2020-11-24 18:58:18 +00:00
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use dashmap::DashMap;
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2020-11-24 21:45:30 +00:00
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use std::{fmt::Display, collections::VecDeque, hash::Hash, time::{Duration, Instant}};
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2020-11-24 18:58:18 +00:00
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/// A simple struct to manage rate limiting.
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///
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/// Does not require a leaky bucket thread to empty it out, but may occassionally need to
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/// trim old keys using [`trim_keys()`].
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///
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2020-11-26 01:37:43 +00:00
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/// [`trim_keys()`]: Self::trim_keys()
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2020-11-24 18:58:18 +00:00
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pub struct RateLimiter<K: Eq + Hash> {
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log: DashMap<K, VecDeque<Instant>>,
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burst: usize,
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period: Duration,
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}
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impl<K: Eq + Hash> RateLimiter<K> {
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/// Create a new ratelimiter that allows at most `burst` connections in `period`
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pub fn new(period: Duration, burst: usize) -> Self {
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Self {
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log: DashMap::with_capacity(8),
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period,
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burst,
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}
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}
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/// Check if a key may pass
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///
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/// If the key has made less than `self.burst` connections in the last `self.period`,
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/// then the key is allowed to connect, which is denoted by an `Ok` result. This will
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/// register as a new connection from that key.
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///
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/// If the key is not allowed to connect, than a [`Duration`] denoting the amount of
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/// time until the key is permitted is returned, wrapped in an `Err`
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pub fn check_key(&self, key: K) -> Result<(), Duration> {
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let now = Instant::now();
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let count_after = now - self.period;
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let mut connections = self.log.entry(key)
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.or_insert_with(||VecDeque::with_capacity(self.burst));
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let connections = connections.value_mut();
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// Chcek if space can be made available. We don't need to trim all expired
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// connections, just the one in question to allow this connection.
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if let Some(earliest_conn) = connections.front() {
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if earliest_conn < &count_after {
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connections.pop_front();
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}
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}
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// Check if the connection should be allowed
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if connections.len() == self.burst {
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Err(connections[0] + self.period - now)
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} else {
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connections.push_back(now);
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Ok(())
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}
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}
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/// Remove any expired keys from the ratelimiter
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///
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/// This only needs to be called if keys are continuously being added. If keys are
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/// being reused, or come from a finite set, then you don't need to worry about this.
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///
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/// If you have many keys coming from a large set, you should infrequently call this
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/// to prevent a memory leak.
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2020-11-24 21:45:30 +00:00
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///
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/// If debug level logging is enabled, this prints an *approximate* number of keys
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/// removed to the log. For more precise output, use [`trim_keys_verbose()`]
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///
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/// [`trim_keys_verbose()`]: RateLimiter::trim_keys_verbose()
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2020-11-24 18:58:18 +00:00
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pub fn trim_keys(&self) {
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let count_after = Instant::now() - self.period;
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2020-11-24 21:45:30 +00:00
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let len: isize = self.log.len() as isize;
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2020-11-24 18:58:18 +00:00
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self.log.retain(|_, conns| conns.back().unwrap() > &count_after);
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2020-11-24 21:45:30 +00:00
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let removed = len - self.log.len() as isize;
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if removed.is_positive() {
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debug!("Pruned approximately {} expired ratelimit keys", removed);
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}
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}
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}
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impl<K: Eq + Hash + Display> RateLimiter<K> {
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/// Remove any expired keys from the ratelimiter
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///
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/// This only needs to be called if keys are continuously being added. If keys are
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/// being reused, or come from a finite set, then you don't need to worry about this.
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///
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/// If you have many keys coming from a large set, you should infrequently call this
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/// to prevent a memory leak.
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///
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/// If debug level logging is on, this prints out any removed keys.
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pub fn trim_keys_verbose(&self) {
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let count_after = Instant::now() - self.period;
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self.log.retain(|ip, conns| {
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let should_keep = conns.back().unwrap() > &count_after;
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if !should_keep {
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debug!("Pruned expired ratelimit key: {}", ip);
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}
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should_keep
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});
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2020-11-24 18:58:18 +00:00
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}
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}
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