feat: directConnection adds unify behavior for replica set discovery

lib/connection_string.js

@@ -37,6 +37,10 @@ function matchesParentDomain(srvAddress, parentDomain) {
 function parseSrvConnectionString(uri, options, callback) {
   const result = URL.parse(uri, true);
 
+  if (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'));
   }
@@ -217,7 +221,8 @@ const CASE_TRANSLATION = {
   tlscertificatekeyfile: 'tlsCertificateKeyFile',
   tlscertificatekeyfilepassword: 'tlsCertificateKeyFilePassword',
   wtimeout: 'wTimeoutMS',
-  j: 'journal'
+  j: 'journal',
+  directconnection: 'directConnection'
 };
 
 /**
@@ -594,10 +599,6 @@ 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;
@@ -613,6 +614,12 @@ function parseConnectionString(uri, options, callback) {
     return callback(parseError);
   }
 
+  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`
@@ -706,6 +713,13 @@ 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'));
+  }
+
   const result = {
     hosts: hosts,
     auth: auth.db || auth.username ? auth : null,

lib/mongo_client.js

@@ -102,7 +102,7 @@ const { connect, validOptions } = require('./operations/connect');
  * @param {number} [options.reconnectInterval=1000] Server will wait # milliseconds between retries
  * @param {boolean} [options.ha=true] Control if high availability monitoring runs for Replicaset or Mongos proxies
  * @param {number} [options.haInterval=10000] The High availability period for replicaset inquiry
- * @param {string} [options.replicaSet=undefined] The Replicaset set name
+ * @param {string} [options.replicaSet] The name of the replica set to connect to
  * @param {number} [options.secondaryAcceptableLatencyMS=15] Cutoff latency point in MS for Replicaset member selection
  * @param {number} [options.acceptableLatencyMS=15] Cutoff latency point in MS for Mongos proxies selection
  * @param {boolean} [options.connectWithNoPrimary=false] Sets if the driver should connect even if no primary is available
@@ -142,6 +142,7 @@ const { connect, validOptions } = require('./operations/connect');
  * @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=true] Determines whether or not to use the new url parser. Enables the new, spec-compliant, url parser shipped in the core driver. This url parser fixes a number of problems with the original parser, and aims to outright replace that parser in the near future. Defaults to true, and must be explicitly set to false to use the legacy url parser.
  * @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] Whether to connect to the deployment in Single topology.
  * @param {AutoEncrypter~AutoEncryptionOptions} [options.autoEncryption] Optionally enable client side auto encryption
  * @returns {MongoClient} a MongoClient instance
  */
@@ -352,7 +353,7 @@ MongoClient.prototype.isConnected = function(options) {
  * @param {number} [options.reconnectInterval=1000] Server will wait # milliseconds between retries
  * @param {boolean} [options.ha=true] Control if high availability monitoring runs for Replicaset or Mongos proxies
  * @param {number} [options.haInterval=10000] The High availability period for replicaset inquiry
- * @param {string} [options.replicaSet=undefined] The Replicaset set name
+ * @param {string} [options.replicaSet] The name of the replica set to connect to
  * @param {number} [options.secondaryAcceptableLatencyMS=15] Cutoff latency point in MS for Replicaset member selection
  * @param {number} [options.acceptableLatencyMS=15] Cutoff latency point in MS for Mongos proxies selection
  * @param {boolean} [options.connectWithNoPrimary=false] Sets if the driver should connect even if no primary is available
@@ -388,6 +389,7 @@ 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] Whether to connect to the deployment in Single topology.
  * @param {MongoClient~connectCallback} [callback] The command result callback
  * @returns {Promise<MongoClient>} returns Promise if no callback passed
  */

lib/operations/connect.js

@@ -111,7 +111,8 @@ const validOptionNames = [
   'tlsCertificateKeyFilePassword',
   'minHeartbeatFrequencyMS',
   'heartbeatFrequencyMS',
-  'waitQueueTimeoutMS'
+  'waitQueueTimeoutMS',
+  'directConnection'
 ];
 
 const ignoreOptionNames = ['native_parser'];

lib/sdam/server_selection.js

@@ -185,6 +185,10 @@ function readPreferenceServerSelector(readPreference) {
       );
     }
 
