added validation when adding a book

internal/api/dto.go

@@ -1,7 +1,7 @@
 package api
 
 type bookPostCreate struct {
-	Title  string `json:"title" binding:"required"`
-	Author string `json:"author"`
+	Title  string `json:"title" binding:"required,max=300"`
+	Author string `json:"author" binding:"max=100"`
 	Rating int    `json:"rating" binding:"min=0,max=10"`
 }

internal/api/routes.go

@@ -1,10 +1,12 @@
 package api
 
 import (
+	"errors"
 	"net/http"
 
 	"git.artlef.fr/PersonalLibraryManager/internal/model"
 	"github.com/gin-gonic/gin"
+	"github.com/go-playground/validator/v10"
 	"gorm.io/gorm"
 )
 
@@ -18,7 +20,12 @@ func PostBookHandler(c *gin.Context, db *gorm.DB) {
 	var book bookPostCreate
 	err := c.ShouldBindJSON(&book)
 	if err != nil {
-		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+		var ve validator.ValidationErrors
+		if errors.As(err, &ve) {
+			c.JSON(http.StatusBadRequest, getValidationErrors(&ve))
+		} else {
+			c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+		}
 		return
 	}
 	bookDb := book.toBook()

internal/api/validator.go

@@ -0,0 +1,35 @@
+package api
+
+import (
+	"fmt"
+
+	"github.com/go-playground/validator/v10"
+)
+
+type apiValidationError struct {
+	Field string `json:"field"`
+	Err   string `json:"error"`
+}
+
+func getValidationErrors(ve *validator.ValidationErrors) []apiValidationError {
+	errors := make([]apiValidationError, len(*ve))
+	for i, fe := range *ve {
+		errors[i] = apiValidationError{
+			Field: fe.Field(),
+			Err:   computeValidationMessage(&fe),
+		}
+	}
+	return errors
+}
+
+func computeValidationMessage(fe *validator.FieldError) string {
+	tag := (*fe).Tag()
+	switch tag {
+	case "required":
+		return fmt.Sprintf("%s is required.", (*fe).Field())
+	case "max":
+		return fmt.Sprintf("%s is too long. It should be under %s characters.", (*fe).Field(), (*fe).Param())
+	default:
+		return fmt.Sprintf("Validation failed for '%s' property.", tag)
+	}
+}