nautilus_network/ratelimiter/
mod.rs

1// -------------------------------------------------------------------------------------------------
2//  Copyright (C) 2015-2025 Posei Systems Pty Ltd. All rights reserved.
3//  https://poseitrader.io
4//
5//  Licensed under the GNU Lesser General Public License Version 3.0 (the "License");
6//  You may not use this file except in compliance with the License.
7//  You may obtain a copy of the License at https://www.gnu.org/licenses/lgpl-3.0.en.html
8//
9//  Unless required by applicable law or agreed to in writing, software
10//  distributed under the License is distributed on an "AS IS" BASIS,
11//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12//  See the License for the specific language governing permissions and
13//  limitations under the License.
14// -------------------------------------------------------------------------------------------------
15
16//! A rate limiter implementation heavily inspired by [governor](https://github.com/antifuchs/governor)
17//!
18//! The governor does not support different quota for different key. It is an open [issue](https://github.com/antifuchs/governor/issues/193)
19pub mod clock;
20mod gcra;
21mod nanos;
22pub mod quota;
23
24use std::{
25    fmt::Debug,
26    hash::Hash,
27    num::NonZeroU64,
28    sync::atomic::{AtomicU64, Ordering},
29    time::Duration,
30};
31
32use dashmap::DashMap;
33use futures_util::StreamExt;
34use tokio::time::sleep;
35
36use self::{
37    clock::{Clock, FakeRelativeClock, MonotonicClock},
38    gcra::{Gcra, NotUntil},
39    nanos::Nanos,
40    quota::Quota,
41};
42
43/// An in-memory representation of a GCRA's rate-limiting state.
44///
45/// Implemented using [`AtomicU64`] operations, this state representation can be used to
46/// construct rate limiting states for other in-memory states: e.g., this crate uses
47/// `InMemoryState` as the states it tracks in the keyed rate limiters it implements.
48///
49/// Internally, the number tracked here is the theoretical arrival time (a GCRA term) in number of
50/// nanoseconds since the rate limiter was created.
51#[derive(Debug, Default)]
52pub struct InMemoryState(AtomicU64);
53
54impl InMemoryState {
55    /// Measures and updates the GCRA's state atomically, retrying on concurrent modifications.
56    ///
57    /// # Errors
58    ///
59    /// Returns an error if the provided closure returns an error.
60    pub(crate) fn measure_and_replace_one<T, F, E>(&self, mut f: F) -> Result<T, E>
61    where
62        F: FnMut(Option<Nanos>) -> Result<(T, Nanos), E>,
63    {
64        let mut prev = self.0.load(Ordering::Acquire);
65        let mut decision = f(NonZeroU64::new(prev).map(|n| n.get().into()));
66        while let Ok((result, new_data)) = decision {
67            match self.0.compare_exchange_weak(
68                prev,
69                new_data.into(),
70                Ordering::Release,
71                Ordering::Relaxed,
72            ) {
73                Ok(_) => return Ok(result),
74                Err(next_prev) => prev = next_prev,
75            }
76            decision = f(NonZeroU64::new(prev).map(|n| n.get().into()));
77        }
78        // This map shouldn't be needed, as we only get here in the error case, but the compiler
79        // can't see it.
80        decision.map(|(result, _)| result)
81    }
82}
83
84/// A concurrent, thread-safe and fairly performant hashmap based on [`DashMap`].
85pub type DashMapStateStore<K> = DashMap<K, InMemoryState>;
86
87/// A way for rate limiters to keep state.
88///
89/// There are two important kinds of state stores: Direct and keyed. The direct kind have only
90/// one state, and are useful for "global" rate limit enforcement (e.g. a process should never
91/// do more than N tasks a day). The keyed kind allows one rate limit per key (e.g. an API
92/// call budget per client API key).
93///
94/// A direct state store is expressed as [`StateStore::Key`] = `NotKeyed`.
95/// Keyed state stores have a
96/// type parameter for the key and set their key to that.
97pub trait StateStore {
98    /// The type of key that the state store can represent.
99    type Key;
100
101    /// Updates a state store's rate limiting state for a given key, using the given closure.
102    ///
103    /// The closure parameter takes the old value (`None` if this is the first measurement) of the
104    /// state store at the key's location, checks if the request an be accommodated and:
105    ///
106    /// * If the request is rate-limited, returns `Err(E)`.
107    /// * If the request can make it through, returns `Ok(T)` (an arbitrary positive return
108    ///   value) and the updated state.
109    ///
110    /// It is `measure_and_replace`'s job then to safely replace the value at the key - it must
111    /// only update the value if the value hasn't changed. The implementations in this
112    /// crate use `AtomicU64` operations for this.
113    ///
114    /// # Errors
115    ///
116    /// Returns `Err(E)` if the closure returns an error or the request is rate-limited.
