doc/man3/d2i_X509.pod

   1 =pod
   2
   3 =begin comment
   4
   5 Any keypair function here that gets deprecated should be moved to
   6 d2i_RSAPrivateKey.pod.
   7
   8 =end comment
   9
  10 =head1 NAME
  11
  12 d2i_ACCESS_DESCRIPTION,
  13 d2i_ADMISSIONS,
  14 d2i_ADMISSION_SYNTAX,
  15 d2i_ASIdOrRange,
  16 d2i_ASIdentifierChoice,
  17 d2i_ASIdentifiers,
  18 d2i_ASN1_BIT_STRING,
  19 d2i_ASN1_BMPSTRING,
  20 d2i_ASN1_ENUMERATED,
  21 d2i_ASN1_GENERALIZEDTIME,
  22 d2i_ASN1_GENERALSTRING,
  23 d2i_ASN1_IA5STRING,
  24 d2i_ASN1_INTEGER,
  25 d2i_ASN1_NULL,
  26 d2i_ASN1_OBJECT,
  27 d2i_ASN1_OCTET_STRING,
  28 d2i_ASN1_PRINTABLE,
  29 d2i_ASN1_PRINTABLESTRING,
  30 d2i_ASN1_SEQUENCE_ANY,
  31 d2i_ASN1_SET_ANY,
  32 d2i_ASN1_T61STRING,
  33 d2i_ASN1_TIME,
  34 d2i_ASN1_TYPE,
  35 d2i_ASN1_UINTEGER,
  36 d2i_ASN1_UNIVERSALSTRING,
  37 d2i_ASN1_UTCTIME,
  38 d2i_ASN1_UTF8STRING,
  39 d2i_ASN1_VISIBLESTRING,
  40 d2i_ASRange,
  41 d2i_AUTHORITY_INFO_ACCESS,
  42 d2i_AUTHORITY_KEYID,
  43 d2i_BASIC_CONSTRAINTS,
  44 d2i_CERTIFICATEPOLICIES,
  45 d2i_CMS_ContentInfo,
  46 d2i_CMS_ReceiptRequest,
  47 d2i_CMS_bio,
  48 d2i_CRL_DIST_POINTS,
  49 d2i_DHxparams,
  50 d2i_DIRECTORYSTRING,
  51 d2i_DISPLAYTEXT,
  52 d2i_DIST_POINT,
  53 d2i_DIST_POINT_NAME,
  54 d2i_DSAPrivateKey,
  55 d2i_DSAPrivateKey_bio,
  56 d2i_DSAPrivateKey_fp,
  57 d2i_DSAPublicKey,
  58 d2i_DSA_PUBKEY,
  59 d2i_DSA_PUBKEY_bio,
  60 d2i_DSA_PUBKEY_fp,
  61 d2i_DSA_SIG,
  62 d2i_DSAparams,
  63 d2i_ECDSA_SIG,
  64 d2i_ECPKParameters,
  65 d2i_ECParameters,
  66 d2i_ECPrivateKey,
  67 d2i_ECPrivateKey_bio,
  68 d2i_ECPrivateKey_fp,
  69 d2i_EC_PUBKEY,
  70 d2i_EC_PUBKEY_bio,
  71 d2i_EC_PUBKEY_fp,
  72 d2i_EDIPARTYNAME,
  73 d2i_ESS_CERT_ID,
  74 d2i_ESS_CERT_ID_V2,
  75 d2i_ESS_ISSUER_SERIAL,
  76 d2i_ESS_SIGNING_CERT,
  77 d2i_ESS_SIGNING_CERT_V2,
  78 d2i_EXTENDED_KEY_USAGE,
  79 d2i_GENERAL_NAME,
  80 d2i_GENERAL_NAMES,
  81 d2i_IPAddressChoice,
  82 d2i_IPAddressFamily,
  83 d2i_IPAddressOrRange,
  84 d2i_IPAddressRange,
  85 d2i_ISSUER_SIGN_TOOL,
  86 d2i_ISSUING_DIST_POINT,
  87 d2i_NAMING_AUTHORITY,
  88 d2i_NETSCAPE_CERT_SEQUENCE,
  89 d2i_NETSCAPE_SPKAC,
  90 d2i_NETSCAPE_SPKI,
  91 d2i_NOTICEREF,
  92 d2i_OCSP_BASICRESP,
  93 d2i_OCSP_CERTID,
  94 d2i_OCSP_CERTSTATUS,
