Allow out_present to be NULL in CBS_get_optional_asn1

This is useful to skip an optional element, and mirrors the behaviour of
CBS_get_optional_asn1_octet_string.

Change-Id: Icb538c5e99a1d4e46412cae3c438184a94fab339
Reviewed-on: https://boringssl-review.googlesource.com/5800
Reviewed-by: Adam Langley <agl@google.com>

1 files changed, 8 insertions, 3 deletions

diff --git a/crypto/bytestring/cbs.c b/crypto/bytestring/cbs.c
index c0fb6773..5e0c538a 100644
--- a/crypto/bytestring/cbs.c
+++ b/crypto/bytestring/cbs.c
@@ -329,14 +329,19 @@ int CBS_get_asn1_uint64(CBS *cbs, uint64_t *out) {
 }
 
 int CBS_get_optional_asn1(CBS *cbs, CBS *out, int *out_present, unsigned tag) {
+  int present = 0;
+
   if (CBS_peek_asn1_tag(cbs, tag)) {
     if (!CBS_get_asn1(cbs, out, tag)) {
       return 0;
     }
-    *out_present = 1;
-  } else {
-    *out_present = 0;
+    present = 1;
+  }
+
+  if (out_present != NULL) {
+    *out_present = present;
   }
+
   return 1;
 }