Introduction

This project implements a game of three server and a client. The server accepts simultaneous games but each game can only be played by 2 players. The clients are designed to play automatically until the game finishes.

Technical architecture

This project follows a classic client-server architecture. The communication between the client and the server is done using websockets.

Both the server and the client are written using Java and Netty. Netty is a framework designed to build high performing network applications. Some of the reasons to choose netty:

• Nonblocking-IO support
• Netty Channels, a socket abstraction that enables the development of modular network applications that are easy to write without sacrificing performance or maintainability.
• Support for native file descriptor monitoring such Epoll and Kqueue
• A high performance buffer api that enables the use of Off-Heap Memory and Zero copy.
• A set of utilities to handle the conversion of network bytes into application objects and vice-versa.

This application is divided into 3 modules:

• Client
  • All the code the client needs to play
• Server
  • Contains the code for server
• Common
  • Contains all the code common to both the server and the client

The use of NonBlocking IO enables high performance at lower memory consumption. This implementation can handle tens of tens of thousands of clients at the same time with minimal memory and CPU usage.

Building and running

Requirements

• Modern Linux or OSX
• Java JDK 8

How to build

./gradlew test bootJar

How to run the client

# Change the gameId to connect to a different game
java -jar server/build/libs/client.jar --game.gameId=123

How to run the server

java -jar server/build/libs/server.jar

Client and server configuration

The following configuration options are available:

• client
  • game.endpoint
    • The server endpoint
  • game.gameId
    • Game the client wants to join
• server
  • server.port
    • the port server is listening on

The application can be configured using any of the methods provided by spring boot. https://docs.spring.io/spring-boot/docs/current/reference/html/boot-features-external-config.html

Testing and quality assurance

The test suite covers the most relevant parts of the code base. Some parts of the codebase such as the network connection boostrapping and configuratin don't benefit form unit testing and integration tests are used instead.

How to run the test suit

./gradlew test jacocoTestReport

Future improvements

• Handle misbehaved clients. The current implementation doesn't care if the message was delivered and doesn't deal with slow clients. A misbehaved client could cause the system to run out of memory
• Improve client unit tests
• Improve integration tests

Testing the game

1. start the server using: java -jar server/build/libs/server.jar

2. start client 1 using: java -jar server/build/libs/client.jar --game.gameId=123

3. start client 2 using : java -jar server/build/libs/client.jar --game.gameId=123

4. The console should output something similar to:

   pt.luissantos.gameofthree.client.Client  : Connecting to: ws://127.0.0.1:8080/websocket?game=123
   p.l.g.client.WebSocketClientHandler      : Connected!
   p.l.g.client.GameMessageHandler          : Starting game: 897
   p.l.g.client.GameMessageHandler          : Got: 299
   p.l.g.client.GameMessageHandler          : Playing: 100
   p.l.g.client.GameMessageHandler          : Got: 33
   p.l.g.client.GameMessageHandler          : Playing: 11
   p.l.g.client.GameMessageHandler          : Game is over: You win!