  95 d2i_OCSP_CRLID,
  96 d2i_OCSP_ONEREQ,
  97 d2i_OCSP_REQINFO,
  98 d2i_OCSP_REQUEST,
  99 d2i_OCSP_RESPBYTES,
 100 d2i_OCSP_RESPDATA,
 101 d2i_OCSP_RESPID,
 102 d2i_OCSP_RESPONSE,
 103 d2i_OCSP_REVOKEDINFO,
 104 d2i_OCSP_SERVICELOC,
 105 d2i_OCSP_SIGNATURE,
 106 d2i_OCSP_SINGLERESP,
 107 d2i_OSSL_CMP_MSG,
 108 d2i_OSSL_CMP_PKIHEADER,
 109 d2i_OSSL_CMP_PKISI,
 110 d2i_OSSL_CRMF_CERTID,
 111 d2i_OSSL_CRMF_CERTTEMPLATE,
 112 d2i_OSSL_CRMF_ENCRYPTEDVALUE,
 113 d2i_OSSL_CRMF_MSG,
 114 d2i_OSSL_CRMF_MSGS,
 115 d2i_OSSL_CRMF_PBMPARAMETER,
 116 d2i_OSSL_CRMF_PKIPUBLICATIONINFO,
 117 d2i_OSSL_CRMF_SINGLEPUBINFO,
 118 d2i_OTHERNAME,
 119 d2i_PBE2PARAM,
 120 d2i_PBEPARAM,
 121 d2i_PBKDF2PARAM,
 122 d2i_PKCS12,
 123 d2i_PKCS12_BAGS,
 124 d2i_PKCS12_MAC_DATA,
 125 d2i_PKCS12_SAFEBAG,
 126 d2i_PKCS12_bio,
 127 d2i_PKCS12_fp,
 128 d2i_PKCS7,
 129 d2i_PKCS7_DIGEST,
 130 d2i_PKCS7_ENCRYPT,
 131 d2i_PKCS7_ENC_CONTENT,
 132 d2i_PKCS7_ENVELOPE,
 133 d2i_PKCS7_ISSUER_AND_SERIAL,
 134 d2i_PKCS7_RECIP_INFO,
 135 d2i_PKCS7_SIGNED,
 136 d2i_PKCS7_SIGNER_INFO,
 137 d2i_PKCS7_SIGN_ENVELOPE,
 138 d2i_PKCS7_bio,
 139 d2i_PKCS7_fp,
 140 d2i_PKCS8_PRIV_KEY_INFO,
 141 d2i_PKCS8_PRIV_KEY_INFO_bio,
 142 d2i_PKCS8_PRIV_KEY_INFO_fp,
 143 d2i_PKCS8_bio,
 144 d2i_PKCS8_fp,
 145 d2i_PKEY_USAGE_PERIOD,
 146 d2i_POLICYINFO,
 147 d2i_POLICYQUALINFO,
 148 d2i_PROFESSION_INFO,
 149 d2i_PROXY_CERT_INFO_EXTENSION,
 150 d2i_PROXY_POLICY,
 151 d2i_RSA_OAEP_PARAMS,
 152 d2i_RSA_PSS_PARAMS,
 153 d2i_SCRYPT_PARAMS,
 154 d2i_SCT_LIST,
 155 d2i_SXNET,
 156 d2i_SXNETID,
 157 d2i_TS_ACCURACY,
 158 d2i_TS_MSG_IMPRINT,
 159 d2i_TS_MSG_IMPRINT_bio,
 160 d2i_TS_MSG_IMPRINT_fp,
 161 d2i_TS_REQ,
 162 d2i_TS_REQ_bio,
 163 d2i_TS_REQ_fp,
 164 d2i_TS_RESP,
 165 d2i_TS_RESP_bio,
 166 d2i_TS_RESP_fp,
 167 d2i_TS_STATUS_INFO,
 168 d2i_TS_TST_INFO,
 169 d2i_TS_TST_INFO_bio,
 170 d2i_TS_TST_INFO_fp,
 171 d2i_USERNOTICE,
 172 d2i_X509,
 173 d2i_X509_ALGOR,
 174 d2i_X509_ALGORS,
 175 d2i_X509_ATTRIBUTE,
 176 d2i_X509_CERT_AUX,
 177 d2i_X509_CINF,
 178 d2i_X509_CRL,
 179 d2i_X509_CRL_INFO,
 180 d2i_X509_CRL_bio,
 181 d2i_X509_CRL_fp,
 182 d2i_X509_EXTENSION,
 183 d2i_X509_EXTENSIONS,
 184 d2i_X509_NAME,
 185 d2i_X509_NAME_ENTRY,
 186 d2i_X509_PUBKEY,
 187 d2i_X509_PUBKEY_bio,
 188 d2i_X509_PUBKEY_fp,
