45 lines
935 B
Go
45 lines
935 B
Go
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package readerutil
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import (
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"io"
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"os"
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)
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// NewReadSeekerFromReaderAt returns a new io.ReadSeeker from a io.ReaderAt.
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// The returned io.ReadSeeker will read from the io.ReaderAt starting at the
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// given base offset.
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func NewReadSeekerFromReaderAt(readerAt io.ReaderAt, base int64) io.ReadSeeker {
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return &readSeekerFromReaderAt{
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readerAt: readerAt,
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base: base,
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pos: 0,
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}
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}
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type readSeekerFromReaderAt struct {
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readerAt io.ReaderAt
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base int64
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pos int64
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}
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func (rs *readSeekerFromReaderAt) Read(p []byte) (n int, err error) {
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n, err = rs.readerAt.ReadAt(p, rs.pos+rs.base)
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rs.pos += int64(n)
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return n, err
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}
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func (rs *readSeekerFromReaderAt) Seek(offset int64, whence int) (int64, error) {
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switch whence {
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case io.SeekStart:
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rs.pos = offset
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case io.SeekCurrent:
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rs.pos += offset
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case io.SeekEnd:
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return 0, io.ErrUnexpectedEOF
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default:
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return 0, os.ErrInvalid
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}
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return rs.pos, nil
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}
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