117    fn measure_and_replace<T, F, E>(&self, key: &Self::Key, f: F) -> Result<T, E>
118    where
119        F: Fn(Option<Nanos>) -> Result<(T, Nanos), E>;
120}
121
122impl<K: Hash + Eq + Clone> StateStore for DashMapStateStore<K> {
123    type Key = K;
124
125    fn measure_and_replace<T, F, E>(&self, key: &Self::Key, f: F) -> Result<T, E>
126    where
127        F: Fn(Option<Nanos>) -> Result<(T, Nanos), E>,
128    {
129        if let Some(v) = self.get(key) {
130            // fast path: measure existing entry
131            return v.measure_and_replace_one(f);
132        }
133        // make an entry and measure that:
134        let entry = self.entry(key.clone()).or_default();
135        (*entry).measure_and_replace_one(f)
136    }
137}
138
139pub struct RateLimiter<K, C>
140where
141    C: Clock,
142{
143    default_gcra: Option<Gcra>,
144    state: DashMapStateStore<K>,
145    gcra: DashMap<K, Gcra>,
146    clock: C,
147    start: C::Instant,
148}
149
150impl<K, C> Debug for RateLimiter<K, C>
151where
152    K: Debug,
153    C: Clock,
154{
155    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
156        f.debug_struct(stringify!(RateLimiter)).finish()
157    }
158}
159
160impl<K> RateLimiter<K, MonotonicClock>
161where
162    K: Eq + Hash,
163{
164    pub fn new_with_quota(base_quota: Option<Quota>, keyed_quotas: Vec<(K, Quota)>) -> Self {
165        let clock = MonotonicClock {};
166        let start = MonotonicClock::now(&clock);
167        let gcra = DashMap::from_iter(keyed_quotas.into_iter().map(|(k, q)| (k, Gcra::new(q))));
168        Self {
169            default_gcra: base_quota.map(Gcra::new),
170            state: DashMapStateStore::new(),
171            gcra,
172            clock,
173            start,
174        }
175    }
176}
177
178impl<K> RateLimiter<K, FakeRelativeClock>
179where
180    K: Hash + Eq + Clone,
181{
182    pub fn advance_clock(&self, by: Duration) {
183        self.clock.advance(by);
184    }
185}
186
187impl<K, C> RateLimiter<K, C>
188where
189    K: Hash + Eq + Clone,
190    C: Clock,
191{
192    pub fn add_quota_for_key(&self, key: K, value: Quota) {
193        self.gcra.insert(key, Gcra::new(value));
194    }
195
196    /// Checks if the given key is allowed under the rate limit.
197    ///
198    /// # Errors
199    ///
200    /// Returns `Err(NotUntil)` if the key is rate-limited, indicating when it will be allowed.
201    pub fn check_key(&self, key: &K) -> Result<(), NotUntil<C::Instant>> {
202        match self.gcra.get(key) {
203            Some(quota) => quota.test_and_update(self.start, key, &self.state, self.clock.now()),
204            None => self.default_gcra.as_ref().map_or(Ok(()), |gcra| {
205                gcra.test_and_update(self.start, key, &self.state, self.clock.now())
206            }),
207        }
208    }
209
210    pub async fn until_key_ready(&self, key: &K) {
211        loop {
212            match self.check_key(key) {
213                Ok(()) => {
214                    break;
215                }
216                Err(neg) => {
217                    sleep(neg.wait_time_from(self.clock.now())).await;
218                }
219            }
220        }
221    }
222
223    pub async fn await_keys_ready(&self, keys: Option<Vec<K>>) {
224        let keys = keys.unwrap_or_default();
225        let tasks = keys.iter().map(|key| self.until_key_ready(key));
226
227        futures::stream::iter(tasks)
228            .for_each_concurrent(None, |key_future| async move {
229                key_future.await;
230            })
231            .await;
232    }
233}
234
235////////////////////////////////////////////////////////////////////////////////
236// Tests
237////////////////////////////////////////////////////////////////////////////////
238#[cfg(test)]
239mod tests {
240    use std::{num::NonZeroU32, time::Duration};
241
242    use dashmap::DashMap;
243    use rstest::rstest;
244
245    use super::{
246        DashMapStateStore, RateLimiter,
247        clock::{Clock, FakeRelativeClock},
248        gcra::Gcra,
249        quota::Quota,
250    };
251
252    fn initialize_mock_rate_limiter() -> RateLimiter<String, FakeRelativeClock> {
253        let clock = FakeRelativeClock::default();
254        let start = clock.now();
255        let gcra = DashMap::new();
256        let base_quota = Quota::per_second(NonZeroU32::new(2).unwrap());
257        RateLimiter {
258            default_gcra: Some(Gcra::new(base_quota)),
259            state: DashMapStateStore::new(),
260            gcra,
261            clock,
262            start,
263        }
264    }
265
266    #[rstest]
267    fn test_default_quota() {
268        let mock_limiter = initialize_mock_rate_limiter();
269
270        // Check base quota is not exceeded
271        assert!(mock_limiter.check_key(&"default".to_string()).is_ok());
272        assert!(mock_limiter.check_key(&"default".to_string()).is_ok());
273
274        // Check base quota is exceeded
