retry

Crate retry provides utilities for retrying operations that can fail.

Documentation

retry has comprehensive documentation available on docs.rs.

Legal

retry is released under the MIT license. See LICENSE.

lib.rs:

Crate retry provides utilities for retrying operations that can fail.

Usage

Retry an operation using the retry function. retry accepts an iterator over Durations and a closure that returns a Result (or OperationResult; see below). The iterator is used to determine how long to wait after each unsuccessful try and how many times to try before giving up and returning Result::Err. The closure determines either the final successful value, or an error value, which can either be returned immediately or used to indicate that the operation should be retried.

Any type that implements Iterator with an associated Item type of Duration can be used to determine retry behavior, though a few useful implementations are provided in the delay module, including a fixed delay and exponential backoff.

let mut collection = vec![1, 2, 3].into_iter();

let result = retry(Fixed::from_millis(100), || {
    match collection.next() {
        Some(n) if n == 3 => Ok("n is 3!"),
        Some(_) => Err("n must be 3!"),
        None => Err("n was never 3!"),
    }
});

assert!(result.is_ok());

The Iterator API can be used to limit or modify the delay strategy. For example, to limit the number of retries to 1:

let mut collection = vec![1, 2, 3].into_iter();

let result = retry(Fixed::from_millis(100).take(1), || {
    match collection.next() {
        Some(n) if n == 3 => Ok("n is 3!"),
        Some(_) => Err("n must be 3!"),
        None => Err("n was never 3!"),
    }
});

assert!(result.is_err());

To deal with fatal errors, return OperationResult, which is like Result, but with a third case to distinguish between errors that should cause a retry and errors that should immediately return, halting retry behavior. (Internally, OperationResult is always used, and closures passed to retry that return plain Result are converted into OperationResult.)

use retry::OperationResult;
let mut collection = vec![1, 2].into_iter();
let value = retry(Fixed::from_millis(1), || {
    match collection.next() {
        Some(n) if n == 2 => OperationResult::Ok(n),
        Some(_) => OperationResult::Retry("not 2"),
        None => OperationResult::Err("not found"),
    }
}).unwrap();

assert_eq!(value, 2);

If your operation needs to know how many times it's been tried, use the retry_with_index function. This works the same as retry, but passes the number of the current try to the closure as an argument.

let mut collection = vec![1, 2, 3, 4, 5].into_iter();

let result = retry_with_index(Fixed::from_millis(100), |current_try| {
    if current_try > 3 {
        return OperationResult::Err("did not succeed within 3 tries");
    }

    match collection.next() {
        Some(n) if n == 5 => OperationResult::Ok("n is 5!"),
        Some(_) => OperationResult::Retry("n must be 5!"),
        None => OperationResult::Retry("n was never 5!"),
    }
});

assert!(result.is_err());

Features

• random: offer some random delay utilities (on by default)