Fix #13, do not test custom TLD

package.json

@@ -34,6 +34,7 @@
     "consola": "^3.2.3",
     "glob": "^10.3.10",
     "node-fetch": "^2.7.0",
+    "tldts": "^6.1.4",
     "yargs": "^17.7.2"
   },
   "devDependencies": {

src/utils.js

@@ -1,3 +1,5 @@
+const tldts = require('tldts');
+
 /**
  * Helper function that takes an array and returns a new one without any
  * duplicate items.
@@ -17,25 +19,35 @@ function unique(arr) {
  * @returns {boolean} Returns true if the domain is valid, false otherwise.
  */
 function validDomain(domain) {
-    if (domain.endsWith('.onion')) {
-        // Note, that we don't count .onion domains valid as their existence
-        // cannot be verified with the urlfilter service.
+    if (domain.startsWith('/') && domain.endsWith('/')) {
+        // Ignore regular expressions.
+        return false;
+    }
+
+    const result = tldts.parse(`https://${domain}/`);
+
+    if (result === null || result.domain === null) {
+        return false;
+    }
+
+    if (result.isIp) {
+        // IP addresses cannot be verified too so just ignore them too.
         return false;
     }
 
-    if (/^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}$/.test(domain)) {
-        // IPv4 addresses cannot be verified too so just ignore them too.
-        // Don't check for IPv6 as they won't be matched by the domain regex.
+    if (result.isPrivate) {
+        // Do not check custom hostnames. It could be an .onion domain or
+        // a different custom TLD which we simply cannot test for existence.
         return false;
     }
 
-    if (!domain.includes('.')) {
+    if (result.domainWithoutSuffix === '') {
         // Ignore top-level domains to avoid false positives on things like:
         // https://github.com/AdguardTeam/DeadDomainsLinter/issues/6
         return false;
     }
 
-    return domain.match(/^[a-z0-9.-]+$/i) !== null;
+    return true;
 }
 
 module.exports = {