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- package main
- import (
- "bytes"
- "crypto/sha256"
- "io"
- )
- 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, 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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