Source file src/pkg/json/decode.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.

// Represents JSON data structure using native Go types: booleans, floats,
// strings, arrays, and maps.

package json

import (
    "container/vector"
    "os"
)

// 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.
//
// 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()
    } else {
        err = &ParseError{Index: errPos, Token: errTok}
    }
    return
}

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{}
}

func newDecoder(container interface{}, key interface{}) *decoder {
    return &decoder{container: container, index: key}
}

func (j *decoder) Int64(i int64) { j.value = float64(i) }

func (j *decoder) Uint64(i uint64) { j.value = float64(i) }

func (j *decoder) Float64(f float64) { j.value = float64(f) }

func (j *decoder) String(s string) { j.value = s }

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)
    if !ok {
        v = new(vector.Vector)
        j.value = v
    }
    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)
}

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()
    }
}

// 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
}