Pitfalls When Parsing Binary Data in Go

• Pitfalls When Parsing Binary Data in Go

for {
  buf := make([]byte, bufSize)
  n, err := r.Read(buf)
  if err == io.EOF {
    return
  } else if err != nil {
    aerr.Store(err)
    return
  }
  ch <- buf[:n]
}

The code returns immediately when err is io.EOF, which is the most likely problem. The docs say:

Callers should always process the n > 0 bytes returned before considering the error err. Doing so correctly handles I/O errors that happen after reading some bytes and also both of the allowed EOF behaviors.

So the program must handle n > 0 first, and then handle err != nil. This differs from the usual assumption that a non-nil err implies no data. io.Reader does not behave that way.