Merge pull request #261 from vector-im/bwindels/fix-192

Don't consider lazy-load member events for room membership changes

src/matrix/Session.js

@@ -517,7 +517,7 @@ export function tests() {
                     }
                 }
             };
-            const newSessionData = await session.writeSync({next_batch: "b"}, 6, syncTxn);
+            const newSessionData = await session.writeSync({next_batch: "b"}, 6, null, syncTxn, {});
             assert(syncSet);
             assert.equal(session.syncToken, "a");
             assert.equal(session.syncFilterId, 5);

src/matrix/e2ee/megolm/decryption/SessionCache.js

@@ -14,15 +14,16 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
+import {BaseLRUCache} from "../../../../utils/LRUCache.js";
 const DEFAULT_CACHE_SIZE = 10;
 
 /**
  * Cache of unpickled inbound megolm session.
  */
-export class SessionCache {
+export class SessionCache extends BaseLRUCache {
-    constructor(size) {
+    constructor(limit) {
-        this._size = typeof size === "number" ? size : DEFAULT_CACHE_SIZE;
+        limit = typeof limit === "number" ? limit : DEFAULT_CACHE_SIZE;
-        this._sessions = [];
+        super(limit);
     }
 
     /**
@@ -32,37 +33,28 @@ export class SessionCache {
      * @return {SessionInfo?}
      */
     get(roomId, senderKey, sessionId) {
-        const idx = this._sessions.findIndex(s => {
+        return this._get(s => {
             return s.roomId === roomId &&
                 s.senderKey === senderKey &&
-                sessionId === s.session.session_id();
+                sessionId === s.sessionId;
         });
-        if (idx !== -1) {
-            const sessionInfo = this._sessions[idx];
-            // move to top
-            if (idx > 0) {
-                this._sessions.splice(idx, 1);
-                this._sessions.unshift(sessionInfo);
-            }
-            return sessionInfo;
-        }
     }
 
     add(sessionInfo) {
         sessionInfo.retain();
-        // add new at top
+        this._set(sessionInfo, s => {
-        this._sessions.unshift(sessionInfo);
+            return s.roomId === sessionInfo.roomId &&
-        if (this._sessions.length > this._size) {
+                s.senderKey === sessionInfo.senderKey &&
-            // free sessions we're about to remove
+                s.sessionId === sessionInfo.sessionId;
-            for (let i = this._size; i < this._sessions.length; i += 1) {
+        });
-                this._sessions[i].release();
-            }
-            this._sessions = this._sessions.slice(0, this._size);
     }
+
+    _onEvictEntry(sessionInfo) {
+        sessionInfo.release();
     }
 
     dispose() {
-        for (const sessionInfo of this._sessions) {
+        for (const sessionInfo of this._entries) {
             sessionInfo.release();
         }
     }

src/matrix/e2ee/megolm/decryption/SessionInfo.js

@@ -27,6 +27,10 @@ export class SessionInfo {
         this._refCounter = 0;
     }
 
+    get sessionId() {
+        return this.session?.session_id();
+    }
+
     retain() {
         this._refCounter += 1;
     }

src/matrix/room/Room.js

@@ -266,6 +266,9 @@ export class Room extends EventEmitter {
         // fetch new members while we have txn open,
         // but don't make any in-memory changes yet
         let heroChanges;
+        // if any hero changes their display name, the summary in the room response
+        // is also updated, which will trigger a RoomSummary update
+        // and make summaryChanges non-falsy here
         if (summaryChanges?.needsHeroes) {
             // room name disappeared, open heroes
             if (!this._heroes) {

src/matrix/room/members/RoomMember.js

@@ -24,7 +24,7 @@ export class RoomMember {
     }
 
     static fromMemberEvent(roomId, memberEvent) {
-        const userId = memberEvent && memberEvent.state_key;
+        const userId = memberEvent?.state_key;
         if (typeof userId !== "string") {
             return;
         }
@@ -103,36 +103,34 @@ export class RoomMember {
     serialize() {
         return this._data;
     }
+
+    equals(other) {
+        const data = this._data;
+        const otherData = other._data;
+        return data.roomId === otherData.roomId &&
+            data.userId === otherData.userId &&
+            data.membership === otherData.membership &&
+            data.displayName === otherData.displayName &&
+            data.avatarUrl === otherData.avatarUrl;
+    }
 }
 
