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.IX Title "ASN1_ITEM_D2I_BIO 3ossl"
.TH ASN1_ITEM_D2I_BIO 3ossl 2026-06-09 3.5.7 OpenSSL
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.nh
.SH NAME
ASN1_item_d2i_ex, ASN1_item_d2i, ASN1_item_d2i_bio_ex, ASN1_item_d2i_bio,
ASN1_item_d2i_fp_ex, ASN1_item_d2i_fp, ASN1_item_i2d_mem_bio,
ASN1_item_pack, ASN1_item_unpack_ex, ASN1_item_unpack
\&\- decode and encode DER\-encoded ASN.1 structures
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/asn1.h>
\&
\& ASN1_VALUE *ASN1_item_d2i_ex(ASN1_VALUE **pval, const unsigned char **in,
\&                              long len, const ASN1_ITEM *it,
\&                              OSSL_LIB_CTX *libctx, const char *propq);
\& ASN1_VALUE *ASN1_item_d2i(ASN1_VALUE **pval, const unsigned char **in,
\&                           long len, const ASN1_ITEM *it);
\&
\& void *ASN1_item_d2i_bio_ex(const ASN1_ITEM *it, BIO *in, void *x,
\&                            OSSL_LIB_CTX *libctx, const char *propq);
\& void *ASN1_item_d2i_bio(const ASN1_ITEM *it, BIO *in, void *x);
\&
\& void *ASN1_item_d2i_fp_ex(const ASN1_ITEM *it, FILE *in, void *x,
\&                           OSSL_LIB_CTX *libctx, const char *propq);
\& void *ASN1_item_d2i_fp(const ASN1_ITEM *it, FILE *in, void *x);
\&
\& BIO *ASN1_item_i2d_mem_bio(const ASN1_ITEM *it, const ASN1_VALUE *val);
\&
\& ASN1_STRING *ASN1_item_pack(void *obj, const ASN1_ITEM *it, ASN1_STRING **oct);
\&
\& void *ASN1_item_unpack(const ASN1_STRING *oct, const ASN1_ITEM *it);
\&
\& void *ASN1_item_unpack_ex(const ASN1_STRING *oct, const ASN1_ITEM *it,
\&                          OSSL_LIB_CTX *libctx, const char *propq);
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
\&\fBASN1_item_d2i_ex()\fR decodes the contents of the data stored in \fI*in\fR of length
\&\fIlen\fR which must be a DER\-encoded ASN.1 structure, using the ASN.1 template
\&\fIit\fR. It places the result in \fI*pval\fR unless \fIpval\fR is NULL. If \fI*pval\fR is
non\-NULL on entry then the \fBASN1_VALUE\fR present there will be reused. Otherwise
a new \fBASN1_VALUE\fR will be allocated. If any algorithm fetches are required
during the process then they will use the \fBOSSL_LIB_CTX\fRprovided in the
\&\fIlibctx\fR parameter and the property query string in \fIpropq\fR. See
"ALGORITHM FETCHING" in \fBcrypto\fR\|(7) for more information about algorithm fetching.
On exit \fI*in\fR will be updated to point to the next byte in the buffer after the
decoded structure.
.PP
\&\fBASN1_item_d2i()\fR is the same as \fBASN1_item_d2i_ex()\fR except that the default
OSSL_LIB_CTX is used (i.e. NULL) and with a NULL property query string.
.PP
\&\fBASN1_item_d2i_bio_ex()\fR decodes the contents of its input BIO \fIin\fR,
which must be a DER\-encoded ASN.1 structure, using the ASN.1 template \fIit\fR
and places the result in \fI*pval\fR unless \fIpval\fR is NULL.
If \fIin\fR is NULL it returns NULL, else a pointer to the parsed structure. If any
algorithm fetches are required during the process then they will use the
\&\fBOSSL_LIB_CTX\fR provided in the \fIlibctx\fR parameter and the property query
string in \fIpropq\fR. See "ALGORITHM FETCHING" in \fBcrypto\fR\|(7) for more information
about algorithm fetching.
