add simple rate-counter

Cargo.lock

@@ -3726,6 +3726,14 @@ dependencies = [
  "rand_core",
 ]
 
+[[package]]
+name = "rate-counter"
+version = "0.1.0"
+dependencies = [
+ "flume",
+ "tokio",
+]
+
 [[package]]
 name = "rayon"
 version = "1.6.1"

Cargo.toml

@@ -3,6 +3,7 @@ members = [
   "deferred-rate-limiter",
   "entities",
   "migration",
+  "rate-counter",
   "redis-rate-limiter",
   "thread-fast-rng",
   "web3_proxy",

rate-counter/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "rate-counter"
+version = "0.1.0"
+authors = ["Bryan Stitt <bryan@llamanodes.com>"]
+edition = "2021"
+
+[dependencies]
+flume = "0.10.14"
+tokio = { version = "1.25.0", features = ["time"] }

rate-counter/src/lib.rs

@@ -0,0 +1,35 @@
+//! A counter of events in a time period.
+use std::collections::VecDeque;
+use tokio::time::{Duration, Instant};
+
+/// Measures ticks in a time period.
+#[derive(Debug)]
+pub struct RateCounter {
+    period: Duration,
+    items: VecDeque<Instant>,
+}
+
+impl RateCounter {
+    pub fn new(period: Duration) -> Self {
+        let items = VecDeque::new();
+
+        Self { period, items }
+    }
+
+    /// update the counter and return the rate for the current period
+    /// true if the current time should be counted
+    pub fn update(&mut self, tick: bool) -> usize {
+        let now = Instant::now();
+        let too_old = now - self.period;
+
+        while self.items.front().map_or(false, |t| *t < too_old) {
+            self.items.pop_front();
+        }
+
+        if tick {
+            self.items.push_back(now);
+        }
+
+        self.items.len()
+    }
+}