275        assert!(mock_limiter.check_key(&"default".to_string()).is_err());
276
277        // Increment clock and check base quota is reset
278        mock_limiter.advance_clock(Duration::from_secs(1));
279        assert!(mock_limiter.check_key(&"default".to_string()).is_ok());
280    }
281
282    #[rstest]
283    fn test_custom_key_quota() {
284        let mock_limiter = initialize_mock_rate_limiter();
285
286        // Add new key quota pair
287        mock_limiter.add_quota_for_key(
288            "custom".to_string(),
289            Quota::per_second(NonZeroU32::new(1).unwrap()),
290        );
291
292        // Check custom quota
293        assert!(mock_limiter.check_key(&"custom".to_string()).is_ok());
294        assert!(mock_limiter.check_key(&"custom".to_string()).is_err());
295
296        // Check that default quota still applies to other keys
297        assert!(mock_limiter.check_key(&"default".to_string()).is_ok());
298        assert!(mock_limiter.check_key(&"default".to_string()).is_ok());
299        assert!(mock_limiter.check_key(&"default".to_string()).is_err());
300    }
301
302    #[rstest]
303    fn test_multiple_keys() {
304        let mock_limiter = initialize_mock_rate_limiter();
305
306        mock_limiter.add_quota_for_key(
307            "key1".to_string(),
308            Quota::per_second(NonZeroU32::new(1).unwrap()),
309        );
310        mock_limiter.add_quota_for_key(
311            "key2".to_string(),
312            Quota::per_second(NonZeroU32::new(3).unwrap()),
313        );
314
315        // Test key1
316        assert!(mock_limiter.check_key(&"key1".to_string()).is_ok());
317        assert!(mock_limiter.check_key(&"key1".to_string()).is_err());
318
319        // Test key2
320        assert!(mock_limiter.check_key(&"key2".to_string()).is_ok());
321        assert!(mock_limiter.check_key(&"key2".to_string()).is_ok());
322        assert!(mock_limiter.check_key(&"key2".to_string()).is_ok());
323        assert!(mock_limiter.check_key(&"key2".to_string()).is_err());
324    }
325
326    #[rstest]
327    fn test_quota_reset() {
328        let mock_limiter = initialize_mock_rate_limiter();
329
330        // Exhaust quota
331        assert!(mock_limiter.check_key(&"reset".to_string()).is_ok());
332        assert!(mock_limiter.check_key(&"reset".to_string()).is_ok());
333        assert!(mock_limiter.check_key(&"reset".to_string()).is_err());
334
335        // Advance clock by less than a second
336        mock_limiter.advance_clock(Duration::from_millis(499));
337        assert!(mock_limiter.check_key(&"reset".to_string()).is_err());
338
339        // Advance clock to reset
340        mock_limiter.advance_clock(Duration::from_millis(501));
341        assert!(mock_limiter.check_key(&"reset".to_string()).is_ok());
342    }
343
344    #[rstest]
345    fn test_different_quotas() {
346        let mock_limiter = initialize_mock_rate_limiter();
347
348        mock_limiter.add_quota_for_key(
349            "per_second".to_string(),
350            Quota::per_second(NonZeroU32::new(2).unwrap()),
351        );
352        mock_limiter.add_quota_for_key(
353            "per_minute".to_string(),
354            Quota::per_minute(NonZeroU32::new(3).unwrap()),
355        );
356
357        // Test per_second quota
358        assert!(mock_limiter.check_key(&"per_second".to_string()).is_ok());
359        assert!(mock_limiter.check_key(&"per_second".to_string()).is_ok());
360        assert!(mock_limiter.check_key(&"per_second".to_string()).is_err());
361
362        // Test per_minute quota
363        assert!(mock_limiter.check_key(&"per_minute".to_string()).is_ok());
364        assert!(mock_limiter.check_key(&"per_minute".to_string()).is_ok());
365        assert!(mock_limiter.check_key(&"per_minute".to_string()).is_ok());
366        assert!(mock_limiter.check_key(&"per_minute".to_string()).is_err());
367
368        // Advance clock and check reset
369        mock_limiter.advance_clock(Duration::from_secs(1));
370        assert!(mock_limiter.check_key(&"per_second".to_string()).is_ok());
371        assert!(mock_limiter.check_key(&"per_minute".to_string()).is_err());
372    }
373
374    #[tokio::test]
375    async fn test_await_keys_ready() {
376        let mock_limiter = initialize_mock_rate_limiter();
377
378        // Check base quota is not exceeded
379        assert!(mock_limiter.check_key(&"default".to_string()).is_ok());
380        assert!(mock_limiter.check_key(&"default".to_string()).is_ok());
381
382        // Check base quota is exceeded
383        assert!(mock_limiter.check_key(&"default".to_string()).is_err());
384
385        // Wait keys to be ready and check base quota is reset
386        mock_limiter.advance_clock(Duration::from_secs(1));
387        mock_limiter
388            .await_keys_ready(Some(vec!["default".to_string()]))
389            .await;
390        assert!(mock_limiter.check_key(&"default".to_string()).is_ok());
391    }
392}
nautilus_network/ratelimiter/mod.rs

nautilus_network/ratelimiter/
mod.rs
