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-rw-r--r--doc/crypto/OBJ_nid2obj.pod21
1 files changed, 20 insertions, 1 deletions
diff --git a/doc/crypto/OBJ_nid2obj.pod b/doc/crypto/OBJ_nid2obj.pod
index 1e45dd40f6bb..b8d289673dee 100644
--- a/doc/crypto/OBJ_nid2obj.pod
+++ b/doc/crypto/OBJ_nid2obj.pod
@@ -33,6 +33,12 @@ functions
The ASN1 object utility functions process ASN1_OBJECT structures which are
a representation of the ASN1 OBJECT IDENTIFIER (OID) type.
+For convenience, OIDs are usually represented in source code as numeric
+identifiers, or B<NID>s. OpenSSL has an internal table of OIDs that
+are generated when the library is built, and their corresponding NIDs
+are available as defined constants. For the functions below, application
+code should treat all returned values -- OIDs, NIDs, or names -- as
+constants.
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,
@@ -96,6 +102,16 @@ 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.
+
+These functions cannot return B<const> because an B<ASN1_OBJECT> can
+represent both an internal, constant, OID and a dynamically-created one.
+The latter cannot be constant because it needs to be freed after use.
+
=head1 EXAMPLES
Create an object for B<commonName>:
@@ -106,12 +122,13 @@ Create an object for B<commonName>:
Check if an object is B<commonName>
if (OBJ_obj2nid(obj) == NID_commonName)
- /* Do something */
+ /* 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);
@@ -133,6 +150,8 @@ than enough to handle any OID encountered in practice.
OBJ_nid2obj() returns an B<ASN1_OBJECT> structure or B<NULL> is an
error occurred.
+It returns a pointer to an internal table and does not
+allocate memory; ASN1_OBJECT_free() will have no effect.
OBJ_nid2ln() and OBJ_nid2sn() returns a valid string or B<NULL>
on error.