Signup: improve error when user already exists

internal/routes/usersignup.go

@@ -9,6 +9,7 @@ import (
 	"git.artlef.fr/PersonalLibraryManager/internal/model"
 	"git.artlef.fr/PersonalLibraryManager/internal/myvalidator"
 	"golang.org/x/crypto/bcrypt"
+	"gorm.io/gorm"
 )
 
 func PostSignupHandler(ac appcontext.AppContext) {
@@ -31,6 +32,21 @@ func PostSignupHandler(ac appcontext.AppContext) {
 		myvalidator.ReturnErrorsAsJsonResponse(&ac, err)
 		return
 	}
+
+	var existingUser model.User
+	err = ac.Db.Where("name = ?", user.Username).First(&existingUser).Error
+	if err != nil && !errors.Is(err, gorm.ErrRecordNotFound) {
+		myvalidator.ReturnErrorsAsJsonResponse(&ac, err)
+		return
+	}
+	if err == nil {
+		myvalidator.ReturnErrorsAsJsonResponse(&ac,
+			myvalidator.HttpError{
+				StatusCode: http.StatusInternalServerError,
+				Err:        errors.New("An user with this name already exists."),
+			})
+		return
+	}
 	err = ac.Db.Model(&model.User{}).Save(&userDb).Error
 	if err != nil {
 		myvalidator.ReturnErrorsAsJsonResponse(&ac, err)