diff --git a/twrpinstall/package.cpp b/twrpinstall/package.cpp
new file mode 100755
index 0000000..ba1d5df
--- /dev/null
+++ b/twrpinstall/package.cpp
@@ -0,0 +1,257 @@
+/*
+ * Copyright (C) 2019 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 "twinstall/package.h"
+
+#include <string.h>
+#include <unistd.h>
+
+#include <android-base/file.h>
+#include <android-base/logging.h>
+#include <android-base/stringprintf.h>
+#include <android-base/unique_fd.h>
+
+#include "otautil/error_code.h"
+#include "otautil/sysutil.h"
+
+// This class wraps the package in memory, i.e. a memory mapped package, or a package loaded
+// to a string/vector.
+class MemoryPackage : public Package {
+ public:
+  // Constructs the class from a file. We will memory maps the file later.
+  MemoryPackage(const std::string& path, std::unique_ptr<MemMapping> map);
+
+  // Constructs the class from the package bytes in |content|.
+  MemoryPackage(std::vector<uint8_t> content);
+
+  ~MemoryPackage() override;
+
+  // Memory maps the package file if necessary. Initializes the start address and size of the
+  // package.
+  uint64_t GetPackageSize() const override {
+    return package_size_;
+  }
+
+  bool ReadFullyAtOffset(uint8_t* buffer, uint64_t byte_count, uint64_t offset) override;
+
+  ZipArchiveHandle GetZipArchiveHandle() override;
+
+  bool UpdateHashAtOffset(const std::vector<HasherUpdateCallback>& hashers, uint64_t start,
+                          uint64_t length) override;
+
+ private:
+  const uint8_t* addr_;    // Start address of the package in memory.
+  uint64_t package_size_;  // Package size in bytes.
+
+  // The memory mapped package.
+  std::unique_ptr<MemMapping> map_;
+  // A copy of the package content, valid only if we create the class with the exact bytes of
+  // the package.
+  std::vector<uint8_t> package_content_;
+  // The physical path to the package, empty if we create the class with the package content.
+  std::string path_;
+
+  // The ZipArchiveHandle of the package.
+  ZipArchiveHandle zip_handle_;
+};
+
+void Package::SetProgress(float progress) {
+  if (set_progress_) {
+    set_progress_(progress);
+  }
+}
+
+class FilePackage : public Package {
+ public:
+  FilePackage(android::base::unique_fd&& fd, uint64_t file_size, const std::string& path,
+              const std::function<void(float)>& set_progress);
+
+  ~FilePackage() override;
+
+  uint64_t GetPackageSize() const override {
+    return package_size_;
+  }
+
+  bool ReadFullyAtOffset(uint8_t* buffer, uint64_t byte_count, uint64_t offset) override;
+
+  ZipArchiveHandle GetZipArchiveHandle() override;
+
+  bool UpdateHashAtOffset(const std::vector<HasherUpdateCallback>& hashers, uint64_t start,
+                          uint64_t length) override;
+
+ private:
+  android::base::unique_fd fd_;  // The underlying fd to the open package.
+  uint64_t package_size_;
+  std::string path_;  // The physical path to the package.
+
+  ZipArchiveHandle zip_handle_;
+};
+
+std::unique_ptr<Package> Package::CreateMemoryPackage(
+    const std::string& path) {
+  std::unique_ptr<MemMapping> mmap = std::make_unique<MemMapping>();
+  if (!mmap->MapFile(path)) {
+    LOG(ERROR) << "failed to map file";
+    return nullptr;
+  }
+
+  return std::make_unique<MemoryPackage>(path, std::move(mmap));
+}
+
+std::unique_ptr<Package> Package::CreateFilePackage(
+    const std::string& path, const std::function<void(float)>& set_progress) {
+  android::base::unique_fd fd(open(path.c_str(), O_RDONLY));
+  if (fd == -1) {
+    PLOG(ERROR) << "Failed to open " << path;
+    return nullptr;
+  }
+
+  off64_t file_size = lseek64(fd.get(), 0, SEEK_END);
+  if (file_size == -1) {
+    PLOG(ERROR) << "Failed to get the package size";
+    return nullptr;
+  }
+
+  return std::make_unique<FilePackage>(std::move(fd), file_size, path, set_progress);
+}
+
+std::unique_ptr<Package> Package::CreateMemoryPackage(
+    std::vector<uint8_t> content) {
+  return std::make_unique<MemoryPackage>(std::move(content));
+}
