hey Vasiliy, I'm not sure I understood your requirements, but let me take a stab at it.
By handlers of the protobuf I imagine you refer to those stubs generated by `protoc`, for the gRPCs. Is it correct ?
They have well defined names/packages that can easily be filtered (grep?) from the the usual function coverage report you get from `go tool covdata func ...`.
After this filtering, you could take an average, in whichever way you feel appropriate. Would this work for your need ?
Btw, I don't know of a golang package to output cover files ... would the command line tools work ? (`go tool covdata` or for instance `go tool cover --to=HTML`)
cheers!
ps.: Just in case it helps:
* To write the coverage information in text format, I suppose the
original blog post still works (it's from 2013)
for unit tests.