How do you implement custom handshaking logic in Spring WebSocket?

Table of Contents

Introduction

In Spring WebSocket, handshaking is the initial process of establishing a WebSocket connection between the client and the server. The WebSocket handshake involves the client sending an HTTP request, and the server responding with an HTTP 101 status code (Switching Protocols), upgrading the connection to WebSocket.

By default, Spring WebSocket handles handshakes automatically, but there are scenarios where you need to implement custom logic during the handshake. This can include handling authentication, session management, CORS checks, or custom header modifications.

In Spring, custom handshaking logic is implemented using the HandshakeInterceptor interface. This allows you to intercept and modify the WebSocket handshake request and response before and after the connection is established.

In this guide, we’ll walk through how to implement custom handshaking logic using HandshakeInterceptor in Spring WebSocket.

1. What is the HandshakeInterceptor Interface?

The HandshakeInterceptor interface in Spring WebSocket provides two main methods that allow you to intervene in the handshake process:

  1. **beforeHandshake**: Invoked before the WebSocket handshake is completed. It allows you to inspect and modify the HTTP request or check for conditions (e.g., authentication).
  2. **afterHandshake**: Called after the WebSocket handshake is completed. This method allows you to modify the response or perform post-handshake tasks (e.g., logging or session tracking).

HandshakeInterceptor Methods:

When to Use HandshakeInterceptor:

  • Authentication: Check whether the user is authenticated before allowing the WebSocket connection.
  • Session Management: Bind session-specific data (e.g., user info) to the WebSocket connection.
  • Custom Headers: Manipulate request or response headers for CORS, logging, or custom processing.
  • Logging: Log connection details or track WebSocket connections.

2. Steps to Implement Custom Handshaking Logic

Let’s walk through the steps to implement custom handshaking logic using HandshakeInterceptor in Spring WebSocket.

Step 1: Implement the HandshakeInterceptor Interface

The first step is to create a custom implementation of the HandshakeInterceptor interface. This implementation will define the custom handshaking logic in the beforeHandshake and afterHandshake methods.

Example 1: Custom Authentication Check During Handshake

In this example:

  • **beforeHandshake** checks if the incoming request contains a valid authorization token in the Authorization header.
  • If the token is valid, the userId is extracted and stored in the connection attributes (this data can be used later).
  • If the token is invalid or missing, the handshake is rejected, and a 403 Forbidden status is returned.

Step 2: Register the HandshakeInterceptor

To make the interceptor work, you need to register it in the Spring WebSocket configuration.

Example: Registering HandshakeInterceptor in WebSocketConfig

Here:

  • The **CustomAuthenticationInterceptor** is registered using the addInterceptors method.
  • We also specify the WebSocket endpoint (/ws) and allow connections from any origin (*).

Step 3: Custom WebSocketHandler

You can create a custom WebSocketHandler to handle messages sent over the WebSocket connection. The session information (such as userId) set in the HandshakeInterceptor can be accessed in the WebSocketHandler.

Example: Custom WebSocketHandler

In this example:

  • The **afterConnectionEstablished** method retrieves the userId stored in the session attributes during the handshake.
  • It then sends a personalized welcome message to the connected client.

3. Advanced Custom Handshaking Logic Use Cases

1. Session Tracking

You can use the HandshakeInterceptor to track and store user-specific session data. For example, store the session ID or user information to tie the WebSocket session to a user or perform custom logging.

2. CORS and Security

You can modify the handshake headers to handle CORS (Cross-Origin Resource Sharing) issues or enforce stricter security policies, such as setting specific allowed origins, or rejecting connections based on certain conditions.

3. Custom Headers

Modify or add custom headers in both the request and response during the handshake. For instance, adding or modifying a User-Agent header, or logging user-agent information to track different client types.

Conclusion

The **HandshakeInterceptor** interface in Spring WebSocket provides an essential tool for implementing custom handshaking logic. By intercepting the WebSocket handshake process, you can:

  • Authenticate and authorize users before allowing them to establish a connection.
  • Track sessions or store additional user data in connection attributes.
  • Modify headers for security, logging, or CORS handling.
  • Perform other custom actions during the WebSocket connection setup.

Implementing custom handshaking logic can greatly enhance the security, manageability, and flexibility of your WebSocket-based applications in Spring.

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