added a json unmarshaling function

struct_utils/json.go

+package struct_utils
+
+import (
+	"encoding/json"
+	"fmt"
+)
+
+// UnmarshalJSON performs a JSON unmarshalling, but on type mismatches it returns a more user friendly error.
+// Used exactly the same as json.Unmarshal
+func UnmarshalJSON(data []byte, val interface{}) error {
+	err := json.Unmarshal(data, &val)
+	if err != nil {
+		typeErr, ok := err.(*json.UnmarshalTypeError)
+		if ok {
+			return fmt.Errorf("invalid type received for field '%s': expected a value of type '%s', but received type '%s'", typeErr.Field, typeErr.Type.Name(), typeErr.Value)
+		}
+	}
+
+	return err
+}