synchronous mode for game master

This allows the local multiplayer mode to work without any
async / await, which simplifies testing. It also allows
using the vanilla JS client more easily without having
to worry about async logic.

Author: nicolodavis

src/client/client.js

@@ -185,8 +185,6 @@ class _ClientImpl {
         }
       }
 
-      this.subscribeCallback();
-
       return result;
     };
 
@@ -195,23 +193,40 @@ class _ClientImpl {
      * which keeps the authoritative version of the state.
      */
     const TransportMiddleware = store => next => action => {
-      const state = store.getState();
+      const baseState = store.getState();
       const result = next(action);
 
       if (action.clientOnly != true) {
-        this.transport.onAction(state, action);
+        this.transport.onAction(baseState, action);
       }
 
       return result;
     };
 
+    /**
+     * Middleware that intercepts actions and invokes the subscription callback.
+     */
+    const SubscriptionMiddleware = () => next => action => {
+      const result = next(action);
+      this.subscribeCallback();
+      return result;
+    };
+
     if (enhancer !== undefined) {
       enhancer = compose(
-        applyMiddleware(LogMiddleware, TransportMiddleware),
+        applyMiddleware(
+          SubscriptionMiddleware,
+          TransportMiddleware,
+          LogMiddleware
+        ),
         enhancer
       );
     } else {
-      enhancer = applyMiddleware(LogMiddleware, TransportMiddleware);
+      enhancer = applyMiddleware(
+        SubscriptionMiddleware,
+        TransportMiddleware,
+        LogMiddleware
+      );
     }
 
     this.store = createStore(this.reducer, initialState, enhancer);

src/client/client.test.js

@@ -148,20 +148,46 @@ describe('multiplayer', () => {
   });
 
   describe('local master', () => {
-    let client;
+    let client0;
+    let client1;
+    let spec;
 
     beforeAll(() => {
-      client = Client(
-        GetOpts({
-          game: Game({ moves: { A: () => {} } }),
-          multiplayer: { local: true },
-        })
-      );
-      client.connect();
+      spec = GetOpts({
+        game: Game({ moves: { A: (G, ctx) => ({ A: ctx.playerID }) } }),
+        multiplayer: { local: true },
+      });
+
+      client0 = Client({ ...spec, playerID: '0' });
+      client1 = Client({ ...spec, playerID: '1' });
+
+      client0.connect();
+      client1.connect();
     });
 
     test('correct transport used', () => {
-      expect(client.transport instanceof Local).toBe(true);
+      expect(client0.transport instanceof Local).toBe(true);
+      expect(client1.transport instanceof Local).toBe(true);
+    });
+
+    test('multiplayer interactions', () => {
+      expect(client0.getState().ctx.currentPlayer).toBe('0');
+      expect(client1.getState().ctx.currentPlayer).toBe('0');
+
+      client0.moves.A();
+
+      expect(client0.getState().G).toEqual({ A: '0' });
+      expect(client1.getState().G).toEqual({ A: '0' });
+
+      client0.events.endTurn();
+
+      expect(client0.getState().ctx.currentPlayer).toBe('1');
+      expect(client1.getState().ctx.currentPlayer).toBe('1');
+
+      client1.moves.A();
+
+      expect(client0.getState().G).toEqual({ A: '1' });
+      expect(client1.getState().G).toEqual({ A: '1' });
     });
   });
 

src/client/react.test.js

@@ -74,7 +74,7 @@ test('custom loading component', () => {
     game: Game({}),
     loading: Loading,
     board: TestBoard,
-    multiplayer: { local: true },
+    multiplayer: true,
   });
   const board = Enzyme.mount(<Board />);
   expect(board.html()).toContain('custom');

src/client/transport/local.js

@@ -31,7 +31,8 @@ export function LocalMaster(game) {
     }
   };
 
-  const master = new Master(game, new InMemory(), { send, sendAll });
+  const master = new Master(game, new InMemory(), { send, sendAll }, false);
+  master.executeSynchronously = true;
   master.connect = (gameID, playerID, callback) => {
     clientCallbacks[playerID] = callback;
   };
@@ -96,19 +97,14 @@ export class Local {
    * Called when an action that has to be relayed to the
    * game master is made.
    */
-  async onAction(state, action) {
-    await this.master.onUpdate(
-      action,
-      state._stateID,
-      this.gameID,
-      this.playerID
-    );
+  onAction(state, action) {
+    this.master.onUpdate(action, state._stateID, this.gameID, this.playerID);
   }
 
   /**
    * Connect to the server.
    */
-  async connect() {
+  connect() {
     this.master.connect(
       this.gameID,
       this.playerID,
@@ -121,7 +117,7 @@ export class Local {
         }
       }
     );
-    await this.master.onSync(this.gameID, this.playerID, this.numPlayers);
+    this.master.onSync(this.gameID, this.playerID, this.numPlayers);
   }
 
   /**
@@ -133,21 +129,21 @@ export class Local {
    * Updates the game id.
    * @param {string} id - The new game id.
    */
-  async updateGameID(id) {
+  updateGameID(id) {
     this.gameID = this.gameName + ':' + id;
     const action = ActionCreators.reset(null);
     this.store.dispatch(action);
-    await this.master.onSync(this.gameID, this.playerID, this.numPlayers);
+    this.master.onSync(this.gameID, this.playerID, this.numPlayers);
   }
 
