json.go

/*
Copyright 2015 The Kubernetes Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package json

import (
	"bytes"
	"encoding/json"
	"io"
)

// NewEncoder delegates to json.NewEncoder
// It is only here so this package can be a drop-in for common encoding/json uses
func NewEncoder(w io.Writer) *json.Encoder {
	return json.NewEncoder(w)
}

// Marshal delegates to json.Marshal
// It is only here so this package can be a drop-in for common encoding/json uses
func Marshal(v interface{}) ([]byte, error) {
	return json.Marshal(v)
}

// Unmarshal unmarshals the given data
// If v is a *map[string]interface{}, numbers are converted to int64 or float64
func Unmarshal(data []byte, v interface{}) error {
	switch v := v.(type) {
	case *map[string]interface{}:
		// Build a decoder from the given data
		decoder := json.NewDecoder(bytes.NewBuffer(data))
		// Preserve numbers, rather than casting to float64 automatically
		decoder.UseNumber()
		// Run the decode
		if err := decoder.Decode(v); err != nil {
			return err
		}
		// If the decode succeeds, post-process the map to convert json.Number objects to int64 or float64
		return convertMapNumbers(*v)

	default:
		return json.Unmarshal(data, v)
	}
}

// convertMapNumbers traverses the map, converting any json.Number values to int64 or float64.
// values which are map[string]interface{} or []interface{} are recursively visited
func convertMapNumbers(m map[string]interface{}) error {
	var err error
	for k, v := range m {
		switch v := v.(type) {
		case json.Number:
			m[k], err = convertNumber(v)
		case map[string]interface{}:
			err = convertMapNumbers(v)
		case []interface{}:
			err = convertSliceNumbers(v)
		}
		if err != nil {
			return err
		}
	}
	return nil
}

// convertSliceNumbers traverses the slice, converting any json.Number values to int64 or float64.
// values which are map[string]interface{} or []interface{} are recursively visited
func convertSliceNumbers(s []interface{}) error {
	var err error
	for i, v := range s {
		switch v := v.(type) {
		case json.Number:
			s[i], err = convertNumber(v)
		case map[string]interface{}:
			err = convertMapNumbers(v)
		case []interface{}:
			err = convertSliceNumbers(v)
		}
		if err != nil {
			return err
		}
	}
	return nil
}

// convertNumber converts a json.Number to an int64 or float64, or returns an error
func convertNumber(n json.Number) (interface{}, error) {
	// Attempt to convert to an int64 first
	if i, err := n.Int64(); err == nil {
		return i, nil
	}
	// Return a float64 (default json.Decode() behavior)
	// An overflow will return an error
	return n.Float64()
}