Add d.ts

Otherwise, the following situation may happen:
- Node 1 is the leader and its term is 24
- Node 2 is a follower of 1, its term is 24 too
- Node 3 also thinks he's the leader, his term is 23, and he doesn't know that a new leader is elected

.eslintrc.js

@@ -0,0 +1,49 @@
+module.exports = {
+    "env": {
+        "es6": true,
+        "node": true
+    },
+    "extends": [
+        "eslint:recommended",
+        "plugin:node/recommended"
+    ],
+    "parserOptions": {
+        "ecmaVersion": 2020
+    },
+    "plugins": [
+    ],
+    "rules": {
+        "indent": [
+            "error",
+            4
+        ],
+        "brace-style": [
+            "error",
+            "allman",
+            { "allowSingleLine": true }
+        ],
+        "linebreak-style": [
+            "error",
+            "unix"
+        ],
+        "semi": [
+            "error",
+            "always"
+        ],
+        "no-useless-escape": [
+            "off"
+        ],
+        "no-control-regex": [
+            "off"
+        ],
+        "no-empty": [
+            "off"
+        ],
+        "no-process-exit": [
+            "off"
+        ],
+        "node/shebang": [
+            "off"
+        ]
+    }
+};

README.md

@@ -0,0 +1,110 @@
+# TinyRaft
+
+Raft leader election isolated from the rest of the algorithm.
+
+TinyRaft doesn't know anything about replication and doesn't require you to
+implement it.
+
+Actual network communication is also abstracted away and hidden behind a simple
+callback interface.
+
+The only task of TinyRaft is to elect the leader and guarantee that there is
+only one leader at each moment.
+
+TinyRaft can be used:
+- As a simple leader election algorithm without replication at all
+- As a building block for the standard Raft algorithm if you add log replication
+- For other variations of "weaker consensus" if you add another method of replication
+
+Some replication ideas for you:
+- Log-less replication: Add a version number for each key in the database
+  and make the leader synchronize follower databases by simply dumping all
+  followers' databases with the newest term (followers with older terms should
+  be ignored), comparing version numbers and making the newest version of each
+  key win.
+- Erasure coding: Suppose you store large values. You can split each value into
+  N parts, add K parity parts to it using Reed-Solomon codes (ISA-L/jerasure)
+  and store them on different nodes in the form of Raft-like logs or similar
+  to the log-less replication with version numbers, and make master synchronize
+  followers by reconstructing every original value.
+
+## Example Application
+
+[AntiEtcd](https://git.yourcmc.ru/vitalif/antietcd/)
+
+## Usage
+
+```js
+const node = new TinyRaft({
+    nodes: [ 1, 2, 3 ],
+    nodeId: 1,
+    electionTimeout: 5000,
+    heartbeatTimeout: 1000,
+    leadershipTimeout: 10000,
+    initialTerm: 0,
+    leaderPriority: 0,
+    send: function(to, msg)
+    {
+        // Function to send message <msg> to node with ID <to>
+        // msg.type is one of TinyRaft.VOTE_REQUEST, TinyRaft.VOTE, TinyRaft.PING, TinyRaft.PONG
+        // msg.leader is the leader ID or null
+        // msg.term is the term number
+        // msg.priority is the optional leadership priority if set in config
+    },
+});
+
+// Watch for election state
+node.on('change', (st) =>
+{
+    console.log(
+        'node '+node.nodeId+': '+(st.state == TinyRaft.FOLLOWER ? 'following '+st.leader : st.state)+
+        ', term '+st.term+(st.state == TinyRaft.LEADER ? ', followers: '+st.followers.join(', ') : '')
+    );
+});
+
+// Start Raft node or start a new election round
+node.start();
+
+// Optional; may be called for a follower when it receives a message from a live leader,
+// for example, a replication message, and causes the follower to move its round expiration forward
+node.markAlive();
+
+// Update cluster node list
+node.setNodes([ 1, 2, 3 ]);
+
+// Incoming messages should be fed to TinyRaft like this (from = ID of the sender):
+node.onReceive(from, msg);
+
+// Stop Raft node
+node.stop();
+```
+
+## Additional features
+
+### Leader expiration
+
+Supports leader expiration like in NuRaft:
+https://github.com/eBay/NuRaft/blob/master/docs/leadership_expiration.md
+
+When leader expiration is enabled, followers respond to leader heartbeats
+(pings) with "pong" messages and if the leader doesn't receive a quorum of
+replies in leadershipTimeout - it starts a new round of voting.
+
+### Leadership priorities
+
+Also supports leader priorities, similar to NuRaft but even simpler:
+if a node receives a VoteRequest message with larger term but with smaller
+priority than its own, it immediately starts a new voting round.
+
+It guarantees that a node with non-maximum priority can't become leader
+without being re-elected.
+
+If all priorities are equal (or just zero), the election algorithm
+becomes identical to the basic algorithm without priorities.
+
+# Author and License
+
+Author: Vitaliy Filippov, 2024
+
+License: [Mozilla Public License 2.0](https://www.mozilla.org/media/MPL/2.0/index.f75d2927d3c1.txt)
+or [Vitastor Network Public License 1.1](https://git.yourcmc.ru/vitalif/vitastor/src/branch/master/VNPL-1.1.txt)

