CORS Socket io v2

Socket.io is a library that enables real-time, bidirectional and event-based communication between the browser and server. It uses Web Sockets, Long Polling and other techniques to achieve this.

CORS stands for Cross-Origin Resource Sharing and it is a security feature implemented by web browsers to prevent a web page from making requests to a domain that is different from the one that served the page.

Socket.io version 2.x has built-in support for CORS and it can be configured to allow cross-origin requests by setting some options.

How to use CORS with Socket.io v2

To enable CORS in your Socket.io v2 application, you need to add some options to the server-side configuration:

const io = require('socket.io')(server, {
  cors: {
    origin: "http://example.com",
    methods: ["GET", "POST"]
  }
});

In this example, we are allowing requests from the domain http://example.com using the HTTP methods GET and POST.

You can also use regular expressions to match multiple origins:

const io = require('socket.io')(server, {
  cors: {
    origin: /example\.com$/,
    methods: ["GET", "POST"]
  }
});

This will match any origin that ends with "example.com".

If you want to allow all origins, you can use the wildcard character:

const io = require('socket.io')(server, {
  cors: {
    origin: "*",
    methods: ["GET", "POST"]
  }
});

This is convenient for development, but it is risky in production environments since it allows any domain to make requests.

Conclusion

Socket.io v2 has built-in support for CORS, making it easy to configure cross-origin requests. By setting the right options on the server-side configuration, you can allow requests from specific domains or all domains. However, you should be careful when using the wildcard character since it could lead to security issues.