openssl/doc/crypto/OBJ_nid2obj.pod

=pod

=head1 NAME

OBJ_nid2obj, OBJ_nid2ln, OBJ_nid2sn, OBJ_obj2nid, OBJ_txt2nid, OBJ_ln2nid, OBJ_sn2nid,
OBJ_cmp, OBJ_dup, OBJ_txt2obj, OBJ_obj2txt, OBJ_create, OBJ_cleanup - ASN1 object utility
functions

=head1 SYNOPSIS

 #include <openssl/objects.h>

 ASN1_OBJECT * OBJ_nid2obj(int n);
 const char *  OBJ_nid2ln(int n);
 const char *  OBJ_nid2sn(int n);

 int OBJ_obj2nid(const ASN1_OBJECT *o);
 int OBJ_ln2nid(const char *ln);
 int OBJ_sn2nid(const char *sn);

 int OBJ_txt2nid(const char *s);

 ASN1_OBJECT * OBJ_txt2obj(const char *s, int no_name);
 int OBJ_obj2txt(char *buf, int buf_len, const ASN1_OBJECT *a, int no_name);

 int OBJ_cmp(const ASN1_OBJECT *a,const ASN1_OBJECT *b);
 ASN1_OBJECT * OBJ_dup(const ASN1_OBJECT *o);

 int OBJ_create(const char *oid,const char *sn,const char *ln);
 void OBJ_cleanup(void);

 size_t OBJ_length(const ASN1_OBJECT *obj);
 const unsigned char *OBJ_get0_data(const ASN1_OBJECT *obj);

=head1 DESCRIPTION

The ASN1 object utility functions process ASN1_OBJECT structures which are
a representation of the ASN1 OBJECT IDENTIFIER (OID) type.

OBJ_nid2obj(), OBJ_nid2ln() and OBJ_nid2sn() convert the NID B<n> to 
an ASN1_OBJECT structure, its long name and its short name respectively,
or B<NULL> is an error occurred.

OBJ_obj2nid(), OBJ_ln2nid(), OBJ_sn2nid() return the corresponding NID
for the object B<o>, the long name <ln> or the short name <sn> respectively
or NID_undef if an error occurred.

OBJ_txt2nid() returns NID corresponding to text string <s>. B<s> can be
a long name, a short name or the numerical representation of an object.

OBJ_txt2obj() converts the text string B<s> into an ASN1_OBJECT structure.
If B<no_name> is 0 then long names and short names will be interpreted
as well as numerical forms. If B<no_name> is 1 only the numerical form
is acceptable.

OBJ_obj2txt() converts the B<ASN1_OBJECT> B<a> into a textual representation.
The representation is written as a null terminated string to B<buf>
at most B<buf_len> bytes are written, truncating the result if necessary.
The total amount of space required is returned. If B<no_name> is 0 then
if the object has a long or short name then that will be used, otherwise
the numerical form will be used. If B<no_name> is 1 then the numerical
form will always be used.

OBJ_cmp() compares B<a> to B<b>. If the two are identical 0 is returned.

OBJ_dup() returns a copy of B<o>.

OBJ_create() adds a new object to the internal table. B<oid> is the 
numerical form of the object, B<sn> the short name and B<ln> the
long name. A new NID is returned for the created object.

OBJ_cleanup() cleans up OpenSSLs internal object table: this should
be called before an application exits if any new objects were added
using OBJ_create().

OBJ_length() returns the size of the content octets of B<obj>.

OBJ_get0_data() returns a pointer to the content octets of B<obj>.
The returned pointer is an internal pointer which B<must not> be freed.

=head1 NOTES

Objects in OpenSSL can have a short name, a long name and a numerical
identifier (NID) associated with them. A standard set of objects is
represented in an internal table. The appropriate values are defined
in the header file B<objects.h>.

For example the OID for commonName has the following definitions:

 #define SN_commonName                   "CN"
 #define LN_commonName                   "commonName"
 #define NID_commonName                  13

New objects can be added by calling OBJ_create().

Table objects have certain advantages over other objects: for example
their NIDs can be used in a C language switch statement. They are
also static constant structures which are shared: that is there
is only a single constant structure for each table object.

Objects which are not in the table have the NID value NID_undef.

Objects do not need to be in the internal tables to be processed,
the functions OBJ_txt2obj() and OBJ_obj2txt() can process the numerical
form of an OID.

Some objects are used to represent algorithms which do not have a
corresponding ASN.1 OBJECT IDENTIFIER encoding (for example no OID currently
exists for a particular algorithm). As a result they B<cannot> be encoded or
decoded as part of ASN.1 structures. Applications can determine if there
is a corresponding OBJECT IDENTIFIER by checking OBJ_length() is not zero.

=head1 EXAMPLES

Create an object for B<commonName>:

 ASN1_OBJECT *o;
 o = OBJ_nid2obj(NID_commonName);

Check if an object is B<commonName>

 if (OBJ_obj2nid(obj) == NID_commonName)
	/* Do something */

Create a new NID and initialize an object from it:

 int new_nid;
 ASN1_OBJECT *obj;
 new_nid = OBJ_create("1.2.3.4", "NewOID", "New Object Identifier");

 obj = OBJ_nid2obj(new_nid);
 
Create a new object directly:

 obj = OBJ_txt2obj("1.2.3.4", 1);

=head1 BUGS

OBJ_obj2txt() is awkward and messy to use: it doesn't follow the 
convention of other OpenSSL functions where the buffer can be set
to B<NULL> to determine the amount of data that should be written.
Instead B<buf> must point to a valid buffer and B<buf_len> should
be set to a positive value. A buffer length of 80 should be more
than enough to handle any OID encountered in practice.

=head1 RETURN VALUES

OBJ_nid2obj() returns an B<ASN1_OBJECT> structure or B<NULL> is an
error occurred.

OBJ_nid2ln() and OBJ_nid2sn() returns a valid string or B<NULL>
on error.

OBJ_obj2nid(), OBJ_ln2nid(), OBJ_sn2nid() and OBJ_txt2nid() return
a NID or B<NID_undef> on error.

=head1 SEE ALSO

L<ERR_get_error(3)|ERR_get_error(3)>

=head1 HISTORY

TBA

=cut