+    if (topologyDescription.type === TopologyType.Unknown) {
+      return [];
+    }
+
     if (
       topologyDescription.type === TopologyType.Single ||
       topologyDescription.type === TopologyType.Sharded

lib/sdam/topology.js

@@ -101,6 +101,8 @@ class Topology extends EventEmitter {
    * @param {number} [options.localThresholdMS=15] The size of the latency window for selecting among multiple suitable servers
    * @param {number} [options.serverSelectionTimeoutMS=30000] How long to block for server selection before throwing an error
    * @param {number} [options.heartbeatFrequencyMS=10000] The frequency with which topology updates are scheduled
+   * @param {boolean} [options.directConnection] Indicates that a client should directly connect to a node without attempting to discover its topology type
+   * @param {string} [options.replicaSet] The name of the replica set to connect to
    */
   constructor(seedlist, options) {
     super();
@@ -136,7 +138,7 @@ class Topology extends EventEmitter {
       }
     });
 
-    const topologyType = topologyTypeFromSeedlist(seedlist, options);
+    const topologyType = topologyTypeFromOptions(options);
     const topologyId = globalTopologyCounter++;
     const serverDescriptions = seedlist.reduce((result, seed) => {
       if (seed.domain_socket) seed.host = seed.domain_socket;
@@ -797,10 +799,23 @@ function parseStringSeedlist(seedlist) {
   }));
 }
 
-function topologyTypeFromSeedlist(seedlist, options) {
-  const replicaSet = options.replicaSet || options.setName || options.rs_name;
-  if (seedlist.length === 1 && !replicaSet) return TopologyType.Single;
-  if (replicaSet) return TopologyType.ReplicaSetNoPrimary;
+/**
+ * Gets the TopologyType from the client options
+ *
+ * @param {object} options mongo client options
+ * @param {boolean} [options.directConnection] Indicates that a client should directly connect to a node without attempting to discover its topology type
+ * @param {string} [options.replicaSet] The name of the replica set to connect to
+ * @returns TopologyType
+ */
+function topologyTypeFromOptions(options) {
+  if (options.directConnection) {
+    return TopologyType.Single;
+  }
+
+  if (options.replicaSet) {
+    return TopologyType.ReplicaSetNoPrimary;
+  }
+
   return TopologyType.Unknown;
 }
 

lib/sdam/topology_description.js

@@ -163,7 +163,7 @@ 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);
@@ -277,9 +277,19 @@ class TopologyDescription {
 }
 
 function topologyTypeForServerType(serverType) {
-  if (serverType === ServerType.Mongos) return TopologyType.Sharded;
-  if (serverType === ServerType.RSPrimary) return TopologyType.ReplicaSetWithPrimary;
-  return TopologyType.ReplicaSetNoPrimary;
+  switch (serverType) {
+    case ServerType.Standalone:
+      return TopologyType.Single;
+    case ServerType.Mongos:
+      return TopologyType.Sharded;
+    case ServerType.RSPrimary:
+      return TopologyType.ReplicaSetWithPrimary;
+    case ServerType.RSOther:
+    case ServerType.RSSecondary:
+      return TopologyType.ReplicaSetNoPrimary;
+    default:
+      return TopologyType.Unknown;
+  }
 }
 
 function compareObjectId(oid1, oid2) {

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.

