OBJ_nid2obj.pod revision 337982 
1=pod
2
3=head1 NAME
4
5OBJ_nid2obj, OBJ_nid2ln, OBJ_nid2sn, OBJ_obj2nid, OBJ_txt2nid, OBJ_ln2nid, OBJ_sn2nid,
6OBJ_cmp, OBJ_dup, OBJ_txt2obj, OBJ_obj2txt, OBJ_create, OBJ_cleanup - ASN1 object utility
7functions
8
9=head1 SYNOPSIS
10
11 #include <openssl/objects.h>
12
13 ASN1_OBJECT * OBJ_nid2obj(int n);
14 const char *  OBJ_nid2ln(int n);
15 const char *  OBJ_nid2sn(int n);
16
17 int OBJ_obj2nid(const ASN1_OBJECT *o);
18 int OBJ_ln2nid(const char *ln);
19 int OBJ_sn2nid(const char *sn);
20
21 int OBJ_txt2nid(const char *s);
22
23 ASN1_OBJECT * OBJ_txt2obj(const char *s, int no_name);
24 int OBJ_obj2txt(char *buf, int buf_len, const ASN1_OBJECT *a, int no_name);
25
26 int OBJ_cmp(const ASN1_OBJECT *a,const ASN1_OBJECT *b);
27 ASN1_OBJECT * OBJ_dup(const ASN1_OBJECT *o);
28
29 int OBJ_create(const char *oid,const char *sn,const char *ln);
30 void OBJ_cleanup(void);
31
32=head1 DESCRIPTION
33
34The ASN1 object utility functions process ASN1_OBJECT structures which are
35a representation of the ASN1 OBJECT IDENTIFIER (OID) type.
36For convenience, OIDs are usually represented in source code as numeric
37identifiers, or B<NID>s.  OpenSSL has an internal table of OIDs that
38are generated when the library is built, and their corresponding NIDs
39are available as defined constants.  For the functions below, application
40code should treat all returned values -- OIDs, NIDs, or names -- as
41constants.
42
43OBJ_nid2obj(), OBJ_nid2ln() and OBJ_nid2sn() convert the NID B<n> to 
44an ASN1_OBJECT structure, its long name and its short name respectively,
45or B<NULL> if an error occurred.
46
47OBJ_obj2nid(), OBJ_ln2nid(), OBJ_sn2nid() return the corresponding NID
48for the object B<o>, the long name <ln> or the short name <sn> respectively
49or NID_undef if an error occurred.
50
51OBJ_txt2nid() returns NID corresponding to text string <s>. B<s> can be
52a long name, a short name or the numerical respresentation of an object.
53
54OBJ_txt2obj() converts the text string B<s> into an ASN1_OBJECT structure.
55If B<no_name> is 0 then long names and short names will be interpreted
56as well as numerical forms. If B<no_name> is 1 only the numerical form
57is acceptable.
58
59OBJ_obj2txt() converts the B<ASN1_OBJECT> B<a> into a textual representation.
60The representation is written as a null terminated string to B<buf>
61at most B<buf_len> bytes are written, truncating the result if necessary.
62The total amount of space required is returned. If B<no_name> is 0 then
63if the object has a long or short name then that will be used, otherwise
64the numerical form will be used. If B<no_name> is 1 then the numerical
65form will always be used.
66
67OBJ_cmp() compares B<a> to B<b>. If the two are identical 0 is returned.
68
69OBJ_dup() returns a copy of B<o>.
70
71OBJ_create() adds a new object to the internal table. B<oid> is the 
72numerical form of the object, B<sn> the short name and B<ln> the
73long name. A new NID is returned for the created object.
74
75OBJ_cleanup() cleans up OpenSSLs internal object table: this should
76be called before an application exits if any new objects were added
77using OBJ_create().
78
79=head1 NOTES
80
81Objects in OpenSSL can have a short name, a long name and a numerical
82identifier (NID) associated with them. A standard set of objects is
83represented in an internal table. The appropriate values are defined
84in the header file B<objects.h>.
85
86For example the OID for commonName has the following definitions:
87
88 #define SN_commonName                   "CN"
89 #define LN_commonName                   "commonName"
90 #define NID_commonName                  13
91
92New objects can be added by calling OBJ_create().
93
94Table objects have certain advantages over other objects: for example
95their NIDs can be used in a C language switch statement. They are
96also static constant structures which are shared: that is there
97is only a single constant structure for each table object.
98
99Objects which are not in the table have the NID value NID_undef.
100
101Objects do not need to be in the internal tables to be processed,
102the functions OBJ_txt2obj() and OBJ_obj2txt() can process the numerical
103form of an OID.
104
105Some objects are used to represent algorithms which do not have a
106corresponding ASN.1 OBJECT IDENTIFIER encoding (for example no OID currently
107exists for a particular algorithm). As a result they B<cannot> be encoded or
108decoded as part of ASN.1 structures. Applications can determine if there
109is a corresponding OBJECT IDENTIFIER by checking OBJ_length() is not zero.
110
111These functions cannot return B<const> because an B<ASN1_OBJECT> can
112represent both an internal, constant, OID and a dynamically-created one.
113The latter cannot be constant because it needs to be freed after use.
114
115=head1 EXAMPLES
116
117Create an object for B<commonName>:
118
119 ASN1_OBJECT *o;
120 o = OBJ_nid2obj(NID_commonName);
121
122Check if an object is B<commonName>
123
124 if (OBJ_obj2nid(obj) == NID_commonName)
125        /* Do something */
126
127Create a new NID and initialize an object from it:
128
129 int new_nid;
130 ASN1_OBJECT *obj;
131
132 new_nid = OBJ_create("1.2.3.4", "NewOID", "New Object Identifier");
133
134 obj = OBJ_nid2obj(new_nid);
135 
136Create a new object directly:
137
138 obj = OBJ_txt2obj("1.2.3.4", 1);
139
140=head1 BUGS
141
142OBJ_obj2txt() is awkward and messy to use: it doesn't follow the 
143convention of other OpenSSL functions where the buffer can be set
144to B<NULL> to determine the amount of data that should be written.
145Instead B<buf> must point to a valid buffer and B<buf_len> should
146be set to a positive value. A buffer length of 80 should be more
147than enough to handle any OID encountered in practice.
148
149=head1 RETURN VALUES
150
151OBJ_nid2obj() returns an B<ASN1_OBJECT> structure or B<NULL> is an
152error occurred.
153It returns a pointer to an internal table and does not
154allocate memory; ASN1_OBJECT_free() will have no effect.
155
156OBJ_nid2ln() and OBJ_nid2sn() returns a valid string or B<NULL>
157on error.
158
159OBJ_obj2nid(), OBJ_ln2nid(), OBJ_sn2nid() and OBJ_txt2nid() return
160a NID or B<NID_undef> on error.
161
162=head1 SEE ALSO
163
164L<ERR_get_error(3)|ERR_get_error(3)>
165
166=head1 HISTORY
167
168TBA
169
170=cut
171