add option to limit the file size for image and file uploads

- add a validator to validate the max file size (FileMaxSizeValidator)
- return the first form error in a JsonResponse so it is actually shown to the
  user instead of a generic error message.

README.rst

@@ -309,6 +309,17 @@ distinguish between image and file upload. Exposing the file upload to
 all/untrusted users poses a risk!
 
 
+Restrict upload file size:
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+You can restrict the maximum size for uploaded images and files by adding
+
+ .. code-block:: python
+
+      CKEDITOR_5_MAX_FILE_SIZE = 5 # Max size in MB
+
+to your config. Default is 0 (allow any file size).
+
+
 Installing from GitHub:
 ^^^^^^^^^^^^^^^^^^^^^^^
   .. code-block:: bash

django_ckeditor_5/forms.py

@@ -2,6 +2,8 @@
 from django.conf import settings
 from django.core.validators import FileExtensionValidator
 
+from django_ckeditor_5.validators import FileMaxSizeValidator
+
 
 class UploadFileForm(forms.Form):
     upload = forms.FileField(
@@ -13,5 +15,6 @@ class UploadFileForm(forms.Form):
                     ["jpg", "jpeg", "png", "gif", "bmp", "webp", "tiff"],
                 ),
             ),
+            FileMaxSizeValidator(getattr(settings, "CKEDITOR_5_MAX_FILE_SIZE", 0))
         ],
     )

django_ckeditor_5/validators.py

@@ -0,0 +1,40 @@
+from django import get_version
+from django.core.exceptions import ValidationError
+from django.utils.deconstruct import deconstructible
+
+if get_version() >= "4.0":
+    from django.utils.translation import gettext_lazy as _
+else:
+    from django.utils.translation import ugettext_lazy as _
+
+
+@deconstructible()
+class FileMaxSizeValidator:
+    """Validate that a file is not bigger than max_size mb, otherwise raise ValidationError.
+    If zero is passed for max_size any file size is allowed.
+    """
+
+    message = _("File should be at most %(max_size)s MB.")
+    code = "invalid_size"
+
+    def __init__(self, max_size):
+        self.max_size = max_size * 1024 * 1024
+        self.orig_max_size = max_size
+
+    def __call__(self, value):
+        if value.size > self.max_size > 0:
+            raise ValidationError(
+                self.message,
+                code=self.code,
+                params={
+                    "max_size": self.orig_max_size,
+                },
+            )
+
+    def __eq__(self, other):
+        return (
+                isinstance(other, self.__class__)
+                and self.max_size == other.max_size
+                and self.message == other.message
+                and self.code == other.code
+        )

django_ckeditor_5/views.py

@@ -74,4 +74,8 @@ def upload_file(request):
         if form.is_valid():
             url = handle_uploaded_file(request.FILES["upload"])
             return JsonResponse({"url": url})
+        else:
+            if form.errors["upload"]:
+                return JsonResponse({"error": {"message": form.errors["upload"][0]}})
+
     raise Http404(_("Page not found."))