Support for Server-Sent-Events

[KUKHUA]

Hello, I was wondering if SSE is possible with this library?

I have been trying to implement it for while, with no success.

The problem seems to be that once the handler function returns, the HTTP connection closes. To support this, there should be a way to tell it to not close the connection automatically.

[ralscha]

I think SSE works. The key is that the handler must stay blocking while streaming. The connection is closed when the handler returns, so as long as the handler does not return the connection stays open.

Here an example that works for me.

	public static void main(String[] args) throws Exception {
		HTTPHandler handler = (req, res) -> {
			String path = req.getPath();
			handleSse(req, res);
		};

		HTTPServerConfiguration config = new HTTPServerConfiguration()
				.withHandler(handler).withListener(new HTTPListenerConfiguration(8080));

		try (HTTPServer server = new HTTPServer().withConfiguration(config)) {
			server.start();
			Thread.currentThread().join();
		}
	}

	private static void handleSse(HTTPRequest req, HTTPResponse res) {
		res.setStatus(200);
		res.setHeader("Content-Type", "text/event-stream");
		res.setHeader("Cache-Control", "no-cache");
		res.setCompress(false);

		int connId = activeConnections.incrementAndGet();
		System.out.printf("[conn %d] SSE client connected. Active connections: %d%n",
				connId, activeConnections.get());

		try (OutputStream out = res.getOutputStream()) {
			int eventId = 0;

			try {
				while (!Thread.currentThread().isInterrupted()) {
					eventId++;

					String event = "id: " + eventId + "\n" + "event: tick\n"
							+ "data: {\"counter\":" + eventId + ",\"time\":\""
							+ Instant.now() + "\"}\n" + "\n";

					out.write(event.getBytes(StandardCharsets.UTF_8));
					res.flush();

					Thread.sleep(1_000);
				}
			}
			catch (IOException e) {
				System.out.printf("[conn %d] SSE client disconnected: %s%n", connId,
						e.getMessage());
			}
			catch (InterruptedException e) {
				Thread.currentThread().interrupt();
			}
			finally {
				activeConnections.decrementAndGet();
				System.out.printf(
						"[conn %d] SSE handler exiting. Active connections: %d%n", connId,
						activeConnections.get());
			}
		}
		catch (IOException e) {
			Thread.currentThread().interrupt();
		}
	}