include/openssl/ex_data.h

// Copyright 1995-2016 The OpenSSL Project Authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#ifndef OPENSSL_HEADER_EX_DATA_H
#define OPENSSL_HEADER_EX_DATA_H

#include <openssl/base.h>  // IWYU pragma: export

#if defined(__cplusplus)
extern "C" {
#endif


// ex_data is a mechanism for associating arbitrary extra data with objects.
// For each type of object that supports ex_data, different users can be
// assigned indexes in which to store their data. Each index has callback
// functions that are called when an object of that type is freed or
// duplicated.


// Type-specific functions.

#if 0  // Sample

// Each type that supports ex_data provides three functions:

// TYPE_get_ex_new_index allocates a new index for `TYPE`. An optional
// `free_func` argument may be provided which is called when the owning object
// is destroyed. See `CRYPTO_EX_free` for details. The `argl` and `argp`
// arguments are opaque values that are passed to the callback. It returns the
// new index or a negative number on error.
OPENSSL_EXPORT int TYPE_get_ex_new_index(long argl, void *argp,
                                         CRYPTO_EX_unused *unused,
                                         CRYPTO_EX_dup *dup_unused,
                                         CRYPTO_EX_free *free_func);

// TYPE_set_ex_data sets an extra data pointer on `t`. The `index` argument
// must have been returned from a previous call to `TYPE_get_ex_new_index`.
OPENSSL_EXPORT int TYPE_set_ex_data(TYPE *t, int index, void *arg);

// TYPE_get_ex_data returns an extra data pointer for `t`, or NULL if no such
// pointer exists. The `index` argument should have been returned from a
// previous call to `TYPE_get_ex_new_index`.
OPENSSL_EXPORT void *TYPE_get_ex_data(const TYPE *t, int index);

// Some types additionally preallocate index zero, with all callbacks set to
// NULL. Applications that do not need the general ex_data machinery may use
// this instead.

// TYPE_set_app_data sets `t`'s application data pointer to `arg`. It returns
// one on success and zero on error.
OPENSSL_EXPORT int TYPE_set_app_data(TYPE *t, void *arg);

// TYPE_get_app_data returns the application data pointer for `t`, or NULL if no
// such pointer exists.
OPENSSL_EXPORT void *TYPE_get_app_data(const TYPE *t);

#endif  // Sample


// Callback types.

// CRYPTO_EX_DATA, in the public API, is an opaque struct that is never returned
// from the library.
typedef struct crypto_ex_data_st CRYPTO_EX_DATA;

// CRYPTO_EX_free is a callback function that is called when an object of the
// class with extra data pointers is being destroyed. For example, if this
// callback has been passed to `SSL_get_ex_new_index` then it may be called each
// time an `SSL*` is destroyed.
//
// `parent` and `ad` will be NULL. Historically, the parent object was passed in
// `parent`, but accessing the pointer was not safe because `parent` was in the
// process of being destroyed. If the callback has access to some other pointer
// to the parent object, it must not pass the pointer to any BoringSSL APIs.
// Mid-destruction, invariants on the parent object no longer hold.
//
// The arguments `argl` and `argp` contain opaque values that were given to
// `CRYPTO_get_ex_new_index_ex`.
//
// This callback may be called with a NULL value for `ptr` if the object has no
// value set for this index. However, the callbacks may also be skipped entirely
// if no extra data pointers are set on the object at all.
typedef void CRYPTO_EX_free(void *parent, void *ptr, CRYPTO_EX_DATA *ad,
                            int index, long argl, void *argp);


// Deprecated functions.

// CRYPTO_cleanup_all_ex_data does nothing.
OPENSSL_EXPORT void CRYPTO_cleanup_all_ex_data(void);

// CRYPTO_EX_dup is a legacy callback function type which is ignored.
typedef int CRYPTO_EX_dup(CRYPTO_EX_DATA *to, const CRYPTO_EX_DATA *from,
                          void **from_d, int index, long argl, void *argp);

// CRYPTO_EX_unused is a placeholder for an unused callback. It is aliased to
// int to ensure non-NULL callers fail to compile rather than fail silently.
typedef int CRYPTO_EX_unused;


#if defined(__cplusplus)
}  // extern C
#endif

#endif  // OPENSSL_HEADER_EX_DATA_H