Enhance WHOIS fallback error handling and add IANA WHOIS parsing utilities

Updated the error messages in the lookupDomain function to provide clearer guidance when RDAP is unavailable or when no WHOIS server is discovered for a TLD. Introduced new utility functions to parse IANA WHOIS responses, improving the discovery process for WHOIS servers and registration information URLs.

src/index.ts

@@ -8,6 +8,8 @@ import { whoisQuery } from "./whois/client.js";
 import {
   extractWhoisReferral,
   ianaWhoisServerForTld,
+  getIanaWhoisTextForTld,
+  parseIanaRegistrationInfoUrl,
 } from "./whois/discovery.js";
 import { normalizeWhois } from "./whois/normalize.js";
 import { WHOIS_TLD_EXCEPTIONS } from "./whois/servers.js";
@@ -54,7 +56,7 @@ export async function lookupDomain(
       if (opts?.rdapOnly) {
         return {
           ok: false,
-          error: "RDAP not available or failed for this TLD",
+          error: `RDAP not available or failed for TLD '${tld}'. Many TLDs do not publish RDAP; try WHOIS fallback (omit rdapOnly).`,
         };
       }
     }
@@ -62,7 +64,18 @@ export async function lookupDomain(
     // WHOIS fallback path
     const whoisServer = await ianaWhoisServerForTld(tld, opts);
     if (!whoisServer) {
-      return { ok: false, error: "No WHOIS server discovered for TLD" };
+      // Provide a clearer, actionable message
+      const ianaText = await getIanaWhoisTextForTld(tld, opts);
+      const regUrl = ianaText
+        ? parseIanaRegistrationInfoUrl(ianaText)
+        : undefined;
+      const hint = regUrl
+        ? ` See registration info at ${regUrl}.`
+        : "";
+      return {
+        ok: false,
+        error: `No WHOIS server discovered for TLD '${tld}'. This registry may not publish public WHOIS over port 43.${hint}`,
+      };
     }
     // Query the TLD server first; if it returns a referral, we follow it below.
     let res = await whoisQuery(whoisServer, domain, opts);