move map type to json middleware and add E type

middleware/json/body-types.go

@@ -0,0 +1,10 @@
+package json
+
+// M is shorthand for a map[string]any. It is provided as a convenience for
+// defining JSON objects in a more concise manner.
+type M map[string]any
+
+// E is shorthand for Error. If you want to return a JSON wrapped error, you can
+// use this type. The JSON response will be {"error": "your error message"}.
+// If the status is not set, it will default to 400.
+type E string

middleware/json/json.go

@@ -55,6 +55,15 @@ func marshalResponseBody(ctx *navaros.Context) {
 		if from != nil {
 			ctx.Headers.Add("Content-Type", "application/json")
 		}
+		switch str := from.(type) {
+		case E:
+			if ctx.Status == 0 {
+				ctx.Status = 400
+			}
+			from = map[string]string{"error": string(str)}
+		case string:
+			from = map[string]string{"message": str}
+		}
 		jsonBytes, err := json.Marshal(from)
 		if err != nil {
 			return nil, err