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