buffer_sequence_view.h

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/* Copyright (c) 2023, 2024, Oracle and/or its affiliates.
 
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   it under the terms of the GNU General Public License, version 2.0,
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/// @file
///
/// Container class that provides a sequence of buffers to the caller.
/// This is intended for capturing the output from compressors.
 
#ifndef MYSQL_CONTAINERS_BUFFERS_BUFFER_SEQUENCE_VIEW_H
#define MYSQL_CONTAINERS_BUFFERS_BUFFER_SEQUENCE_VIEW_H
 
#include <algorithm>                     // std::min
#include <cassert>                       // assert
#include <cstring>                       // std::memcpy
#include <limits>                        // std::numeric_limits
#include <memory>                        // std::allocator
#include <type_traits>                   // std::conditional
#include <vector>                        // std::vector
#include "mysql/allocators/allocator.h"  // mysql::allocators::Allocator
 
#include "mysql/containers/buffers/buffer_view.h"      // Buffer_view
#include "mysql/containers/buffers/grow_calculator.h"  // Grow_calculator
#include "mysql/containers/buffers/grow_status.h"      // Grow_status
#include "mysql/utils/nodiscard.h"                     // NODISCARD
 
#include "mysql/binlog/event/wrapper_functions.h"  // BAPI_TRACE
 
/// @addtogroup GroupLibsMysqlContainers
/// @{
 
namespace mysql::containers::buffers {
 
/// Sequence of memory buffers.
///
/// This is a minimal class with just a sequence of buffers.  It does
/// not have a read/write position (@see Rw_buffer_sequence).  It does
/// not have methods to grow the buffer sequence (@see
/// Managed_buffer_sequence).
///
/// @tparam Char_tp The type of elements stored in the buffer:
/// typically unsigned char.
///
/// @tparam Container_tp The type of container to hold the buffers.
/// This defaults to std::vector, but std::list is also possible.
///
/// @tparam const_tp If true, use const iterators instead of non-const
/// iterators to represent the beginning and end of the container.
template <class Char_tp = unsigned char,
          template <class Element_tp, class Allocator_tp> class Container_tp =
              std::vector,
          bool const_tp = false>
class Buffer_sequence_view {
 public:
  using Char_t = Char_tp;
  using Size_t = std::size_t;
  using Buffer_view_t = Buffer_view<Char_t>;
  using Buffer_allocator_t = mysql::allocators::Allocator<Buffer_view_t>;
  using Container_t = Container_tp<Buffer_view_t, Buffer_allocator_t>;
  using Const_iterator_t = typename Container_t::const_iterator;
  using Iterator_t =
      typename std::conditional<const_tp, Const_iterator_t,
                                typename Container_t::iterator>::type;
 
 private:
  /// Indicates that @c m_size has not yet been computed.
  static constexpr Size_t uninitialized_size =
      std::numeric_limits<Size_t>::max();
 
 public:
  /// Construct a Buffer_sequence_view with buffers in the range given by
  /// the iterators.
  ///
  /// This copies only the iterators; the underlying container and the
  /// buffers contained in the container are not copied.
  ///
  /// @param begin_arg Iterator to the first buffer.
  ///
  /// @param end_arg Iterator to one-past-the-last buffer.
  ///
  /// @param size_arg The total size of all buffers from begin_arg to
  /// end_arg.  This is an optimization only: if the parameter is
  /// omitted, it will be computed the next time it is needed.
  Buffer_sequence_view(Iterator_t begin_arg, Iterator_t end_arg,
                       Size_t size_arg = uninitialized_size)
      : m_begin(begin_arg), m_end(end_arg), m_size(size_arg) {}
 
  // Disallow copy, implement move.
  Buffer_sequence_view(Buffer_sequence_view &) = delete;
  Buffer_sequence_view(Buffer_sequence_view &&other) noexcept = default;
  Buffer_sequence_view &operator=(Buffer_sequence_view &) = delete;
  Buffer_sequence_view &operator=(Buffer_sequence_view &&) noexcept = default;
 
  virtual ~Buffer_sequence_view() = default;
 
