From 4cebded04f159c154d526a81cdf70b30593f3b95 Mon Sep 17 00:00:00 2001
From: Kegan Dougal <kegan@matrix.org>
Date: Wed, 22 Mar 2017 15:06:52 +0000
Subject: [PATCH] Add canResetTimeline callback and thread it through to
 TimelinePanel

---
 src/components/structures/LoggedInView.js  |  7 +++++++
 src/components/structures/MatrixChat.js    | 24 +++++++++++++++++++++-
 src/components/structures/RoomView.js      |  7 +++++++
 src/components/structures/TimelinePanel.js |  4 ++++
 4 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/src/components/structures/LoggedInView.js b/src/components/structures/LoggedInView.js
index c2243820cd..6e2f0a3a5b 100644
--- a/src/components/structures/LoggedInView.js
+++ b/src/components/structures/LoggedInView.js
@@ -81,6 +81,13 @@ export default React.createClass({
         return this._scrollStateMap[roomId];
     },
 
+    canResetTimelineInRoom: function(roomId) {
+        if (!this.refs.roomView) {
+            return true;
+        }
+        return this.refs.roomView.canResetTimeline();
+    },
+
     _onKeyDown: function(ev) {
             /*
             // Remove this for now as ctrl+alt = alt-gr so this breaks keyboards which rely on alt-gr for numbers
diff --git a/src/components/structures/MatrixChat.js b/src/components/structures/MatrixChat.js
index 2337d62fd8..9b51e7f3fb 100644
--- a/src/components/structures/MatrixChat.js
+++ b/src/components/structures/MatrixChat.js
@@ -806,9 +806,31 @@ module.exports = React.createClass({
      * (useful for setting listeners)
      */
     _onWillStartClient() {
+        var self = this;
         var cli = MatrixClientPeg.get();
 
-        var self = this;
+        // Allow the JS SDK to reap timeline events. This reduces the amount of
+        // memory consumed as the JS SDK stores multiple distinct copies of room
+        // state (each of which can be 10s of MBs) for each DISJOINT timeline. This is
+        // particularly noticeable when there are lots of 'limited' /sync responses
+        // such as when laptops unsleep.
+        // https://github.com/vector-im/riot-web/issues/3307#issuecomment-282895568
+        cli.setCanResetTimelineCallback(function(roomId) {
+            console.log("Request to reset timeline in room ", roomId, " viewing:", self.state.currentRoomId);
+            if (roomId !== self.state.currentRoomId) {
+                // It is safe to remove events from rooms we are not viewing.
+                return true;
+            }
+            // We are viewing the room which we want to reset. It is only safe to do
+            // this if we are not scrolled up in the view. To find out, delegate to
+            // the timeline panel. If the timeline panel doesn't exist, then we assume
+            // it is safe to reset the timeline.
+            if (!self.refs.loggedInView) {
+                return true;
+            }
+            return self.refs.loggedInView.canResetTimelineInRoom(roomId);
+        });
+
         cli.on('sync', function(state, prevState) {
             self.updateStatusIndicator(state, prevState);
             if (state === "SYNCING" && prevState === "SYNCING") {
diff --git a/src/components/structures/RoomView.js b/src/components/structures/RoomView.js
index 345d0f6b80..b22d867acf 100644
--- a/src/components/structures/RoomView.js
+++ b/src/components/structures/RoomView.js
@@ -490,6 +490,13 @@ module.exports = React.createClass({
         }
     },
 
+    canResetTimeline: function() {
+        if (!this.refs.messagePanel) {
+            return true;
+        }
+        return this.refs.messagePanel.canResetTimeline();
+    },
+
     // called when state.room is first initialised (either at initial load,
     // after a successful peek, or after we join the room).
     _onRoomLoaded: function(room) {
diff --git a/src/components/structures/TimelinePanel.js b/src/components/structures/TimelinePanel.js
index cb42f701a3..8ef0e7631f 100644
--- a/src/components/structures/TimelinePanel.js
+++ b/src/components/structures/TimelinePanel.js
@@ -431,6 +431,10 @@ var TimelinePanel = React.createClass({
         }
     },
 
+    canResetTimeline: function() {
+        return this.refs.messagePanel && this.refs.messagePanel.isAtBottom();
+    },
+
     onRoomRedaction: function(ev, room) {
         if (this.unmounted) return;