 export class MemberChange {
-    constructor(roomId, memberEvent) {
+    constructor(member, previousMembership) {
-        this._roomId = roomId;
+        this.member = member;
-        this._memberEvent = memberEvent;
+        this.previousMembership = previousMembership;
-        this._member = null;
-    }
-
-    get member() {
-        if (!this._member) {
-            this._member = RoomMember.fromMemberEvent(this._roomId, this._memberEvent);
-        }
-        return this._member;
     }
 
     get roomId() {
-        return this._roomId;
+        return this.member.roomId;
     }
 
     get userId() {
-        return this._memberEvent.state_key;
+        return this.member.userId;
-    }
-
-    get previousMembership() {
-        return getPrevContentFromStateEvent(this._memberEvent)?.membership;
     }
 
     get membership() {
-        return this._memberEvent.content?.membership;
+        return this.member.membership;
     }
 
     get hasLeft() {

src/matrix/room/timeline/persistence/GapWriter.js

@@ -112,10 +112,10 @@ export class GapWriter {
             const event = events[i];
             key = key.nextKeyForDirection(direction);
             const eventStorageEntry = createEventEntry(key, this._roomId, event);
-            const memberData = this._findMemberData(event.sender, state, events, i, direction);
+            const member = this._findMember(event.sender, state, events, i, direction);
-            if (memberData) {
+            if (member) {
-                eventStorageEntry.displayName = memberData?.displayName;
+                eventStorageEntry.displayName = member.displayName;
-                eventStorageEntry.avatarUrl = memberData?.avatarUrl;
+                eventStorageEntry.avatarUrl = member.avatarUrl;
             }
             txn.timelineEvents.insert(eventStorageEntry);
             const eventEntry = new EventEntry(eventStorageEntry, this._fragmentIdComparer);
@@ -124,7 +124,7 @@ export class GapWriter {
         return entries;
     }
 
-    _findMemberData(userId, state, events, index, direction) {
+    _findMember(userId, state, events, index, direction) {
         function isOurUser(event) {
             return event.type === MEMBER_EVENT_TYPE && event.state_key === userId;
         }
@@ -133,7 +133,7 @@ export class GapWriter {
         for (let i = index + inc; i >= 0 && i < events.length; i += inc) {
             const event = events[i];
             if (isOurUser(event)) {
-                return RoomMember.fromMemberEvent(this._roomId, event)?.serialize();
+                return RoomMember.fromMemberEvent(this._roomId, event);
             }
         }
         // look into newer events, but using prev_content if found.
@@ -143,14 +143,14 @@ export class GapWriter {
         for (let i = index; i >= 0 && i < events.length; i -= inc) {
             const event = events[i];
             if (isOurUser(event)) {
-                return RoomMember.fromReplacingMemberEvent(this._roomId, event)?.serialize();
+                return RoomMember.fromReplacingMemberEvent(this._roomId, event);
             }
         }
         // assuming the member hasn't changed within the chunk, just take it from state if it's there.
         // Don't assume state is set though, as it can be empty at the top of the timeline in some circumstances 
         const stateMemberEvent = state?.find(isOurUser);
         if (stateMemberEvent) {
-            return RoomMember.fromMemberEvent(this._roomId, stateMemberEvent)?.serialize();
+            return RoomMember.fromMemberEvent(this._roomId, stateMemberEvent);
         }
     }
 

