I've written custom versions of MarshalJSON
and UnmarshalJSON
. My UnmarshalJSON
gets called the way I want it to, but I can't get it to work with MarshalJSON
. Here's code that summarizes my problem:
package main
import (
"bytes"
"encoding/json"
"fmt"
"log"
"os"
)
type myStruct struct {
Data string `json:"data"`
}
func (s *myStruct) MarshalJSON() ([]byte, error) {
return []byte(`{"data":"charlie"}`), nil
}
func (s *myStruct) UnmarshalJSON(b []byte) error {
// Insert the string directly into the Data member
return json.Unmarshal(b, &s.Data)
}
func main() {
// Create a struct with initial content "alpha"
ms := myStruct{"alpha"}
// Replace content with "bravo" using custom UnmarshalJSON() (SUCCESSFUL)
if err := json.NewDecoder(bytes.NewBufferString(`"bravo"`)).Decode(&ms); err != nil {
log.Fatal(err)
}
// Use custom MarshalJSON() to get "charlie" back (UNSUCCESSFUL)
if err := json.NewEncoder(os.Stdout).Encode(ms); err != nil {
log.Fatal(err)
}
// Trying another method (UNSUCCESSFUL)
if ret, err := json.Marshal(ms); err != nil {
log.Fatal(err)
} else {
fmt.Println(string(ret))
}
// Verify that the Marshaler interface is correctly implemented
var marsh json.Marshaler
marsh = &ms
ret, _ := marsh.MarshalJSON()
fmt.Println(string(ret)) // Prints "charlie"
}
In short, the program encodes the struct
"automatically" in two ways, and then finally calls MarshalJSON
manually. The response I want is "charlie"
. Running the code generates the following output:
{"data":"bravo"}
{"data":"bravo"}
{"data":"charlie"}
Try it at Go Playground: http://play.golang.org/p/SJ05S8rAYN