diff --git a/lz4diff/lz4diff.cc b/lz4diff/lz4diff.cc
new file mode 100644
index 0000000..5525dd1
--- /dev/null
+++ b/lz4diff/lz4diff.cc
@@ -0,0 +1,249 @@
+//
+// 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 "lz4diff.h"
+#include "lz4diff_compress.h"
+
+#include <bsdiff/bsdiff.h>
+#include <bsdiff/constants.h>
+#include <bsdiff/patch_writer_factory.h>
+#include <bsdiff/patch_writer.h>
+#include <puffin/common.h>
+#include <puffin/puffdiff.h>
+#include <lz4.h>
+#include <lz4hc.h>
+
+#include "update_engine/common/utils.h"
+#include "update_engine/common/hash_calculator.h"
+#include "update_engine/payload_generator/deflate_utils.h"
+#include "update_engine/payload_generator/delta_diff_generator.h"
+#include "lz4diff/lz4diff.pb.h"
+#include "lz4diff_format.h"
+
+namespace chromeos_update_engine {
+
+bool StoreDstCompressedFileInfo(std::string_view recompressed_blob,
+                                std::string_view target_blob,
+                                const CompressedFile& dst_file_info,
+                                Lz4diffHeader* output) {
+  *output->mutable_dst_info()->mutable_algo() = dst_file_info.algo;
+  output->mutable_dst_info()->set_zero_padding_enabled(
+      dst_file_info.zero_padding_enabled);
+  const auto& block_info = dst_file_info.blocks;
+  auto& dst_block_info = *output->mutable_dst_info()->mutable_block_info();
+  dst_block_info.Clear();
+  size_t offset = 0;
+  for (const auto& block : block_info) {
+    auto& pb_block = *dst_block_info.Add();
+    pb_block.set_uncompressed_offset(block.uncompressed_offset);
+    pb_block.set_uncompressed_length(block.uncompressed_length);
+    pb_block.set_compressed_length(block.compressed_length);
+    CHECK_LT(offset, recompressed_blob.size());
+    auto s1 = recompressed_blob.substr(offset, block.compressed_length);
+    auto s2 = target_blob.substr(offset, block.compressed_length);
+    if (s1 != s2) {
+      ScopedTempFile patch;
+      int err =
+          bsdiff::bsdiff(reinterpret_cast<const unsigned char*>(s1.data()),
+                         s1.size(),
+                         reinterpret_cast<const unsigned char*>(s2.data()),
+                         s2.size(),
+                         patch.path().c_str(),
+                         nullptr);
+      CHECK_EQ(err, 0);
+      LOG(WARNING) << "Recompress Postfix patch size: "
+                   << utils::FileSize(patch.path());
+      std::string patch_content;
+      TEST_AND_RETURN_FALSE(utils::ReadFile(patch.path(), &patch_content));
+      pb_block.set_postfix_bspatch(std::move(patch_content));
+    }
+    // Include recompressed blob hash, so we can determine if the device
+    // produces same compressed output
+    Blob recompressed_blob_hash;
+    TEST_AND_RETURN_FALSE(HashCalculator::RawHashOfBytes(
+        s1.data(), s1.length(), &recompressed_blob_hash));
+    pb_block.set_sha256_hash(recompressed_blob_hash.data(),
+                             recompressed_blob_hash.size());
+
+    offset += block.compressed_length;
+  }
+  return true;
+}
+
+template <typename Blob>
+static bool TryBsdiff(Blob src, Blob dst, Blob* output) noexcept {
+  static constexpr auto kLz4diffDefaultBrotliQuality = 9;
+  CHECK_NE(output, nullptr);
+  ScopedTempFile patch;
+
+  Blob bsdiff_delta;
+  bsdiff::BsdiffPatchWriter patch_writer(patch.path(),
+                                         {bsdiff::CompressorType::kBrotli},
+                                         kLz4diffDefaultBrotliQuality);
+  TEST_AND_RETURN_FALSE(0 == bsdiff::bsdiff(src.data(),
+                                            src.size(),
+                                            dst.data(),
+                                            dst.size(),
+                                            &patch_writer,
+                                            nullptr));
+
+  TEST_AND_RETURN_FALSE(utils::ReadFile(patch.path(), &bsdiff_delta));
+  TEST_AND_RETURN_FALSE(!bsdiff_delta.empty());
+  *output = std::move(bsdiff_delta);
+  return true;
+}
+
+bool TryFindDeflates(puffin::Buffer data,
+                     std::vector<puffin::BitExtent>* deflates) {
+  if (puffin::LocateDeflatesInZipArchive(data, deflates)) {
+    return true;
+  }
+  deflates->clear();
+  if (puffin::LocateDeflatesInGzip(data, deflates)) {
+    return true;
+  }
+  deflates->clear();
+  return false;
+}
+
+static bool ConstructLz4diffPatch(Blob inner_patch,
+                                  const Lz4diffHeader& header,
+                                  Blob* output) {
+  Blob patch;
+  patch.resize(kLz4diffHeaderSize);
+  std::memcpy(patch.data(), kLz4diffMagic.data(), kLz4diffMagic.size());
+  *reinterpret_cast<uint32_t*>(patch.data() + kLz4diffMagic.size()) =
+      htobe32(kLz4diffVersion);
+
+  std::string serialized_pb;
+  TEST_AND_RETURN_FALSE(header.SerializeToString(&serialized_pb));
+  *reinterpret_cast<uint32_t*>(patch.data() + kLz4diffMagic.size() + 4) =
+      htobe32(serialized_pb.size());
+  patch.insert(patch.end(), serialized_pb.begin(), serialized_pb.end());
+  patch.insert(patch.end(), inner_patch.begin(), inner_patch.end());
+
+  *output = std::move(patch);
+  return true;
+}
+
+static bool TryPuffdiff(puffin::Buffer src,
+                        puffin::Buffer dst,
+                        Blob* output) noexcept {
+  CHECK_NE(output, nullptr);
+  std::vector<puffin::BitExtent> src_deflates;
+  TEST_AND_RETURN_FALSE(TryFindDeflates(src, &src_deflates));
+  std::vector<puffin::BitExtent> dst_deflates;
+  TEST_AND_RETURN_FALSE(TryFindDeflates(dst, &dst_deflates));
+  if (src_deflates.empty() || dst_deflates.empty()) {
+    return false;
+  }
+
+  Blob puffdiff_delta;
+  ScopedTempFile temp_file("puffdiff-delta.XXXXXX");
+  // Perform PuffDiff operation.