src/matrix/room/timeline/persistence/MemberWriter.js

@@ -0,0 +1,226 @@
+/*
+Copyright 2021 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import {MemberChange, RoomMember, EVENT_TYPE as MEMBER_EVENT_TYPE} from "../../members/RoomMember.js";
+import {LRUCache} from "../../../../utils/LRUCache.js";
+
+export class MemberWriter {
+    constructor(roomId) {
+        this._roomId = roomId;
+        this._cache = new LRUCache(5, member => member.userId);
+    }
+
+    writeTimelineMemberEvent(event, txn) {
+        return this._writeMemberEvent(event, false, txn);
+    }
+
+    writeStateMemberEvent(event, isLimited, txn) {
+        // member events in the state section when the room response
+        // is not limited must always be lazy loaded members.
+        // If they are not, they will be repeated in the timeline anyway.
+        return this._writeMemberEvent(event, !isLimited, txn);
+    }
+
+    async _writeMemberEvent(event, isLazyLoadingMember, txn) {
+        const userId = event.state_key;
+        if (!userId) {
+            return;
+        }
+        const member = RoomMember.fromMemberEvent(this._roomId, event);
+        if (!member) {
+            return;
+        }
+
+        let existingMember = this._cache.get(userId);
+        if (!existingMember) {
+            const memberData = await txn.roomMembers.get(this._roomId, userId);
+            if (memberData) {
+                existingMember = new RoomMember(memberData);
+            }
+        }
+
+        // either never heard of the member, or something changed
+        if (!existingMember || !existingMember.equals(member)) {
+            txn.roomMembers.set(member.serialize());
+            this._cache.set(member);
+            // we also return a member change for lazy loading members if something changed,
+            // so when the dupe timeline event comes and it doesn't see a diff
+            // with the cache, we already returned the event here.
+            // 
+            // it's just important that we don't consider the first LL event
+            // for a user we see as a membership change, or we'll share keys with
+            // them, etc...
+            if (isLazyLoadingMember && !existingMember) {
+                // we don't have a previous member, but we know this is not a
+                // membership change as it's a lazy loaded
+                // member so take the membership from the member
+                return new MemberChange(member, member.membership);
+            }
+            return new MemberChange(member, existingMember?.membership);
+        }
+    }
+
+    async lookupMember(userId, timelineEvents, txn) {
+        let member = this._cache.get(userId);
+        if (!member) {
+            const memberData = await txn.roomMembers.get(this._roomId, userId);
+            if (memberData) {
+                member = new RoomMember(memberData);
+                this._cache.set(member);
+            }
+        }
+        if (!member) {
+            // sometimes the member event isn't included in state, but rather in the timeline,
+            // even if it is not the first event in the timeline. In this case, go look for the
+            // first occurence
+            const memberEvent = timelineEvents.find(e => {
+                return e.type === MEMBER_EVENT_TYPE && e.state_key === userId;
+            });
+            if (memberEvent) {
+                member = RoomMember.fromMemberEvent(this._roomId, memberEvent);
+                // adding it to the cache, but not storing it for now;
+                // we'll do that when we get to the event
+                this._cache.set(member);
+            }
+        }
+        return member;
+    }
+}
+
+export function tests() {
+
+    function createMemberEvent(membership, userId, displayName, avatarUrl) {
+        return {
+            content: {
+                membership,
+                "displayname": displayName,
+                "avatar_url": avatarUrl
+            },
+            sender: userId,
+            "state_key": userId,
+            type: "m.room.member"
+        };
+    }
+
+
+    function createStorage(initialMembers = []) {
+        const members = new Map();
+        for (const m of initialMembers) {
+            members.set(m.userId, m);
+        }
+        return {
+            members,
+            roomMembers: {
+                async get(_, userId) {
+                    return members.get(userId);
+                },
+                set(member) {
+                    members.set(member.userId, member);
+                }
+            }
+        }
+    }
+
+    function member(...args) {
+        return RoomMember.fromMemberEvent(roomId, createMemberEvent.apply(null, args));
+    }
+
+    const roomId = "abc";
+    const alice = "@alice:hs.tld";
+    const avatar = "mxc://hs.tld/def";
+
+    return {
+        "new join through state": async assert => {
+            const writer = new MemberWriter(roomId);
+            const txn = createStorage();
+            const change = await writer.writeStateMemberEvent(createMemberEvent("join", alice), true, txn);
+            assert(change.hasJoined);
+            assert.equal(txn.members.get(alice).membership, "join");
+        },
+        "accept invite through state": async assert => {
+            const writer = new MemberWriter(roomId);
+            const txn = createStorage([member("invite", alice)]);
+            const change = await writer.writeStateMemberEvent(createMemberEvent("join", alice), true, txn);
+            assert.equal(change.previousMembership, "invite");
+            assert(change.hasJoined);
+            assert.equal(txn.members.get(alice).membership, "join");
+        },
+        "change display name through timeline": async assert => {
+            const writer = new MemberWriter(roomId);
+            const txn = createStorage([member("join", alice, "Alice")]);
+            const change = await writer.writeTimelineMemberEvent(createMemberEvent("join", alice, "Alies"), txn);
+            assert(!change.hasJoined);
+            assert.equal(change.member.displayName, "Alies");
+            assert.equal(txn.members.get(alice).displayName, "Alies");
+        },
+        "set avatar through timeline": async assert => {
+            const writer = new MemberWriter(roomId);
+            const txn = createStorage([member("join", alice, "Alice")]);
+            const change = await writer.writeTimelineMemberEvent(createMemberEvent("join", alice, "Alice", avatar), txn);
+            assert(!change.hasJoined);
+            assert.equal(change.member.avatarUrl, avatar);
+            assert.equal(txn.members.get(alice).avatarUrl, avatar);
+        },
+        "ignore redundant member event": async assert => {
+            const writer = new MemberWriter(roomId);
+            const txn = createStorage([member("join", alice, "Alice", avatar)]);
+            const change = await writer.writeTimelineMemberEvent(createMemberEvent("join", alice, "Alice", avatar), txn);
+            assert(!change);
+        },
+        "leave": async assert => {
+            const writer = new MemberWriter(roomId);
+            const txn = createStorage([member("join", alice, "Alice")]);
+            const change = await writer.writeTimelineMemberEvent(createMemberEvent("leave", alice, "Alice"), txn);
+            assert(change.hasLeft);
+            assert(!change.hasJoined);
+        },
+        "ban": async assert => {
+            const writer = new MemberWriter(roomId);
+            const txn = createStorage([member("join", alice, "Alice")]);
+            const change = await writer.writeTimelineMemberEvent(createMemberEvent("ban", alice, "Alice"), txn);
+            assert(change.hasLeft);
+            assert(!change.hasJoined);
+        },
+        "reject invite": async assert => {
+            const writer = new MemberWriter(roomId);
+            const txn = createStorage([member("invite", alice, "Alice")]);
+            const change = await writer.writeTimelineMemberEvent(createMemberEvent("leave", alice, "Alice"), txn);
+            assert(!change.hasLeft);
+            assert(!change.hasJoined);
+        },
+        "lazy loaded member we already know about doens't return change": async assert => {
+            const writer = new MemberWriter(roomId);
+            const txn = createStorage([member("join", alice, "Alice")]);
+            const change = await writer.writeStateMemberEvent(createMemberEvent("join", alice, "Alice"), false, txn);
+            assert(!change);
+        },
+        "lazy loaded member we already know about changes display name": async assert => {
+            const writer = new MemberWriter(roomId);
+            const txn = createStorage([member("join", alice, "Alice")]);
+            const change = await writer.writeStateMemberEvent(createMemberEvent("join", alice, "Alies"), false, txn);
+            assert.equal(change.member.displayName, "Alies");
+        },
+        "unknown lazy loaded member returns change, but not considered a membership change": async assert => {
+            const writer = new MemberWriter(roomId);
+            const txn = createStorage();
+            const change = await writer.writeStateMemberEvent(createMemberEvent("join", alice, "Alice"), false, txn);
+            assert(!change.hasJoined);
+            assert(!change.hasLeft);
+            assert.equal(change.member.membership, "join");
+            assert.equal(txn.members.get(alice).displayName, "Alice");
+        },
+    };
+}

