fix(operations): do not call require in a hot path

lib/operations/collection_ops.js

@@ -18,10 +18,14 @@ const handleCallback = require('../utils').handleCallback;
 const indexInformationDb = require('./db_ops').indexInformation;
 const isObject = require('../utils').isObject;
 const Long = require('mongodb-core').BSON.Long;
+const makeLazyLoader = require('../utils').makeLazyLoader;
 const MongoError = require('mongodb-core').MongoError;
 const ReadPreference = require('mongodb-core').ReadPreference;
 const toError = require('../utils').toError;
 
+const loadCollection = makeLazyLoader(`${__dirname}/../collection`);
+const loadDb = makeLazyLoader(`${__dirname}/../db`);
+
 /**
  * Group function helper
  * @ignore
@@ -987,7 +991,7 @@ function mapReduce(coll, map, reduce, options, callback) {
     if (result.result != null && typeof result.result === 'object') {
       const doc = result.result;
       // Return a collection from another db
-      const Db = require('../db');
+      let Db = loadDb();
       collection = new Db(doc.db, coll.s.db.s.topology, coll.s.db.s.options).collection(
         doc.collection
       );
@@ -1204,7 +1208,7 @@ function removeDocuments(coll, selector, options, callback) {
  * @param {Collection~collectionResultCallback} [callback] The results callback
  */
 function rename(coll, newName, options, callback) {
-  const Collection = require('../collection');
+  let Collection = loadCollection();
   // Check the collection name
   checkCollectionName(newName);
   // Build the command

lib/operations/cursor_ops.js

@@ -3,9 +3,12 @@
 const buildCountCommand = require('./collection_ops').buildCountCommand;
 const formattedOrderClause = require('../utils').formattedOrderClause;
 const handleCallback = require('../utils').handleCallback;
+const makeLazyLoader = require('../utils').makeLazyLoader;
 const MongoError = require('mongodb-core').MongoError;
 const push = Array.prototype.push;
 
+const loadCursor = makeLazyLoader(`${__dirname}/../cursor`);
+
 /**
  * Get the count of documents for this cursor.
  *
@@ -74,7 +77,7 @@ function count(cursor, applySkipLimit, opts, callback) {
  * @param {Cursor~resultCallback} callback The result callback.
  */
 function each(cursor, callback) {
-  const Cursor = require('../cursor');
+  let Cursor = loadCursor();
 
   if (!callback) throw MongoError.create({ message: 'callback is mandatory', driver: true });
   if (cursor.isNotified()) return;
@@ -114,7 +117,7 @@ function each(cursor, callback) {
  * @param {Cursor~resultCallback} [callback] The result callback.
  */
 function hasNext(cursor, callback) {
-  const Cursor = require('../cursor');
+  let Cursor = loadCursor();
 
   if (cursor.s.currentDoc) {
     return callback(null, true);
@@ -165,7 +168,7 @@ function next(cursor, callback) {
 
 // Get the next available document from the cursor, returns null if no more documents are available.
 function nextObject(cursor, callback) {
-  const Cursor = require('../cursor');
+  let Cursor = loadCursor();
 
   if (cursor.s.state === Cursor.CLOSED || (cursor.isDead && cursor.isDead()))
     return handleCallback(
@@ -196,7 +199,7 @@ function nextObject(cursor, callback) {
  * @param {Cursor~toArrayResultCallback} [callback] The result callback.
  */
 function toArray(cursor, callback) {
-  const Cursor = require('../cursor');
+  let Cursor = loadCursor();
 
   const items = [];
 

lib/operations/db_ops.js

@@ -6,6 +6,7 @@ const resolveReadPreference = require('../utils').resolveReadPreference;
 const crypto = require('crypto');
 const debugOptions = require('../utils').debugOptions;
 const handleCallback = require('../utils').handleCallback;
+const makeLazyLoader = require('../utils').makeLazyLoader;
 const MongoError = require('mongodb-core').MongoError;
 const parseIndexOptions = require('../utils').parseIndexOptions;
 const ReadPreference = require('mongodb-core').ReadPreference;
@@ -17,6 +18,9 @@ const findOne = require('./collection_ops').findOne;
 const remove = require('./collection_ops').remove;
 const updateOne = require('./collection_ops').updateOne;
 
+const loadCollection = makeLazyLoader(`${__dirname}/../collection`);
+const loadDb = makeLazyLoader(`${__dirname}/../db`);
+
 const debugFields = [
   'authSource',
   'w',
@@ -64,7 +68,7 @@ const illegalCommandFields = [
  * @param {Db~resultCallback} [callback] The command result callback
  */
 function addUser(db, username, password, options, callback) {
-  const Db = require('../db');
+  let Db = loadDb();
 
   // Did the user destroy the topology
   if (db.serverConfig && db.serverConfig.isDestroyed())
@@ -132,7 +136,7 @@ function addUser(db, username, password, options, callback) {
  * @param {Db~collectionsResultCallback} [callback] The results callback
  */
 function collections(db, options, callback) {
-  const Collection = require('../collection');
+  let Collection = loadCollection();
 
   options = Object.assign({}, options, { nameOnly: true });
   // Let's get the collection names
@@ -172,7 +176,7 @@ function collections(db, options, callback) {
  * @param {Db~collectionResultCallback} [callback] The results callback
  */
 function createCollection(db, name, options, callback) {
-  const Collection = require('../collection');
+  let Collection = loadCollection();
 
   // Get the write concern options
   const finalOptions = applyWriteConcern(Object.assign({}, options), { db }, options);
@@ -632,7 +636,7 @@ function profilingLevel(db, options, callback) {
  * @param {Db~resultCallback} [callback] The command result callback
  */
 function removeUser(db, username, options, callback) {
-  const Db = require('../db');
+  let Db = loadDb();
 
   // Attempt to execute command
   executeAuthRemoveUserCommand(db, username, options, (err, result) => {

lib/operations/mongo_client_ops.js

@@ -3,6 +3,7 @@
 const authenticate = require('../authenticate');
 const deprecate = require('util').deprecate;
 const Logger = require('mongodb-core').Logger;
+const makeLazyLoader = require('../utils').makeLazyLoader;
 const MongoError = require('mongodb-core').MongoError;
 const Mongos = require('../topologies/mongos');
 const parse = require('mongodb-core').parseConnectionString;
@@ -11,6 +12,8 @@ const ReplSet = require('../topologies/replset');
 const Server = require('../topologies/server');
 const ServerSessionPool = require('mongodb-core').Sessions.ServerSessionPool;
 
+const loadClient = makeLazyLoader(`${__dirname}/../mongo_client`);
+
 const monitoringEvents = [
   'timeout',
   'close',
@@ -127,7 +130,7 @@ function clearAllEvents(topology) {
 
 // Collect all events in order from SDAM
 function collectEvents(mongoClient, topology) {
-  const MongoClient = require('../mongo_client');
+  let MongoClient = loadClient();
   const collectedEvents = [];
 
   if (mongoClient instanceof MongoClient) {

lib/utils.js

@@ -694,6 +694,16 @@ function deprecateOptions(config, fn) {
   return deprecated;
 }
 
+function makeLazyLoader(modulePath) {
+  let mod;
+  return function lazyLoad() {
+    if (!mod) {
+      mod = require(modulePath);
+    }
+    return mod;
+  };
+}
+
 module.exports = {
   filterOptions,
   mergeOptions,
@@ -719,5 +729,6 @@ module.exports = {
   isPromiseLike,
   decorateWithCollation,
   decorateWithReadConcern,
-  deprecateOptions
+  deprecateOptions,
+  makeLazyLoader
 };