python/descriptor_containers.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

#ifndef PYUPB_DESCRIPTOR_CONTAINERS_H__
#define PYUPB_DESCRIPTOR_CONTAINERS_H__

// This file defines immutable Python containiner types whose data comes from
// an underlying descriptor (def).
//
// Because there are many instances of these types that vend different kinds of
// data (fields, oneofs, enums, etc) these types accept a "vtable" of function
// pointers. This saves us from having to define numerous distinct Python types
// for each kind of data we want to vend.
//
// The underlying upb APIs follow a consistent pattern that allows us to use
// those functions directly inside these vtables, greatly reducing the amount of
// "adaptor" code we need to write.

#include <stdbool.h>

#include "protobuf.h"
#include "upb/reflection/def.h"

// -----------------------------------------------------------------------------
// PyUpb_GenericSequence
// -----------------------------------------------------------------------------

// A Python object that vends a sequence of descriptors.

typedef struct {
  // Returns the number of elements in the map.
  int (*get_elem_count)(const void* parent);
  // Returns an element by index.
  const void* (*index)(const void* parent, int idx);
  // Returns a Python object wrapping this element, caller owns a ref.
  PyObject* (*get_elem_wrapper)(const void* elem);
} PyUpb_GenericSequence_Funcs;

// Returns a new GenericSequence.  The vtable `funcs` must outlive this object
// (generally it should be static).  The GenericSequence will take a ref on
// `parent_obj`, which must be sufficient to keep `parent` alive.  The object
// `parent` will be passed as an argument to the functions in `funcs`.
PyObject* PyUpb_GenericSequence_New(const PyUpb_GenericSequence_Funcs* funcs,
                                    const void* parent, PyObject* parent_obj);

// -----------------------------------------------------------------------------
// PyUpb_ByNameMap
// -----------------------------------------------------------------------------

// A Python object that vends a name->descriptor map.

typedef struct {
  PyUpb_GenericSequence_Funcs base;
  // Looks up by name and returns either a pointer to the element or NULL.
  const void* (*lookup)(const void* parent, const char* key);
  // Returns the name associated with this element.
  const char* (*get_elem_name)(const void* elem);
} PyUpb_ByNameMap_Funcs;

// Returns a new ByNameMap.  The vtable `funcs` must outlive this object
// (generally it should be static).  The ByNameMap will take a ref on
// `parent_obj`, which must be sufficient to keep `parent` alive.  The object
// `parent` will be passed as an argument to the functions in `funcs`.
PyObject* PyUpb_ByNameMap_New(const PyUpb_ByNameMap_Funcs* funcs,
                              const void* parent, PyObject* parent_obj);

// -----------------------------------------------------------------------------
// PyUpb_ByNumberMap
// -----------------------------------------------------------------------------

// A Python object that vends a number->descriptor map.

typedef struct {
  PyUpb_GenericSequence_Funcs base;
  // Looks up by name and returns either a pointer to the element or NULL.
  const void* (*lookup)(const void* parent, int num);
  // Returns the name associated with this element.
  int (*get_elem_num)(const void* elem);
} PyUpb_ByNumberMap_Funcs;

// Returns a new ByNumberMap.  The vtable `funcs` must outlive this object
// (generally it should be static).  The ByNumberMap will take a ref on
// `parent_obj`, which must be sufficient to keep `parent` alive.  The object
// `parent` will be passed as an argument to the functions in `funcs`.
PyObject* PyUpb_ByNumberMap_New(const PyUpb_ByNumberMap_Funcs* funcs,
                                const void* parent, PyObject* parent_obj);

bool PyUpb_InitDescriptorContainers(PyObject* m);

#endif  // PYUPB_DESCRIPTOR_CONTAINERS_H__