src/matrix/room/timeline/persistence/SyncWriter.js

@@ -1,5 +1,6 @@
 /*
 Copyright 2020 Bruno Windels <bruno@windels.cloud>
+Copyright 2020 The Matrix.org Foundation C.I.C.
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -18,7 +19,8 @@ import {EventKey} from "../EventKey.js";
 import {EventEntry} from "../entries/EventEntry.js";
 import {FragmentBoundaryEntry} from "../entries/FragmentBoundaryEntry.js";
 import {createEventEntry} from "./common.js";
-import {MemberChange, RoomMember, EVENT_TYPE as MEMBER_EVENT_TYPE} from "../../members/RoomMember.js";
+import {EVENT_TYPE as MEMBER_EVENT_TYPE} from "../../members/RoomMember.js";
+import {MemberWriter} from "./MemberWriter.js";
 
 // Synapse bug? where the m.room.create event appears twice in sync response
 // when first syncing the room
@@ -37,6 +39,7 @@ function deduplicateEvents(events) {
 export class SyncWriter {
     constructor({roomId, fragmentIdComparer}) {
         this._roomId = roomId;
+        this._memberWriter = new MemberWriter(roomId);
         this._fragmentIdComparer = fragmentIdComparer;
         this._lastLiveKey = null;
     }
@@ -130,38 +133,20 @@ export class SyncWriter {
         return currentKey;
     }
 
