inline void check_ipv4()

in src/filtration/packet.h [128:168]

• 27 lines of code
• 8 McCabe index (conditional complexity)

    inline void check_ipv4() __attribute__((always_inline))
    {
        if(dlen < sizeof(IPv4Header)) return;
        auto header = reinterpret_cast<const IPv4Header*>(data);

        if(header->version() != 4) return;

        /*
            IP packet may be fragmented by NIC or snaplen parameter of libpcap
            IP is fragmented AND it is first part of original (offset == 0)
            - Ok, pass it.

            IP is fragmented AND it is not first part of it (offset != 0)
             - DISCARD IT! We do not reassemble fragmented IP packets at all
        */
        if(header->is_fragmented_and_not_the_first_part())
        {
            return; // discard tail of fragmented ip packets
        }

        const uint32_t ihl = header->ihl();
        if(dlen < ihl) return;               // truncated packet
        if((header->length()) < ihl) return; // incorrect packet

        data += ihl;
        dlen = (std::min((uint16_t)dlen, header->length())) - ihl; // trunk data to length of IP packet

        switch(header->protocol())
        {
        case ip::NextProtocol::TCP:
            check_tcp();
            break;
        case ip::NextProtocol::UDP:
            check_udp();
            break;
        default:
            return;
        }

        ipv4 = header;
    }