A demo of using DataKernel for Server Sent Events

ServerSentEventsDemo.java

import io.datakernel.bytebuf.ByteBufStrings;
import io.datakernel.csp.ChannelSupplier;
import io.datakernel.di.annotation.Provides;
import io.datakernel.http.AsyncServlet;
import io.datakernel.http.HttpHeaders;
import io.datakernel.http.HttpResponse;
import io.datakernel.http.RoutingServlet;
import io.datakernel.launchers.http.HttpServerLauncher;
import io.datakernel.promise.Promises;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.time.Duration;
import java.util.Date;

public final class ServerSentEventsDemo extends HttpServerLauncher {
	private static final DateFormat DATE_FORMATTER = new SimpleDateFormat("HH:mm:ss");

	private static final String HTML = "<h1>Open developer console to see server-sent messages</h1>" +
			"<script>new EventSource(\"/sse\").onmessage = event => console.log(\"message: \" + event.data)</script>\n";

	@Provides
	public AsyncServlet mainServlet() {
		return RoutingServlet.create()
				.map("/", request -> HttpResponse.ok200().withHtml(HTML))
				.map("/sse", request -> HttpResponse.ok200()
						.withHeader(HttpHeaders.CONTENT_TYPE, "text/event-stream")
						.withBodyStream(ChannelSupplier.of(() -> Promises.delay(Duration.ofSeconds(1), new Date())
								.map(ServerSentEventsDemo::encodeDateAsEvent)
								.map(ByteBufStrings::wrapUtf8))));
	}

	private static String encodeDateAsEvent(Date date) {
		String formattedDate = DATE_FORMATTER.format(date);
		return "data: {time: " + formattedDate + "}\n\n";
	}

	public static void main(String[] args) throws Exception {
		new ServerSentEventsDemo().launch(args);
	}
}

Many thanks for this example!