From fafdf669db16a6bcbbc1bb946795371ccaeede34 Mon Sep 17 00:00:00 2001
From: Bruno Windels <brunow@matrix.org>
Date: Thu, 20 Aug 2020 15:23:56 +0200
Subject: [PATCH] use prev_content from later events before state

---
 src/matrix/room/members/RoomMember.js         | 13 +++++++++-
 .../room/timeline/persistence/GapWriter.js    | 26 +++++++++----------
 2 files changed, 25 insertions(+), 14 deletions(-)

diff --git a/src/matrix/room/members/RoomMember.js b/src/matrix/room/members/RoomMember.js
index b794369e..4c38f66b 100644
--- a/src/matrix/room/members/RoomMember.js
+++ b/src/matrix/room/members/RoomMember.js
@@ -27,7 +27,18 @@ export class RoomMember {
         if (typeof userId !== "string") {
             return;
         }
-        const {content} = memberEvent;
+        return this._fromMemberEventContent(roomId, userId, memberEvent.content);
+    }
+
+    static fromReplacingMemberEvent(roomId, memberEvent) {
+        const userId = memberEvent && memberEvent.state_key;
+        if (typeof userId !== "string") {
+            return;
+        }
+        return this._fromMemberEventContent(roomId, userId, memberEvent.prev_content);
+    }
+
+    static _fromMemberEventContent(roomId, userId, content) {
         const membership = content?.membership;
         const avatarUrl = content?.avatar_url;
         const displayName = content?.displayname;
diff --git a/src/matrix/room/timeline/persistence/GapWriter.js b/src/matrix/room/timeline/persistence/GapWriter.js
index f64b1690..7a7ab4f5 100644
--- a/src/matrix/room/timeline/persistence/GapWriter.js
+++ b/src/matrix/room/timeline/persistence/GapWriter.js
@@ -108,9 +108,8 @@ export class GapWriter {
             const event = events[i];
             key = key.nextKeyForDirection(direction);
             const eventStorageEntry = createEventEntry(key, this._roomId, event);
-            const memberEvent = this._findMemberEvent(event.sender, state, events, i, direction);
-            if (memberEvent) {
-                const memberData = RoomMember.fromMemberEvent(memberEvent)?.serialize();
+            const memberData = this._findMemberData(event.sender, state, events, i, direction);
+            if (memberData) {
                 eventStorageEntry.displayName = memberData?.displayName;
                 eventStorageEntry.avatarUrl = memberData?.avatarUrl;
             }
@@ -121,29 +120,30 @@ export class GapWriter {
         return entries;
     }
 
-    _findMemberEvent(userId, state, events, index, direction) {
+    _findMemberData(userId, state, events, index, direction) {
         function isOurUser(event) {
             return event.type === MEMBER_EVENT_TYPE && event.state_key === userId;
         }
-        // older messages are further in the array when going backwards
+        // older messages are at a higher index in the array when going backwards
         const inc = direction.isBackward ? 1 : -1;
         for (let i = index + inc; i >= 0 && i < events.length; i += inc) {
             const event = events[i];
             if (isOurUser(event)) {
-                return event;
+                return RoomMember.fromMemberEvent(this._roomId, event)?.serialize();
             }
         }
-        const stateMemberEvent = state.find(isOurUser);
-        if (stateMemberEvent) {
-            return stateMemberEvent;
-        }
-        // look into newer events as a fallback, even though it is techically not correct
-        for (let i = index - inc; i >= 0 && i < events.length; i -= inc) {
+        // look into newer events, but using prev_content if found
+        for (let i = index; i >= 0 && i < events.length; i -= inc) {
             const event = events[i];
             if (isOurUser(event)) {
-                return event;
+                return RoomMember.fromReplacingMemberEvent(this._roomId, event)?.serialize();
             }
         }
+        // assuming the member hasn't changed within the chunk, just take it from state if it's there
+        const stateMemberEvent = state.find(isOurUser);
+        if (stateMemberEvent) {
+            return RoomMember.fromMemberEvent(this._roomId, stateMemberEvent)?.serialize();
+        }
     }
 
     async _updateFragments(fragmentEntry, neighbourFragmentEntry, end, entries, txn) {