Hello, We are trying to use both SSE and HTTP/2.0 features of Undertow. The idea is to open an SSE connection with HTTP/2.0 as protocol. We've tried with the following piece of code: ____________________________________________ ServerSentEventHandler sseHandler; sseHandler = new ServerSentEventHandler(new SseConnectionCallback(source)); String bindAddress = System.getProperty("bind.address", "localhost"); SSLContext sslContext = createSSLContext(loadKeyStore("server.keystore"), loadKeyStore("server.truststore")); Undertow server = Undertow.builder() .setServerOption(UndertowOptions.ENABLE_HTTP2, true) .setServerOption(UndertowOptions.ENABLE_SPDY, true) .addHttpsListener(8443, bindAddress, sslContext) .setHandler(path().addPrefixPath("/sse", sseHandler)) .build(); server.start(); ____________________________________________ But when connecting to https://localhost:8443/sse, nothing happens in the client side while we are sending into the ServerSentEventConnection data every 5 seconds We think it is related to the HTTP/2.0 frame stuff but we are not sure about this hypothesis. On the other hand, we have modified the ServerSentEventConnection to expose a flush() method that calls the underlying flush() of its sink. ____________________________________________ public class ServerSentEventConnection implements Channel, Attachable { ... public boolean flush() throws IOException { return this.sink.flush(); } } ____________________________________________ And somewhere in our callback, we do: ____________________________________________ public class SseConnectionCallback implements ServerSentEventConnectionCallback { ... if (connection.isOpen()) { connection.send(data, "data", UUID.randomUUID().toString(), new ServerSentEventConnection.EventCallback() { @Override public void done(ServerSentEventConnection aConnection, String aData, String aEvent, String aId) { LOGGER.info("Sent!"); try { connection.flush(); } catch (IOException e) { e.printStackTrace(); } } @Override public void failed(ServerSentEventConnection aConnection, String aData, String aEvent, String aId, IOException e) { LOGGER.info("failed!"); } }); } ____________________________________________ And we get the SSE events on the client side. So, we were wondering whether our solution was right or whether there is another solution for our issue. Thanks in advance! Best regards, Cédric.