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Side by Side Diff: extensions/browser/content_hash_tree.cc

Issue 274243004: Add code to compute the root hash for a hash tree (Closed) Base URL: svn://svn.chromium.org/chrome/trunk/src
Patch Set: responded to review feedback Created 6 years, 7 months ago
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1 // Copyright 2014 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4
5 #include "extensions/browser/content_hash_tree.h"
6
7 #include "base/memory/scoped_ptr.h"
8 #include "base/stl_util.h"
9 #include "crypto/secure_hash.h"
10 #include "crypto/sha2.h"
11
12 namespace extensions {
13
14 std::string ComputeTreeHashRoot(const std::vector<std::string>& leaf_hashes,
15 int branch_factor) {
16 if (leaf_hashes.empty() || branch_factor < 2)
17 return std::string();
18
19 // The nodes of the tree we're currently operating on.
20 std::vector<std::string> current_nodes;
21
22 // We avoid having to copy all of the input leaf nodes into |current_nodes|
23 // by using a pointer. So the first iteration of the loop this points at
24 // |leaf_hashes|, but thereafter it points at |current_nodes|.
25 const std::vector<std::string>* current = &leaf_hashes;
26
27 // Where we're inserting new hashes computed from the current level.
28 std::vector<std::string> parent_nodes;
29
30 while (current->size() > 1) {
31 // Iterate over the current level of hashes, computing the hash of up to
32 // |branch_factor| elements to form the hash of each parent node.
33 std::vector<std::string>::const_iterator i = current->begin();
34 while (i != current->end()) {
35 scoped_ptr<crypto::SecureHash> hash(
36 crypto::SecureHash::Create(crypto::SecureHash::SHA256));
37 for (int j = 0; j < branch_factor && i != current->end(); j++) {
38 hash->Update(i->data(), i->size());
39 ++i;
40 }
41 parent_nodes.push_back(std::string(crypto::kSHA256Length, 0));
42 std::string* output = &(parent_nodes.back());
43 hash->Finish(string_as_array(output), output->size());
44 }
45 current_nodes.swap(parent_nodes);
46 parent_nodes.clear();
47 current = &current_nodes;
48 }
49 DCHECK_EQ(1u, current->size());
50 return (*current)[0];
51 }
52
53 } // namespace extensions
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