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package reflink
import (
"errors"
"io"
)
// sectionWriter is a helper used when we need to fallback into copying data manually
type sectionWriter struct {
w io.WriterAt // target file
base int64 // base position in file
off int64 // current relative offset
}
// Write writes & updates offset
func (s *sectionWriter) Write(p []byte) (int, error) {
n, err := s.w.WriteAt(p, s.base+s.off)
s.off += int64(n)
return n, err
}
func (s *sectionWriter) Seek(offset int64, whence int) (int64, error) {
switch whence {
case io.SeekStart:
// nothing needed
case io.SeekCurrent:
offset += s.off
case io.SeekEnd:
// we don't support io.SeekEnd
fallthrough
default:
return s.off, errors.New("Seek: invalid whence")
}
if offset < 0 {
return s.off, errors.New("Seek: invalid offset")
}
s.off = offset
return offset, nil
}
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