src/pkg/json/struct.go

// Copyright 2009 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.

// Marshalling and unmarshalling of
// JSON data into Go structs using reflection.

package json

import (
	"bytes"
	"fmt"
	"io"
	"os"
	"reflect"
	"strings"
)

type structBuilder struct {
	val reflect.Value

	// if map_ != nil, write val to map_[key] on each change
	map_ *reflect.MapValue
	key  reflect.Value
}

var nobuilder *structBuilder

func isfloat(v reflect.Value) bool {
	switch v.(type) {
	case *reflect.FloatValue, *reflect.Float32Value, *reflect.Float64Value:
		return true
	}
	return false
}

func setfloat(v reflect.Value, f float64) {
	switch v := v.(type) {
	case *reflect.FloatValue:
		v.Set(float(f))
	case *reflect.Float32Value:
		v.Set(float32(f))
	case *reflect.Float64Value:
		v.Set(float64(f))
	}
}

func setint(v reflect.Value, i int64) {
	switch v := v.(type) {
	case *reflect.IntValue:
		v.Set(int(i))
	case *reflect.Int8Value:
		v.Set(int8(i))
	case *reflect.Int16Value:
		v.Set(int16(i))
	case *reflect.Int32Value:
		v.Set(int32(i))
	case *reflect.Int64Value:
		v.Set(int64(i))
	case *reflect.UintValue:
		v.Set(uint(i))
	case *reflect.Uint8Value:
		v.Set(uint8(i))
	case *reflect.Uint16Value:
		v.Set(uint16(i))
	case *reflect.Uint32Value:
		v.Set(uint32(i))
	case *reflect.Uint64Value:
		v.Set(uint64(i))
	}
}

// If updating b.val is not enough to update the original,
// copy a changed b.val out to the original.
func (b *structBuilder) Flush() {
	if b == nil {
		return
	}
	if b.map_ != nil {
		b.map_.SetElem(b.key, b.val)
	}
}

func (b *structBuilder) Int64(i int64) {
	if b == nil {
		return
	}
	v := b.val
	if isfloat(v) {
		setfloat(v, float64(i))
	} else {
		setint(v, i)
	}
}

func (b *structBuilder) Uint64(i uint64) {
	if b == nil {
		return
	}
	v := b.val
	if isfloat(v) {
		setfloat(v, float64(i))
	} else {
		setint(v, int64(i))
	}
}

func (b *structBuilder) Float64(f float64) {
	if b == nil {
		return
	}
	v := b.val
	if isfloat(v) {
		setfloat(v, f)
	} else {
		setint(v, int64(f))
	}
}

func (b *structBuilder) Null() {}

func (b *structBuilder) String(s string) {
	if b == nil {
		return
	}
	if v, ok := b.val.(*reflect.StringValue); ok {
		v.Set(s)
	}
}

func (b *structBuilder) Bool(tf bool) {
	if b == nil {
		return
	}
	if v, ok := b.val.(*reflect.BoolValue); ok {
		v.Set(tf)
	}
}

func (b *structBuilder) Array() {
	if b == nil {
		return
	}
	if v, ok := b.val.(*reflect.SliceValue); ok {
		if v.IsNil() {
			v.Set(reflect.MakeSlice(v.Type().(*reflect.SliceType), 0, 8))
		}
	}
}

func (b *structBuilder) Elem(i int) Builder {
	if b == nil || i < 0 {
		return nobuilder
	}
	switch v := b.val.(type) {
	case *reflect.ArrayValue:
		if i < v.Len() {
			return &structBuilder{val: v.Elem(i)}
		}
	case *reflect.SliceValue:
		if i >= v.Cap() {
			n := v.Cap()
			if n < 8 {
				n = 8
			}
			for n <= i {
				n *= 2
			}
			nv := reflect.MakeSlice(v.Type().(*reflect.SliceType), v.Len(), n)
			reflect.ArrayCopy(nv, v)
			v.Set(nv)
		}
		if v.Len() <= i && i < v.Cap() {
			v.SetLen(i + 1)
		}
		if i < v.Len() {
			return &structBuilder{val: v.Elem(i)}
		}
	}
	return nobuilder
}

