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# Conflicts: # README.md
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Zhi Guan
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doc/crypto/CRYPTO_get_ex_new_index.pod
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doc/crypto/CRYPTO_get_ex_new_index.pod
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=pod
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=head1 NAME
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CRYPTO_EX_new, CRYPTO_EX_free, CRYPTO_EX_dup,
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CRYPTO_free_ex_index, CRYPTO_get_ex_new_index, CRYPTO_set_ex_data,
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CRYPTO_get_ex_data, CRYPTO_free_ex_data, CRYPTO_new_ex_data
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- functions supporting application-specific data
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=head1 SYNOPSIS
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#include <openssl/crypto.h>
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int CRYPTO_get_ex_new_index(int class_index,
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long argl, void *argp,
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CRYPTO_EX_new *new_func,
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CRYPTO_EX_dup *dup_func,
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CRYPTO_EX_free *free_func);
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typedef int CRYPTO_EX_new(void *parent, void *ptr, CRYPTO_EX_DATA *ad,
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int idx, long argl, void *argp);
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typedef void CRYPTO_EX_free(void *parent, void *ptr, CRYPTO_EX_DATA *ad,
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int idx, long argl, void *argp);
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typedef int CRYPTO_EX_dup(CRYPTO_EX_DATA *to, const CRYPTO_EX_DATA *from,
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void *from_d, int idx, long argl, void *argp);
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int CRYPTO_new_ex_data(int class_index, void *obj, CRYPTO_EX_DATA *ad)
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int CRYPTO_set_ex_data(CRYPTO_EX_DATA *r, int idx, void *arg);
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void *CRYPTO_get_ex_data(CRYPTO_EX_DATA *r, int idx);
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void CRYPTO_free_ex_data(int class_index, void *obj, CRYPTO_EX_DATA *r);
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int CRYPTO_free_ex_index(int class_index, int idx);
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=head1 DESCRIPTION
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Several OpenSSL structures can have application-specific data attached to them,
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known as "exdata."
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The specific structures are:
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SSL
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SSL_CTX
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SSL_SESSION
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X509
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X509_STORE
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X509_STORE_CTX
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DH
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DSA
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EC_KEY
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RSA
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ENGINE
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UI
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BIO
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Each is identified by an B<CRYPTO_EX_INDEX_xxx> define in the B<crypto.h>
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header file. In addition, B<CRYPTO_EX_INDEX_APP> is reserved for
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applications to use this facility for their own structures.
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The API described here is used by OpenSSL to manipulate exdata for specific
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structures. Since the application data can be anything at all it is passed
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and retrieved as a B<void *> type.
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The B<CRYPTO_EX_DATA> type is opaque. To initialize the exdata part of
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a structure, call CRYPTO_new_ex_data(). This is only necessary for
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B<CRYPTO_EX_INDEX_APP> objects.
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Exdata types are identified by an B<index>, an integer guaranteed to be
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unique within structures for the lifetime of the program. Applications
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using exdata typically call B<CRYPTO_get_ex_new_index> at startup, and
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store the result in a global variable, or write a wrapper function to
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provide lazy evaluation. The B<class_index> should be one of the
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B<CRYPTO_EX_INDEX_xxx> values. The B<argl> and B<argp> parameters are saved
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to be passed to the callbacks but are otherwise not used. In order to
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transparently manipulate exdata, three callbacks must be provided. The
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semantics of those callbacks are described below.
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When copying or releasing objects with exdata, the callback functions
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are called in increasing order of their B<index> value.
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If a dynamic library can be unloaded, it should call CRYPTO_free_ex_index()
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when this is done.
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This will replace the callbacks with no-ops
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so that applications don't crash. Any existing exdata will be leaked.
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To set or get the exdata on an object, the appropriate type-specific
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routine must be used. This is because the containing structure is opaque
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and the B<CRYPTO_EX_DATA> field is not accessible. In both API's, the
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B<idx> parameter should be an already-created index value.
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When setting exdata, the pointer specified with a particular index is saved,
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and returned on a subsequent "get" call. If the application is going to
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release the data, it must make sure to set a B<NULL> value at the index,
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to avoid likely double-free crashes.
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The function B<CRYPTO_free_ex_data> is used to free all exdata attached
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to a structure. The appropriate type-specific routine must be used.
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The B<class_index> identifies the structure type, the B<obj> is
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be the pointer to the actual structure, and B<r> is a pointer to the
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structure's exdata field.
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=head2 Callback Functions
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This section describes how the callback functions are used. Applications
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that are defining their own exdata using B<CYPRTO_EX_INDEX_APP> must
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call them as described here.
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When a structure is initially allocated (such as RSA_new()) then the
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new_func() is called for every defined index. There is no requirement
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that the entire parent, or containing, structure has been set up.
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The new_func() is typically used only to allocate memory to store the
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exdata, and perhaps an "initialized" flag within that memory.
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The exdata value should be set by calling CRYPTO_set_ex_data().
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When a structure is free'd (such as SSL_CTX_free()) then the
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free_func() is called for every defined index. Again, the state of the
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parent structure is not guaranteed. The free_func() may be called with a
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NULL pointer.
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Both new_func() and free_func() take the same parameters.
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The B<parent> is the pointer to the structure that contains the exdata.
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The B<ptr> is the current exdata item; for new_func() this will typically
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be NULL. The B<r> parameter is a pointer to the exdata field of the object.
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The B<idx> is the index and is the value returned when the callbacks were
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initially registered via CRYPTO_get_ex_new_index() and can be used if
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the same callback handles different types of exdata.
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dup_func() is called when a structure is being copied. This is only done
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for B<SSL> and B<SSL_SESSION> objects. The B<to> and B<from> parameters
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are pointers to the destination and source B<CRYPTO_EX_DATA> structures,
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respectively. The B<srcp> parameter is a pointer to the source exdata.
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When the dup_func() returns, the value in B<srcp> is copied to the
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destination ex_data. If the pointer contained in B<srcp> is not modified
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by the dup_func(), then both B<to> and B<from> will point to the same data.
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The B<idx>, B<argl> and B<argp> parameters are as described for the other
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two callbacks.
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=head1 RETURN VALUES
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CRYPTO_get_ex_new_index() returns a new index or -1 on failure; the
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value B<0> is reserved for the legacy "app_data" API's.
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CRYPTO_free_ex_index() and
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CRYPTO_set_ex_data() return 1 on success or 0 on failure.
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CRYPTO_get_ex_data() returns the application data or NULL on failure;
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note that NULL may be a valid value.
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dup_func() should return 0 for failure and 1 for success.
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=head1 COPYRIGHT
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Copyright 2015-2016 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the OpenSSL license (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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