Connect Five

This is a variation on the Connect Four game. To win in this version connect five tiles in a vertical, hortizontal, accending or descending lines!

Overview

The game is implemented as a client-server solution. The Connect Five Server uses websockets technology to receive and publish events on three endpoints:

• A /topic/games/ topic that provides all the information related to games
• A specific game topic/topic/games/{gameId } that provides information related to a specific game
• A user queue /user/queue/game that provides user specific events

There are three modules making up the implementation:

• connect-five-events - Java Implementation of shared events
• connect-five-server - Java Implementation of the Connect Five Server
• connect-five-client - Java Implementation of the Connect Five Client

Assumptions

• Only two users connect at any one time. While the server and client have been designed to support multi game sessions, further work would be required to make this completely work.
• The algorithm to solve tile connects is very simple. A design is in place that allows that algorithm to be swapped with something more efficient. For example, there are other approaches to solving tile connects like the use of bitmasks, or graph traversal solutions.
• The server is a single instance only. The design allows for swapping the currentin memory implementation of the game data with an external data store for example, database or redis server.
• There is no security

Build

• The project uses Maven https://maven.apache.org/ to build and manage dependencies.
• The project build was tested with Maven 3.6.0 and Java 1.8.

To build: mvn clean install

To run the server:

• cd connect-five-server
• java -jar target/connect-five-server-0.0.1-SNAPSHOT.jar

To run a client:

• cd connect-five-client
• java -jar target/connect-five-client-0.0.1-SNAPSHOT.jar

Design

Websockets

The WebSocket protocol allows you to implement bidirectional communication between applications. In this case websockets are used between the client and server. HTTP is used for the initial handshake.

The WebSocket protocol is a low-level protocol. It defines how a stream of bytes is transformed into frames. In this implementation I am using Spring Boot implementation of websockets, and using the STOMP sub-protocol to control communication of the websocket frames.

The server can recieve messages over websocket channels from the client, and respond with messages. In the Connect Five implementation a GameEvent is sent and received over all channels, containing different "action" depending on the outcome. For example, when a player, wants to start a game, a GameEvent with an InitiateGameActionRequest action is sent to the server on the /topic/games/ topic. The server repiles with a GameOpenActionResponse action to the client. The client can decide what happens on each response, for example, in this case, the client waits for more players to join.

Game Setup Phase

• (1) Player Alice initiates a game on the client. An initiate request is sent to the server.
• (2) Player Bob decides to join a game on another client. A join request is sent to the server.
• (3) A Ready response is received over the general game channel. Each player is connected to a specific game channel that will receive that game events only.

Game Play Phase

• (1) The initiator always starts play. So in this case, Alice is offered a move. She makes a decision and a move request is sent to the server.
• (2) All game players receive a Board status updates from the server.
• (3) The other player is offered a move. This continues in round robin fashion.
• (4) If a player, for instance Bob, makes an invalid move, an Invalid response is recieved from the server.

Any of the players can decide to end the game at the time of their move.

Event Overview

Channel	Endpoint	Request	Response
General	/topic/games/	InitiateGameActionRequest	GameOpenActionResponse
		JoinGameActionRequest	ReadyGameActionResponse
		JoinGameActionRequest	UnavailableGameActionResponse
			GameDeletedActionResponse
Game Only	/topic/games/{gameId}		BoardStatusGameActionResponse
		CompletedGameActionRequest	GameDeletedActionResponse
User Only	/user/queue/game	MakeMoveGameActionRequest	CompletedMoveGameActionResponse
			InvalidGameActionResponse