+  TEST_AND_RETURN_FALSE(puffin::PuffDiff(
+      src, dst, src_deflates, dst_deflates, temp_file.path(), &puffdiff_delta));
+  TEST_AND_RETURN_FALSE(!puffdiff_delta.empty());
+
+  *output = std::move(puffdiff_delta);
+  return true;
+}
+
+static void StoreSrcCompressedFileInfo(const CompressedFile& src_file_info,
+                                       Lz4diffHeader* header) {
+  *header->mutable_src_info()->mutable_algo() = src_file_info.algo;
+  auto& src_blocks = *header->mutable_src_info()->mutable_block_info();
+  src_blocks.Clear();
+  for (const auto& block : src_file_info.blocks) {
+    auto& block_info = *src_blocks.Add();
+    block_info.set_uncompressed_length(block.uncompressed_length);
+    block_info.set_uncompressed_offset(block.uncompressed_offset);
+    block_info.set_compressed_length(block.compressed_length);
+  }
+  return;
+}
+
+bool Lz4Diff(std::string_view src,
+             std::string_view dst,
+             const CompressedFile& src_file_info,
+             const CompressedFile& dst_file_info,
+             const bool zero_padding_enabled,
+             Blob* output,
+             InstallOperation::Type* op_type) noexcept {
+  const auto& src_block_info = src_file_info.blocks;
+  const auto& dst_block_info = dst_file_info.blocks;
+
+  auto decompressed_src =
+      TryDecompressBlob(src, src_block_info, zero_padding_enabled);
+  auto decompressed_dst =
+      TryDecompressBlob(dst, dst_block_info, zero_padding_enabled);
+  if (decompressed_src.empty() || decompressed_dst.empty()) {
+    LOG(ERROR) << "Failed to decompress input data";
+    return false;
+  }
+
+  Lz4diffHeader header;
+  // BSDIFF isn't supposed to fail, so return error if BSDIFF failed.
+  Blob patch_data;
+  TEST_AND_RETURN_FALSE(
+      TryBsdiff(decompressed_src, decompressed_dst, &patch_data));
+  header.set_inner_type(InnerPatchType::BSDIFF);
+  if (op_type) {
+    *op_type = InstallOperation::LZ4DIFF_BSDIFF;
+  }
+  // PUFFDIFF might fail, as the input data might not be deflate compressed.
+
+  Blob puffdiff_delta;
+  if (TryPuffdiff(decompressed_src, decompressed_dst, &puffdiff_delta) &&
+      puffdiff_delta.size() < patch_data.size()) {
+    patch_data = std::move(puffdiff_delta);
+    header.set_inner_type(InnerPatchType::PUFFDIFF);
+    if (op_type) {
+      *op_type = InstallOperation::LZ4DIFF_PUFFDIFF;
+    }
+  }
+  // Free up memory used by |decompressed_src| , as we don't need it anymore.
+  decompressed_src = {};
+
+  auto recompressed_blob = TryCompressBlob(ToStringView(decompressed_dst),
+                                           dst_block_info,
+                                           zero_padding_enabled,
+                                           dst_file_info.algo);
+  TEST_AND_RETURN_FALSE(recompressed_blob.size() > 0);
+
+  StoreSrcCompressedFileInfo(src_file_info, &header);
+  StoreDstCompressedFileInfo(
+      ToStringView(recompressed_blob), dst, dst_file_info, &header);
+  return ConstructLz4diffPatch(std::move(patch_data), header, output);
+}
+
+bool Lz4Diff(const Blob& src,
+             const Blob& dst,
+             const CompressedFile& src_file_info,
+             const CompressedFile& dst_file_info,
+             const bool zero_padding_enabled,
+             Blob* output,
+             InstallOperation::Type* op_type) noexcept {
+  return Lz4Diff(ToStringView(src),
+                 ToStringView(dst),
+                 src_file_info,
+                 dst_file_info,
+                 zero_padding_enabled,
+                 output,
+                 op_type);
+}
+
+}  // namespace chromeos_update_engine