upload.py: Support using non S3-providers.

With #14378, we regressed back to the state of that
prior to 7e0ea61b00.

We fix this by getting our avatar bucket on
object initialization, and use the appropriate means
of gathering the network location for the urls.

Fixes #14484.

zerver/lib/upload.py

@@ -356,6 +356,11 @@ class S3UploadBackend(ZulipUploadBackend):
     def __init__(self) -> None:
         self.session = boto3.Session(settings.S3_KEY, settings.S3_SECRET_KEY)
 
+        self.avatar_bucket = get_bucket(self.session, settings.S3_AVATAR_BUCKET)
+        network_location = urllib.parse.urlparse(
+            self.avatar_bucket.meta.client.meta.endpoint_url).netloc
+        self.avatar_bucket_url = f"https://{self.avatar_bucket.name}.{network_location}"
+
     def delete_file_from_s3(self, path_id: str, bucket_name: str) -> bool:
         bucket = get_bucket(self.session, bucket_name)
         key = bucket.Object(path_id)
@@ -468,15 +473,13 @@ class S3UploadBackend(ZulipUploadBackend):
         self.write_avatar_images(s3_target_file_name, target_profile, image_data, content_type)
 
     def get_avatar_url(self, hash_key: str, medium: bool=False) -> str:
-        bucket = settings.S3_AVATAR_BUCKET
         medium_suffix = "-medium.png" if medium else ""
         # ?x=x allows templates to append additional parameters with &s
-        return f"https://{bucket}.s3.amazonaws.com/{hash_key}{medium_suffix}?x=x"
+        return f"{self.avatar_bucket_url}/{hash_key}{medium_suffix}?x=x"
 
     def get_export_tarball_url(self, realm: Realm, export_path: str) -> str:
-        bucket = settings.S3_AVATAR_BUCKET
         # export_path has a leading /
-        return f"https://{bucket}.s3.amazonaws.com{export_path}"
+        return f"{self.avatar_bucket_url}{export_path}"
 
     def realm_avatar_and_logo_path(self, realm: Realm) -> str:
         return os.path.join(str(realm.id), 'realm')
@@ -507,9 +510,8 @@ class S3UploadBackend(ZulipUploadBackend):
         # that users use gravatar.)
 
     def get_realm_icon_url(self, realm_id: int, version: int) -> str:
-        bucket = settings.S3_AVATAR_BUCKET
         # ?x=x allows templates to append additional parameters with &s
-        return f"https://{bucket}.s3.amazonaws.com/{realm_id}/realm/icon.png?version={version}"
+        return f"{self.avatar_bucket_url}/{realm_id}/realm/icon.png?version={version}"
 
     def upload_realm_logo_image(self, logo_file: File, user_profile: UserProfile,
                                 night: bool) -> None:
@@ -542,13 +544,12 @@ class S3UploadBackend(ZulipUploadBackend):
         # that users use gravatar.)
 
     def get_realm_logo_url(self, realm_id: int, version: int, night: bool) -> str:
-        bucket = settings.S3_AVATAR_BUCKET
         # ?x=x allows templates to append additional parameters with &s
         if not night:
             file_name = 'logo.png'
         else:
             file_name = 'night_logo.png'
-        return f"https://{bucket}.s3.amazonaws.com/{realm_id}/realm/{file_name}?version={version}"
+        return f"{self.avatar_bucket_url}/{realm_id}/realm/{file_name}?version={version}"
 
     def ensure_medium_avatar_image(self, user_profile: UserProfile) -> None:
         file_path = user_avatar_path(user_profile)
@@ -615,10 +616,9 @@ class S3UploadBackend(ZulipUploadBackend):
         )
 
     def get_emoji_url(self, emoji_file_name: str, realm_id: int) -> str:
-        bucket = settings.S3_AVATAR_BUCKET
         emoji_path = RealmEmoji.PATH_ID_TEMPLATE.format(realm_id=realm_id,
                                                         emoji_file_name=emoji_file_name)
-        return f"https://{bucket}.s3.amazonaws.com/{emoji_path}"
+        return f"{self.avatar_bucket_url}/{emoji_path}"
 
     def upload_export_tarball(self, realm: Optional[Realm], tarball_path: str) -> str:
         def percent_callback(bytes_transferred: Any) -> None: