=pod

=head1 NAME

X509v3_get_ext_count, X509v3_get_ext, X509v3_get_ext_by_NID,
X509v3_get_ext_by_OBJ, X509v3_get_ext_by_critical, X509v3_delete_ext,
X509v3_add_ext, X509_get0_extensions, X509_CRL_get0_extensions,
X509_REVOKED_get0_extensions, X509_get_ext_count, X509_get_ext,
X509_get_ext_by_NID, X509_get_ext_by_OBJ, X509_get_ext_by_critical,
X509_delete_ext, X509_add_ext, X509_CRL_get_ext_count, X509_CRL_get_ext,
X509_CRL_get_ext_by_NID, X509_CRL_get_ext_by_OBJ, X509_CRL_get_ext_by_critical,
X509_CRL_delete_ext, X509_CRL_add_ext, X509_REVOKED_get_ext_count,
X509_REVOKED_get_ext, X509_REVOKED_get_ext_by_NID, X509_REVOKED_get_ext_by_OBJ,
X509_REVOKED_get_ext_by_critical, X509_REVOKED_delete_ext,
X509_REVOKED_add_ext - extension stack utility functions.

=head1 SYNOPSIS

 #include <openssl/x509.h>

 int X509v3_get_ext_count(const STACK_OF(X509_EXTENSION) *x);
 X509_EXTENSION *X509v3_get_ext(const STACK_OF(X509_EXTENSION) *x, int loc);

 int X509v3_get_ext_by_NID(const STACK_OF(X509_EXTENSION) *x,
                           int nid, int lastpos);
 int X509v3_get_ext_by_OBJ(const STACK_OF(X509_EXTENSION) *x,
                           ASN1_OBJECT *obj, int lastpos);
 int X509v3_get_ext_by_critical(const STACK_OF(X509_EXTENSION) *x,
                                int crit, int lastpos);
 X509_EXTENSION *X509v3_delete_ext(STACK_OF(X509_EXTENSION) *x, int loc);
 STACK_OF(X509_EXTENSION) *X509v3_add_ext(STACK_OF(X509_EXTENSION) **x,
                                          X509_EXTENSION *ex, int loc);

 STACK_OF(X509_EXTENSION) *X509_get0_extensions(const X509 *x);
 STACK_OF(X509_EXTENSION) *X509_CRL_get0_extensions(X509_CRL *crl);
 STACK_OF(X509_EXTENSION) *X509_REVOKED_get0_extensions(X509_REVOKED *r);

 int X509_get_ext_count(X509 *x);
 X509_EXTENSION *X509_get_ext(X509 *x, int loc);
 int X509_get_ext_by_NID(X509 *x, int nid, int lastpos);
 int X509_get_ext_by_OBJ(X509 *x, ASN1_OBJECT *obj, int lastpos);
 int X509_get_ext_by_critical(X509 *x, int crit, int lastpos);
 X509_EXTENSION *X509_delete_ext(X509 *x, int loc);
 int X509_add_ext(X509 *x, X509_EXTENSION *ex, int loc);

 int X509_CRL_get_ext_count(X509_CRL *x);
 X509_EXTENSION *X509_CRL_get_ext(X509_CRL *x, int loc);
 int X509_CRL_get_ext_by_NID(X509_CRL *x, int nid, int lastpos);
 int X509_CRL_get_ext_by_OBJ(X509_CRL *x, ASN1_OBJECT *obj, int lastpos);
 int X509_CRL_get_ext_by_critical(X509_CRL *x, int crit, int lastpos);
 X509_EXTENSION *X509_CRL_delete_ext(X509_CRL *x, int loc);
 int X509_CRL_add_ext(X509_CRL *x, X509_EXTENSION *ex, int loc);

 int X509_REVOKED_get_ext_count(X509_REVOKED *x);
 X509_EXTENSION *X509_REVOKED_get_ext(X509_REVOKED *x, int loc);
 int X509_REVOKED_get_ext_by_NID(X509_REVOKED *x, int nid, int lastpos);
 int X509_REVOKED_get_ext_by_OBJ(X509_REVOKED *x, ASN1_OBJECT *obj,
                                int lastpos);
 int X509_REVOKED_get_ext_by_critical(X509_REVOKED *x, int crit, int lastpos);
 X509_EXTENSION *X509_REVOKED_delete_ext(X509_REVOKED *x, int loc);
 int X509_REVOKED_add_ext(X509_REVOKED *x, X509_EXTENSION *ex, int loc);

=head1 DESCRIPTION

X509v3_get_ext_count() retrieves the number of extensions in B<x>.

