In scope of SERVER-10637, MongoDB 4.2 will return a connectionId in the hello response. This is a number that can be correlated against server log messages, e.g. for this server message:

2018-06-05T13:50:11.978-0400 I NETWORK  [conn2] received client metadata from 127.0.0.1:50254 conn2: { driver: { name: "PyMongo", version: "3.5.1" }, os: { type: "Darwin", name: "Darwin", architecture: "x86_64", version: "10.13.5" }, platform: "CPython 2.7.10.final.0" }

The connectionid reported in the hello response will be 2.

Drivers should sync their command monitoring tests with this commit, update their APM logic to append a new serverConnectionId field to commandStartedEvent, commandSucceededEvent and commandFailedEvent when it is available, and update their test runners to handle UTF schema version 1.6 (featuring the new hasServerConnectionId assertion).