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// Copyright (C) 2014 Jakob Borg and other contributors. All rights reserved.
// Use of this source code is governed by an MIT-style license that can be
// found in the LICENSE file.
package scanner
import (
"bytes"
"crypto/sha256"
"io"
)
const StandardBlockSize = 128 * 1024
type Block struct {
Offset int64
Size uint32
Hash []byte
}
// Blocks returns the blockwise hash of the reader.
func Blocks(r io.Reader, blocksize int) ([]Block, error) {
var blocks []Block
var offset int64
for {
lr := &io.LimitedReader{R: r, N: int64(blocksize)}
hf := sha256.New()
n, err := io.Copy(hf, lr)
if err != nil {
return nil, err
}
if n == 0 {
break
}
b := Block{
Offset: offset,
Size: uint32(n),
Hash: hf.Sum(nil),
}
blocks = append(blocks, b)
offset += int64(n)
}
if len(blocks) == 0 {
// Empty file
blocks = append(blocks, Block{
Offset: 0,
Size: 0,
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},
})
}
return blocks, nil
}
// BlockDiff returns lists of common and missing (to transform src into tgt)
// blocks. Both block lists must have been created with the same block size.
func BlockDiff(src, tgt []Block) (have, need []Block) {
if len(tgt) == 0 && len(src) != 0 {
return nil, nil
}
if len(tgt) != 0 && len(src) == 0 {
// Copy the entire file
return nil, tgt
}
for i := range tgt {
if i >= len(src) || bytes.Compare(tgt[i].Hash, src[i].Hash) != 0 {
// Copy differing block
need = append(need, tgt[i])
} else {
have = append(have, tgt[i])
}
}
return have, need
}
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