[undertow-dev] permessage-deflate extension is not supported, getInstalledExtensions() returns empty set in ServerWebSocketContainer.java

--- Problem: client's request for compression is ignored. The client sends the request for compression: Sec-WebSocket-Extensions: permessage-deflate; client_no_context_takeover; client_max_window_bits\r\n Webserver receives the client request, org.springframework.web.socket.server.support.AbstractHandshakeHandler.java: doHandshake function: try to see if requested extension is supported String subProtocol = selectProtocol(headers.getSecWebSocketProtocol(), wsHandler); List<WebSocketExtension> requested = headers.getSecWebSocketExtensions(); List<WebSocketExtension> supported = this.requestUpgradeStrategy.getSupportedExtensions(request); List<WebSocketExtension> extensions = filterRequestedExtensions(request, requested, supported); getSupportedExtensions calls into the following function, which always returns empty set for installed extensions. io.undertow.websockets.jsr.ServerWebSocketContainer.java: public Set<Extension> getInstalledExtensions() { return Collections.emptySet(); } My question is: how to tell spring framework that the permessage-deflate extension is supported by undertow? Environement: Undertow 1.3.22 Final is used by springframework: +- org.springframework.boot:spring-boot-starter-undertow:jar:1.3.5.RELEASE:compile [INFO] | | +- io.undertow:undertow-core:jar:1.3.22.Final:compile [INFO] | | +- io.undertow:undertow-servlet:jar:1.3.22.Final:compile [INFO] | | +- io.undertow:undertow-websockets-jsr:jar:1.3.22.Final:compile Thanks