Add IP connectivity test script

README.md

@@ -134,6 +134,12 @@ Each script includes detailed documentation on what it does and how it works in
 
         This is a low-level hook that applies to _all_ network connections. This ensures that all connections are forcibly redirected to the target proxy server, even those which ignore proxy settings or make other raw socket connections.
 
+* `utilities/test-ip-connectivity.js`
+
+    You probably don't want to use this normally as part of interception itself, but it can be very useful as part of your configuration setup.
+
+    This script allows you to configure a list of possible IP addresses and a target port, and will then send the results of those connectivity tests for each IP:PORT address back to the Frida client, so you can confirm which IP address of a proxy host (e.g. your computer) is reachable from your target device.
+
 ---
 
 These scripts are part of [a broader HTTP Toolkit project](https://httptoolkit.com/blog/frida-mobile-interception-funding/), funded through the [NGI Zero Entrust Fund](https://nlnet.nl/entrust), established by [NLnet](https://nlnet.nl) with financial support from the European Commission's [Next Generation Internet](https://ngi.eu) program. Learn more on the [NLnet project page](https://nlnet.nl/project/F3-AppInterception#ack).

utilities/test-ip-connectivity.js

@@ -0,0 +1,55 @@
+/**
+ * This script is a little different from the others, and is designed to help with setup,
+ * particularly in automated scenarios, rather than supporting interception/unpinning/etc.
+ *
+ * Using this script, you can provide a list of IP addresses and a port, and the script will
+ * send messages back to your Frida client for each IP:PORT address that is reachable from
+ * the target device. When your proxy is running on a remote device from the target host,
+ * this can be useful to work out which proxy IP address should be used.
+ *
+ * Source available at https://github.com/httptoolkit/frida-interception-and-unpinning/
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ * SPDX-FileCopyrightText: Tim Perry <tim@httptoolkit.com>
+ */
+
+// Modify this to specify the addresses you'd like to test:
+const IP_ADDRESSES_TO_TEST = [
+];
+
+const TARGET_PORT = 0;
+
+
+
+
+// ----------------------------------------------------------------------------
+// You don't need to modify any of the below - this is the logic that does the
+// checks themselves.
+// ----------------------------------------------------------------------------
+
+if (IP_ADDRESSES_TO_TEST.length === 0) {
+    throw new Error('No IP addresses provided to check - please modify IP_ADDRESSES_TO_TEST');
+}
+
+if (TARGET_PORT === 0) {
+    throw new Error('No target port provided to check - please modify TARGET_PORT');
+}
+
+async function testAddress(ip, port) {
+    try {
+        const socket = await Socket.connect({ host: ip, port });
+        socket.close();
+        return true;
+    } catch (e) {
+        return false;
+    }
+}
+
+IP_ADDRESSES_TO_TEST.forEach(async (ip) => {
+    const result = await testAddress(ip, TARGET_PORT);
+    send({
+        type: 'connectivity-result',
+        ip,
+        port: TARGET_PORT,
+        result
+    });
+});