include/openssl/ex_data.h

/*
 * Copyright 1995-2016 The OpenSSL Project Authors. All Rights Reserved.
 *
 * Licensed under the OpenSSL license (the "License").  You may not use
 * this file except in compliance with the License.  You can obtain a copy
 * in the file LICENSE in the source distribution or at
 * https://www.openssl.org/source/license.html
 */

#ifndef OPENSSL_HEADER_EX_DATA_H
#define OPENSSL_HEADER_EX_DATA_H

#include <openssl/base.h>

#include <openssl/stack.h>

#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.


typedef struct crypto_ex_data_st CRYPTO_EX_DATA;


// 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_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.
//
// The callback is passed the to-be-destroyed object (i.e. the |SSL*|) in
// |parent|. As |parent| will shortly be destroyed, callers must not perform
// operations that would increment its reference count, pass ownership, or
// assume the object outlives the function call. 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 |parent| has no
// value set for this index. However, the callbacks may also be skipped entirely
// if no extra data pointers are set on |parent| 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);


// Private structures.

// 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;

struct crypto_ex_data_st {
  STACK_OF(void) *sk;
};


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

#endif  // OPENSSL_HEADER_EX_DATA_H