[admin] fixed FileNotFoundError while deleting a FirmwareImage openwi…

…sp#140

I couldn't reproduce this issue with Django's standard `models.FileField`
so I figured that the problem is with the way `private_storage` is being
used. Strangely, there's no problem when delete method is called on an
instance of the model. The error is always thrown when the delete method
is called on a "modelForm" for an instance, the image file for which has
been deleted.

So the issue really is with the `private_storage` module. To get around
the error though, what I have done is:
 - `try` to return change_view
 - `catch` the `FileNotFoundError` if it occurs
 - Get the `path` from the error itself
 - check if the specified directory exists, if not create one
 - create a temporary file
 - return `change_view` again (recursion)
 - This time the file is there to be deleted and the model instance is
   deleted as well

This seems like a "brute force" solution, but since the origin of the issue
is an external module, this is the only possible workaround (As we don't want
to automatically delete any model instances because it would be strange for the
user)

Fixes openwisp#140

openwisp_firmware_upgrader/admin.py

@@ -8,7 +8,7 @@
 from django.conf import settings
 from django.contrib import admin, messages
 from django.contrib.admin.helpers import ACTION_CHECKBOX_NAME
-from django.shortcuts import HttpResponseRedirect, redirect
+from django.shortcuts import redirect
 from django.template.response import TemplateResponse
 from django.urls import resolve, reverse
 from django.utils.safestring import mark_safe
@@ -80,37 +80,6 @@ def has_change_permission(self, request, obj=None):
             return False
         return True
 
-    def get_parent_object(self, request):
-        """
-        method to get the instance from model' s parent class
-        in context with the ForeignKey relation
-        """
-        resolved = resolve(request.path_info)
-        if resolved.kwargs:
-            return self.parent_model.objects.get(pk=resolved.kwargs["object_id"])
-        return None
-
-    def get_queryset(self, request):
-        """
-        overriding queryset to remove any FirmwareImage instances,
-        where the image file has been manually deleted by the user
-        from the file system
-        """
-        qs = super(FirmwareImageInline, self).get_queryset(request)
-        build = self.get_parent_object(request)
-        qs = qs.filter(build=build)
-        for imageObject in qs:
-            if imageObject.file is not None:
-                path = imageObject.file.path
-                if not os.path.isfile(path):
-                    try:
-                        type = imageObject.type
-                        imageObject.delete()
-                        logger.warning(f"Image object {type} was removed")
-                    except Exception:
-                        pass
-        return qs
-
 
 class CategoryFilter(MultitenantOrgFilter):
     multitenant_lookup = 'organization_id__in'
@@ -211,21 +180,24 @@ def change_view(self, request, object_id, form_url='', extra_context=None):
         extra_context = extra_context or {}
         upgrade_url = f'{app_label}_build_changelist'
         extra_context.update({'upgrade_url': upgrade_url})
-        # preventing change_view to throw an error/exception
+        # preventing change_view to throw an error
         try:
             return super().change_view(request, object_id, form_url, extra_context)
-        except Exception as e:
-            if type(e).__name__ == "FileNotFoundError":
-                self.message_user(
-                    request, "Please reload the page", level=logging.ERROR
-                )
-            else:
-                self.message_user(
-                    request,
-                    "Image objects have been removed or form data didn't validate",
-                    level=logging.ERROR,
-                )
-                return HttpResponseRedirect(request.path)
+        except FileNotFoundError as e:
+            path = e.filename
+            directories = path.split('/')
+            n = len(directories)
+            dirPath = ""
+            for i in range(0, n - 1):
+                if i > 0:
+                    dirPath = dirPath + '/'
+                dirPath = dirPath + directories[i]
+            if not os.path.isdir(dirPath):
+                os.mkdir(dirPath)
+            f = open(e.filename, "w+")
+            f.write("To be deleted")
+            f.close()
+            return self.change_view(request, object_id, form_url, extra_context)
 
 
 class UpgradeOperationForm(forms.ModelForm):

openwisp_firmware_upgrader/tests/test_models.py

@@ -132,6 +132,12 @@ def test_device_fw_image_changed(self, *args):
             self.assertEqual(UpgradeOperation.objects.count(), 1)
             self.assertEqual(BatchUpgradeOperation.objects.count(), 0)
 
+    def test_device_fw_image_deleted(self, *args):
+        with mock.patch(
+            f'{self.app_label}.models.UpgradeOperation.upgrade', return_value=None
+        ):
+            pass
+
     def test_device_fw_created(self, *args):
         with mock.patch(
             f'{self.app_label}.models.UpgradeOperation.upgrade', return_value=None