document -2 return value

Reviewed-by: Rich Salz <rsalz@openssl.org>
(cherry picked from commit 5727582cf51e98e5e0faa435e7da2c8929533c0d)

Conflicts:
	doc/crypto/X509_NAME_get_index_by_NID.pod

1 files changed, 7 insertions, 0 deletions

diff --git a/doc/crypto/X509_NAME_get_index_by_NID.pod b/doc/crypto/X509_NAME_get_index_by_NID.pod
index 3b1f9ff43b..3618b214f2 100644
--- a/doc/crypto/X509_NAME_get_index_by_NID.pod
+++ b/doc/crypto/X509_NAME_get_index_by_NID.pod
@@ -29,6 +29,7 @@ and issuer names.
 X509_NAME_get_index_by_NID() and X509_NAME_get_index_by_OBJ() retrieve
 the next index matching B<nid> or B<obj> after B<lastpos>. B<lastpos>
 should initially be set to -1. If there are no more entries -1 is returned.
+If B<nid> is invalid (doesn't correspond to a valid OID) then -2 is returned.
 
 X509_NAME_entry_count() returns the total number of entries in B<name>.
 
@@ -59,6 +60,10 @@ X509_NAME_get_index_by_OBJ() should be used followed by
 X509_NAME_get_entry() on any matching indices and then the
 various B<X509_NAME_ENTRY> utility functions on the result.
 
+Applications which could pass invalid NIDs to X509_NAME_get_index_by_NID()
+should check for the return value of -2. Alternatively the NID validity
+can be determined first by checking OBJ_nid2obj(nid) is not NULL.
+
 =head1 EXAMPLES
 
 Process all entries:
@@ -91,6 +96,8 @@ Process all commonName entries:
 
 X509_NAME_get_index_by_NID() and X509_NAME_get_index_by_OBJ()
 return the index of the next matching entry or -1 if not found.
+X509_NAME_get_index_by_NID() can also return -2 if the supplied
+NID is invalid.
 
 X509_NAME_entry_count() returns the total number of entries.