Fix ProtobufJS Mapping for Spot Account Orders

[tienryo-2]

I’m integrating MEXC’s WebSocket stream for Spot Account Orders in a NestJS project. I'm using protobufjs to decode messages from the spot@private.orders.v3.api.pb topic.

Below is the relevant NestJS code I’m using to connect and decode messages:

import { Injectable, OnModuleInit, OnModuleDestroy, Logger } from '@nestjs/common';
import { MexcService } from 'src/services/mexc.service';
import * as WebSocket from 'ws';
import * as protobuf from 'protobufjs';

let PrivateOrdersV3Api: protobuf.Type;

protobuf.load('proto/PrivateOrdersV3Api.proto').then((root) => {
    PrivateOrdersV3Api = root.lookupType('PrivateOrdersV3Api');
});

@Injectable()
export class StreamService implements OnModuleInit, OnModuleDestroy {
    private readonly logger = new Logger(StreamService.name);
    private listenKey: string;
    private ws: WebSocket;
    private renewInterval: NodeJS.Timeout;

    constructor(
        private readonly mexcService: MexcService,
    ) {
        this.mexcService = mexcService
    }

    async onModuleInit() {
        this.logger.log('Initializing MEXC WebSocket...');
        await this.connectWebSocket();
    }

    async onModuleDestroy() {
        this.logger.warn('Cleaning up MEXC WebSocket...');
        if (this.ws) this.ws.terminate();
        clearInterval(this.renewInterval);
        await this.mexcService.closeListenKey()
    }

    private async connectWebSocket() {
        try {
            const { listenKey } = await this.mexcService.createListenKey();
            this.listenKey = listenKey
            this.logger.log(`🔑 listenKey: ${this.listenKey}`);

            this.ws = new WebSocket(`wss://wbs-api.mexc.com/ws?listenKey=${this.listenKey}`);

            this.ws.on('open', async () => {
                this.logger.log('✅ WebSocket connected');

                const payload = {
                    method: 'SUBSCRIPTION',
                    "params": [
                        "spot@private.orders.v3.api.pb"
                    ]
                };
                this.ws.send(JSON.stringify(payload));

                await this.mexcService.keepListenKey()
            });

            this.ws.on('message', (data) => {
                try {
                    const decode = PrivateOrdersV3Api.decode(data);
                    const decodeObj = PrivateOrdersV3Api.toObject(decode);

                    console.log('🌐 Decode:',decode,  decodeObj);
                } catch (err) {
                    console.error(data)
                    this.logger.error('❌ Message error:', err.message);
                }
            });

            this.ws.on('error', (err) => {
                this.logger.error('❌ WebSocket error:', err.message);
                this.reconnect();
            });

            this.ws.on('close', () => {
                this.logger.warn('🔌 WebSocket closed');
                this.reconnect();
            });


            // Renew listenKey every 30 minutes
            clearInterval(this.renewInterval);
            this.renewInterval = setInterval(() => this.mexcService.keepListenKey(), 1000 * 60 * 60);
        } catch (err) {
            this.logger.error('❌ Failed to connect WebSocket', err.message);
            setTimeout(() => this.connectWebSocket(), 5000);
        }
    }

    private async reconnect() {
        this.logger.warn('🔁 Reconnecting WebSocket...');
        if (this.ws) {
            this.ws.removeAllListeners();
            this.ws.terminate();
            this.ws = null;
        }
        clearInterval(this.renewInterval);
        await this.mexcService.closeListenKey()
        await this.connectWebSocket();
    }
}

The .proto file I'm using is named PrivateOrdersV3Api.proto and contains the following definition:

// spot@private.orders.v3.api.pb

syntax = "proto3";

option java_package = "com.mxc.push.common.protobuf";
option optimize_for = SPEED;
option java_multiple_files = true;
option java_outer_classname = "PrivateOrdersV3ApiProto";

message PrivateOrdersV3Api {

  string id = 1;
  string clientId = 2;

  string price = 3;
  string quantity = 4;
  string amount = 5;
  string avgPrice = 6;

  int32 orderType = 7;
  int32 tradeType = 8;
  bool isMaker = 9;

  string remainAmount = 10;
  string remainQuantity= 11;
  optional string lastDealQuantity = 12;
  string cumulativeQuantity = 13;
  string cumulativeAmount = 14;

  int32 status = 15;
  int64 createTime = 16;

  optional string market = 17;
  optional int32 triggerType = 18;
  optional string triggerPrice= 19;
  optional int32 state = 20;

  optional string ocoId = 21;
  optional string routeFactor = 22;

  optional string symbolId = 23;
  optional string marketId = 24;

  optional string marketCurrencyId = 25;
  optional string currencyId = 26;
}

❗️Issues Encountered

WebSocket connection closes after a few minutes :
→ Possibly due to listenKey expiration or incorrect keep-alive handling.

Protobuf decoding returns invalid or malformed data
Example decoded output:

🌐 Decode: PrivateOrdersV3Api {
  status: 34,
  cumulativeQuantity: '":0,"code":0,"msg":"spot@private.orders.v3.api.pb"}'
} {
  cumulativeQuantity: '":0,"code":0,"msg":"spot@private.orders.v3.api.pb"}',
  status: 34
}

→ It seems the incoming message is not a valid protobuf buffer, or perhaps there is an outer wrapper message structure that I’m missing.