WebSocket Connection

When to Use

You can use WebSocket to establish a bidirectional connection between a server and a client. Before doing this, you need to use the createWebSocket() API to create a WebSocket object and then use the connect() API to connect to the server. If the connection is successful, the client will receive a callback of the open event. Then, the client can communicate with the server using the send() API. When the server sends a message to the client, the client will receive a callback of the message event. If the client no longer needs this connection, it can call the close() API to disconnect from the server. Then, the client will receive a callback of the close event.

If an error occurs in any of the preceding processes, the client will receive a callback of the error event.

Available APIs

The WebSocket connection function is mainly implemented by the WebSocket module. To use related APIs, you must declare the ohos.permission.INTERNET permission. The following table describes the related APIs.

API Description
createWebSocket() Creates a WebSocket connection.
connect() Establishes a WebSocket connection to a given URL.
send() Sends data through the WebSocket connection.
close() Closes a WebSocket connection.
on(type: 'open') Enables listening for open events of a WebSocket connection.
off(type: 'open') Disables listening for open events of a WebSocket connection.
on(type: 'message') Enables listening for message events of a WebSocket connection.
off(type: 'message') Disables listening for message events of a WebSocket connection.
on(type: 'close') Enables listening for close events of a WebSocket connection.
off(type: 'close') Disables listening for close events of a WebSocket connection.
on(type: 'error') Enables listening for error events of a WebSocket connection.
off(type: 'error') Disables listening for error events of a WebSocket connection.

How to Develop

  1. Import the required webSocket module.

  2. Create a WebSocket object.

  3. (Optional) Subscribe to WebSocket open, message, close, and error events.

  4. Establish a WebSocket connection to a given URL.

  5. Close the WebSocket connection if it is no longer needed.

import webSocket from '@ohos.net.webSocket';

var defaultIpAddress = "ws://";
let ws = webSocket.createWebSocket();
ws.on('open', (err, value) => {
  console.log("on open, status:" + JSON.stringify(value));
  // When receiving the on('open') event, the client can use the send() API to communicate with the server.
  ws.send("Hello, server!", (err, value) => {
    if (!err) {
      console.log("Message sent successfully");
    } else {
      console.log("Failed to send the message. Err:" + JSON.stringify(err));
    }
  });
});
ws.on('message', (err, value) => {
  console.log("on message, message:" + value);
  // When receiving the `bye` message (the actual message name may differ) from the server, the client proactively disconnects from the server.
  if (value === 'bye') {
    ws.close((err, value) => {
      if (!err) {
        console.log("Connection closed successfully");
      } else {
        console.log("Failed to close the connection. Err: " + JSON.stringify(err));
      }
    });
  }
});
ws.on('close', (err, value) => {
  console.log("on close, code is " + value.code + ", reason is " + value.reason);
});
ws.on('error', (err) => {
  console.log("on error, error:" + JSON.stringify(err));
});
ws.connect(defaultIpAddress, (err, value) => {
  if (!err) {
    console.log("Connected successfully");
  } else {
    console.log("Connection failed. Err:" + JSON.stringify(err));
  }
});