faketimer.js

@@ -0,0 +1,44 @@
+// Fake timer for node.js which _guarantees_ that all asynchronous timer
+// callbacks are called during a tested period
+
+function FakeTimer(startTime)
+{
+    this.time = Number(startTime)||0;
+    this.timers = [];
+    this.id = 0;
+    this.setTimeout = (func, ms) =>
+    {
+        this.timers.push({ id: ++this.id, func, at: this.time+ms });
+        return this.id;
+    };
+    this.setInterval = (func, ms) =>
+    {
+        this.timers.push({ id: ++this.id, func, at: this.time+ms, repeat: ms });
+        return this.id;
+    };
+    this.clearInterval = this.clearTimeout = (id) =>
+    {
+        this.timers = this.timers.filter(t => t.id != id);
+    };
+    this.setImmediate = (func) => this.setTimeout(func, 0);
+    this.runFor = (ms) =>
+    {
+        const end = this.time+ms;
+        this.timers.sort((a, b) => a.at - b.at);
+        while (this.timers.length && this.timers[0].at <= end)
+        {
+            const { func, at, repeat } = this.timers[0];
+            if (!repeat)
+                this.timers.shift();
+            else
+                this.timers[0].at += repeat;
+            if (at > this.time)
+                this.time = at;
+            func();
+            this.timers.sort((a, b) => a.at - b.at);
+        }
+        this.time = end;
+    };
+}
+
+module.exports = FakeTimer;

package.json

@@ -0,0 +1,35 @@
+{
+  "name": "tinyraft",
+  "version": "1.0.1",
+  "description": "Tiny & abstract Raft leader election algorithm",
+  "main": "tinyraft.js",
+  "scripts": {
+    "lint": "eslint tinyraft.js tinyraft.spec.js faketimer.js",
+    "test": "node tinyraft.spec.js"
+  },
+  "repository": {
+    "type": "git",
+    "url": "https://git.yourcmc.ru/vitalif/tinyraft"
+  },
+  "homepage": "https://git.yourcmc.ru/vitalif/tinyraft",
+  "bugs": {
+    "url": "https://git.yourcmc.ru/vitalif/tinyraft/issues"
+  },
+  "files": [
+    "tinyraft.js",
+    "tinyraft.d.ts",
+    "README.md"
+  ],
+  "keywords": [
+    "raft"
+  ],
+  "author": "Vitaliy Filippov",
+  "license": "MPL-2.0",
+  "engines": {
+    "node": ">=12.0.0"
+  },
+  "devDependencies": {
+    "eslint": "^8.0.0",
+    "eslint-plugin-node": "^11.1.0"
+  }
+}

tinyraft.d.ts

@@ -0,0 +1,36 @@
+import type { EventEmitter } from 'events';
+
+export type TinyRaftEvents = {
+    change: {
+        state: 'LEADER'|'FOLLOWER'|'CANDIDATE',
+        term: number,
+        leader: string|number,
+        followers: (string|number)[],
+    }[],
+};
+
+export type RaftMessage = {
+    type: 'VOTE_REQUEST'|'VOTE'|'PING'|'PONG',
+    term: number,
+    leader?: string|number,
+    priority?: number,
+};
+
+export class TinyRaft extends EventEmitter<TinyRaftEvents>
+{
+    constructor(cfg: {
+        nodes: (number|string)[],
+        nodeId: number|string,
+        electionTimeout?: number,
+        heartbeatTimeout?: number,
+        leadershipTimeout?: number,
+        initialTerm?: number,
+        leaderPriority?: number,
+        send: (to: number|string, msg: RaftMessage) => void,
+    });
+    start();
+    stop();
+    onReceive(from: number|string, msg: RaftMessage);
+    markAlive();
+    setNodes(nodes: (number|string)[]);
+}

