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# GCRA: A basic implementation

Library which implements the core
[GCRA](https://en.wikipedia.org/wiki/Generic_cell_rate_algorithm) functionality in rust.

## Features

- `rate-limiter` a LRU + expiring rate limiter. Implements `Send + Sync` so can be used asynchronously.

## Usage

```rust
use gcra::{RateLimit, RatelimitGuard};

fn check_rate_limit() {
    const LIMIT: u32 = 1;
    // Create a rate limit that allows `1/1s`
    let rate_limit = RateLimit::per_sec(LIMIT);
    let mut rate_limit_guard = RateLimitGuard::new_state(rate_limit);

    assert!(rate_limit_guard.check_and_modify(1).is_ok());
    assert!(
        rate_limit_guard.check_and_modify(1).is_err(),
        "We should be over the limit now"
    );
}
```

### With `rate-limiter`

```rust
use std::sync::Arc;
use gcra::{GcraError, RateLimit, RateLimiter};

#[tokio::main]
async fn main() -> Result<(), GcraError> {
    let rate_limit = RateLimit::per_sec(2);
    let rate_limiter = Arc::new(RateLimiter::new(4));

    rate_limiter.check("key", &rate_limit, 1).await?;
    rate_limiter.check("key", &rate_limit, 1).await?;

    match rate_limiter.check("key", rate_limit.clone(), 1).await {
        Err(GcraError::DeniedUntil { next_allowed_at }) => {
            print!("Denied: Request next at {:?}", next_allowed_at);
            Ok(())
        }
        unexpected => panic!("Opps something went wrong! {:?}", unexpected),
    }
}
```