lazily_loaded_file.h

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//
// Copyright (C) 2025 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.
#pragma once
 
#include <stddef.h>
 
#include <memory>
#include <string>
 
#include "cuttlefish/common/libs/utils/result.h"
 
namespace cuttlefish {
 
class LazilyLoadedFileReadCallback {
 public:
  virtual ~LazilyLoadedFileReadCallback();
 
  virtual Result<size_t> Read(char* buf, size_t count) = 0;
  virtual Result<size_t> Seek(size_t offset) = 0;
};
 
class LazilyLoadedFile {
 public:
  static Result<LazilyLoadedFile> Create(
      std::string filename, std::unique_ptr<LazilyLoadedFileReadCallback>);
 
  LazilyLoadedFile(LazilyLoadedFile&&);
  ~LazilyLoadedFile();
  LazilyLoadedFile& operator=(LazilyLoadedFile&&);
 
  Result<size_t> Read(char*, size_t);
  Result<void> Seek(size_t);
 
 private:
  struct Impl;
 
  LazilyLoadedFile(std::unique_ptr<Impl>);
 
  std::unique_ptr<Impl> impl_;
};
 
}  // namespace cuttlefish