tinyraft.js

@@ -11,6 +11,18 @@
 //
 // Supports leader expiration like in NuRaft:
 // https://github.com/eBay/NuRaft/blob/master/docs/leadership_expiration.md
+//
+// Also supports leader priorities, similar to NuRaft but even simpler:
+// If a node receives a VoteRequest message with larger term but with smaller
+// priority than its own, it immediately starts a new voting round.
+// It guarantees that a node with non-maximum priority can't become leader
+// without being re-elected.
+// If all priorities are equal (or just zero), the election algorithm
+// becomes identical to the basic algorithm without priorities.
+//
+// (c) Vitaliy Filippov, 2024
+// License: Mozilla Public License 2.0 or Vitastor Network Public License 1.1
+// (https://git.yourcmc.ru/vitalif/vitastor/src/branch/master/VNPL-1.1.txt)
 
 const EventEmitter = require('events');
 
@@ -32,7 +44,10 @@ class TinyRaft extends EventEmitter
     //     heartbeatTimeout?: number,
     //     leadershipTimeout?: number,
     //     initialTerm?: number,
+    //     leaderPriority?: number,
     // }
+    // NOTE: leadershipTimeout, if enabled, should be > heartbeatTimeout, and ideally < electionTimeout
+    // In that case a leader with dead network will be expired before being re-elected
     constructor(config)
     {
         super();
@@ -43,6 +58,7 @@ class TinyRaft extends EventEmitter
         this.randomTimeout = config.randomTimeout > 0 ? Number(config.randomTimeout) : this.electionTimeout;
         this.heartbeatTimeout = Number(config.heartbeatTimeout) || 1000;
         this.leadershipTimeout = Number(config.leadershipTimeout) || 0;
+        this.leaderPriority = Number(config.leaderPriority) || undefined;
         if (!this.nodeId || this.nodeId instanceof Object ||
             !(this.nodes instanceof Array) || this.nodes.filter(n => !n || n instanceof Object).length > 0 ||
             !(this.send instanceof Function))
@@ -52,18 +68,19 @@ class TinyRaft extends EventEmitter
             this.term = 0;
         this.state = null;
         this.leader = null;
+        this.confirmed = {};
     }
 
     _nextTerm(after)
     {
         if (this.electionTimer)
         {
-            clearTimeout(this.electionTimer);
+            TinyRaft.clearTimeout(this.electionTimer);
             this.electionTimer = null;
         }
         if (after >= 0)
         {
-            this.electionTimer = setTimeout(() => this.start(), after + this.randomTimeout * Math.random());
+            this.electionTimer = TinyRaft.setTimeout(() => this.start(), after + this.randomTimeout * Math.random());
         }
     }
 
