Inspector proxy: Add ping/pong keepalive/heartbeat to debugger connec…

…tion (facebook#44086)

Summary:

When a debugger frontend is connected to inspector-proxy via another proxy or tunnel that times out on idle (such as [VS Code's remote tunnel](https://github.com/microsoft/vscode/blob/main/src/vs/platform/tunnel/node/tunnelService.ts)), the connection between proxy and debugger may be dropped.

In addition, when the connection is dropped without a closing handshake, the proxy does *not* detect the disconnection - no disconnect is logged to the reporter and no notifications are sent to any connected devices.

This adds a mechanism using the WebSocket-standard `ping` and `pong` frames to:
1. Keep the connection alive
2. Detect when the debugger has gone away

Note that as all WebSocket clients already **must** reply to a ping with a pong, this is non-breaking for compliant implementations: https://datatracker.ietf.org/doc/html/rfc6455#section-5.5.2

Changelog:
[General][Added] Inspector proxy: Add ping/pong keepalive to debugger connections.

Reviewed By: hoxyq

Differential Revision: D56069185

packages/dev-middleware/src/inspector-proxy/InspectorProxy.js

@@ -19,9 +19,14 @@ import type {
   PageDescription,
 } from './types';
 import type {IncomingMessage, ServerResponse} from 'http';
+// $FlowFixMe[cannot-resolve-module] libdef missing in RN OSS
+import type {Timeout} from 'timers';
 
 import Device from './Device';
 import nullthrows from 'nullthrows';
+// Import these from node:timers to get the correct Flow types.
+// $FlowFixMe[cannot-resolve-module] libdef missing in RN OSS
+import {clearTimeout, setTimeout} from 'timers';
 import url from 'url';
 import WS from 'ws';
 
@@ -32,6 +37,8 @@ const WS_DEBUGGER_URL = '/inspector/debug';
 const PAGES_LIST_JSON_URL = '/json';
 const PAGES_LIST_JSON_URL_2 = '/json/list';
 const PAGES_LIST_JSON_VERSION_URL = '/json/version';
+const MAX_PONG_LATENCY_MS = 5000;
+const DEBUGGER_HEARTBEAT_INTERVAL_MS = 10000;
 
 const INTERNAL_ERROR_CODE = 1011;
 
@@ -264,6 +271,8 @@ export default class InspectorProxy implements InspectorProxyQueries {
           throw new Error('Unknown device with ID ' + deviceId);
         }
 
+        this.#startHeartbeat(socket, DEBUGGER_HEARTBEAT_INTERVAL_MS);
+
         device.handleDebuggerConnection(socket, pageId, {
           userAgent: req.headers['user-agent'] ?? query.userAgent ?? null,
         });
@@ -279,4 +288,45 @@ export default class InspectorProxy implements InspectorProxyQueries {
     });
     return wss;
   }
+
+  // Starts pinging the socket at the given interval. Compliant clients will
+  // respond with pong frame. This serves both to detect when the client
+  // has gone away without sending a close frame, and as a keepalive in cases
+  // where proxies may drop idle connections (e.g., VS Code tunnels).
+  //
+  // https://datatracker.ietf.org/doc/html/rfc6455#section-5.5.2
+  #startHeartbeat(socket: WS, intervalMs: number) {
+    let terminateTimeout = null;
+
+    const pingTimeout: Timeout = setTimeout(() => {
+      if (socket.readyState !== WS.OPEN) {
+        // May be connecting or closing, try again later.
+        pingTimeout.refresh();
+        return;
+      }
+      socket.ping();
+      terminateTimeout = setTimeout(() => {
+        if (socket.readyState !== WS.OPEN) {
+          return;
+        }
+        // We don't use close() here because that initiates a closing handshake,
+        // which will not complete if the other end has gone away - 'close'
+        // would not be emitted.
+        //
+        // terminate() emits 'close' immediately, allowing us to handle it and
+        // inform any clients.
+        socket.terminate();
+      }, MAX_PONG_LATENCY_MS).unref();
+    }, intervalMs).unref();
+
+    socket.on('pong', () => {
+      terminateTimeout && clearTimeout(terminateTimeout);
+      pingTimeout.refresh();
+    });
+
+    socket.on('close', () => {
+      terminateTimeout && clearTimeout(terminateTimeout);
+      clearTimeout(pingTimeout);
+    });
+  }
 }