> For the complete documentation index, see [llms.txt](https://www.socketio4j.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://www.socketio4j.org/client-api/api-docs.md). # API docs Please check the clients and API docs for reference {% hint style="warning" %} **Warning:** Use client versions compatible with **Socket.IO Server v4**. Previous versions **may not be supported and may not work** correctly {% endhint %}

Language	Website
Java	https://github.com/socketio/socket.io-client-java
JavaScript (browser, Node.js or React Native)	- Installation steps - API - Source code
JavaScript (for WeChat Mini-Programs)	https://github.com/weapp-socketio/weapp.socket.io
C++	https://github.com/socketio/socket.io-client-cpp
Swift	https://github.com/socketio/socket.io-client-swift
Dart	https://github.com/rikulo/socket.io-client-dart
Python	https://github.com/miguelgrinberg/python-socketio
.Net	https://github.com/doghappy/socket.io-client-csharp
Rust	https://github.com/1c3t3a/rust-socketio
Kotlin	https://github.com/icerockdev/moko-socket-io
PHP	https://github.com/ElephantIO/elephant.io
Golang	https://github.com/maldikhan/go.socket.io

{% hint style="danger" %} Not all client-side APIs may be available in the server implementation, and vice versa. {% endhint %} ## Compatibility Matrix

Client API	Netty‑SocketIO Support	JavaScript Client	Java Client	Python Client	C++ Client	Swift Client	Dart/Flutter Client	.NET Client	PHP Client	Go Client	Notes
Connect	✅ Yes	`io(url, opts)`	`IO.socket(url)`	`sio.connect(url)`	`socket.connect()`	`socket.connect()`	`socket.connect()`	`socket.Connect()`	`client->Connect()`	`socket.Connect()`	Standard connect method
Disconnect	✅ Yes	`socket.disconnect()`	`socket.disconnect()`	`sio.disconnect()`	`socket.disconnect()`	`socket.disconnect()`	`socket.disconnect()`	`socket.Disconnect()`	`client->Disconnect()`	`socket.Disconnect()`	Client disconnects from server
Event listen	✅ Yes	`socket.on(event, cb)`	`socket.on(EVENT, listener)`	`@sio.on(event)`	`socket.on(event, cb)`	`socket.on(event, cb)`	`socket.on(event, cb)`	`socket.On(event, cb)`	`client->On(event, cb)`	`socket.On(event, cb)`	Standard event handler
One‑time listener	✅ Yes	`socket.once(event, cb)`	`socket.once(EVENT, listener)`	`@sio.once(event)`	`socket.once(event, cb)`	`socket.once(event, cb)`	`socket.once(event, cb)`	`socket.Once(event, cb)`	`client->Once(event, cb)`	`socket.Once(event, cb)`	Some clients don’t have built‑in once
Remove listener	✅ Yes	`socket.off()` / `socket.removeListener()`	`socket.off(EVENT)`	`sio.off(event)`	`socket.off(event)`	`socket.off(event)`	`socket.off(event)`	`socket.Off(event)`	`client->Off(event)`	`socket.Off(event)`	Most clients support listener removal cycles
Emit event	✅ Yes	`socket.emit(event, …args)`	`socket.emit(event, …args)`	`sio.emit(event, data)`	`socket.emit(event, data)`	`socket.emit(event, data)`	`socket.emit(event, data)`	`socket.Emit(event, data)`	`client->Emit(event, data)`	`socket.Emit(event, data)`	Standard emit
Emit with ack	✅ Yes	`socket.emit(event, …, callback)` / `emitWithAck()`	`socket.emit(event, …args, AckCallback)`	`sio.call(event, data)` / `await sio.emit(event, data, callback)`	`socket.emit(event, data, cb)`	`socket.emit(event, data, cb)`	`socket.emit(event, data, cb)`	`socket.Emit(event, data, cb)`	`client->Emit(event, data, cb)`	`socket.Emit(event, data, cb)`	Ack support varies
Namespace API	✅ Yes	`io(url/ns)` / `socket.nsp`	`socket.of("/ns")`	`sio.connect(url, namespaces=["/ns"])`	`socket.of("/ns")`	`socket.of("/ns")`	`socket.of("/ns")`	`socket.Of("/ns")`	`client->Of("/ns")`	`socket.Of("/ns")`	Most multi‑namespace clients support
Query / Auth	⚠️ Limited	`io(url, { auth, query })`	`IO.Options.query`/`setAuth(Map<String,Object>)`	`sio.connect(url, auth={…})`	`socket.setAuth(data)`	`socket.setAuth(data)`	`socket.setAuth(data)`	`socket.SetAuth(data)`	`client->SetAuth(data)`	`socket.SetAuth(data)`	Handshake params pass through
Reconnection control	⚠️ Partial	Managed by client options	`socket.io().reconnection(true/false)`	`sio.reconnect()` or handled by `sio.connect()`	Client library dependent	Client library dependent	Client library dependent	Client library dependent	Client library dependent	Client library dependent	Auto reconnect logic client
Volatile emit	⚠️ Limited	`socket.volatile.emit()`	JS-only / no standard in Java client	⚠️ Rare / not standard	Varies	Varies	Varies	Varies	Varies	Varies	Not consistently implemented
Compression flags	⚠️ Internal	`socket.compress()`	Not standard	Not standard	Not standard	Varies	Varies	Varies	Varies	Varies	Usually internal
Client middleware (`use()`)	❌ No	JS only	❌	❌	❌	❌	❌	❌	❌	❌	Middleware API largely JS only
Engine/Manager internals	❌ No	`socket.io` / Manager	Internal	Internal	Internal	Internal	Internal	Internal	Internal	Internal	Client internals not mirrored on server

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