# `rate-guard-core`
A comprehensive rate limiting library for Rust applications with multiple thread-safe algorithms.
[](https://crates.io/crates/rate-guard-core)
[](https://docs.rs/rate-guard-core)
[](https://opensource.org/licenses/MIT)
[](https://opensource.org/licenses/Apache-2.0)
## Features
**4 Rate Limiting Algorithms**: Token Bucket, Fixed Window Counter, Sliding Window Counter, and Approximate Sliding Window
**Thread-Safe**: All algorithms use non-blocking locks
**Zero Dependencies**: Lightweight with no external dependencies
**Flexible Time**: Works with any time unit via abstract "ticks"
**Configurable Tick Precision**: Compile-time feature flags allow choosing `u64` (default) or `u128` for tick units
**Rust 1.60+**: Compatible with older Rust versions
---
## Quick Start
### from crate.io
Add to your `Cargo.toml`:
```toml
[dependencies]
rate-guard-core = { version = "0.7.0" }
```
### from Github
Add to your `Cargo.toml`:
```toml
[dependencies]
rate-guard-core = { git = "https://github.com/Kuanlin/rate-guard-core", tag = "v0.7.0" }
```
---
## Tick Precision (u64 / u128)
By default, the crate uses `u64` as the tick unit, allowing up to ~584 years of nanosecond-resolution time.
If your application needs ultra-long durations or ultra-high precision, you can enable `u128` support via feature flags:
### from crate.io
```toml
[dependencies]
rate-guard-core = { version = "0.7.0", default-features = false, features = ["tick-u128"] }
```
### from Github
```toml
[dependencies]
rate-guard-core = { git = "https://github.com/Kuanlin/rate-guard-core", tag = "v0.7.0", default-features = false, features = ["tick-u128"] }
```
---
## Usage Examples
### Token Bucket
Perfect for APIs that allow occasional bursts while maintaining average rate:
```rust
use rate_guard_core::cores::{TokenBucketCore, TokenBucketCoreConfig};
let config = TokenBucketCoreConfig {
capacity: 100,
refill_interval: 5,
refill_amount: 10,
};
// Option 1: Using `into()` – idiomatic Rust way to convert config into limiter
let limiter: TokenBucketCore = config.into();
// Option 2: Using `from()` – explicitly convert config into limiter
let limiter_alt = TokenBucketCore::from(config);
```
---
### Fixed Window Counter
```rust
use rate_guard_core::cores::{FixedWindowCounterCore, FixedWindowCounterCoreConfig};
let config = FixedWindowCounterCoreConfig {
capacity: 100,
window_size: 60,
};
// Option 1: Using `into()` – idiomatic Rust way to convert config into limiter
let limiter: FixedWindowCounterCore = config.into();
// Option 2: Using `from()` – explicitly convert config into limiter
let limiter_alt = FixedWindowCounterCore::from(config);
```
---
### Sliding Window Counter
```rust
use rate_guard_core::cores::{SlidingWindowCounterCore, SlidingWindowCounterCoreConfig};
let config = SlidingWindowCounterCoreConfig {
capacity: 100,
bucket_ticks: 10,
bucket_count: 6,
};
// Option 1: Using `into()` – idiomatic Rust way to convert config into limiter
let limiter: SlidingWindowCounterCore = config.into();
// Option 2: Using `from()` – explicitly convert config into limiter
let limiter_alt = SlidingWindowCounterCore::from(config);
```
---
### Approximate Sliding Window
A memory-optimized version of sliding window counter.
Formula:
`Used = (1 - X%) * lastWindow + currentWindow` where X is the proportion of request time within the current window.
```rust
use rate_guard_core::cores::{ApproximateSlidingWindowCore, ApproximateSlidingWindowCoreConfig};
let config = ApproximateSlidingWindowCoreConfig {
capacity: 100,
window_ticks: 60,
};
// Option 1: Using `into()` – idiomatic Rust way to convert config into limiter
let limiter: ApproximateSlidingWindowCore = config.into();
// Option 2: Using `from()` – explicitly convert config into limiter
let limiter_alt = ApproximateSlidingWindowCore::from(config);
```
Both `into()` and `from()` are functionally equivalent in Rust.
`into()` is shorter and idiomatic; `from()` is more explicit and beginner-friendly.
These examples are duplicated to help both Rust newcomers and non-Rust readers understand the conversion logic.
---
### Approximate Sliding Window
A memory-optimized version of sliding window counter.
Formula:
`Used = (1 - X%) * lastWindow + currentWindow` where X is the proportion of request time within the current window.
```rust
use rate_guard_core::cores::{ApproximateSlidingWindowCore, ApproximateSlidingWindowCoreConfig};
let config = ApproximateSlidingWindowCoreConfig {
capacity: 100,
window_ticks: 60,
};
let limiter: ApproximateSlidingWindowCore = ApproximateSlidingWindowCore::from(config);
```
---
## Error Handling
All limiters' try_acquire_at returns `SimpleRateLimitResult`:
```Rust
use rate_guard_core::{SimpleRateLimitError, SimpleRateLimitResult};
match limiter.try_acquire_at(tick, 1) {
Ok(()) => {
// Request allowed
},
Err(SimpleRateLimitError::InsufficientCapacity) => {
// Rate limit exceeded
},
Err(SimpleRateLimitError::BeyondCapacity) => {
// Acquiring too much
},
Err(SimpleRateLimitError::ExpiredTick) => {
// Time went backwards
},
Err(SimpleRateLimitError::ContentionFailure) => {
// Lock contention, you can do sleep and retry here.
},
}
```
---
## Verbose Error Reporting
Each limiter also supports `try_acquire_verbose_at(tick, tokens)`, which returns a `VerboseRateLimitError` with richer diagnostics:
`ContentionFailure`: Lock was unavailable
`ExpiredTick { min_acceptable_tick }`: Time went backwards
`BeyondCapacity { acquiring, capacity }`: Requested tokens exceed max
`InsufficientCapacity { acquiring, available, retry_after_ticks }`: Not enough tokens now, but suggests how long to wait before retrying
```Rust
use rate_guard_core::{VerboseRateLimitError, VerboseRateLimitResult};
match limiter.try_acquire_verbose_at(tick, 5) {
Ok(()) => {
// Request allowed
}
Err(VerboseRateLimitError::InsufficientCapacity { retry_after_ticks, .. }) => {
println!("Retry after {} ticks", retry_after_ticks);
}
Err(e) => {
println!("Rate limit error: {:?}", e);
}
}
```
`try_acquire_verbose_at` is useful for retry logic, logging, or adaptive throttling.
---
## Time Management
The library uses abstract "ticks" for time. You can map any time source:
```Rust
// Seconds
let tick = SystemTime::now().duration_since(UNIX_EPOCH).unwrap().as_secs();
// Milliseconds
let tick = SystemTime::now().duration_since(UNIX_EPOCH).unwrap().as_millis() as u64;
// Custom time
let tick = my_monotonic_timer.elapsed_ticks();
```
---
## Thread Safety
```Rust
use std::sync::Arc;
use std::thread;
use rate_guard_core::cores::TokenBucketCore;
let limiter = Arc::new(TokenBucketCore::new(100, 1, 10));
for _ in 0..10 {
let limiter = limiter.clone();
thread::spawn(move || {
match limiter.try_acquire_at(get_current_tick(), 1) {
Ok(()) => println!("Request processed"),
Err(e) => println!("Rate limited: {}", e),
}
});
}
```
---
## License
Licensed under either of Apache License, Version 2.0 or MIT license at your option.
---
## Contributing
Contributions are welcome! Please feel free to submit a Pull Request.