func (b *structBuilder) Map() {
	if b == nil {
		return
	}
	if v, ok := b.val.(*reflect.PtrValue); ok && v.IsNil() {
		if v.IsNil() {
			v.PointTo(reflect.MakeZero(v.Type().(*reflect.PtrType).Elem()))
			b.Flush()
		}
		b.map_ = nil
		b.val = v.Elem()
	}
	if v, ok := b.val.(*reflect.MapValue); ok && v.IsNil() {
		v.Set(reflect.MakeMap(v.Type().(*reflect.MapType)))
	}
}

func (b *structBuilder) Key(k string) Builder {
	if b == nil {
		return nobuilder
	}
	switch v := reflect.Indirect(b.val).(type) {
	case *reflect.StructValue:
		t := v.Type().(*reflect.StructType)
		// Case-insensitive field lookup.
		k = strings.ToLower(k)
		for i := 0; i < t.NumField(); i++ {
			if strings.ToLower(t.Field(i).Name) == k {
				return &structBuilder{val: v.Field(i)}
			}
		}
	case *reflect.MapValue:
		t := v.Type().(*reflect.MapType)
		if t.Key() != reflect.Typeof(k) {
			break
		}
		key := reflect.NewValue(k)
		elem := v.Elem(key)
		if elem == nil {
			v.SetElem(key, reflect.MakeZero(t.Elem()))
			elem = v.Elem(key)
		}
		return &structBuilder{val: elem, map_: v, key: key}
	}
	return nobuilder
}

// Unmarshal parses the JSON syntax string s and fills in
// an arbitrary struct or slice pointed at by val.
// It uses the reflect package to assign to fields
// and arrays embedded in val.  Well-formed data that does not fit
// into the struct is discarded.
//
// For example, given these definitions:
//
//	type Email struct {
//		Where string;
//		Addr string;
//	}
//
//	type Result struct {
//		Name string;
//		Phone string;
//		Email []Email
//	}
//
//	var r = Result{ "name", "phone", nil }
//
// unmarshalling the JSON syntax string
//
//	{
//	  "email": [
//	    {
//	      "where": "home",
//	      "addr": "gre@example.com"
//	    },
//	    {
//	      "where": "work",
//	      "addr": "gre@work.com"
//	    }
//	  ],
//	  "name": "Grace R. Emlin",
//	  "address": "123 Main Street"
//	}
//
// via Unmarshal(s, &r) is equivalent to assigning
//
//	r = Result{
//		"Grace R. Emlin",	// name
//		"phone",		// no phone given
//		[]Email{
//			Email{ "home", "gre@example.com" },
//			Email{ "work", "gre@work.com" }
//		}
//	}
//
// Note that the field r.Phone has not been modified and
// that the JSON field "address" was discarded.
//
// Because Unmarshal uses the reflect package, it can only
// assign to upper case fields.  Unmarshal uses a case-insensitive
// comparison to match JSON field names to struct field names.
//
// To unmarshal a top-level JSON array, pass in a pointer to an empty
// slice of the correct type.
//
// On success, Unmarshal returns with ok set to true.
// On a syntax error, it returns with ok set to false and errtok
// set to the offending token.
func Unmarshal(s string, val interface{}) (ok bool, errtok string) {
	v := reflect.NewValue(val)
	var b *structBuilder

	// If val is a pointer to a slice, we append to the slice.
	if ptr, ok := v.(*reflect.PtrValue); ok {
		if slice, ok := ptr.Elem().(*reflect.SliceValue); ok {
			b = &structBuilder{val: slice}
		}
	}

	if b == nil {
		b = &structBuilder{val: v}
	}

	ok, _, errtok = Parse(s, b)
	if !ok {
		return false, errtok
	}
	return true, ""
}

type MarshalError struct {
	T reflect.Type
}

func (e *MarshalError) String() string {
	return "json cannot encode value of type " + e.T.String()
}

type writeState struct {
	bytes.Buffer
	indent   string
	newlines bool
	depth    int
}

func (s *writeState) descend(bra byte) {
	s.depth++
	s.WriteByte(bra)
}

func (s *writeState) ascend(ket byte) {
	s.depth--
	s.writeIndent()
	s.WriteByte(ket)
}