 189 d2i_X509_REQ,
 190 d2i_X509_REQ_INFO,
 191 d2i_X509_REQ_bio,
 192 d2i_X509_REQ_fp,
 193 d2i_X509_REVOKED,
 194 d2i_X509_SIG,
 195 d2i_X509_VAL,
 196 i2d_ACCESS_DESCRIPTION,
 197 i2d_ADMISSIONS,
 198 i2d_ADMISSION_SYNTAX,
 199 i2d_ASIdOrRange,
 200 i2d_ASIdentifierChoice,
 201 i2d_ASIdentifiers,
 202 i2d_ASN1_BIT_STRING,
 203 i2d_ASN1_BMPSTRING,
 204 i2d_ASN1_ENUMERATED,
 205 i2d_ASN1_GENERALIZEDTIME,
 206 i2d_ASN1_GENERALSTRING,
 207 i2d_ASN1_IA5STRING,
 208 i2d_ASN1_INTEGER,
 209 i2d_ASN1_NULL,
 210 i2d_ASN1_OBJECT,
 211 i2d_ASN1_OCTET_STRING,
 212 i2d_ASN1_PRINTABLE,
 213 i2d_ASN1_PRINTABLESTRING,
 214 i2d_ASN1_SEQUENCE_ANY,
 215 i2d_ASN1_SET_ANY,
 216 i2d_ASN1_T61STRING,
 217 i2d_ASN1_TIME,
 218 i2d_ASN1_TYPE,
 219 i2d_ASN1_UNIVERSALSTRING,
 220 i2d_ASN1_UTCTIME,
 221 i2d_ASN1_UTF8STRING,
 222 i2d_ASN1_VISIBLESTRING,
 223 i2d_ASN1_bio_stream,
 224 i2d_ASRange,
 225 i2d_AUTHORITY_INFO_ACCESS,
 226 i2d_AUTHORITY_KEYID,
 227 i2d_BASIC_CONSTRAINTS,
 228 i2d_CERTIFICATEPOLICIES,
 229 i2d_CMS_ContentInfo,
 230 i2d_CMS_ReceiptRequest,
 231 i2d_CMS_bio,
 232 i2d_CRL_DIST_POINTS,
 233 i2d_DHxparams,
 234 i2d_DIRECTORYSTRING,
 235 i2d_DISPLAYTEXT,
 236 i2d_DIST_POINT,
 237 i2d_DIST_POINT_NAME,
 238 i2d_DSAPrivateKey,
 239 i2d_DSAPrivateKey_bio,
 240 i2d_DSAPrivateKey_fp,
 241 i2d_DSAPublicKey,
 242 i2d_DSA_PUBKEY,
 243 i2d_DSA_PUBKEY_bio,
 244 i2d_DSA_PUBKEY_fp,
 245 i2d_DSA_SIG,
 246 i2d_DSAparams,
 247 i2d_ECDSA_SIG,
 248 i2d_ECPKParameters,
 249 i2d_ECParameters,
 250 i2d_ECPrivateKey,
 251 i2d_ECPrivateKey_bio,
 252 i2d_ECPrivateKey_fp,
 253 i2d_EC_PUBKEY,
 254 i2d_EC_PUBKEY_bio,
 255 i2d_EC_PUBKEY_fp,
 256 i2d_EDIPARTYNAME,
 257 i2d_ESS_CERT_ID,
 258 i2d_ESS_CERT_ID_V2,
 259 i2d_ESS_ISSUER_SERIAL,
 260 i2d_ESS_SIGNING_CERT,
 261 i2d_ESS_SIGNING_CERT_V2,
 262 i2d_EXTENDED_KEY_USAGE,
 263 i2d_GENERAL_NAME,
 264 i2d_GENERAL_NAMES,
 265 i2d_IPAddressChoice,
 266 i2d_IPAddressFamily,
 267 i2d_IPAddressOrRange,
 268 i2d_IPAddressRange,
 269 i2d_ISSUER_SIGN_TOOL,
 270 i2d_ISSUING_DIST_POINT,
 271 i2d_NAMING_AUTHORITY,
 272 i2d_NETSCAPE_CERT_SEQUENCE,
 273 i2d_NETSCAPE_SPKAC,
 274 i2d_NETSCAPE_SPKI,
 275 i2d_NOTICEREF,
 276 i2d_OCSP_BASICRESP,
 277 i2d_OCSP_CERTID,
 278 i2d_OCSP_CERTSTATUS,
 279 i2d_OCSP_CRLID,
 280 i2d_OCSP_ONEREQ,