test/spec/server-discovery-and-monitoring/rs/compatible.yml

@@ -1,5 +1,7 @@
 description: "Replica set member with large maxWireVersion"
+
 uri: "mongodb://a,b/?replicaSet=rs"
+
 phases: [
     {
         responses: [

test/spec/server-discovery-and-monitoring/rs/compatible_unknown.yml

@@ -1,5 +1,7 @@
 description: "Replica set member and an unknown server"
+
 uri: "mongodb://a,b/?replicaSet=rs"
+
 phases: [
     {
         responses: [

test/spec/server-discovery-and-monitoring/rs/discover_arbiters.json

@@ -1,6 +1,6 @@
 {
-  "description": "Discover arbiters",
-  "uri": "mongodb://a/?replicaSet=rs",
+  "description": "Discover arbiters with directConnection URI option",
+  "uri": "mongodb://a/?directConnection=false",
   "phases": [
     {
       "responses": [

test/spec/server-discovery-and-monitoring/rs/discover_arbiters.yml

@@ -1,6 +1,6 @@
-description: "Discover arbiters"
+description: "Discover arbiters with directConnection URI option"
 
-uri: "mongodb://a/?replicaSet=rs"
+uri: "mongodb://a/?directConnection=false"
 
 phases: [
 

test/spec/server-discovery-and-monitoring/rs/discover_arbiters_replicaset.json

@@ -0,0 +1,41 @@
+{
+  "description": "Discover arbiters with replicaSet URI option",
+  "uri": "mongodb://a/?replicaSet=rs",
+  "phases": [
+    {
+      "responses": [
+        [
+          "a:27017",
+          {
+            "ok": 1,
+            "ismaster": true,
+            "hosts": [
+              "a:27017"
+            ],
+            "arbiters": [
+              "b:27017"
+            ],
+            "setName": "rs",
+            "minWireVersion": 0,
+            "maxWireVersion": 6
+          }
+        ]
+      ],
+      "outcome": {
+        "servers": {
+          "a:27017": {
+            "type": "RSPrimary",
+            "setName": "rs"
+          },
+          "b:27017": {
+            "type": "Unknown",
+            "setName": null
+          }
+        },
+        "topologyType": "ReplicaSetWithPrimary",
+        "logicalSessionTimeoutMinutes": null,
+        "setName": "rs"
+      }
+    }
+  ]
+}

test/spec/server-discovery-and-monitoring/rs/discover_arbiters_replicaset.yml

@@ -0,0 +1,43 @@
+description: "Discover arbiters with replicaSet URI option"
+
+uri: "mongodb://a/?replicaSet=rs"
+
+phases: [
+
+    {
+        responses: [
+
+                ["a:27017", {
+
+                    ok: 1,
+                    ismaster: true,
+                    hosts: ["a:27017"],
+                    arbiters: ["b:27017"],
+                    setName: "rs",
+                    minWireVersion: 0,
+                    maxWireVersion: 6
+                }]
+        ],
+
+        outcome: {
+
+            servers: {
+
+                "a:27017": {
+
+                    type: "RSPrimary",
+                    setName: "rs"
+                },
+
+                "b:27017": {
+
+                    type: "Unknown",
+                    setName:
+                }
+            },
+            topologyType: "ReplicaSetWithPrimary",
+            logicalSessionTimeoutMinutes: null,
+            setName: "rs"
+        }
+    }
+]

test/spec/server-discovery-and-monitoring/rs/discover_ghost.json

@@ -0,0 +1,31 @@
+{
+  "description": "Discover ghost with directConnection URI option",
+  "uri": "mongodb://b/?directConnection=false",
+  "phases": [
+    {
+      "responses": [
+        [
+          "b:27017",
+          {
+            "ok": 1,
+            "ismaster": false,
+            "isreplicaset": true,
+            "minWireVersion": 0,
+            "maxWireVersion": 6
+          }
+        ]
+      ],
+      "outcome": {
+        "servers": {
+          "b:27017": {
+            "type": "RSGhost",
+            "setName": null
+          }
+        },
+        "topologyType": "Unknown",
+        "logicalSessionTimeoutMinutes": null,
+        "setName": null
+      }
+    }
+  ]
+}