50 lines
1.3 KiB
Go
50 lines
1.3 KiB
Go
package azure
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import (
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"bytes"
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"io"
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)
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type blockBlobWriter interface {
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GetSize(container, blob string) (int64, error)
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WriteBlobAt(container, blob string, offset int64, chunk io.Reader) (int64, error)
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}
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// zeroFillWriter enables writing to an offset outside a block blob's size
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// by offering the chunk to the underlying writer as a contiguous data with
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// the gap in between filled with NUL (zero) bytes.
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type zeroFillWriter struct {
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blockBlobWriter
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}
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func newZeroFillWriter(b blockBlobWriter) zeroFillWriter {
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w := zeroFillWriter{}
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w.blockBlobWriter = b
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return w
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}
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// Write writes the given chunk to the specified existing blob even though
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// offset is out of blob's size. The gaps are filled with zeros. Returned
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// written number count does not include zeros written.
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func (z *zeroFillWriter) Write(container, blob string, offset int64, chunk io.Reader) (int64, error) {
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size, err := z.blockBlobWriter.GetSize(container, blob)
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if err != nil {
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return 0, err
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}
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var reader io.Reader
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var zeroPadding int64
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if offset <= size {
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reader = chunk
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} else {
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zeroPadding = offset - size
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offset = size // adjust offset to be the append index
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zeros := bytes.NewReader(make([]byte, zeroPadding))
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reader = io.MultiReader(zeros, chunk)
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}
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nn, err := z.blockBlobWriter.WriteBlobAt(container, blob, offset, reader)
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nn -= zeroPadding
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return nn, err
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}
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