 281 i2d_OCSP_REQINFO,
 282 i2d_OCSP_REQUEST,
 283 i2d_OCSP_RESPBYTES,
 284 i2d_OCSP_RESPDATA,
 285 i2d_OCSP_RESPID,
 286 i2d_OCSP_RESPONSE,
 287 i2d_OCSP_REVOKEDINFO,
 288 i2d_OCSP_SERVICELOC,
 289 i2d_OCSP_SIGNATURE,
 290 i2d_OCSP_SINGLERESP,
 291 i2d_OSSL_CMP_MSG,
 292 i2d_OSSL_CMP_PKIHEADER,
 293 i2d_OSSL_CMP_PKISI,
 294 i2d_OSSL_CRMF_CERTID,
 295 i2d_OSSL_CRMF_CERTTEMPLATE,
 296 i2d_OSSL_CRMF_ENCRYPTEDVALUE,
 297 i2d_OSSL_CRMF_MSG,
 298 i2d_OSSL_CRMF_MSGS,
 299 i2d_OSSL_CRMF_PBMPARAMETER,
 300 i2d_OSSL_CRMF_PKIPUBLICATIONINFO,
 301 i2d_OSSL_CRMF_SINGLEPUBINFO,
 302 i2d_OTHERNAME,
 303 i2d_PBE2PARAM,
 304 i2d_PBEPARAM,
 305 i2d_PBKDF2PARAM,
 306 i2d_PKCS12,
 307 i2d_PKCS12_BAGS,
 308 i2d_PKCS12_MAC_DATA,
 309 i2d_PKCS12_SAFEBAG,
 310 i2d_PKCS12_bio,
 311 i2d_PKCS12_fp,
 312 i2d_PKCS7,
 313 i2d_PKCS7_DIGEST,
 314 i2d_PKCS7_ENCRYPT,
 315 i2d_PKCS7_ENC_CONTENT,
 316 i2d_PKCS7_ENVELOPE,
 317 i2d_PKCS7_ISSUER_AND_SERIAL,
 318 i2d_PKCS7_NDEF,
 319 i2d_PKCS7_RECIP_INFO,
 320 i2d_PKCS7_SIGNED,
 321 i2d_PKCS7_SIGNER_INFO,
 322 i2d_PKCS7_SIGN_ENVELOPE,
 323 i2d_PKCS7_bio,
 324 i2d_PKCS7_fp,
 325 i2d_PKCS8PrivateKeyInfo_bio,
 326 i2d_PKCS8PrivateKeyInfo_fp,
 327 i2d_PKCS8_PRIV_KEY_INFO,
 328 i2d_PKCS8_PRIV_KEY_INFO_bio,
 329 i2d_PKCS8_PRIV_KEY_INFO_fp,
 330 i2d_PKCS8_bio,
 331 i2d_PKCS8_fp,
 332 i2d_PKEY_USAGE_PERIOD,
 333 i2d_POLICYINFO,
 334 i2d_POLICYQUALINFO,
 335 i2d_PROFESSION_INFO,
 336 i2d_PROXY_CERT_INFO_EXTENSION,
 337 i2d_PROXY_POLICY,
 338 i2d_RSA_OAEP_PARAMS,
 339 i2d_RSA_PSS_PARAMS,
 340 i2d_SCRYPT_PARAMS,
 341 i2d_SCT_LIST,
 342 i2d_SXNET,
 343 i2d_SXNETID,
 344 i2d_TS_ACCURACY,
 345 i2d_TS_MSG_IMPRINT,
 346 i2d_TS_MSG_IMPRINT_bio,
 347 i2d_TS_MSG_IMPRINT_fp,
 348 i2d_TS_REQ,
 349 i2d_TS_REQ_bio,
 350 i2d_TS_REQ_fp,
 351 i2d_TS_RESP,
 352 i2d_TS_RESP_bio,
 353 i2d_TS_RESP_fp,
 354 i2d_TS_STATUS_INFO,
 355 i2d_TS_TST_INFO,
 356 i2d_TS_TST_INFO_bio,
 357 i2d_TS_TST_INFO_fp,
 358 i2d_USERNOTICE,
 359 i2d_X509,
 360 i2d_X509_ALGOR,
 361 i2d_X509_ALGORS,
 362 i2d_X509_ATTRIBUTE,
 363 i2d_X509_CERT_AUX,
 364 i2d_X509_CINF,
 365 i2d_X509_CRL,
 366 i2d_X509_CRL_INFO,
 367 i2d_X509_CRL_bio,
 368 i2d_X509_CRL_fp,
 369 i2d_X509_EXTENSION,
 370 i2d_X509_EXTENSIONS,
 371 i2d_X509_NAME,
 372 i2d_X509_NAME_ENTRY,
 373 i2d_X509_PUBKEY,
