Websocket extensions not working

[piotrblasiak]

Affects: \5.3.3

---

In spring, one can add an undertow websocket extension by:
 

@Bean
    public WebServerFactoryCustomizer<UndertowServletWebServerFactory> deploymentCustomizer() {
        return factory -> {
            UndertowDeploymentInfoCustomizer customizer = deploymentInfo -> {

                WebSocketDeploymentInfo webSocketDeploymentInfo = new WebSocketDeploymentInfo();
                webSocketDeploymentInfo.addExtension(new PerMessageDeflateHandshake());
                deploymentInfo.addServletContextAttribute(WebSocketDeploymentInfo.ATTRIBUTE_NAME, webSocketDeploymentInfo);
            };
            factory.addDeploymentInfoCustomizers(customizer); 
        };
    }

But that extension does not work when processing requests. I have found that spring wraps extensions in
org.springframework.web.socket.server.standard.AbstractStandardUpgradeStrategy.getInstalledExtensions(...)

protected List<WebSocketExtension> getInstalledExtensions(WebSocketContainer container) {
		List<WebSocketExtension> result = new ArrayList<>();
		for (Extension extension : container.getInstalledExtensions()) {
			result.add(new StandardToWebSocketExtensionAdapter(extension));
		}
		return result;
	}

which breaks the extension matching in 

org.springframework.web.socket.server.support.filterRequestedExtensions(...)

protected List<WebSocketExtension> filterRequestedExtensions(ServerHttpRequest request,
			List<WebSocketExtension> requestedExtensions, List<WebSocketExtension> supportedExtensions) {

		List<WebSocketExtension> result = new ArrayList<>(requestedExtensions.size());
		for (WebSocketExtension extension : requestedExtensions) {
			if (supportedExtensions.contains(extension)) {
				result.add(extension);
			}
		}
		return result;
	}

I have been unable to find a workaround for this, and I am not sure what an appropriate fix would be.

[rstoyanchev]

How does it break? Does it not find the installed extensions or something in the equals() of the wrapper?

[piotrblasiak]

@rstoyanchev it finds the installed extension but it wraps it in a StandardToWebSocketExtensionAdapter, which makes the filterRequestedExtensions method not include it in the final list of extensions to apply to the request. I am thinking perhaps it should not be wrapped or the filterRequestedExtensions could be changed to filter by name and not Collection.contains().

[rstoyanchev]

Okay so WebSocketExtension has an equals method but the getClass() check would fail to match, WebSocketExtension for the requested vs StandardToWebSocketExtensionAdapter for the installed.

[rstoyanchev]

I'll add a fix. A workaround could be to override getInstalledExtensions and return WebSocketExtension instances and plug the RequestUpgradeStrategy into the DefaultHandshakeHandler.