[xdp_drop_udp] - New protocol and port functions

[Dwctor]

Being able to translate benchmarks/dropudp should be possible with a few extra auxiliary functions. Similar to issue #46, but a bit more complicated. One of the things that we need listed there is the function to get the ethhdr struct from the ctx, read issue #46 for that one.

Other than that, here is a list of the other functions and parts that we still don't have.

First up, we need this boundary check somewhere in these functions for us to be able to run the program without the BPF verifier impeding it:

    // Verifier use this boundary check
    if (data + nh_off > data_end)
        return XDP_ABORTED;

I'll leave it up to the one that solves this issue to decide where it would be most adequate.

We should have a function that returns the "ipproto" given the ipv4 or ipv6 nature of the packet. Preferably, we would have only one function for both ipv4 and ipv6, so one function should be able to do all of the following:

    if (eth->h_proto == htons(ETH_P_IP))
        ipproto = getProtocolIPv4(data, &nh_off, data_end);
    else if (eth->h_proto == htons(ETH_P_IPV6))
        ipproto = getProtocolIPv6(data, &nh_off, data_end);
    else
        return XDP_PASS;

both the getProtocolIPv4 and getProtocolIPv6 functions can be temporarily added into the lib/honey/boilerplates.ex file.

We then could represent the uint16_t dest_port = ntohs(getDestPortUDP(data, nh_off, data_end)); as a new function.

Finally, we would need a function to represent editDestPortUDP(data, nh_off, data_end, 3000);

Most other abstractions and parts should be doable with the current translation. I heavily suggest having #46 solved before this.

As in #46, functions should be implemented in the lib/honey/translator.ex near the def to_c({{:., _, [Honey.Bpf_helpers, function]}, _, params}, context) do and def to_c({{:., _, [Honey.Bpf.Global, function]}, _, _params}, _context) do with a new namespace (or possibly the same namespace of #46 depending on what was chosen).

Anyone willing to help with this issue should make a pull request with the changes. I'll review them if I haven't solved it by then!

[Dwctor]

This is mostly done in the Type Propagation branch. I will close the issue once it's merged into main.