What is the code for Tracker API?

we are trying to add some custom logic to fork a copy of all piwik tracking requests to our own storage and analysis system, as soon as the requests enter piwik tracking server.

so I guess the place to add it is the tracking API code, could anybody point me to the actual code where the request actually hits the server? it should be somewhere in these: matomo/core/Tracker at master · matomo-org/matomo · GitHub ? or is there an existing module/plugin framework to insert this logic? Piwik's Extensibility Points: DevelopInDepth - Matomo Analytics (formerly Piwik Analytics) - Developer Docs - v3 is not very clear.

also,regarding the wiki on Event Handlers Piwik’s Extensibility Points: DevelopInDepth - Matomo Analytics (formerly Piwik Analytics) - Developer Docs - v3 , does the "event’ here refer to an event on the client browser side (java script event, or user action event just as mouse click, mouse hover etc), or an event in the processing logic chain on the server side?

thanks a lot
yang