throttlecrab

A high-performance GCRA (Generic Cell Rate Algorithm) rate limiter library for Rust.

Features

• Pure Rust: Zero-dependency GCRA rate limiter implementation
• GCRA algorithm: Implements the Generic Cell Rate Algorithm for smooth and predictable rate limiting
• High performance: Lock-free design with minimal overhead
• Flexible parameters: Different rate limits per key with dynamic configuration
• TTL support: Automatic cleanup of expired entries
• Multiple store implementations: Choose the right storage strategy for your use case

Installation

Add this to your Cargo.toml:

[dependencies]
throttlecrab = "0.2"

Usage

use std::time::SystemTime;
use throttlecrab::{RateLimiter, PeriodicStore};

fn main() {
    // Create a rate limiter with an in-memory store
    let mut limiter = RateLimiter::new(PeriodicStore::new());

    // Check if a request is allowed
    // Parameters: key, max_burst, count_per_period, period (seconds), quantity, timestamp
    let (allowed, result) = limiter
        .rate_limit("api_key_123", 10, 100, 60, 1, SystemTime::now())
        .unwrap();

    if allowed {
        println!("Request allowed! Remaining: {}", result.remaining);
    } else {
        println!("Rate limit exceeded! Retry after: {:?}", result.retry_after);
    }
}

Store Implementations

The library provides several store implementations optimized for different use cases:

• PeriodicStore: Cleans up expired entries at regular intervals (default)
• AdaptiveStore: Dynamically adapts cleanup frequency based on usage patterns
• ProbabilisticStore: Each operation has a probability of triggering cleanup

What is GCRA?

The Generic Cell Rate Algorithm (GCRA) is a rate limiting algorithm that provides:

• Smooth traffic shaping: No sudden bursts followed by long waits
• Precise rate limiting: Exact control over request rates
• Fairness: All clients get predictable access to resources
• Memory efficiency: O(1) space per key

GCRA works by tracking the "Theoretical Arrival Time" (TAT) of requests, ensuring consistent spacing between allowed requests while permitting controlled bursts.

Server

Looking for a standalone rate limiting server? Check out throttlecrab-server which provides HTTP and gRPC interfaces.

License

Licensed under the MIT license (LICENSE or http://opensource.org/licenses/MIT)