil {
+			// Array.  Zero the rest.
+			z := reflect.MakeZero(av.Type().(*reflect.ArrayType).Elem())
+			for ; i < av.Len(); i++ {
+				av.Elem(i).SetValue(z)
+			}
+		} else {
+			sv.SetLen(i)
+		}
 	}
 }
 
-// Get the value built by this builder.
-func (j *decoder) Data() interface{} {
-	switch v := j.value.(type) {
-	case *vector.Vector:
-		return v.Data()
-	}
-	return j.value
+// matchName returns true if key should be written to a field named name.
+func matchName(key, name string) bool {
+	return strings.ToLower(key) == strings.ToLower(name)
+}
+
+// object consumes an object from d.data[d.off-1:], decoding into the value v.
+// the first byte of the object ('{') has been read already.
+func (d *decodeState) object(v reflect.Value) {
+	// Check for unmarshaler.
+	unmarshaler, pv := d.indirect(v, false)
+	if unmarshaler != nil {
+		d.off--
+		err := unmarshaler.UnmarshalJSON(d.next())
+		if err != nil {
+			d.error(err)
+		}
+		return
+	}
+	v = pv
+
+	// Decoding into nil interface?  Switch to non-reflect code.
+	iv, ok := v.(*reflect.InterfaceValue)
+	if ok {
+		iv.Set(reflect.NewValue(d.objectInterface()))
+		return
+	}
+
+	// Check type of target: struct or map[string]T
+	var (
+		mv *reflect.MapValue
+		sv *reflect.StructValue
+	)
+	switch v := v.(type) {
+	case *reflect.MapValue:
+		// map must have string type
+		t := v.Type().(*reflect.MapType)
+		if t.Key() != reflect.Typeof("") {
+			d.saveError(&UnmarshalTypeError{"object", v.Type()})
+			break
+		}
+		mv = v
+		if mv.IsNil() {
+			mv.SetValue(reflect.MakeMap(t))
+		}
+	case *reflect.StructValue:
+		sv = v
+	default:
+		d.saveError(&UnmarshalTypeError{"object", v.Type()})
+	}
+
+	if mv == nil && sv == nil {
+		d.off--
+		d.next() // skip over { } in input
+		return
+	}
+
+	for {
+		// Read opening " of string key or closing }.
+		op := d.scanWhile(scanSkipSpace)
+		if op == scanEndObject {
+			// closing } - can only happen on first iteration.
+			break
+		}
+		if op != scanBeginLiteral {
+			d.error(errPhase)
+		}
+
+		// Read string key.
+		start := d.off - 1
+		op = d.scanWhile(scanContinue)
+		item := d.data[start : d.off-1]
+		key, ok := unquote(item)
+		if !ok {
+			d.error(errPhase)
+		}
+
+		// Figure out
+		var subv reflect.Value
+		if mv != nil {
+			subv = reflect.MakeZero(mv.Type().(*reflect.MapType).Elem())
+		} else {
+			for i := 0; i < sv.NumField(); i++ {
+				f := sv.Type().(*reflect.StructType).Field(i)
+				if f.Tag == key {
+					subv = sv.Field(i)
+					break
+				}
+			}
+			if subv == nil {
+				subv = sv.FieldByNameFunc(func(s string) bool { return matchName(key, s) })
+			}
+		}
+
+		// Read : before value.
+		if op == scanSkipSpace {
+			op = d.scanWhile(scanSkipSpace)
+		}
+		if op != scanObjectKey {
+			d.error(errPhase)
+		}
+
+		// Read value.
+		d.value(subv)
+
+		// Write value back to map;
+		// if using struct, subv points into struct already.
+		if mv != nil {
+			mv.SetElem(reflect.NewValue(key), subv)
+		}
+
+		// Next token must be , or }.
