package streaming import ( "errors" "io" ) type Writer struct { data []byte offset int } func NewWriter(data []byte) *Writer { return &Writer{data, 0} } func (w *Writer) Write(data []byte) (int, error) { length := len(data) if w.offset+length > len(w.data) { length = len(w.data) - w.offset } if length == 0 { return 0, errors.New("cannot write past end of buffer") } copy(w.data[w.offset:], data[:length]) w.offset += length return length, nil } func (w *Writer) Seek(offset int64, whence int) (int64, error) { result := w.offset switch whence { case io.SeekStart: result = int(offset) case io.SeekCurrent: result = w.offset + int(offset) case io.SeekEnd: result = len(w.data) - int(offset) } if result < 0 { return int64(w.offset), errors.New("cannot seek before beginning of buffer") } if result >= len(w.data) { return int64(w.offset), errors.New("cannot seek past end of buffer") } w.offset = result return int64(w.offset), nil }