scan := bufio.NewScanner(input)
scan.Buffer(make([]byte,largeNum,largeNum),largeNum)
// up to here we dont know how long the maximum accepted line of text may be
// as the chunk size of the underlying io.Reader is unknown
scan.MaxConsecutiveEmptyReads(8192)
// with this setting the scanner will surely be able to process lines of length 8192 bytes
// with a worst-case chunk size of 1 byte or much more with a bigger chunk size.

func lengthPrefixedUint32BESplitFunc(data []byte, atEOF bool) (advance int, token []byte, err error) {
	const prefixBytes int = 4
	if atEOF {
		return 0, nil, nil
	}
	if len(data) < prefixBytes {
		// request more data
		return 0, nil, nil
	}
	l := binary.BigEndian.Uint32(data)
	bytesToRead := int(l)
	if len(data)-prefixBytes >= bytesToRead {
		return prefixBytes + bytesToRead, data[prefixBytes : prefixBytes+bytesToRead], nil
	} else {
		// request more data
		return 0, nil, nil
	}
}