game-state-sync

Tools for keeping clients in sync with server game state

Installing

npm install game-state-sync

Example usage

In addition to gss.reliable, which is used in the examples, there are also gss.unreliable, gss.reliableDiff, and gss.unreliableDiff.

The unreliable variants can deal with data sent from one side doesn't reach the other side, or arrived in the wrong order (think UDP), while the reliable variants require that each sent piece of data from server reaches the client in the right order and vice versa (think TCP).

The Diff-suffixed variants sends differential updates as opposed to the whole state on every state publish. The Server part takes a single function diffStates(newState, oldState) that returns the difference between two states, while the Client part takes a single function applyDiff(oldState, diff) which returns the new state by using the old state and the difference returned from diffStates. Essentially, applyDiff(oldState, diffStates(newState, oldState)) should equal newState.

Same process

var gss = require('game-state-sync');

var server = new gss.reliable.Server();
var client = new gss.reliable.Client();

// Link server and client together.
// 'data' is JSON-serializable (provided the published state also is)
server.on('sendData', (data) => {
    client.emit('data', data);
});

client.on('sendData', (data) => {
    server.emit('data', data);
});

// Start publishing
client.on('newState', (state) => {
    console.log(state); // --> { number: 42 }
});

server.publish({ number: 42 });

TCP

Server

var net = require('net');
var ndjson = require('ndjson');
var gss = require('game-state-sync');

net.createServer((socket) => {
    // Set up streams
    var stringify = ndjson.stringify();
    var parse = ndjson.parse();

    stringify.pipe(socket).pipe(parse);

    // Create and link up Server instance
    var server = new gss.reliable.Server();

    server.on('sendData', (data) => {
        stringify.write(data);
    });
    parse.on('data', (data) => {
        server.emit('data', data);
    });

    // Publish some state to this client
    var counter = 1;
    setInterval(() => {
        server.publish({ number: counter++ });
    }, 1000);
})
.listen(22000)

Client

var net = require('net');
var ndjson = require('ndjson');
var gss = require('game-state-sync');

// Set up streams
var stringify = ndjson.stringify();
var parse = ndjson.parse();
var socket = net.connect(22000, 'localhost');

stringify.pipe(socket).pipe(parse);

// Create and link up Client instance
var client = new gss.reliable.Client();

client.on('sendData', (data) => {
    stringify.write(data);
});
parse.on('data', (data) => {
    client.emit('data', data);
});

// Receive states from server
client.on('newState', (state) => {
    console.log(state);
    // --> { number: [num] }, where [num] starts at 1 and increases by 1
});