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 (
	"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 array 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.
//
// 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) {
	b := &structBuilder{val: reflect.NewValue(val)};
	ok, _, errtok = Parse(s, b);
	if !ok {
		return false, errtok;
	}
	return true, "";
}