Crate leaky_bucket

A token-based rate limiter based on the leaky bucket algorithm.

If the tokens are already available, the acquisition will be instant through a fast path, and the acquired number of tokens will be added to the bucket.

If the bucket overflows (i.e. goes over max), the task that tried to acquire the tokens will be suspended until the required number of tokens has been added.

Usage

Add the following to your Cargo.toml:

leaky-bucket = "0.8.1"

Example

If the project is built with the static feature (default), you can use LeakyBucket directly as long as you are inside a Tokio runtime, like so:

use leaky_bucket::LeakyBucket;
use std::{error::Error, time::Duration};

#[tokio::main]
async fn main() -> Result<(), Box<dyn Error>> {
    let rate_limiter = LeakyBucket::builder()
        .max(5)
        .tokens(5)
        .build()?;

    println!("Waiting for permit...");
    // should take about 5 seconds to acquire.
    rate_limiter.acquire(10).await?;
    println!("I made it!");
    Ok(())
}

Note that only one coordinator instance will be lazily created, and it's associated with the runtime from within it was constructed. To use multiple runtimes you must use an explicit coordinator as documented in the next section.

Example using explicit coordinator

Leaky buckets require coordination. By default, this will happen through a static coordinator spawned through tokio::spawn at first use. If you want to spawn the coordinator yourself, you can do the following with LeakyBuckets:

use leaky_bucket::LeakyBuckets;
use std::{error::Error, time::Duration};

#[tokio::main]
async fn main() -> Result<(), Box<dyn Error>> {
    let mut buckets = LeakyBuckets::new();
    let coordinator = buckets.coordinate()?;

    // spawn the coordinate thread to refill the rate limiter.
    tokio::spawn(async move { coordinator.await.expect("coordinator errored") });

    let rate_limiter = buckets
        .rate_limiter()
        .max(5)
        .tokens(5)
        .build()?;

    println!("Waiting for permit...");
    // should take about 5 seconds to acquire.
    rate_limiter.acquire(10).await?;
    println!("I made it!");
    Ok(())
}

Note that since this coordinator uses timing facilities from tokio it has to be spawned within a Tokio runtime with the time feature enabled.

Structs

Builder	Builder for a leaky bucket.
LeakyBucket	The leaky bucket.
LeakyBuckets	Coordinator for rate limiters. Is used to create new rate limiters as needed.

Enums

Error

Error type for the rate limiter.