syncthing/blocks.go

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2013-12-15 10:43:31 +00:00
package main
import (
"bytes"
"crypto/sha256"
"io"
)
type BlockList []Block
type Block struct {
Offset uint64
Length uint32
Hash []byte
}
// Blocks returns the blockwise hash of the reader.
func Blocks(r io.Reader, blocksize int) (BlockList, error) {
var blocks BlockList
var offset uint64
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,
Length: uint32(n),
Hash: hf.Sum(nil),
}
blocks = append(blocks, b)
offset += uint64(n)
}
return blocks, nil
}
// To returns the list of blocks necessary to transform src into dst.
// Both block lists must have been created with the same block size.
func (src BlockList) To(tgt BlockList) (have, need BlockList) {
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
}