doc/internal/man3/evp_generic_fetch.pod

   1 =pod
   2
   3 =head1 NAME
   4
   5 evp_generic_fetch - generic algorithm fetcher and method creator for EVP
   6
   7 =head1 SYNOPSIS
   8
   9  /* Only for EVP source */
  10  #include "evp_locl.h"
  11
  12  void *evp_generic_fetch(OPENSSL_CTX *libctx, int operation_id,
  13                          const char *name, const char *properties,
  14                          void *(*new_method)(const OSSL_DISPATCH *fns,
  15                                              OSSL_PROVIDER *prov),
  16                          int (*upref_method)(void *),
  17                          void (*free_method)(void *));
  18
  19 =head1 DESCRIPTION
  20
  21 evp_generic_fetch() calls ossl_method_construct() with the given
  22 C<libctx>, C<operation_id>, C<name>, and C<properties> and uses
  23 it to create an EVP method with the help of the functions
  24 C<new_method>, C<upref_method>, and C<free_method>.
  25
  26 The three functions are supposed to:
  27
  28 =over 4
  29
  30 =item new_method()
  31
  32 creates an internal method from function pointers found in the
  33 dispatch table C<fns>.
  34
  35 =item upref_method()
  36
  37 increments the reference counter for the given method, if there is
  38 one.
  39
  40 =item free_method()
  41
  42 frees the given method.
  43
  44 =back
  45
  46 =head1 RETURN VALUES
  47
  48 evp_generic_fetch() returns a method on success, or B<NULL> on error.
  49
  50 =head1 EXAMPLES
  51
  52 This is a short example of the fictitious EVP API and operation called
  53 C<EVP_FOO>.
  54
  55 To begin with, let's assume something like this in
  56 C<include/openssl/core_numbers.h>:
  57
  58     #define OSSL_OP_FOO                         100
  59
  60     #define OSSL_OP_FOO_NEWCTX_FUNC            2001
  61     #define OSSL_OP_FOO_INIT                   2002
  62     #define OSSL_OP_FOO_OPERATE                2003
  63     #define OSSL_OP_FOO_CLEANCTX_FUNC          2004
  64     #define OSSL_OP_FOO_FREECTX_FUNC           2005
  65     OSSL_CORE_MAKE_FUNC(void *,OP_foo_newctx,(void))
  66     OSSL_CORE_MAKE_FUNC(int,OP_foo_init,(void *vctx))
  67     OSSL_CORE_MAKE_FUNC(int,OP_foo_operate,(void *vctx,
  68                                             unsigned char *out, size_t *out_l,
  69                                             unsigned char *in, size_t in_l))
  70     OSSL_CORE_MAKE_FUNC(void,OP_foo_cleanctx,(void *vctx))
  71     OSSL_CORE_MAKE_FUNC(void,OP_foo_freectx,(void *vctx))
  72
  73 And here's the implementation of the FOO method fetcher:
  74
  75     /* typedef struct evp_foo_st EVP_FOO */
  76     struct evp_foo_st {
  77         OSSL_PROVIDER *prov;
  78         CRYPTO_REF_COUNT refcnt;
  79         OSSL_OP_foo_newctx_fn *newctx;
  80         OSSL_OP_foo_init_fn *init;
  81         OSSL_OP_foo_operate_fn *operate;
  82         OSSL_OP_foo_cleanctx_fn *cleanctx;
  83         OSSL_OP_foo_freectx_fn *freectx;
  84     };
  85
  86     /*
  87      * In this example, we have a public method creator and destructor.
  88      * It's not absolutely necessary, but is in the spirit of OpenSSL.
