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514//! Generic retry with exponential backoff and jitter.
//!
//! Provides a configurable, async-aware retry utility that can be used for
//! LLM API calls, network operations, channel message delivery, and any
//! other fallible async operation across the OpenFang codebase.
//!
//! Jitter uses `std::time::SystemTime` UNIX nanos as a seed to avoid
//! requiring the `rand` crate as a dependency.
use tracing::{debug, warn};
// ---------------------------------------------------------------------------
// Types
// ---------------------------------------------------------------------------
/// Configuration for retry behavior.
#[derive(Debug, Clone)]
pub struct RetryConfig {
/// Maximum number of attempts (including the first try).
pub max_attempts: u32,
/// Minimum delay between retries in milliseconds.
pub min_delay_ms: u64,
/// Maximum delay between retries in milliseconds.
pub max_delay_ms: u64,
/// Jitter factor (0.0 = no jitter, 1.0 = full jitter).
///
/// The actual sleep is `delay * (1 + random_fraction * jitter)`, where
/// `random_fraction` is in `[0, 1)`.
pub jitter: f64,
}
impl Default for RetryConfig {
fn default() -> Self {
Self {
max_attempts: 3,
min_delay_ms: 300,
max_delay_ms: 30_000,
jitter: 0.2,
}
}
}
/// Result of a retry operation.
#[derive(Debug)]
pub enum RetryOutcome<T, E> {
/// The operation succeeded.
Success {
/// The successful result.
result: T,
/// Total number of attempts made (1 = first try succeeded).
attempts: u32,
},
/// All retries exhausted without success.
Exhausted {
/// The error from the last attempt.
last_error: E,
/// Total number of attempts made.
attempts: u32,
},
}
// ---------------------------------------------------------------------------
// Backoff computation
// ---------------------------------------------------------------------------
/// Compute the delay for a given attempt (0-indexed).
///
/// Formula: `min(min_delay * 2^attempt, max_delay) * (1 + random * jitter)`
///
/// Uses `std::time::SystemTime` nanos as a lightweight pseudo-random source
/// instead of requiring the `rand` crate.
pub fn compute_backoff(config: &RetryConfig, attempt: u32) -> u64 {
// Exponential base: min_delay * 2^attempt, capped at max_delay.
let base = config
.min_delay_ms
.saturating_mul(1u64.checked_shl(attempt).unwrap_or(u64::MAX));
let capped = base.min(config.max_delay_ms);
// Jitter: multiply by (1 + random_fraction * jitter).
if config.jitter <= 0.0 {
return capped;
}
let frac = pseudo_random_fraction();
let jitter_offset = (capped as f64) * frac * config.jitter;
let with_jitter = (capped as f64) + jitter_offset;
// Clamp to max_delay (jitter can push slightly above).
(with_jitter as u64).min(config.max_delay_ms)
}
/// Return a pseudo-random fraction in `[0, 1)` using the current system time
/// nanos. This is NOT cryptographically secure, but good enough for jitter.
fn pseudo_random_fraction() -> f64 {
let nanos = std::time::SystemTime::now()
.duration_since(std::time::UNIX_EPOCH)
.unwrap_or_default()
.subsec_nanos();
// Mix the bits a bit to reduce predictability.
let mixed = nanos.wrapping_mul(2654435761); // Knuth multiplicative hash
(mixed as f64) / (u32::MAX as f64)
}
// ---------------------------------------------------------------------------
// Core retry function
// ---------------------------------------------------------------------------
/// Execute an async operation with retry.
///
/// # Parameters
///
/// - `config` — retry configuration (attempts, delays, jitter).
/// - `operation` — the async closure to execute. Called once per attempt.
/// - `should_retry` — predicate that inspects the error and returns `true`
/// if the operation should be retried.
/// - `retry_after_hint` — optional hint extractor. If it returns `Some(ms)`,
/// that delay is used instead of the computed backoff (but still capped at
/// `max_delay_ms`).
