netcode.test.ts

import { equal } from 'assert';
import { FIRST_FRAME } from './Netcode';
import { NetcodeClient } from './NetcodeClient';
import { NetcodeServer } from './NetcodeServer';

type UserId = 'a' | 'b';
type Input = 'RUN' | null;

interface Entity {
  x: number;
  v: number;
  i: Input;
}

type State = Record<UserId, Entity>;

const initialState: State = {
  a: { x: -10, v: 3, i: null },
  b: { x: 10, v: -3, i: null },
};

function simulate(state: State): State {
  const entries = Object.entries(state).map(([id, entity]) => [
    id,
    {
      x: entity.x + entity.v,
      v: entity.v + (entity.i === 'RUN' ? 1 : 0),
    },
  ]);

  return Object.fromEntries(entries);
}

describe('Netcode state management', () => {
  it('should be identical after one frame', () => {
    const client = new NetcodeClient(simulate, initialState);
    const server = new NetcodeServer(simulate, initialState);

    client.runFrame();
    server.runFrame();

    equal(client.serialize(), server.serialize());
  });

  it('client should respect incoming state over its own', () => {
    const client = new NetcodeClient(simulate, {
      a: { x: 0, v: 0, i: null },
      b: { x: 0, v: 0, i: null },
    });
    const server = new NetcodeServer(simulate, initialState);

    client.reciveState(server.serialize());

    client.runFrame();
    server.runFrame();

    equal(client.serialize(), server.serialize());
  });

  it('client should rewrite history if server says it was different', () => {
    const client = new NetcodeClient(simulate, initialState);
    const server = new NetcodeServer(simulate, {
      ...initialState,
      a: { ...initialState.a, v: 0 },
    });

    client.runFrame();
    client.runFrame();

    client.reciveState(server.serialize());

    server.runFrame();
    server.runFrame();

    equal(client.serialize(), server.serialize());
  });

  it('client should rewrite history if a frame is altered', () => {
    const client = new NetcodeClient(simulate, initialState);
    const server = new NetcodeServer(simulate, {
      ...initialState,
      a: { ...initialState.a, i: 'RUN' },
    });

    client.runFrame();
    client.runFrame();

    client.alterFrame(FIRST_FRAME, (state) => ({
      ...state,
      a: { ...state.a, i: 'RUN' },
    }));

    server.runFrame();
    server.runFrame();

    equal(client.serialize(), server.serialize());
  });
});