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path: root/src/handshake/ratelimiter.rs
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use std::collections::HashMap;
use std::net::IpAddr;
use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::Arc;
use std::time::{Duration, Instant};
use spin::{RwLock, Mutex};

use tokio::prelude::future;
use future::{loop_fn, Future, Loop, lazy};
use tokio::timer::Delay;

use lazy_static::lazy_static;

const PACKETS_PER_SECOND: u64 = 20;
const PACKETS_BURSTABLE: u64 = 5;
const PACKET_COST: u64 = 1_000_000_000 / PACKETS_PER_SECOND;
const MAX_TOKENS: u64 = PACKET_COST * PACKETS_BURSTABLE;

lazy_static! {
    pub static ref GC_INTERVAL: Duration = Duration::new(1, 0);
}

struct Entry {
    pub last_time: Instant,
    pub tokens: u64,
}

pub struct RateLimiter(Arc<RateLimiterInner>);

struct RateLimiterInner{
    gc_running: AtomicBool,
    table: RwLock<HashMap<IpAddr, Mutex<Entry>>>,
}

impl RateLimiter {
    pub fn new() -> Self {
        RateLimiter (
            Arc::new(RateLimiterInner {
                gc_running: AtomicBool::from(false),
                table: RwLock::new(HashMap::new()),
            })
        )
    }

    pub fn allow(&self, addr: &IpAddr) -> bool {
        // check if allowed
        let allowed = {
            // check for existing entry (required read lock)
            if let Some(entry) = self.0.table.read().get(addr) {
                // update existing entry
                let mut entry = entry.lock();

                // add tokens earned since last time
                entry.tokens =
                    MAX_TOKENS.min(entry.tokens + u64::from(entry.last_time.elapsed().subsec_nanos()));
                entry.last_time = Instant::now();

                // subtract cost of packet
                if entry.tokens > PACKET_COST {
                    entry.tokens -= PACKET_COST;
                    return true;
                } else {
                    return false;
                }
            }
        
            // add new entry (write lock)
            self.0.table.write().insert(
                *addr,
                Mutex::new(Entry {
                    last_time: Instant::now(),
                    tokens: MAX_TOKENS - PACKET_COST,
                }),
            );
            true
        };

        // check that GC is scheduled
        if !self.0.gc_running.swap(true, Ordering::Relaxed) {
            let limiter = self.0.clone();
            tokio::spawn(
                loop_fn((), move |_| {
                    let limiter = limiter.clone();
                    let next_gc = Instant::now() + *GC_INTERVAL;
                    Delay::new(next_gc)
                        .map_err(|_| ())
                        .and_then(move |_| {
                            let mut tw = limiter.table.write();
                            tw.retain(|_, ref mut entry| entry.lock().last_time.elapsed() <= *GC_INTERVAL);
                            if tw.len() > 0 {
                                Ok(Loop::Continue(()))
                            } else {
                                limiter.gc_running.store(false, Ordering::Relaxed);
                                Ok(Loop::Break(()))
                            }
                        })
                })
            );
        }

        allowed
    }

}

#[cfg(test)]
mod tests {
    use super::*;
    use std;

    struct Result {
        allowed: bool,
        text: &'static str,
        wait: Duration,
    }

    #[test]
    fn test_ratelimiter() {
        tokio::run(lazy(|| {
            let mut ratelimiter = RateLimiter::new();
            let mut expected = vec![];
            let ips = vec![
                "127.0.0.1".parse().unwrap(),
                "192.168.1.1".parse().unwrap(),
                "172.167.2.3".parse().unwrap(),
                "97.231.252.215".parse().unwrap(),
                "248.97.91.167".parse().unwrap(),
                "188.208.233.47".parse().unwrap(),
                "104.2.183.179".parse().unwrap(),
                "72.129.46.120".parse().unwrap(),
                "2001:0db8:0a0b:12f0:0000:0000:0000:0001".parse().unwrap(),
                "f5c2:818f:c052:655a:9860:b136:6894:25f0".parse().unwrap(),
                "b2d7:15ab:48a7:b07c:a541:f144:a9fe:54fc".parse().unwrap(),
                "a47b:786e:1671:a22b:d6f9:4ab0:abc7:c918".parse().unwrap(),
                "ea1e:d155:7f7a:98fb:2bf5:9483:80f6:5445".parse().unwrap(),
                "3f0e:54a2:f5b4:cd19:a21d:58e1:3746:84c4".parse().unwrap(),
            ];

            for _ in 0..PACKETS_BURSTABLE {
                expected.push(Result {
                    allowed: true,
                    wait: Duration::new(0, 0),
                    text: "inital burst",
                });
            }

            expected.push(Result {
                allowed: false,
                wait: Duration::new(0, 0),
                text: "after burst",
            });

            expected.push(Result {
                allowed: true,
                wait: Duration::new(0, PACKET_COST as u32),
                text: "filling tokens for single packet",
            });

            expected.push(Result {
                allowed: false,
                wait: Duration::new(0, 0),
                text: "not having refilled enough",
            });

            expected.push(Result {
                allowed: true,
                wait: Duration::new(0, 2 * PACKET_COST as u32),
                text: "filling tokens for 2 * packet burst",
            });

            expected.push(Result {
                allowed: true,
                wait: Duration::new(0, 0),
                text: "second packet in 2 packet burst",
            });

            expected.push(Result {
                allowed: false,
                wait: Duration::new(0, 0),
                text: "packet following 2 packet burst",
            });

            for item in expected {
                std::thread::sleep(item.wait);
                for ip in ips.iter() {
                    if ratelimiter.allow(&ip) != item.allowed {
                        panic!(
                            "test failed for {} on {}. expected: {}, got: {}",
                            ip, item.text, item.allowed, !item.allowed
                        )
                    }
                }
            }

            Ok(())
        }));
    }
}