From e96fbc27ba19cdbc9e0f38737cd1464f9cd0b184 Mon Sep 17 00:00:00 2001
From: Kenneth Allen <kenneth@mostly.me>
Date: Fri, 15 Oct 2021 19:00:18 +1100
Subject: [PATCH] Add client ACK

---
 packages/ketchup-client/index.ts              | 49 +++++++++++++++++--
 packages/ketchup-common/index.ts              | 13 ++++-
 packages/ketchup-server/index.ts              | 16 +++---
 .../wonders-client/src/components/App/App.tsx |  9 ++--
 4 files changed, 68 insertions(+), 19 deletions(-)

diff --git a/packages/ketchup-client/index.ts b/packages/ketchup-client/index.ts
index 9cd6d44..213a0dd 100644
--- a/packages/ketchup-client/index.ts
+++ b/packages/ketchup-client/index.ts
@@ -1,5 +1,5 @@
 import { ExponentialBackoff, Websocket, WebsocketBuilder } from 'websocket-ts'
-import { ActionClientMessage, ActionServerMessage, ConfirmServerMessage, HandshakeClientMessage, HandshakeServerMessage, ServerMessage, KetchupSynced } from 'ketchup-common'
+import { ActionClientMessage, ActionServerMessage, ConfirmServerMessage, HandshakeClientMessage, HandshakeServerMessage, ServerMessage, KetchupSynced, HeartbeatClientMessage } from 'ketchup-common'
 import EventEmitter from 'events'
 
 export default class KetchupClient<State, Action> extends EventEmitter {
@@ -7,11 +7,13 @@ export default class KetchupClient<State, Action> extends EventEmitter {
   synced?: KetchupSynced<State, Action>
   clientId?: number
   lastTimestamp?: number
+  scheduledAck?: NodeJS.Timeout
 
   constructor(
     url: string,
     readonly reducer: (state: State, action: Action) => State,
-    private readonly timeSource = Date.now
+    private readonly timeSource = Date.now,
+    private readonly ackDebounce = 5000,
   ) {
     super()
     this.ws = new WebsocketBuilder(url)
@@ -19,6 +21,7 @@ export default class KetchupClient<State, Action> extends EventEmitter {
         this.synced = undefined
         this.clientId = undefined
         this.lastTimestamp = undefined
+        this.cancelAck()
       })
       .onOpen(ws => {
         ws.send(JSON.stringify({
@@ -41,16 +44,19 @@ export default class KetchupClient<State, Action> extends EventEmitter {
         this.synced = new KetchupSynced(hMsg.confState, hMsg.confBefore, this.reducer, hMsg.unconfActions)
         this.synced.on('projection', proj => this.emit('projection', proj))
         this.emit('projection', this.synced.projState)
+        this.considerAck()
         break
 
       case 'action':
         this.synced!.tryProcess(msg as ActionServerMessage<Action>)
+        this.considerAck()
         break
 
       case 'confirm':
         this.synced!.confirmBefore((msg as ConfirmServerMessage).confBefore)
+        this.considerAck()
         break
-      
+
       default:
         throw new Error(`Unknown message from server: ${msg}`)
     }
@@ -63,7 +69,8 @@ export default class KetchupClient<State, Action> extends EventEmitter {
       timestamp = this.lastTimestamp + 1
     }
 
-    if (this.synced?.tryProcess({ timestamp, action, clientId: this.clientId! })) {
+    if (this.synced!.tryProcess({ timestamp, action, clientId: this.clientId! })) {
+      this.cancelAck()
       this.lastTimestamp = timestamp
       this.ws.send(JSON.stringify({
         message: 'action',
@@ -72,4 +79,38 @@ export default class KetchupClient<State, Action> extends EventEmitter {
       } as ActionClientMessage<Action>))
     }
   }
+
+  considerAck() {
+    if (this.scheduledAck) {
+      return
+    }
+
+    let oldestUnconfTimestamp = this.synced?.oldestUnconfTimestamp
+    if (oldestUnconfTimestamp !== undefined && this.lastTimestamp !== undefined) {
+      let behind = oldestUnconfTimestamp - this.lastTimestamp
+      if (behind > this.ackDebounce) { // Way behind, ACK now
+        this.sendAck()
+      } else if (behind >= 0) { // Somewhat behind, ACK soon if we don't send an action
+        this.scheduledAck = setTimeout(
+          () => { this.sendAck(); this.scheduledAck = undefined },
+          this.ackDebounce - behind,
+        )
+      }
+    }
+  }
+
+  sendAck() {
+    this.lastTimestamp = this.timeSource()
+    this.ws.send(JSON.stringify({
+      message: 'heartbeat',
+      timestamp: this.lastTimestamp,
+    } as HeartbeatClientMessage))
+  }
+
+  cancelAck() {
+    if (this.scheduledAck) {
+      clearTimeout(this.scheduledAck)
+      this.scheduledAck = undefined
+    }
+  }
 }
diff --git a/packages/ketchup-common/index.ts b/packages/ketchup-common/index.ts
index c2e5b71..df6e857 100644
--- a/packages/ketchup-common/index.ts
+++ b/packages/ketchup-common/index.ts
@@ -88,7 +88,7 @@ export class KetchupSynced<State, Action> extends EventEmitter {
     while (lo < hi) {
       const mid = Math.floor((lo + hi) / 2)
       const comp = compareTimed(x, this.projs[mid])
-      if (comp === 0 ) {
+      if (comp === 0) {
         return { idx: mid, exact: true }
       } else if (comp > 0) {
         lo = mid + 1
@@ -98,6 +98,10 @@ export class KetchupSynced<State, Action> extends EventEmitter {
     }
     return { idx: lo, exact: false }
   }
+
+  get oldestUnconfTimestamp() {
+    return this.projs?.[0]?.timestamp
+  }
 }
 
