upload: Add charset even on content-types guessed at download time.

zerver/tests/test_upload.py

@@ -189,6 +189,17 @@ class FileUploadTest(UploadSerializeMixin, ZulipTestCase):
         self.assertEqual(result["Content-Type"], "application/octet-stream")
         consume_response(result)
 
+        # Old files may be stored without a content-type in the
+        # database, in which case we try to guess at download time.
+        attachment = Attachment.objects.get(file_name="somefile")
+        self.assertEqual(attachment.content_type, "application/octet-stream")
+        attachment.content_type = None
+        attachment.save(update_fields=["content_type"])
+        result = self.client_get(url)
+        self.assertEqual(result.status_code, 200)
+        self.assertEqual(result["Content-Type"], "application/octet-stream")
+        consume_response(result)
+
         uploaded_file = SimpleUploadedFile("somefile.txt", b"zulip!", content_type="")
         result = self.api_post(
             self.example_user("hamlet"), "/api/v1/user_uploads", {"file": uploaded_file}
@@ -202,6 +213,16 @@ class FileUploadTest(UploadSerializeMixin, ZulipTestCase):
         self.assertEqual(result["Content-Type"], 'text/plain; charset="ascii"')
         consume_response(result)
 
+        # As above, test without a stored content_type
+        attachment = Attachment.objects.get(file_name="somefile.txt")
+        self.assertEqual(attachment.content_type, 'text/plain; charset="ascii"')
+        attachment.content_type = None
+        attachment.save(update_fields=["content_type"])
+        result = self.client_get(url)
+        self.assertEqual(result.status_code, 200)
+        self.assertEqual(result["Content-Type"], 'text/plain; charset="ascii"')
+        consume_response(result)
+
     def test_guess_content_type_charset(self) -> None:
         uploaded_file = SimpleUploadedFile(
             "somefile.txt", "नाम में क्या रक्खा हे".encode(), content_type="text/plain"

zerver/views/upload.py

@@ -38,8 +38,10 @@ from zerver.lib.thumbnail import (
     get_image_thumbnail_path,
 )
 from zerver.lib.upload import (
+    attachment_vips_source,
     check_upload_within_quota,
     get_public_upload_root_url,
+    maybe_add_charset,
     upload_message_attachment_from_request,
 )
 from zerver.lib.upload.local import assert_is_local_storage_path
@@ -132,6 +134,8 @@ def serve_local(
 
     if content_type is None:
         content_type = guess_type(filename)[0] or "application/octet-stream"
+
+    content_type = maybe_add_charset(content_type, attachment_vips_source(path_id))
     download = force_download or bare_content_type(content_type) not in INLINE_MIME_TYPES
 
     if settings.DEVELOPMENT: