feat(NODE-3467): implement srvMaxHosts, srvServiceName options

.mocharc.json

@@ -5,8 +5,8 @@
     "ts"
   ],
   "require": [
-    "ts-node/register",
     "source-map-support/register",
+    "ts-node/register",
     "test/tools/runner/chai-addons",
     "test/tools/runner/circular-dep-hack"
   ],

package.json

@@ -47,6 +47,7 @@
     "@types/node": "^16.10.3",
     "@types/saslprep": "^1.0.1",
     "@types/semver": "^7.3.8",
+    "@types/sinon": "^10.0.6",
     "@types/whatwg-url": "^8.2.1",
     "@typescript-eslint/eslint-plugin": "^4.33.0",
     "@typescript-eslint/parser": "^4.33.0",
@@ -69,7 +70,7 @@
     "prettier": "^2.4.1",
     "rimraf": "^3.0.2",
     "semver": "^7.3.5",
-    "sinon": "^11.1.2",
+    "sinon": "^12.0.1",
     "sinon-chai": "^3.7.0",
     "source-map-support": "^0.5.20",
     "standard-version": "^9.3.1",

src/connection_string.ts

@@ -34,7 +34,7 @@ import { PromiseProvider } from './promise_provider';
 import { Encrypter } from './encrypter';
 import { Compressor, CompressorName } from './cmap/wire_protocol/compression';
 
-const VALID_TXT_RECORDS = ['authSource', 'replicaSet', 'loadBalanced'];
+const VALID_TXT_RECORDS = ['authSource', 'replicaSet', 'loadBalanced', 'srvMaxHosts'];
 
 const LB_SINGLE_HOST_ERROR = 'loadBalanced option only supported with a single host in the URI';
 const LB_REPLICA_SET_ERROR = 'loadBalanced option not supported with a replicaSet option';
@@ -75,7 +75,7 @@ export function resolveSRVRecord(options: MongoOptions, callback: Callback<HostA
 
   // Resolve the SRV record and use the result as the list of hosts to connect to.
   const lookupAddress = options.srvHost;
-  dns.resolveSrv(`_mongodb._tcp.${lookupAddress}`, (err, addresses) => {
+  dns.resolveSrv(`_${options.srvServiceName}._tcp.${lookupAddress}`, (err, addresses) => {
     if (err) return callback(err);
 
     if (addresses.length === 0) {
@@ -116,12 +116,21 @@ export function resolveSRVRecord(options: MongoOptions, callback: Callback<HostA
           );
         }
 
+        if (VALID_TXT_RECORDS.some(option => txtRecordOptions.get(option) === '')) {
+          return callback(new MongoParseError('Cannot have empty URI params in DNS TXT Record'));
+        }
+
         const source = txtRecordOptions.get('authSource') ?? undefined;
         const replicaSet = txtRecordOptions.get('replicaSet') ?? undefined;
         const loadBalanced = txtRecordOptions.get('loadBalanced') ?? undefined;
+        const srvMaxHostsString = txtRecordOptions.get('srvMaxHosts') ?? undefined;
 
-        if (source === '' || replicaSet === '') {
-          return callback(new MongoParseError('Cannot have empty URI params in DNS TXT Record'));
+        if (srvMaxHostsString) {
+          try {
+            options.srvMaxHosts = getUint('srvMaxHosts', txtRecordOptions.get('srvMaxHosts'));
+          } catch (error) {
+            return callback(error);
+          }
         }
 
         if (!options.userSpecifiedAuthSource && source) {
@@ -132,6 +141,14 @@ export function resolveSRVRecord(options: MongoOptions, callback: Callback<HostA
           options.replicaSet = replicaSet;
         }
 
+        if (
+          options.replicaSet &&
+          typeof options.srvMaxHosts === 'number' &&
+          options.srvMaxHosts !== 0
+        ) {
+          return callback(new MongoParseError('Cannot combine replicaSet option with srvMaxHosts'));
+        }
+
         if (loadBalanced === 'true') {
           options.loadBalanced = true;
         }
@@ -254,9 +271,6 @@ export function parseOptions(
   if (isSRV) {
     // SRV Record is resolved upon connecting
     mongoOptions.srvHost = hosts[0];
-    if (!url.searchParams.has('tls') && !url.searchParams.has('ssl')) {
-      options.tls = true;
-    }
   }
 
   const urlOptions = new CaseInsensitiveMap();
@@ -315,6 +329,16 @@ export function parseOptions(
 
   const allOptions = new CaseInsensitiveMap();
 
