feat(shell-api): add support for snapshot reads MONGOSH-1151 (#1237)

Author: addaleax

packages/shell-api/src/mongo.ts

@@ -21,6 +21,8 @@ import {
 } from './decorators';
 import {
   ChangeStreamOptions,
+  ClientSessionOptions,
+  CommandOperationOptions,
   Document,
   generateUri,
   ListDatabasesOptions,
@@ -451,22 +453,37 @@ export default class Mongo extends ShellApiClass {
 
   @topologies([Topologies.ReplSet])
   startSession(options: Document = {}): Session {
-    const driverOptions = {};
-    if (options === undefined) {
-      return new Session(this, driverOptions, this._serviceProvider.startSession(driverOptions));
+    const allTransactionOptions = [
+      'readConcern', 'writeConcern', 'readPreference', 'maxCommitTimeMS'
+    ] as const;
+    // eslint-disable-next-line @typescript-eslint/no-unused-vars
+    function assertAllTransactionOptionsUsed(_options: (typeof allTransactionOptions)[number]) {
+      // These typechecks might look weird, but will tell us if we are missing
+      // support for a newly introduced driver option when it is being added
+      // to the driver API.
+    }
+    assertAllTransactionOptionsUsed('' as Exclude<keyof TransactionOptions, keyof CommandOperationOptions>);
+    const defaultTransactionOptions: TransactionOptions = {};
+    for (const key of allTransactionOptions) {
+      if (typeof options[key] !== 'undefined') {
+        defaultTransactionOptions[key] = options[key];
+      }
+    }
+
+    const allSessionOptions = [ 'causalConsistency', 'snapshot' ] as const;
+    // eslint-disable-next-line @typescript-eslint/no-unused-vars
+    function assertAllSessionOptionsUsed(_options: (typeof allSessionOptions)[number] | 'defaultTransactionOptions') {}
+    assertAllSessionOptionsUsed('' as keyof ClientSessionOptions);
+    const driverOptions: ClientSessionOptions = {};
+    if (Object.keys(defaultTransactionOptions).length > 0) {
+      driverOptions.defaultTransactionOptions = defaultTransactionOptions;
+    }
+    for (const key of allSessionOptions) {
+      if (typeof options[key] !== 'undefined') {
+        driverOptions[key] = options[key];
+      }
     }
-    const defaultTransactionOptions = {} as TransactionOptions;
 
-    // Only include option if not undef
-    Object.assign(defaultTransactionOptions,
-      options.readConcern && { readConcern: options.readConcern },
-      options.writeConcern && { writeConcern: options.writeConcern },
-      options.readPreference && { readPreference: options.readPreference }
-    );
-    Object.assign(driverOptions,
-      Object.keys(defaultTransactionOptions).length > 0 && { defaultTransactionOptions: defaultTransactionOptions },
-      options.causalConsistency !== undefined && { causalConsistency: options.causalConsistency }
-    );
     return new Session(this, driverOptions, this._serviceProvider.startSession(driverOptions));
   }
 

packages/shell-api/src/session.spec.ts

@@ -13,7 +13,7 @@ import {
   ALL_TOPOLOGIES
 } from './enums';
 import { CliServiceProvider } from '../../service-provider-server';
-import { startTestCluster, skipIfApiStrict } from '../../../testing/integration-testing-hooks';
+import { startTestCluster, skipIfServerVersion, skipIfApiStrict } from '../../../testing/integration-testing-hooks';
 import { ensureMaster, ensureSessionExists } from '../../../testing/helpers';
 import Database from './database';
 import { CommonErrors, MongoshInvalidInputError } from '@mongosh/errors';
@@ -227,6 +227,22 @@ describe('Session', () => {
         }
         expect.fail('Error not thrown');
       });
+      context('with 5.0+ server', () => {
+        skipIfApiStrict();
+        skipIfServerVersion(srv0, '< 5.0');
+        it('starts a session with snapshot reads if requested', async() => {
+          session = mongo.startSession({ snapshot: true });
+          await session.getDatabase(databaseName).getCollection('coll').findOne({});
+          try {
+            await session.getDatabase(databaseName).getCollection('coll').insertOne({});
+            expect.fail('missed exception');
+          } catch (e) {
+            expect(e.message).to.include('snapshot'); // Cannot do writes with snapshot: true
+          }
+          expect(session._session.snapshotEnabled).to.equal(true);
+          await session.endSession();
+        });
+      });
     });
     describe('transaction methods are called', () => {
       it('cannot call start transaction twice', () => {