.PP
When reading from \fIin\fR, decoding consumes one complete DER\-encoded structure
and leaves any following bytes in the BIO, so concatenated structures can be
read with successive calls. Reaching the end of the input cleanly, at a
structure boundary, is not treated as an error: the function returns NULL
without adding to the error queue. If the end of the input is reached in the
middle of a structure, or an indefinite\-length value is missing its
end\-of\-contents octets (that is, the input is truncated), an error is queued
with reason code \fBASN1_R_NOT_ENOUGH_DATA\fR. The same applies to
\&\fBASN1_item_d2i_fp_ex()\fR.
.PP
\&\fBASN1_item_d2i_bio()\fR is the same as \fBASN1_item_d2i_bio_ex()\fR except that the
default \fBOSSL_LIB_CTX\fR is used (i.e. NULL) and with a NULL property query
string.
.PP
\&\fBASN1_item_d2i_fp_ex()\fR is the same as \fBASN1_item_d2i_bio_ex()\fR except that a FILE
pointer is provided instead of a BIO.
.PP
\&\fBASN1_item_d2i_fp()\fR is the same as \fBASN1_item_d2i_fp_ex()\fR except that the
default \fBOSSL_LIB_CTX\fR is used (i.e. NULL) and with a NULL property query
string.
.PP
\&\fBASN1_item_i2d_mem_bio()\fR encodes the given ASN.1 value \fIval\fR
using the ASN.1 template \fIit\fR and returns the result in a memory BIO.
.PP
\&\fBASN1_item_pack()\fR encodes the given ASN.1 value in \fIobj\fR using the
ASN.1 template \fIit\fR and returns an \fBASN1_STRING\fR object. If the passed in
\&\fI*oct\fR is not NULL then this is used to store the returned result, otherwise
a new \fBASN1_STRING\fR object is created. If \fIoct\fR is not NULL and \fI*oct\fR is NULL
then the returned return is also set into \fI*oct\fR. If there is an error the optional
passed in \fBASN1_STRING\fR will not be freed, but the previous value may be cleared when
ASN1_STRING_set0(*oct, NULL, 0) is called internally.
.PP
\&\fBASN1_item_unpack()\fR uses \fBASN1_item_d2i()\fR to decode the DER\-encoded \fBASN1_STRING\fR
\&\fIoct\fR using the ASN.1 template \fIit\fR.
.PP
\&\fBASN1_item_unpack_ex()\fR is similar to \fBASN1_item_unpack()\fR, but uses \fBASN1_item_d2i_ex()\fR so
that the \fIlibctx\fR and \fIpropq\fR can be used when doing algorithm fetching.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBASN1_item_d2i_bio()\fR, \fBASN1_item_unpack_ex()\fR and \fBASN1_item_unpack()\fR return a pointer to
an \fBASN1_VALUE\fR or NULL on error.
.PP
The \fBASN1_item_d2i_bio()\fR and \fBASN1_item_d2i_fp()\fR functions, including their
\&\fB_ex\fR variants, also return NULL at a clean end of input. In that case the
error queue is left unchanged, so a caller reading concatenated structures in
a loop can distinguish a clean end of input from a decoding error by
inspecting the error queue, for example with \fBERR_peek_error\fR\|(3).
.PP
\&\fBASN1_item_i2d_mem_bio()\fR returns a pointer to a memory BIO or NULL on error.
.PP
\&\fBASN1_item_pack()\fR returns a pointer to an \fBASN1_STRING\fR or NULL on error.
.SH HISTORY
.IX Header "HISTORY"
The functions \fBASN1_item_d2i_ex()\fR, \fBASN1_item_d2i_bio_ex()\fR, \fBASN1_item_d2i_fp_ex()\fR
and \fBASN1_item_i2d_mem_bio()\fR were added in OpenSSL 3.0.
.PP
The function \fBASN1_item_unpack_ex()\fR was added in OpenSSL 3.2.
.SH COPYRIGHT
.IX Header "COPYRIGHT"
Copyright 2021\-2026 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the Apache License 2.0 (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>.
