Add the WPACKET_reserve_bytes() function

WPACKET_allocate_bytes() requires you to know the size of the data you
are allocating for, before you create it. Sometimes this isn't the case,
for example we know the maximum size that a signature will be before we
create it, but not the actual size. WPACKET_reserve_bytes() enables us to
reserve bytes in the WPACKET, but not count them as written yet. We then
subsequently need to acall WPACKET_allocate_bytes to actually count them as
written.

Reviewed-by: Rich Salz <rsalz@openssl.org>

1 files changed, 26 insertions, 7 deletions

diff --git a/ssl/packet.c b/ssl/packet.c
index 4077de5c33..7c240a4a82 100644
--- a/ssl/packet.c
+++ b/ssl/packet.c
@@ -14,6 +14,27 @@
 
 int WPACKET_allocate_bytes(WPACKET *pkt, size_t len, unsigned char **allocbytes)
 {
+    if (!WPACKET_reserve_bytes(pkt, len, allocbytes))
+        return 0;
+    pkt->written += len;
+    pkt->curr += len;
+
+    return 1;
+}
+
+int WPACKET_sub_allocate_bytes__(WPACKET *pkt, size_t len,
+                                 unsigned char **allocbytes, size_t lenbytes)
+{
+    if (!WPACKET_start_sub_packet_len__(pkt, lenbytes)
+            || !WPACKET_allocate_bytes(pkt, len, allocbytes)
+            || !WPACKET_close(pkt))
+        return 0;
+
+    return 1;
+}
+
+int WPACKET_reserve_bytes(WPACKET *pkt, size_t len, unsigned char **allocbytes)
+{
     /* Internal API, so should not fail */
     assert(pkt->subs != NULL && len != 0);
     if (pkt->subs == NULL || len == 0)
@@ -39,20 +60,18 @@ int WPACKET_allocate_bytes(WPACKET *pkt, size_t len, unsigned char **allocbytes)
             return 0;
     }
     *allocbytes = (unsigned char *)pkt->buf->data + pkt->curr;
-    pkt->written += len;
-    pkt->curr += len;
 
     return 1;
 }
 
-int WPACKET_sub_allocate_bytes__(WPACKET *pkt, size_t len,
-                                 unsigned char **allocbytes, size_t lenbytes)
+int WPACKET_sub_reserve_bytes__(WPACKET *pkt, size_t len,
+                                unsigned char **allocbytes, size_t lenbytes)
 {
-    if (!WPACKET_start_sub_packet_len__(pkt, lenbytes)
-            || !WPACKET_allocate_bytes(pkt, len, allocbytes)
-            || !WPACKET_close(pkt))
+    if (!WPACKET_reserve_bytes(pkt, lenbytes + len, allocbytes))
         return 0;
 
+    *allocbytes += lenbytes;
+
     return 1;
 }