tools/test/p4src/p4-14/include/parser.p4

#ifndef __PARSER_P4__
#define __PARSER_P4__
#include "defines.p4"
#include "headers.p4"

header packet_in_t packet_in_hdr;
header packet_out_t packet_out_hdr;
header ethernet_t ethernet;
header ipv4_t ipv4;
header tcp_t tcp;
header udp_t udp;

parser start {
    #ifdef __TOFINO_BUILD__
    // Hack to force deparsing of packet_in hdr.
    // We assume it's impossible to receive a pkt with the first 8 bits of etherType 0.
    // p4c-tofino complains when switching over 16 bits, i.e. the full etherType
    // FIXME: This solution appears to be very brittle!!!
    return select(current(96, 8)) {
        0 : parse_pkt_in;
    #else
    return select(EGR_PORT_FIELD) {
        CPU_PORT : parse_pkt_in;
    #endif
        default  : default_parser;
    }
}

parser parse_pkt_in {
    extract(packet_in_hdr);
    return parse_ethernet;
}

parser default_parser {
    return select(IGR_PORT_FIELD) {
        CPU_PORT : parse_pkt_out;
        default  : parse_ethernet;
    }
}

parser parse_pkt_out {
    extract(packet_out_hdr);
    return parse_ethernet;
}

parser parse_ethernet {
    extract(ethernet);
    return select(latest.etherType) {
        ETHERTYPE_IPV4 : parse_ipv4;
        default : ingress;
    }
}

parser parse_ipv4 {
    extract(ipv4);
    return select(latest.fragOffset, latest.protocol) {
        IP_PROTOCOLS_TCP : parse_tcp;
        IP_PROTOCOLS_UDP : parse_udp;
        default: ingress;
    }
}

parser parse_tcp {
    extract(tcp);
    return ingress;
}

parser parse_udp {
    extract(udp);
    return ingress;
}

#endif