//! Adds a table, chain and a rule that blocks all traffic to a given MAC address
//!
//! Run the following to print out current active tables, chains and rules in netfilter. Must be
//! executed as root:
//! ```bash
//! # nft list ruleset
//! ```
//! After running this example, the output should be the following:
//! ```ignore
//! table inet example-filter-ethernet {
//!         chain chain-for-outgoing-packets {
//!                 type filter hook output priority 3; policy accept;
//!                 ether daddr 00:00:00:00:00:00 drop
//!                 counter packets 0 bytes 0 meta random > 2147483647 counter packets 0 bytes 0
//!         }
//! }
//! ```
//!
//!
//! Everything created by this example can be removed by running
//! ```bash
//! # nft delete table inet example-filter-ethernet
//! ```

use rustables::{nft_expr, query::send_batch, sys::libc, Batch, Chain, ProtoFamily, Rule, Table};
use std::{ffi::CString, rc::Rc};

const TABLE_NAME: &str = "example-filter-ethernet";
const OUT_CHAIN_NAME: &str = "chain-for-outgoing-packets";

const BLOCK_THIS_MAC: &[u8] = &[0, 0, 0, 0, 0, 0];

fn main() {
    // For verbose explanations of what all these lines up until the rule creation does, see the
    // `add-rules` example.
    let mut batch = Batch::new();
    let table = Rc::new(Table::new(
        &CString::new(TABLE_NAME).unwrap(),
        ProtoFamily::Inet,
    ));
    batch.add(&Rc::clone(&table), rustables::MsgType::Add);

    let mut out_chain = Chain::new(&CString::new(OUT_CHAIN_NAME).unwrap(), Rc::clone(&table));
    out_chain.set_hook(rustables::Hook::Out, 3);
    out_chain.set_policy(rustables::Policy::Accept);
    let out_chain = Rc::new(out_chain);
    batch.add(&Rc::clone(&out_chain), rustables::MsgType::Add);

    // === ADD RULE DROPPING ALL TRAFFIC TO THE MAC ADDRESS IN `BLOCK_THIS_MAC` ===

    let mut block_ethernet_rule = Rule::new(Rc::clone(&out_chain));

    // Check that the interface type is an ethernet interface. Must be done before we can check
    // payload values in the ethernet header.
    block_ethernet_rule.add_expr(&nft_expr!(meta iiftype));
    block_ethernet_rule.add_expr(&nft_expr!(cmp == libc::ARPHRD_ETHER));

    // Compare the ethernet destination address against the MAC address we want to drop
    block_ethernet_rule.add_expr(&nft_expr!(payload ethernet daddr));
    block_ethernet_rule.add_expr(&nft_expr!(cmp == BLOCK_THIS_MAC));

    // Drop the matching packets.
    block_ethernet_rule.add_expr(&nft_expr!(verdict drop));

    batch.add(&block_ethernet_rule, rustables::MsgType::Add);

    // === FOR FUN, ADD A PACKET THAT MATCHES 50% OF ALL PACKETS ===

    // This packet has a counter before and after the check that has 50% chance of matching.
    // So after a number of packets has passed through this rule, the first counter should have a
    // value approximately double that of the second counter. This rule has no verdict, so it never
    // does anything with the matching packets.
    let mut random_rule = Rule::new(Rc::clone(&out_chain));
    // This counter expression will be evaluated (and increment the counter) for all packets coming
    // through.
    random_rule.add_expr(&nft_expr!(counter));

    // Load a pseudo-random 32 bit unsigned integer into the netfilter register.
    random_rule.add_expr(&nft_expr!(meta random));
    // Check if the random integer is larger than `u32::MAX/2`, thus having 50% chance of success.
    random_rule.add_expr(&nft_expr!(cmp > (::std::u32::MAX / 2).to_be()));

    // Add a second counter. This will only be incremented for the packets passing the random check.
    random_rule.add_expr(&nft_expr!(counter));

    batch.add(&random_rule, rustables::MsgType::Add);

    // === FINALIZE THE TRANSACTION AND SEND THE DATA TO NETFILTER ===

    match batch.finalize() {
        Some(mut finalized_batch) => {
            send_batch(&mut finalized_batch).expect("Couldn't process the batch");
        }
        None => todo!(),
    }
}