X509v3_get_ext() retrieves extension B<loc> from B<x>. The index B<loc>
can take any value from B<0> to X509_get_ext_count(x) - 1. The returned
extension is an internal pointer which B<must not> be freed up by the
application.

X509v3_get_ext_by_NID() and X509v3_get_ext_by_OBJ() look for an extension
with B<nid> or B<obj> from extension stack B<x>. The search starts from the
extension after B<lastpos> or from the beginning if <lastpos> is B<-1>. If
the extension is found its index is returned otherwise B<-1> is returned.

X509v3_get_ext_by_critical() is similar to X509v3_get_ext_by_NID() except it
looks for an extension of criticality B<crit>. A zero value for B<crit>
looks for a non-critical extension a non-zero value looks for a critical
extension.

X509v3_delete_ext() deletes the extension with index B<loc> from B<x>. The
deleted extension is returned and must be freed by the caller. If B<loc>
is in invalid index value B<NULL> is returned.

X509v3_add_ext() adds extension B<ex> to stack B<*x> at position B<loc>. If
B<loc> is B<-1> the new extension is added to the end. If B<*x> is B<NULL>
a new stack will be allocated. The passed extension B<ex> is duplicated
internally so it must be freed after use.

X509_get0_extensions(), X509_CRL_get0_extensions() and
X509_REVOKED_get0_extensions() retrieve the extensions from a certificate
a CRL or a CRL entry respectively.

X509_get_ext_count(), X509_get_ext(), X509_get_ext_by_NID(),
X509_get_ext_by_OBJ(), X509_get_ext_by_critical(), X509_delete_ext()
and X509_add_ext() operate on the extensions of certificate B<x> they are
otherwise identical to the X509v3 functions.

X509_CRL_get_ext_count(), X509_CRL_get_ext(), X509_CRL_get_ext_by_NID(),
X509_CRL_get_ext_by_OBJ(), X509_CRL_get_ext_by_critical(),
X509_CRL_delete_ext() and X509_CRL_add_ext() operate on the extensions of
CRL B<x> they are otherwise identical to the X509v3 functions.

X509_REVOKED_get_ext_count(), X509_REVOKED_get_ext(),
X509_REVOKED_get_ext_by_NID(), X509_REVOKED_get_ext_by_OBJ(),
X509_REVOKED_get_ext_by_critical(), X509_REVOKED_delete_ext() and
X509_REVOKED_add_ext() operate on the extensions of CRL entry B<x>
they are otherwise identical to the X509v3 functions.

=head1 NOTES

These functions are used to examine stacks of extensions directly. Many
applications will want to parse or encode and add an extension: they should
use the extension encode and decode functions instead such as
X509_add1_ext_i2d() and X509_get_ext_d2i().

Extension indices start from zero, so a zero index return value is B<not> an
error. These search functions start from the extension B<after> the B<lastpos>
parameter so it should initially be set to B<-1>, if it is set to zero the
initial extension will not be checked.

=head1 RETURN VALUES

X509v3_get_ext_count() returns the extension count.

X509v3_get_ext() and X509v3_delete_ext() return an B<X509_EXTENSION> pointer
or B<NULL> if an error occurs.

X509v3_get_ext_by_NID() X509v3_get_ext_by_OBJ() and
X509v3_get_ext_by_critical() return the an extension index or B<-1> if an
error occurs.

X509v3_add_ext() returns a stack of extensions or B<NULL> on error.

X509_get0_extensions(), X509_CRL_get0_extensions() and
X509_REVOKED_get0_extensions() return a stack of extensions. If the extensions
field is absent it will return B<NULL>: this is B<not> an error condition.

=head1 SEE ALSO

L<X509V3_get_d2i(3)>

=head1 COPYRIGHT

Copyright 2015-2016 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
