//
// Copyright (C) 2015 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 "update_engine/payload_generator/delta_diff_utils.h"

#include <endian.h>
#if defined(__clang__)
// TODO(*): Remove these pragmas when b/35721782 is fixed.
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wmacro-redefined"
#endif
#include <ext2fs/ext2fs.h>
#if defined(__clang__)
#pragma clang diagnostic pop
#endif
#include <unistd.h>

#include <algorithm>
#include <functional>
#include <list>
#include <map>
#include <memory>
#include <numeric>
#include <utility>

#include <base/files/file_util.h>
#include <base/format_macros.h>
#include <base/strings/string_util.h>
#include <base/strings/stringprintf.h>
#include <base/threading/simple_thread.h>
#include <base/time/time.h>
#include <brillo/data_encoding.h>
#include <bsdiff/bsdiff.h>
#include <bsdiff/patch_writer_factory.h>
#include <puffin/utils.h>

#include "update_engine/common/hash_calculator.h"
#include "update_engine/common/subprocess.h"
#include "update_engine/common/utils.h"
#include "update_engine/payload_consumer/payload_constants.h"
#include "update_engine/payload_generator/ab_generator.h"
#include "update_engine/payload_generator/block_mapping.h"
#include "update_engine/payload_generator/bzip.h"
#include "update_engine/payload_generator/deflate_utils.h"
#include "update_engine/payload_generator/delta_diff_generator.h"
#include "update_engine/payload_generator/extent_ranges.h"
#include "update_engine/payload_generator/extent_utils.h"
#include "update_engine/payload_generator/squashfs_filesystem.h"
#include "update_engine/payload_generator/xz.h"

using std::list;
using std::map;
using std::string;
using std::vector;

namespace chromeos_update_engine {
namespace {

// The maximum destination size allowed for bsdiff. In general, bsdiff should
// work for arbitrary big files, but the payload generation and payload
// application requires a significant amount of RAM. We put a hard-limit of
// 200 MiB that should not affect any released board, but will limit the
// Chrome binary in ASan builders.
const uint64_t kMaxBsdiffDestinationSize = 200 * 1024 * 1024;  // bytes

// The maximum destination size allowed for puffdiff. In general, puffdiff
// should work for arbitrary big files, but the payload application is quite
// memory intensive, so we limit these operations to 150 MiB.
const uint64_t kMaxPuffdiffDestinationSize = 150 * 1024 * 1024;  // bytes

const int kBrotliCompressionQuality = 11;

// Storing a diff operation has more overhead over replace operation in the
// manifest, we need to store an additional src_sha256_hash which is 32 bytes
// and not compressible, and also src_extents which could use anywhere from a
// few bytes to hundreds of bytes depending on the number of extents.
// This function evaluates the overhead tradeoff and determines if it's worth to
// use a diff operation with data blob of |diff_size| and |num_src_extents|
// extents over an existing |op| with data blob of |old_blob_size|.
bool IsDiffOperationBetter(const InstallOperation& op,
                           size_t old_blob_size,
                           size_t diff_size,
                           size_t num_src_extents) {
  if (!diff_utils::IsAReplaceOperation(op.type()))
    return diff_size < old_blob_size;

  // Reference: https://developers.google.com/protocol-buffers/docs/encoding
  // For |src_sha256_hash| we need 1 byte field number/type, 1 byte size and 32
  // bytes data, for |src_extents| we need 1 byte field number/type and 1 byte
  // size.
  constexpr size_t kDiffOverhead = 1 + 1 + 32 + 1 + 1;
  // Each extent has two variable length encoded uint64, here we use a rough
  // estimate of 6 bytes overhead per extent, since |num_blocks| is usually
  // very small.
  constexpr size_t kDiffOverheadPerExtent = 6;

  return diff_size + kDiffOverhead + num_src_extents * kDiffOverheadPerExtent <
         old_blob_size;
}

// Returns the levenshtein distance between string |a| and |b|.
// https://en.wikipedia.org/wiki/Levenshtein_distance
int LevenshteinDistance(const string& a, const string& b) {
  vector<int> distances(a.size() + 1);
  std::iota(distances.begin(), distances.end(), 0);

  for (size_t i = 1; i <= b.size(); i++) {
    distances[0] = i;
    int previous_distance = i - 1;
    for (size_t j = 1; j <= a.size(); j++) {
      int new_distance =
          std::min({distances[j] + 1,
                    distances[j - 1] + 1,
                    previous_distance + (a[j - 1] == b[i - 1] ? 0 : 1)});
      previous_distance = distances[j];
      distances[j] = new_distance;
    }
  }
  return distances.back();
}
}  // namespace