  89      */
  90     EVP_FOO *EVP_FOO_meth_from_dispatch(const OSSL_DISPATCH *fns,
  91                                         OSSL_PROVIDER *prov)
  92     {
  93         EVP_FOO *foo = NULL;
  94
  95         if ((foo = OPENSSL_zalloc(sizeof(*foo))) == NULL)
  96             return NULL;
  97
  98         for (; fns->function_id != 0; fns++) {
  99             switch (fns->function_id) {
 100             case OSSL_OP_FOO_NEWCTX_FUNC:
 101                 foo->newctx = OSSL_get_OP_foo_newctx(fns);
 102                 break;
 103             case OSSL_OP_FOO_INIT:
 104                 foo->init = OSSL_get_OP_foo_init(fns);
 105                 break;
 106             case OSSL_OP_FOO_OPERATE:
 107                 foo->operate = OSSL_get_OP_foo_operate(fns);
 108                 break;
 109             case OSSL_OP_FOO_CLEANCTX_FUNC:
 110                 foo->cleanctx = OSSL_get_OP_foo_cleanctx(fns);
 111                 break;
 112             case OSSL_OP_FOO_FREECTX_FUNC:
 113                 foo->freectx = OSSL_get_OP_foo_freectx(fns);
 114                 break;
 115             }
 116         }
 117         foo->prov = prov;
 118         if (prov)
 119             ossl_provider_upref(prov);
 120
 121         return foo;
 122     }
 123
 124     EVP_FOO_meth_free(EVP_FOO *foo)
 125     {
 126         if (foo != NULL) {
 127             OSSL_PROVIDER *prov = foo->prov;
 128
 129             OPENSSL_free(foo);
 130             ossl_provider_free(prov);
 131         }
 132     }
 133
 134     static void *foo_from_dispatch(const OSSL_DISPATCH *fns,
 135                                    OSSL_PROVIDER *prov)
 136     {
 137         return EVP_FOO_meth_from_dispatch(fns, prov);
 138     }
 139
 140     static int foo_upref(void *vfoo)
 141     {
 142         EVP_FOO *foo = vfoo;
 143         int ref = 0;
 144
 145         CRYPTO_UP_REF(&foo->refcnt, &ref, foo_lock);
 146         return 1;
 147     }
 148
 149     static void foo_free(void *vfoo)
 150     {
 151         EVP_FOO_meth_free(vfoo);
 152     }
 153
 154     EVP_FOO *EVP_FOO_fetch(OPENSSL_CTX *ctx,
 155                            const char *name,
 156                            const char *properties)
 157     {
 158         EVP_FOO *foo =
 159             evp_generic_fetch(ctx, OSSL_OP_FOO, name, properties,
 160                               foo_from_dispatch, foo_upref, foo_free);
 161
 162         /*
 163          * If this method exists in legacy form, with a constant NID for the
 164          * given |name|, this is the spot to find that NID and set it in
 165          * the newly constructed EVP_FOO instance.
 166          */
 167
 168         return foo;
 169
 170     }
 171
 172 And finally, the library functions:
 173
 174     /* typedef struct evp_foo_st EVP_FOO_CTX */
 175     struct evp_foo_ctx_st {
 176         const EVP_FOO *foo;
 177         void *provctx;          /* corresponding provider context */
 178     };
 179
 180     int EVP_FOO_CTX_reset(EVP_FOO_CTX *c)
 181     {
 182         if (c == NULL)
 183             return 1;
 184         if (c->foo != NULL && c->foo->cleanctx != NULL)
 185             c->foo->cleanctx(c->provctx);
 186         return 1;
 187     }
 188
 189     EVP_FOO_CTX *EVP_FOO_CTX_new(void)
 190     {
 191         return OPENSSL_zalloc(sizeof(EVP_FOO_CTX));
 192     }
 193
 194     void EVP_FOO_CTX_free(EVP_FOO_CTX *c)
 195     {
 196         EVP_FOO_CTX_reset(c);
 197         c->foo->freectx(c->provctx);
 198         OPENSSL_free(c);
 199     }
 200
 201     int EVP_FooInit(EVP_FOO_CTX *c, const EVP_FOO *foo)
 202     {
 203         int ok = 1;
 204
 205         c->foo = foo;
 206         if (c->provctx == NULL)
 207             c->provctx = c->foo->newctx();
 208
 209         ok = c->foo->init(c->provctx);
 210
 211         return ok;
 212     }
 213
 214     int EVP_FooOperate(EVP_FOO_CTX *c, unsigned char *out, size_t *outl,
 215                        const unsigned char *in, size_t inl)
 216     {
 217         int ok = 1;
 218
 219         ok = c->foo->update(c->provctx, out, inl, &outl, in, inl);
 220         return ok;
 221     }
 222
 223 =head1 SEE ALSO
 224
 225 L<ossl_method_construct>
 226
 227 =head1 HISTORY
 228
 229 The functions described here were all added in OpenSSL 3.0.
 230
 231 =head1 COPYRIGHT
 232
 233 Copyright 2019 The OpenSSL Project Authors. All Rights Reserved.
 234
 235 Licensed under the Apache License 2.0 (the "License").  You may not use
 236 this file except in compliance with the License.  You can obtain a copy
 237 in the file LICENSE in the source distribution or at
 238 L<https://www.openssl.org/source/license.html>.
 239
 240 =cut