   /**
    * Updates the player associated with this client.
    * @param {string} id - The new player id.
    */
-  async updatePlayerID(id) {
+  updatePlayerID(id) {
     this.playerID = id;
     const action = ActionCreators.reset(null);
     this.store.dispatch(action);
-    await this.master.onSync(this.gameID, this.playerID, this.numPlayers);
+    this.master.onSync(this.gameID, this.playerID, this.numPlayers);
   }
 }

src/master/master.js

@@ -11,6 +11,8 @@ import { MAKE_MOVE, GAME_EVENT } from '../core/action-types';
 import { createStore } from 'redux';
 import * as logging from '../core/logger';
 
+const GameMetadataKey = gameID => `${gameID}:metadata`;
+
 /**
  * Redact the log.
  *
@@ -53,6 +55,45 @@ export function redactLog(redactedMoves, log, playerID) {
   });
 }
 
+/**
+ * Verifies that the move came from a player with the
+ * appropriate credentials.
+ */
+export const isActionFromAuthenticPlayer = ({
+  action,
+  gameMetadata,
+  playerID,
+}) => {
+  if (!gameMetadata) {
+    return true;
+  }
+
+  if (!action.payload) {
+    return true;
+  }
+
+  const hasCredentials = Object.keys(gameMetadata.players).some(key => {
+    return !!(
+      gameMetadata.players[key] && gameMetadata.players[key].credentials
+    );
+  });
+  if (!hasCredentials) {
+    return true;
+  }
+
+  if (!action.payload.credentials) {
+    return false;
+  }
+
+  if (
+    action.payload.credentials !== gameMetadata.players[playerID].credentials
+  ) {
+    return false;
+  }
+
+  return true;
+};
+
 /**
  * Master
  *
@@ -61,14 +102,16 @@ export function redactLog(redactedMoves, log, playerID) {
  * storageAPI to communicate with the database.
  */
 export class Master {
-  constructor(game, storageAPI, transportAPI, isActionFromAuthenticPlayer) {
+  constructor(game, storageAPI, transportAPI, auth) {
     this.game = game;
     this.storageAPI = storageAPI;
     this.transportAPI = transportAPI;
-    this.isActionFromAuthenticPlayer = () => true;
+    this.auth = () => true;
 
-    if (isActionFromAuthenticPlayer !== undefined) {
-      this.isActionFromAuthenticPlayer = isActionFromAuthenticPlayer;
+    if (auth === true) {
+      this.auth = isActionFromAuthenticPlayer;
+    } else if (typeof auth === 'function') {
+      this.auth = auth;
     }
   }
 
@@ -78,8 +121,37 @@ export class Master {
    * along with a deltalog.
    */
   async onUpdate(action, stateID, gameID, playerID) {
+    let isActionAuthentic;
+
+    if (this.executeSynchronously) {
+      const gameMetadata = this.storageAPI.get(GameMetadataKey(gameID));
+      isActionAuthentic = this.auth({
+        action,
+        gameMetadata,
+        gameID,
+        playerID,
+      });
+    } else {
+      const gameMetadata = await this.storageAPI.get(GameMetadataKey(gameID));
+      isActionAuthentic = this.auth({
+        action,
+        gameMetadata,
+        gameID,
+        playerID,
+      });
+    }
+    if (!isActionAuthentic) {
+      return { error: 'unauthorized action' };
+    }
+
     const key = gameID;
-    let state = await this.storageAPI.get(key);
+
+    let state;
+    if (this.executeSynchronously) {
+      state = this.storageAPI.get(key);
+    } else {
+      state = await this.storageAPI.get(key);
+    }
 
     if (state === undefined) {
       logging.error(`game not found, gameID=[${key}]`);
@@ -92,16 +164,6 @@ export class Master {
     });
     const store = createStore(reducer, state);
 
-    const isActionAuthentic = await this.isActionFromAuthenticPlayer({
-      action,
-      db: this.storageAPI,
-      gameID,
-      playerID,
-    });
-    if (!isActionAuthentic) {
-      return { error: 'unauthorized action' };
-    }
-
     // Check whether the player is allowed to make the move.
     if (
       action.type == MAKE_MOVE &&
@@ -162,7 +224,11 @@ export class Master {
     log = [...log, ...state.deltalog];
     const stateWithLog = { ...state, log };
 
-    await this.storageAPI.set(key, stateWithLog);
+    if (this.executeSynchronously) {
+      this.storageAPI.set(key, stateWithLog);
+    } else {
+      await this.storageAPI.set(key, stateWithLog);
+    }
   }
 
   /**
@@ -172,14 +238,26 @@ export class Master {
   async onSync(gameID, playerID, numPlayers) {
     const key = gameID;
 
-    let state = await this.storageAPI.get(key);
+    let state;
+
+    if (this.executeSynchronously) {
+      state = this.storageAPI.get(key);
+    } else {
+      state = await this.storageAPI.get(key);
+    }
 
     // If the game doesn't exist, then create one on demand.
     // TODO: Move this out of the sync call.
     if (state === undefined) {
       state = InitializeGame({ game: this.game, numPlayers });
-      await this.storageAPI.set(key, state);
-      state = await this.storageAPI.get(key);
+
+      if (this.executeSynchronously) {
+        this.storageAPI.set(key, state);
+        state = this.storageAPI.get(key);
+      } else {
+        await this.storageAPI.set(key, state);
+        state = await this.storageAPI.get(key);
+      }
     }
 
     const filteredState = {