Many functions on AsyncDBClient chain via _call(). To allow AsyncDBClient to serve exhaust responses, we need to separate out the "source" part of its pattern as _waitForResponse(). We can then write runExhaustCommand()/runExhaustCommandRequest() commands that call the "source" part as long as OpMsg::kMoreToCome is set. To test this, we'll want a trivial command that we can treat as exhaust with little other logic: sleep.

In summary, there are three parts:

• Make sleep an exhaust command
• Write and integrate AsyncDBClient::_waitForResponse() to allow tailing.
• Test AsyncDBClient::runExhaustCommand() with sleep in integration test.