Add CBB_discard_child(), which allows for a child CBB to be discarded.

Based on BoringSSL.

2 files changed, 22 insertions, 2 deletions

diff --git a/src/lib/libssl/bs_cbb.c b/src/lib/libssl/bs_cbb.c
index 9de75fbb02..bf7de3fd33 100644
--- a/src/lib/libssl/bs_cbb.c
+++ b/src/lib/libssl/bs_cbb.c
@@ -1,4 +1,4 @@
-/*      $OpenBSD: bs_cbb.c,v 1.17 2017/08/12 02:50:05 jsing Exp $       */
+/*      $OpenBSD: bs_cbb.c,v 1.18 2017/11/28 16:34:20 jsing Exp $       */
 /*
  * Copyright (c) 2014, Google Inc.
  *
@@ -271,6 +271,20 @@ CBB_flush(CBB *cbb)
         return 1;
 }
 
+void
+CBB_discard_child(CBB *cbb)
+{
+        if (cbb->child == NULL)
+                return;
+
+        cbb->base->len = cbb->offset;
+        
+        cbb->child->base = NULL;
+        cbb->child = NULL;
+        cbb->pending_len_len = 0;
+        cbb->pending_is_asn1 = 0;
+        cbb->offset = 0;
+}
 
 static int
 cbb_add_length_prefixed(CBB *cbb, CBB *out_contents, size_t len_len)
diff --git a/src/lib/libssl/bytestring.h b/src/lib/libssl/bytestring.h
index d8c8e6ada6..2e89a5791a 100644
--- a/src/lib/libssl/bytestring.h
+++ b/src/lib/libssl/bytestring.h
@@ -1,4 +1,4 @@
-/*      $OpenBSD: bytestring.h,v 1.15 2016/11/04 18:28:58 guenther Exp $        */
+/*      $OpenBSD: bytestring.h,v 1.16 2017/11/28 16:34:20 jsing Exp $   */
 /*
  * Copyright (c) 2014, Google Inc.
  *
@@ -394,6 +394,12 @@ int CBB_finish(CBB *cbb, uint8_t **out_data, size_t *out_len);
 int CBB_flush(CBB *cbb);
 
 /*
+ * CBB_discard_child discards the current unflushed child of |cbb|. Neither the
+ * child's contents nor the length prefix will be included in the output.
+ */
+void CBB_discard_child(CBB *cbb);
+
+/*
  * CBB_add_u8_length_prefixed sets |*out_contents| to a new child of |cbb|. The
  * data written to |*out_contents| will be prefixed in |cbb| with an 8-bit
  * length. It returns one on success or zero on error.