mainline 6.1.1

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 std::{
    fmt::{self, Debug, Formatter},
    net::SocketAddrV4,
    time::Instant,
};

use tracing::trace;

const SECRET_SIZE: usize = 20;
const TOKEN_SIZE: usize = 4;
const CASTAGNOLI: Crc<u32> = Crc::<u32>::new(&CRC_32_ISCSI);

/// Tokens generator.
///
/// Read [BEP_0005](https://www.bittorrent.org/beps/bep_0005.html) for more information.
#[derive(Clone)]
pub struct Tokens {
    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 {
    /// Create a Tokens generator.
    pub fn new() -> Self {
        Tokens {
            prev_secret: random(),
            curr_secret: random(),
            last_updated: Instant::now(),
        }
    }

    // === Public Methods ===

    /// Returns `true` if the current secret needs to be updated after an interval.
    pub fn should_update(&self) -> bool {
        self.last_updated.elapsed() > crate::common::TOKEN_ROTATE_INTERVAL
    }

    /// Validate that the token was generated within the past 10 minutes
    pub fn validate(&mut self, address: SocketAddrV4, token: &[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
    }

    /// Rotate the tokens secret.
    pub fn rotate(&mut self) {
        trace!("Rotating secrets");

        self.prev_secret = self.curr_secret;
        self.curr_secret = random();

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

    /// Generates a new token for a remote peer.
    pub fn generate_token(&mut self, address: SocketAddrV4) -> [u8; 4] {
        self.internal_generate_token(address, self.curr_secret)
    }

    // === Private Methods ===

    fn internal_generate_token(
        &mut self,
        address: SocketAddrV4,
        secret: [u8; SECRET_SIZE],
    ) -> [u8; TOKEN_SIZE] {
        let mut digest = CASTAGNOLI.digest();

        let octets: Box<[u8]> = address.ip().octets().into();

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

        let checksum = digest.finalize();

        checksum.to_be_bytes()
    }
}

impl Default for Tokens {
    fn default() -> Self {
        Self::new()
    }
}

fn random() -> [u8; SECRET_SIZE] {
    let mut bytes = [0_u8; SECRET_SIZE];
    getrandom::fill(&mut bytes).expect("getrandom");

    bytes
}

#[cfg(test)]
mod test {

    use super::*;

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

        let address = SocketAddrV4::new([127, 0, 0, 1].into(), 6881);
        let token = tokens.generate_token(address);

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