feat(NODE-6060): set fire-and-forget protocol when writeConcern is w: 0

[aditi-khare-mongoDB]

Description

When writeConcern.w = 0 is set on an operation that's run through OP_MSG, the driver will set moreToCome on the request so that the server will not send a response.

What is changing?

• When an operation being run through OP_MSG has writeConcern.w === 0, the driver
  • sets the moreToCome bit on the outgoing request.
  • returns from operation execution without waiting for a server response
  • set CommandSucceededEvent.reply to { ok: 1 } regardless of server reply
• TSDoc for WriteConcern now contains extra context.

Is there new documentation needed for these changes?

No, none other than the TSDoc changes.

What is the motivation for this change?

Support spec-defined fire-and-forget protocol.

Release Highlight

Write Operations with WriteConcern.w set to 0 trigger unacknowledged write protocol

When WriteConcern.w is set to 0 on a write operation, either through operation options or the client settings, writes will be unacknowledged by the server. This means the server will not send a response after the request is sent and therefore, the return value from the operation will not contain any information from the server, including whether the server has processed the request yet.

In addition, when command monitoring is enabled, the reply field of a CommandSucceededEvent of an unacknowledged write will always be { ok: 1 }.

Double check the following

• Ran npm run check:lint script
• Self-review completed using the steps outlined here
• PR title follows the correct format: type(NODE-xxxx)[!]: description
  • Example: feat(NODE-1234)!: rewriting everything in coffeescript
• Changes are covered by tests
• New TODOs have a related JIRA ticket