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unmarshal.go
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unmarshal.go
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package jsonutil
import (
"encoding/base64"
"encoding/json"
"fmt"
"io"
"io/ioutil"
"reflect"
"time"
)
// UnmarshalJSON reads a stream and unmarshals the results in object v.
func UnmarshalJSON(v interface{}, stream io.Reader) error {
var out interface{}
b, err := ioutil.ReadAll(stream)
if err != nil {
return err
}
if len(b) == 0 {
return nil
}
if err := json.Unmarshal(b, &out); err != nil {
return err
}
return unmarshalAny(reflect.ValueOf(v), out, "")
}
func unmarshalAny(value reflect.Value, data interface{}, tag reflect.StructTag) error {
vtype := value.Type()
if vtype.Kind() == reflect.Ptr {
vtype = vtype.Elem() // check kind of actual element type
}
t := tag.Get("type")
if t == "" {
switch vtype.Kind() {
case reflect.Struct:
// also it can't be a time object
if _, ok := value.Interface().(*time.Time); !ok {
t = "structure"
}
case reflect.Slice:
// also it can't be a byte slice
if _, ok := value.Interface().([]byte); !ok {
t = "list"
}
case reflect.Map:
t = "map"
}
}
switch t {
case "structure":
if field, ok := vtype.FieldByName("_"); ok {
tag = field.Tag
}
return unmarshalStruct(value, data, tag)
case "list":
return unmarshalList(value, data, tag)
case "map":
return unmarshalMap(value, data, tag)
default:
return unmarshalScalar(value, data, tag)
}
}
func unmarshalStruct(value reflect.Value, data interface{}, tag reflect.StructTag) error {
if data == nil {
return nil
}
mapData, ok := data.(map[string]interface{})
if !ok {
return fmt.Errorf("JSON value is not a structure (%#v)", data)
}
t := value.Type()
if value.Kind() == reflect.Ptr {
if value.IsNil() { // create the structure if it's nil
s := reflect.New(value.Type().Elem())
value.Set(s)
value = s
}
value = value.Elem()
t = t.Elem()
}
// unwrap any payloads
if payload := tag.Get("payload"); payload != "" {
field, _ := t.FieldByName(payload)
return unmarshalAny(value.FieldByName(payload), data, field.Tag)
}
for i := 0; i < t.NumField(); i++ {
field := t.Field(i)
if field.PkgPath != "" {
continue // ignore unexported fields
}
// figure out what this field is called
name := field.Name
if locName := field.Tag.Get("locationName"); locName != "" {
name = locName
}
member := value.FieldByIndex(field.Index)
err := unmarshalAny(member, mapData[name], field.Tag)
if err != nil {
return err
}
}
return nil
}
func unmarshalList(value reflect.Value, data interface{}, tag reflect.StructTag) error {
if data == nil {
return nil
}
listData, ok := data.([]interface{})
if !ok {
return fmt.Errorf("JSON value is not a list (%#v)", data)
}
if value.IsNil() {
l := len(listData)
value.Set(reflect.MakeSlice(value.Type(), l, l))
}
for i, c := range listData {
err := unmarshalAny(value.Index(i), c, "")
if err != nil {
return err
}
}
return nil
}
func unmarshalMap(value reflect.Value, data interface{}, tag reflect.StructTag) error {
if data == nil {
return nil
}
mapData, ok := data.(map[string]interface{})
if !ok {
return fmt.Errorf("JSON value is not a map (%#v)", data)
}
if value.IsNil() {
value.Set(reflect.MakeMap(value.Type()))
}
for k, v := range mapData {
kvalue := reflect.ValueOf(k)
vvalue := reflect.New(value.Type().Elem()).Elem()
unmarshalAny(vvalue, v, "")
value.SetMapIndex(kvalue, vvalue)
}
return nil
}
func unmarshalScalar(value reflect.Value, data interface{}, tag reflect.StructTag) error {
errf := func() error {
return fmt.Errorf("unsupported value: %v (%s)", value.Interface(), value.Type())
}
switch d := data.(type) {
case nil:
return nil // nothing to do here
case string:
switch value.Interface().(type) {
case *string:
value.Set(reflect.ValueOf(&d))
case []byte:
b, err := base64.StdEncoding.DecodeString(d)
if err != nil {
return err
}
value.Set(reflect.ValueOf(b))
default:
return errf()
}
case float64:
switch value.Interface().(type) {
case *int64:
di := int64(d)
value.Set(reflect.ValueOf(&di))
case *float64:
value.Set(reflect.ValueOf(&d))
case *time.Time:
t := time.Unix(int64(d), 0).UTC()
value.Set(reflect.ValueOf(&t))
default:
return errf()
}
case bool:
switch value.Interface().(type) {
case *bool:
value.Set(reflect.ValueOf(&d))
default:
return errf()
}
default:
return fmt.Errorf("unsupported JSON value (%v)", data)
}
return nil
}