decompressor.h

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#ifndef MYSQL_BINLOG_EVENT_COMPRESSION_DECOMPRESSOR_H
#define MYSQL_BINLOG_EVENT_COMPRESSION_DECOMPRESSOR_H
 
#include "mysql/binlog/event/compression/base.h"               // type
#include "mysql/binlog/event/compression/decompress_status.h"  // Decompress_status
#include "mysql/containers/buffers/grow_constraint.h"  // Grow_constraint
#include "mysql/containers/buffers/managed_buffer.h"   // Managed_buffer
 
namespace mysql::binlog::event::compression {
 
/// Abstract base class for decompressors.
///
/// Each subclass normally corresponds to a compression
/// algorithm, and maintains the algorithm-specific state for it.
///
/// An instance of this class can be reused to decompress several
/// different *frames*.  Each frame input may be split into multiple
/// pieces. @see Compressor.
///
/// To decompress one or more frames in one piece, use this API as
/// follows:
/// 1. Call @c feed to provide all input
/// 2. Repeatedly call @c decompress, each time producing as much
///    output as you need.
///
/// To decompress one or more frames in multiple pieces, use this API
/// as follows:
/// 1. Repeatedly call @c decompress, each time producing as much
///    output as you need. Whenever it returns eof or truncated, call
///    @c feed to provide more input, and try again.
///
/// This class uses a @c buffer::Managed_buffer to store output.
class Decompressor {
 public:
  using Char_t = unsigned char;
  using Size_t = mysql::containers::buffers::Buffer_view<Char_t>::Size_t;
  using Managed_buffer_t = mysql::containers::buffers::Managed_buffer<Char_t>;
  using Grow_constraint_t = mysql::containers::buffers::Grow_constraint;
 
 private:
  using Grow_status_t = mysql::containers::buffers::Grow_status;
 
 public:
  Decompressor() = default;
  Decompressor(const Decompressor &) = delete;
  Decompressor(const Decompressor &&) = delete;
  const Decompressor &operator=(const Decompressor &) = delete;
  const Decompressor &operator=(const Decompressor &&) = delete;
  virtual ~Decompressor() = default;
 
  /// @return the compression type.
  type get_type_code() const;
 
  /// Reset the frame.
  ///
  /// This cancels the current frame and starts a new one.
  void reset();
 
  /// Submit data to decompress.
  ///
  /// @param input_data The buffer of input data that this decompressor
  /// will read.
  ///
  /// @param input_size The size of the input buffer.
  template <class Input_char_t>
  void feed(const Input_char_t *input_data, Size_t input_size) {
    feed_char_t(reinterpret_cast<const Char_t *>(input_data), input_size);
  }
 
  /// Decompress an exact, given number of bytes.
  ///
  /// @param out The output buffer.  This function first grows the
  /// write part of `out` to at least `output_size` bytes, then
  /// decompresses into the write part, and then moves the
  /// decompressed bytes from the beginning of the write part to the
  /// end of the read part.
  ///
  /// @param output_size Number of bytes to decompress.
  ///
  /// @retval success Decompression succeeded.  The requested bytes
  /// are available in @c out.
  ///
  /// @retval eof There were no more bytes to decompress.  The out
  /// buffer has not been changed and the frame has not been reset.
  ///
  /// @retval truncated All input was consumed, but produced less
  /// output than requested.  The out buffer has been changed and the
  /// frame has not been reset.  The caller may resume decompression
  /// after calling @c feed.
  ///
  /// @retval corrupted The compression library detected that the data
  /// was corrupted.  The frame has been reset.
  ///
  /// @retval out_of_memory The operation failed due to an out of
  /// memory error.  The frame has been reset.
  ///
  /// @retval exceeds_max_capacity The requested size exceeds the
  /// maximium capacity configured for the Managed_buffer.  The out
  /// buffer has not been changed and the frame has not been reset.
  /// The caller may resume decompression after increasing the
  /// capacity, or resetting the buffer (perhaps after moving the data
  /// elsewhere), or using a different output buffer, or similar.
  [[nodiscard]] Decompress_status decompress(Managed_buffer_t &out,
                                             Size_t output_size);
 
  /// Decompress an exact, given number of bytes.
  ///
  /// @param out The output buffer.
  ///
  /// @param output_size The number of bytes to decompress.
  ///
  /// @returns a pair where the first component is a Decompress_status
  /// value and the second component is the number of bytes that were
  /// successfully stored in out.  The Decompress_status has the same
  /// possible values as for @c decompress(Managed_buffer_t,
  /// output_size), except it cannot take the value
  /// exceeds_max_capacity.  The size will be equal to output_size if
  /// the status is success; strictly between 0 and output_size if the
  /// status is truncated; and 0 for the other cases.
  [[nodiscard]] std::pair<Decompress_status, Size_t> decompress(
      Char_t *out, Size_t output_size);
 
  /// Return a `Grow_constraint` that may be used with the
  /// Managed_buffer storing the output, in order to optimize memory
  /// usage for a particular compression algorithm.
  Grow_constraint_t get_grow_constraint_hint() const;
 
 private:
  /// Implement @c get_type_code.
  virtual type do_get_type_code() const = 0;
 
  /// Implement @c do_reset.
  virtual void do_reset() = 0;
 
  void feed_char_t(const Char_t *input_data, Size_t input_size);
 
  /// Implement @c feed.
  virtual void do_feed(const Char_t *input_data, Size_t input_size) = 0;
 
  /// Implement @c decompress.
  ///
  /// This differs from @c decompress in that it does not have to
  /// reset the frame when returning out_of_memory or corrupted; the
  /// caller does that.
  [[nodiscard]] virtual std::pair<Decompress_status, Size_t> do_decompress(
      Char_t *out, Size_t output_size) = 0;
 
  /// Implement @c get_grow_constraint_hint.
  ///
  /// In this base class, the function returns a default-constructed
  /// Grow_constraint, i.e., one which does not limit the
  /// Grow_calculator.
  virtual Grow_constraint_t do_get_grow_constraint_hint() const;
};
 
}  // namespace mysql::binlog::event::compression
 
#endif  // ifndef MYSQL_BINLOG_EVENT_COMPRESSION_DECOMPRESSOR_H