examples: add examples/vweb/server_sent_events; implement vweb.sse

examples/vweb/server_sent_events/server.v

@@ -0,0 +1,38 @@
+module main
+
+import rand
+import time
+import vweb
+import vweb.sse
+
+struct App {
+	vweb.Context
+}
+
+fn main() {
+	vweb.run<App>(8081)
+}
+
+pub fn (mut app App) init_once() {
+	app.serve_static('/favicon.ico', 'favicon.ico', 'img/x-icon')
+	app.handle_static('.')
+}
+
+pub fn (mut app App) index() vweb.Result {
+	title := 'SSE Example'
+	return $vweb.html()
+}
+
+fn (mut app App) sse() vweb.Result {
+	mut session := sse.new_connection(app.conn)
+	// NB: you can setup session.write_timeout and session.headers here
+	session.start() or { return app.server_error(501) }
+	session.send_message(data: 'ok') or { return app.server_error(501) }
+	for {
+		data := '{"time": "$time.now().str()", "random_id": "$rand.ulid()"}'
+		session.send_message(event: 'ping', data: data) or { return app.server_error(501) }
+		println('> sent event: $data')
+		time.sleep_ms(1000)
+	}
+	return app.server_error(501)
+}