payload_consumer/xor_extent_writer_unittest.cc - platform/system/update_engine - Git at Google

 //
 // Copyright (C) 2021 The Android Open Source Project
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //      http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
 //

 #include <algorithm>
 #include <memory>

 #include <unistd.h>

 #include <android-base/file.h>
 #include <gtest/gtest.h>
 #include <libsnapshot/mock_cow_writer.h>

 #include "update_engine/common/utils.h"
 #include "update_engine/payload_consumer/extent_map.h"
 #include "update_engine/payload_consumer/file_descriptor.h"
 #include "update_engine/payload_consumer/xor_extent_writer.h"
 #include "update_engine/payload_generator/delta_diff_generator.h"
 #include "update_engine/payload_generator/extent_ranges.h"
 #include "update_engine/payload_generator/merge_sequence_generator.h"
 #include "update_engine/update_metadata.pb.h"

 namespace chromeos_update_engine {

 using testing::_;
 using testing::Args;
 using testing::Return;

 class XorExtentWriterTest : public ::testing::Test {
  public:
   static constexpr size_t NUM_BLOCKS = 50;
   void SetUp() override {
     ASSERT_EQ(ftruncate64(source_part_.fd, kBlockSize * NUM_BLOCKS), 0);
     ASSERT_EQ(ftruncate64(target_part_.fd, kBlockSize * NUM_BLOCKS), 0);

     // Fill source part with arbitrary data, as we are computing XOR between
     // source and target data later.
     ASSERT_EQ(lseek(source_part_.fd, 0, SEEK_SET), 0);
     brillo::Blob buffer(kBlockSize);
     for (size_t i = 0; i < kBlockSize; i++) {
       buffer[i] = i & 0xFF;
     }
     for (size_t i = 0; i < NUM_BLOCKS; i++) {
       ASSERT_EQ(write(source_part_.fd, buffer.data(), buffer.size()),
                 static_cast<ssize_t>(buffer.size()));
     }
     ASSERT_EQ(fsync(source_part_.fd), 0);
     ASSERT_EQ(fsync(target_part_.fd), 0);
     ASSERT_TRUE(source_fd_->Open(source_part_.path, O_RDONLY | O_CREAT, 0644));
   }
   InstallOperation op_;
   FileDescriptorPtr source_fd_ = std::make_shared<EintrSafeFileDescriptor>();
   ExtentMap<const CowMergeOperation*> xor_map_;
   android::snapshot::MockCowWriter cow_writer_;
   TemporaryFile source_part_;
   TemporaryFile target_part_;
 };

 MATCHER_P2(BytesEqual,
            bytes,
            size,
            "Check if args match expected value byte for byte") {
   return std::get<1>(arg) == size && std::get<0>(arg) != nullptr &&
          memcmp(std::get<0>(arg), bytes, size) == 0;
 }

 TEST_F(XorExtentWriterTest, StreamTest) {
   constexpr auto COW_XOR = CowMergeOperation::COW_XOR;
   ON_CALL(cow_writer_, AddXorBlocks(_, _, _, _, _)).WillByDefault(Return(true));
   const auto op1 = CreateCowMergeOperation(
       ExtentForRange(5, 2), ExtentForRange(5, 2), COW_XOR);
   ASSERT_TRUE(xor_map_.AddExtent(op1.dst_extent(), &op1));
   *op_.add_src_extents() = op1.src_extent();
   *op_.add_dst_extents() = op1.dst_extent();

   const auto op2 = CreateCowMergeOperation(
       ExtentForRange(45, 2), ExtentForRange(456, 2), COW_XOR);
   ASSERT_TRUE(xor_map_.AddExtent(op2.dst_extent(), &op2));
   *op_.add_src_extents() = ExtentForRange(45, 3);
   *op_.add_dst_extents() = ExtentForRange(455, 3);

   const auto op3 = CreateCowMergeOperation(
       ExtentForRange(12, 2), ExtentForRange(321, 2), COW_XOR, 777);
   ASSERT_TRUE(xor_map_.AddExtent(op3.dst_extent(), &op3));
   *op_.add_src_extents() = ExtentForRange(12, 4);
   *op_.add_dst_extents() = ExtentForRange(320, 4);
   XORExtentWriter writer_{
       op_, source_fd_, &cow_writer_, xor_map_, NUM_BLOCKS * kBlockSize};

