Namespace

Namespaces

Namespaces provide logical separation of features and event handling within the SocketIO server. They allow different parts of an application to operate independently using a single physical connection.

Namespaces do not create separate socket connections. A client connects once and can join multiple namespaces over the same underlying WebSocket/TCP session.

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Default Namespace

If a client connects without specifying a namespace, it is attached to the default namespace ("").

Configuration config = new Configuration();
config.setPort(9092);

SocketIOServer server = new SocketIOServer(config);
// default namespace exists implicitly
server.start();

Custom Namespace

Custom namespaces separate application concerns and event scopes.

SocketIOServer server = new SocketIOServer(config);

Namespace chat = server.addNamespace("/chat");
Namespace admin = server.addNamespace("/auth");

server.start();

Please do not forget to add "/", its always "/namespace" NOT just "namespace".

Each namespace defines:

• its own event listeners

• its own connection lifecycle

• its own authorization logic

• its own broadcast operations

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Public Namespace Example (/chat)

The /chat namespace is open and allows general messaging without authentication.

Server

Configuration config = new Configuration();
config.setPort(9092);

SocketIOServer server = new SocketIOServer(config);
Namespace chat = server.addNamespace("/chat");

// new client connection
chat.addConnectListener(client -> {
    log.info("[/chat] connected -> {}", client.getSessionId());
});

// message event
chat.addEventListener("message", String.class, (client, data, ack) -> {
    // broadcast to all clients in /chat
    chat.getBroadcastOperations().sendEvent("message", data);
});

server.start();

Client

const chat = io("http://localhost:9092/chat");

chat.on("connect", () => console.log("connected to /chat"));
chat.emit("message", "hello everyone");

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Authenticated Namespace Example (/auth)

The /auth namespace restricts access using authorization logic executed during connection.

Server

Configuration config = new Configuration();
config.setPort(9092);

SocketIOServer server = new SocketIOServer(config);
Namespace admin = server.addNamespace("/auth");

// verify token on namespace connect
admin.setAuthorizationListener(data -> {
    String token = data.getSingleUrlParam("token");
    return "secret123".equals(token);
});

// privileged alert event
admin.addEventListener("alert", String.class, (client, data, ack) -> {
    admin.getBroadcastOperations().sendEvent("alert", data);
});

server.start();

Authorized Client

const auth = io("http://localhost:9092/auth", {
    query: { token: "secret123" }
});

admin.emit("alert", "restart service");

Unauthorized Client

io("http://localhost:9092/auth", {
    query: { token: "invalid" }
});

Expected server output:

[/auth] authorization failed -> connection rejected

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