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blocks.go
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blocks.go
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// Copyright (C) 2014 The Syncthing Authors.
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this file,
// You can obtain one at http://mozilla.org/MPL/2.0/.
package scanner
import (
"bytes"
"crypto/sha256"
"fmt"
"io"
"sync/atomic"
"github.com/syncthing/syncthing/lib/protocol"
)
var SHA256OfNothing = []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}
// Blocks returns the blockwise hash of the reader.
func Blocks(r io.Reader, blocksize int, sizehint int64, counter *int64) ([]protocol.BlockInfo, error) {
var blocks []protocol.BlockInfo
if sizehint > 0 {
blocks = make([]protocol.BlockInfo, 0, int(sizehint/int64(blocksize)))
}
var offset int64
hf := sha256.New()
for {
lr := &io.LimitedReader{R: r, N: int64(blocksize)}
n, err := io.Copy(hf, lr)
if err != nil {
return nil, err
}
if n == 0 {
break
}
if counter != nil {
atomic.AddInt64(counter, int64(n))
}
b := protocol.BlockInfo{
Size: int32(n),
Offset: offset,
Hash: hf.Sum(nil),
}
blocks = append(blocks, b)
offset += int64(n)
hf.Reset()
}
if len(blocks) == 0 {
// Empty file
blocks = append(blocks, protocol.BlockInfo{
Offset: 0,
Size: 0,
Hash: SHA256OfNothing,
})
}
return blocks, nil
}
// PopulateOffsets sets the Offset field on each block
func PopulateOffsets(blocks []protocol.BlockInfo) {
var offset int64
for i := range blocks {
blocks[i].Offset = offset
offset += int64(blocks[i].Size)
}
}
// 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 []protocol.BlockInfo) (have, need []protocol.BlockInfo) {
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
}
// Verify returns nil or an error describing the mismatch between the block
// list and actual reader contents
func Verify(r io.Reader, blocksize int, blocks []protocol.BlockInfo) error {
hf := sha256.New()
for i, block := range blocks {
lr := &io.LimitedReader{R: r, N: int64(blocksize)}
_, err := io.Copy(hf, lr)
if err != nil {
return err
}
hash := hf.Sum(nil)
hf.Reset()
if bytes.Compare(hash, block.Hash) != 0 {
return fmt.Errorf("hash mismatch %x != %x for block %d", hash, block.Hash, i)
}
}
// We should have reached the end now
bs := make([]byte, 1)
n, err := r.Read(bs)
if n != 0 || err != io.EOF {
return fmt.Errorf("file continues past end of blocks")
}
return nil
}
func VerifyBuffer(buf []byte, block protocol.BlockInfo) ([]byte, error) {
if len(buf) != int(block.Size) {
return nil, fmt.Errorf("length mismatch %d != %d", len(buf), block.Size)
}
hf := sha256.New()
_, err := hf.Write(buf)
if err != nil {
return nil, err
}
hash := hf.Sum(nil)
if !bytes.Equal(hash, block.Hash) {
return hash, fmt.Errorf("hash mismatch %x != %x", hash, block.Hash)
}
return hash, nil
}
// BlocksEqual returns whether two slices of blocks are exactly the same hash
// and index pair wise.
func BlocksEqual(src, tgt []protocol.BlockInfo) bool {
if len(tgt) != len(src) {
return false
}
for i, sblk := range src {
if !bytes.Equal(sblk.Hash, tgt[i].Hash) {
return false
}
}
return true
}