fix: support empty TXT records in legacy url parser

The recent changes to our testing infrastructured uncovered a bug
in the legacy url parser, if an empty result was returned the logic
failed because `authSource` and `replicaSet` were not provided

lib/url_parser.js

@@ -1,11 +1,13 @@
 'use strict';
 
-const ReadPreference = require('./core').ReadPreference,
-  parser = require('url'),
-  f = require('util').format,
-  Logger = require('./core').Logger,
-  dns = require('dns');
+const ReadPreference = require('./core').ReadPreference;
+const parser = require('url');
+const f = require('util').format;
+const Logger = require('./core').Logger;
+const dns = require('dns');
 const ReadConcern = require('./read_concern');
+const qs = require('querystring');
+const MongoParseError = require('./core/error').MongoParseError;
 
 module.exports = function(url, options, callback) {
   if (typeof options === 'function') (callback = options), (options = {});
@@ -87,20 +89,20 @@ module.exports = function(url, options, callback) {
     }
 
     dns.resolveTxt(result.host, function(err, record) {
-      if (err && err.code !== 'ENODATA') return callback(err);
+      if (err && err.code !== 'ENODATA' && err.code !== 'ENOTFOUND') return callback(err);
       if (err && err.code === 'ENODATA') record = null;
 
       if (record) {
         if (record.length > 1) {
-          return callback(new Error('Multiple text records not allowed'));
+          return callback(new MongoParseError('Multiple text records not allowed'));
         }
 
-        record = record[0];
-        if (record.length > 1) record = record.join('');
-        else record = record[0];
-
-        if (!record.includes('authSource') && !record.includes('replicaSet')) {
-          return callback(new Error('Text record must only set `authSource` or `replicaSet`'));
+        record = record[0].join('');
+        const parsedRecord = qs.parse(record);
+        if (Object.keys(parsedRecord).some(key => key !== 'authSource' && key !== 'replicaSet')) {
+          return callback(
+            new MongoParseError('Text record must only set `authSource` or `replicaSet`')
+          );
         }
 
         connectionStringOptions.push(record);