   // OTA op:
   // [5-6] => [5-6], [45-47] => [455-457], [12-15] => [320-323]

   // merge op:
   // [5-6] => [5-6], [45-46] => [456-457], [12-13] => [321-322]

   // Expected result:
   // [5-7], [45-47], [12-14] should be XOR blocks
   // [320], [323], [455] should be regular replace blocks

   auto zeros = utils::GetReadonlyZeroBlock(kBlockSize * 10);
   EXPECT_CALL(cow_writer_,
               AddRawBlocks(455, zeros->data() + 2 * kBlockSize, kBlockSize))
       .With(Args<1, 2>(BytesEqual(zeros->data(), kBlockSize)))
       .WillOnce(Return(true));
   EXPECT_CALL(cow_writer_,
               AddRawBlocks(320, zeros->data() + 5 * kBlockSize, kBlockSize))
       .With(Args<1, 2>(BytesEqual(zeros->data(), kBlockSize)))
       .WillOnce(Return(true));
   EXPECT_CALL(cow_writer_,
               AddRawBlocks(323, zeros->data() + 8 * kBlockSize, kBlockSize))
       .With(Args<1, 2>(BytesEqual(zeros->data(), kBlockSize)))
       .WillOnce(Return(true));

   EXPECT_CALL(cow_writer_, AddXorBlocks(5, _, kBlockSize * 2, 5, 0))
       .WillOnce(Return(true));
   EXPECT_CALL(cow_writer_, AddXorBlocks(456, _, kBlockSize * 2, 45, 0))
       .WillOnce(Return(true));
   EXPECT_CALL(cow_writer_, AddXorBlocks(321, _, kBlockSize * 2, 12, 777))
       .WillOnce(Return(true));

   ASSERT_TRUE(writer_.Init(op_.dst_extents(), kBlockSize));
   ASSERT_TRUE(writer_.Write(zeros->data(), 9 * kBlockSize));
 }

 TEST_F(XorExtentWriterTest, SubsetExtentTest) {
   constexpr auto COW_XOR = CowMergeOperation::COW_XOR;
   ON_CALL(cow_writer_, AddXorBlocks(_, _, _, _, _)).WillByDefault(Return(true));

   const auto op3 = CreateCowMergeOperation(
       ExtentForRange(12, 4), ExtentForRange(320, 4), COW_XOR, 777);
   ASSERT_TRUE(xor_map_.AddExtent(op3.dst_extent(), &op3));

   *op_.add_src_extents() = ExtentForRange(12, 3);
   *op_.add_dst_extents() = ExtentForRange(320, 3);
   *op_.add_src_extents() = ExtentForRange(20, 3);
   *op_.add_dst_extents() = ExtentForRange(420, 3);
   *op_.add_src_extents() = ExtentForRange(15, 1);
   *op_.add_dst_extents() = ExtentForRange(323, 1);
   XORExtentWriter writer_{
       op_, source_fd_, &cow_writer_, xor_map_, NUM_BLOCKS * kBlockSize};

   // OTA op:
   // [12-14] => [320-322], [20-22] => [420-422], [15-16] => [323-324]

   // merge op:
   // [12-16] => [321-322]

   // Expected result:
   // [12-16] should be XOR blocks
   // [420-422] should be regular replace blocks

   auto zeros = utils::GetReadonlyZeroBlock(kBlockSize * 7);
   EXPECT_CALL(cow_writer_,
               AddRawBlocks(420, zeros->data() + 3 * kBlockSize, kBlockSize * 3))
       .WillOnce(Return(true));

   EXPECT_CALL(cow_writer_, AddXorBlocks(320, _, kBlockSize * 3, 12, 777))
       .WillOnce(Return(true));
   EXPECT_CALL(cow_writer_, AddXorBlocks(323, _, kBlockSize, 15, 777))
       .WillOnce(Return(true));

