mainline 0.4.2

Simple, robust, BitTorrent's Mainline DHT implementation
Documentation 
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//! Manage tokens for remote client IPs.

use crc::{Crc, CRC_32_ISCSI};
use rand::{rngs::ThreadRng, Rng};
use std::{
    fmt::{self, Debug, Formatter},
    net::SocketAddr,
    time::{Duration, Instant},
};

const SECRET_SIZE: usize = 20;
const TOKEN_SIZE: usize = 4;
const ROTATE_INTERVAL: Duration = Duration::from_secs(60 * 5);
const CASTAGNOLI: Crc<u32> = Crc::<u32>::new(&CRC_32_ISCSI);

pub struct Tokens {
    rng: ThreadRng,
    prev_secret: [u8; SECRET_SIZE],
    curr_secret: [u8; SECRET_SIZE],
    last_updated: Instant,
}

impl Debug for Tokens {
    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
        write!(f, "Tokens (_)")
    }
}

impl Tokens {
    pub fn new() -> Self {
        let mut rng = rand::thread_rng();

        let prev_secret = rng.gen();
        let curr_secret = rng.gen();

        Tokens {
            rng,
            prev_secret,
            curr_secret,
            last_updated: Instant::now(),
        }
    }

    // === Public Methods ===

    pub fn should_update(&self) -> bool {
        self.last_updated.elapsed() > ROTATE_INTERVAL
    }

    /// Validate that the token was generated within the past 10 minutes
    pub fn validate(&mut self, address: SocketAddr, token: &Vec<u8>) -> bool {
        let prev = self.internal_generate_token(address, self.prev_secret);
        let curr = self.internal_generate_token(address, self.curr_secret);

        token == &curr || token == &prev
    }

    pub fn rotate(&mut self) {
        self.prev_secret = self.curr_secret;
        self.curr_secret = self.rng.gen();

        self.last_updated = Instant::now();
    }

    pub fn generate_token(&mut self, address: SocketAddr) -> [u8; 4] {
        self.internal_generate_token(address, self.curr_secret)
    }

    // === Private Methods ===

    fn internal_generate_token(
        &mut self,
        address: SocketAddr,
        secret: [u8; SECRET_SIZE],
    ) -> [u8; TOKEN_SIZE] {
        let mut digest = CASTAGNOLI.digest();

        let octets = match address.ip() {
            std::net::IpAddr::V4(v4) => v4.octets().to_vec(),
            std::net::IpAddr::V6(v6) => v6.octets().to_vec(),
        };

        digest.update(&octets);
        digest.update(&secret);

        let checksum = digest.finalize();

        checksum.to_be_bytes()
    }
}

#[cfg(test)]
mod test {

    use super::*;

    #[test]
    fn valid_tokens() {
        let mut tokens = Tokens::new();

        let address = SocketAddr::from(([127, 0, 0, 1], 6881));
        let token = tokens.generate_token(address);

        assert!(tokens.validate(address, &token.to_vec()))
    }
}