Remove retry for default interface and cache the used one

lib/tc.js

@@ -1,30 +1,25 @@
 import shell from './shell.js';
 import sudo from './sudo.js';
 
-const delay = (ms) => new Promise((result) => setTimeout(result, ms));
-
 async function getDefaultInterface() {
-  const command =
-    "sudo ip route | awk '/default/ {print $5; exit}' | tr -d '\n'";
-
-  // Retry a few times since GitHub Actions sometimes temporarily loses the default route
-  for (let attempt = 0; attempt < 3; attempt++) {
-    const result = await shell(command);
-    if (result.stdout.length > 0) {
-      return result.stdout;
-    }
-    if (result.stderr.length > 0) {
-      throw new Error(
-        'There was an error getting the default interface:\n\n' + result.stderr
-      );
-    }
-    await delay(1000);
+  // Try the default route first
+  const routeResult = await shell(
+    "sudo ip route | awk '/default/ {print $5; exit}' | tr -d '\n'"
+  );
+  if (routeResult.stdout.length > 0) {
+    return routeResult.stdout;
   }
 
-  const result = await shell('sudo ip route show');
-  throw new Error(
-    `There was an error getting the default interface ${result.stdout}`
+  // Fall back to finding the interface with a global IP address,
+  // since the default route may be gone while throttling is active
+  const addrResult = await shell(
+    "ip -o -4 addr show scope global | awk '{print $2; exit}'"
   );
+  if (addrResult.stdout.trim().length > 0) {
+    return addrResult.stdout.trim();
+  }
+
+  throw new Error('Could not find the default network interface');
 }
 
 async function moduleProbe() {