75 lines
1.5 KiB
Go
75 lines
1.5 KiB
Go
package scanner
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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 Block struct {
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Offset int64
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Size 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) ([]Block, error) {
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var blocks []Block
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var offset int64
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for {
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lr := &io.LimitedReader{R: r, N: 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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Size: 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 += int64(n)
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}
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if len(blocks) == 0 {
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// Empty file
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blocks = append(blocks, Block{
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Offset: 0,
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Size: 0,
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Hash: []uint8{0xe3, 0xb0, 0xc4, 0x42, 0x98, 0xfc, 0x1c, 0x14, 0x9a, 0xfb, 0xf4, 0xc8, 0x99, 0x6f, 0xb9, 0x24, 0x27, 0xae, 0x41, 0xe4, 0x64, 0x9b, 0x93, 0x4c, 0xa4, 0x95, 0x99, 0x1b, 0x78, 0x52, 0xb8, 0x55},
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})
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}
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return blocks, nil
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}
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// BlockDiff returns lists of common and missing (to transform src into tgt)
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// blocks. Both block lists must have been created with the same block size.
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func BlockDiff(src, tgt []Block) (have, need []Block) {
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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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