dns: use char code conversion instead of Buffer for nsec epsilons

bench/nsec.js

@@ -0,0 +1,16 @@
+'use strict';
+
+const bench = require('./bench');
+const nsec = require('../lib/dns/nsec');
+const {TYPE_MAP_EMPTY} = require('../lib/dns/common');
+
+const tld = 'dollarydoo';
+const ops = 100000;
+
+const end = bench('nsec');
+for (let i = 0; i < ops; i++) {
+  const prev = nsec.prevName(tld);
+  const next = nsec.nextName(tld);
+  nsec.create(prev, next, TYPE_MAP_EMPTY);
+}
+end(ops);

lib/dns/nsec.js

@@ -27,9 +27,9 @@ function nextName(tld) {
   // increment last character by one
   if (tld.length === 63) {
     // Assuming no escaped octets are present
-    const next = Buffer.from(tld, 'ascii');
-    next[next.length-1]++;
-    return next.toString() + '.';
+    let last = tld.charCodeAt(62);
+    last = String.fromCharCode(last + 1);
+    return tld.slice(0, -1) + last + '.';
   }
 
   return tld + '\\000.';
@@ -42,9 +42,9 @@ function prevName(tld) {
 
   // Decrement the last character by 1
   // assuming no escaped octets are present
-  let prev = Buffer.from(tld, 'ascii');
-  prev[prev.length-1]--;
-  prev = prev.toString();
+  let last = tld.charCodeAt(tld.length - 1);
+  last = String.fromCharCode(last - 1);
+  tld = tld.slice(0, -1) + last;
 
   // See RFC4034 6.1 Canonical DNS Name Order
   // https://tools.ietf.org/html/rfc4034#section-6.1
@@ -54,11 +54,11 @@ function prevName(tld) {
   // smaller name is `helln` append `\255`
   // to ensure that helln\255 > hellna
   // while keeping helln\255 < hello
-  if (prev.length < 63) {
-    prev += '\\255';
+  if (tld.length < 63) {
+    tld += '\\255';
   }
 
-  return util.fqdn(prev);
+  return util.fqdn(tld);
 }
 
 exports.create = create;