waffle/src/gateway/index.ts

import { Server } from "node:http";
import { performance } from "node:perf_hooks";
import { WebSocketServer, WebSocket } from "ws";
import { decodeTokenOrNull, getPublicUserObject } from "../auth";
import { query } from "../database";
import { gatewayErrors } from "../errors";
import { GatewayPayload } from "../types/gatewaypayload";
import { GatewayPayloadType } from "./gatewaypayloadtype";

const GATEWAY_BATCH_INTERVAL = 50000;
const GATEWAY_PING_INTERVAL = 40000;
const MAX_CLIENT_MESSAGES_PER_BATCH = 6; // TODO: how well does this work for weak connections?
const MAX_GATEWAY_SESSIONS_PER_USER = 5;

// mapping between a dispatch id and a websocket client
const dispatchChannels = new Map<string, Set<WebSocket>>();

// mapping between a user id and the websocket sessions it has
const sessionsByUserId = new Map<number, Set<WebSocket>>();

function clientSubscribe(ws: WebSocket, dispatchChannel: string) {
    ws.state.dispatchChannels.add(dispatchChannel);
    if (!dispatchChannels.get(dispatchChannel)) {
        dispatchChannels.set(dispatchChannel, new Set());
    }

    dispatchChannels.get(dispatchChannel)?.add(ws);
}

function clientUnsubscribe(ws: WebSocket, dispatchChannel: string) {
    if (!ws.state) return;

    ws.state.dispatchChannels.delete(dispatchChannel);

    const set = dispatchChannels.get(dispatchChannel);
    if (!set) return;

    set.delete(ws);
    if (set.size < 1) {
        dispatchChannels.delete(dispatchChannel);
    }
}

export function dispatchChannelSubscribe(target: string, dispatchChannel: string) {
    const set = dispatchChannels.get(target);
    if (!set) return;

    set.forEach(c => {
        clientSubscribe(c, dispatchChannel);
    });
}

function clientUnsubscribeAll(ws: WebSocket) {
    if (!ws.state) return;

    ws.state.dispatchChannels.forEach(e => {
        const set = dispatchChannels.get(e);
        if (!set) return;

        set.delete(ws);
        if (set && set.size < 1) {
            dispatchChannels.delete(e);
        }
    });

    ws.state.dispatchChannels = new Set();
}

export function dispatch(channel: string, message: GatewayPayload) {
    const members = dispatchChannels.get(channel);
    if (!members) return;
        
    members.forEach(e => {
        e.send(JSON.stringify(message));
    });
}

function closeWithError(ws: WebSocket, { code, message }: { code: number, message: string }) {
    return ws.close(code, message);
}

function closeWithBadPayload(ws: WebSocket, hint: string) {
    return ws.close(gatewayErrors.BAD_PAYLOAD.code, `${gatewayErrors.BAD_PAYLOAD.message}: ${hint}`);
}

function parseJsonOrNull(payload: string): any {
    try {
        return JSON.parse(payload);
    } catch (e) {
        return null;
    }
}

// The function below ensures `payload` is of the GatewayPayload
// interface payload. If it does not match, null is returned.
function ensureFormattedGatewayPayload(payload: any): GatewayPayload | null {
    if (!payload) {
        return null;
    }

    let foundT = false;
    let foundD = false;
    for (const [k, v] of Object.entries(payload)) {
        if (k === "t" && typeof v === "number") {
            foundT = true;
        } else if (k === "d") {
            foundD = true;
        } else {
            return null;
        }
    }
    if (!foundT || !foundD) {
        return null;
    }
    const asPayload = payload as GatewayPayload;
    return asPayload;
}

function sendPayload(ws: WebSocket, payload: GatewayPayload) {
    ws.send(JSON.stringify(payload));
}

export default function(server: Server) {
    const wss = new WebSocketServer({ server });