-    _writeMember(event, txn) {
+    async _writeStateEvents(roomResponse, memberChanges, isLimited, txn, log) {
-        const userId = event.state_key;
-        if (userId) {
-            const memberChange = new MemberChange(this._roomId, event);
-            const {member} = memberChange;
-            if (member) {
-                // TODO: can we avoid writing redundant members here by checking
-                // if this is not a limited sync and the state is not in the timeline?
-                txn.roomMembers.set(member.serialize());
-                return memberChange;
-            }
-        }
-    }
-
-    _writeStateEvent(event, txn) {
-        if (event.type === MEMBER_EVENT_TYPE) {
-            return this._writeMember(event, txn);
-        } else {
-            txn.roomState.set(this._roomId, event);
-        }
-    }
-
-    _writeStateEvents(roomResponse, memberChanges, txn, log) {
         // persist state
         const {state} = roomResponse;
         if (Array.isArray(state?.events)) {
             log.set("stateEvents", state.events.length);
             for (const event of state.events) {
-                const memberChange = this._writeStateEvent(event, txn);
+                if (event.type === MEMBER_EVENT_TYPE) {
+                    const memberChange = await this._memberWriter.writeStateMemberEvent(event, isLimited, txn);
                     if (memberChange) {
                         memberChanges.set(memberChange.userId, memberChange);
                     }
+                } else {
+                    txn.roomState.set(this._roomId, event);
+                }
             }
         }
     }
@@ -177,21 +162,27 @@ export class SyncWriter {
                 // store event in timeline
                 currentKey = currentKey.nextKey();
                 const entry = createEventEntry(currentKey, this._roomId, event);
-                let memberData = await this._findMemberData(event.sender, events, txn);
+                let member = await this._memberWriter.lookupMember(event.sender, events, txn);
-                if (memberData) {
+                if (member) {
-                    entry.displayName = memberData.displayName;
+                    entry.displayName = member.displayName;
-                    entry.avatarUrl = memberData.avatarUrl;
+                    entry.avatarUrl = member.avatarUrl;
                 }
                 txn.timelineEvents.insert(entry);
                 entries.push(new EventEntry(entry, this._fragmentIdComparer));
 
-                // process live state events first, so new member info is available
+                // update state events after writing event, so for a member event,
+                // we only update the member info after having written the member event
+                // to the timeline, as we want that event to have the old profile info
                 if (typeof event.state_key === "string") {
                     timelineStateEventCount += 1;
-                    const memberChange = this._writeStateEvent(event, txn);
+                    if (event.type === MEMBER_EVENT_TYPE) {
+                        const memberChange = await this._memberWriter.writeTimelineMemberEvent(event, txn);
                         if (memberChange) {
                             memberChanges.set(memberChange.userId, memberChange);
                         }
+                    } else {
+                        txn.roomState.set(this._roomId, event);
+                    }
                 }
             }
             log.set("timelineStateEventCount", timelineStateEventCount);
@@ -199,24 +190,6 @@ export class SyncWriter {
         return currentKey;
     }
 
-    async _findMemberData(userId, events, txn) {
-        // TODO: perhaps add a small cache here?
-        const memberData = await txn.roomMembers.get(this._roomId, userId);
-        if (memberData) {
-            return memberData;
-        } else {
-            // sometimes the member event isn't included in state, but rather in the timeline,
-            // even if it is not the first event in the timeline. In this case, go look for the
-            // first occurence
-            const memberEvent = events.find(e => {
-                return e.type === MEMBER_EVENT_TYPE && e.state_key === userId;
-            });
-            if (memberEvent) {
-                return RoomMember.fromMemberEvent(this._roomId, memberEvent)?.serialize(); 
-            }
-        }
-    }
-
     /**
      * @type {SyncWriterResult}
      * @property {Array<BaseEntry>} entries new timeline entries written
@@ -233,7 +206,7 @@ export class SyncWriter {
         const memberChanges = new Map();
         // important this happens before _writeTimeline so
         // members are available in the transaction
-        this._writeStateEvents(roomResponse, memberChanges, txn, log);
+        await this._writeStateEvents(roomResponse, memberChanges, timeline?.limited, txn, log);
         const currentKey = await this._writeTimeline(entries, timeline, this._lastLiveKey, memberChanges, txn, log);
         log.set("memberChanges", memberChanges.size);
         return {entries, newLiveKey: currentKey, memberChanges};

