(POC) GODRIVER-3444 Adjust getMore maxTimeMS Calculation for tailable awaitData Cursors

[prestonvasquez]

GODRIVER-3444

Summary

If maxAwaitTime option is set, use the min(maxAwaitTimeMS, remaining timeoutMS) as the maxTimeMS field on getMore commands.

Background & Motivation

From the DRIVERS-2868 proposal:

For tailable awaitData cursors we use the min(maxAwaitTimeMS, remaining timeoutMS - minRoundTripTime) to allow the server more opportunities to respond with an empty batch before a client-side timeout. Additionally, this change is
required to prevent an unnecessary client-side timeout during a pending read when checking out a connection. For
example, maxAwaitTimeMS=1000 and remaining timeoutMS=100 will cause a pending read to hang for 900ms.

[mongodb-drivers-pr-bot]

API Change Report

No changes found!

[matthewdale]

It's unconventional to pass the error to be returned in as a parameter. Instead, consider letting CalculateMaxTimeMS return just the int64 value, and let the caller form the error value.

E.g. use in batch_cursor.go:

maxTimeMS = driverutil.CalculateMaxTimeMS(ctx, rttMonitor.Min())
if maxTimeMS <= 0 {
	return nil, fmt.Errorf(
		"calculated server-side timeout (%v ms) is less than or equal to 0 (%v): %w",
		maxTimeMS,
		rttMonitor.Stats(),
		ErrDeadlineWouldBeExceeded)
}