Change exponential backoff algorithm for federation send (#4597)

* Limit federation send retry interval to one hour

* clippy

* avoid overflow

* change base for exp backoff

* ignore first error

* fix day duration

crates/api_common/src/lib.rs

@@ -27,7 +27,7 @@ pub extern crate lemmy_utils;
 
 pub use lemmy_utils::LemmyErrorType;
 use serde::{Deserialize, Serialize};
-use std::time::Duration;
+use std::{cmp::min, time::Duration};
 
 #[derive(Debug, Serialize, Deserialize, Clone)]
 #[cfg_attr(feature = "full", derive(ts_rs::TS))]
@@ -43,7 +43,39 @@ impl Default for SuccessResponse {
   }
 }
 
-/// how long to sleep based on how many retries have already happened
+// TODO: use from_days once stabilized
+// https://github.com/rust-lang/rust/issues/120301
+const DAY: Duration = Duration::from_secs(24 * 60 * 60);
+
+/// Calculate how long to sleep until next federation send based on how many
+/// retries have already happened. Uses exponential backoff with maximum of one day. The first
+/// error is ignored.
 pub fn federate_retry_sleep_duration(retry_count: i32) -> Duration {
-  Duration::from_secs_f64(2.0_f64.powf(f64::from(retry_count)))
+  debug_assert!(retry_count != 0);
+  if retry_count == 1 {
+    return Duration::from_secs(0);
+  }
+  let retry_count = retry_count - 1;
+  let pow = 1.25_f64.powf(retry_count.into());
+  let pow = Duration::try_from_secs_f64(pow).unwrap_or(DAY);
+  min(DAY, pow)
+}
+
+#[cfg(test)]
+pub(crate) mod tests {
+  use super::*;
+
+  #[test]
+  fn test_federate_retry_sleep_duration() {
+    assert_eq!(Duration::from_secs(0), federate_retry_sleep_duration(1));
+    assert_eq!(
+      Duration::new(1, 250000000),
+      federate_retry_sleep_duration(2)
+    );
+    assert_eq!(
+      Duration::new(2, 441406250),
+      federate_retry_sleep_duration(5)
+    );
+    assert_eq!(DAY, federate_retry_sleep_duration(100));
+  }
 }

scripts/test.sh

@@ -6,7 +6,7 @@ CWD="$(cd -P -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd -P)"
 cd $CWD/../
 
 PACKAGE="$1"
-echo "$PACKAGE"
+TEST="$2"
 
 source scripts/start_dev_db.sh
 
@@ -17,7 +17,7 @@ export RUST_BACKTRACE=1
 
 if [ -n "$PACKAGE" ];
 then
-  cargo test -p $PACKAGE --all-features --no-fail-fast
+  cargo test -p $PACKAGE --all-features --no-fail-fast $TEST
 else
   cargo test --workspace --no-fail-fast
 fi