better basic_tunnel

[xiatongchen]

// SPDX-License-Identifier: Apache-2.0
/* -- P4_16 -- */
#include <core.p4>
#include <v1model.p4>

// NOTE: new type added here
const bit<16> TYPE_MYTUNNEL = 0x1212;
const bit<16> TYPE_IPV4 = 0x800;

/*************************************************************************
*********************** H E A D E R S ***********************************
*************************************************************************/

typedef bit<9> egressSpec_t;
typedef bit<48> macAddr_t;
typedef bit<32> ip4Addr_t;

header ethernet_t {
macAddr_t dstAddr;
macAddr_t srcAddr;
bit<16> etherType;
}

// NOTE: added new header type
header myTunnel_t {
bit<16> proto_id;
bit<16> dst_id;
}

header ipv4_t {
bit<4> version;
bit<4> ihl;
bit<8> diffserv;
bit<16> totalLen;
bit<16> identification;
bit<3> flags;
bit<13> fragOffset;
bit<8> ttl;
bit<8> protocol;
bit<16> hdrChecksum;
ip4Addr_t srcAddr;
ip4Addr_t dstAddr;
}

struct metadata {
/* empty */
}

// NOTE: Added new header type to headers struct
struct headers {
ethernet_t ethernet;
myTunnel_t myTunnel;
ipv4_t ipv4;
}

/*************************************************************************
*********************** P A R S E R ***********************************
*************************************************************************/

parser MyParser(packet_in packet,
out headers hdr,
inout metadata meta,
inout standard_metadata_t standard_metadata) {

state start {
    transition parse_ethernet;
}

state parse_ethernet {
    packet.extract(hdr.ethernet);
    transition select(hdr.ethernet.etherType) {
        TYPE_MYTUNNEL : parse_myTunnel; 
        TYPE_IPV4 : parse_ipv4;
        default : accept;
    }
}


state parse_myTunnel 

{
packet.extract(hdr.myTunnel);
transition select(hdr.myTunnel.proto_id) {
TYPE_IPV4 : parse_ipv4;
default : accept;
}
}

state parse_ipv4 {
    packet.extract(hdr.ipv4);
    transition accept;
}

}

/*************************************************************************
************ C H E C K S U M V E R I F I C A T I O N *************
*************************************************************************/

control MyVerifyChecksum(inout headers hdr, inout metadata meta) {
apply { }
}

/*************************************************************************
************** I N G R E S S P R O C E S S I N G *******************
*************************************************************************/

control MyIngress(inout headers hdr,
inout metadata meta,
inout standard_metadata_t standard_metadata) {

action drop() {
    mark_to_drop(standard_metadata);
}

action myTunnel_forward(bit<9> port) {
    standard_metadata.egress_spec = port;
}

action ipv4_forward(macAddr_t dstAddr, egressSpec_t port) {
    standard_metadata.egress_spec = port;
    hdr.ethernet.srcAddr = hdr.ethernet.dstAddr;
    hdr.ethernet.dstAddr = dstAddr;
    hdr.ipv4.ttl = hdr.ipv4.ttl - 1;
}

table myTunnel_exact {
    key = {
        hdr.myTunnel.dst_id: exact;
    }
    actions = {
        myTunnel_forward;
        drop;
    }
    size = 1024;
    default_action = drop;
}

table ipv4_lpm {
    key = {
        hdr.ipv4.dstAddr: lpm;
    }
    actions = {
        ipv4_forward;
        drop;
        NoAction;
    }
    size = 1024;
    default_action = drop();
}

apply {
    if (hdr.myTunnel.isValid()) {
        myTunnel_exact.apply();
    } else if (hdr.ipv4.isValid()) {
        ipv4_lpm.apply();
    }
}

}

/*************************************************************************
**************** E G R E S S P R O C E S S I N G *******************
*************************************************************************/

control MyEgress(inout headers hdr,
inout metadata meta,
inout standard_metadata_t standard_metadata) {
apply { }
}

/*************************************************************************
************* C H E C K S U M C O M P U T A T I O N **************
*************************************************************************/

control MyComputeChecksum(inout headers hdr, inout metadata meta) {
apply {
update_checksum(
hdr.ipv4.isValid(),
{ hdr.ipv4.version,
hdr.ipv4.ihl,
hdr.ipv4.diffserv,
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);
}
}

/*************************************************************************
*********************** D E P A R S E R *******************************
*************************************************************************/

control MyDeparser(packet_out packet, in headers hdr) {
apply {
packet.emit(hdr.ethernet);
// TODO: emit myTunnel header as well
packet.emit(hdr.ipv4);
}
}

/*************************************************************************
*********************** S W I T C H *******************************
*************************************************************************/

V1Switch(
MyParser(),
MyVerifyChecksum(),
MyIngress(),
MyEgress(),
MyComputeChecksum(),
MyDeparser()
) main;

[jafingerhut]

The code in your comment is very similar to that in the file exercises/basic_tunnel/solution/basic_tunnel.p4

Can you explain what you are improving?