   ASSERT_TRUE(writer_.Init(op_.dst_extents(), kBlockSize));
   ASSERT_TRUE(writer_.Write(zeros->data(), zeros->size()));
 }

 TEST_F(XorExtentWriterTest, LastBlockTest) {
   constexpr auto COW_XOR = CowMergeOperation::COW_XOR;
   ON_CALL(cow_writer_, AddXorBlocks(_, _, _, _, _)).WillByDefault(Return(true));

   const auto op3 = CreateCowMergeOperation(
       ExtentForRange(NUM_BLOCKS - 1, 1), ExtentForRange(2, 1), COW_XOR, 777);
   ASSERT_TRUE(xor_map_.AddExtent(op3.dst_extent(), &op3));

   *op_.add_src_extents() = ExtentForRange(12, 3);
   *op_.add_dst_extents() = ExtentForRange(320, 3);

   *op_.add_src_extents() = ExtentForRange(20, 3);
   *op_.add_dst_extents() = ExtentForRange(420, 3);

   *op_.add_src_extents() = ExtentForRange(NUM_BLOCKS - 3, 3);
   *op_.add_dst_extents() = ExtentForRange(2, 3);
   XORExtentWriter writer_{
       op_, source_fd_, &cow_writer_, xor_map_, NUM_BLOCKS * kBlockSize};

   // OTA op:
   // [12-14] => [320-322], [20-22] => [420-422], [NUM_BLOCKS-3] => [2-5]

   // merge op:
   // [NUM_BLOCKS-1] => [2]

   // Expected result:
   // [320-322] should be REPLACE blocks
   // [420-422] should be REPLACE blocks
   // [2] should be XOR blocks, with 0 offset to avoid out of bound read
   // [3-5] should be REPLACE BLOCKS

   auto zeros = utils::GetReadonlyZeroBlock(kBlockSize * 9);
   EXPECT_CALL(cow_writer_, AddRawBlocks(320, zeros->data(), kBlockSize * 3))
       .WillOnce(Return(true));
   EXPECT_CALL(cow_writer_,
               AddRawBlocks(420, zeros->data() + 3 * kBlockSize, kBlockSize * 3))
       .WillOnce(Return(true));

   EXPECT_CALL(cow_writer_, AddXorBlocks(2, _, kBlockSize, NUM_BLOCKS - 1, 0))
       .WillOnce(Return(true));
   EXPECT_CALL(cow_writer_,
               AddRawBlocks(3, zeros->data() + kBlockSize * 7, kBlockSize * 2))
       .WillOnce(Return(true));

   ASSERT_TRUE(writer_.Init(op_.dst_extents(), kBlockSize));
   ASSERT_TRUE(writer_.Write(zeros->data(), zeros->size()));
 }

 TEST_F(XorExtentWriterTest, LastMultiBlockTest) {
   constexpr auto COW_XOR = CowMergeOperation::COW_XOR;

   const auto op3 = CreateCowMergeOperation(
       ExtentForRange(NUM_BLOCKS - 4, 4), ExtentForRange(2, 4), COW_XOR, 777);
   ASSERT_TRUE(xor_map_.AddExtent(op3.dst_extent(), &op3));

   *op_.add_src_extents() = ExtentForRange(NUM_BLOCKS - 4, 4);
   *op_.add_dst_extents() = ExtentForRange(2, 4);
   XORExtentWriter writer_{
       op_, source_fd_, &cow_writer_, xor_map_, NUM_BLOCKS * kBlockSize};

   // OTA op:
   // [NUM_BLOCKS-4] => [2-5]

   // merge op:
   // [NUM_BLOCKS-4] => [2-5]

   // Expected result:
   // [12-16] should be REPLACE blocks
   // [420-422] should be REPLACE blocks
   // [2-3] should be XOR blocks
   // [4] should be XOR blocks with 0 offset to avoid out of bound read

