[Node] Gracefully handle connection errors in the outbound network proxy (#2370)

## Motivation for the change, related issues

As discovered in Automattic/studio#1491, adding
a timeout before closing the network connection in the outbound network
proxy prevents freezing the PHP runtime when the target cannot be
reached.

This PR adds such a timeout.

The exact reason behind this behavior isn't well understood yet. The
freeze is not deterministic or easy to reproduce, which is why this PR
does not ship any tests. We should keep an eye on this and, if it ever
comes up again, invest some time in a proper deep dive to understand all
the factors at play.

Related to Automattic/studio#1491

cc @gavande1 @mho22

Author: adamziel

packages/php-wasm/node/src/lib/networking/outbound-ws-to-tcp-proxy.ts

@@ -8,9 +8,9 @@
 'use strict';
 
 import * as dns from 'dns';
-import * as util from 'node:util';
-import * as net from 'net';
 import * as http from 'http';
+import * as net from 'net';
+import * as util from 'node:util';
 import { WebSocketServer } from 'ws';
 import { debugLog } from './utils';
 
@@ -146,6 +146,15 @@ async function onWsConnect(client: any, request: http.IncomingMessage) {
 		return;
 	}
 
+	// Validate port range
+	if (reqTargetPort < 0 || reqTargetPort > 65535) {
+		clientLog('Invalid port number: ' + reqTargetPort);
+		// Send empty binary data to notify requester that connection failed
+		client.send([]);
+		client.close(3000);
+		return;
+	}
+
 	// eslint-disable-next-line prefer-const
 	let target: any;
 	const recvQueue: Buffer[] = [];
@@ -207,7 +216,11 @@ async function onWsConnect(client: any, request: http.IncomingMessage) {
 			// Send empty binary data to notify requester that connection was
 			// initiated
 			client.send([]);
-			client.close(3000);
+			// Without this random timeout, PHP sometimes doesn't notice the socket
+			// disconnected. TODO: figure out why.
+			setTimeout(() => {
+				client.close(3000);
+			});
 			return;
 		}
 	} else {
@@ -238,7 +251,16 @@ async function onWsConnect(client: any, request: http.IncomingMessage) {
 	});
 	target.on('error', function (e: any) {
 		clientLog('target connection error', e);
-		target.end();
-		client.close(3000);
+		client.send([]);
+		// Without this random timeout, PHP sometimes doesn't notice the socket
+		// disconnected. TODO: figure out why.
+		setTimeout(() => {
+			client.close(3000);
+			try {
+				target.end();
+			} catch {
+				// Ignore
+			}
+		});
 	});
 }