 374 i2d_X509_PUBKEY_bio,
 375 i2d_X509_PUBKEY_fp,
 376 i2d_X509_REQ,
 377 i2d_X509_REQ_INFO,
 378 i2d_X509_REQ_bio,
 379 i2d_X509_REQ_fp,
 380 i2d_X509_REVOKED,
 381 i2d_X509_SIG,
 382 i2d_X509_VAL,
 383 - convert objects from/to ASN.1/DER representation
 384
 385 =head1 SYNOPSIS
 386
 387 =for openssl generic
 388
 389  TYPE *d2i_TYPE(TYPE **a, const unsigned char **ppin, long length);
 390  TYPE *d2i_TYPE_bio(BIO *bp, TYPE **a);
 391  TYPE *d2i_TYPE_fp(FILE *fp, TYPE **a);
 392
 393  int i2d_TYPE(const TYPE *a, unsigned char **ppout);
 394  int i2d_TYPE(TYPE *a, unsigned char **ppout);
 395  int i2d_TYPE_fp(FILE *fp, const TYPE *a);
 396  int i2d_TYPE_fp(FILE *fp, TYPE *a);
 397  int i2d_TYPE_bio(BIO *bp, const TYPE *a);
 398  int i2d_TYPE_bio(BIO *bp, TYPE *a);
 399
 400 =head1 DESCRIPTION
 401
 402 In the description here, B<I<TYPE>> is used a placeholder
 403 for any of the OpenSSL datatypes, such as B<X509_CRL>.
 404 The function parameters I<ppin> and I<ppout> are generally
 405 either both named I<pp> in the headers, or I<in> and I<out>.
 406
 407 These functions convert OpenSSL objects to and from their ASN.1/DER
 408 encoding.  Unlike the C structures which can have pointers to sub-objects
 409 within, the DER is a serialized encoding, suitable for sending over the
 410 network, writing to a file, and so on.
 411
 412 B<d2i_I<TYPE>>() attempts to decode I<len> bytes at I<*ppin>. If successful a
 413 pointer to the B<I<TYPE>> structure is returned and I<*ppin> is incremented to
 414 the byte following the parsed data.  If I<a> is not NULL then a pointer
 415 to the returned structure is also written to I<*a>.  If an error occurred
 416 then NULL is returned.
 417
 418 On a successful return, if I<*a> is not NULL then it is assumed that I<*a>
 419 contains a valid B<I<TYPE>> structure and an attempt is made to reuse it. This
 420 "reuse" capability is present for historical compatibility but its use is
 421 B<strongly discouraged> (see BUGS below, and the discussion in the RETURN
 422 VALUES section).
 423
 424 B<d2i_I<TYPE>_bio>() is similar to B<d2i_I<TYPE>>() except it attempts
 425 to parse data from BIO I<bp>.
 426
 427 B<d2i_I<TYPE>_fp>() is similar to B<d2i_I<TYPE>>() except it attempts
 428 to parse data from FILE pointer I<fp>.