   // Send arbitrary data, just to confirm that XORExtentWriter did XOR the
   // source data with target data
   std::vector<uint8_t> op_data(kBlockSize * 4);
   for (size_t i = 0; i < op_data.size(); i++) {
     if (i % kBlockSize == 0) {
       op_data[i] = 1;
     } else {
       op_data[i] = (op_data[i - 1] * 3) & 0xFF;
     }
   }
   auto&& verify_xor_data = [source_fd_(source_fd_), &op_data](
                                uint32_t new_block_start,
                                const void* data,
                                size_t size,
                                uint32_t old_block,
                                uint16_t offset) -> bool {
     std::vector<uint8_t> source_data(size);
     ssize_t bytes_read{};
     TEST_AND_RETURN_FALSE_ERRNO(utils::PReadAll(source_fd_,
                                                 source_data.data(),
                                                 source_data.size(),
                                                 old_block * kBlockSize + offset,
                                                 &bytes_read));
     TEST_EQ(bytes_read, static_cast<ssize_t>(source_data.size()));
     std::transform(source_data.begin(),
                    source_data.end(),
                    static_cast<const uint8_t*>(data),
                    source_data.begin(),
                    std::bit_xor<uint8_t>{});
     if (memcmp(source_data.data(), op_data.data(), source_data.size()) != 0) {
       LOG(ERROR) << "XOR data received does not appear to be an XOR between "
                     "source and target data";
       return false;
     }
     return true;
   };
   EXPECT_CALL(cow_writer_,
               AddXorBlocks(2, _, kBlockSize * 3, NUM_BLOCKS - 4, 777))
       .WillOnce(verify_xor_data);
   EXPECT_CALL(cow_writer_, AddXorBlocks(5, _, kBlockSize, NUM_BLOCKS - 1, 0))
       .WillOnce(verify_xor_data);

   ASSERT_TRUE(writer_.Init(op_.dst_extents(), kBlockSize));
   ASSERT_TRUE(writer_.Write(op_data.data(), op_data.size()));
 }

 }  // namespace chromeos_update_engine
	//
	// Copyright (C) 2021 The Android Open Source Project
	//
	// Licensed under the Apache License, Version 2.0 (the "License");
	// you may not use this file except in compliance with the License.
	// You may obtain a copy of the License at
	//
	// http://www.apache.org/licenses/LICENSE-2.0
	//
	// Unless required by applicable law or agreed to in writing, software
	// distributed under the License is distributed on an "AS IS" BASIS,
	// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	// See the License for the specific language governing permissions and
	// limitations under the License.
	//

	#include <algorithm>
	#include <memory>

	#include <unistd.h>

	#include <android-base/file.h>
	#include <gtest/gtest.h>
	#include <libsnapshot/mock_cow_writer.h>

	#include "update_engine/common/utils.h"
	#include "update_engine/payload_consumer/extent_map.h"
	#include "update_engine/payload_consumer/file_descriptor.h"
	#include "update_engine/payload_consumer/xor_extent_writer.h"
	#include "update_engine/payload_generator/delta_diff_generator.h"
	#include "update_engine/payload_generator/extent_ranges.h"
	#include "update_engine/payload_generator/merge_sequence_generator.h"
	#include "update_engine/update_metadata.pb.h"

	namespace chromeos_update_engine {

	using testing::_;
	using testing::Args;
	using testing::Return;

	class XorExtentWriterTest : public ::testing::Test {
	public:
	static constexpr size_t NUM_BLOCKS = 50;
	void SetUp() override {
	ASSERT_EQ(ftruncate64(source_part_.fd, kBlockSize * NUM_BLOCKS), 0);
	ASSERT_EQ(ftruncate64(target_part_.fd, kBlockSize * NUM_BLOCKS), 0);

