@seriousme/opifex/server/handlers/handleSubscribe.ts

MQTT client & server for Deno & NodeJS

import type { Context } from "../context.ts";
import {
  PacketType,
  type SubscribePacket,
  type Subscription,
  type Topic,
} from "../deps.ts";

/**
 * @constant {number} SubscriptionFailure
 * @description Code indicating a failed subscription attempt
 */
const SubscriptionFailure = 0x80;

/**
 * Checks if a client is authorized to subscribe to a topic
 * @param  ctx - The connection context
 * @param  topicFilter - The topic filter to check authorization for
 * @returns True if authorized, false otherwise
 */
function authorizedToSubscribe(ctx: Context, topicFilter: Topic) {
  if (ctx.handlers.isAuthorizedToSubscribe) {
    return ctx.handlers.isAuthorizedToSubscribe(ctx, topicFilter);
  }
  return true;
}

/**
 * @function handleSubscribe
 * @description Processes an MQTT SUBSCRIBE packet
 * @param {Context} ctx - The connection context
 * @param {SubscribePacket} packet - The SUBSCRIBE packet received from the client
 * @returns {Promise<void>}
 * @throws {Error} If subscription processing fails
 * @remarks The order of return codes in the SUBACK Packet MUST match the order of Topic Filters in the SUBSCRIBE Packet [MQTT-3.9.3-1]
 */
export async function handleSubscribe(
  ctx: Context,
  packet: SubscribePacket,
): Promise<void> {
  /*
   * The order of return codes in the SUBACK Packet MUST match the order of
   * Topic Filters in the SUBSCRIBE Packet [MQTT-3.9.3-1].
   */
  const validSubscriptions: Subscription[] = [];
  const returnCodes = packet.subscriptions.map((sub) => {
    if (ctx.store) {
      if (!authorizedToSubscribe(ctx, sub.topicFilter)) {
        return SubscriptionFailure;
      }
      ctx.persistence.subscribe(ctx.store, sub.topicFilter, sub.qos);
      validSubscriptions.push(sub);
      return sub.qos;
    }
    return SubscriptionFailure;
  });

  await ctx.send({
    type: PacketType.suback,
    id: packet.id,
    returnCodes: returnCodes,
  });

  /*
   * send any retained messages that match these subscriptions
   */
  if (ctx.store) {
    ctx.persistence.handleRetained(ctx.store.clientId);
  }
}