feat: directConnection adds unify behavior for replica set discovery

Adds `directConnection` option to unify behavior around configuration for replica set discovery. Migrated mongodb/specifications tests from commit "e56f5eceed7729f8b9b43a4a1f76c7e5840db49f". Skips SDAM tests for legacy topology / behavior that we do not intend to introduce to the legacy topology types. Users should switch to the unified topology.

NODE-2452

Author: Thomas Reggi

lib/core/sdam/topology.js

@@ -813,10 +813,16 @@ function parseStringSeedlist(seedlist) {
 }
 
 function topologyTypeFromSeedlist(seedlist, options) {
+  if (options.directConnection) {
+    return TopologyType.Single;
+  }
+
   const replicaSet = options.replicaSet || options.setName || options.rs_name;
-  if (seedlist.length === 1 && !replicaSet) return TopologyType.Single;
-  if (replicaSet) return TopologyType.ReplicaSetNoPrimary;
-  return TopologyType.Unknown;
+  if (replicaSet == null) {
+    return TopologyType.Unknown;
+  }
+
+  return TopologyType.ReplicaSetNoPrimary;
 }
 
 function randomSelection(array) {

lib/core/sdam/topology_description.js

@@ -161,7 +161,7 @@ class TopologyDescription {
     }
 
     if (topologyType === TopologyType.Unknown) {
-      if (serverType === ServerType.Standalone) {
+      if (serverType === ServerType.Standalone && this.servers.size !== 1) {
         serverDescriptions.delete(address);
       } else {
         topologyType = topologyTypeForServerType(serverType);
@@ -274,8 +274,22 @@ class TopologyDescription {
 }
 
 function topologyTypeForServerType(serverType) {
-  if (serverType === ServerType.Mongos) return TopologyType.Sharded;
-  if (serverType === ServerType.RSPrimary) return TopologyType.ReplicaSetWithPrimary;
+  if (serverType === ServerType.Standalone) {
+    return TopologyType.Single;
+  }
+
+  if (serverType === ServerType.Mongos) {
+    return TopologyType.Sharded;
+  }
+
+  if (serverType === ServerType.RSPrimary) {
+    return TopologyType.ReplicaSetWithPrimary;
+  }
+
+  if (serverType === ServerType.RSGhost || serverType === ServerType.Unknown) {
+    return TopologyType.Unknown;
+  }
+
   return TopologyType.ReplicaSetNoPrimary;
 }
 

lib/core/uri_parser.js

@@ -37,6 +37,10 @@ function matchesParentDomain(srvAddress, parentDomain) {
 function parseSrvConnectionString(uri, options, callback) {
   const result = URL.parse(uri, true);
 
+  if (options.directConnection || options.directconnection) {
+    return callback(new MongoParseError('directConnection not supported with SRV URI'));
+  }
+
   if (result.hostname.split('.').length < 3) {
     return callback(new MongoParseError('URI does not have hostname, domain name and tld'));
   }
@@ -215,7 +219,8 @@ const CASE_TRANSLATION = {
   tlscertificatekeyfile: 'tlsCertificateKeyFile',
   tlscertificatekeyfilepassword: 'tlsCertificateKeyFilePassword',
   wtimeout: 'wTimeoutMS',
-  j: 'journal'
+  j: 'journal',
+  directconnection: 'directConnection'
 };
 
 /**
@@ -565,10 +570,6 @@ function parseConnectionString(uri, options, callback) {
     return callback(new MongoParseError('Invalid protocol provided'));
   }
 
-  if (protocol === PROTOCOL_MONGODB_SRV) {
-    return parseSrvConnectionString(uri, options, callback);
-  }
-
   const dbAndQuery = cap[4].split('?');
   const db = dbAndQuery.length > 0 ? dbAndQuery[0] : null;
   const query = dbAndQuery.length > 1 ? dbAndQuery[1] : null;
@@ -581,6 +582,11 @@ function parseConnectionString(uri, options, callback) {
   }
 
   parsedOptions = Object.assign({}, parsedOptions, options);
+
+  if (protocol === PROTOCOL_MONGODB_SRV) {
+    return parseSrvConnectionString(uri, parsedOptions, callback);
+  }
+
   const auth = { username: null, password: null, db: db && db !== '' ? qs.unescape(db) : null };
   if (parsedOptions.auth) {
     // maintain support for legacy options passed into `MongoClient`
@@ -674,6 +680,22 @@ function parseConnectionString(uri, options, callback) {
     return callback(new MongoParseError('No hostname or hostnames provided in connection string'));
   }
 
