This repository demonstrates that "EOF" errors are not propagated as io.EOF errors through gocircuit workers (current master: a6d1f33804). When the WriteCloser of a channel is closed, the Reader receives an "EOF" error that is not equal to io.EOF. This makes ioutil.ReadAll return an "EOF" error even though it's documentation says, it should not do so.
The source for the behaviour is here: https://github.com/gocircuit/circuit/blob/7c97d0da1167d27da64ea8457a4e3d4766d084f2/kit/x/io/io.go#L50