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how to unmarshal a custom type in go
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package main | |
import ( | |
"bytes" | |
"encoding/json" | |
"fmt" | |
"log" | |
"github.com/jinzhu/copier" | |
) | |
type theStruct struct { | |
Thing string | |
} | |
// UnmarshalJSON unmarshals the bytes into the struct, performing custom | |
// error checking on the struct values | |
func (t *theStruct) UnmarshalJSON(data []byte) error { | |
fmt.Println("unmarshaling in my custom handler") | |
type structAlias theStruct | |
aux := &struct { | |
*structAlias | |
}{ | |
structAlias: (*structAlias)(t), | |
} | |
err := json.Unmarshal(data, aux) | |
if err != nil { | |
return err | |
} | |
// perform custom checking on the aux struct | |
if aux.Thing == "doesn't work" { | |
return fmt.Errorf("value for Thing is invalid : %s", aux.Thing) | |
} | |
// it's all good - put it in the pointer we're working with | |
// if we wanted we could manually set all the fields or for laziness we | |
// could just use a library like this :-) | |
return copier.Copy(t, aux) | |
} | |
func main() { | |
// marshal a dummy struct into the bytes | |
t := theStruct{ | |
Thing: "doesn't work", | |
} | |
data, err := json.Marshal(t) | |
if err != nil { | |
log.Println(err) | |
} | |
// turn the bytes into an io.Reader and | |
// try to decode these bytes into the struct | |
dest := theStruct{} | |
err = json.NewDecoder(bytes.NewReader(data)).Decode(&dest) | |
if err != nil { | |
log.Println(err) | |
} | |
// do it again with a struct that passes the validation | |
src2 := theStruct{ | |
Thing: "works", | |
} | |
data2, err := json.Marshal(&src2) | |
if err != nil { | |
log.Println(err) | |
} | |
dest2 := theStruct{} | |
err = json.NewDecoder(bytes.NewReader(data2)).Decode(&dest2) | |
if err != nil { | |
log.Println(err) | |
} | |
fmt.Printf("%+v\n", dest2) | |
} |
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