Add code to compute the root hash for a hash tree

extensions/browser/content_hash_tree_unittest.cc

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/memory/scoped_ptr.h"
+#include "base/stl_util.h"
+#include "crypto/secure_hash.h"
+#include "crypto/sha2.h"
+#include "extensions/browser/content_hash_tree.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+using crypto::kSHA256Length;
+using crypto::SecureHash;
+
+// Helper to return a fake sha256 signature based on a seed.
+static std::string FakeSignatureWithSeed(int seed) {
+  std::string input;
+  for (int i = 0; i < seed * 3; i++) {
+    input.push_back(static_cast<char>(((i + 19) * seed) % 256));
+  }
+  return crypto::SHA256HashString(input);
+}
+
+namespace extensions {
+
+TEST(ContentHashTreeTest, HashTreeBasics) {
+  std::vector<std::string> nodes;
+  // Empty array.
+  EXPECT_EQ(std::string(), ComputeTreeHashRoot(nodes, 16));
+
+  // One node.
+  std::string node1 = FakeSignatureWithSeed(1);
+  nodes.push_back(node1);
+  EXPECT_EQ(node1, ComputeTreeHashRoot(nodes, 16));
+
+  // Two nodes.
+  std::string node2 = FakeSignatureWithSeed(2);
+  nodes.push_back(node2);
+
+  std::string expected(kSHA256Length, 0);
+  scoped_ptr<SecureHash> hash(SecureHash::Create(SecureHash::SHA256));
+  hash->Update(node1.data(), node1.size());
+  hash->Update(node2.data(), node2.size());
+  hash->Finish(string_as_array(&expected), expected.size());
+  EXPECT_EQ(expected, ComputeTreeHashRoot(nodes, 16));
+}
+
+TEST(ContentHashTreeTest, HashTreeMultipleLevels) {
+  std::vector<std::string> nodes;
+  for (int i = 0; i < 3; i++) {
+    std::string node;
+    nodes.push_back(FakeSignatureWithSeed(i));
+  }
+
+  // First try a test where our branch factor is >= 3, so we expect the result
+  // to be the hash of all 3 concatenated together. E.g the expected top hash
+  // should be 4 in the following diagram:
+  //   4
+  // 1 2 3
+  std::string expected =
+      crypto::SHA256HashString(nodes[0] + nodes[1] + nodes[2]);
+  EXPECT_EQ(expected, ComputeTreeHashRoot(nodes, 4));
+
+  // Now try making the branch factor be 2, so that we
+  // should get the following:
+  //   6
+  //  4 5
+  // 1 2 3
+  // where 4 is the hash of 1 and 2, 5 is the hash of 3, and 6 is the
+  // hash of 4 and 5.
+  std::string hash_of_first_2 = crypto::SHA256HashString(nodes[0] + nodes[1]);
+  std::string hash_of_third = crypto::SHA256HashString(nodes[2]);
+  expected = crypto::SHA256HashString(hash_of_first_2 + hash_of_third);
+  EXPECT_EQ(expected, ComputeTreeHashRoot(nodes, 2));
+}
+
+}  // namespace extensions