nat: refactor mss_clamping to not depend on snat_main_t

Type: refactor
Signed-off-by: Ole Troan <ot@cisco.com>
Change-Id: I1110e425859a4f1f07952c91b50f263cb7323836

1 files changed, 66 insertions, 0 deletions

diff --git a/src/plugins/nat/lib/nat_inlines.h b/src/plugins/nat/lib/nat_inlines.h
new file mode 100644
index 00000000000..fc8e160bb2b
--- /dev/null
+++ b/src/plugins/nat/lib/nat_inlines.h
@@ -0,0 +1,66 @@
+/*
+ * Copyright (c) 2020 Cisco and/or its affiliates.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <vnet/tcp/tcp_packet.h>
+#include <vnet/ip/ip4_packet.h>
+
+always_inline void
+mss_clamping (u16 mss_clamping, tcp_header_t * tcp, ip_csum_t * sum)
+{
+  u8 *data;
+  u8 opt_len, opts_len, kind;
+  u16 mss;
+
+  if (!(mss_clamping && tcp_syn (tcp)))
+    return;
+
+  opts_len = (tcp_doff (tcp) << 2) - sizeof (tcp_header_t);
+  data = (u8 *) (tcp + 1);
+  for (; opts_len > 0; opts_len -= opt_len, data += opt_len)
+    {
+      kind = data[0];
+
+      if (kind == TCP_OPTION_EOL)
+	break;
+      else if (kind == TCP_OPTION_NOOP)
+	{
+	  opt_len = 1;
+	  continue;
+	}
+      else
+	{
+	  if (opts_len < 2)
+	    return;
+	  opt_len = data[1];
+
+	  if (opt_len < 2 || opt_len > opts_len)
+	    return;
+	}
+
+      if (kind == TCP_OPTION_MSS)
+	{
+	  mss = *(u16 *) (data + 2);
+	  if (clib_net_to_host_u16 (mss) > mss_clamping)
+	    {
+	      u16 mss_value_net = clib_host_to_net_u16(mss_clamping);
+	      *sum =
+		ip_csum_update (*sum, mss, mss_value_net, ip4_header_t,
+				length);
+	      clib_memcpy_fast (data + 2, &mss_value_net, 2);
+	    }
+	  return;
+	}
+    }
+}