Fix shutdown with active WebSocket clients

server.js

@@ -11,6 +11,7 @@ const PORT = Number.parseInt(process.env.PORT || '3000', 10);
 const HOST = process.env.HOST || '127.0.0.1';
 const TAIL_LINES = Number.parseInt(process.env.TAIL_LINES || '200', 10);
 const WATCH_INTERVAL_MS = Number.parseInt(process.env.WATCH_INTERVAL_MS || '500', 10);
+const SHUTDOWN_TIMEOUT_MS = Number.parseInt(process.env.SHUTDOWN_TIMEOUT_MS || '3000', 10);
 const PUBLIC_DIR = path.join(__dirname, 'public');
 const LOG_FILE = path.resolve(process.env.LOG_FILE || process.argv[2] || 'sample.log');
 
@@ -275,14 +276,53 @@ async function main() {
     console.log(`Streaming ${LOG_FILE}`);
   });
 
-  function shutdown() {
-    fs.unwatchFile(LOG_FILE);
-    wss.close();
-    server.close(() => process.exit(0));
+  let shuttingDown = false;
+
+  function shutdown(signal) {
+    if (shuttingDown) {
+      console.error(`${signal} received again; forcing shutdown.`);
+      process.exit(1);
     }
 
-  process.on('SIGINT', shutdown);
-  process.on('SIGTERM', shutdown);
+    shuttingDown = true;
+    console.log(`${signal} received; shutting down.`);
+    fs.unwatchFile(LOG_FILE);
+
+    const shutdownTimer = setTimeout(() => {
+      console.error(`Shutdown exceeded ${SHUTDOWN_TIMEOUT_MS}ms; forcing exit.`);
+      process.exit(1);
+    }, SHUTDOWN_TIMEOUT_MS);
+    shutdownTimer.unref();
+
+    const terminateTimer = setTimeout(() => {
+      for (const client of wss.clients) {
+        if (client.readyState !== WebSocket.CLOSED) {
+          client.terminate();
+        }
+      }
+    }, Math.min(500, SHUTDOWN_TIMEOUT_MS));
+    terminateTimer.unref();
+
+    for (const client of wss.clients) {
+      client.close(1001, 'Server shutting down');
+    }
+
+    wss.close();
+
+    server.close((error) => {
+      clearTimeout(shutdownTimer);
+
+      if (error) {
+        console.error(error);
+        process.exit(1);
+      }
+
+      process.exit(0);
+    });
+  }
+
+  process.on('SIGINT', () => shutdown('SIGINT'));
+  process.on('SIGTERM', () => shutdown('SIGTERM'));
 }
 
 main().catch((error) => {