How to display all data from a map in json format - Golang?

I am creating a API in golang which will simply display all data from a map in json format.
endpoint: /keys

type UserController struct{}
    
// NewUserController function
func NewUserController() *UserController {
    return &UserController{}
}
        
// Data struct
type Data struct {
    Datakey   int    `json:"key"`
    Datavalue string `json:"value"`
}
        
var datamap = make(map[int]string)

func (uc UserController) getallkeys(w http.ResponseWriter, r *http.Request, p httprouter.Params) {
    type Users []Data
    var uj Users
    for k, v := range datamap {
        uj = Users{
    	    Data{
    		    Datakey:   k,
    			Datavalue: v,
    		},
    	}
    }
    
    result, _ := json.Marshal(uj)
    w.Header().Set("Content-Type", "application/json")
    w.WriteHeader(200)
    fmt.Fprintf(w, "%s", result)
}

For eg:
The response should be something like

[
  {
    "key":somekey,
    "value":"somevalue"
  },
  {
    "key":somekey,
    "value":"somevalue"
  }
]

I am not clear how to implement this. The above code is displaying just the last data from the map. This is incorrect but I am not sure how to proceed. It would be great if someone could help me with this.

Thanks.

At least two different problems.

First, a JSON Map cannot have an `int' key. That is part of the JSON spec. Either change it to a string or you will have to implement the MarshalJSON and UnmarshalJSON interfaces for the map, i.e, for the type

    type MyMap map[int]string

Google golang UnmarshalJSON time.Duration for a number of basic examples. Also, against map and your specific key type.

Second, for a slice type

    type Users []Data

adding elements requires append

    uj := make(Users,0)
    for k, v := range datamap {
        d := Data{k,v}
        uj = append(uj, d) 
    }

Of course, marshaling a slice produces a keyless JSON map -- likely not what you want.