@@ -76,16 +93,17 @@ class TinyRaft extends EventEmitter
         this.votes = { [this.nodeId]: [ this.nodeId ] };
         this.state = CANDIDATE;
         this.followers = null;
+        this.confirmed = {};
         this.leader = this.nodeId;
         if (!this.heartbeatTimer)
         {
-            this.heartbeatTimer = setInterval(() => this._heartbeat(), this.heartbeatTimeout);
+            this.heartbeatTimer = TinyRaft.setInterval(() => this._heartbeat(), this.heartbeatTimeout);
         }
         for (const node of this.nodes)
         {
             if (node != this.nodeId)
             {
-                this.send(node, { type: VOTE_REQUEST, term: this.term, leader: this.leader });
+                this.send(node, { type: VOTE_REQUEST, term: this.term, leader: this.leader, priority: this.leaderPriority });
             }
         }
         // Next term will start right after this one times out
@@ -97,12 +115,12 @@ class TinyRaft extends EventEmitter
     {
         if (this.electionTimer)
         {
-            clearTimeout(this.electionTimer);
+            TinyRaft.clearTimeout(this.electionTimer);
             this.electionTimer = null;
         }
         if (this.heartbeatTimer)
         {
-            clearTimeout(this.heartbeatTimer);
+            TinyRaft.clearInterval(this.heartbeatTimer);
             this.heartbeatTimer = null;
         }
     }
@@ -111,11 +129,12 @@ class TinyRaft extends EventEmitter
     {
         if (this.state == LEADER)
         {
-            for (const node of this.votes[this.nodeId])
+            this.confirmed = {};
+            for (const node of (this.leadershipTimeout ? this.followers : this.nodes))
             {
                 if (node != this.nodeId)
                 {
-                    this.send(node, { type: PING, term: this.term });
+                    this.send(node, { type: PING, term: this.term, priority: this.leaderPriority });
                 }
             }
         }
@@ -124,22 +143,82 @@ class TinyRaft extends EventEmitter
     onReceive(from, msg)
     {
         if (msg.type == VOTE_REQUEST)
+        {
+            this._onReceiveVoteRequest(from, msg);
+        }
+        else if (msg.type == VOTE)
+        {
+            this._onReceiveVote(from, msg);
+        }
+        else if (msg.type == PING)
+        {
+            this._onReceivePing(from, msg);
+        }
+        else if (msg.type == PONG)
+        {
+            this._onReceivePong(from, msg);
+        }
+    }
+
+    _onReceiveVoteRequest(from, msg)
     {
         if (msg.term > this.term && msg.leader)
+        {
+            if (this.leaderPriority && (msg.priority||0) < this.leaderPriority)
+            {
+                this.term = msg.term;
+                this.start();
+            }
+            else
             {
                 this.leader = msg.leader;
                 this.term = msg.term;
                 this.state = CANDIDATE;
+                this.followers = null;
+                this.confirmed = {};
                 this._nextTerm(this.heartbeatTimeout*2 + this.electionTimeout);
                 this.emit('change', { state: this.state, term: this.term, leader: this.leader });
             }
-            this.send(from, { type: VOTE, term: this.term, leader: this.leader });
         }
-        else if (msg.type == VOTE && msg.term == this.term)
+        const prio = (this.leader == this.nodeId ? this.leaderPriority : undefined);
+        this.send(from, { type: VOTE, term: this.term, leader: this.leader, priority: prio });
+    }
+
+    _onReceiveVote(from, msg)
+    {
+        if (!msg.leader || msg.term < this.term)
+        {
+            return;
+        }
+        if (msg.term > this.term)
+        {
+            this.term = msg.term;
+            this.state = FOLLOWER;
+            this.followers = null;
+            this.confirmed = {};
+            this.leader = msg.leader;
+            this.votes = {};
+            this.emit('change', { state: this.state, term: this.term, leader: this.leader });
+            // Repeat VOTE to the leader to join it
+            this.send(this.leader, { type: VOTE, term: this.term, leader: this.leader, priority: msg.priority });
+            return;
+        }
+        // add <from> as voter for <msg.leader>
+        this.votes[msg.leader] = this.votes[msg.leader] || [];
+        let found = false;
+        for (const voter of this.votes[msg.leader])
+        {
+            if (voter == from)
+            {
+                found = true;
+                break;
+            }
+        }
+        if (!found)
         {
             this.voted++;
-            this.votes[msg.leader] = this.votes[msg.leader] || [];
             this.votes[msg.leader].push(from);
+        }
         const n = this.votes[msg.leader].length;
         if (n == 1 + (0 | this.nodes.length/2))
         {
@@ -147,16 +226,11 @@ class TinyRaft extends EventEmitter
             {
                 this.leader = msg.leader;
                 this.state = LEADER;
+                this.confirmed = {};
                 this._nextTerm(this.leadershipTimeout > 0 ? this.leadershipTimeout : -1);
                 this.followers = this.votes[this.nodeId];
-                    for (const follower of this.followers)
-                    {
-                        if (follower != this.nodeId)
-                        {
                 // Send a heartbeat to confirm leadership
-                            this.send(follower, { type: PING, term: this.term });
-                        }
-                    }
+                this._heartbeat();
                 this.emit('change', { state: this.state, term: this.term, leader: this.nodeId, followers: this.votes[this.nodeId] });
             }
             else
@@ -168,7 +242,7 @@ class TinyRaft extends EventEmitter
         {
             this.followers = this.votes[this.nodeId];
             // Send a heartbeat to confirm leadership
-                this.send(from, { type: PING, term: this.term });
+            this.send(from, { type: PING, term: this.term, priority: this.leaderPriority });
             this.emit('change', { state: this.state, term: this.term, leader: this.nodeId, followers: this.votes[this.nodeId] });
         }
         else if (this._isVotingFailed())
@@ -176,35 +250,47 @@ class TinyRaft extends EventEmitter
             this._nextTerm(0);
         }
     }
-        else if (msg.type == PING)
+
+    _onReceivePing(from, msg)
     {
         if (this.state == CANDIDATE && this.term == msg.term && from == this.leader)
         {
             this.state = FOLLOWER;
-                this.emit('change', { state: this.state, term: this.term, leader: this.nodeId });
+            this.emit('change', { state: this.state, term: this.term, leader: this.leader });
         }
         if (this.state == FOLLOWER && from == this.leader)
         {
             this.markAlive();
         }
-            if (this.leadershipTimeout > 0)
+        if (this.leadershipTimeout > 0 || this.state == FOLLOWER && from != this.leader)
         {
             this.send(from, { type: PONG, term: this.term, leader: this.leader });
         }
     }
-        else if (msg.type == PONG && this.state == LEADER)
+
+    _onReceivePong(from, msg)
     {
-            this._nextTerm(-1);
-            if (msg.leader != this.nodeId)
+        if (this.state != LEADER)
+        {
+            return;
+        }
+        if (msg.leader != this.nodeId || msg.term != this.term)
         {
             this.start();
         }
+        else if (this.leadershipTimeout > 0)
+        {
+            this.confirmed[from] = true;
+            if (Object.keys(this.confirmed).length >= (1 + (0 | this.nodes.length/2)))
+            {
+                // We have quorum
+                this._nextTerm(this.leadershipTimeout);
+            }
         }
     }
 
