68 lines
1.2 KiB
Go
68 lines
1.2 KiB
Go
package main
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import (
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"bytes"
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"crypto/sha256"
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"io"
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)
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type BlockList []Block
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type Block struct {
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Offset uint64
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Length uint32
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Hash []byte
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}
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// Blocks returns the blockwise hash of the reader.
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func Blocks(r io.Reader, blocksize int) (BlockList, error) {
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var blocks BlockList
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var offset uint64
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for {
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lr := &io.LimitedReader{r, int64(blocksize)}
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hf := sha256.New()
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n, err := io.Copy(hf, lr)
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if err != nil {
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return nil, err
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}
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if n == 0 {
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break
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}
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b := Block{
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Offset: offset,
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Length: uint32(n),
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Hash: hf.Sum(nil),
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}
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blocks = append(blocks, b)
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offset += uint64(n)
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}
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return blocks, nil
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}
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// To returns the list of blocks necessary to transform src into dst.
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// Both block lists must have been created with the same block size.
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func (src BlockList) To(tgt BlockList) (have, need BlockList) {
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if len(tgt) == 0 && len(src) != 0 {
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return nil, nil
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}
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if len(tgt) != 0 && len(src) == 0 {
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// Copy the entire file
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return nil, tgt
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}
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for i := range tgt {
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if i >= len(src) || bytes.Compare(tgt[i].Hash, src[i].Hash) != 0 {
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// Copy differing block
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need = append(need, tgt[i])
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} else {
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have = append(have, tgt[i])
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}
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}
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return have, need
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}
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