    const batchInterval = setInterval(() => {
        wss.clients.forEach((e) => {
            const now = performance.now();
            if (e.state && (now - e.state.lastAliveCheck) >= GATEWAY_PING_INTERVAL) {
                if (!e.state.ready) {
                    return closeWithError(e, gatewayErrors.AUTHENTICATION_TIMEOUT);
                }
                if (!e.state.alive) {
                    return closeWithError(e, gatewayErrors.NO_PING);
                }
                e.state.messagesSinceLastCheck = 0;
            }
        });
    }, GATEWAY_BATCH_INTERVAL);

    wss.on("close", () => {
        console.warn("gateway: websocket server closed");
        console.warn("gateway: clearing batch interval due to websocket server close");
        clearInterval(batchInterval);
    });

    wss.on("connection", (ws) => {
        ws.state = {
            user: undefined,
            alive: false,
            ready: false,
            lastAliveCheck: performance.now(),
            dispatchChannels: new Set(),
            messagesSinceLastCheck: 0
        };

        sendPayload(ws, {
            t: GatewayPayloadType.Hello,
            d: {
                pingInterval: GATEWAY_PING_INTERVAL
            }
        });

        ws.on("close", () => {
            clientUnsubscribeAll(ws);
            if (ws.state.user && ws.state.user.id) {
                const sessions = sessionsByUserId.get(ws.state.user.id);
                if (sessions) {
                    sessions.delete(ws);
                    if (sessions.size < 1) {
                        sessionsByUserId.delete(ws.state.user.id);
                    }
                }
            }
        });

        ws.on("message", async (rawData, isBinary) => {
            if (isBinary) {
                return closeWithBadPayload(ws, "Binary messages are not supported");
            }

            ws.state.messagesSinceLastCheck++;
            if (ws.state.messagesSinceLastCheck > MAX_CLIENT_MESSAGES_PER_BATCH) {
                return closeWithError(ws, gatewayErrors.FLOODING);
            }
            
            const stringData = rawData.toString();
            if (stringData.length > 2048) {
                return closeWithError(ws, gatewayErrors.PAYLOAD_TOO_LARGE);
            }

            const payload = ensureFormattedGatewayPayload(parseJsonOrNull(stringData));
            if (!payload) {
                return closeWithBadPayload(ws, "Invalid JSON or message does not match schema");
            }

            switch (payload.t) {
                case GatewayPayloadType.Authenticate: {
                    if (ws.state.ready) {
                        return closeWithError(ws, gatewayErrors.ALREADY_AUTHENTICATED);
                    }

                    const token = payload.d;
                    if (typeof token !== "string") {
                        return closeWithBadPayload(ws, "d: expected string");
                    }
                    const user = await decodeTokenOrNull(token);
                    if (!user) {
                        return closeWithError(ws, gatewayErrors.BAD_AUTH);
                    }

                    let sessions = sessionsByUserId.get(user.id);
                    if (sessions) {
                        if ((sessions.size + 1) > MAX_GATEWAY_SESSIONS_PER_USER) {
                            return closeWithError(ws, gatewayErrors.TOO_MANY_SESSIONS);
                        }
                    } else {
                        sessions = new Set();
                        sessionsByUserId.set(user.id, sessions);
                    }
                    sessions.add(ws);

                    // TODO: each user should have their own list of channels that they join
                    const channels = await query("SELECT id, name, owner_id FROM channels ORDER BY id ASC");

                    clientSubscribe(ws, "*");
                    channels.rows.forEach(c => {
                        clientSubscribe(ws, `channel:${c.id}`);
                    });

                    ws.state.user = user;
                    ws.state.ready = true;

                    sendPayload(ws, {
                        t: GatewayPayloadType.Ready,
                        d: {
                            user: getPublicUserObject(ws.state.user),
                            channels: channels.rows
                        }
                    })
                    break;
                }
                case GatewayPayloadType.Ping: {
                    if (payload.d !== 0) {
                        return closeWithBadPayload(ws, "d: expected numeric '0'");
                    }

                    // TODO: also check session here
                    ws.state.alive = true;
                    break;
                }
                default: {
                    return closeWithBadPayload(ws, "t: unknown type");
                }
            }
        });
    });
};