From d69b88566ad48dc17c1b27c1f3c6f2a7442595b4 Mon Sep 17 00:00:00 2001
From: Benjamin Lee <benjamin@computer.surgery>
Date: Thu, 16 May 2024 15:51:30 -0700
Subject: [PATCH] implement per-event filtering for ephemeral events in /sync

I've asked a few times for clarification on whether the `senders` field
in the filter applies to userids mentioned in the typing/receipt ephemeral
events, and never got a response. Synapse does not filter these userids by
sender, so we're gonna go with that.
---
 src/api/client_server/sync.rs | 64 ++++++++++++++++++-----------------
 src/utils/filter.rs           | 17 ++++++++--
 2 files changed, 48 insertions(+), 33 deletions(-)

diff --git a/src/api/client_server/sync.rs b/src/api/client_server/sync.rs
index 7e23294f..f991ac98 100644
--- a/src/api/client_server/sync.rs
+++ b/src/api/client_server/sync.rs
@@ -22,9 +22,12 @@ use ruma::{
         uiaa::UiaaResponse,
     },
     events::{
+        receipt::ReceiptEventContent,
         room::member::{MembershipState, RoomMemberEventContent},
-        StateEventType, TimelineEventType,
+        typing::TypingEventContent,
+        StateEventType, StaticEventContent, TimelineEventType,
     },
+    serde::Raw,
     uint, DeviceId, EventId, JsOption, OwnedRoomId, OwnedUserId, RoomId, UInt,
     UserId,
 };
@@ -933,39 +936,38 @@ async fn load_joined_room(
     let room_events: Vec<_> =
         timeline_pdus.iter().map(|(_, pdu)| pdu.to_sync_room_event()).collect();
 
-    let edus = if filter.room.ephemeral.room_allowed(room_id) {
-        let mut edus: Vec<_> = services()
-            .rooms
-            .edus
-            .read_receipt
-            .readreceipts_since(room_id, since)
-            .filter_map(Result::ok)
-            .map(|(_, _, v)| v)
-            .collect();
-
-        if services().rooms.edus.typing.last_typing_update(room_id).await?
-            > since
-        {
-            edus.push(
-                serde_json::from_str(
-                    &serde_json::to_string(
-                        &services()
-                            .rooms
-                            .edus
-                            .typing
-                            .typings_all(room_id)
-                            .await?,
-                    )
-                    .expect("event is valid, we just created it"),
-                )
-                .expect("event is valid, we just created it"),
+    let mut edus = vec![];
+    if filter.room.ephemeral.room_allowed(room_id) {
+        // We only filter on event type for ephemeral events because none of the
+        // other filter parameters apply to the specific ephemeral
+        // events we're generating (m.room.receipt and m.room.typing).
+        // If we add fields to either of these events, or start
+        // generating other event types in the future, we need to
+        // reevaluate this.
+        if filter.room.ephemeral.type_allowed(ReceiptEventContent::TYPE) {
+            edus.extend(
+                services()
+                    .rooms
+                    .edus
+                    .read_receipt
+                    .readreceipts_since(room_id, since)
+                    .filter_map(Result::ok)
+                    .map(|(_, _, v)| v),
             );
         }
 
-        edus
-    } else {
-        vec![]
-    };
+        if filter.room.ephemeral.type_allowed(TypingEventContent::TYPE)
+            && services().rooms.edus.typing.last_typing_update(room_id).await?
+                > since
+        {
+            let edu = services().rooms.edus.typing.typings_all(room_id).await?;
+            edus.push(
+                Raw::new(&edu)
+                    .expect("event is valid, we just created it")
+                    .cast(),
+            );
+        }
+    }
 
     let account_data_events = if filter.room.account_data.room_allowed(room_id)
     {
diff --git a/src/utils/filter.rs b/src/utils/filter.rs
index 47afaba7..aeb460d7 100644
--- a/src/utils/filter.rs
+++ b/src/utils/filter.rs
@@ -15,6 +15,10 @@
 //! top-level `filter.rooms.room`. Similarly, when a room is rejected for all
 //! events in a particular category, we can skip work generating events in that
 //! category for the rejected room.
+//!
+//! The second exception is ephemeral event types (`type`/`not_type` in
+//! `filter.room.ephemeral`). For these, we can skip work generating events of a
+//! particular type in `/sync` if it is rejected.
 
 use std::{borrow::Cow, collections::HashSet, hash::Hash};
 
@@ -258,6 +262,15 @@ impl CompiledRoomEventFilter<'_> {
         self.rooms.allowed(room_id)
     }
 
+    /// Returns `true` if an event type is allowed by the `types` and
+    /// `not_types` fields.
+    ///
+    /// This is mainly useful to skip work generating events for a particular
+    /// type, if that event type is always rejected by the filter.
+    pub(crate) fn type_allowed(&self, kind: &str) -> bool {
+        self.types.allowed(kind)
+    }
+
     /// Returns `true` if a PDU event is allowed by the filter.
     ///
     /// This tests against the `senders`, `not_senders`, `types`, `not_types`,
@@ -269,7 +282,7 @@ impl CompiledRoomEventFilter<'_> {
     /// [`CompiledRoomFilter::rooms`].
     pub(crate) fn pdu_event_allowed(&self, pdu: &PduEvent) -> bool {
         self.senders.allowed(&pdu.sender)
-            && self.types.allowed(&pdu.kind.to_string())
+            && self.type_allowed(&pdu.kind.to_string())
             && self.allowed_by_url_filter(pdu)
     }
 
@@ -305,7 +318,7 @@ impl CompiledRoomEventFilter<'_> {
 
         allowed_by_url_filter
             && self.senders.allowed(&event.sender)
-            && self.types.allowed(&event.kind)
+            && self.type_allowed(&event.kind)
     }
 
     // TODO: refactor this as well?