server-sent events (#177)

* server-sent events

* remove stale clients

* ping as message

server-sent-events/benchmark.js

@@ -0,0 +1,60 @@
+const http = require('http')
+
+const n = 1000;
+let connected = 0;
+let messages = 0;
+let start = Date.now();
+let phase = 'connecting';
+let connection_time;
+let broadcast_time;
+
+let message = process.argv[2] || 'msg';
+let expected_data = "data: " + message;
+
+for (let i = 0; i < n; i++) {
+    http.get({
+        host: 'localhost',
+        port: 8080,
+        path: '/events'
+    }, response => {
+        response.on('data', data => {
+            if (data.includes(expected_data)) {
+                messages += 1;
+            } else if (data.includes("data: connected\n")) {
+                connected += 1;
+            }
+        })
+    }).on('error', (_) => {});
+}
+
+setInterval(() => {
+    if (phase === 'connecting' && connected === n) {
+        // done connecting
+        phase = 'messaging';
+        connection_time = Date.now() - start;
+    }
+
+    if (phase === 'messaging') {
+        phase = 'waiting';
+        start = Date.now();
+
+        http.get({
+            host: 'localhost',
+            port: 8080,
+            path: '/broadcast/' + message
+        }, response => {
+            response.on('data', _ => {})
+        })
+    }
+
+    if (phase === 'waiting' && messages >= n) {
+        // all messages received
+        broadcast_time = Date.now() - start;
+        phase = 'paused';
+        messages = 0;
+        phase = 'messaging';
+    }
+
+    process.stdout.write("\r\x1b[K");
+    process.stdout.write(`Connected: ${connected}, connection time: ${connection_time} ms, total broadcast time: ${broadcast_time} ms`);
+}, 20)