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CRYPTO_GET_EX_NEW_INDEX(3)          OpenSSL         CRYPTO_GET_EX_NEW_INDEX(3)
NAME
       CRYPTO_EX_new, CRYPTO_EX_free, CRYPTO_EX_dup, CRYPTO_free_ex_index,
       CRYPTO_get_ex_new_index, CRYPTO_set_ex_data, CRYPTO_get_ex_data,
       CRYPTO_free_ex_data, CRYPTO_new_ex_data - functions supporting
       application-specific data
SYNOPSIS
        #include <openssl/crypto.h>
        int CRYPTO_get_ex_new_index(int class_index,
                                    long argl, void *argp,
                                    CRYPTO_EX_new *new_func,
                                    CRYPTO_EX_dup *dup_func,
                                    CRYPTO_EX_free *free_func);
        typedef void CRYPTO_EX_new(void *parent, void *ptr, CRYPTO_EX_DATA *ad,
                                   int idx, long argl, void *argp);
        typedef void CRYPTO_EX_free(void *parent, void *ptr, CRYPTO_EX_DATA *ad,
                                    int idx, long argl, void *argp);
        typedef int CRYPTO_EX_dup(CRYPTO_EX_DATA *to, const CRYPTO_EX_DATA *from,
                                  void *from_d, int idx, long argl, void *argp);
        int CRYPTO_new_ex_data(int class_index, void *obj, CRYPTO_EX_DATA *ad)
        int CRYPTO_set_ex_data(CRYPTO_EX_DATA *r, int idx, void *arg);
        void *CRYPTO_get_ex_data(CRYPTO_EX_DATA *r, int idx);
        void CRYPTO_free_ex_data(int class_index, void *obj, CRYPTO_EX_DATA *r);
        int CRYPTO_free_ex_index(int class_index, int idx);
DESCRIPTION
       Several OpenSSL structures can have application-specific data attached
       to them, known as "exdata."  The specific structures are:
           APP
           BIO
           DH
           DRBG
           DSA
           EC_KEY
           ENGINE
           RSA
           SSL
           SSL_CTX
           SSL_SESSION
           UI
           UI_METHOD
           X509
           X509_STORE
           X509_STORE_CTX
       Each is identified by an CRYPTO_EX_INDEX_xxx define in the crypto.h
       header file.  In addition, CRYPTO_EX_INDEX_APP is reserved for
       applications to use this facility for their own structures.
       The API described here is used by OpenSSL to manipulate exdata for
       specific structures.  Since the application data can be anything at all
       it is passed and retrieved as a void * type.
       The CRYPTO_EX_DATA type is opaque.  To initialize the exdata part of a
       structure, call CRYPTO_new_ex_data(). This is only necessary for
       CRYPTO_EX_INDEX_APP objects.
       Exdata types are identified by an index, an integer guaranteed to be
       unique within structures for the lifetime of the program.  Applications
       using exdata typically call CRYPTO_get_ex_new_index at startup, and
       store the result in a global variable, or write a wrapper function to
       provide lazy evaluation.  The class_index should be one of the
       CRYPTO_EX_INDEX_xxx values. The argl and argp parameters are saved to
       be passed to the callbacks but are otherwise not used.  In order to
       transparently manipulate exdata, three callbacks must be provided. The
       semantics of those callbacks are described below.
       When copying or releasing objects with exdata, the callback functions
       are called in increasing order of their index value.
       If a dynamic library can be unloaded, it should call
       CRYPTO_free_ex_index() when this is done.  This will replace the
       callbacks with no-ops so that applications don't crash.  Any existing
       exdata will be leaked.
       To set or get the exdata on an object, the appropriate type-specific
       routine must be used.  This is because the containing structure is
       opaque and the CRYPTO_EX_DATA field is not accessible.  In both API's,
       the idx parameter should be an already-created index value.
       When setting exdata, the pointer specified with a particular index is
       saved, and returned on a subsequent "get" call.  If the application is
       going to release the data, it must make sure to set a NULL value at the
       index, to avoid likely double-free crashes.
       The function CRYPTO_free_ex_data is used to free all exdata attached to
       a structure. The appropriate type-specific routine must be used.  The
       class_index identifies the structure type, the obj is a pointer to the
       actual structure, and r is a pointer to the structure's exdata field.
   Callback Functions
       This section describes how the callback functions are used.
       Applications that are defining their own exdata using
       CYPRTO_EX_INDEX_APP must call them as described here.
       When a structure is initially allocated (such as RSA_new()) then the
       new_func() is called for every defined index. There is no requirement
       that the entire parent, or containing, structure has been set up.  The
       new_func() is typically used only to allocate memory to store the
       exdata, and perhaps an "initialized" flag within that memory.  The
       exdata value should be set by calling CRYPTO_set_ex_data().
       When a structure is free'd (such as SSL_CTX_free()) then the
       free_func() is called for every defined index.  Again, the state of the
       parent structure is not guaranteed.  The free_func() may be called with
       a NULL pointer.
       Both new_func() and free_func() take the same parameters.  The parent
       is the pointer to the structure that contains the exdata.  The ptr is
       the current exdata item; for new_func() this will typically be NULL.
       The r parameter is a pointer to the exdata field of the object.  The
       idx is the index and is the value returned when the callbacks were
       initially registered via CRYPTO_get_ex_new_index() and can be used if
       the same callback handles different types of exdata.
       dup_func() is called when a structure is being copied.  This is only
       done for SSL, SSL_SESSION, EC_KEY objects and BIO chains via
       BIO_dup_chain().  The to and from parameters are pointers to the
       destination and source CRYPTO_EX_DATA structures, respectively.  The
       from_d parameter needs to be cast to a void **pptr as the API has
       currently the wrong signature; that will be changed in a future
       version.  The *pptr is a pointer to the source exdata.  When the
       dup_func() returns, the value in *pptr is copied to the destination
       ex_data.  If the pointer contained in *pptr is not modified by the
       dup_func(), then both to and from will point to the same data.  The
       idx, argl and argp parameters are as described for the other two
       callbacks.  If the dup_func() returns 0 the whole CRYPTO_dup_ex_data()
       will fail.
RETURN VALUES
       CRYPTO_get_ex_new_index() returns a new index or -1 on failure.
       CRYPTO_free_ex_index() and CRYPTO_set_ex_data() return 1 on success or
       0 on failure.
       CRYPTO_get_ex_data() returns the application data or NULL on failure;
       note that NULL may be a valid value.
       dup_func() should return 0 for failure and 1 for success.
COPYRIGHT
       Copyright 2015-2019 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>;.
1.1.1k                            2021-03-25        CRYPTO_GET_EX_NEW_INDEX(3)