     markAlive()
     {
-        this.leaderTimedOut = false;
         this._nextTerm(this.heartbeatTimeout*2 + this.electionTimeout);
     }
 
@@ -230,16 +316,22 @@ class TinyRaft extends EventEmitter
         if (this.state == LEADER)
         {
             this.votes[this.nodeId] = this.votes[this.nodeId].filter(n => nodes.indexOf(n) >= 0);
+            if (this.votes[this.nodeId].length < (1 + (0 | this.nodes.length/2)))
+                this.start();
+            else
                 this.emit('change', { state: this.state, term: this.term, leader: this.nodeId, followers: this.votes[this.nodeId] });
         }
         else if (this.state == FOLLOWER && nodes.indexOf(this.leader) < 0 || this.state == CANDIDATE)
         {
-            r.nextTerm(-1);
-            r.start();
+            this.start();
         }
     }
 }
 
+TinyRaft.setTimeout = setTimeout;
+TinyRaft.clearTimeout = clearTimeout;
+TinyRaft.setInterval = setInterval;
+TinyRaft.clearInterval = clearInterval;
 TinyRaft.VOTE_REQUEST = VOTE_REQUEST;
 TinyRaft.VOTE = VOTE;
 TinyRaft.PING = PING;

tinyraft.spec.js

@@ -1,9 +1,16 @@
 const TinyRaft = require('./tinyraft.js');
+const FakeTimer = require('./faketimer.js');
 
