go get github.com/spf13/cast

   cast.ToString("mayonegg")         // "mayonegg"
   cast.ToString(8)                  // "8"
   cast.ToString(8.31)               // "8.31"
   cast.ToString([]byte("one time")) // "one time"
   cast.ToString(nil)                // ""

   var foo interface{} = "one more time"
   cast.ToString(foo)                // "one more time"

   cast.ToInt(8)                  // 8
   cast.ToInt(8.31)               // 8
   cast.ToInt("8")                // 8
   cast.ToInt(true)               // 1
   cast.ToInt(false)              // 0

   var eight interface{} = 8
   cast.ToInt(eight)              // 8
   cast.ToInt(nil)                // 0

func ToStringMapE(i interface{}) (map[string]interface{}, error) {
   var m = map[string]interface{}{}

   switch v := i.(type) {
   case map[interface{}]interface{}:
      for k, val := range v {
         m[ToString(k)] = val
      }
      return m, nil
   case map[string]interface{}:
      return v, nil
   case string:
      err := jsonStringToObject(v, &m)
      return m, err
   default:
      return m, fmt.Errorf("unable to cast %#v of type %T to map[string]interface{}", i, i)
   }
}

func jsonStringToObject(s string, v interface{}) error {
   data := []byte(s)
   return json.Unmarshal(data, v)
}