import_util: Fix file extensions of emoji files downloaded from Slack.

The Slack API when returning the emoji records, returns the record for
its thumbsup_all emoji with the url ending with .png, even though the
file is a gif.

For that reason, we have to make that code correct file extensions based
on the response content-type. Emojis are the smallest set of images to
download, so for simplicity of implementation, we remove the
parallelization of the downloads in favor of just processing them
serially.

(cherry picked from commit 9cad9644e7)

zerver/data_import/import_util.py

@@ -15,8 +15,11 @@ from django.utils.timezone import now as timezone_now
 
 from zerver.data_import.sequencer import NEXT_ID
 from zerver.lib.avatar_hash import user_avatar_base_path_from_ids
+from zerver.lib.mime_types import guess_extension
 from zerver.lib.partial import partial
 from zerver.lib.stream_color import STREAM_ASSIGNMENT_COLORS as STREAM_COLORS
+from zerver.lib.thumbnail import THUMBNAIL_ACCEPT_IMAGE_TYPES, BadImageError
+from zerver.lib.upload.base import INLINE_MIME_TYPES
 from zerver.models import (
     Attachment,
     DirectMessageGroup,
@@ -685,9 +688,7 @@ def build_realm_emoji(realm_id: int, name: str, id: int, file_name: str) -> Zerv
     )
 
 
-def get_emojis(emoji_dir: str, upload: list[str]) -> None:
-    emoji_url = upload[0]
-    emoji_path = upload[1]
+def get_emojis(emoji_dir: str, emoji_url: str, emoji_path: str) -> str | None:
     upload_emoji_path = os.path.join(emoji_dir, emoji_path)
 
     response = requests.get(emoji_url, stream=True)
@@ -695,6 +696,8 @@ def get_emojis(emoji_dir: str, upload: list[str]) -> None:
     with open(upload_emoji_path, "wb") as emoji_file:
         shutil.copyfileobj(response.raw, emoji_file)
 
+    return response.headers.get("Content-Type")
+
 
 def process_emojis(
     zerver_realmemoji: list[ZerverFieldsT],
@@ -711,7 +714,6 @@ def process_emojis(
     3. emoji_url_map: Maps emoji name to its url
     """
     emoji_records = []
-    upload_emoji_list = []
     logging.info("######### GETTING EMOJIS #########\n")
     logging.info("DOWNLOADING EMOJIS .......\n")
     for emoji in zerver_realmemoji:
@@ -720,8 +722,6 @@ def process_emojis(
             realm_id=emoji["realm"], emoji_file_name=emoji["name"]
         )
 
-        upload_emoji_list.append([emoji_url, emoji_path])
-
         emoji_record = dict(emoji)
         emoji_record["path"] = emoji_path
         emoji_record["s3_path"] = emoji_path
@@ -730,8 +730,33 @@ def process_emojis(
 
         emoji_records.append(emoji_record)
 
-    # Run downloads in parallel
-    run_parallel_wrapper(partial(get_emojis, emoji_dir), upload_emoji_list, threads=threads)
+        # Directly download the emoji and patch the file_name with the correct extension
+        # based on the content-type returned by the server. This is needed because Slack
+        # sometimes returns an emoji url with .png extension despite the file being a gif.
+        content_type = get_emojis(emoji_dir, emoji_url, emoji_path)
+        if content_type is None:
+            logging.warning(
+                "Emoji %s has an unspecified content type. Using the original file extension.",
+                emoji["name"],
+            )
+            continue
+
+        if (
+            content_type not in THUMBNAIL_ACCEPT_IMAGE_TYPES
+            or content_type not in INLINE_MIME_TYPES
+        ):
+            raise BadImageError(
+                f"Emoji {emoji['name']} is not an image file. Content type: {content_type}"
+            )
+
+        file_extension = guess_extension(content_type, strict=False)
+        assert file_extension is not None
+
+        old_file_name = emoji_record["file_name"]
+        new_file_name = f"{old_file_name.rsplit('.', 1)[0]}{file_extension}"
+
+        emoji_record["file_name"] = new_file_name
+        emoji["file_name"] = new_file_name
 
     logging.info("######### GETTING EMOJIS FINISHED #########\n")
     return emoji_records