namespace diff_utils {

// This class encapsulates a file delta processing thread work. The
// processor computes the delta between the source and target files;
// and write the compressed delta to the blob.
class FileDeltaProcessor : public base::DelegateSimpleThread::Delegate {
 public:
  FileDeltaProcessor(const string& old_part,
                     const string& new_part,
                     const PayloadVersion& version,
                     const vector<Extent>& old_extents,
                     const vector<Extent>& new_extents,
                     const vector<puffin::BitExtent>& old_deflates,
                     const vector<puffin::BitExtent>& new_deflates,
                     const string& name,
                     ssize_t chunk_blocks,
                     BlobFileWriter* blob_file)
      : old_part_(old_part),
        new_part_(new_part),
        version_(version),
        old_extents_(old_extents),
        new_extents_(new_extents),
        new_extents_blocks_(utils::BlocksInExtents(new_extents)),
        old_deflates_(old_deflates),
        new_deflates_(new_deflates),
        name_(name),
        chunk_blocks_(chunk_blocks),
        blob_file_(blob_file) {}

  bool operator>(const FileDeltaProcessor& other) const {
    return new_extents_blocks_ > other.new_extents_blocks_;
  }

  ~FileDeltaProcessor() override = default;

  // Overrides DelegateSimpleThread::Delegate.
  // Calculate the list of operations and write their corresponding deltas to
  // the blob_file.
  void Run() override;

  // Merge each file processor's ops list to aops.
  bool MergeOperation(vector<AnnotatedOperation>* aops);

 private:
  const string& old_part_;  // NOLINT(runtime/member_string_references)
  const string& new_part_;  // NOLINT(runtime/member_string_references)
  const PayloadVersion& version_;

  // The block ranges of the old/new file within the src/tgt image
  const vector<Extent> old_extents_;
  const vector<Extent> new_extents_;
  const size_t new_extents_blocks_;
  const vector<puffin::BitExtent> old_deflates_;
  const vector<puffin::BitExtent> new_deflates_;
  const string name_;
  // Block limit of one aop.
  const ssize_t chunk_blocks_;
  BlobFileWriter* blob_file_;

  // The list of ops to reach the new file from the old file.
  vector<AnnotatedOperation> file_aops_;

  bool failed_ = false;

  DISALLOW_COPY_AND_ASSIGN(FileDeltaProcessor);
};

void FileDeltaProcessor::Run() {
  TEST_AND_RETURN(blob_file_ != nullptr);
  base::TimeTicks start = base::TimeTicks::Now();

  if (!DeltaReadFile(&file_aops_,
                     old_part_,
                     new_part_,
                     old_extents_,
                     new_extents_,
                     old_deflates_,
                     new_deflates_,
                     name_,
                     chunk_blocks_,
                     version_,
                     blob_file_)) {
    LOG(ERROR) << "Failed to generate delta for " << name_ << " ("
               << new_extents_blocks_ << " blocks)";
    failed_ = true;
    return;
  }

  if (!ABGenerator::FragmentOperations(
          version_, &file_aops_, new_part_, blob_file_)) {
    LOG(ERROR) << "Failed to fragment operations for " << name_;
    failed_ = true;
    return;
  }

  LOG(INFO) << "Encoded file " << name_ << " (" << new_extents_blocks_
            << " blocks) in " << (base::TimeTicks::Now() - start);
}

bool FileDeltaProcessor::MergeOperation(vector<AnnotatedOperation>* aops) {
  if (failed_)
    return false;
  aops->reserve(aops->size() + file_aops_.size());
  std::move(file_aops_.begin(), file_aops_.end(), std::back_inserter(*aops));
  return true;
}

FilesystemInterface::File GetOldFile(
    const map<string, FilesystemInterface::File>& old_files_map,
    const string& new_file_name) {
  if (old_files_map.empty())
    return {};

  auto old_file_iter = old_files_map.find(new_file_name);
  if (old_file_iter != old_files_map.end())
    return old_file_iter->second;

  // No old file matches the new file name. Use a similar file with the
  // shortest levenshtein distance instead.
  // This works great if the file has version number in it, but even for
  // a completely new file, using a similar file can still help.
  int min_distance =
      LevenshteinDistance(new_file_name, old_files_map.begin()->first);
  const FilesystemInterface::File* old_file = &old_files_map.begin()->second;
  for (const auto& pair : old_files_map) {
    int distance = LevenshteinDistance(new_file_name, pair.first);
    if (distance < min_distance) {
      min_distance = distance;
      old_file = &pair.second;
    }
  }
  LOG(INFO) << "Using " << old_file->name << " as source for " << new_file_name;
  return *old_file;
}

bool DeltaReadPartition(vector<AnnotatedOperation>* aops,
                        const PartitionConfig& old_part,
                        const PartitionConfig& new_part,
                        ssize_t hard_chunk_blocks,
                        size_t soft_chunk_blocks,
                        const PayloadVersion& version,
                        BlobFileWriter* blob_file) {
  ExtentRanges old_visited_blocks;
  ExtentRanges new_visited_blocks;

