Intercept global fetch in Node 18.2.0+

While global fetch was supported in Node 18, it was impossible to use
with proxies until 18.2.0. From this point onwards, it is usable as
long as you use a separate Undici dependency to do that configuration.

Author: pimterry

overrides/js/package-lock.json

@@ -5,6 +5,7 @@
   "license": "AGPL-3.0-or-later",
   "dependencies": {
     "global-agent": "3.0.0",
-    "global-tunnel-ng": "2.7.1"
+    "global-tunnel-ng": "2.7.1",
+    "undici": "^5.2.0"
   }
 }

overrides/js/package.json

@@ -112,4 +112,13 @@ if (MAJOR_NODEJS_VERSION >= 10) {
     // `global-tunnel-ng` works only with Node.js v10 and below.
     const globalTunnel = require('global-tunnel-ng');
     globalTunnel.initialize();
+}
+
+if (MAJOR_NODEJS_VERSION >= 18 || global.fetch) {
+    // Node 18 enables fetch by default (available previously behind a flag). This does not use
+    // the existing agent API, so is not intercepted by global-agent. Instead, the only way to
+    // set the HTTP proxy is to separately import Undici (used internally by Node) and configure
+    // Undici's global proxy agent. We bundle our own Undici dep so we can do this reliably,
+    // and here we import it to trigger the Undici setup hook defined above.
+    require('undici');
 }

overrides/js/prepend-node.js

@@ -5,6 +5,12 @@ require('http').get('http://example.test/js/http');
 require('https').get('https://example.test/js/https');
 
 function sendRequestsTo(baseUrl) {
+    if (global.fetch) {
+        // Only in Node 18+ so this isn't actually covered by unit tests, but
+        // it's useful for manually testing.
+        fetch(baseUrl + '/global-fetch');
+    }
+
     require('request').get(baseUrl + '/request');
     require('axios').get(baseUrl + '/axios');
     require('superagent').get(baseUrl + '/superagent').end(() => {});