-function newNode(id, nodes, partitions)
+const fake = new FakeTimer();
+TinyRaft.setTimeout = fake.setTimeout;
+TinyRaft.clearTimeout = fake.clearTimeout;
+TinyRaft.setInterval = fake.setInterval;
+TinyRaft.clearInterval = fake.clearInterval;
+
+function newNode(id, nodes, partitions, mod)
 {
     partitions = partitions || {};
-    let n = new TinyRaft({
+    let cfg = {
         nodes: [ 1, 2, 3, 4, 5 ],
         nodeId: id,
         heartbeatTimeout: 100,
@@ -12,28 +19,33 @@ function newNode(id, nodes, partitions)
         {
             if (!partitions[n.nodeId+'-'+to] && !partitions[to+'-'+n.nodeId] && nodes[to])
             {
-                console.log('received from '+n.nodeId+' to '+to+': '+JSON.stringify(msg));
-                setImmediate(function() { nodes[to].onReceive(n.nodeId, msg); });
+                console.log('['+fake.time+'] received from '+n.nodeId+' to '+to+': '+JSON.stringify(msg));
+                fake.setImmediate(function() { nodes[to].onReceive(n.nodeId, msg); });
             }
+            else
+                console.log('['+fake.time+'] failed to send from '+n.nodeId+' to '+to+': '+JSON.stringify(msg));
         },
-    });
+    };
+    if (mod)
+        mod(cfg);
+    let n = new TinyRaft(cfg);
     n.on('change', (st) =>
     {
         console.log(
-            'node '+n.nodeId+': '+(st.state == TinyRaft.FOLLOWER ? 'following '+st.leader : st.state)+
+            '['+fake.time+'] node '+n.nodeId+': '+(st.state == TinyRaft.FOLLOWER ? 'following '+st.leader : st.state)+
             ', term '+st.term+(st.state == TinyRaft.LEADER ? ', followers: '+st.followers.join(', ') : '')
         );
     });
     nodes[id] = n;
 }
 
-function newNodes(count, partitions)
+function newNodes(count, partitions, mod)
 {
     partitions = partitions || {};
     const nodes = {};
     for (let i = 1; i <= count; i++)
     {
-        newNode(i, nodes, partitions);
+        newNode(i, nodes, partitions, mod);
     }
     for (let i = 1; i <= count; i++)
     {
@@ -45,6 +57,7 @@ function newNodes(count, partitions)
 function checkQuorum(nodes, count)
 {
     let leaders = 0;
+    let out = 0;
     for (const i in nodes)
     {
         if (nodes[i].state == TinyRaft.LEADER)
@@ -55,6 +68,8 @@ function checkQuorum(nodes, count)
         }
         else if (nodes[i].state != TinyRaft.FOLLOWER)
         {
+            out++;
+            if (out > nodes.length-count)
                 throw new Error('node '+i+' is not in quorum: state '+nodes[i].state);
         }
     }
@@ -62,7 +77,7 @@ function checkQuorum(nodes, count)
     {
         throw new Error('we have '+leaders+' leaders instead of exactly 1');
     }
-    console.log('OK: '+count+' nodes in quorum');
+    console.log('['+fake.time+'] OK: '+count+' nodes in quorum');
 }
 
 function checkNoQuorum(nodes)
@@ -72,11 +87,12 @@ function checkNoQuorum(nodes)
     {
         throw new Error('we have non-candidates ('+nc.map(n => n.nodeId).join(', ')+'), but we should not');
     }
-    console.log('OK: '+Object.keys(nodes).length+' candidates, no quorum');
+    console.log('['+fake.time+'] OK: '+Object.keys(nodes).length+' candidates, no quorum');
 }
 
 async function testStartThenRemoveNode()
 {
+    console.log('--------------------------------------------------------------------------------');
     console.log('testStartThenRemoveNode');
     const nodes = newNodes(5);
     let leaderChanges = 0, prevLeader = null;
@@ -88,7 +104,7 @@ async function testStartThenRemoveNode()
             leaderChanges++;
         }
     });
-    await new Promise(ok => setTimeout(ok, 2000));
+    fake.runFor(2000);
     checkQuorum(nodes, 5);
     if (leaderChanges >= 3)
     {
@@ -100,7 +116,7 @@ async function testStartThenRemoveNode()
     nodes[leader].stop();
     delete nodes[leader];
     // Check quorum after 2000ms
-    await new Promise(ok => setTimeout(ok, 2000));
+    fake.runFor(2000);
     checkQuorum(nodes, 4);
     // Stop the leader again
     leader = nodes[Object.keys(nodes)[0]].leader;
@@ -108,7 +124,7 @@ async function testStartThenRemoveNode()
     nodes[leader].stop();
     delete nodes[leader];
     // Check quorum after 2000ms
-    await new Promise(ok => setTimeout(ok, 2000));
+    fake.runFor(2000);
     checkQuorum(nodes, 3);
     // Stop the leader again
     leader = nodes[Object.keys(nodes)[0]].leader;
@@ -116,7 +132,7 @@ async function testStartThenRemoveNode()
     nodes[leader].stop();
     delete nodes[leader];
     // Check that no quorum exists
-    await new Promise(ok => setTimeout(ok, 2000));
+    fake.runFor(2000);
     checkNoQuorum(nodes);
     // Clean up
     for (const id in nodes)
@@ -128,9 +144,10 @@ async function testStartThenRemoveNode()
 