  // If verity is enabled, mark those blocks as visited to skip generating
  // operations for them.
  if (version.minor >= kVerityMinorPayloadVersion &&
      !new_part.verity.IsEmpty()) {
    LOG(INFO) << "Skipping verity hash tree blocks: "
              << ExtentsToString({new_part.verity.hash_tree_extent});
    new_visited_blocks.AddExtent(new_part.verity.hash_tree_extent);
    LOG(INFO) << "Skipping verity FEC blocks: "
              << ExtentsToString({new_part.verity.fec_extent});
    new_visited_blocks.AddExtent(new_part.verity.fec_extent);
  }

  ExtentRanges old_zero_blocks;
  TEST_AND_RETURN_FALSE(DeltaMovedAndZeroBlocks(aops,
                                                old_part.path,
                                                new_part.path,
                                                old_part.size / kBlockSize,
                                                new_part.size / kBlockSize,
                                                soft_chunk_blocks,
                                                version,
                                                blob_file,
                                                &old_visited_blocks,
                                                &new_visited_blocks,
                                                &old_zero_blocks));

  bool puffdiff_allowed = version.OperationAllowed(InstallOperation::PUFFDIFF);
  map<string, FilesystemInterface::File> old_files_map;
  if (old_part.fs_interface) {
    vector<FilesystemInterface::File> old_files;
    TEST_AND_RETURN_FALSE(deflate_utils::PreprocessPartitionFiles(
        old_part, &old_files, puffdiff_allowed));
    for (const FilesystemInterface::File& file : old_files)
      old_files_map[file.name] = file;
  }

  TEST_AND_RETURN_FALSE(new_part.fs_interface);
  vector<FilesystemInterface::File> new_files;
  TEST_AND_RETURN_FALSE(deflate_utils::PreprocessPartitionFiles(
      new_part, &new_files, puffdiff_allowed));

  list<FileDeltaProcessor> file_delta_processors;

  // The processing is very straightforward here, we generate operations for
  // every file (and pseudo-file such as the metadata) in the new filesystem
  // based on the file with the same name in the old filesystem, if any.
  // Files with overlapping data blocks (like hardlinks or filesystems with tail
  // packing or compression where the blocks store more than one file) are only
  // generated once in the new image, but are also used only once from the old
  // image due to some simplifications (see below).
  for (const FilesystemInterface::File& new_file : new_files) {
    // Ignore the files in the new filesystem without blocks. Symlinks with
    // data blocks (for example, symlinks bigger than 60 bytes in ext2) are
    // handled as normal files. We also ignore blocks that were already
    // processed by a previous file.
    vector<Extent> new_file_extents =
        FilterExtentRanges(new_file.extents, new_visited_blocks);
    new_visited_blocks.AddExtents(new_file_extents);

    if (new_file_extents.empty())
      continue;

    // We can't visit each dst image inode more than once, as that would
    // duplicate work. Here, we avoid visiting each source image inode
    // more than once. Technically, we could have multiple operations
    // that read the same blocks from the source image for diffing, but
    // we choose not to avoid complexity. Eventually we will move away
    // from using a graph/cycle detection/etc to generate diffs, and at that
    // time, it will be easy (non-complex) to have many operations read
    // from the same source blocks. At that time, this code can die. -adlr
    FilesystemInterface::File old_file =
        GetOldFile(old_files_map, new_file.name);
    auto old_file_extents =
        FilterExtentRanges(old_file.extents, old_zero_blocks);
    old_visited_blocks.AddExtents(old_file_extents);

    file_delta_processors.emplace_back(old_part.path,
                                       new_part.path,
                                       version,
                                       std::move(old_file_extents),
                                       std::move(new_file_extents),
                                       old_file.deflates,
                                       new_file.deflates,
                                       new_file.name,  // operation name
                                       hard_chunk_blocks,
                                       blob_file);
  }
  // Process all the blocks not included in any file. We provided all the unused
  // blocks in the old partition as available data.
  vector<Extent> new_unvisited = {
      ExtentForRange(0, new_part.size / kBlockSize)};
  new_unvisited = FilterExtentRanges(new_unvisited, new_visited_blocks);
  if (!new_unvisited.empty()) {
    vector<Extent> old_unvisited;
    if (old_part.fs_interface) {
      old_unvisited.push_back(ExtentForRange(0, old_part.size / kBlockSize));
      old_unvisited = FilterExtentRanges(old_unvisited, old_visited_blocks);
    }

