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=pod

=head1 NAME

ASN1_TYPE_get, ASN1_TYPE_set, ASN1_TYPE_set1, ASN1_TYPE_cmp, ASN1_TYPE_unpack_sequence, ASN1_TYPE_pack_sequence - ASN1_TYPE utility
functions

=head1 SYNOPSIS

 #include <openssl/asn1.h>

 int ASN1_TYPE_get(const ASN1_TYPE *a);
 void ASN1_TYPE_set(ASN1_TYPE *a, int type, void *value);
 int ASN1_TYPE_set1(ASN1_TYPE *a, int type, const void *value);
 int ASN1_TYPE_cmp(const ASN1_TYPE *a, const ASN1_TYPE *b);

 void *ASN1_TYPE_unpack_sequence(const ASN1_ITEM *it, const ASN1_TYPE *t);
 ASN1_TYPE *ASN1_TYPE_pack_sequence(const ASN1_ITEM *it, void *s,
                                    ASN1_TYPE **t);

=head1 DESCRIPTION

These functions allow an ASN1_TYPE structure to be manipulated. The
ASN1_TYPE structure can contain any ASN.1 type or constructed type
such as a SEQUENCE: it is effectively equivalent to the ASN.1 ANY type.

ASN1_TYPE_get() returns the type of B<a>.

ASN1_TYPE_set() sets the value of B<a> to B<type> and B<value>. This
function uses the pointer B<value> internally so it must B<not> be freed
up after the call.

ASN1_TYPE_set1() sets the value of B<a> to B<type> a copy of B<value>.

ASN1_TYPE_cmp() compares ASN.1 types B<a> and B<b> and returns 0 if
they are identical and non-zero otherwise.

ASN1_TYPE_unpack_sequence() attempts to parse the SEQUENCE present in
B<t> using the ASN.1 structure B<it>. If successful it returns a pointer
to the ASN.1 structure corresponding to B<it> which must be freed by the
caller. If it fails it return NULL.

ASN1_TYPE_pack_sequence() attempts to encode the ASN.1 structure B<s>
corresponding to B<it> into an ASN1_TYPE. If successful the encoded
ASN1_TYPE is returned. If B<t> and B<*t> are not NULL the encoded type
is written to B<t> overwriting any existing data. If B<t> is not NULL
but B<*t> is NULL the returned ASN1_TYPE is written to B<*t>.

=head1 NOTES

The type and meaning of the B<value> parameter for ASN1_TYPE_set() and
ASN1_TYPE_set1() is determined by the B<type> parameter.
If B<type> is V_ASN1_NULL B<value> is ignored. If B<type> is V_ASN1_BOOLEAN
then the boolean is set to TRUE if B<value> is not NULL. If B<type> is
V_ASN1_OBJECT then value is an ASN1_OBJECT structure. Otherwise B<type>
is and ASN1_STRING structure. If B<type> corresponds to a primitive type
(or a string type) then the contents of the ASN1_STRING contain the content
octets of the type. If B<type> corresponds to a constructed type or
a tagged type (V_ASN1_SEQUENCE, V_ASN1_SET or V_ASN1_OTHER) then the
ASN1_STRING contains the entire ASN.1 encoding verbatim (including tag and
length octets).

ASN1_TYPE_cmp() may not return zero if two types are equivalent but have
different encodings. For example the single content octet of the boolean TRUE
value under BER can have any non-zero encoding but ASN1_TYPE_cmp() will
only return zero if the values are the same.

If either or both of the parameters passed to ASN1_TYPE_cmp() is NULL the
return value is non-zero. Technically if both parameters are NULL the two
types could be absent OPTIONAL fields and so should match, however passing
NULL values could also indicate a programming error (for example an
unparsable type which returns NULL) for types which do B<not> match. So
applications should handle the case of two absent values separately.

=head1 RETURN VALUES

ASN1_TYPE_get() returns the type of the ASN1_TYPE argument.

ASN1_TYPE_set() does not return a value.

ASN1_TYPE_set1() returns 1 for success and 0 for failure.

ASN1_TYPE_cmp() returns 0 if the types are identical and non-zero otherwise.

ASN1_TYPE_unpack_sequence() returns a pointer to an ASN.1 structure or
NULL on failure.

ASN1_TYPE_pack_sequence() return an ASN1_TYPE structure if it succeeds or
NULL on failure.

=head1 COPYRIGHT

Copyright 2015-2020 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
L<https://www.openssl.org/source/license.html>.

=cut