The simplest story would be to generate and upload reports when the counter file is rotated, but uploads might fail, so that would not be enough. The proposed way is to start a separate command each time the counter package starts.
The code could be in the counter package, or in a separate package, or in a separate command, for instance ‘go telemetry upload’. The latter ties updates to the ‘go’ command release cycle, and separates the upload code from the counter package. Thus the code will be in the upload package.
The init() function in upload.go handles this. It checks to see if the program was invoked with a single argument __telemetry_upload__, and if so, executes the code to generate reports and upload them. If not it spawns a copy of the current program with that argument.
This commentary can be moved to the upload package when it is checked in.
There are a bunch of TODOs. Also there are many places in the upload code where log messages are written, but it's unclear how to recover from the errors. The log messages are written to files named telemetry-<pid>.log in os.TempDir().