How to unmarshall different json format - json

Question

I read lots of similar questions but not able to find the right solution yet. Hope someone can give me better idea.
My error response could be one of these format:
var errProxy = `{"errors":{"id": "1", "message": "failed to resolve the ip", "status": "failed"}}`
var errServer = `{"errors": "failed to ping the dns server."}`
I am trying to solve this by using two structs and trying to unmarshall one after another until err is nil and return:
// ErrorServer and ErrorProxy is my two struct to represent my above two error response.
type ErrorServer struct {
Error string `json:"errors"`
}
type ErrorResponse struct {
ID string `json:"id"`
Message string `json:"message"`
Status string `json:"status"`
}
type ErrorProxy struct {
ErrorResponse
}
This is the function I used to parse it:
func parseErrorResponse(body io.ReadCloser) (string, error) {
var errServer ErrorServer
var errProxy ErrorProxy
err := json.NewDecoder(body).Decode(&errServer)
if err != nil {
err = json.NewDecoder(body).Decode(&errProxy)
if err != nil {
return "", err
}
return errProxy.Error, nil
}
return errServer.Errors, nil
}

Answer 1

I think a custom unmarshal function is good for this case
type ErrorServer struct {
Error string
}
type ErrorResponse struct {
ID string
Message string
Status string
}
type ErrorProxy struct {
Err ErrorResponse
}
func parseErrorResponse(body io.Reader) (interface{}, error) {
data := make(map[string]interface{})
if err := json.NewDecoder(body).Decode(&data); err != nil {
return nil, err
}
// Check type of errors field
switch errors := data["errors"].(type) {
case string:
// Unmarshal for ErrorServer
errServer := &ErrorServer{
Error: errors,
}
return errServer, nil
case map[string]interface{}:
// Unmarshal for ErrorProxy
errProxy := &ErrorProxy{
Err: ErrorResponse{
ID: errors["id"].(string),
Message: errors["message"].(string),
Status: errors["status"].(string),
},
}
return errProxy, nil
default:
return nil, fmt.Errorf(`failed to parse "errors" field`)
}
}
func main() {
body := bytes.NewReader([]byte(`{"errors": "failed to ping the dns server."}`))
//body := bytes.NewReader([]byte(`{"errors":{"id": "1", "message": "failed to resolve the ip", "status": "failed"}}`))
parsedErr, _ := parseErrorResponse(body)
switch err := parsedErr.(type) {
case *ErrorServer:
fmt.Printf("err server: %+v \n", err)
case *ErrorProxy:
fmt.Printf("err response: %+v \n", err)
}
}

Answer 2

Another way to do that is using type assertion. You can unmarshal that json string into map[string]interface{} and check whether that value interface{} is a string or map[string]interface{}. Depends on its type, you know which kind of error it is and construct a struct from that.

Answer 3

Funny enough, I just gave the answer to this problem here: Use a customized UnmarshalJSON function. How do you modify this struct in Golang to accept two different results?
Applied to your situation:
package main
import (
"encoding/json"
"fmt"
"log"
)
type Answer struct {
Errors Error `json:"errors"`
}
type ErrorResponse struct {
ID string `json:"id"`
Message string `json:"message"`
Status string `json:"status"`
}
type Error struct {
Error string
ErrorResponse ErrorResponse
}
func (s *Error) UnmarshalJSON(b []byte) error {
if len(b) == 0 {
// no data, nothing to do
return nil
}
if b[0] == '{' {
// is object
return json.Unmarshal(b, &s.ErrorResponse)
}
return json.Unmarshal(b, &s.Error)
}
func main() {
var errProxy = []byte(`{"errors":{"id": "1", "message": "failed to resolve the ip", "status": "failed"}}`)
var errServer = []byte(`{"errors": "failed to ping the dns server."}`)
var answ Answer
if err := json.Unmarshal(errProxy, &answ); err != nil {
log.Fatal(err)
}
fmt.Println(answ)
answ = Answer{}
if err := json.Unmarshal(errServer, &answ); err != nil {
log.Fatal(err)
}
fmt.Println(answ)
}
Go PlayGround
Key in the above example is the type that contains both variations. We can also simplify that as both errors could be contained within the ErrorResponse type:
type Answer struct {
Errors ErrorResponse `json:"errors"`
}
type ErrorResponse struct {
ID string
Message string
Status string
}
func (s *ErrorResponse) UnmarshalJSON(b []byte) error {
if len(b) == 0 {
// no data, nothing to do
return nil
}
if b[0] == '{' {
// is object
var tmp struct {
ID string `json:"id"`
Message string `json:"message"`
Status string `json:"status"`
}
if err := json.Unmarshal(b, &tmp); err != nil {
return err
}
s.ID = tmp.ID
s.Message = tmp.Message
s.Status = tmp.Status
return nil
}
return json.Unmarshal(b, &s.Message)
}
The Error struct is not needed here.