From 9cfb3c8e9503b939f13771b39e520ce26c24c768 Mon Sep 17 00:00:00 2001
From: Bruno Windels <brunow@element.io>
Date: Mon, 9 Nov 2020 16:49:16 +0100
Subject: [PATCH] only check to pre-share new megolm session every minute

---
 src/matrix/e2ee/RoomEncryption.js | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/matrix/e2ee/RoomEncryption.js b/src/matrix/e2ee/RoomEncryption.js
index 94522e60..4829a8d7 100644
--- a/src/matrix/e2ee/RoomEncryption.js
+++ b/src/matrix/e2ee/RoomEncryption.js
@@ -20,6 +20,10 @@ import {mergeMap} from "../../utils/mergeMap.js";
 import {makeTxnId} from "../common.js";
 
 const ENCRYPTED_TYPE = "m.room.encrypted";
+// how often ensureMessageKeyIsShared can check if it needs to
+// create a new outbound session
+// note that encrypt could still create a new session
+const MIN_PRESHARE_INTERVAL = 60 * 1000; // 1min
 
 function encodeMissingSessionKey(senderKey, sessionId) {
     return `${senderKey}|${sessionId}`;
@@ -55,6 +59,7 @@ export class RoomEncryption {
         this._clock = clock;
         this._disposed = false;
         this._isFlushingRoomKeyShares = false;
+        this._lastKeyPreShareTime = null;
     }
 
     async enableSessionBackup(sessionBackup) {
@@ -248,6 +253,10 @@ export class RoomEncryption {
 
     /** shares the encryption key for the next message if needed */
     async ensureMessageKeyIsShared(hsApi) {
+        if (this._lastKeyPreShareTime && this._lastKeyPreShareTime.measure() < MIN_PRESHARE_INTERVAL) {
+            return;
+        }
+        this._lastKeyPreShareTime = this._clock.createMeasure();
         const roomKeyMessage = await this._megolmEncryption.ensureOutboundSession(this._room.id, this._encryptionParams);
         if (roomKeyMessage) {
             await this._deviceTracker.trackRoom(this._room);