frostfs-s3-gw/api/layer/writer.go
Evgeniy Kulikov 8ff289ea4f Simplify OffsetWriter
Signed-off-by: Evgeniy Kulikov <kim@nspcc.ru>
2020-12-10 18:15:43 +03:00

54 lines
1 KiB
Go

package layer
import "io"
type offsetWriter struct {
io.Writer
written int64
skipped int64
offset int64
length int64
}
func newWriter(w io.Writer, offset, length int64) *offsetWriter {
return &offsetWriter{
Writer: w,
offset: offset,
length: length,
}
}
func (w *offsetWriter) Write(p []byte) (int, error) {
ln := len(p)
length := int64(ln)
offset := w.offset - w.skipped
if length-offset < 0 {
w.skipped += length
return ln, nil
}
length -= offset
// Writer should write enough and stop writing
// 1. When passed zero length, it should write all bytes except offset
// 2. When the written buffer is almost filled (left < length),
// should write some bytes to fill up the buffer
// 3. When the written buffer is filled, should stop to write
if left := w.length - w.written; left == 0 && w.length != 0 {
return 0, nil
} else if left > 0 && left < length {
length = left
}
n, err := w.Writer.Write(p[offset : offset+length])
w.written += int64(n)
w.skipped += offset
return n, err
}