    LOG(INFO) << "Scanning " << utils::BlocksInExtents(new_unvisited)
              << " unwritten blocks using chunk size of " << soft_chunk_blocks
              << " blocks.";
    // We use the soft_chunk_blocks limit for the <non-file-data> as we don't
    // really know the structure of this data and we should not expect it to
    // have redundancy between partitions.
    file_delta_processors.emplace_back(
        old_part.path,
        new_part.path,
        version,
        std::move(old_unvisited),
        std::move(new_unvisited),
        vector<puffin::BitExtent>{},  // old_deflates,
        vector<puffin::BitExtent>{},  // new_deflates
        "<non-file-data>",            // operation name
        soft_chunk_blocks,
        blob_file);
  }

  size_t max_threads = GetMaxThreads();

  // Sort the files in descending order based on number of new blocks to make
  // sure we start the largest ones first.
  if (file_delta_processors.size() > max_threads) {
    file_delta_processors.sort(std::greater<FileDeltaProcessor>());
  }

  base::DelegateSimpleThreadPool thread_pool("incremental-update-generator",
                                             max_threads);
  thread_pool.Start();
  for (auto& processor : file_delta_processors) {
    thread_pool.AddWork(&processor);
  }
  thread_pool.JoinAll();

  for (auto& processor : file_delta_processors) {
    TEST_AND_RETURN_FALSE(processor.MergeOperation(aops));
  }

  return true;
}

bool DeltaMovedAndZeroBlocks(vector<AnnotatedOperation>* aops,
                             const string& old_part,
                             const string& new_part,
                             size_t old_num_blocks,
                             size_t new_num_blocks,
                             ssize_t chunk_blocks,
                             const PayloadVersion& version,
                             BlobFileWriter* blob_file,
                             ExtentRanges* old_visited_blocks,
                             ExtentRanges* new_visited_blocks,
                             ExtentRanges* old_zero_blocks) {
  vector<BlockMapping::BlockId> old_block_ids;
  vector<BlockMapping::BlockId> new_block_ids;
  TEST_AND_RETURN_FALSE(MapPartitionBlocks(old_part,
                                           new_part,
                                           old_num_blocks * kBlockSize,
                                           new_num_blocks * kBlockSize,
                                           kBlockSize,
                                           &old_block_ids,
                                           &new_block_ids));

  // A mapping from the block_id to the list of block numbers with that block id
  // in the old partition. This is used to lookup where in the old partition
  // is a block from the new partition.
  map<BlockMapping::BlockId, vector<uint64_t>> old_blocks_map;

  for (uint64_t block = old_num_blocks; block-- > 0;) {
    if (old_block_ids[block] != 0 && !old_visited_blocks->ContainsBlock(block))
      old_blocks_map[old_block_ids[block]].push_back(block);

    // Mark all zeroed blocks in the old image as "used" since it doesn't make
    // any sense to spend I/O to read zeros from the source partition and more
    // importantly, these could sometimes be blocks discarded in the SSD which
    // would read non-zero values.
    if (old_block_ids[block] == 0)
      old_zero_blocks->AddBlock(block);
  }
  old_visited_blocks->AddRanges(*old_zero_blocks);

  // The collection of blocks in the new partition with just zeros. This is a
  // common case for free-space that's also problematic for bsdiff, so we want
  // to optimize it using REPLACE_BZ operations. The blob for a REPLACE_BZ of
  // just zeros is so small that it doesn't make sense to spend the I/O reading
  // zeros from the old partition.
  vector<Extent> new_zeros;

  vector<Extent> old_identical_blocks;
  vector<Extent> new_identical_blocks;

  for (uint64_t block = 0; block < new_num_blocks; block++) {
    // Only produce operations for blocks that were not yet visited.
    if (new_visited_blocks->ContainsBlock(block))
      continue;
    if (new_block_ids[block] == 0) {
      AppendBlockToExtents(&new_zeros, block);
      continue;
    }

    auto old_blocks_map_it = old_blocks_map.find(new_block_ids[block]);
    // Check if the block exists in the old partition at all.
    if (old_blocks_map_it == old_blocks_map.end() ||
        old_blocks_map_it->second.empty())
      continue;

    AppendBlockToExtents(&old_identical_blocks,
                         old_blocks_map_it->second.back());
    AppendBlockToExtents(&new_identical_blocks, block);
  }

  if (chunk_blocks == -1)
    chunk_blocks = new_num_blocks;