	// Fill source part with arbitrary data, as we are computing XOR between
	// source and target data later.
	ASSERT_EQ(lseek(source_part_.fd, 0, SEEK_SET), 0);
	brillo::Blob buffer(kBlockSize);
	for (size_t i = 0; i < kBlockSize; i++) {
	buffer[i] = i & 0xFF;
	}
	for (size_t i = 0; i < NUM_BLOCKS; i++) {
	ASSERT_EQ(write(source_part_.fd, buffer.data(), buffer.size()),
	static_cast<ssize_t>(buffer.size()));
	}
	ASSERT_EQ(fsync(source_part_.fd), 0);
	ASSERT_EQ(fsync(target_part_.fd), 0);
	ASSERT_TRUE(source_fd_->Open(source_part_.path, O_RDONLY \| O_CREAT, 0644));
	}
	InstallOperation op_;
	FileDescriptorPtr source_fd_ = std::make_shared<EintrSafeFileDescriptor>();
	ExtentMap<const CowMergeOperation*> xor_map_;
	android::snapshot::MockCowWriter cow_writer_;
	TemporaryFile source_part_;
	TemporaryFile target_part_;
	};

	MATCHER_P2(BytesEqual,
	bytes,
	size,
	"Check if args match expected value byte for byte") {
	return std::get<1>(arg) == size && std::get<0>(arg) != nullptr &&
	memcmp(std::get<0>(arg), bytes, size) == 0;
	}

	TEST_F(XorExtentWriterTest, StreamTest) {
	constexpr auto COW_XOR = CowMergeOperation::COW_XOR;
	ON_CALL(cow_writer_, AddXorBlocks(_, _, _, _, _)).WillByDefault(Return(true));
	const auto op1 = CreateCowMergeOperation(
	ExtentForRange(5, 2), ExtentForRange(5, 2), COW_XOR);
	ASSERT_TRUE(xor_map_.AddExtent(op1.dst_extent(), &op1));
	*op_.add_src_extents() = op1.src_extent();
	*op_.add_dst_extents() = op1.dst_extent();

	const auto op2 = CreateCowMergeOperation(
	ExtentForRange(45, 2), ExtentForRange(456, 2), COW_XOR);
	ASSERT_TRUE(xor_map_.AddExtent(op2.dst_extent(), &op2));
	*op_.add_src_extents() = ExtentForRange(45, 3);
	*op_.add_dst_extents() = ExtentForRange(455, 3);

	const auto op3 = CreateCowMergeOperation(
	ExtentForRange(12, 2), ExtentForRange(321, 2), COW_XOR, 777);
	ASSERT_TRUE(xor_map_.AddExtent(op3.dst_extent(), &op3));
	*op_.add_src_extents() = ExtentForRange(12, 4);
	*op_.add_dst_extents() = ExtentForRange(320, 4);
	XORExtentWriter writer_{
	op_, source_fd_, &cow_writer_, xor_map_, NUM_BLOCKS * kBlockSize};

	// OTA op:
	// [5-6] => [5-6], [45-47] => [455-457], [12-15] => [320-323]

	// merge op:
	// [5-6] => [5-6], [45-46] => [456-457], [12-13] => [321-322]

	// Expected result:
	// [5-7], [45-47], [12-14] should be XOR blocks
	// [320], [323], [455] should be regular replace blocks

	auto zeros = utils::GetReadonlyZeroBlock(kBlockSize * 10);
	EXPECT_CALL(cow_writer_,
	AddRawBlocks(455, zeros->data() + 2 * kBlockSize, kBlockSize))
	.With(Args<1, 2>(BytesEqual(zeros->data(), kBlockSize)))
	.WillOnce(Return(true));
	EXPECT_CALL(cow_writer_,
	AddRawBlocks(320, zeros->data() + 5 * kBlockSize, kBlockSize))
	.With(Args<1, 2>(BytesEqual(zeros->data(), kBlockSize)))
	.WillOnce(Return(true));
	EXPECT_CALL(cow_writer_,
	AddRawBlocks(323, zeros->data() + 8 * kBlockSize, kBlockSize))
	.With(Args<1, 2>(BytesEqual(zeros->data(), kBlockSize)))
	.WillOnce(Return(true));

	EXPECT_CALL(cow_writer_, AddXorBlocks(5, _, kBlockSize * 2, 5, 0))
	.WillOnce(Return(true));
	EXPECT_CALL(cow_writer_, AddXorBlocks(456, _, kBlockSize * 2, 45, 0))
	.WillOnce(Return(true));
	EXPECT_CALL(cow_writer_, AddXorBlocks(321, _, kBlockSize * 2, 12, 777))
	.WillOnce(Return(true));