+  if (isSRV) {
+    // SRV turns on TLS by default, but users can override and turn it off
+    const noUserSpecifiedTLS = !objectOptions.has('tls') && !urlOptions.has('tls');
+    const noUserSpecifiedSSL = !objectOptions.has('ssl') && !urlOptions.has('ssl');
+    if (noUserSpecifiedTLS && noUserSpecifiedSSL) {
+      objectOptions.set('tls', true);
+      objectOptions.set('ssl', true);
+    }
+  }
+
   const allKeys = new Set<string>([
     ...urlOptions.keys(),
     ...objectOptions.keys(),
@@ -366,6 +390,14 @@ export function parseOptions(
     setOption(mongoOptions, key, descriptor, values);
   }
 
+  if (
+    typeof mongoOptions.srvMaxHosts === 'number' &&
+    mongoOptions.srvMaxHosts !== 0 &&
+    typeof mongoOptions.replicaSet === 'string'
+  ) {
+    throw new MongoParseError('Cannot combine replicaSet option and maxSrvHosts');
+  }
+
   if (mongoOptions.credentials) {
     const isGssapi = mongoOptions.credentials.mechanism === AuthMechanism.MONGODB_GSSAPI;
     const isX509 = mongoOptions.credentials.mechanism === AuthMechanism.MONGODB_X509;
@@ -439,6 +471,10 @@ function validateLoadBalancedOptions(
     if (mongoOptions.directConnection) {
       return new MongoParseError(LB_DIRECT_CONNECTION_ERROR);
     }
+
+    if (mongoOptions.srvHost && mongoOptions.srvMaxHosts) {
+      return new MongoParseError('Cannot limit srv hosts with loadBalanced enabled');
+    }
   }
 }
 
@@ -902,6 +938,7 @@ export const OPTIONS = {
   replicaSet: {
     type: 'string'
   },
+  rescanSrvIntervalMS: { type: 'uint', default: 60000 },
   retryReads: {
     default: true,
     type: 'boolean'
@@ -924,6 +961,13 @@ export const OPTIONS = {
     default: 0,
     type: 'uint'
   },
+  srvMaxHosts: {
+    type: 'uint'
+  },
+  srvServiceName: {
+    type: 'string',
+    default: 'mongodb'
+  },
   ssl: {
     target: 'tls',
     type: 'boolean'

src/mongo_client.ts

@@ -132,6 +132,18 @@ export interface MongoClientOptions extends BSONSerializeOptions, SupportedNodeC
   compressors?: CompressorName[] | string;
   /** An integer that specifies the compression level if using zlib for network compression. */
   zlibCompressionLevel?: 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | undefined;
+  /** The maximum number of hosts to connect to when using an srv connection string */
+  srvMaxHosts?: number;
+  /**
+   * Modifies the srv URI to look like:
+   *
+   * `_{srvServiceName}._tcp.{hostname}.{domainname}`
+   *
+   * Querying this DNS URI is expected to respond with SRV records
+   */
+  srvServiceName?: string;
+  /** Frequency with which to scan SRV record changes */
+  rescanSrvIntervalMS?: number;
   /** The maximum number of connections in the connection pool. */
   maxPoolSize?: number;
   /** The minimum number of connections in the connection pool. */
@@ -643,9 +655,12 @@ export interface MongoOptions
         | 'retryWrites'
         | 'serverSelectionTimeoutMS'
         | 'socketTimeoutMS'
+        | 'srvMaxHosts'
+        | 'srvServiceName'
         | 'tlsAllowInvalidCertificates'
         | 'tlsAllowInvalidHostnames'
         | 'tlsInsecure'
+        | 'rescanSrvIntervalMS'
         | 'waitQueueTimeoutMS'
         | 'zlibCompressionLevel'
       >

src/operations/connect.ts

@@ -1,7 +1,8 @@
+import type * as dns from 'dns';
 import { MongoRuntimeError, MongoInvalidArgumentError } from '../error';
 import { Topology, TOPOLOGY_EVENTS } from '../sdam/topology';
 import { resolveSRVRecord } from '../connection_string';
-import type { Callback } from '../utils';
+import { Callback, shuffle } from '../utils';
 import type { MongoClient, MongoOptions } from '../mongo_client';
 import { CMAP_EVENTS } from '../cmap/connection_pool';
 import { APM_EVENTS } from '../cmap/connection';
@@ -51,7 +52,13 @@ export function connect(
   if (typeof options.srvHost === 'string') {
     return resolveSRVRecord(options, (err, hosts) => {
       if (err || !hosts) return callback(err);
-      for (const [index, host] of hosts.entries()) {
+
+      const selectedHosts =
+        options.srvMaxHosts === 0 || options.srvMaxHosts >= hosts.length
+          ? hosts
+          : shuffle(hosts, options.srvMaxHosts);
+
+      for (const [index, host] of selectedHosts.entries()) {
         options.hosts[index] = host;
       }