feat: Add std support for no-std without global rand seed (Xuanwo#169)

Split Xuanwo#168 into two PRs as requested, this is the one for no_std support. --------- Co-authored-by: Xuanwo <[email protected]>
wackazong · Dec 17, 2024 · e42e968 · e42e968
1 parent 7339faa
commit e42e968
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diff --git a/backon/Cargo.toml b/backon/Cargo.toml
@@ -22,6 +22,8 @@ targets = [
 [features]
 default = ["std", "std-blocking-sleep", "tokio-sleep", "gloo-timers-sleep"]
 std = ["fastrand/std"]
+default = ["std", "std-blocking-sleep", "tokio-sleep", "gloo-timers-sleep"]
+std = ["fastrand/std"]
 std-blocking-sleep = []
 gloo-timers-sleep = ["gloo-timers/futures"]
 tokio-sleep = ["tokio/time"]

diff --git a/backon/src/backoff/exponential.rs b/backon/src/backoff/exponential.rs
@@ -42,6 +42,7 @@ pub struct ExponentialBuilder {
     max_delay: Option<Duration>,
     max_times: Option<usize>,
     seed: Option<u64>,
+    seed: Option<u64>,
 }
 
 impl Default for ExponentialBuilder {
@@ -53,11 +54,13 @@ impl Default for ExponentialBuilder {
             max_delay: Some(Duration::from_secs(60)),
             max_times: Some(3),
             seed: None,
+            seed: None,
         }
     }
 }
 
 impl ExponentialBuilder {
+    /// Enable jitter for the backoff.
     /// Enable jitter for the backoff.
     ///
     /// When jitter is enabled, [`ExponentialBackoff`] will add a random jitter within `(0, min_delay)`
@@ -73,6 +76,12 @@ impl ExponentialBuilder {
         self
     }
 
+    /// Set the seed value for the jitter random number generator. If no seed is given, a random seed is used in std and default seed is used in no_std.
+    pub fn with_jitter_seed(mut self, seed: u64) -> Self {
+        self.seed = Some(seed);
+        self
+    }
+
     /// Set the factor for the backoff.
     ///
     /// # Panics
@@ -145,6 +154,17 @@ impl BackoffBuilder for ExponentialBuilder {
 
                 rng
             },
+            rng: if let Some(seed) = self.seed {
+                fastrand::Rng::with_seed(seed)
+            } else {
+                #[cfg(feature = "std")]
+                let rng = fastrand::Rng::new();
+
+                #[cfg(not(feature = "std"))]
+                let rng = fastrand::Rng::with_seed(super::RANDOM_SEED);
+
+                rng
+            },
             factor: self.factor,
             min_delay: self.min_delay,
             max_delay: self.max_delay,
@@ -172,6 +192,7 @@ impl BackoffBuilder for &ExponentialBuilder {
 pub struct ExponentialBackoff {
     jitter: bool,
     rng: fastrand::Rng,
+    rng: fastrand::Rng,
     factor: f32,
     min_delay: Duration,
     max_delay: Option<Duration>,
@@ -215,6 +236,7 @@ impl Iterator for ExponentialBackoff {
         // If jitter is enabled, add random jitter based on min delay.
         if self.jitter {
             tmp_cur = tmp_cur.saturating_add(self.min_delay.mul_f32(self.rng.f32()));
+            tmp_cur = tmp_cur.saturating_add(self.min_delay.mul_f32(self.rng.f32()));
         }
         Some(tmp_cur)
     }
@@ -333,6 +355,7 @@ mod tests {
     fn test_exponential_max_delay_without_default_1() {
         let mut exp = ExponentialBuilder {
             jitter: false,
+            seed: Some(0x2fdb0020ffc7722b),
             seed: 0x2fdb0020ffc7722b,
             factor: 10_000_000_000_f32,
             min_delay: Duration::from_secs(1),
@@ -351,6 +374,7 @@ mod tests {
     fn test_exponential_max_delay_without_default_2() {
         let mut exp = ExponentialBuilder {
             jitter: true,
+            seed: Some(0x2fdb0020ffc7722b),
             seed: 0x2fdb0020ffc7722b,
             factor: 10_000_000_000_f32,
             min_delay: Duration::from_secs(10_000_000_000),
@@ -369,6 +393,7 @@ mod tests {
     fn test_exponential_max_delay_without_default_3() {
         let mut exp = ExponentialBuilder {
             jitter: false,
+            seed: Some(0x2fdb0020ffc7722b),
             seed: 0x2fdb0020ffc7722b,
             factor: 10_000_000_000_f32,
             min_delay: Duration::from_secs(10_000_000_000),

diff --git a/backon/src/backoff/mod.rs b/backon/src/backoff/mod.rs
@@ -14,4 +14,5 @@ pub use exponential::ExponentialBackoff;
 pub use exponential::ExponentialBuilder;
 
 // Random seed value for no_std (the value is "backon" in hex)
+#[cfg(not(feature = "std"))]
 const RANDOM_SEED: u64 = 0x6261636b6f6e;