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io.fetchSockets() fails with createSentinel #573
Description
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)
Activity
barisusakli commentedon May 5, 2026
I traced the code to see what was happening when fetchSockets was called.
socket.io-redis adapter makes this call in dist/utils.js
Which goes into
@redis/client/dist/lib/sentinel/index.jssendCommand function. But that function has the below signature, so all the parameters are put intoisReadonly.This causes args and options to be undefined which causes the error and the stacktrace in the first post.
Regular redis client has a
sendCommandfunction as well, but as far as I can see it doesn't have this firstisReadonlyparam.https://github.com/redis/node-redis/blob/master/packages/client/lib/client/index.ts#L1169-L1172