src/utils/LRUCache.js

@@ -0,0 +1,146 @@
+/*
+Copyright 2021 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+/**
+ * Very simple least-recently-used cache implementation
+ * that should be fast enough for very small cache sizes
+ */
+export class BaseLRUCache {
+    constructor(limit) {
+        this._limit = limit;
+        this._entries = [];
+    }
+
+    _get(findEntryFn) {
+        const idx = this._entries.findIndex(findEntryFn);
+        if (idx !== -1) {
+            const entry = this._entries[idx];
+            // move to top
+            if (idx > 0) {
+                this._entries.splice(idx, 1);
+                this._entries.unshift(entry);
+            }
+            return entry;
+        }
+    }
+
+    _set(value, findEntryFn) {
+        let indexToRemove = this._entries.findIndex(findEntryFn);
+        this._entries.unshift(value);
+        if (indexToRemove === -1) {
+            if (this._entries.length > this._limit) {
+                indexToRemove = this._entries.length - 1;
+            }
+        } else {
+            // we added the entry at the start since we looked for the index
+            indexToRemove += 1;
+        }
+        if (indexToRemove !== -1) {
+            this._onEvictEntry(this._entries[indexToRemove]);
+            this._entries.splice(indexToRemove, 1);
+        }
+    }
+
+    _onEvictEntry() {}
+}
+
+export class LRUCache extends BaseLRUCache {
+    constructor(limit, keyFn) {
+        super(limit);
+        this._keyFn = keyFn;
+    }
+
+    get(key) {
+        return this._get(e => this._keyFn(e) === key);
+    }
+
+    set(value) {
+        const key = this._keyFn(value);
+        this._set(value, e => this._keyFn(e) === key);
+    }
+}
+
+export function tests() {
+    return {
+        "can retrieve added entries": assert => {
+            const cache = new LRUCache(2, e => e.id);
+            cache.set({id: 1, name: "Alice"});
+            cache.set({id: 2, name: "Bob"});
+            assert.equal(cache.get(1).name, "Alice");
+            assert.equal(cache.get(2).name, "Bob");
+        },
+        "first entry is evicted first": assert => {
+            const cache = new LRUCache(2, e => e.id);
+            cache.set({id: 1, name: "Alice"});
+            cache.set({id: 2, name: "Bob"});
+            cache.set({id: 3, name: "Charly"});
+            assert.equal(cache.get(1), undefined);
+            assert.equal(cache.get(2).name, "Bob");
+            assert.equal(cache.get(3).name, "Charly");
+            assert.equal(cache._entries.length, 2);
+        },
+        "second entry is evicted if first is requested": assert => {
+            const cache = new LRUCache(2, e => e.id);
+            cache.set({id: 1, name: "Alice"});
+            cache.set({id: 2, name: "Bob"});
+            cache.get(1);
+            cache.set({id: 3, name: "Charly"});
+            assert.equal(cache.get(1).name, "Alice");
+            assert.equal(cache.get(2), undefined);
+            assert.equal(cache.get(3).name, "Charly");
+            assert.equal(cache._entries.length, 2);
+        },
+        "setting an entry twice removes the first": assert => {
+            const cache = new LRUCache(2, e => e.id);
+            cache.set({id: 1, name: "Alice"});
+            cache.set({id: 2, name: "Bob"});
+            cache.set({id: 1, name: "Al Ice"});
+            cache.set({id: 3, name: "Charly"});
+            assert.equal(cache.get(1).name, "Al Ice");
+            assert.equal(cache.get(2), undefined);
+            assert.equal(cache.get(3).name, "Charly");
+            assert.equal(cache._entries.length, 2);
+        },
+        "evict callback is called": assert => {
+            let evictions = 0;
+            class CustomCache extends LRUCache {
+                _onEvictEntry(entry) {
+                    assert.equal(entry.name, "Alice");
+                    evictions += 1;
+                }
+            }
+            const cache = new CustomCache(2, e => e.id);
+            cache.set({id: 1, name: "Alice"});
+            cache.set({id: 2, name: "Bob"});
+            cache.set({id: 3, name: "Charly"});
+            assert.equal(evictions, 1);
+        },
+        "evict callback is called when replacing entry with same identity": assert => {
+            let evictions = 0;
+            class CustomCache extends LRUCache {
+                _onEvictEntry(entry) {
+                    assert.equal(entry.name, "Alice");
+                    evictions += 1;
+                }
+            }
+            const cache = new CustomCache(2, e => e.id);
+            cache.set({id: 1, name: "Alice"});
+            cache.set({id: 1, name: "Bob"});
+            assert.equal(evictions, 1);
+        },
+        
+    };
+}