 async function testAddNode()
 {
+    console.log('--------------------------------------------------------------------------------');
     console.log('testAddNode');
-    const nodes = newNodes(5);
-    await new Promise(ok => setTimeout(ok, 2000));
+    const nodes = newNodes(5, {}, cfg => cfg.initialTerm = 1000);
+    fake.runFor(2000);
     checkQuorum(nodes, 5);
     // Add node
     newNode(6, nodes);
@@ -138,7 +155,7 @@ async function testAddNode()
         nodes[i].setNodes([ 1, 2, 3, 4, 5, 6 ]);
     nodes[6].start();
     // Check quorum after 2000ms
-    await new Promise(ok => setTimeout(ok, 2000));
+    fake.runFor(2000);
     checkQuorum(nodes, 6);
     // Clean up
     for (const id in nodes)
@@ -148,10 +165,200 @@ async function testAddNode()
     console.log('testAddNode: OK');
 }
 
+async function testLeadershipExpiration()
+{
+    console.log('--------------------------------------------------------------------------------');
+    console.log('testLeadershipExpiration');
+    const partitions = {};
+    const nodes = newNodes(5, partitions, cfg => cfg.leadershipTimeout = 1500);
+    // Check that 5 nodes are in quorum after 2000ms
+    fake.runFor(2000);
+    checkQuorum(nodes, 5);
+    // Break network on the leader
+    let leader = nodes[1].leader;
+    console.log("["+fake.time+"] --> stopping the leader's ("+leader+") network");
+    for (let i = 1; i <= 5; i++)
+    {
+        partitions[i+'-'+leader] = true;
+        partitions[leader+'-'+i] = true;
+    }
+    // Check that the leader loses leadership after 2 * leadershipTimeout
+    fake.runFor(3000);
+    if (nodes[leader].state != TinyRaft.CANDIDATE)
+    {
+        throw new Error("leadership expiration doesn't work");
+    }
+    // Clean up
+    for (const id in nodes)
+    {
+        nodes[id].stop();
+    }
+    console.log('testLeadershipExpiration: OK');
+}
+
+async function testRestart()
+{
+    console.log('--------------------------------------------------------------------------------');
+    console.log('testRestart');
+    const nodes = newNodes(5, {}, cfg => cfg.initialTerm = 1000);
+    let leaderChanges = 0, prevLeader = null;
+    nodes[2].on('change', (st) =>
+    {
+        const leader = st.state == TinyRaft.CANDIDATE ? null : st.leader;
+        if (leader != prevLeader)
+        {
+            prevLeader = leader;
+            leaderChanges++;
+        }
+    });
+    // Check that 5 nodes are in quorum after 2000ms
+    fake.runFor(2000);
+    checkQuorum(nodes, 5);
+    if (leaderChanges >= 3)
+    {
+        throw new Error("leaderChanges = "+leaderChanges+" (expected < 3)");
+    }
+    // Stop a follower
+    let restarted = 1 + (prevLeader % 5);
+    if (restarted == 2)
+    {
+        restarted = 1 + (prevLeader + 1) % 5;
+    }
+    console.log("["+fake.time+"] --> stopping a follower (node "+restarted+")");
+    nodes[restarted].stop();
+    delete nodes[restarted];
+    // Wait 2000ms
+    fake.runFor(2000);
+    // Restart a follower
+    console.log("["+fake.time+"] --> restarting a follower (node "+restarted+")");
+    leaderChanges = 0;
+    newNode(restarted, nodes, {}, null);
+    nodes[restarted].start();
+    // Check quorum and the fact that the leader didn't change after 2000ms
+    fake.runFor(2000);
+    checkQuorum(nodes, 5);
+    if (leaderChanges > 0)
+    {
+        throw new Error("leader changed after restart of a follower");
+    }
+    // Clean up
+    for (const id in nodes)
+    {
+        nodes[id].stop();
+    }
+    console.log('testRestart: OK');
