From a44c0c8f4154c33ce402045c98d32143fc466cfa Mon Sep 17 00:00:00 2001
From: jsing <jsing@openbsd.org>
Date: Wed, 15 Dec 2021 17:23:34 +0000
Subject: [PATCH] Provide CBS_get_last_u8().

This will be used in the TLSv1.3 record layer.

From BoringSSL.

ok tb@
---
 lib/libssl/bs_cbs.c     | 13 ++++++++++++-
 lib/libssl/bytestring.h |  8 +++++++-
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/lib/libssl/bs_cbs.c b/lib/libssl/bs_cbs.c
index ab76b789272..627c609bb9e 100644
--- a/lib/libssl/bs_cbs.c
+++ b/lib/libssl/bs_cbs.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: bs_cbs.c,v 1.21 2021/10/31 06:48:54 jsing Exp $	*/
+/*	$OpenBSD: bs_cbs.c,v 1.22 2021/12/15 17:23:34 jsing Exp $	*/
 /*
  * Copyright (c) 2014, Google Inc.
  *
@@ -190,6 +190,17 @@ CBS_get_u32(CBS *cbs, uint32_t *out)
 	return cbs_get_u(cbs, out, 4);
 }
 
+int
+CBS_get_last_u8(CBS *cbs, uint8_t *out)
+{
+	if (cbs->len == 0)
+		return 0;
+
+	*out = cbs->data[cbs->len - 1];
+	cbs->len--;
+	return 1;
+}
+
 int
 CBS_get_bytes(CBS *cbs, CBS *out, size_t len)
 {
diff --git a/lib/libssl/bytestring.h b/lib/libssl/bytestring.h
index 9e55dd44d64..4ab2828d09f 100644
--- a/lib/libssl/bytestring.h
+++ b/lib/libssl/bytestring.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: bytestring.h,v 1.19 2021/05/16 10:58:27 jsing Exp $	*/
+/*	$OpenBSD: bytestring.h,v 1.20 2021/12/15 17:23:34 jsing Exp $	*/
 /*
  * Copyright (c) 2014, Google Inc.
  *
@@ -133,6 +133,12 @@ int CBS_get_u24(CBS *cbs, uint32_t *out);
  */
 int CBS_get_u32(CBS *cbs, uint32_t *out);
 
+/*
+ * CBS_get_last_u8 sets |*out| to the last uint8_t from |cbs| and shortens
+ * |cbs|. It returns one on success and zero on error.
+ */
+int CBS_get_last_u8(CBS *cbs, uint8_t *out);
+
 /*
  * CBS_get_bytes sets |*out| to the next |len| bytes from |cbs| and advances
  * |cbs|. It returns one on success and zero on error.
-- 
2.20.1