  // Produce operations for the zero blocks split per output extent.
  size_t num_ops = aops->size();
  new_visited_blocks->AddExtents(new_zeros);
  for (const Extent& extent : new_zeros) {
    if (version.OperationAllowed(InstallOperation::ZERO)) {
      for (uint64_t offset = 0; offset < extent.num_blocks();
           offset += chunk_blocks) {
        uint64_t num_blocks =
            std::min(static_cast<uint64_t>(extent.num_blocks()) - offset,
                     static_cast<uint64_t>(chunk_blocks));
        InstallOperation operation;
        operation.set_type(InstallOperation::ZERO);
        *(operation.add_dst_extents()) =
            ExtentForRange(extent.start_block() + offset, num_blocks);
        aops->push_back({.name = "<zeros>", .op = operation});
      }
    } else {
      TEST_AND_RETURN_FALSE(DeltaReadFile(aops,
                                          "",
                                          new_part,
                                          {},        // old_extents
                                          {extent},  // new_extents
                                          {},        // old_deflates
                                          {},        // new_deflates
                                          "<zeros>",
                                          chunk_blocks,
                                          version,
                                          blob_file));
    }
  }
  LOG(INFO) << "Produced " << (aops->size() - num_ops) << " operations for "
            << utils::BlocksInExtents(new_zeros) << " zeroed blocks";

  // Produce MOVE/SOURCE_COPY operations for the moved blocks.
  num_ops = aops->size();
  uint64_t used_blocks = 0;
  old_visited_blocks->AddExtents(old_identical_blocks);
  new_visited_blocks->AddExtents(new_identical_blocks);
  for (const Extent& extent : new_identical_blocks) {
    // We split the operation at the extent boundary or when bigger than
    // chunk_blocks.
    for (uint64_t op_block_offset = 0; op_block_offset < extent.num_blocks();
         op_block_offset += chunk_blocks) {
      aops->emplace_back();
      AnnotatedOperation* aop = &aops->back();
      aop->name = "<identical-blocks>";
      aop->op.set_type(InstallOperation::SOURCE_COPY);

      uint64_t chunk_num_blocks =
          std::min(static_cast<uint64_t>(extent.num_blocks()) - op_block_offset,
                   static_cast<uint64_t>(chunk_blocks));

      // The current operation represents the move/copy operation for the
      // sublist starting at |used_blocks| of length |chunk_num_blocks| where
      // the src and dst are from |old_identical_blocks| and
      // |new_identical_blocks| respectively.
      StoreExtents(
          ExtentsSublist(old_identical_blocks, used_blocks, chunk_num_blocks),
          aop->op.mutable_src_extents());

      Extent* op_dst_extent = aop->op.add_dst_extents();
      op_dst_extent->set_start_block(extent.start_block() + op_block_offset);
      op_dst_extent->set_num_blocks(chunk_num_blocks);
      CHECK(
          vector<Extent>{*op_dst_extent} ==  // NOLINT(whitespace/braces)
          ExtentsSublist(new_identical_blocks, used_blocks, chunk_num_blocks));

      used_blocks += chunk_num_blocks;
    }
  }
  LOG(INFO) << "Produced " << (aops->size() - num_ops) << " operations for "
            << used_blocks << " identical blocks moved";

  return true;
}

bool DeltaReadFile(vector<AnnotatedOperation>* aops,
                   const string& old_part,
                   const string& new_part,
                   const vector<Extent>& old_extents,
                   const vector<Extent>& new_extents,
                   const vector<puffin::BitExtent>& old_deflates,
                   const vector<puffin::BitExtent>& new_deflates,
                   const string& name,
                   ssize_t chunk_blocks,
                   const PayloadVersion& version,
                   BlobFileWriter* blob_file) {
  brillo::Blob data;
  InstallOperation operation;

  uint64_t total_blocks = utils::BlocksInExtents(new_extents);
  if (chunk_blocks == 0) {
    LOG(ERROR) << "Invalid number of chunk_blocks. Cannot be 0.";
    return false;
  }

  if (chunk_blocks == -1)
    chunk_blocks = total_blocks;

  for (uint64_t block_offset = 0; block_offset < total_blocks;
       block_offset += chunk_blocks) {
    // Split the old/new file in the same chunks. Note that this could drop
    // some information from the old file used for the new chunk. If the old
    // file is smaller (or even empty when there's no old file) the chunk will
    // also be empty.
    vector<Extent> old_extents_chunk =
        ExtentsSublist(old_extents, block_offset, chunk_blocks);
    vector<Extent> new_extents_chunk =
        ExtentsSublist(new_extents, block_offset, chunk_blocks);
    NormalizeExtents(&old_extents_chunk);
    NormalizeExtents(&new_extents_chunk);

    TEST_AND_RETURN_FALSE(ReadExtentsToDiff(old_part,
                                            new_part,
                                            old_extents_chunk,
                                            new_extents_chunk,
                                            old_deflates,
                                            new_deflates,
                                            version,
                                            &data,
                                            &operation));

    // Check if the operation writes nothing.
    if (operation.dst_extents_size() == 0) {
      LOG(ERROR) << "Empty non-MOVE operation";
      return false;
    }

