feat(CSOT) - feature branch

[W-A-James]

Description

What is changing?

New Error

• Added MongoOperationTimeoutError class that is thrown when a CSOT timeout is encountered

Changes to Timeout

• Add Timeout.throwIfExpired() method
• Add Timeout.remainingTime getter method

Updates to AbstractOperation

• Add timeout field
  • timeout is set at construction if the timeoutMS option is provided

Implementing CSOT behaviour for server selection

• Update Topology.selectServer to accept a timeout option which it will use determine whether it has timed out when defined. Otherwise, constructs a Timeout using the serverSelectionMS option as before
• Update Topology.selectServer to throw a MongoOperationTimeoutError on timeout when options.timeout is provided and retain previous error behaviour otherwise.
• Update Topology._connect to pass down timeout to Server.command call used to execute ping on first connection

Implementing CSOT behaviour for connection checkout

• Update Server.command to accept timeout option.
• Update ConnectionPool.checkOut to accept timeout option
  • only uses the passed in timeout if the configured serverSelectionTimeoutMS is greater than the duration on the timeout, otherwise, computes the time elapsed since server selection completed and creates timeout for the serverSelectionTimeoutMS deadline

Test changes

• Implement Server Selection prose tests from CSOT spec. Left out last two since they require implementation of the connection creation cancellation behaviour that was decided against in DRIVERS-2347
• Implement unit tests from CSOT spec related to server selection and connection checkout. Skipped tests with appropriate messages

Misc changes

• Update resolveOptions to handle timeoutMS option propagation
• • Add csotMin helper method that implements the CSOT min algorithm described here

Is there new documentation needed for these changes?

What is the motivation for this change?

Release Highlight

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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

[W-A-James]

Evergreen link

[aditi-khare-mongoDB]

Bookkeeping: Waiting for Warren to respond to Bailey's comments and will proceed with review then.

[W-A-James]

@aditi-khare-mongoDB @nbbeeken should we conditionally clear the timeout on success/a non-timeout failure based on whether or not we created the timeout inside the function that we race the timeout with? I ask because we don't always own Timeout instance we're using in Topology.selectServer or in ConnectionPool.checkOut.