  /// Iterator to the first buffer.
  Iterator_t begin() { return m_begin; }
 
  /// Iterator to the last buffer.
  Iterator_t end() { return m_end; }
 
  /// Iterator to the first buffer.
  Const_iterator_t begin() const { return m_begin; }
 
  /// Iterator to the last buffer.
  Const_iterator_t end() const { return m_end; }
 
  /// Const iterator pointing to the first buffer.
  Const_iterator_t cbegin() const { return m_begin; }
 
  /// Const iterator pointing to the last buffer.
  Const_iterator_t cend() const { return m_end; }
 
  /// Copy all data to the given, contiguous output buffer.
  ///
  /// The caller is responsible for providing a buffer of at
  /// least @c size() bytes.
  ///
  /// @param destination The target buffer.
  template <class Destination_char_t>
  void copy(Destination_char_t *destination) const {
    BAPI_TRACE;
    Size_t position = 0;
    for (const auto &buffer : *this) {
      std::memcpy(destination + position, buffer.data(), buffer.size());
      position += buffer.size();
    }
  }
 
  /// Return a copy of all the data in this object, as a `std::string`
  /// object.
  template <class Str_char_t = char,
            class Str_traits_t = std::char_traits<Str_char_t>,
            class Str_allocator_t = std::allocator<Str_char_t>>
  std::basic_string<Str_char_t, Str_traits_t, Str_allocator_t> str(
      const Str_allocator_t &allocator = Str_allocator_t()) {
    std::basic_string<Str_char_t, Str_traits_t, Str_allocator_t> ret(
        this->size(), '\0', allocator);
    copy(ret.data());
    return ret;
  }
 
  /// Return the total size of all buffers.
  Size_t size() const {
    if (m_size == uninitialized_size) {
      Size_t size = 0;
      for (const auto &buffer : *this) size += buffer.size();
      m_size = size;
    }
    return m_size;
  }
 
  /// In debug mode, return a string that describes the internal
  /// structure of this object, to use for debugging.
  ///
  /// @param show_contents If true, includes the buffer contents.
  /// Otherwise, just pointers and sizes.
  ///
  /// @param indent If 0, put all info on one line. Otherwise, put
  /// each field on its own line and indent the given number of
  /// two-space levels.
  ///
  /// @return String that describes the internal structure of this
  /// Buffer_sequence_view.
  std::string debug_string([[maybe_unused]] bool show_contents = false,
                           [[maybe_unused]] int indent = 0) const {
#ifdef NDEBUG
    return "";
#else
    std::ostringstream ss;
    // whitespace following the comma: newline + indentation, or just space
    std::string ws;
    if (indent != 0)
      ws = std::string("\n") +
           std::string(static_cast<std::string::size_type>(indent * 2), ' ');
    else
      ws = " ";
    // separator = comma + whitespace
    std::string sep = "," + ws;
    // whitespace / separator with one level deeper indentation
    std::string ws2 = (indent != 0) ? (ws + "  ") : ws;
    std::string sep2 = (indent != 0) ? (sep + "  ") : sep;
    // clang-format off
    ss << "Buffer_sequence_view(ptr=" << (const void *)this
       << sep << "size=" << size()
       << sep << "buffers.ptr=" << (const void *)&*this->begin()
       << sep << "buffers=[";
    // clang-format on
    bool first = true;
    for (auto &buffer : *this) {
      if (first) {
        if (indent != 0) ss << ws2;
        first = false;
      } else {
        ss << sep2;
      }
      ss << buffer.debug_string(show_contents);
    }
    ss << "])";
    return ss.str();
#endif
  }
 
 private:
  /// Iterator to beginning of buffer.
  Iterator_t m_begin;
 
  /// Iterator to end of buffer.
  Iterator_t m_end;
 
  /// Total size of all buffers, cached.
  mutable Size_t m_size;
};
 
}  // namespace mysql::containers::buffers
 
/// @}
 
#endif  // MYSQL_CONTAINERS_BUFFERS_BUFFER_SEQUENCE_VIEW_H