+  const directConnection = !!parsedOptions.directConnection;
+  if (directConnection && hosts.length !== 1) {
+    // If the option is set to true, the driver MUST validate that there is exactly one host given
+    // in the host list in the URI, and fail client creation otherwise.
+    return callback(new MongoParseError('directConnection option requires exactly one host'));
+  }
+
+  // NOTE: this behavior will go away in v4.0, we will always auto discover there
+  if (
+    parsedOptions.directConnection == null &&
+    hosts.length === 1 &&
+    parsedOptions.replicaSet == null
+  ) {
+    parsedOptions.directConnection = true;
+  }
+
   const result = {
     hosts: hosts,
     auth: auth.db || auth.username ? auth : null,

lib/mongo_client.js

@@ -145,6 +145,7 @@ const validOptions = require('./operations/connect').validOptions;
  * @param {boolean} [options.useUnifiedTopology] Enables the new unified topology layer
  * @param {AutoEncrypter~AutoEncryptionOptions} [options.autoEncryption] Optionally enable client side auto encryption
  * @param {DriverInfoOptions} [options.driverInfo] Allows a wrapping driver to amend the client metadata generated by the driver to include information about the wrapping driver
+ * @param {boolean} [options.directConnection=false] Enable directConnection
  * @param {MongoClient~connectCallback} [callback] The command result callback
  * @return {MongoClient} a MongoClient instance
  */
@@ -406,6 +407,7 @@ MongoClient.prototype.isConnected = function(options) {
  * @param {number} [options.numberOfRetries=5] The number of retries for a tailable cursor
  * @param {boolean} [options.auto_reconnect=true] Enable auto reconnecting for single server instances
  * @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.directConnection=false] Enable directConnection
  * @param {MongoClient~connectCallback} [callback] The command result callback
  * @return {Promise<MongoClient>} returns Promise if no callback passed
  */

lib/operations/connect.js

@@ -153,7 +153,8 @@ const validOptionNames = [
   'tlsCertificateKeyFilePassword',
   'minHeartbeatFrequencyMS',
   'heartbeatFrequencyMS',
-  'waitQueueTimeoutMS'
+  'waitQueueTimeoutMS',
+  'directConnection'
 ];
 
 const ignoreOptionNames = ['native_parser'];

test/functional/core/replset_state.test.js

@@ -12,11 +12,21 @@ describe('ReplicaSet state', function() {
 
   fs.readdirSync(path)
     .filter(x => x.indexOf('.json') !== -1)
-    .filter(x => !x.includes('repeated'))
     .forEach(x => {
-      var testData = require(f('%s/%s', path, x));
+      const testData = require(f('%s/%s', path, x));
+      const description = testData.description;
+      it(description, function(done) {
+        if (
+          description.match(/Repeated ismaster response must be processed/) ||
+          description.match(/Primary mismatched me is not removed/) ||
+          description.match(/replicaSet URI option causes starting topology to be RSNP/) ||
+          description.match(/Discover secondary with directConnection URI option/) ||
+          description.match(/Discover ghost with directConnection URI option/)
+        ) {
+          this.skip();
+          return;
+        }
 
-      it(testData.description, function(done) {
         executeEntry(testData, done);
       });
     });

test/spec/initial-dns-seedlist-discovery/direct-connection-false.json

@@ -0,0 +1,14 @@
+{
+  "uri": "mongodb+srv://test3.test.build.10gen.cc/?directConnection=false",
+  "seeds": [
+    "localhost.test.build.10gen.cc:27017"
+  ],
+  "hosts": [
+    "localhost:27017",
+    "localhost:27018",
+    "localhost:27019"
+  ],
+  "options": {
+    "ssl": true
+  }
+}

test/spec/initial-dns-seedlist-discovery/direct-connection-false.yml

@@ -0,0 +1,9 @@
+uri: "mongodb+srv://test3.test.build.10gen.cc/?directConnection=false"
+seeds:
+    - localhost.test.build.10gen.cc:27017
+hosts:
+    - localhost:27017
+    - localhost:27018
+    - localhost:27019
+options:
+    ssl: true

test/spec/initial-dns-seedlist-discovery/direct-connection-true.json

@@ -0,0 +1,7 @@
+{
+  "uri": "mongodb+srv://test3.test.build.10gen.cc/?directConnection=true",
+  "seeds": [],
+  "hosts": [],
+  "error": true,
+  "comment": "Should fail because directConnection=true is incompatible with SRV URIs."
+}

test/spec/initial-dns-seedlist-discovery/direct-connection-true.yml

@@ -0,0 +1,5 @@
+uri: "mongodb+srv://test3.test.build.10gen.cc/?directConnection=true"
+seeds: []
+hosts: []
+error: true
+comment: Should fail because directConnection=true is incompatible with SRV URIs.