Resolve fallback dns addrs during build

ts/scripts/generate-dns-fallback.ts

@@ -0,0 +1,71 @@
+// Copyright 2024 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { join } from 'path';
+import { lookup as lookupCb } from 'dns';
+import { writeFile } from 'fs/promises';
+import { promisify } from 'util';
+import type { ResolvedEndpoint } from 'electron';
+
+import { isNotNil } from '../util/isNotNil';
+
+const lookup = promisify(lookupCb);
+
+const FALLBACK_DOMAINS = [
+  'chat.signal.org',
+  'storage.signal.org',
+  'cdsi.signal.org',
+  'cdn.signal.org',
+  'cdn2.signal.org',
+  'cdn3.signal.org',
+  'updates2.signal.org',
+  'sfu.voip.signal.org',
+  'create.signal.art',
+];
+
+async function main() {
+  const config = await Promise.all(
+    FALLBACK_DOMAINS.sort().map(async domain => {
+      const addresses = await lookup(domain, { all: true });
+
+      const endpoints = addresses
+        .map(({ address, family }): ResolvedEndpoint | null => {
+          if (family === 4) {
+            return { family: 'ipv4', address };
+          }
+          if (family === 6) {
+            return { family: 'ipv6', address };
+          }
+          return null;
+        })
+        .filter(isNotNil)
+        .sort((a, b) => {
+          if (a.family < b.family) {
+            return -1;
+          }
+          if (a.family > b.family) {
+            return 1;
+          }
+
+          if (a.address < b.address) {
+            return -1;
+          }
+          if (a.address > b.address) {
+            return 1;
+          }
+          return 0;
+        });
+
+      return { domain, endpoints };
+    })
+  );
+
+  const outPath = join(__dirname, '../../build/dns-fallback.json');
+
+  await writeFile(outPath, `${JSON.stringify(config, null, 2)}\n`);
+}
+
+main().catch(error => {
+  console.error(error);
+  process.exit(1);
+});