Implement changes to MSC2285 (hidden read receipts) (#12168)

* Changes hidden read receipts to be a separate receipt type
  (instead of a field on `m.read`).
* Updates the `/receipts` endpoint to accept `m.fully_read`.

synapse/handlers/receipts.py

@@ -14,7 +14,7 @@
 import logging
 from typing import TYPE_CHECKING, Iterable, List, Optional, Tuple
 
-from synapse.api.constants import ReadReceiptEventFields, ReceiptTypes
+from synapse.api.constants import ReceiptTypes
 from synapse.appservice import ApplicationService
 from synapse.streams import EventSource
 from synapse.types import JsonDict, ReadReceipt, UserID, get_domain_from_id
@@ -112,7 +112,7 @@ class ReceiptsHandler:
             )
 
             if not res:
-                # res will be None if this read receipt is 'old'
+                # res will be None if this receipt is 'old'
                 continue
 
             stream_id, max_persisted_id = res
@@ -138,7 +138,7 @@ class ReceiptsHandler:
         return True
 
     async def received_client_receipt(
-        self, room_id: str, receipt_type: str, user_id: str, event_id: str, hidden: bool
+        self, room_id: str, receipt_type: str, user_id: str, event_id: str
     ) -> None:
         """Called when a client tells us a local user has read up to the given
         event_id in the room.
@@ -148,16 +148,14 @@ class ReceiptsHandler:
             receipt_type=receipt_type,
             user_id=user_id,
             event_ids=[event_id],
-            data={"ts": int(self.clock.time_msec()), "hidden": hidden},
+            data={"ts": int(self.clock.time_msec())},
         )
 
         is_new = await self._handle_new_receipts([receipt])
         if not is_new:
             return
 
-        if self.federation_sender and not (
-            self.hs.config.experimental.msc2285_enabled and hidden
-        ):
+        if self.federation_sender and receipt_type != ReceiptTypes.READ_PRIVATE:
             await self.federation_sender.send_read_receipt(receipt)
 
 
@@ -168,6 +166,13 @@ class ReceiptEventSource(EventSource[int, JsonDict]):
 
     @staticmethod
     def filter_out_hidden(events: List[JsonDict], user_id: str) -> List[JsonDict]:
+        """
+        This method takes in what is returned by
+        get_linearized_receipts_for_rooms() and goes through read receipts
+        filtering out m.read.private receipts if they were not sent by the
+        current user.
+        """
+
         visible_events = []
 
         # filter out hidden receipts the user shouldn't see
@@ -176,37 +181,21 @@ class ReceiptEventSource(EventSource[int, JsonDict]):
             new_event = event.copy()
             new_event["content"] = {}
 
-            for event_id in content.keys():
-                event_content = content.get(event_id, {})
-                m_read = event_content.get(ReceiptTypes.READ, {})
+            for event_id, event_content in content.items():
+                receipt_event = {}
+                for receipt_type, receipt_content in event_content.items():
+                    if receipt_type == ReceiptTypes.READ_PRIVATE:
+                        user_rr = receipt_content.get(user_id, None)
+                        if user_rr:
+                            receipt_event[ReceiptTypes.READ_PRIVATE] = {
+                                user_id: user_rr.copy()
+                            }
+                    else:
+                        receipt_event[receipt_type] = receipt_content.copy()
 
-                # If m_read is missing copy over the original event_content as there is nothing to process here
-                if not m_read:
-                    new_event["content"][event_id] = event_content.copy()
-                    continue
-
-                new_users = {}
-                for rr_user_id, user_rr in m_read.items():
-                    try:
-                        hidden = user_rr.get("hidden")
-                    except AttributeError:
-                        # Due to https://github.com/matrix-org/synapse/issues/10376
-                        # there are cases where user_rr is a string, in those cases
-                        # we just ignore the read receipt
-                        continue
-
-                    if hidden is not True or rr_user_id == user_id:
-                        new_users[rr_user_id] = user_rr.copy()
-                        # If hidden has a value replace hidden with the correct prefixed key
-                        if hidden is not None:
-                            new_users[rr_user_id].pop("hidden")
-                            new_users[rr_user_id][
-                                ReadReceiptEventFields.MSC2285_HIDDEN
-                            ] = hidden
-
-                # Set new users unless empty
-                if len(new_users.keys()) > 0:
-                    new_event["content"][event_id] = {ReceiptTypes.READ: new_users}
+                # Only include the receipt event if it is non-empty.
+                if receipt_event:
+                    new_event["content"][event_id] = receipt_event
 
             # Append new_event to visible_events unless empty
             if len(new_event["content"].keys()) > 0: