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Syncer Deploy
306
packages/engine/src/server.ts
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306
packages/engine/src/server.ts
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import type {
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ClientStateContext,
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ClientStateReport,
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GameDefinition,
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InputContext,
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InputPacket,
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PlayerId,
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StateSnapshot,
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ValidationResult,
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} from "./types.js";
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export interface ServerEngineOptions {
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historyTicks?: number;
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maxPastTicks?: number;
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maxFutureTicks?: number;
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}
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export interface InputDecision {
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accepted: boolean;
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reason?: "unknown-player" | "duplicate" | "invalid" | "past" | "future";
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}
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export interface Acknowledgement {
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playerId: PlayerId;
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sequence: number;
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}
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export interface ServerStepResult {
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tick: number;
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acknowledgements: Acknowledgement[];
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validations: ValidationResult[];
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snapshotDue: boolean;
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}
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interface QueuedInput<Input> {
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playerId: PlayerId;
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packet: InputPacket<Input>;
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}
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interface QueuedReport<State> {
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playerId: PlayerId;
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report: ClientStateReport<State>;
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}
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export class AuthoritativeEngine<State, Input> {
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readonly game: GameDefinition<State, Input>;
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private readonly historyTicks: number;
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private readonly maxPastTicks: number;
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private readonly maxFutureTicks: number;
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private readonly snapshotEveryTicks: number;
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private readonly players = new Set<PlayerId>();
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private readonly lastReceivedSequence = new Map<PlayerId, number>();
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private readonly acknowledgedSequence = new Map<PlayerId, number>();
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private readonly history = new Map<number, State>();
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private queuedInputs: QueuedInput<Input>[] = [];
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private queuedReports: QueuedReport<State>[] = [];
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private state: State;
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private currentTick = 0;
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constructor(
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game: GameDefinition<State, Input>,
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options: ServerEngineOptions = {},
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) {
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this.game = game;
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this.historyTicks = options.historyTicks ?? game.tickRateHz * 2;
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this.maxPastTicks = options.maxPastTicks ?? 2;
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this.maxFutureTicks = options.maxFutureTicks ?? game.tickRateHz;
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this.snapshotEveryTicks = game.tickRateHz / game.snapshotRateHz;
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this.state = game.createInitialState();
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this.storeHistory();
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}
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get tick(): number {
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return this.currentTick;
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}
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get currentState(): Readonly<State> {
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return this.state;
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}
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addPlayer(playerId: PlayerId): void {
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if (this.players.has(playerId)) {
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return;
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}
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this.players.add(playerId);
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this.game.addPlayer?.(this.state, { playerId, tick: this.currentTick });
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this.assertValidState();
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this.storeHistory();
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}
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removePlayer(playerId: PlayerId): void {
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if (!this.players.delete(playerId)) {
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return;
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}
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this.game.removePlayer?.(this.state, {
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playerId,
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tick: this.currentTick,
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});
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this.lastReceivedSequence.delete(playerId);
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this.acknowledgedSequence.delete(playerId);
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this.queuedInputs = this.queuedInputs.filter(
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(queued) => queued.playerId !== playerId,
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);
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this.queuedReports = this.queuedReports.filter(
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(queued) => queued.playerId !== playerId,
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);
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this.assertValidState();
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this.storeHistory();
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}
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submitInput(playerId: PlayerId, packet: InputPacket<Input>): InputDecision {
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if (!this.players.has(playerId)) {
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return { accepted: false, reason: "unknown-player" };
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}
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const previousSequence = this.lastReceivedSequence.get(playerId) ?? 0;
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if (packet.sequence <= previousSequence) {
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return { accepted: false, reason: "duplicate" };
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}
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if (packet.targetTick < this.currentTick - this.maxPastTicks) {
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return { accepted: false, reason: "past" };
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}
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if (packet.targetTick > this.currentTick + this.maxFutureTicks) {
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return { accepted: false, reason: "future" };
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}
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const context = this.inputContext(playerId, packet);
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if (!this.game.validateInput(packet.input, context)) {
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return { accepted: false, reason: "invalid" };
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}
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this.lastReceivedSequence.set(playerId, packet.sequence);
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this.queuedInputs.push({ playerId, packet });
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return { accepted: true };
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}
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submitStateReport(
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playerId: PlayerId,
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report: ClientStateReport<State>,
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): ValidationResult | null {
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if (report.tick > this.currentTick + this.maxFutureTicks) {
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return {
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playerId,
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tick: report.tick,
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valid: false,
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reason: "too-far-ahead",
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};
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}
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if (report.tick > this.currentTick) {
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this.queuedReports = this.queuedReports.filter(
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(queued) => queued.playerId !== playerId,
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);
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this.queuedReports.push({ playerId, report });
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return null;
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}
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return this.validateReport(playerId, report);
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}
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step(): ServerStepResult {
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this.currentTick += 1;
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const deltaSeconds = 1 / this.game.tickRateHz;
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const acknowledgementByPlayer = new Map<PlayerId, number>();
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const dueInputs: QueuedInput<Input>[] = [];
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const futureInputs: QueuedInput<Input>[] = [];
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for (const queued of this.queuedInputs) {
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(queued.packet.targetTick <= this.currentTick
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? dueInputs
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: futureInputs
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).push(queued);
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}
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this.queuedInputs = futureInputs;
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dueInputs.sort(
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(left, right) =>
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left.packet.targetTick - right.packet.targetTick ||
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left.playerId - right.playerId ||
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left.packet.sequence - right.packet.sequence,
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);
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for (const queued of dueInputs) {
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const { playerId, packet } = queued;
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this.game.applyInput(
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this.state,
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packet.input,
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this.inputContext(playerId, packet),
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);
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const previousAck = this.acknowledgedSequence.get(playerId) ?? 0;
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if (packet.sequence > previousAck) {
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this.acknowledgedSequence.set(playerId, packet.sequence);
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acknowledgementByPlayer.set(playerId, packet.sequence);
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}
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}
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this.game.step(this.state, {
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tick: this.currentTick,
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deltaSeconds,
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});
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this.assertValidState();
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this.storeHistory();
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const validations: ValidationResult[] = [];
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const futureReports: QueuedReport<State>[] = [];
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for (const queued of this.queuedReports) {
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if (queued.report.tick <= this.currentTick) {
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validations.push(
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this.validateReport(queued.playerId, queued.report),
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);
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} else {
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futureReports.push(queued);
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}
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}
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this.queuedReports = futureReports;
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return {
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tick: this.currentTick,
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acknowledgements: [...acknowledgementByPlayer].map(
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([playerId, sequence]) => ({ playerId, sequence }),
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),
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validations,
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snapshotDue: this.currentTick % this.snapshotEveryTicks === 0,
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};
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}
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createSnapshot(serverTime: number): StateSnapshot<State> {
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return {
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tick: this.currentTick,
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serverTime,
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state: this.game.cloneState(this.state),
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};
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}
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private inputContext(
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playerId: PlayerId,
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packet: InputPacket<Input>,
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): InputContext {
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return {
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playerId,
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sequence: packet.sequence,
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targetTick: packet.targetTick,
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observedTick: packet.observedTick ?? packet.targetTick,
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tick: this.currentTick,
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deltaSeconds: 1 / this.game.tickRateHz,
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};
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}
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private validateReport(
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playerId: PlayerId,
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report: ClientStateReport<State>,
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): ValidationResult {
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const authoritative = this.history.get(report.tick);
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if (!authoritative) {
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return {
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playerId,
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tick: report.tick,
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valid: false,
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reason: "outside-history",
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};
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}
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const context: ClientStateContext = { playerId, tick: report.tick };
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const valid = this.game.validateClientState
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? this.game.validateClientState(authoritative, report.state, context)
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: (this.game.validateState?.(report.state, {
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tick: report.tick,
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deltaSeconds: 1 / this.game.tickRateHz,
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}) ?? true);
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return {
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playerId,
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tick: report.tick,
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valid,
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...(valid ? {} : { reason: "mismatch" as const }),
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};
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}
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private assertValidState(): void {
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if (
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this.game.validateState &&
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!this.game.validateState(this.state, {
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tick: this.currentTick,
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deltaSeconds: 1 / this.game.tickRateHz,
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})
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) {
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throw new Error(`Game produced invalid state at tick ${this.currentTick}`);
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}
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}
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private storeHistory(): void {
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this.history.set(this.currentTick, this.game.cloneState(this.state));
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const oldestTick = this.currentTick - this.historyTicks;
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for (const tick of this.history.keys()) {
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if (tick < oldestTick) {
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this.history.delete(tick);
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}
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}
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}
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}
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