fix: return application/problem+json when body is empty

Author: bfabio

README.md

@@ -57,6 +57,22 @@ curl -X QUERY "http://localhost:3000/v1/validate" -H "Content-Type: application/
     }
   ]
 }
+
+### Example error response
+
+All error responses are returned as [application/problem+json](https://www.rfc-editor.org/rfc/rfc9457.html)
+
+```http
+HTTP/1.1 400 Bad Request
+Content-Type: application/problem+json
+```
+
+```json
+{
+  "title": "empty body",
+  "detail": "need a body to validate",
+  "status": 400
+}
 ```
 
 ## Contributing

internal/handlers/validate.go

@@ -6,6 +6,7 @@ import (
 
 	"github.com/gofiber/fiber/v2"
 	publiccodeParser "github.com/italia/publiccode-parser-go/v5"
+	"github.com/italia/publiccode-validator-api/internal/common"
 )
 
 type PubliccodeymlValidatorHandler struct {
@@ -43,9 +44,7 @@ func (vh *PubliccodeymlValidatorHandler) Query(ctx *fiber.Ctx) error {
 	// }
 
 	if len(ctx.Body()) == 0 {
-		return ctx.Status(fiber.StatusBadRequest).JSON(fiber.Map{
-			"error": "empty body",
-		})
+		return common.Error(fiber.StatusBadRequest, "empty body", "need a body to validate")
 	}
 
 	results := make(publiccodeParser.ValidationResults, 0)