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lossless.go
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lossless.go
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// json-lossless populates structs from JSON and allows serialization
// back to JSON without losing fields that are not explicitly defined
// in the struct.
//
// Source code: https://github.com/joeshaw/json-lossless
package lossless
import (
"encoding/json"
"errors"
"reflect"
"strings"
"github.com/hargrave81/json-lossless/simplejson"
)
// The JSON type contains the state of the decoded data. Embed this
// type in your type and implement MarshalJSON and UnmarshalJSON
// methods to add lossless encoding and decoding.
//
// Example:
//
// type Person struct {
// lossless.JSON `json:"-"`
//
// Name string
// Age int
// Address string
// }
//
// func (p *Person) UnmarshalJSON(data []byte) error {
// return p.JSON.UnmarshalJSON(p, data)
// }
//
// func (p Person) MarshalJSON() ([]byte, error) {
// return p.JSON.MarshalJSON(p)
// }
type JSON struct {
json *simplejson.Json
}
func (js *JSON) maybeInit() {
if js.json == nil {
js.json, _ = simplejson.NewJson([]byte("{}"))
}
}
// Sets a JSON value not represented in the struct type. The
// argument list is a set of strings referring to the JSON path,
// with the value to be set as the last value.
//
// Example:
//
// // This sets {"Phone": {"Mobile": "614-555-1212"}} in the JSON
// p.Set("Phone", "Mobile", "614-555-1212")
func (js *JSON) Set(args ...interface{}) error {
js.maybeInit()
if len(args) < 2 {
return errors.New("rs must contain a path and value")
}
v := args[len(args)-1]
key, ok := args[len(args)-2].(string)
if !ok {
return errors.New("all args except last must be strings")
}
j := js.json
for _, p := range args[:len(args)-2] {
strp, ok := p.(string)
if !ok {
return errors.New("all args except last must be strings")
}
newj, ok := j.CheckGet(strp)
if !ok {
j.Set(strp, make(map[string]interface{}))
j = j.Get(strp)
} else {
j = newj
}
}
j.Set(key, v)
return nil
}
// Unmarshals JSON data into the given destination. Users should
// call this from their type's UnmarshalJSON method.
//
// Example:
//
// func (p *Person) UnmarshalJSON(data []byte) error {
// return p.JSON.UnmarshalJSON(p, data)
// }
func (js *JSON) UnmarshalJSON(dest interface{}, data []byte) error {
j, err := simplejson.NewJson(data)
if err != nil {
return err
}
js.json = j
return syncToStruct(dest, j)
}
// Marshals the given source into JSON data. Users should
// call this from their type's MarshalJSON method.
//
// Example:
//
// func (p Person) MarshalJSON() ([]byte, error) {
// return p.JSON.MarshalJSON(p)
// }
func (js *JSON) MarshalJSON(src interface{}) ([]byte, error) {
js.maybeInit()
err := syncFromStruct(src, js.json)
if err != nil {
return nil, err
}
return json.Marshal(js.json)
}
func syncToStruct(dest interface{}, j *simplejson.Json) error {
dv := reflect.Indirect(reflect.ValueOf(dest))
dt := dv.Type()
// Probably a good candidate for future caching
tagmap := make(map[string]string)
for i := 0; i < dt.NumField(); i++ {
sf := dt.Field(i)
tag := sf.Tag.Get("json")
if tag == "-" {
continue
}
if strings.Index(tag, ",") > 0 { // this just strips the omit part
tag = strings.Split(tag, ",")[0]
}
tagmap[sf.Name] = sf.Name
if tag == "" {
tagmap[strings.ToLower(sf.Name)] = sf.Name
} else {
tagmap[tag] = sf.Name
}
}
m, err := j.Map()
if err != nil {
return err
}
for k, v := range m {
name, ok := tagmap[k]
if !ok {
continue
}
f := dv.FieldByName(name)
if !f.IsValid() {
continue
}
if reflect.TypeOf(v) == f.Type() {
f.Set(reflect.ValueOf(v))
} else {
// If the default encoding/json decoded type does
// not match our target type -- for instance, a
// time.Time that was parsed as a string but we
// want to store it in a time.Time field --
// re-marshal and unmarshal it into the target
// type. Gross, yes.
marsh, err := json.Marshal(v)
if err != nil {
return err
}
fv := f.Addr().Interface()
err = json.Unmarshal(marsh, fv)
if err != nil {
return err
}
}
}
return nil
}
func syncFromStruct(src interface{}, j *simplejson.Json) error {
dv := reflect.Indirect(reflect.ValueOf(src))
dt := dv.Type()
// This skips the encoding/json "json" tag's "omitempty"
// value.
for i := 0; i < dt.NumField(); i++ {
sf := dt.Field(i)
tag := sf.Tag.Get("json")
omitable := false
if tag == "-" {
continue
}
if strings.Index(tag, ",") > 0 { // this just strips the omit part
tag = strings.Split(tag, ",")[0]
if strings.Split(tag, ",")[1] == "omitempty" {
omitable = true
}
}
var name string
if tag == "" {
name = sf.Name
} else {
name = tag
}
f := dv.Field(i)
if omitable && f.Interface() == nil {
j.Set(name, nil)
} else {
j.Set(name, f.Interface())
}
}
return nil
}