protobuf/upb/message/internal/message.h

// Protocol Buffers - Google's data interchange format
// Copyright 2023 Google LLC.  All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file or at
// https://developers.google.com/open-source/licenses/bsd

/*
** Our memory representation for parsing tables and messages themselves.
** Functions in this file are used by generated code and possibly reflection.
**
** The definitions in this file are internal to upb.
**/

#ifndef UPB_MESSAGE_INTERNAL_MESSAGE_H_
#define UPB_MESSAGE_INTERNAL_MESSAGE_H_

#include <stdlib.h>
#include <string.h>

#include "upb/mem/arena.h"
#include "upb/message/internal/extension.h"
#include "upb/mini_table/message.h"

// Must be last.
#include "upb/port/def.inc"

#ifdef __cplusplus
extern "C" {
#endif

extern const float kUpb_FltInfinity;
extern const double kUpb_Infinity;
extern const double kUpb_NaN;

/* Internal members of a upb_Message that track unknown fields and/or
 * extensions. We can change this without breaking binary compatibility.  We put
 * these before the user's data.  The user's upb_Message* points after the
 * upb_Message_Internal. */

typedef struct {
  /* Total size of this structure, including the data that follows.
   * Must be aligned to 8, which is alignof(upb_Extension) */
  uint32_t size;

  /* Offsets relative to the beginning of this structure.
   *
   * Unknown data grows forward from the beginning to unknown_end.
   * Extension data grows backward from size to ext_begin.
   * When the two meet, we're out of data and have to realloc.
   *
   * If we imagine that the final member of this struct is:
   *   char data[size - overhead];  // overhead =
   * sizeof(upb_Message_InternalData)
   *
   * Then we have:
   *   unknown data: data[0 .. (unknown_end - overhead)]
   *   extensions data: data[(ext_begin - overhead) .. (size - overhead)] */
  uint32_t unknown_end;
  uint32_t ext_begin;
  /* Data follows, as if there were an array:
   *   char data[size - sizeof(upb_Message_InternalData)]; */
} upb_Message_InternalData;

typedef struct {
  union {
    upb_Message_InternalData* internal;

    // Force 8-byte alignment, since the data members may contain members that
    // require 8-byte alignment.
    double d;
  };
} upb_Message_Internal;

struct upb_Message {
  int unused;  // Placeholder cuz Windows won't compile an empty struct.
};

UPB_INLINE size_t upb_msg_sizeof(const upb_MiniTable* m) {
  return m->UPB_PRIVATE(size) + sizeof(upb_Message_Internal);
}

// Inline version upb_Message_New(), for internal use.
UPB_INLINE struct upb_Message* _upb_Message_New(const upb_MiniTable* mini_table,
                                                upb_Arena* arena) {
  size_t size = upb_msg_sizeof(mini_table);
  void* mem = upb_Arena_Malloc(arena, size + sizeof(upb_Message_Internal));
  if (UPB_UNLIKELY(!mem)) return NULL;
  struct upb_Message* msg =
      UPB_PTR_AT(mem, sizeof(upb_Message_Internal), struct upb_Message);
  memset(mem, 0, size);
  return msg;
}

UPB_INLINE upb_Message_Internal* upb_Message_Getinternal(
    const struct upb_Message* msg) {
  ptrdiff_t size = sizeof(upb_Message_Internal);
  return (upb_Message_Internal*)((char*)msg - size);
}

// Discards the unknown fields for this message only.
void _upb_Message_DiscardUnknown_shallow(struct upb_Message* msg);

// Adds unknown data (serialized protobuf data) to the given message.
// The data is copied into the message instance.
bool UPB_PRIVATE(_upb_Message_AddUnknown)(struct upb_Message* msg,
                                          const char* data, size_t len,
                                          upb_Arena* arena);

bool UPB_PRIVATE(_upb_Message_Realloc)(struct upb_Message* msg, size_t need,
                                       upb_Arena* arena);

#ifdef __cplusplus
} /* extern "C" */
#endif

#include "upb/port/undef.inc"

#endif /* UPB_MESSAGE_INTERNAL_MESSAGE_H_ */