io.fetchSockets() fails with createSentinel

[barisusakli]

I created a minimal example below.

const { Server } = require("socket.io");
const { createClient, createSentinel } = require("redis");
const { createAdapter } = require("@socket.io/redis-adapter");

const port = process.argv[2] || 3000;

async function setupWithCreateSentinel() {
  const sentinelOptions = {
    name: 'mymaster',
    sentinelRootNodes: [
      { host: '127.0.0.1', port: 26379 },
      { host: '127.0.0.1', port: 26380 }
    ],
  };

  const pubClient = await createSentinel(sentinelOptions);
  const subClient = await createSentinel(sentinelOptions);

  pubClient.on('error', (err) => console.error('Pub Redis Error', err));
  subClient.on('error', (err) => console.error('Sub Redis Error', err));

  try {
    await Promise.all([pubClient.connect(), subClient.connect()]);
    console.log(`Connected via createSentinel to group: ${sentinelOptions.name}`);
  } catch (err) {
    console.error('Sentinel connection failed:', err);
    process.exit(1);
  }

  const io = new Server(port, {
    cors: { origin: "*" }
  });

  io.adapter(createAdapter(pubClient, subClient));

  console.log(`Socket.io server running on port ${port}`);

  setInterval(async () => {
    try {
      const sockets = await io.fetchSockets();
    } catch (err) {
      console.error('Fetch sockets error:', err);
    }
  }, 3000);
}

setupWithCreateSentinel();

Running this with node index.js 4567 throws the below error when calling io.fetchSockets()

Fetch sockets error: TypeError: Cannot read properties of undefined (reading 'length')
    at encodeCommand (socket.io-sentinel\node_modules\@redis\client\dist\lib\RESP\encoder.js:6:30)
    at RedisCommandsQueue.commandsToWrite (socket.io-sentinel\node_modules\@redis\client\dist\lib\client\commands-queue.js:379:49)
    at commandsToWrite.next (<anonymous>)
    at RedisSocket.write (socket.io-sentinel\node_modules\@redis\client\dist\lib\client\socket.js:274:20)
    at #write (socket.io-sentinel\node_modules\@redis\client\dist\lib\client\index.js:844:22)
    at Immediate.<anonymous> (socket.io-sentinel\node_modules\@redis\client\dist\lib\client\index.js:851:24)
    at process.processImmediate (node:internal/timers:504:21)

[barisusakli]

I traced the code to see what was happening when fetchSockets was called.

socket.io-redis adapter makes this call in dist/utils.js

  // redis@4 standalone
   return redisClient
       .sendCommand(["PUBSUB", arg, channel])
       .then(parseNumSubResponse);

Which goes into @redis/client/dist/lib/sentinel/index.js sendCommand function. But that function has the below signature, so all the parameters are put into isReadonly.

 async sendCommand(isReadonly, args, options) {
       return this._execute(isReadonly, client => client.sendCommand(args, options));
}

This causes args and options to be undefined which causes the error and the stacktrace in the first post.

Regular redis client has a sendCommand function as well, but as far as I can see it doesn't have this first isReadonly param.

https://github.com/redis/node-redis/blob/master/packages/client/lib/client/index.ts#L1169-L1172