update embeded decision

simple-IDS/unikernel.ml

@@ -268,16 +268,21 @@ module Main
         | true ->  
           let options = ipv4_hdr.options in 
           let custom_opt = Custom_option.init in
-          Custom_option.add_entry custom_opt (Int32.of_int 0) 255 255;
+          Custom_option.add_entry custom_opt (Int32.of_int 0) 255 0;
+          let custom_opt_cs = Custom_option.of_cstruct custom_opt in
+          let len_option_cs = Cstruct.length custom_opt_cs in
           match Cstruct.length options with
           | 0 -> (
-            let new_ipv4_hdr = {ipv4_hdr with options= Custom_option.of_cstruct custom_opt} in
-            let new_packet = Ipv4_packet.Marshal.make_cstruct ~payload_len:10 new_ipv4_hdr in
+            let new_ipv4_hdr = {ipv4_hdr with options= custom_opt_cs} in
+            let len_new_ipv4_hdr = 20 + len_option_cs in
+            let new_packet = Ipv4_packet.Marshal.make_cstruct ~payload_len:len_new_ipv4_hdr new_ipv4_hdr in
             output_ether_private4 header.Ethernet.Packet.source header.Ethernet.Packet.destination new_packet)
 
           | _ -> (
+            let len_old_option_cs = Cstruct.length ipv4_hdr.options in
+            let len_new_ipv4_hdr = 20 + len_option_cs +len_old_option_cs in
             let new_ipv4_hdr = {ipv4_hdr with options= Cstruct.append ipv4_hdr.options (Custom_option.of_cstruct custom_opt)} in
-            let new_packet = Ipv4_packet.Marshal.make_cstruct ~payload_len:10 new_ipv4_hdr in
+            let new_packet = Ipv4_packet.Marshal.make_cstruct ~payload_len:len_new_ipv4_hdr new_ipv4_hdr in
             output_ether_private4 header.Ethernet.Packet.source header.Ethernet.Packet.destination new_packet)
     in