read_exact.h

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//
// Copyright (C) 2026 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 <stdint.h>
 
#include <optional>
 
#include "cuttlefish/io/io.h"
#include "cuttlefish/result/expect.h"
#include "cuttlefish/result/result_type.h"
 
namespace cuttlefish {
 
Result<void> ReadExact(Reader&, char* buf, size_t size);
 
template <typename T>
Result<T> ReadExactBinary(Reader& reader) {
  T data;
  char* const data_char = reinterpret_cast<char*>(&data);
  CF_EXPECT(ReadExact(reader, data_char, sizeof(data)));
  return data;
}
 
Result<void> PReadExact(const ReaderSeeker&, char* buf, size_t size,
                        uint64_t offset);
 
// Similar to ReadExact, but returns false instead of an error if zero bytes are
// read because of EOF. A partial read is still an error.
Result<bool> ReadExactOrEof(Reader&, char* buf, size_t size);
 
template <typename T>
Result<T> PReadExactBinary(const ReaderSeeker& reader, uint64_t offset) {
  T data;
  char* const data_char = reinterpret_cast<char*>(&data);
  CF_EXPECT(PReadExact(reader, data_char, sizeof(data), offset));
  return data;
}
 
template <typename T>
Result<std::optional<T>> ReadExactBinaryOrEof(Reader& reader) {
  T data;
  char* data_char = reinterpret_cast<char*>(&data);
  if (!CF_EXPECT(ReadExactOrEof(reader, data_char, sizeof(data)))) {
    return std::nullopt;
  }
  return data;
}
 
}  // namespace cuttlefish