func (s *writeState) writeIndent() {
	if s.newlines {
		s.WriteByte('\n')
	}
	for i := 0; i < s.depth; i++ {
		s.WriteString(s.indent)
	}
}

func (s *writeState) writeArrayOrSlice(val reflect.ArrayOrSliceValue) {
	s.descend('[')

	for i := 0; i < val.Len(); i++ {
		s.writeIndent()
		s.writeValue(val.Elem(i))
		if i < val.Len()-1 {
			s.WriteByte(',')
		}
	}

	s.ascend(']')
}

func (s *writeState) writeMap(val *reflect.MapValue) {
	key := val.Type().(*reflect.MapType).Key()
	if _, ok := key.(*reflect.StringType); !ok {
		panic(&MarshalError{val.Type()})
	}

	s.descend('{')

	keys := val.Keys()
	for i := 0; i < len(keys); i++ {
		s.writeIndent()
		fmt.Fprintf(s, "%s:", Quote(keys[i].(*reflect.StringValue).Get()))
		s.writeValue(val.Elem(keys[i]))
		if i < len(keys)-1 {
			s.WriteByte(',')
		}
	}

	s.ascend('}')
}

func (s *writeState) writeStruct(val *reflect.StructValue) {
	s.descend('{')

	typ := val.Type().(*reflect.StructType)

	for i := 0; i < val.NumField(); i++ {
		s.writeIndent()
		fmt.Fprintf(s, "%s:", Quote(typ.Field(i).Name))
		s.writeValue(val.Field(i))
		if i < val.NumField()-1 {
			s.WriteByte(',')
		}
	}

	s.ascend('}')
}

func (s *writeState) writeValue(val reflect.Value) {
	if val == nil {
		fmt.Fprint(s, "null")
		return
	}

	switch v := val.(type) {
	case *reflect.StringValue:
		fmt.Fprint(s, Quote(v.Get()))
	case *reflect.ArrayValue:
		s.writeArrayOrSlice(v)
	case *reflect.SliceValue:
		s.writeArrayOrSlice(v)
	case *reflect.MapValue:
		s.writeMap(v)
	case *reflect.StructValue:
		s.writeStruct(v)
	case *reflect.ChanValue,
		*reflect.UnsafePointerValue,
		*reflect.FuncValue:
		panic(&MarshalError{val.Type()})
	case *reflect.InterfaceValue:
		if v.IsNil() {
			fmt.Fprint(s, "null")
		} else {
			s.writeValue(v.Elem())
		}
	case *reflect.PtrValue:
		if v.IsNil() {
			fmt.Fprint(s, "null")
		} else {
			s.writeValue(v.Elem())
		}
	case *reflect.UintptrValue:
		fmt.Fprintf(s, "%d", v.Get())
	case *reflect.Uint64Value:
		fmt.Fprintf(s, "%d", v.Get())
	case *reflect.Uint32Value:
		fmt.Fprintf(s, "%d", v.Get())
	case *reflect.Uint16Value:
		fmt.Fprintf(s, "%d", v.Get())
	case *reflect.Uint8Value:
		fmt.Fprintf(s, "%d", v.Get())
	default:
		value := val.(reflect.Value)
		fmt.Fprintf(s, "%#v", value.Interface())
	}
}

func (s *writeState) marshal(w io.Writer, val interface{}) (err os.Error) {
	defer func() {
		if e := recover(); e != nil {
			err = e.(*MarshalError)
		}
	}()
	s.writeValue(reflect.NewValue(val))
	if s.newlines {
		s.WriteByte('\n')
	}
	_, err = s.WriteTo(w)
	return
}

// Marshal writes the JSON encoding of val to w.
//
// Due to limitations in JSON, val cannot include cyclic data
// structures, channels, functions, or maps.
func Marshal(w io.Writer, val interface{}) os.Error {
	s := &writeState{indent: "", newlines: false, depth: 0}
	return s.marshal(w, val)
}

// MarshalIndent writes the JSON encoding of val to w,
// indenting nested values using the indent string.
//
// Due to limitations in JSON, val cannot include cyclic data
// structures, channels, functions, or maps.
func MarshalIndent(w io.Writer, val interface{}, indent string) os.Error {
	s := &writeState{indent: indent, newlines: true, depth: 0}
	return s.marshal(w, val)
}