Cache for follower synchronization results

daemon.py

@@ -120,6 +120,7 @@ from inbox import save_post_to_inbox_queue
 from inbox import populate_replies
 from inbox import receive_edit_to_post
 from follow import get_followers_sync_json
+from follow import get_followers_sync_hash
 from follow import follower_approval_active
 from follow import is_following_actor
 from follow import get_following_feed
@@ -16917,12 +16918,24 @@ class PubServer(BaseHTTPRequestHandler):
             # check authorized fetch
             if self._secure_mode(curr_session, proxy_type):
                 nickname = get_nickname_from_actor(self.path)
-                sync_json = \
-                    get_followers_sync_json(self.server.base_dir,
-                                            nickname, self.server.domain,
-                                            self.server.http_prefix,
-                                            self.server.domain_full,
-                                            calling_domain)
+                foll_sync_key = nickname + ':' + calling_domain
+                sync_dict = self.server.followers_sync_cache
+                if sync_dict.get(foll_sync_key):
+                    sync_hash = sync_dict[foll_sync_key]['hash']
+                    sync_json = sync_dict[foll_sync_key]['response']
+                else:
+                    sync_json = \
+                        get_followers_sync_json(self.server.base_dir,
+                                                nickname, self.server.domain,
+                                                self.server.http_prefix,
+                                                self.server.domain_full,
+                                                calling_domain)
+                    sync_hash = get_followers_sync_hash(sync_json)
+                    if sync_hash:
+                        self.server.followers_sync_cache[foll_sync_key] = {
+                            "hash": sync_hash,
+                            "response": sync_json
+                        }
                 msg_str = json.dumps(sync_json, ensure_ascii=False)
                 msg_str = self._convert_domains(calling_domain, referer_domain,
                                                 msg_str)
@@ -23382,6 +23395,9 @@ def run_daemon(max_hashtags: int,
     # lock for followers synchronization
     httpd.followers_synchronization = False
 
+    # cache containing followers synchronization hashes and json
+    httpd.followers_sync_cache = {}
+
     # permitted sites from which the buy button may be displayed
     httpd.buy_sites = load_buy_sites(base_dir)
 

follow.py

@@ -9,6 +9,7 @@ __module_group__ = "ActivityPub"
 
 from pprint import pprint
 import os
+from hashlib import sha256
 from utils import get_user_paths
 from utils import acct_handle_dir
 from utils import has_object_string_object
@@ -1401,6 +1402,7 @@ def _get_followers_for_domain(base_dir: str,
                     break
         elif '://' + search_domain in line_str:
             result.append(line_str)
+    result.sort()
     return result
 
 
@@ -1426,6 +1428,24 @@ def get_followers_sync_json(base_dir: str,
     return sync_json
 
 
+def get_followers_sync_hash(sync_json: {}) -> str:
+    """Returns a hash used within the Collection-Synchronization http header
+    See https://github.com/mastodon/mastodon/pull/14510
+    """
+    if not sync_json:
+        return None
+    sync_hash = None
+    for actor in sync_json['orderedItems']:
+        actor_hash = sha256(actor.encode('utf-8'))
+        if sync_hash:
+            sync_hash = sync_hash ^ actor_hash
+        else:
+            sync_hash = actor_hash
+    if sync_hash:
+        sync_hash = sync_hash.hexdigest()
+    return sync_hash
+
+
 def get_followers_of_actor(base_dir: str, actor: str, debug: bool) -> {}:
     """In a shared inbox if we receive a post we know who it's from
     and if it's addressed to followers then we need to get a list of those.