Keep in mind that the example_extension present in master is not updated, if you want a reference you can look at https://github.com/trailofbits/osquery/pull/5/commits/10992bf08f7b584c62b0fed963acf3c62091b5e2 or https://github.com/trailofbits/osquery-extensions/tree/extension_porting_4.0.1. I will try to get that fix we have in the first PR on upstream, so at least the base example extension works; we were also restoring an example for the extension group but I'd actually like to change how the extension grouping works, because issues arises when multiple extension groups exists.