///
/// # Returns
///
/// A `RetryOutcome` indicating success or exhaustion.
pub async fn retry_async<F, Fut, T, E, P, H>(
config: &RetryConfig,
mut operation: F,
should_retry: P,
retry_after_hint: H,
) -> RetryOutcome<T, E>
where
F: FnMut() -> Fut,
Fut: std::future::Future<Output = Result<T, E>>,
P: Fn(&E) -> bool,
H: Fn(&E) -> Option<u64>,
E: std::fmt::Debug,
{
let max = config.max_attempts.max(1);
let mut last_error: Option<E> = None;
for attempt in 0..max {
match operation().await {
Ok(result) => {
if attempt > 0 {
debug!(
attempt = attempt + 1,
"retry succeeded after {} previous failures", attempt
);
}
return RetryOutcome::Success {
result,
attempts: attempt + 1,
};
}
Err(err) => {
let is_last = attempt + 1 >= max;
if is_last || !should_retry(&err) {
if !should_retry(&err) {
debug!(
attempt = attempt + 1,
"error is not retryable, giving up: {:?}", err
);
} else {
warn!(
attempt = attempt + 1,
max_attempts = max,
"all retry attempts exhausted: {:?}",
err
);
}
return RetryOutcome::Exhausted {
last_error: err,
attempts: attempt + 1,
};
}
// Determine delay.
let hint = retry_after_hint(&err);
let delay_ms = if let Some(hinted) = hint {
// Respect the hint, but cap it.
hinted.min(config.max_delay_ms)
} else {
compute_backoff(config, attempt)
};
debug!(
attempt = attempt + 1,
delay_ms, "retrying after error: {:?}", err
);
tokio::time::sleep(std::time::Duration::from_millis(delay_ms)).await;
last_error = Some(err);
}
}
}
// Should not be reachable, but handle gracefully.
RetryOutcome::Exhausted {
last_error: last_error.expect("at least one attempt should have been made"),
attempts: max,
}
}
// ---------------------------------------------------------------------------
// Pre-built configs
// ---------------------------------------------------------------------------
/// Retry config for LLM API calls.
///
/// 3 attempts, 1s initial delay, up to 60s, 20% jitter.
pub fn llm_retry_config() -> RetryConfig {
RetryConfig {
max_attempts: 3,
min_delay_ms: 1_000,
max_delay_ms: 60_000,
jitter: 0.2,
}
}
/// Retry config for network operations (webhooks, fetches).
///
/// 3 attempts, 500ms initial delay, up to 30s, 10% jitter.
pub fn network_retry_config() -> RetryConfig {
RetryConfig {
max_attempts: 3,
min_delay_ms: 500,
max_delay_ms: 30_000,
jitter: 0.1,
}
}
/// Retry config for channel message delivery.
///
/// 3 attempts, 400ms initial delay, up to 15s, 10% jitter.
pub fn channel_retry_config() -> RetryConfig {
RetryConfig {
max_attempts: 3,
min_delay_ms: 400,
max_delay_ms: 15_000,
jitter: 0.1,
}
}
// ===========================================================================
// Tests
// ===========================================================================
#[cfg(test)]
mod tests {
use super::*;
use std::sync::atomic::{AtomicU32, Ordering};
use std::sync::Arc;
#[test]
fn test_retry_config_defaults() {
let config = RetryConfig::default();
assert_eq!(config.max_attempts, 3);
assert_eq!(config.min_delay_ms, 300);
assert_eq!(config.max_delay_ms, 30_000);
assert!((config.jitter - 0.2).abs() < f64::EPSILON);
}
#[test]
fn test_compute_backoff_exponential() {
let config = RetryConfig {
max_attempts: 5,
min_delay_ms: 100,
max_delay_ms: 100_000,
jitter: 0.0, // no jitter for deterministic test
};
// 100 * 2^0 = 100
assert_eq!(compute_backoff(&config, 0), 100);
// 100 * 2^1 = 200
assert_eq!(compute_backoff(&config, 1), 200);
// 100 * 2^2 = 400
assert_eq!(compute_backoff(&config, 2), 400);
// 100 * 2^3 = 800
assert_eq!(compute_backoff(&config, 3), 800);
}
#[test]
fn test_compute_backoff_capped() {
let config = RetryConfig {
max_attempts: 10,
min_delay_ms: 1_000,
max_delay_ms: 5_000,
jitter: 0.0,
};
// 1000 * 2^0 = 1000
assert_eq!(compute_backoff(&config, 0), 1_000);
// 1000 * 2^1 = 2000
assert_eq!(compute_backoff(&config, 1), 2_000);
// 1000 * 2^2 = 4000
assert_eq!(compute_backoff(&config, 2), 4_000);
// 1000 * 2^3 = 8000, capped at 5000
assert_eq!(compute_backoff(&config, 3), 5_000);
// Further attempts stay capped