    // Now, insert into the list of operations.
    AnnotatedOperation aop;
    aop.name = name;
    if (static_cast<uint64_t>(chunk_blocks) < total_blocks) {
      aop.name = base::StringPrintf(
          "%s:%" PRIu64, name.c_str(), block_offset / chunk_blocks);
    }
    aop.op = operation;

    // Write the data
    TEST_AND_RETURN_FALSE(aop.SetOperationBlob(data, blob_file));
    aops->emplace_back(aop);
  }
  return true;
}

bool GenerateBestFullOperation(const brillo::Blob& new_data,
                               const PayloadVersion& version,
                               brillo::Blob* out_blob,
                               InstallOperation::Type* out_type) {
  if (new_data.empty())
    return false;

  if (version.OperationAllowed(InstallOperation::ZERO) &&
      std::all_of(
          new_data.begin(), new_data.end(), [](uint8_t x) { return x == 0; })) {
    // The read buffer is all zeros, so produce a ZERO operation. No need to
    // check other types of operations in this case.
    *out_blob = brillo::Blob();
    *out_type = InstallOperation::ZERO;
    return true;
  }

  bool out_blob_set = false;

  // Try compressing |new_data| with xz first.
  if (version.OperationAllowed(InstallOperation::REPLACE_XZ)) {
    brillo::Blob new_data_xz;
    if (XzCompress(new_data, &new_data_xz) && !new_data_xz.empty()) {
      *out_type = InstallOperation::REPLACE_XZ;
      *out_blob = std::move(new_data_xz);
      out_blob_set = true;
    }
  }

  // Try compressing it with bzip2.
  if (version.OperationAllowed(InstallOperation::REPLACE_BZ)) {
    brillo::Blob new_data_bz;
    // TODO(deymo): Implement some heuristic to determine if it is worth trying
    // to compress the blob with bzip2 if we already have a good REPLACE_XZ.
    if (BzipCompress(new_data, &new_data_bz) && !new_data_bz.empty() &&
        (!out_blob_set || out_blob->size() > new_data_bz.size())) {
      // A REPLACE_BZ is better or nothing else was set.
      *out_type = InstallOperation::REPLACE_BZ;
      *out_blob = std::move(new_data_bz);
      out_blob_set = true;
    }
  }

  // If nothing else worked or it was badly compressed we try a REPLACE.
  if (!out_blob_set || out_blob->size() >= new_data.size()) {
    *out_type = InstallOperation::REPLACE;
    // This needs to make a copy of the data in the case bzip or xz didn't
    // compress well, which is not the common case so the performance hit is
    // low.
    *out_blob = new_data;
  }
  return true;
}

bool ReadExtentsToDiff(const string& old_part,
                       const string& new_part,
                       const vector<Extent>& old_extents,
                       const vector<Extent>& new_extents,
                       const vector<puffin::BitExtent>& old_deflates,
                       const vector<puffin::BitExtent>& new_deflates,
                       const PayloadVersion& version,
                       brillo::Blob* out_data,
                       InstallOperation* out_op) {
  InstallOperation operation;

  // We read blocks from old_extents and write blocks to new_extents.
  uint64_t blocks_to_read = utils::BlocksInExtents(old_extents);
  uint64_t blocks_to_write = utils::BlocksInExtents(new_extents);

  // Disable bsdiff, and puffdiff when the data is too big.
  bool bsdiff_allowed =
      version.OperationAllowed(InstallOperation::SOURCE_BSDIFF);
  if (bsdiff_allowed &&
      blocks_to_read * kBlockSize > kMaxBsdiffDestinationSize) {
    LOG(INFO) << "bsdiff ignored, data too big: " << blocks_to_read * kBlockSize
              << " bytes";
    bsdiff_allowed = false;
  }

  bool puffdiff_allowed = version.OperationAllowed(InstallOperation::PUFFDIFF);
  if (puffdiff_allowed &&
      blocks_to_read * kBlockSize > kMaxPuffdiffDestinationSize) {
    LOG(INFO) << "puffdiff ignored, data too big: "
              << blocks_to_read * kBlockSize << " bytes";
    puffdiff_allowed = false;
  }

  // Make copies of the extents so we can modify them.
  vector<Extent> src_extents = old_extents;
  vector<Extent> dst_extents = new_extents;

  // Read in bytes from new data.
  brillo::Blob new_data;
  TEST_AND_RETURN_FALSE(utils::ReadExtents(new_part,
                                           new_extents,
                                           &new_data,
                                           kBlockSize * blocks_to_write,
                                           kBlockSize));
  TEST_AND_RETURN_FALSE(!new_data.empty());

  // Data blob that will be written to delta file.
  brillo::Blob data_blob;

