serialized.h

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// Copyright (c) Microsoft Corporation. All rights reserved.
// Licensed under the Apache 2.0 License.
#pragma once
 
#include <cstdint>
#include <cstring>
#include <stdexcept>
#include <string>
#include <vector>
 
#define FMT_HEADER_ONLY
#include <fmt/format.h>
 
namespace serialized
{
  class InsufficientSpaceException : public std::exception
  {
  private:
    std::string msg;
 
  public:
    InsufficientSpaceException(const std::string& msg_) : msg(msg_) {}
 
    const char* what() const throw() override
    {
      return msg.c_str();
    }
  };
 
  template <class T>
  T peek(const uint8_t*& data, size_t& size)
  {
    // This should only be used for numeric types and small structs
    static constexpr auto max_size = 32u;
    static_assert(sizeof(T) <= max_size);
 
    if (size < sizeof(T))
    {
      throw InsufficientSpaceException(
        fmt::format("Insufficient space (peek<T>: {} < {})", size, sizeof(T)));
    }
 
    static constexpr auto alignment = alignof(T);
    if (reinterpret_cast<std::uintptr_t>(data) % alignment != 0)
    {
      // Data is not aligned - copy to scratch memory
      alignas(T) uint8_t scratch[max_size];
      std::memcpy(scratch, data, sizeof(T));
      return *(T*)scratch;
    }
    else
    {
      // Cast directly from source memory
      return *(T*)data;
    }
  }
 
  template <class T>
  T read(const uint8_t*& data, size_t& size)
  {
    if (size < sizeof(T))
    {
      throw InsufficientSpaceException(
        fmt::format("Insufficient space (read<T>: {} < {})", size, sizeof(T)));
    }
 
    T v;
    std::memcpy(reinterpret_cast<uint8_t*>(&v), data, sizeof(T));
    data += sizeof(T);
    size -= sizeof(T);
    return v;
  }
 
  template <>
  inline std::string read(const uint8_t*& data, size_t& size)
  {
    size_t len = read<size_t>(data, size);
    if (size < len)
    {
      throw InsufficientSpaceException(
        fmt::format("Insufficient space (read string: {} < {})", size, len));
    }
 
    std::string v(data, data + len);
    data += len;
    size -= len;
    return v;
  }
 
  inline std::vector<uint8_t> read(
    const uint8_t*& data, size_t& size, size_t block_size)
  {
    if (size < block_size)
    {
      throw InsufficientSpaceException(fmt::format(
        "Insufficient space (read block: {} < {})", size, block_size));
    }
 
    std::vector<uint8_t> v(data, data + block_size);
    data += block_size;
    size -= block_size;
    return v;
  }
 
  template <class T>
  void write(uint8_t*& data, size_t& size, const T& v)
  {
    if (size < sizeof(T))
    {
      throw InsufficientSpaceException(
        fmt::format("Insufficient space (write<T>: {} < {})", size, sizeof(T)));
    }
 
    const auto src = reinterpret_cast<const uint8_t*>(&v);
    std::memcpy(data, src, sizeof(T));
    data += sizeof(T);
    size -= sizeof(T);
  }
 
  inline void write(
    uint8_t*& data, size_t& size, const uint8_t* block, size_t block_size)
  {
    if (size < block_size)
    {
      throw InsufficientSpaceException(fmt::format(
        "Insufficient space (write block: {} < {})", size, block_size));
    }
 
    if (block_size > 0)
    {
      std::memcpy(data, block, block_size);
    }
 
    data += block_size;
    size -= block_size;
  }
 
  inline void write(uint8_t*& data, size_t& size, const std::string& v)
  {
    const auto string_size = sizeof(size_t) + v.size();
    if (size < string_size)
    {
      throw InsufficientSpaceException(fmt::format(
        "Insufficient space (write string: {} < {})", size, string_size));
    }
 
    write(data, size, v.size());
    write(data, size, (const uint8_t*)v.data(), v.size());
  }
 
  template <class T>
  T& overlay(const uint8_t*& data, size_t& size)
  {
    if (size < sizeof(T))
    {
      throw InsufficientSpaceException(fmt::format(
        "Insufficient space (overlay<T>: {} < {})", size, sizeof(T)));
    }
 
    T* v = (T*)data;
    data += sizeof(T);
    size -= sizeof(T);
    return *v;
  }
 
  inline void skip(const uint8_t*& data, size_t& size, size_t skip)
  {
    if (size < skip)
    {
      throw InsufficientSpaceException(
        fmt::format("Insufficient space (skip: {} < {})", size, skip));
    }
 
    data += skip;
    size -= skip;
  }
}