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use std::time::Duration;
use std::iter::Iterator;
use std::u64::MAX as U64_MAX;
#[derive(Debug, Clone)]
pub struct ExponentialBackoff {
current: u64,
base: u64,
factor: u64,
max_delay: Option<Duration>,
}
impl ExponentialBackoff {
pub fn from_millis(base: u64) -> ExponentialBackoff {
ExponentialBackoff {
current: base,
base: base,
factor: 1u64,
max_delay: None,
}
}
pub fn factor(mut self, factor: u64) -> ExponentialBackoff {
self.factor = factor;
self
}
pub fn max_delay(mut self, duration: Duration) -> ExponentialBackoff {
self.max_delay = Some(duration);
self
}
}
impl Iterator for ExponentialBackoff {
type Item = Duration;
fn next(&mut self) -> Option<Duration> {
let duration = if let Some(duration) = self.current.checked_mul(self.factor) {
Duration::from_millis(duration)
} else {
Duration::from_millis(U64_MAX)
};
if let Some(ref max_delay) = self.max_delay {
if duration > *max_delay {
return Some(*max_delay);
}
}
if let Some(next) = self.current.checked_mul(self.base) {
self.current = next;
} else {
self.current = U64_MAX;
}
Some(duration)
}
}
#[test]
fn returns_some_exponential_base_10() {
let mut s = ExponentialBackoff::from_millis(10);
assert_eq!(s.next(), Some(Duration::from_millis(10)));
assert_eq!(s.next(), Some(Duration::from_millis(100)));
assert_eq!(s.next(), Some(Duration::from_millis(1000)));
}
#[test]
fn returns_some_exponential_base_2() {
let mut s = ExponentialBackoff::from_millis(2);
assert_eq!(s.next(), Some(Duration::from_millis(2)));
assert_eq!(s.next(), Some(Duration::from_millis(4)));
assert_eq!(s.next(), Some(Duration::from_millis(8)));
}
#[test]
fn saturates_at_maximum_value() {
let mut s = ExponentialBackoff::from_millis(U64_MAX - 1);
assert_eq!(s.next(), Some(Duration::from_millis(U64_MAX - 1)));
assert_eq!(s.next(), Some(Duration::from_millis(U64_MAX)));
assert_eq!(s.next(), Some(Duration::from_millis(U64_MAX)));
}
#[test]
fn can_use_factor_to_get_seconds() {
let factor = 1000;
let mut s = ExponentialBackoff::from_millis(2).factor(factor);
assert_eq!(s.next(), Some(Duration::from_secs(2)));
assert_eq!(s.next(), Some(Duration::from_secs(4)));
assert_eq!(s.next(), Some(Duration::from_secs(8)));
}
#[test]
fn stops_increasing_at_max_delay() {
let mut s = ExponentialBackoff::from_millis(2).max_delay(Duration::from_millis(4));
assert_eq!(s.next(), Some(Duration::from_millis(2)));
assert_eq!(s.next(), Some(Duration::from_millis(4)));
assert_eq!(s.next(), Some(Duration::from_millis(4)));
}
#[test]
fn returns_max_when_max_less_than_base() {
let mut s = ExponentialBackoff::from_millis(20).max_delay(Duration::from_millis(10));
assert_eq!(s.next(), Some(Duration::from_millis(10)));
assert_eq!(s.next(), Some(Duration::from_millis(10)));
}