Just FYI... within Google, `strconv.Itoa()` is prefered to convert integers to strings (if indeed prefixLen is an `int`).
Also, `prefixLen` is long for a temp variable in Go.  Maybe `s`.
Additionally, is `_` an `err` that is being ignored here?  Should it be?
If it will always succeed, then it should not return an `err` at all.

And hey... if I'm being annoying, please let me know.  At one point I think someone on this team asked me to try to help with idiomatic Go from the perspective of a Googler (and again, I am not a Go expert and am learning it myself)... so please feel free to tell me to tone it down a bit and I will.  :-)