fix(reconnect): preserve game state across disconnects

src/Client.ts

@@ -101,6 +101,14 @@ class Client {
 	setSkips = (skips: number) => {
 		this.skips = skips
 	}
+
+	/** Adopt the connection from another Client (used on reconnect) */
+	replaceConnection = (other: Client) => {
+		this.address = other.address
+		this.sendAction = other.sendAction
+		this.closeConnection = other.closeConnection
+		this.reconnectToken = other.reconnectToken
+	}
 }
 
 export default Client

src/Lobby.ts

@@ -32,7 +32,7 @@ export const getEnemy = (client: Client): [Lobby | null, Client | null] => {
 const RECONNECT_GRACE_PERIOD = 60000;
 
 interface DisconnectedSlot {
-	reconnectToken: string;
+	client: Client;
 	role: 'host' | 'guest';
 	timer: ReturnType<typeof setTimeout>;
 }
@@ -130,7 +130,7 @@ class Lobby {
 		console.log(`Player ${client.id} disconnected from lobby ${this.code}, reserving slot for ${RECONNECT_GRACE_PERIOD / 1000}s`)
 
 		this.disconnectedSlot = {
-			reconnectToken: client.reconnectToken,
+			client,
 			role,
 			timer: setTimeout(() => {
 				// Grace period expired, do a full leave
@@ -152,40 +152,55 @@ class Lobby {
 		enemy?.sendAction({ action: "enemyDisconnected" });
 	};
 
-	/** Reconnecting client reclaims their slot */
-	rejoin = (newClient: Client, reconnectToken: string): boolean => {
-		if (!this.disconnectedSlot || this.disconnectedSlot.reconnectToken !== reconnectToken) {
-			return false;
+	/** Reconnecting client reclaims their slot.
+	 *  Returns the restored Client (with all game state intact) on success, or null on failure.
+	 *  The caller MUST use the returned client for all future messages on this socket. */
+	rejoin = (newClient: Client, reconnectToken: string): Client | null => {
+		if (!this.disconnectedSlot || this.disconnectedSlot.client.reconnectToken !== reconnectToken) {
+			return null;
 		}
 
-		const { role, timer } = this.disconnectedSlot;
+		const { client: oldClient, role, timer } = this.disconnectedSlot;
 		clearTimeout(timer);
 		this.disconnectedSlot = null;
 
-		// Place the new client in the correct slot
+		// Swap the new socket/connection onto the old client, preserving all game state
+		oldClient.replaceConnection(newClient);
+
+		// Place the old client back in the correct slot
 		if (role === 'host') {
-			this.host = newClient;
+			this.host = oldClient;
 		} else {
-			this.guest = newClient;
+			this.guest = oldClient;
 		}
 
-		newClient.setLobby(this);
-		this.handyAllowMPExtension.set(newClient.id, false);
+		oldClient.setLobby(this);
+		this.handyAllowMPExtension.set(oldClient.id, false);
 
 		// Send rejoin confirmation with new reconnect token
-		newClient.sendAction({
+		oldClient.sendAction({
 			action: "rejoinedLobby",
 			code: this.code,
 			type: this.gameMode,
-			reconnectToken: newClient.reconnectToken,
+			reconnectToken: oldClient.reconnectToken,
 		});
 
 		// Notify the other player
 		const enemy = role === 'host' ? this.guest : this.host;
 		enemy?.sendAction({ action: "enemyReconnected" });
 
+		// Re-sync game state so both sides have correct values
+		oldClient.sendAction({ action: "playerInfo", lives: oldClient.lives });
+		enemy?.sendAction({
+			action: "enemyInfo",
+			handsLeft: oldClient.handsLeft,
+			score: oldClient.score.toString(),
+			skips: oldClient.skips,
+			lives: oldClient.lives,
+		});
+
 		this.broadcastLobbyInfo();
-		return true;
+		return oldClient;
 	};
 
 	join = (client: Client) => {

src/actionHandlers.ts

@@ -84,7 +84,7 @@ const disconnectFromLobbyAction = (client: Client) => {
 const rejoinLobbyAction = (
 	{ code, reconnectToken }: ActionHandlerArgs<ActionRejoinLobby>,
 	client: Client,
-) => {
+): Client | undefined => {
 	const lobby = Lobby.get(code);
 	if (!lobby) {
 		client.sendAction({
@@ -94,12 +94,15 @@ const rejoinLobbyAction = (
 		return;
 	}
 
-	if (!lobby.rejoin(client, reconnectToken)) {
+	const restoredClient = lobby.rejoin(client, reconnectToken);
+	if (!restoredClient) {
 		client.sendAction({
 			action: "error",
 			message: "Could not rejoin lobby. Token invalid or slot expired.",
 		});
+		return;
 	}
+	return restoredClient;
 };
 
 const lobbyInfoAction = (client: Client) => {

src/main.ts

@@ -122,7 +122,7 @@ const server = createServer((socket) => {
 	// Enable OS-level TCP keepalive as secondary dead connection detection
 	socket.setKeepAlive(true, 10000)
 
-	const client = new Client(socket.address(), sendActionToSocket(socket), socket.end)
+	let client = new Client(socket.address(), sendActionToSocket(socket), socket.end)
 	client.sendAction({ action: 'connected' })
 	client.sendAction({ action: 'version' })
 
@@ -205,12 +205,14 @@ const server = createServer((socket) => {
 							client,
 						)
 						break
-					case 'rejoinLobby':
-						actionHandlers.rejoinLobby(
+					case 'rejoinLobby': {
+						const restored = actionHandlers.rejoinLobby(
 							actionArgs as ActionHandlerArgs<ActionRejoinLobby>,
 							client,
 						)
+						if (restored) client = restored
 						break
+					}
 					case 'lobbyInfo':
 						actionHandlers.lobbyInfo(client)
 						break