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fix(NODE-5225): eagerly clear MongoClient.topology in MongoClient.close() #3652

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alecgibson wants to merge 1 commit into mongodb:main from alecgibson:NODE-5225

Commits on Apr 24, 2023

fix(NODE-5225): eagerly clear MongoClient.topology in MongoClient.clo…

…se()

At the moment, calling `MongoClient.close()` in quick succession leads
to an error:

```
TypeError: Cannot read properties of undefined (reading 'close')
  at node-mongodb-native/src/mongo_client.ts:530:16
  at new Promise (<anonymous>)
  at LegacyMongoClient.close (src/mongo_client.ts:529:11)
  at processTicksAndRejections (node:internal/process/task_queues:95:5)
  at async Promise.all (index 1)
  at async Context.<anonymous> (test/integration/node-specific/mongo_client.test.ts:393:5)
```

This happens because:

1. The first call attempts to asynchronously [close][1] the session pool
   sessions
2. While this is happening, the second call passes the topology
   [null check][2] (since `this.topology` hasn't yet been [unset][3],
   and tries to also close session pool sessions
3. Both calls then set [`const topology = this.topology`][4] but the
   second call will get undefined since the first call [unset][3]
   `this.topology`
4. The second call now tries to call [`close()`][5] on an `undefined`
   `topology` and throws

This change fixes the issue by moving the `topology` unset immediately
after the `null` check, so we know it's always correctly set.

[1]: https://github.com/mongodb/node-mongodb-native/blob/325c4bc37decdf12e957bfad8bd4ee4d28b1bf95/src/mongo_client.ts#L516
[2]: https://github.com/mongodb/node-mongodb-native/blob/325c4bc37decdf12e957bfad8bd4ee4d28b1bf95/src/mongo_client.ts#L503
[3]: https://github.com/mongodb/node-mongodb-native/blob/325c4bc37decdf12e957bfad8bd4ee4d28b1bf95/src/mongo_client.ts#L527
[4]: https://github.com/mongodb/node-mongodb-native/blob/325c4bc37decdf12e957bfad8bd4ee4d28b1bf95/src/mongo_client.ts#L526
[5]: https://github.com/mongodb/node-mongodb-native/blob/325c4bc37decdf12e957bfad8bd4ee4d28b1bf95/src/mongo_client.ts#L530

alecgibson committed Apr 24, 2023