mettle

A resilience toolkit for Rust.

Composable, testable primitives for handling failure. Documentation.

Install

cargo add mettle

Blocking only, without an async runtime (no tokio):

cargo add mettle --no-default-features --features blocking

Example

use mettle::retry;
use std::time::Duration;

// Retry with sensible defaults (exponential backoff, up to 3 retries),
// then override only what you need.
let body = retry(|| async { fetch(&url).await })
    .when(|e: &FetchError| e.is_transient())   // skip permanent errors
    .max_elapsed(Duration::from_secs(30))       // give up after ~30s total
    .await?;

No async runtime? The blocking twin is identical but ends in .call() instead of .await.

Tools

Each tool comes with a runnable example. Start there:

retry: async examples/retry.rs · blocking examples/blocking_retry.rs

Retries emit tracing events out of the box (target mettle::retry). Install any subscriber (e.g. tracing_subscriber::fmt::init()) to see them.

Status

v0.x, with async (Tokio) and blocking APIs. Expect breaking changes before 1.0.

License

Licensed under either of

at your option.