	ASSERT_TRUE(writer_.Init(op_.dst_extents(), kBlockSize));
	ASSERT_TRUE(writer_.Write(zeros->data(), 9 * kBlockSize));
	}

	TEST_F(XorExtentWriterTest, SubsetExtentTest) {
	constexpr auto COW_XOR = CowMergeOperation::COW_XOR;
	ON_CALL(cow_writer_, AddXorBlocks(_, _, _, _, _)).WillByDefault(Return(true));

	const auto op3 = CreateCowMergeOperation(
	ExtentForRange(12, 4), ExtentForRange(320, 4), COW_XOR, 777);
	ASSERT_TRUE(xor_map_.AddExtent(op3.dst_extent(), &op3));

	*op_.add_src_extents() = ExtentForRange(12, 3);
	*op_.add_dst_extents() = ExtentForRange(320, 3);
	*op_.add_src_extents() = ExtentForRange(20, 3);
	*op_.add_dst_extents() = ExtentForRange(420, 3);
	*op_.add_src_extents() = ExtentForRange(15, 1);
	*op_.add_dst_extents() = ExtentForRange(323, 1);
	XORExtentWriter writer_{
	op_, source_fd_, &cow_writer_, xor_map_, NUM_BLOCKS * kBlockSize};

	// OTA op:
	// [12-14] => [320-322], [20-22] => [420-422], [15-16] => [323-324]

	// merge op:
	// [12-16] => [321-322]

	// Expected result:
	// [12-16] should be XOR blocks
	// [420-422] should be regular replace blocks

	auto zeros = utils::GetReadonlyZeroBlock(kBlockSize * 7);
	EXPECT_CALL(cow_writer_,
	AddRawBlocks(420, zeros->data() + 3 * kBlockSize, kBlockSize * 3))
	.WillOnce(Return(true));

	EXPECT_CALL(cow_writer_, AddXorBlocks(320, _, kBlockSize * 3, 12, 777))
	.WillOnce(Return(true));
	EXPECT_CALL(cow_writer_, AddXorBlocks(323, _, kBlockSize, 15, 777))
	.WillOnce(Return(true));

	ASSERT_TRUE(writer_.Init(op_.dst_extents(), kBlockSize));
	ASSERT_TRUE(writer_.Write(zeros->data(), zeros->size()));
	}

	TEST_F(XorExtentWriterTest, LastBlockTest) {
	constexpr auto COW_XOR = CowMergeOperation::COW_XOR;
	ON_CALL(cow_writer_, AddXorBlocks(_, _, _, _, _)).WillByDefault(Return(true));

	const auto op3 = CreateCowMergeOperation(
	ExtentForRange(NUM_BLOCKS - 1, 1), ExtentForRange(2, 1), COW_XOR, 777);
	ASSERT_TRUE(xor_map_.AddExtent(op3.dst_extent(), &op3));

	*op_.add_src_extents() = ExtentForRange(12, 3);
	*op_.add_dst_extents() = ExtentForRange(320, 3);

	*op_.add_src_extents() = ExtentForRange(20, 3);
	*op_.add_dst_extents() = ExtentForRange(420, 3);

	*op_.add_src_extents() = ExtentForRange(NUM_BLOCKS - 3, 3);
	*op_.add_dst_extents() = ExtentForRange(2, 3);
	XORExtentWriter writer_{
	op_, source_fd_, &cow_writer_, xor_map_, NUM_BLOCKS * kBlockSize};

	// OTA op:
	// [12-14] => [320-322], [20-22] => [420-422], [NUM_BLOCKS-3] => [2-5]

	// merge op:
	// [NUM_BLOCKS-1] => [2]

