feat(client-ops): allow bypassing creation of topologies on connect

Author: mbroadst

lib/operations/mongo_client_ops.js

@@ -31,7 +31,8 @@ const monitoringEvents = [
   'ping',
   'ha',
   'all',
-  'fullsetup'
+  'fullsetup',
+  'open'
 ];
 const ignoreOptionNames = ['native_parser'];
 const legacyOptionNames = ['server', 'replset', 'replSet', 'mongos', 'db'];
@@ -132,11 +133,11 @@ function collectEvents(mongoClient, topology) {
   if (mongoClient instanceof MongoClient) {
     monitoringEvents.forEach(event => {
       topology.on(event, (object1, object2) => {
-        collectedEvents.push({
-          event: event,
-          object1: object1,
-          object2: object2
-        });
+        if (event === 'open') {
+          collectedEvents.push({ event: event, object1: mongoClient });
+        } else {
+          collectedEvents.push({ event: event, object1: object1, object2: object2 });
+        }
       });
     });
   }
@@ -346,11 +347,11 @@ function createServer(mongoClient, options, callback) {
   // Set default options
   const servers = translateOptions(options);
 
-  // Propagate the events to the client
-  const collectedEvents = collectEvents(mongoClient, servers[0]);
-
   const server = servers[0];
 
+  // Propagate the events to the client
+  const collectedEvents = collectEvents(mongoClient, server);
+
   // Connect to topology
   server.connect(options, (err, topology) => {
     if (err) {
@@ -389,8 +390,11 @@ function createTopology(mongoClient, topologyType, options, callback) {
   // Pass in the promise library
   options.promiseLibrary = mongoClient.s.promiseLibrary;
 
+  const translationOptions = {};
+  if (topologyType === 'unified') translationOptions.createServers = false;
+
   // Set default options
-  const servers = translateOptions(options);
+  const servers = translateOptions(options, translationOptions);
 
   // Create the topology
   let topology;
@@ -571,7 +575,9 @@ function transformUrlOptions(_object) {
   return object;
 }
 
-function translateOptions(options) {
+function translateOptions(options, translationOptions) {
+  translationOptions = Object.assign({}, { createServers: true }, translationOptions);
+
   // If we have a readPreference passed in by the db options
   if (typeof options.readPreference === 'string' || typeof options.read_preference === 'string') {
     options.readPreference = new ReadPreference(options.readPreference || options.read_preference);
@@ -591,6 +597,10 @@ function translateOptions(options) {
   if (options.socketTimeoutMS == null) options.socketTimeoutMS = 360000;
   if (options.connectTimeoutMS == null) options.connectTimeoutMS = 30000;
 
+  if (!translationOptions.createServers) {
+    return;
+  }
+
   // Create server instances
   return options.servers.map(serverObj => {
     return serverObj.domain_socket