使用`json：“，string“`返回无效使用，string struct标签，试图解组未引用的值

Question

When trying to parse a json with a float value for distance to the following struct

type CreateBookingRequest struct {
    Distance          float64           `json:"distance,string"`
    DistanceSource    string            `json:"distanceSource"`
}

I get the following error

json: invalid use of ,string struct tag, trying to unmarshal unquoted value into [34 100 105 115 116 97 110 99 101 34]%!(EXTRA *reflect.rtype=dto.CreateBookingRequest)

Is there a way for me to avoid the error/get a better error message?

Edit: I am actually expecting the users of the API to pass in a string value but if they for some reason pass in a non-string value, I would like to be able to tell them clearly, instead of this hard to read error message.

Answer 1

This error happens when the "distance" JSON value is encoded as a number instead of a string (per the "string" tag on the "Distance") field:

str := []byte(`{"distance":1.23,"distanceSource":"foo"}`)
// Note JSON number -------^
var cbr CreateBookingRequest
err := json.Unmarshal(str, &cbr)
// err => json: invalid use of ,string struct tag, trying to unmarshal unquoted value into [34 100 105 115 116 97 110 99 101 34]%!(EXTRA *reflect.rtype=main.CreateBookingRequest)

If you change the type of the distance value to a string (per the tag) then it works fine:

str := []byte(`{"distance":"1.23","distanceSource":"foo"}`)
// Note JSON string -------^

You could change the error message by identifying that specific error somehow and provide a different message. You might also consider changing the tag for the Distance type to simply accept a number instead of a string:

type CreateBookingRequest struct {
  Distance       float64 `json:"distance"`
  ...
}

...
  str := []byte(`{"distance":1.23,"distanceSource":"foo"}`)