 429
 430 B<i2d_I<TYPE>>() encodes the structure pointed to by I<a> into DER format.
 431 If I<ppout> is not NULL, it writes the DER encoded data to the buffer
 432 at I<*ppout>, and increments it to point after the data just written.
 433 If the return value is negative an error occurred, otherwise it
 434 returns the length of the encoded data.
 435
 436 If I<*ppout> is NULL memory will be allocated for a buffer and the encoded
 437 data written to it. In this case I<*ppout> is not incremented and it points
 438 to the start of the data just written.
 439
 440 B<i2d_I<TYPE>_bio>() is similar to B<i2d_I<TYPE>>() except it writes
 441 the encoding of the structure I<a> to BIO I<bp> and it
 442 returns 1 for success and 0 for failure.
 443
 444 B<i2d_I<TYPE>_fp>() is similar to B<i2d_I<TYPE>>() except it writes
 445 the encoding of the structure I<a> to FILE pointer I<fp> and it
 446 returns 1 for success and 0 for failure.
 447
 448 These routines do not encrypt private keys and therefore offer no
 449 security; use L<PEM_write_PrivateKey(3)> or similar for writing to files.
 450
 451 =head1 NOTES
 452
 453 The letters B<i> and B<d> in B<i2d_I<TYPE>>() stand for
 454 "internal" (that is, an internal C structure) and "DER" respectively.
 455 So B<i2d_I<TYPE>>() converts from internal to DER.
 456
 457 The functions can also understand B<BER> forms.
 458
 459 The actual TYPE structure passed to B<i2d_I<TYPE>>() must be a valid
 460 populated B<I<TYPE>> structure -- it B<cannot> simply be fed with an
 461 empty structure such as that returned by TYPE_new().
 462
 463 The encoded data is in binary form and may contain embedded zeros.
 464 Therefore, any FILE pointers or BIOs should be opened in binary mode.
 465 Functions such as strlen() will B<not> return the correct length
 466 of the encoded structure.
 467
 468 The ways that I<*ppin> and I<*ppout> are incremented after the operation
 469 can trap the unwary. See the B<WARNINGS> section for some common
 470 errors.
 471 The reason for this-auto increment behaviour is to reflect a typical
 472 usage of ASN1 functions: after one structure is encoded or decoded
 473 another will be processed after it.
 474
 475 The following points about the data types might be useful:
 476
 477 =over 4
 478
 479 =item B<ASN1_OBJECT>
 480
 481 Represents an ASN1 OBJECT IDENTIFIER.
 482
 483 =item B<DHparams>
 484
 485 Represents a PKCS#3 DH parameters structure.
 486
 487 =item B<DHxparams>
 488
 489 Represents an ANSI X9.42 DH parameters structure.
 490
 491 =item B<DSA_PUBKEY>
 492
 493 Represents a DSA public key using a B<SubjectPublicKeyInfo> structure.
 494
 495 =item B<DSAPublicKey>, B<DSAPrivateKey>
 496
 497 Use a non-standard OpenSSL format and should be avoided; use B<DSA_PUBKEY>,
 498 L<PEM_write_PrivateKey(3)>, or similar instead.
 499
 500 =item B<ECDSA_SIG>
 501
 502 Represents an ECDSA signature.
 503
 504 =item B<X509_ALGOR>
 505
 506 Represents an B<AlgorithmIdentifier> structure as used in IETF RFC 6960 and
 507 elsewhere.
 508
 509 =item B<X509_Name>
 510
 511 Represents a B<Name> type as used for subject and issuer names in
 512 IETF RFC 6960 and elsewhere.
 513
 514 =item B<X509_REQ>
 515
 516 Represents a PKCS#10 certificate request.
 517
 518 =item B<X509_SIG>
 519
 520 Represents the B<DigestInfo> structure defined in PKCS#1 and PKCS#7.
 521
 522 =back
 523
 524 =head1 RETURN VALUES
 525
 526 B<d2i_I<TYPE>>(), B<d2i_I<TYPE>_bio>() and B<d2i_I<TYPE>_fp>() return a valid
 527 B<I<TYPE>> structure or NULL if an error occurs.  If the "reuse" capability has
 528 been used with a valid structure being passed in via I<a>, then the object is
 529 freed in the event of error and I<*a> is set to NULL.
