Fix thumbnail generation crash after resizing

misago/attachments/management/commands/processimageattachments.py

@@ -71,7 +71,11 @@ def process_attachment(self, settings: DynamicSettings, attachment: Attachment):
 
         if width > thumbnail_width or height > thumbnail_height:
             generate_attachment_thumbnail(
-                attachment, image, thumbnail_width, thumbnail_height
+                attachment,
+                image,
+                image.format,
+                thumbnail_width,
+                thumbnail_height,
             )
 
         attachment.save(

misago/attachments/tests/test_generate_attachment_thumbnail.py

@@ -1,3 +1,5 @@
+import pytest
+
 from PIL import Image
 
 from ..thumbnails import generate_attachment_thumbnail
@@ -7,9 +9,35 @@ def test_generate_attachment_thumbnail_generates_thumbnail_image_and_updates_att
     image_attachment, image_large, teardown_attachments
 ):
     image = Image.open(image_large)
-    generate_attachment_thumbnail(image_attachment, image, 400, 300)
+    generate_attachment_thumbnail(image_attachment, image, image.format, 400, 300)
 
     assert image_attachment.thumbnail
     assert image_attachment.thumbnail.url
     assert image_attachment.thumbnail_dimensions == "300x300"
     assert image_attachment.thumbnail_size
+    assert image_attachment.thumbnail_format == image.format
+
+
+@pytest.mark.parametrize(
+    [
+        "img_height",
+        "img_width",
+    ],
+    [
+        pytest.param(1000, 400, id="max_height_greater"),
+        pytest.param(400, 1000, id="max_width_greater"),
+    ],
+)
+def test_generate_attachment_thumbnail_generates_thumbnail_image_and_updates_attachment_gt_max_dimensions(
+    img_height, img_width, image_attachment, image_large, teardown_attachments
+):
+    image = Image.open(image_large)
+    generate_attachment_thumbnail(
+        image_attachment, image, image.format, img_width, img_height
+    )
+
+    assert image_attachment.thumbnail
+    assert image_attachment.thumbnail.url
+    assert image_attachment.thumbnail_dimensions == "400x400"
+    assert image_attachment.thumbnail_size
+    assert image_attachment.thumbnail_format == image.format

misago/attachments/thumbnails.py

@@ -7,7 +7,7 @@
 
 
 def generate_attachment_thumbnail(
-    attachment: Attachment, image, width: int, height: int
+    attachment: Attachment, image, format: str, width: int, height: int
 ):
     thumbnail_stream = BytesIO()
     format = image.format
@@ -23,5 +23,6 @@ def generate_attachment_thumbnail(
 
     attachment.thumbnail_dimensions = "x".join(map(str, image.size))
     attachment.thumbnail_size = attachment.thumbnail.size
+    attachment.thumbnail_format = format
 
     del thumbnail_stream

misago/attachments/upload.py

@@ -163,7 +163,11 @@ def _store_attachment_image(
 
     if image.width > thumbnail_width or image.height > thumbnail_height:
         generate_attachment_thumbnail(
-            attachment, image, thumbnail_width, thumbnail_height
+            attachment,
+            image,
+            image_format,
+            thumbnail_width,
+            thumbnail_height,
         )