 export interface ActionServerMessage<Action> extends UnconfAction<Action> {
@@ -128,6 +132,11 @@ export interface HandshakeClientMessage {
   message: 'handshake'
   timestamp: number
 }
+export interface HeartbeatClientMessage {
+  message: 'heartbeat'
+  timestamp: number
+}
 export type ClientMessage<State, Action> =
   ActionClientMessage<Action> |
-  HandshakeClientMessage
+  HandshakeClientMessage |
+  HeartbeatClientMessage
diff --git a/packages/ketchup-server/index.ts b/packages/ketchup-server/index.ts
index b164b11..5f9f16b 100644
--- a/packages/ketchup-server/index.ts
+++ b/packages/ketchup-server/index.ts
@@ -1,6 +1,6 @@
 import WebSocket from 'ws'
 import min from 'lodash/min'
-import { ActionClientMessage, KetchupSynced as KetchupSynced, ActionServerMessage, HandshakeServerMessage, ConfirmServerMessage, ClientMessage, HandshakeClientMessage } from 'ketchup-common'
+import { ActionClientMessage, KetchupSynced as KetchupSynced, ActionServerMessage, HandshakeServerMessage, ConfirmServerMessage, ClientMessage, HandshakeClientMessage, HeartbeatClientMessage } from 'ketchup-common'
 
 interface RemoteClient {
   syncedAt?: number
@@ -15,11 +15,11 @@ export default class KetchupServer<State, Action> {
 
   constructor(
     initState: State,
-    reducer: (state: State, action: Action) => State, 
+    reducer: (state: State, action: Action) => State,
   ) {
     this.synced = new KetchupSynced<State, Action>(
-      initState, 
-      Date.now() - 1000, // TODO: Handle clients joining with clocks running significantly behind
+      initState,
+      Date.now() - (1000 * 60 * 60 * 24), // TODO: Handle clients joining with clocks running significantly behind
       reducer,
     )
   }
@@ -55,6 +55,11 @@ export default class KetchupServer<State, Action> {
         }
         break
 
+      case 'heartbeat':
+        client.syncedAt = (msg as HeartbeatClientMessage).timestamp
+        this.considerConfirm()
+        break
+
       default:
         throw new Error(`Invalid message from client: ${JSON.stringify(msg)}`)
     }
@@ -93,7 +98,6 @@ export default class KetchupServer<State, Action> {
   private considerConfirm() {
     const oldestSync = min([...this.clients.values()].map(c => c.syncedAt))
     if (oldestSync !== undefined && this.synced.confirmBefore(oldestSync) > 0) {
-      console.log('Confirming before', oldestSync)
       const msg = JSON.stringify({
         message: 'confirm',
         confBefore: this.synced.confBefore,
@@ -101,8 +105,6 @@ export default class KetchupServer<State, Action> {
       for (const client of this.clients.values()) {
         client.ws.send(msg)
       }
-    } else {
-      console.log('Not confirming before', oldestSync)
     }
   }
 }
diff --git a/packages/wonders-client/src/components/App/App.tsx b/packages/wonders-client/src/components/App/App.tsx
index f082b3c..8c82593 100644
--- a/packages/wonders-client/src/components/App/App.tsx
+++ b/packages/wonders-client/src/components/App/App.tsx
@@ -1,4 +1,4 @@
-import { useEffect, useState } from 'react';
+import { useState } from 'react';
 import useKetchup from 'ketchup-react'
 import { addPlayerAction, reducer, removePlayerAction, resetAction } from 'wonders-common'
 import './App.css';
@@ -10,9 +10,6 @@ import Row from 'react-bootstrap/Row'
 
 export default function App() {
   const [state, dispatch] = useKetchup('ws://localhost:4000', reducer)
-  useEffect(() => {
-    console.debug('State', state)
-  }, [state])
 
   const [user, setUser] = useState<string>()
   function selectUser(name?: string) {
@@ -29,10 +26,10 @@ export default function App() {
   }
 
   return <Container fluid>
-    <UserSelector user={user} selectUser={selectUser} removeUser={removeUser} users={state?.players.map(p => p.name) ?? []} locked={state !== undefined && state.stage !== 'starting'}/>
+    <UserSelector user={user} selectUser={selectUser} removeUser={removeUser} users={state?.players.map(p => p.name) ?? []} locked={state !== undefined && state.stage !== 'starting'} />
     {state
       ? <>
-        <Game state={state} dispatch={dispatch} playerName={user}/>
+        <Game state={state} dispatch={dispatch} playerName={user} />
         <button onClick={() => window.confirm('Reset game?') && dispatch(resetAction())}> Reset</button>
       </>
       : <Row>Loading...</Row>