How do you enable CORS for WebSocket connections in Spring?

Table of Contents

Introduction

In Spring WebSocket applications, you may need to enable CORS (Cross-Origin Resource Sharing) to allow WebSocket connections from different origins (i.e., from a different domain, protocol, or port). By default, browsers block cross-origin requests for security reasons, including WebSocket connections.

To facilitate secure cross-origin WebSocket communication, you can configure CORS support in Spring WebSocket applications. This configuration allows WebSocket clients from different origins to establish connections with your WebSocket server.

In this guide, we’ll walk you through the process of enabling CORS for WebSocket connections in Spring.

1. Why Enable CORS for WebSocket Connections?

CORS is essential in scenarios where:

  • The WebSocket client (usually a browser) and server are on different domains or ports.
  • You need to allow cross-origin WebSocket connections for remote clients to interact with your WebSocket server.
  • Security policies require you to explicitly control which origins are allowed to connect.

Enabling CORS for WebSocket connections ensures that only authorized domains are allowed to establish WebSocket connections, enhancing the security and flexibility of your application.

2. Steps to Enable CORS for WebSocket in Spring

There are two primary ways to enable CORS for WebSocket connections in Spring:

  • Using **WebSocketHandlerRegistry** in Spring WebSocket configuration.
  • Customizing the CORS mapping in a global configuration class (using CorsRegistry).

1. Enabling CORS in **WebSocketConfigurer**

The first approach is to enable CORS directly in the WebSocket configuration class by using the WebSocketHandlerRegistry. This method is the most common and provides a simple way to configure CORS for WebSocket endpoints.

Example: Enabling CORS in WebSocketConfigurer

Explanation:

  • **setAllowedOrigins()**: This method is used to configure the allowed origins for WebSocket connections. You can specify multiple origins as a comma-separated list, such as "http://example.com" and "http://another-origin.com".
  • Cross-origin WebSocket connections from any of the specified origins are now permitted.

2. Enabling CORS with **CorsRegistry**

If you want to enable global CORS configuration across your entire application (including WebSocket endpoints), you can configure CORS globally using the **CorsRegistry** in a @Configuration class.

Example: Global CORS Configuration for WebSocket

Explanation:

  • **addCorsMappings()**: This method allows you to configure CORS mappings for all HTTP requests, including WebSocket connections.
  • **/ws/****: This mapping specifies the WebSocket URL pattern (you can modify it to fit your WebSocket endpoint).
  • **allowedOrigins()**: Allows only specified origins to access the WebSocket endpoint.
  • **allowedMethods()**: Specifies the allowed HTTP methods (though WebSocket connections are not strictly tied to HTTP methods, you can control which methods are allowed).
  • **allowedHeaders()**: Specifies which headers are allowed in cross-origin requests.

3. Using WebSocket STOMP Protocol and CORS

If you are using the STOMP protocol with WebSockets (e.g., in a Spring-based messaging application), you still need to enable CORS for the WebSocket handshake and the STOMP messages.

Example: STOMP WebSocket Configuration with CORS

Explanation:

  • **/ws-stomp**: This is the WebSocket endpoint used for STOMP communication.
  • **setAllowedOrigins()**: Specifies the origins allowed to establish a WebSocket connection.
  • SockJS: This enables the fallback for browsers that don’t support WebSockets.

4. Handling CORS with Custom Handshake Interceptor

You can also use a custom handshake interceptor to manipulate headers and manage CORS at a finer level during the WebSocket handshake.

Example: Custom CORS Handshake Interceptor

In this case:

  • You intercept the WebSocket handshake and add the necessary CORS headers.
  • You can extend this further to allow dynamic origin checks based on the incoming request or perform additional security checks.

Conclusion

Enabling CORS for WebSocket connections in Spring is an essential step to allow secure cross-origin communication between the client and the server. There are various ways to achieve this in Spring WebSocket applications:

  • Using **WebSocketHandlerRegistry** to configure allowed origins for specific WebSocket endpoints.
  • Configuring global CORS mappings through the CorsRegistry to allow cross-origin WebSocket connections across the entire application.
  • Using a custom handshake interceptor to manually add CORS headers during the WebSocket handshake.

By configuring CORS appropriately, you can enable secure and controlled access to WebSocket services, ensuring your WebSocket application works seamlessly across different domains and origins.

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