feat(urlParser): use core URL parser

Adds the ability to opt-in to using the new spec-compliant url
parser.

Fixes NODE-1304

lib/mongo_client.js

@@ -1,11 +1,12 @@
 'use strict';
 
-const parse = require('./url_parser');
+const parse = require('mongodb-core').parseConnectionString;
 const Server = require('./topologies/server');
 const Mongos = require('./topologies/mongos');
 const ReplSet = require('./topologies/replset');
 const EventEmitter = require('events').EventEmitter;
 const inherits = require('util').inherits;
+const deprecate = require('util').deprecate;
 const ReadPreference = require('mongodb-core').ReadPreference;
 const Logger = require('mongodb-core').Logger;
 const MongoError = require('mongodb-core').MongoError;
@@ -17,6 +18,12 @@ const authenticate = require('./authenticate');
 const ServerSessionPool = require('mongodb-core').Sessions.ServerSessionPool;
 const executeOperation = require('./utils').executeOperation;
 
+const legacyParse = deprecate(
+  require('./url_parser'),
+  'current URL string parser is deprecated, and will be removed in a future version. ' +
+    'To use the new parser, pass option { useNewUrlParser: true } to MongoClient.connect.'
+);
+
 /**
  * @fileOverview The **MongoClient** class is a class that allows for making Connections to MongoDB.
  *
@@ -107,9 +114,54 @@ var validOptionNames = [
   'auto_reconnect',
   'minSize',
   'monitorCommands',
-  'retryWrites'
+  'retryWrites',
+  'useNewUrlParser'
 ];
 
+const validOptionsLowerCaseToCamelCase = validOptionNames.reduce((obj, name) => {
+  obj[name.toLowerCase()] = name;
+  return obj;
+}, {});
+
+function transformUrlOptions(_object) {
+  let object = Object.assign({ servers: _object.hosts }, _object.options);
+  for (let name in object) {
+    const camelCaseName = validOptionsLowerCaseToCamelCase[name];
+    if (camelCaseName) {
+      object[camelCaseName] = object[name];
+    }
+  }
+  if (_object.auth) {
+    const auth = _object.auth;
+    for (let i in auth) {
+      if (auth[i]) {
+        object[i] = auth[i];
+      }
+    }
+    if (auth.username) {
+      object.auth = auth;
+      object.user = auth.username;
+    }
+    if (auth.db) {
+      object.dbName = auth.db;
+    }
+  }
+  if (object.maxpoolsize) {
+    object.poolSize = object.maxpoolsize;
+  }
+  if (object.readconcernlevel) {
+    object.readConcern = { level: object.readconcernlevel };
+  }
+  if (object.wtimeoutms) {
+    object.wtimeout = object.wtimeoutms;
+  }
+  return object;
+}
+
+function legacyTransformUrlOptions(object) {
+  return mergeOptions(createUnifiedOptions({}, object), object, false);
+}
+
 var ignoreOptionNames = ['native_parser'];
 var legacyOptionNames = ['server', 'replset', 'replSet', 'mongos', 'db'];
 
@@ -202,6 +254,7 @@ function validOptions(options) {
  * @param {boolean} [options.auto_reconnect=true] Enable auto reconnecting for single server instances
  * @param {boolean} [options.monitorCommands=false] Enable command monitoring for this client
  * @param {number} [options.minSize] If present, the connection pool will be initialized with minSize connections, and will never dip below minSize connections
+ * @param {boolean} [options.useNewUrlParser=false] Determines whether or not to use the new url parser
  * @param {MongoClient~connectCallback} [callback] The command result callback
  * @return {MongoClient} a MongoClient instance
  */
@@ -921,14 +974,18 @@ var connect = function(self, url, options, callback) {
     );
   }
 
-  parse(url, options, function(err, object) {
+  const parseFn = options.useNewUrlParser ? parse : legacyParse;
+  const transform = options.useNewUrlParser ? transformUrlOptions : legacyTransformUrlOptions;
+
+  parseFn(url, options, function(err, _object) {
     // Do not attempt to connect if parsing error
     if (err) return callback(err);
 
+    // Flatten
+    const object = transform(_object);
+
     // Parse the string
-    var _finalOptions = createUnifiedOptions({}, object);
-    _finalOptions = mergeOptions(_finalOptions, object, false);
-    _finalOptions = createUnifiedOptions(_finalOptions, options);
+    const _finalOptions = createUnifiedOptions(object, options);
 
     // Check if we have connection and socket timeout set
     if (_finalOptions.socketTimeoutMS == null) _finalOptions.socketTimeoutMS = 360000;