SliceWriteSeeker implements WriteSeeker on a slice. There was a brief discussion on adding such a feature to the stdlib.
s := slicewriteseek.New()
// write to it
if _, err := s.Write([]byte{1, 2, 3}); err != nil {
panic(err)
}
// seek it
if off, err := s.Seek(0, io.SeekStart); err != nil || off != 0 {
panic("Unexpected seek")
}
// read it
b := make([]byte, 1)
if _, err := s.Read(b); err != nil {
panic(err)
}