+
+MemoryPackage::MemoryPackage(const std::string& path, std::unique_ptr<MemMapping> map)
+    : map_(std::move(map)), path_(path), zip_handle_(nullptr) {
+  addr_ = map_->addr;
+  package_size_ = map_->length;
+}
+
+MemoryPackage::MemoryPackage(std::vector<uint8_t> content)
+    : package_content_(std::move(content)), zip_handle_(nullptr) {
+  CHECK(!package_content_.empty());
+  addr_ = package_content_.data();
+  package_size_ = package_content_.size();
+}
+
+MemoryPackage::~MemoryPackage() {
+  if (zip_handle_) {
+    CloseArchive(zip_handle_);
+  }
+}
+
+bool MemoryPackage::ReadFullyAtOffset(uint8_t* buffer, uint64_t byte_count, uint64_t offset) {
+  if (byte_count > package_size_ || offset > package_size_ - byte_count) {
+    LOG(ERROR) << "Out of bound read, offset: " << offset << ", size: " << byte_count
+               << ", total package_size: " << package_size_;
+    return false;
+  }
+  memcpy(buffer, addr_ + offset, byte_count);
+  return true;
+}
+
+bool MemoryPackage::UpdateHashAtOffset(const std::vector<HasherUpdateCallback>& hashers,
+                                       uint64_t start, uint64_t length) {
+  if (length > package_size_ || start > package_size_ - length) {
+    LOG(ERROR) << "Out of bound read, offset: " << start << ", size: " << length
+               << ", total package_size: " << package_size_;
+    return false;
+  }
+
+  for (const auto& hasher : hashers) {
+    hasher(addr_ + start, length);
+  }
+  return true;
+}
+
+ZipArchiveHandle MemoryPackage::GetZipArchiveHandle() {
+  if (zip_handle_) {
+    return zip_handle_;
+  }
+
+  if (auto err = OpenArchiveFromMemory(const_cast<uint8_t*>(addr_), package_size_, path_.c_str(),
+                                       &zip_handle_);
+      err != 0) {
+    LOG(ERROR) << "Can't open package" << path_ << " : " << ErrorCodeString(err);
+    return nullptr;
+  }
+
+  return zip_handle_;
+}
+
+FilePackage::FilePackage(android::base::unique_fd&& fd, uint64_t file_size, const std::string& path,
+                         const std::function<void(float)>& set_progress)
+    : fd_(std::move(fd)), package_size_(file_size), path_(path), zip_handle_(nullptr) {
+  set_progress_ = set_progress;
+}
+
+FilePackage::~FilePackage() {
+  if (zip_handle_) {
+    CloseArchive(zip_handle_);
+  }
+}
+
+bool FilePackage::ReadFullyAtOffset(uint8_t* buffer, uint64_t byte_count, uint64_t offset) {
+  if (byte_count > package_size_ || offset > package_size_ - byte_count) {
+    LOG(ERROR) << "Out of bound read, offset: " << offset << ", size: " << byte_count
+               << ", total package_size: " << package_size_;
+    return false;
+  }
+
+  if (!android::base::ReadFullyAtOffset(fd_.get(), buffer, byte_count, offset)) {
+    PLOG(ERROR) << "Failed to read " << byte_count << " bytes data at offset " << offset;
+    return false;
+  }
+
+  return true;
+}
+
+bool FilePackage::UpdateHashAtOffset(const std::vector<HasherUpdateCallback>& hashers,
+                                     uint64_t start, uint64_t length) {
+  if (length > package_size_ || start > package_size_ - length) {
+    LOG(ERROR) << "Out of bound read, offset: " << start << ", size: " << length
+               << ", total package_size: " << package_size_;
+    return false;
+  }
+
+  uint64_t so_far = 0;
+  while (so_far < length) {
+    uint64_t read_size = std::min<uint64_t>(length - so_far, 16 * MiB);
+    std::vector<uint8_t> buffer(read_size);
+    if (!ReadFullyAtOffset(buffer.data(), read_size, start + so_far)) {
+      return false;
+    }
+
+    for (const auto& hasher : hashers) {
+      hasher(buffer.data(), read_size);
+    }
+    so_far += read_size;
+  }
+
+  return true;
+}
+
+ZipArchiveHandle FilePackage::GetZipArchiveHandle() {
+  if (zip_handle_) {
+    return zip_handle_;
+  }
+
+  if (auto err = OpenArchiveFd(fd_.get(), path_.c_str(), &zip_handle_); err != 0) {
+    LOG(ERROR) << "Can't open package" << path_ << " : " << ErrorCodeString(err);
+    return nullptr;
+  }
+
+  return zip_handle_;
+}