Decode JSON value which can be either string or number - json

Question

When I make an HTTP call to a REST API I may get the JSON value count back as a Number or String. I'ld like to marshal it to be an integer in either case. How can I deal with this in Go?.

Answer 1

Use the "string" field tag option to specify that strings should be converted to numbers. The documentation for the option is:
The "string" option signals that a field is stored as JSON inside a JSON-encoded string. It applies only to fields of string, floating point, integer, or boolean types. This extra level of encoding is sometimes used when communicating with JavaScript programs:
Here's an example use:
type S struct {
Count int `json:"count,string"`
}
playground example
If the JSON value can be number or string, then unmarshal to interface{} and convert to int after unmarshaling:
Count interface{} `json:"count,string"`
Use this function to convert the interface{} value to an int:
func getInt(v interface{}) (int, error) {
switch v := v.(type) {
case float64:
return int(v), nil
case string:
c, err := strconv.Atoi(v)
if err != nil {
return 0, err
}
return c, nil
default:
return 0, fmt.Errorf("conversion to int from %T not supported", v)
}
}

Answer 2

// Format of your expected request
type request struct {
ACTIVE string `json:"active"`
CATEGORY string `json:"category"`
}
// struct to read JSON input
var myReq request
// Decode the received JSON request to struct
decoder := json.NewDecoder(r.Body)
err := decoder.Decode(&myReq)
if err != nil {
log.Println( err)
// Handler for invalid JSON received or if you want to decode the request using another struct with int.
return
}
defer r.Body.Close()
// Convert string to int
numActive, err = strconv.Atoi(myReq.ACTIVE)
if err != nil {
log.Println(err)
// Handler for invalid int received
return
}
// Convert string to int
numCategory, err = strconv.Atoi(myReq.CATEGORY)
if err != nil {
log.Println(err)
// Handler for invalid int received
return
}

Answer 3

I had the same problem with a list of values where the values were string or struct. The solution I'm using is to create a helper struct with fields of expected types and parse value into the correct field.
type Flag struct {
ID string `json:"id"`
Type string `json:"type"`
}
type FlagOrString struct {
Flag *Flag
String *string
}
func (f *FlagOrString) UnmarshalJSON(b []byte) error {
start := []byte("\"")
for idx := range start {
if b[idx] != start[idx] {
return json.Unmarshal(b, &f.Flag)
}
}
return json.Unmarshal(b, &f.String)
}
var MainStruct struct {
Vals []FlagOrString
}
Custom Unmarshaller simplifies a code. Personally I prefer this over interface{} as it explicitly states what a developer expects.