Spring Boot dont establish connection with browser using transports: websocket

[DanielBotnik]

Hey, I have followed the guide on https://github.com/socketio/engine.io-server-java/blob/master/docs/spring-integration.rst
and have succsfully connected engine.io socket using Node.js application with the following code.

Bean

@Bean
public EngineIoServer engineIoServer(){
    EngineIoServerOptions options = EngineIoServerOptions.newFromDefault();
    options.setAllowedCorsOrigins(null);
    options.setPingTimeout(30000);
    EngineIoServer engineIoServer = new EngineIoServer(options);
    engineIoServer.on("connection", args -> {
        System.out.println("CONNECTION");
    });
    return engineIoServer;
}

Node.js Code

const { Socket } = require('engine.io-client');

const socket = new Socket('http://localhost:4919', {
    transports: ['websocket'],
});

socket.on('open', () => {
    console.log('Connected');    
});

but the same code just for the browser doesnt work.
Browser Code

<script>
    const socket = eio('http://localhost:4919', {
        transports: ['websocket'],
    });

    socket.on('open', function() {
        console.log('open!');
    });
</script>

and we can see that there is no response from the server

I have found out that by changing the transports to 'polling' insted of 'websocket' let the browser connect to the server, but I still rather use websocket insted of long polling.

I am using engine.io-server 6.0.1 and Java 17.
the error occured on chrome and edge, didnt check different browsers.

[DanielBotnik]

After Debugging, I have found the issue is not related to this library, but rather its a problem laying in spring.
I have the problem is caused because the browser Origin HTTP Header, which the node.js application one doesn't have.
the OriginHandshakeInterceptor.beforeHandshake() treat the origin header, even if its null as a String ("null"), therefore it fails all the checks and the connection is dropped.
I have found a quickfix, but I am no expert to determine if its a good one.

@Override
public boolean beforeHandshake(ServerHttpRequest request, ServerHttpResponse response, WebSocketHandler wsHandler, Map<String, Object> attributes) {
    System.out.println("IN here");
    attributes.put(ATTRIBUTE_ENGINEIO_QUERY, request.getURI().getQuery());
    attributes.put(ATTRIBUTE_ENGINEIO_HEADERS,request.getHeaders());
    // fix start.
    if("null".equals(request.getHeaders().getOrigin()))
        request.getHeaders().remove("Origin");
    // fix end.
    return true;
}