Add experimental update stream

src/site/api/update_stream.js

@@ -0,0 +1,30 @@
+const {Readable} = require("stream")
+
+const streams = new Set()
+
+setInterval((new (function() {
+	const payload = `:keepalive ${Date.now()}\n\n`
+	for (const stream of streams.values()) {
+		stream.push(payload)
+	}
+})).constructor, 50000)
+
+module.exports = [
+	{
+		route: "/api/update_stream", methods: ["GET"], code: async () => {
+			const stream = new Readable({
+				read: function() {},
+				destroy: function() {
+					streams.delete(stream)
+				}
+			})
+			streams.add(stream)
+
+			return {
+				statusCode: 200,
+				contentType: "text/event-stream",
+				stream
+			}
+		}
+	}
+]