assert_eq!(compute_backoff(&config, 10), 5_000);
}
#[tokio::test]
async fn test_retry_success_first_try() {
let config = RetryConfig {
max_attempts: 3,
min_delay_ms: 10,
max_delay_ms: 100,
jitter: 0.0,
};
let outcome = retry_async(
&config,
|| async { Ok::<&str, &str>("hello") },
|_| true,
|_: &&str| None,
)
.await;
match outcome {
RetryOutcome::Success { result, attempts } => {
assert_eq!(result, "hello");
assert_eq!(attempts, 1);
}
_ => panic!("expected success"),
}
}
#[tokio::test]
async fn test_retry_success_after_failures() {
let config = RetryConfig {
max_attempts: 5,
min_delay_ms: 1, // tiny delays for test speed
max_delay_ms: 10,
jitter: 0.0,
};
let counter = Arc::new(AtomicU32::new(0));
let counter_clone = counter.clone();
let outcome = retry_async(
&config,
move || {
let c = counter_clone.clone();
async move {
let n = c.fetch_add(1, Ordering::SeqCst);
if n < 2 {
Err("not yet")
} else {
Ok("finally")
}
}
},
|_| true,
|_: &&str| None,
)
.await;
match outcome {
RetryOutcome::Success { result, attempts } => {
assert_eq!(result, "finally");
assert_eq!(attempts, 3); // failed twice, succeeded on 3rd
}
_ => panic!("expected success"),
}
}
#[tokio::test]
async fn test_retry_exhausted() {
let config = RetryConfig {
max_attempts: 3,
min_delay_ms: 1,
max_delay_ms: 10,
jitter: 0.0,
};
let outcome = retry_async(
&config,
|| async { Err::<(), &str>("always fails") },
|_| true,
|_: &&str| None,
)
.await;
match outcome {
RetryOutcome::Exhausted {
last_error,
attempts,
} => {
assert_eq!(last_error, "always fails");
assert_eq!(attempts, 3);
}
_ => panic!("expected exhausted"),
}
}
#[tokio::test]
async fn test_retry_non_retryable_error() {
let config = RetryConfig {
max_attempts: 5,
min_delay_ms: 1,
max_delay_ms: 10,
jitter: 0.0,
};
let counter = Arc::new(AtomicU32::new(0));
let counter_clone = counter.clone();
let outcome = retry_async(
&config,
move || {
let c = counter_clone.clone();
async move {
c.fetch_add(1, Ordering::SeqCst);
Err::<(), &str>("fatal error")
}
},
|_| false, // never retry
|_: &&str| None,
)
.await;
match outcome {
RetryOutcome::Exhausted {
last_error,
attempts,
} => {
assert_eq!(last_error, "fatal error");
assert_eq!(attempts, 1); // gave up immediately
}
_ => panic!("expected exhausted"),
}
assert_eq!(counter.load(Ordering::SeqCst), 1);
}
#[tokio::test]
async fn test_retry_with_hint_delay() {
let config = RetryConfig {
max_attempts: 3,
min_delay_ms: 10_000, // large base delay
max_delay_ms: 60_000,
jitter: 0.0,
};
let counter = Arc::new(AtomicU32::new(0));
let counter_clone = counter.clone();
let start = std::time::Instant::now();
let outcome = retry_async(
&config,
move || {
let c = counter_clone.clone();
async move {
let n = c.fetch_add(1, Ordering::SeqCst);
if n < 1 {
Err("transient")
} else {
Ok("ok")
}
}
},
|_| true,
|_: &&str| Some(1), // hint: 1ms delay (overrides 10s base)
)
.await;
let elapsed = start.elapsed();
match outcome {
RetryOutcome::Success { result, attempts } => {
assert_eq!(result, "ok");
assert_eq!(attempts, 2);
// Should complete in well under 1 second (hint was 1ms,
// not the 10s base delay).
assert!(
elapsed.as_millis() < 5_000,
"retry took too long: {:?} — hint should have overridden base delay",
elapsed
);
}
_ => panic!("expected success"),
}
}
#[test]
fn test_llm_retry_config() {
let config = llm_retry_config();
assert_eq!(config.max_attempts, 3);
assert_eq!(config.min_delay_ms, 1_000);
assert_eq!(config.max_delay_ms, 60_000);
assert!((config.jitter - 0.2).abs() < f64::EPSILON);
}
#[test]
fn test_channel_retry_config() {
let config = channel_retry_config();
assert_eq!(config.max_attempts, 3);
assert_eq!(config.min_delay_ms, 400);
assert_eq!(config.max_delay_ms, 15_000);
assert!((config.jitter - 0.1).abs() < f64::EPSILON);
}
#[test]
fn test_network_retry_config() {
let config = network_retry_config();
assert_eq!(config.max_attempts, 3);
assert_eq!(config.min_delay_ms, 500);
assert_eq!(config.max_delay_ms, 30_000);
assert!((config.jitter - 0.1).abs() < f64::EPSILON);
}
}