+}
+
+async function testChangeNodes()
+{
+    console.log('--------------------------------------------------------------------------------');
+    console.log('testChangeNodes');
+    console.log('['+fake.time+'] --> starting nodes 1-5');
+    const nodes = newNodes(5, {}, cfg => cfg.initialTerm = 1000);
+    // Check that 5 nodes are in quorum after 2000ms
+    fake.runFor(2000);
+    checkQuorum(nodes, 5);
+    // Stop node 4
+    console.log('['+fake.time+'] --> stopping node 4');
+    nodes[4].stop();
+    delete nodes[4];
+    // Wait 1000ms
+    fake.runFor(1000);
+    // Change nodes from 1 2 3 4 5 to 1 2 3 5 6
+    console.log('['+fake.time+'] --> starting node 6');
+    newNode(6, nodes);
+    nodes[6].start();
+    nodes[1].setNodes([ 1, 2, 3, 5, 6 ]);
+    nodes[2].setNodes([ 1, 2, 3, 5, 6 ]);
+    nodes[3].setNodes([ 1, 2, 3, 5, 6 ]);
+    nodes[5].setNodes([ 1, 2, 3, 5, 6 ]);
+    nodes[6].setNodes([ 1, 2, 3, 5, 6 ]);
+    // Check that 5 nodes are in quorum after 2000ms
+    fake.runFor(2000);
+    checkQuorum(nodes, 5);
+    // Clean up
+    for (const id in nodes)
+    {
+        if (nodes[id])
+            nodes[id].stop();
+    }
+    console.log('testChangeNodes: OK');
+}
+
+async function testLeaderPriority()
+{
+    console.log('--------------------------------------------------------------------------------');
+    console.log('testLeaderPriority');
+    console.log('['+fake.time+'] --> starting nodes 1-5');
+    const nodes = newNodes(5, {}, cfg => cfg.leaderPriority = cfg.nodeId+1);
+    // Check that 5 nodes are in quorum after 2000ms
+    fake.runFor(2000);
+    checkQuorum(nodes, 5);
+    if (nodes[1].leader != 5)
+    {
+        throw new Error('leader is not 5');
+    }
+    // Stop node 5
+    console.log('['+fake.time+'] --> stopping node 5');
+    nodes[5].stop();
+    delete nodes[5];
+    // Wait 2000ms and check that the leader is now 4
+    fake.runFor(2000);
+    checkQuorum(nodes, 4);
+    if (nodes[1].leader != 4)
+    {
+        throw new Error('leader is not 4');
+    }
+    // Stop node 4
+    console.log('['+fake.time+'] --> stopping node 4');
+    nodes[4].stop();
+    delete nodes[4];
+    // Wait 2000ms and check that the leader is now 3
+    fake.runFor(2000);
+    checkQuorum(nodes, 3);
+    if (nodes[1].leader != 3)
+    {
+        throw new Error('leader is not 3');
+    }
+    // Clean up
+    for (const id in nodes)
+    {
+        if (nodes[id])
+            nodes[id].stop();
+    }
+    console.log('testLeaderPriority: OK');
+}
+
+async function testPartition1_3()
+{
+    console.log('--------------------------------------------------------------------------------');
+    console.log('testPartition1_3');
+    const partitions = { '1-3': true, '3-1': true };
+    const nodes = newNodes(3, partitions, cfg => cfg.nodes = [ 1, 2, 3 ]);
+    // Check that 2 or 3 nodes are in quorum after 5000ms
+    // This situation should be fixed by "prevote protocol", but it breaks other things
+    fake.runFor(5000);
+    if (nodes[2].leader == 2)
+        checkQuorum(nodes, 3);
+    else
+        checkQuorum(nodes, 2);
+    // Clean up
+    for (const id in nodes)
+    {
+        nodes[id].stop();
+    }
+    console.log('testPartition1_3: OK');
+}
+
 async function run()
 {
     await testStartThenRemoveNode();
     await testAddNode();
+    await testLeadershipExpiration();
+    await testRestart();
+    await testChangeNodes();
+    await testLeaderPriority();
+    await testPartition1_3();
     process.exit(0);
 }