+		op = d.scanWhile(scanSkipSpace)
+		if op == scanEndObject {
+			break
+		}
+		if op != scanObjectValue {
+			d.error(errPhase)
+		}
+	}
+}
+
+// literal consumes a literal from d.data[d.off-1:], decoding into the value v.
+// The first byte of the literal has been read already
+// (that's how the caller knows it's a literal).
+func (d *decodeState) literal(v reflect.Value) {
+	// All bytes inside literal return scanContinue op code.
+	start := d.off - 1
+	op := d.scanWhile(scanContinue)
+
+	// Scan read one byte too far; back up.
+	d.off--
+	d.scan.undo(op)
+	item := d.data[start:d.off]
+
+	// Check for unmarshaler.
+	wantptr := item[0] == 'n' // null
+	unmarshaler, pv := d.indirect(v, wantptr)
+	if unmarshaler != nil {
+		err := unmarshaler.UnmarshalJSON(item)
+		if err != nil {
+			d.error(err)
+		}
+		return
+	}
+	v = pv
+
+	switch c := item[0]; c {
+	case 'n': // null
+		switch v.(type) {
+		default:
+			d.saveError(&UnmarshalTypeError{"null", v.Type()})
+		case *reflect.InterfaceValue, *reflect.PtrValue, *reflect.MapValue:
+			v.SetValue(nil)
+		}
+
+	case 't', 'f': // true, false
+		value := c == 't'
+		switch v := v.(type) {
+		default:
+			d.saveError(&UnmarshalTypeError{"bool", v.Type()})
+		case *reflect.BoolValue:
+			v.Set(value)
+		case *reflect.InterfaceValue:
+			v.Set(reflect.NewValue(value))
+		}
+
+	case '"': // string
+		s, ok := unquote(item)
+		if !ok {
+			d.error(errPhase)
+		}
+		switch v := v.(type) {
+		default:
+			d.saveError(&UnmarshalTypeError{"string", v.Type()})
+		case *reflect.StringValue:
+			v.Set(s)
+		case *reflect.InterfaceValue:
+			v.Set(reflect.NewValue(s))
+		}
+
+	default: // number
+		if c != '-' && (c < '0' || c > '9') {
+			d.error(errPhase)
+		}
+		s := string(item)
+		switch v := v.(type) {
+		default:
+			d.error(&UnmarshalTypeError{"number", v.Type()})
+		case *reflect.InterfaceValue:
+			n, err := strconv.Atof64(s)
+			if err != nil {
+				d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
+				break
+			}
+			v.Set(reflect.NewValue(n))
+
+		case *reflect.IntValue:
+			n, err := strconv.Atoi(s)
+			if err != nil {
+				d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
+				break
+			}
+			v.Set(n)
+		case *reflect.Int8Value:
+			n, err := strconv.Atoi(s)
+			if err != nil || int(int8(n)) != n {
+				d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
+				break
+			}
+			v.Set(int8(n))
+		case *reflect.Int16Value:
+			n, err := strconv.Atoi(s)
+			if err != nil || int(int16(n)) != n {
+				d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
+				break
+			}
+			v.Set(int16(n))
+		case *reflect.Int32Value:
+			n, err := strconv.Atoi(s)
+			if err != nil || int(int32(n)) != n {
+				d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
+				break
+			}
+			v.Set(int32(n))
+		case *reflect.Int64Value:
+			n, err := strconv.Atoi64(s)
+			if err != nil {
+				d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
+				break
+			}
+			v.Set(n)
+
+		case *reflect.UintValue:
+			n, err := strconv.Atoui(s)
+			if err != nil {
+				d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
+				break
+			}
+			v.Set(n)
+		case *reflect.Uint8Value:
+			n, err := strconv.Atoui(s)
+			if err != nil || uint(uint8(n)) != n {
+				d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
+				break
+			}
+			v.Set(uint8(n))
+		case *reflect.Uint16Value:
+			n, err := strconv.Atoui(s)
+			if err != nil || uint(uint16(n)) != n {
