nautilus_network/ratelimiter/
quota.rs

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14// -------------------------------------------------------------------------------------------------
15
16use std::{num::NonZeroU32, time::Duration};
17
18use super::nanos::Nanos;
19
20/// A rate-limiting quota.
21///
22/// Quotas are expressed in a positive number of "cells" (the maximum number of positive decisions /
23/// allowed items until the rate limiter needs to replenish) and the amount of time for the rate
24/// limiter to replenish a single cell.
25///
26/// Neither the number of cells nor the replenishment unit of time may be zero.
27///
28/// # Burst Sizes
29/// There are multiple ways of expressing the same quota: a quota given as `Quota::per_second(1)`
30/// allows, on average, the same number of cells through as a quota given as `Quota::per_minute(60)`.
31/// The quota of `Quota::per_minute(60)` has a burst size of 60 cells, meaning it is
32/// possible to accommodate 60 cells in one go, after which the equivalent of a minute of inactivity
33/// is required for the burst allowance to be fully restored.
34///
35/// Burst size gets really important when you construct a rate limiter that should allow multiple
36/// elements through at one time (using [`RateLimiter.check_n`](struct.RateLimiter.html#method.check_n)
37/// and its related functions): Only
38/// at most as many cells can be let through in one call as are given as the burst size.
39///
40/// In other words, the burst size is the maximum number of cells that the rate limiter will ever
41/// allow through without replenishing them.
42#[derive(Debug, PartialEq, Eq, Clone, Copy)]
43pub struct Quota {
44    pub(crate) max_burst: NonZeroU32,
45    pub(crate) replenish_1_per: Duration,
46}
47
48/// Constructors for Quotas
49impl Quota {
50    /// Constructs a quota for a number of cells per second. The given number of cells is also
51    /// assumed to be the maximum burst size.
52    ///
53    /// Returns `None` if `max_burst` is so large that the replenish interval rounds to zero
54    /// nanoseconds (i.e. `max_burst > 1_000_000_000`).
55    #[must_use]
56    pub const fn per_second(max_burst: NonZeroU32) -> Option<Self> {
57        let replenish_interval_ns = Duration::from_secs(1).as_nanos() / (max_burst.get() as u128);
58        if replenish_interval_ns == 0 {
59            return None;
60        }
61        Some(Self {
62            max_burst,
63            replenish_1_per: Duration::from_nanos(replenish_interval_ns as u64),
64        })
65    }
66
67    /// Constructs a quota for a number of cells per 60-second period. The given number of cells
68    /// is also assumed to be the maximum burst size.
69    #[must_use]
70    pub const fn per_minute(max_burst: NonZeroU32) -> Self {
71        let replenish_interval_ns = Duration::from_mins(1).as_nanos() / (max_burst.get() as u128);
72        Self {
73            max_burst,
74            replenish_1_per: Duration::from_nanos(replenish_interval_ns as u64),
75        }
76    }
77
78    /// Constructs a quota for a number of cells per 60-minute period. The given number of cells
79    /// is also assumed to be the maximum burst size.
80    #[must_use]
81    pub const fn per_hour(max_burst: NonZeroU32) -> Self {
82        let replenish_interval_ns = Duration::from_hours(1).as_nanos() / (max_burst.get() as u128);
83        Self {
84            max_burst,
85            replenish_1_per: Duration::from_nanos(replenish_interval_ns as u64),
86        }
87    }
88
89    /// Constructs a quota that replenishes one cell in a given interval.
90    ///
91    /// If the time interval is zero, returns `None`.
92    #[must_use]
93    pub const fn with_period(replenish_1_per: Duration) -> Option<Self> {
94        if replenish_1_per.as_nanos() == 0 {
95            None
96        } else {
97            Some(Self {
98                max_burst: NonZeroU32::MIN,
99                replenish_1_per,
100            })
101        }
102    }
103
104    /// Adjusts the maximum burst size for a quota to construct a rate limiter with a capacity
105    /// for at most the given number of cells.
106    #[must_use]
107    pub const fn allow_burst(self, max_burst: NonZeroU32) -> Self {
108        Self { max_burst, ..self }
109    }
110}
111
112/// Retrieving information about a quota
113impl Quota {
114    /// The time it takes for a rate limiter with an exhausted burst budget to replenish
115    /// a single element.
116    #[must_use]
117    pub const fn replenish_interval(&self) -> Duration {
118        self.replenish_1_per
119    }
120
121    /// The maximum number of cells that can be allowed in one burst.
122    #[must_use]
123    pub const fn burst_size(&self) -> NonZeroU32 {
124        self.max_burst
125    }
126
127    /// The time it takes to replenish the entire maximum burst size.
128    ///
129    /// Saturates at [`Duration::MAX`] if the full duration cannot be represented.
130    #[must_use]
131    pub const fn burst_size_replenished_in(&self) -> Duration {
132        self.replenish_1_per.saturating_mul(self.max_burst.get())
133    }
134}
135
136impl Quota {
137    /// A way to reconstruct a Quota from an in-use Gcra.
138    ///
139    /// This is useful mainly for [`crate::middleware::RateLimitingMiddleware`]
140    /// where custom code may want to construct information based on
141    /// the amount of burst balance remaining.
142    ///
143    /// # Panics
144    ///
145    /// Panics if the division result is 0 or exceeds `u32::MAX`.
146    pub(crate) fn from_gcra_parameters(t: Nanos, tau: Nanos) -> Self {
147        let t_u64 = t.as_u64();
148        let tau_u64 = tau.as_u64();
149
150        // Validate division won't be zero or overflow
151        assert!(t_u64 != 0, "Invalid GCRA parameter: t cannot be zero");
152
153        let division_result = tau_u64 / t_u64;
154        assert!(
155            division_result != 0,
156            "Invalid GCRA parameters: tau/t results in zero burst capacity"
157        );
158        assert!(
159            u32::try_from(division_result).is_ok(),
160            "Invalid GCRA parameters: tau/t exceeds u32::MAX"
161        );
162
163        // We've verified the result is non-zero and fits in u32
164        let max_burst = NonZeroU32::new(division_result as u32)
165            .expect("Division result should be non-zero after validation");
166        let replenish_1_per = t.into();
167        Self {
168            max_burst,
169            replenish_1_per,
170        }
171    }
172}
nautilus_network/ratelimiter/quota.rs

nautilus_network/ratelimiter/
quota.rs