	// Expected result:
	// [320-322] should be REPLACE blocks
	// [420-422] should be REPLACE blocks
	// [2] should be XOR blocks, with 0 offset to avoid out of bound read
	// [3-5] should be REPLACE BLOCKS

	auto zeros = utils::GetReadonlyZeroBlock(kBlockSize * 9);
	EXPECT_CALL(cow_writer_, AddRawBlocks(320, zeros->data(), kBlockSize * 3))
	.WillOnce(Return(true));
	EXPECT_CALL(cow_writer_,
	AddRawBlocks(420, zeros->data() + 3 * kBlockSize, kBlockSize * 3))
	.WillOnce(Return(true));

	EXPECT_CALL(cow_writer_, AddXorBlocks(2, _, kBlockSize, NUM_BLOCKS - 1, 0))
	.WillOnce(Return(true));
	EXPECT_CALL(cow_writer_,
	AddRawBlocks(3, zeros->data() + kBlockSize * 7, kBlockSize * 2))
	.WillOnce(Return(true));

	ASSERT_TRUE(writer_.Init(op_.dst_extents(), kBlockSize));
	ASSERT_TRUE(writer_.Write(zeros->data(), zeros->size()));
	}

	TEST_F(XorExtentWriterTest, LastMultiBlockTest) {
	constexpr auto COW_XOR = CowMergeOperation::COW_XOR;

	const auto op3 = CreateCowMergeOperation(
	ExtentForRange(NUM_BLOCKS - 4, 4), ExtentForRange(2, 4), COW_XOR, 777);
	ASSERT_TRUE(xor_map_.AddExtent(op3.dst_extent(), &op3));

	*op_.add_src_extents() = ExtentForRange(NUM_BLOCKS - 4, 4);
	*op_.add_dst_extents() = ExtentForRange(2, 4);
	XORExtentWriter writer_{
	op_, source_fd_, &cow_writer_, xor_map_, NUM_BLOCKS * kBlockSize};

	// OTA op:
	// [NUM_BLOCKS-4] => [2-5]

	// merge op:
	// [NUM_BLOCKS-4] => [2-5]

	// Expected result:
	// [12-16] should be REPLACE blocks
	// [420-422] should be REPLACE blocks
	// [2-3] should be XOR blocks
	// [4] should be XOR blocks with 0 offset to avoid out of bound read

	// Send arbitrary data, just to confirm that XORExtentWriter did XOR the
	// source data with target data
	std::vector<uint8_t> op_data(kBlockSize * 4);
	for (size_t i = 0; i < op_data.size(); i++) {
	if (i % kBlockSize == 0) {
	op_data[i] = 1;
	} else {
	op_data[i] = (op_data[i - 1] * 3) & 0xFF;
	}
	}
	auto&& verify_xor_data = [source_fd_(source_fd_), &op_data](
	uint32_t new_block_start,
	const void* data,
	size_t size,
	uint32_t old_block,
	uint16_t offset) -> bool {
	std::vector<uint8_t> source_data(size);
	ssize_t bytes_read{};
	TEST_AND_RETURN_FALSE_ERRNO(utils::PReadAll(source_fd_,
	source_data.data(),
	source_data.size(),
	old_block * kBlockSize + offset,
	&bytes_read));
	TEST_EQ(bytes_read, static_cast<ssize_t>(source_data.size()));
	std::transform(source_data.begin(),
	source_data.end(),
	static_cast<const uint8_t*>(data),
	source_data.begin(),
	std::bit_xor<uint8_t>{});
	if (memcmp(source_data.data(), op_data.data(), source_data.size()) != 0) {
	LOG(ERROR) << "XOR data received does not appear to be an XOR between "
	"source and target data";
	return false;
	}
	return true;
	};
	EXPECT_CALL(cow_writer_,
	AddXorBlocks(2, _, kBlockSize * 3, NUM_BLOCKS - 4, 777))
	.WillOnce(verify_xor_data);
	EXPECT_CALL(cow_writer_, AddXorBlocks(5, _, kBlockSize, NUM_BLOCKS - 1, 0))
	.WillOnce(verify_xor_data);

	ASSERT_TRUE(writer_.Init(op_.dst_extents(), kBlockSize));
	ASSERT_TRUE(writer_.Write(op_data.data(), op_data.size()));
	}

	} // namespace chromeos_update_engine