  // Try generating a full operation for the given new data, regardless of the
  // old_data.
  InstallOperation::Type op_type;
  TEST_AND_RETURN_FALSE(
      GenerateBestFullOperation(new_data, version, &data_blob, &op_type));
  operation.set_type(op_type);

  brillo::Blob old_data;
  if (blocks_to_read > 0) {
    // Read old data.
    TEST_AND_RETURN_FALSE(utils::ReadExtents(old_part,
                                             src_extents,
                                             &old_data,
                                             kBlockSize * blocks_to_read,
                                             kBlockSize));
    if (old_data == new_data) {
      // No change in data.
      operation.set_type(InstallOperation::SOURCE_COPY);
      data_blob = brillo::Blob();
    } else if (IsDiffOperationBetter(
                   operation, data_blob.size(), 0, src_extents.size())) {
      // No point in trying diff if zero blob size diff operation is
      // still worse than replace.
      if (bsdiff_allowed) {
        base::FilePath patch;
        TEST_AND_RETURN_FALSE(base::CreateTemporaryFile(&patch));
        ScopedPathUnlinker unlinker(patch.value());

        std::unique_ptr<bsdiff::PatchWriterInterface> bsdiff_patch_writer;
        InstallOperation::Type operation_type = InstallOperation::SOURCE_BSDIFF;
        if (version.OperationAllowed(InstallOperation::BROTLI_BSDIFF)) {
          bsdiff_patch_writer =
              bsdiff::CreateBSDF2PatchWriter(patch.value(),
                                             bsdiff::CompressorType::kBrotli,
                                             kBrotliCompressionQuality);
          operation_type = InstallOperation::BROTLI_BSDIFF;
        } else {
          bsdiff_patch_writer = bsdiff::CreateBsdiffPatchWriter(patch.value());
        }

        brillo::Blob bsdiff_delta;
        TEST_AND_RETURN_FALSE(0 == bsdiff::bsdiff(old_data.data(),
                                                  old_data.size(),
                                                  new_data.data(),
                                                  new_data.size(),
                                                  bsdiff_patch_writer.get(),
                                                  nullptr));

        TEST_AND_RETURN_FALSE(utils::ReadFile(patch.value(), &bsdiff_delta));
        CHECK_GT(bsdiff_delta.size(), static_cast<brillo::Blob::size_type>(0));
        if (IsDiffOperationBetter(operation,
                                  data_blob.size(),
                                  bsdiff_delta.size(),
                                  src_extents.size())) {
          operation.set_type(operation_type);
          data_blob = std::move(bsdiff_delta);
        }
      }
      if (puffdiff_allowed) {
        // Find all deflate positions inside the given extents and then put all
        // deflates together because we have already read all the extents into
        // one buffer.
        vector<puffin::BitExtent> src_deflates;
        TEST_AND_RETURN_FALSE(deflate_utils::FindAndCompactDeflates(
            src_extents, old_deflates, &src_deflates));

        vector<puffin::BitExtent> dst_deflates;
        TEST_AND_RETURN_FALSE(deflate_utils::FindAndCompactDeflates(
            dst_extents, new_deflates, &dst_deflates));

        puffin::RemoveEqualBitExtents(
            old_data, new_data, &src_deflates, &dst_deflates);

        // See crbug.com/915559.
        if (version.minor <= kPuffdiffMinorPayloadVersion) {
          TEST_AND_RETURN_FALSE(puffin::RemoveDeflatesWithBadDistanceCaches(
              old_data, &src_deflates));

          TEST_AND_RETURN_FALSE(puffin::RemoveDeflatesWithBadDistanceCaches(
              new_data, &dst_deflates));
        }

        // Only Puffdiff if both files have at least one deflate left.
        if (!src_deflates.empty() && !dst_deflates.empty()) {
          brillo::Blob puffdiff_delta;
          string temp_file_path;
          TEST_AND_RETURN_FALSE(utils::MakeTempFile(
              "puffdiff-delta.XXXXXX", &temp_file_path, nullptr));
          ScopedPathUnlinker temp_file_unlinker(temp_file_path);

          // Perform PuffDiff operation.
          TEST_AND_RETURN_FALSE(puffin::PuffDiff(old_data,
                                                 new_data,
                                                 src_deflates,
                                                 dst_deflates,
                                                 temp_file_path,
                                                 &puffdiff_delta));
          TEST_AND_RETURN_FALSE(puffdiff_delta.size() > 0);
          if (IsDiffOperationBetter(operation,
                                    data_blob.size(),
                                    puffdiff_delta.size(),
                                    src_extents.size())) {
            operation.set_type(InstallOperation::PUFFDIFF);
            data_blob = std::move(puffdiff_delta);
          }
        }
      }
    }
  }

