chore: bump mongodb from 3.1.13 to 3.2.1

[dependabot-preview]

Bumps mongodb from 3.1.13 to 3.2.1.

Release notes

Sourced from mongodb's releases.

v3.2.1

The MongoDB Node.js team is pleased to announce version 3.2.1 of the driver.

Due to a publishing snafu v3.2.1 was immediately published without a proper v3.2.0 release

Release Highlights

2.x EOL

With the v3.1.0 release we officially deprecated the 2.x driver. With this release that driver is effectively EOL, and will no longer be supported. Please update your driver as soon as possible.

Unified Topology

In this release we are very excited to announce the immediate availability of a complete rewrite of the driver's "topology" layer. This is the core brains of the driver responsible for things like server selection, server discovery and monitoring. This work combines the three existing topology concepts (`Mongos`, `ReplSet`, and `Server`) into a single type `Topology`. The new `Topology` type uses the same machinery to represent all three types, greatly improving our ability to maintain the code, and reducing the chance for bug duplication.

The Topology class no longer uses a callback store, instead relying on a server selection loop for operation execution. This means failed operations will fail faster, with more accurate stack traces and specifics about the failure. It generally makes it much easier to reason about what the driver is doing each time an operation is executed.

You can enable it with the useUnifiedTopology feature flag passed to your MongoClient constructor, like so:

const client = MongoClient('mongodb://localhost:27017', { useUnifiedTopology: true });

This topology layer will replace the existing topologies in a breaking 4.x release later this year, so we strongly encourage our users to try it out as soon as possible.

`withTransaction` helper

Reliably committing a transaction in the face of errors can be a complicated endeavor using the MongoDB 4.0 drivers API. This version introduces a `withTransaction` helper method on the `ClientSession` object that allows application logic to be executed within a transaction. This method is capable of retrying either the commit operation or entire transaction as needed (and when the error permits) to better ensure that the transaction can complete successfully. Consider using this for all but the most complicated of transactions use cases.

A call to withTransaction begins a new transaction, executes the provided function, and then attempts to commit the transaction. The function passed to withTransaction must take a session parameter, and this session must be passed to all methods within the function. If some error is encountered, it will attempt to re-commit the transaction before ultimately failing back to the user after aborting the transaction.
NOTE: A mentioned, the passed in function MAY be retried multiple times, please keep this in mind when executing non-database operations within the function.

Here’s an example of it in action:

const client = new MongoClient();
await client.connect();

const session = client.startSession();

// NOTE: the `withTransaction` method only supports functions that return a `Promise`
try {
  await session.withTransaction(async function(session) {
     const coll = client.db('foo').collection('coll');
     await coll.insertOne({ a: 42 }, { session });
  });
} catch (err) {
  // transaction failed after attempted retry
  console.dir({ err });
}

Cursors support asyncInterator and for..await..of loops

`Symbol.asyncIterator` is defined on cursors for Node.js versions that support it (>=v10.x.x). This allows you to use for..await..of loops with cursors: ... (truncated)

Changelog

Sourced from mongodb's changelog.

3.2.1 (2019-03-21)

Features

• core: update to mongodb-core v3.2.1 (30b0100)

3.2.0 (2019-03-21)

Bug Fixes

• aggregate: do not send batchSize for aggregation with $out (ddb8d90)
• bulkWrite: always count undefined values in bson size for bulk (436d340)
• db_ops: rename db to add user on (79931af)
• mongo_client_ops: only skip authentication if no authMechanism is specified (3b6957d)
• mongo-client: ensure close callback is called with client (f39e881)

Features

• core: pin to mongodb-core v3.2.0 (22af15a)
• Cursor: adds support for AsyncIterator in cursors (b972c1e)
• db: add database-level aggregation (b629b21)
• mongo-client: remove deprecated logout and print warning (542859d)
• topology-base: support passing callbacks to close method (7c111e0)
• transactions: support pinning mongos for sharded txns (3886127)
• unified-sdam: backport unified SDAM to master for v3.2.0 (79f33ca)

Commits

• 0e6153b chore(release): 3.2.1
• 30b0100 feat(core): update to mongodb-core v3.2.1
• 2604bc7 chore(release): 3.2.0
• 22af15a feat(core): pin to mongodb-core v3.2.0
• eebb6c8 test: fix change stream expectations for mongodb-latest
• 9002ca4 docs: updating documentation version and branch
• d7123a9 Added links to compatibility with MongoDB & NodeJS.
• caf1169 Added links to compatibility with MongoDB & NodeJS.
• 305f4c0 doc: merge 3.1.1 release notes into master
• c6fd568 refactor: put recovery tokens behind a feature flag for now
• Additional commits viewable in compare view

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