// create file called "X.[messageid].tmp" located in the store
// the contents of the file is the bytes of the message, then
// rename it to "X.[messageid].msg", overwriting any existing
// message with the same id
// X will be 'i' for inbound messages, and O for outbound messages
func write(store, key string, m packets.ControlPacket) {
temppath := tmppath(store, key)
f, err := os.Create(temppath)
chkerr(err)
werr := m.Write(f)
chkerr(werr)
cerr := f.Close()
chkerr(cerr)
rerr := os.Rename(temppath, fullpath(store, key))
chkerr(rerr)
}