+				d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
+				break
+			}
+			v.Set(uint16(n))
+		case *reflect.Uint32Value:
+			n, err := strconv.Atoui(s)
+			if err != nil || uint(uint32(n)) != n {
+				d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
+				break
+			}
+			v.Set(uint32(n))
+		case *reflect.Uint64Value:
+			n, err := strconv.Atoui64(s)
+			if err != nil {
+				d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
+				break
+			}
+			v.Set(n)
+		case *reflect.UintptrValue:
+			n, err := strconv.Atoui64(s)
+			if err != nil || uint64(uintptr(n)) != n {
+				d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
+				break
+			}
+			v.Set(uintptr(n))
+
+		case *reflect.FloatValue:
+			n, err := strconv.Atof(s)
+			if err != nil {
+				d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
+				break
+			}
+			v.Set(n)
+		case *reflect.Float32Value:
+			n, err := strconv.Atof32(s)
+			if err != nil {
+				d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
+				break
+			}
+			v.Set(n)
+		case *reflect.Float64Value:
+			n, err := strconv.Atof64(s)
+			if err != nil {
+				d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
+				break
+			}
+			v.Set(n)
+		}
+	}
+}
+
+// The xxxInterface routines build up a value to be stored
+// in an empty interface.  They are not strictly necessary,
+// but they avoid the weight of reflection in this common case.
+
+// valueInterface is like value but returns interface{}
+func (d *decodeState) valueInterface() interface{} {
+	switch d.scanWhile(scanSkipSpace) {
+	default:
+		d.error(errPhase)
+	case scanBeginArray:
+		return d.arrayInterface()
+	case scanBeginObject:
+		return d.objectInterface()
+	case scanBeginLiteral:
+		return d.literalInterface()
+	}
+	panic("unreachable")
+}
+
+// arrayInterface is like array but returns []interface{}.
+func (d *decodeState) arrayInterface() []interface{} {
+	var v vector.Vector
+	for {
+		// Look ahead for ] - can only happen on first iteration.
+		op := d.scanWhile(scanSkipSpace)
+		if op == scanEndArray {
+			break
+		}
+
+		// Back up so d.value can have the byte we just read.
+		d.off--
+		d.scan.undo(op)
+
+		v.Push(d.valueInterface())
+
+		// Next token must be , or ].
+		op = d.scanWhile(scanSkipSpace)
+		if op == scanEndArray {
+			break
+		}
+		if op != scanArrayValue {
+			d.error(errPhase)
+		}
+	}
+	return v
+}
+
+// objectInterface is like object but returns map[string]interface{}.
+func (d *decodeState) objectInterface() map[string]interface{} {
+	m := make(map[string]interface{})
+	for {
+		// Read opening " of string key or closing }.
+		op := d.scanWhile(scanSkipSpace)
+		if op == scanEndObject {
+			// closing } - can only happen on first iteration.
+			break
+		}
+		if op != scanBeginLiteral {
+			d.error(errPhase)
+		}
+
+		// Read string key.
+		start := d.off - 1
+		op = d.scanWhile(scanContinue)
+		item := d.data[start : d.off-1]
+		key, ok := unquote(item)
+		if !ok {
+			d.error(errPhase)
+		}
+
+		// Read : before value.
+		if op == scanSkipSpace {
+			op = d.scanWhile(scanSkipSpace)
+		}
+		if op != scanObjectKey {
+			d.error(errPhase)
+		}
+
+		// Read value.
+		m[key] = d.valueInterface()
+
+		// Next token must be , or }.
+		op = d.scanWhile(scanSkipSpace)
+		if op == scanEndObject {
+			break
+		}
+		if op != scanObjectValue {
+			d.error(errPhase)
+		}
+	}
+	return m
+}
+
+
+// literalInterface is like literal but returns an interface value.