  // WARNING: We always set legacy |src_length| and |dst_length| fields for
  // BSDIFF. For SOURCE_BSDIFF we only set them for minor version 3 and
  // lower. This is needed because we used to use these two parameters in the
  // SOURCE_BSDIFF for minor version 3 and lower, but we do not need them
  // anymore in higher minor versions. This means if we stop adding these
  // parameters for those minor versions, the delta payloads will be invalid.
  if (operation.type() == InstallOperation::SOURCE_BSDIFF &&
      version.minor <= kOpSrcHashMinorPayloadVersion) {
    operation.set_src_length(old_data.size());
    operation.set_dst_length(new_data.size());
  }

  // Embed extents in the operation. Replace (all variants), zero and discard
  // operations should not have source extents.
  if (!IsNoSourceOperation(operation.type())) {
    StoreExtents(src_extents, operation.mutable_src_extents());
  }
  // All operations have dst_extents.
  StoreExtents(dst_extents, operation.mutable_dst_extents());

  *out_data = std::move(data_blob);
  *out_op = operation;
  return true;
}

bool IsAReplaceOperation(InstallOperation::Type op_type) {
  return (op_type == InstallOperation::REPLACE ||
          op_type == InstallOperation::REPLACE_BZ ||
          op_type == InstallOperation::REPLACE_XZ);
}

bool IsNoSourceOperation(InstallOperation::Type op_type) {
  return (IsAReplaceOperation(op_type) || op_type == InstallOperation::ZERO ||
          op_type == InstallOperation::DISCARD);
}

bool InitializePartitionInfo(const PartitionConfig& part, PartitionInfo* info) {
  info->set_size(part.size);
  HashCalculator hasher;
  TEST_AND_RETURN_FALSE(hasher.UpdateFile(part.path, part.size) ==
                        static_cast<off_t>(part.size));
  TEST_AND_RETURN_FALSE(hasher.Finalize());
  const brillo::Blob& hash = hasher.raw_hash();
  info->set_hash(hash.data(), hash.size());
  LOG(INFO) << part.path << ": size=" << part.size
            << " hash=" << brillo::data_encoding::Base64Encode(hash);
  return true;
}

bool CompareAopsByDestination(AnnotatedOperation first_aop,
                              AnnotatedOperation second_aop) {
  // We want empty operations to be at the end of the payload.
  if (!first_aop.op.dst_extents().size() || !second_aop.op.dst_extents().size())
    return ((!first_aop.op.dst_extents().size()) <
            (!second_aop.op.dst_extents().size()));
  uint32_t first_dst_start = first_aop.op.dst_extents(0).start_block();
  uint32_t second_dst_start = second_aop.op.dst_extents(0).start_block();
  return first_dst_start < second_dst_start;
}

bool IsExtFilesystem(const string& device) {
  brillo::Blob header;
  // See include/linux/ext2_fs.h for more details on the structure. We obtain
  // ext2 constants from ext2fs/ext2fs.h header but we don't link with the
  // library.
  if (!utils::ReadFileChunk(
          device, 0, SUPERBLOCK_OFFSET + SUPERBLOCK_SIZE, &header) ||
      header.size() < SUPERBLOCK_OFFSET + SUPERBLOCK_SIZE)
    return false;

  const uint8_t* superblock = header.data() + SUPERBLOCK_OFFSET;

  // ext3_fs.h: ext3_super_block.s_blocks_count
  uint32_t block_count =
      *reinterpret_cast<const uint32_t*>(superblock + 1 * sizeof(int32_t));

  // ext3_fs.h: ext3_super_block.s_log_block_size
  uint32_t log_block_size =
      *reinterpret_cast<const uint32_t*>(superblock + 6 * sizeof(int32_t));

  // ext3_fs.h: ext3_super_block.s_magic
  uint16_t magic =
      *reinterpret_cast<const uint16_t*>(superblock + 14 * sizeof(int32_t));

  block_count = le32toh(block_count);
  log_block_size = le32toh(log_block_size) + EXT2_MIN_BLOCK_LOG_SIZE;
  magic = le16toh(magic);

  if (magic != EXT2_SUPER_MAGIC)
    return false;

  // Validation check the parameters.
  TEST_AND_RETURN_FALSE(log_block_size >= EXT2_MIN_BLOCK_LOG_SIZE &&
                        log_block_size <= EXT2_MAX_BLOCK_LOG_SIZE);
  TEST_AND_RETURN_FALSE(block_count > 0);
  return true;
}

// Return the number of CPUs on the machine, and 4 threads in minimum.
size_t GetMaxThreads() {
  return std::max(sysconf(_SC_NPROCESSORS_ONLN), 4L);
}

}  // namespace diff_utils

}  // namespace chromeos_update_engine