iobufio*Reader.ReadBytes function with '/r' set as the delimiter. Further processing is done by using ReadByte function and comparing it sequentially with each byte of the delimiter and unreading them if necessary (which looks quite tedious)
Using Scanner with a custom split function, which does not look too trivial as well.
I wonder whether there are any other better options, functionality seems so common that it is hard to believe that it is not possible to just define delimiter for tcp stream and extract messages from it.