w      *io.PipeWriter
	r      *io.PipeReader
	wg     *sync.WaitGroup
	buffer map[int64][]byte
	err    error

	nextOffset int64
	m          sync.Mutex
}

func (w *writerAt) WriteAt(b []byte, offset int64) (n int, err error) {
	w.m.Lock()
	defer w.m.Unlock()

	if w.nextOffset == offset {
		n, err = w.w.Write(b)
		w.nextOffset += int64(n)
	} else {

pkg io, type WriteSeeker interface, Write([]uint8) (int, error)
pkg io, type Writer interface { Write }
pkg io, type Writer interface, Write([]uint8) (int, error)
pkg io, type WriterAt interface { WriteAt }
pkg io, type WriterAt interface, WriteAt([]uint8, int64) (int, error)
pkg io, type WriterTo interface { WriteTo }
pkg io, type WriterTo interface, WriteTo(Writer) (int64, error)
pkg io, var EOF error
pkg io, var ErrClosedPipe error

pkg io/fs, var SkipAll error #47209
pkg io, func NewOffsetWriter(WriterAt, int64) *OffsetWriter #45899
pkg io, method (*OffsetWriter) Seek(int64, int) (int64, error) #45899
pkg io, method (*OffsetWriter) WriteAt([]uint8, int64) (int, error) #45899
pkg io, method (*OffsetWriter) Write([]uint8) (int, error) #45899
pkg io, type OffsetWriter struct #45899
pkg math/rand, func Read //deprecated #20661