@seriousme/opifex/dist/mqttPacket/subscribe.js

MQTT client & server for Deno & NodeJS

import { PacketType } from "./PacketType.js";
import { BitMask } from "./BitMask.js";
import { Encoder } from "./encoder.js";
import { booleanFlag, Decoder, DecoderError } from "./decoder.js";
export const subscribe = {
    encode(packet) {
        // Bits 3,2,1 and 0 of the fixed header of the SUBSCRIBE Control Packet are reserved and
        // MUST be set to 0,0,1 and 0 respectively. The Server MUST treat any other value as
        // malformed and close the Network Connection [MQTT-3.8.1-1].
        const flags = 0b0010;
        const encoder = new Encoder();
        encoder.setInt16(packet.id);
        for (const sub of packet.subscriptions) {
            encoder.setTopic(sub.topicFilter);
            encoder.setByte(sub.qos);
        }
        return { flags, bytes: encoder.done() };
    },
    decode(buffer, flags) {
        // Bits 3,2,1 and 0 of the fixed header of the SUBSCRIBE Control Packet are reserved and
        // MUST be set to 0,0,1 and 0 respectively. The Server MUST treat any other value as
        // malformed and close the Network Connection [MQTT-3.8.1-1].
        if (!booleanFlag(flags, BitMask.bit1)) {
            throw new DecoderError("Invalid header");
        }
        const decoder = new Decoder(buffer);
        const id = decoder.getInt16();
        const subscriptions = [];
        // The payload of a SUBSCRIBE packet MUST contain at least one Topic Filter / QoS pair.
        // A SUBSCRIBE packet with no payload is a protocol violation [MQTT-3.8.3-3].
        do {
            const topicFilter = decoder.getTopicFilter();
            const qos = decoder.getByte();
            if (qos !== 0 && qos !== 1 && qos !== 2) {
                throw new DecoderError("Invalid qos");
            }
            if (qos > 0 && id === 0) {
                throw new DecoderError("Invalid packet identifier");
            }
            subscriptions.push({
                topicFilter: topicFilter,
                qos,
            });
        } while (!decoder.atEnd());
        decoder.done();
        return {
            type: PacketType.subscribe,
            id,
            subscriptions,
        };
    },
};
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