feat(inital-cluster-time): allow session to define initia value

NODE-1088

lib/sessions.js

@@ -13,9 +13,13 @@ class ClientSession {
     }
 
     this.topology = topology;
-    this.options = options || {};
     this.hasEnded = false;
     this._serverSession = undefined; // TBD
+
+    options = options || {};
+    if (typeof options.initialClusterTime !== 'undefined') {
+      this.clusterTime = options.initialClusterTime;
+    }
   }
 
   /**
@@ -26,6 +30,12 @@ class ClientSession {
       return callback(null, null);
     }
 
+    // TODO:
+    //   When connected to a sharded cluster the endSessions command
+    //   can be sent to any mongos. When connected to a replica set the
+    //   endSessions command MUST be sent to the primary if the primary
+    //   is available, otherwise it MUST be sent to any available secondary.
+
     this.topology.command('admin.$cmd', { endSessions: 1, ids: [this.id] }, err => {
       this.hasEnded = true;
 

test/tests/unit/sessions_tests.js

@@ -4,10 +4,33 @@ const Server = require('../../..').Server,
   mock = require('../../mock'),
   expect = require('chai').expect,
   ServerSessionPool = require('../../../lib/sessions').ServerSessionPool,
-  ServerSession = require('../../../lib/sessions').ServerSession;
+  ServerSession = require('../../../lib/sessions').ServerSession,
+  ClientSession = require('../../../lib/sessions').ClientSession,
+  genClusterTime = require('./common').genClusterTime;
 
 let test = {};
 describe('Sessions', function() {
+  describe('ClientSession', function() {
+    it('should default to `null` for `clusterTime`', {
+      metadata: { requires: { topology: 'single' } },
+      test: function() {
+        const client = new Server();
+        const session = new ClientSession(client);
+        expect(session.clusterTime).to.not.exist;
+      }
+    });
+
+    it('should set the internal clusterTime to `initialClusterTime` if provided', {
+      metadata: { requires: { topology: 'single' } },
+      test: function() {
+        const clusterTime = genClusterTime(Date.now());
+        const client = new Server();
+        const session = new ClientSession(client, { initialClusterTime: clusterTime });
+        expect(session.clusterTime).to.eql(clusterTime);
+      }
+    });
+  });
+
   describe('ServerSessionPool', function() {
     afterEach(() => {
       test.client.destroy();
@@ -41,7 +64,6 @@ describe('Sessions', function() {
 
     it('should create a new session if the pool is empty', {
       metadata: { requires: { topology: 'single' } },
-
       test: function(done) {
         const pool = new ServerSessionPool(test.client);
         expect(pool.sessions).to.have.length(0);