 530
 531 B<i2d_I<TYPE>>() returns the number of bytes successfully encoded or a negative
 532 value if an error occurs.
 533
 534 B<i2d_I<TYPE>_bio>() and B<i2d_I<TYPE>_fp>() return 1 for success and 0 if an
 535 error occurs.
 536
 537 =head1 EXAMPLES
 538
 539 Allocate and encode the DER encoding of an X509 structure:
 540
 541  int len;
 542  unsigned char *buf;
 543
 544  buf = NULL;
 545  len = i2d_X509(x, &buf);
 546  if (len < 0)
 547      /* error */
 548
 549 Attempt to decode a buffer:
 550
 551  X509 *x;
 552  unsigned char *buf;
 553  const unsigned char *p;
 554  int len;
 555
 556  /* Set up buf and len to point to the input buffer. */
 557  p = buf;
 558  x = d2i_X509(NULL, &p, len);
 559  if (x == NULL)
 560      /* error */
 561
 562 Alternative technique:
 563
 564  X509 *x;
 565  unsigned char *buf;
 566  const unsigned char *p;
 567  int len;
 568
 569  /* Set up buf and len to point to the input buffer. */
 570  p = buf;
 571  x = NULL;
 572
 573  if (d2i_X509(&x, &p, len) == NULL)
 574      /* error */
 575
 576 =head1 WARNINGS
 577
 578 Using a temporary variable is mandatory. A common
 579 mistake is to attempt to use a buffer directly as follows:
 580
 581  int len;
 582  unsigned char *buf;
 583
 584  len = i2d_X509(x, NULL);
 585  buf = OPENSSL_malloc(len);
 586  ...
 587  i2d_X509(x, &buf);
 588  ...
 589  OPENSSL_free(buf);
 590
 591 This code will result in I<buf> apparently containing garbage because
 592 it was incremented after the call to point after the data just written.
 593 Also I<buf> will no longer contain the pointer allocated by OPENSSL_malloc()
 594 and the subsequent call to OPENSSL_free() is likely to crash.
 595
 596 Another trap to avoid is misuse of the I<a> argument to B<d2i_I<TYPE>>():
 597
 598  X509 *x;
 599
 600  if (d2i_X509(&x, &p, len) == NULL)
 601      /* error */
 602
 603 This will probably crash somewhere in d2i_X509(). The reason for this
 604 is that the variable I<x> is uninitialized and an attempt will be made to
 605 interpret its (invalid) value as an B<X509> structure, typically causing
 606 a segmentation violation. If I<x> is set to NULL first then this will not
 607 happen.
 608
 609 =head1 BUGS
 610
 611 In some versions of OpenSSL the "reuse" behaviour of B<d2i_I<TYPE>>() when
 612 I<*a> is valid is broken and some parts of the reused structure may
 613 persist if they are not present in the new one. Additionally, in versions of
 614 OpenSSL prior to 1.1.0, when the "reuse" behaviour is used and an error occurs
 615 the behaviour is inconsistent. Some functions behaved as described here, while
 616 some did not free I<*a> on error and did not set I<*a> to NULL.
 617
 618 As a result of the above issues the "reuse" behaviour is strongly discouraged.
 619
 620 B<i2d_I<TYPE>>() will not return an error in many versions of OpenSSL,
 621 if mandatory fields are not initialized due to a programming error
 622 then the encoded structure may contain invalid data or omit the
 623 fields entirely and will not be parsed by B<d2i_I<TYPE>>(). This may be
 624 fixed in future so code should not assume that B<i2d_I<TYPE>>() will
 625 always succeed.
 626
 627 Any function which encodes a structure (B<i2d_I<TYPE>>(),
 628 B<i2d_I<TYPE>>() or B<i2d_I<TYPE>>()) may return a stale encoding if the
 629 structure has been modified after deserialization or previous
 630 serialization. This is because some objects cache the encoding for
 631 efficiency reasons.
 632
 633 =head1 COPYRIGHT
 634
 635 Copyright 1998-2020 The OpenSSL Project Authors. All Rights Reserved.
 636
 637 Licensed under the Apache License 2.0 (the "License").  You may not use
 638 this file except in compliance with the License.  You can obtain a copy
 639 in the file LICENSE in the source distribution or at
 640 L<https://www.openssl.org/source/license.html>.
 641
 642 =cut