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