Trigger ipv4 checksumming after nat64 translation

p4src/checksums.p4

@@ -69,6 +69,24 @@ control MyComputeChecksum(inout headers  hdr, inout metadata meta) {
             hdr.icmp.checksum,
             HashAlgorithm.csum16
         );
+
+	    update_checksum(meta.chk_ipv4 == 1,
+            {
+                hdr.ipv4.version,
+	            hdr.ipv4.ihl,
+                hdr.ipv4.dscp,
+                hdr.ipv4.ecn,
+                hdr.ipv4.totalLen,
+                hdr.ipv4.identification,
+                hdr.ipv4.flags,
+                hdr.ipv4.fragOffset,
+                hdr.ipv4.ttl,
+                hdr.ipv4.protocol,
+                hdr.ipv4.srcAddr,
+                hdr.ipv4.dstAddr
+            },
+            hdr.ipv4.hdrChecksum,
+            HashAlgorithm.csum16);
     }
 }
 

p4src/headers.p4

@@ -211,6 +211,7 @@ struct metadata {
     bit<1> chk_icmp6_na_ns;
     bit<1> chk_icmp6;
     bit<1> chk_icmp;
+    bit<1> chk_ipv4;
 
     bit<16> tcp_length;
     bit<32> cast_length;

p4src/static-mapping.p4

@@ -74,6 +74,7 @@ control MyIngress(inout headers hdr,
     /* NAT64 protocol unspecific changes */
     action nat64_generic(ipv4_addr_t src, ipv4_addr_t dst) {
 		hdr.ipv4.setValid();
+        meta.chk_ipv4 = 1; /* need to calculate the hdrchecksum */
 
         /* Stuff that might need to be fixed */
         hdr.ipv4.version        = (bit<4>)4;