feat(causal-consistency): support afterClusterTime in readConcern

NODE-1106

Author: mbroadst

lib/collection.js

@@ -367,7 +367,9 @@ Collection.prototype.find = function() {
 
   // Merge in options to command
   for (var name in newOptions) {
-    if (newOptions[name] != null) findCommand[name] = newOptions[name];
+    if (newOptions[name] != null && name !== 'session') {
+      findCommand[name] = newOptions[name];
+    }
   }
 
   // Format the fields
@@ -2403,13 +2405,23 @@ function decorateWithCollation(command, self, options) {
   }
 }
 
-function decorateWithReadConcern(command, self, options) {  // eslint-disable-line
-  let readConcern = {};
+function decorateWithReadConcern(command, self, options) {
+  let readConcern = Object.assign({}, command.readConcern || {});
   if (self.s.readConcern) {
     Object.assign(readConcern, self.s.readConcern);
   }
 
-  Object.assign(command, readConcern);
+  if (
+    options.session &&
+    options.session.supports.causalConsistency &&
+    options.session.operationTime
+  ) {
+    Object.assign(readConcern, { afterClusterTime: options.session.operationTime });
+  }
+
+  if (Object.keys(readConcern).length > 0) {
+    Object.assign(command, { readConcern: readConcern });
+  }
 }
 
 /**

package.json

@@ -13,7 +13,7 @@
     "official"
   ],
   "dependencies": {
-    "mongodb-core": "mongodb-js/mongodb-core#3.0.0"
+    "mongodb-core": "mongodb-js/mongodb-core#causally-consistent-reads"
   },
   "devDependencies": {
     "betterbenchmarks": "^0.1.0",

test/unit/sessions/collection_tests.js

@@ -0,0 +1,55 @@
+'use strict';
+const MongoClient = require('../../..').MongoClient,
+  Timestamp = require('bson').Timestamp,
+  expect = require('chai').expect,
+  mock = require('../../mock');
+
+const test = {};
+describe('Sessions', function() {
+  describe('Collection', function() {
+    afterEach(() => mock.cleanup());
+    beforeEach(() => {
+      return mock.createServer().then(server => {
+        test.server = server;
+      });
+    });
+
+    it('should include `afterClusterTime` in read command with causal consistency', {
+      metadata: { requires: { topology: 'single' } },
+
+      test: function() {
+        let findCommand;
+        let insertOperationTime = Timestamp.fromNumber(Date.now());
+        test.server.setMessageHandler(request => {
+          const doc = request.document;
+          if (doc.ismaster) {
+            request.reply(mock.DEFAULT_ISMASTER_36);
+          } else if (doc.insert) {
+            request.reply({ ok: 1, operationTime: insertOperationTime });
+          } else if (doc.find) {
+            findCommand = doc;
+            request.reply({ ok: 1 });
+          } else if (doc.endSessions) {
+            request.reply({ ok: 1 });
+          }
+        });
+
+        return MongoClient.connect(`mongodb://${test.server.uri()}/test`).then(client => {
+          const session = client.startSession({ causalConsistency: true });
+          const coll = client.db('foo').collection('bar');
+
+          return coll
+            .insert({ a: 42 }, { session: session })
+            .then(() =>
+              coll.findOne({}, null, { session: session, readConcern: { level: 'majoroy' } })
+            )
+            .then(() => {
+              expect(findCommand.readConcern).to.have.keys(['level', 'afterClusterTime']);
+              expect(findCommand.readConcern.afterClusterTime).to.eql(insertOperationTime);
+              return client.close();
+            });
+        });
+      }
+    });
+  });
+});