+func (d *decodeState) literalInterface() interface{} {
+	// All bytes inside literal return scanContinue op code.
+	start := d.off - 1
+	op := d.scanWhile(scanContinue)
+
+	// Scan read one byte too far; back up.
+	d.off--
+	d.scan.undo(op)
+	item := d.data[start:d.off]
+
+	switch c := item[0]; c {
+	case 'n': // null
+		return nil
+
+	case 't', 'f': // true, false
+		return c == 't'
+
+	case '"': // string
+		s, ok := unquote(item)
+		if !ok {
+			d.error(errPhase)
+		}
+		return s
+
+	default: // number
+		if c != '-' && (c < '0' || c > '9') {
+			d.error(errPhase)
+		}
+		n, err := strconv.Atof64(string(item))
+		if err != nil {
+			d.saveError(&UnmarshalTypeError{"number " + string(item), reflect.Typeof(float64(0))})
+		}
+		return n
+	}
+	panic("unreachable")
+}
+
+// getu4 decodes \uXXXX from the beginning of s, returning the hex value,
+// or it returns -1.
+func getu4(s []byte) int {
+	if len(s) < 6 || s[0] != '\\' || s[1] != 'u' {
+		return -1
+	}
+	rune, err := strconv.Btoui64(string(s[2:6]), 16)
+	if err != nil {
+		return -1
+	}
+	return int(rune)
+}
+
+// unquote converts a quoted JSON string literal s into an actual string t.
+// The rules are different than for Go, so cannot use strconv.Unquote.
+func unquote(s []byte) (t string, ok bool) {
+	if len(s) < 2 || s[0] != '"' || s[len(s)-1] != '"' {
+		return
+	}
+	b := make([]byte, len(s)+2*utf8.UTFMax)
+	w := 0
+	for r := 1; r < len(s)-1; {
+		// Out of room?  Can only happen if s is full of
+		// malformed UTF-8 and we're replacing each
+		// byte with RuneError.
+		if w >= len(b)-2*utf8.UTFMax {
+			nb := make([]byte, (len(b)+utf8.UTFMax)*2)
+			copy(nb, b[0:w])
+			b = nb
+		}
+		switch c := s[r]; {
+		case c == '\\':
+			r++
+			if r >= len(s)-1 {
+				return
+			}
+			switch s[r] {
+			default:
+				return
+			case '"', '\\', '/', '\'':
+				b[w] = s[r]
+				r++
+				w++
+			case 'b':
+				b[w] = '\b'
+				r++
+				w++
+			case 'f':
+				b[w] = '\f'
+				r++
+				w++
+			case 'n':
+				b[w] = '\n'
+				r++
+				w++
+			case 'r':
+				b[w] = '\r'
+				r++
+				w++
+			case 't':
+				b[w] = '\t'
+				r++
+				w++
+			case 'u':
+				r--
+				rune := getu4(s[r:])
+				if rune < 0 {
+					return
+				}
+				r += 6
+				if utf16.IsSurrogate(rune) {
+					rune1 := getu4(s[r:])
+					if dec := utf16.DecodeRune(rune, rune1); dec != unicode.ReplacementChar {
+						// A valid pair; consume.
+						r += 6
+						w += utf8.EncodeRune(dec, b[w:])
+						break
+					}
+					// Invalid surrogate; fall back to replacement rune.
+					rune = unicode.ReplacementChar
+				}
+				w += utf8.EncodeRune(rune, b[w:])
+			}
+
+		// Quote, control characters are invalid.
+		case c == '"', c < ' ':
+			return
+
+		// ASCII
+		case c < utf8.RuneSelf:
+			b[w] = c
+			r++
+			w++
+
+		// Coerce to well-formed UTF-8.
+		default:
+			rune, size := utf8.DecodeRune(s[r:])
+			r += size
+			w += utf8.EncodeRune(rune, b[w:])
+		}
+	}
+	return string(b[0:w]), true
 }