Update dns-in-google-sheets.mdx to include cache support in the NSLookup function.

Adding internal caching of the results on the NSLookup function to limit the number of the DNS resolver requests and speed up the results - especially in larger Google Sheets.

Author: beltofte

src/content/docs/1.1.1.1/other-ways-to-use-1.1.1.1/dns-in-google-sheets.mdx

@@ -12,7 +12,7 @@ import { Details } from "~/components"
 1.1.1.1 works directly inside Google Sheets. To get started, create a [Google Function](https://developers.google.com/apps-script/guides/sheets/functions) with the following code:
 
 ```js
-function NSLookup(type, domain) {
+function NSLookup(type, domain, usecache = true, cachettl = 1800) {
 
   if (typeof type == 'undefined') {
     throw new Error('Missing parameter 1 dns type');
@@ -22,10 +22,31 @@ function NSLookup(type, domain) {
     throw new Error('Missing parameter 2 domain name');
   }
 
+  if (typeof usecache != "boolean") {
+    throw new Error('Only boolean values allowed in 3 use cache');
+  }
+
+  if (typeof cachettl != "number") {
+    throw new Error('Only numeric values allowed in 4 cache ttl');
+  }
+
   type = type.toUpperCase();
+  domain = domain.toLowerCase();
+
+  if (usecache == true) {
+    // Cache key and hash
+    cacheKey = domain + "@" + type;
+    cacheHash = Utilities.base64Encode(cacheKey);
+    cacheBinKey = "nslookup-result-" + cacheHash;
+
+    var cache = CacheService.getScriptCache();
+    var cachedResult = cache.get(cacheBinKey);
+    if (cachedResult != null) {
+      return cachedResult;
+    }
+  }
 
   var url = 'https://cloudflare-dns.com/dns-query?name=' + encodeURIComponent(domain) + '&type=' + encodeURIComponent(type);
-
   var options = {
     muteHttpExceptions: true,
     headers: {
@@ -68,6 +89,10 @@ function NSLookup(type, domain) {
 
   var outputString = outputData.join(',');
 
+  if (usecache == true) {
+    cache.put(cacheBinKey, outputString, cachettl);
+  }
+  
   return outputString;
 }
 ```
@@ -76,6 +101,7 @@ function NSLookup(type, domain) {
 
 When you feed the function `NSLookup` a record type and a domain, you will get a DNS record value in the cell you called `NSLookup`.
 
+The function by default cache the returned DNS record value for 1800 seconds, to limit the number of DNS lookups and speed up the results especially in larger Google Sheets. Both the cache usage and the cache TTL can be controlled in argument 3 and 4.
 
 <Details header="Supported DNS record types">