From f0900c3821417ec0cd97873212a1a1236ae02ded Mon Sep 17 00:00:00 2001
From: Nico Schottelius <nico@nico-notebook.schottelius.org>
Date: Mon, 15 Jul 2019 16:48:24 +0200
Subject: [PATCH] update tcp checksumming

---
 doc/plan.org                    | 11 +++++++++++
 p4src/actions_delta_checksum.p4 | 10 +++++++---
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/doc/plan.org b/doc/plan.org
index 59f10f1..5218118 100644
--- a/doc/plan.org
+++ b/doc/plan.org
@@ -5255,6 +5255,17 @@ we get on the wire:
 
 sum 0x324a (incorrect -> 0x5429),
 
+Using
+    /* filtering code copied from scapy */
+    tmp = (tmp >> 16) + (tmp & 0xffff);
+    tmp = tmp + (tmp >> 16);
+    tmp = ~tmp;
+    meta.v6sum = (bit<16>) ((((tmp>>8) & 0xff)|tmp<<8) & 0xffff) ;
+
+we get
+
+sum 0x48ad (incorrect -> 0x85eb)
+
 ** The NetPFGA saga
 Problems encountered:
 - The logfile for a compile run is 10k+ lines
diff --git a/p4src/actions_delta_checksum.p4 b/p4src/actions_delta_checksum.p4
index 008ae29..8b71612 100644
--- a/p4src/actions_delta_checksum.p4
+++ b/p4src/actions_delta_checksum.p4
@@ -73,14 +73,18 @@ action delta_udp_from_v4_to_v6()
 
 action delta_tcp_from_v4_to_v6()
 {
-    delta_prepare();
-    hdr.tcp.checksum = hdr.tcp.checksum + meta.headerdiff;
+    v4sum();
+    v6sum();
+
+    /* here is also a possible overflow in both directions */
+    hdr.tcp.checksum = hdr.tcp.checksum + meta.v6sum - meta.v4sum;
 }
 
 action delta_ipv4_from_v6_to_v4()
 {
     delta_prepare();
-    hdr.tcp.checksum = hdr.tcp.checksum + ~meta.headerdiff;
+    /* TO BE DONE! */
+
 }
 
 #endif
\ No newline at end of file