feat: round-7 abstractions — BgJoiner, MiddlewarePipeline, RateLimitedQueue

crates/mytheclipse-queue/src/error.rs

@@ -11,6 +11,8 @@ pub enum QueueError {
     Serialization(String),
     /// A timeout occurred while waiting for an operation.
     Timeout,
+    /// The operation was rejected because of a rate limit.
+    RateLimit(String),
 }
 
 impl std::fmt::Display for QueueError {
@@ -20,6 +22,7 @@ impl std::fmt::Display for QueueError {
             Self::NotFound(s) => write!(f, "queue not found: {s}"),
             Self::Serialization(s) => write!(f, "serialization error: {s}"),
             Self::Timeout => write!(f, "queue operation timed out"),
+            Self::RateLimit(s) => write!(f, "queue rate limited: {s}"),
         }
     }
 }

crates/mytheclipse-queue/src/lib.rs

@@ -59,7 +59,11 @@ pub mod batch;
 #[cfg(feature = "in-memory")]
 pub mod backpressure_enqueue;
 #[cfg(feature = "in-memory")]
+pub mod rate_limited;
+#[cfg(feature = "in-memory")]
 pub use backpressure_enqueue::{BackpressureEnforcer, BackpressureError, enqueue_with_backpressure};
+#[cfg(feature = "in-memory")]
+pub use rate_limited::{RateLimitedQueue, RateLimitQueueError};
 
 #[cfg(feature = "in-memory")]
 pub mod pipeline;

crates/mytheclipse-queue/src/rate_limited.rs

@@ -0,0 +1,157 @@
+//! Rate-limited queue wrapper.
+//!
+//! [`RateLimitedQueue`] wraps any [`Queue`] implementation and applies a
+//! token-bucket rate limiter before enqueuing. If the bucket is empty the
+//! enqueue is rejected with [`RateLimitQueueError::RateLimited`] instead of
+//! blocking.
+
+use std::sync::Arc;
+use std::time::Duration;
+
+use tokio::sync::Mutex;
+use tokio::time::Instant;
+
+use crate::error::QueueError;
+use crate::traits::Queue;
+use async_trait::async_trait;
+
+/// Error returned by [`RateLimitedQueue::enqueue`].
+#[derive(Debug)]
+pub enum RateLimitQueueError {
+    RateLimited,
+    Other(QueueError),
+}
+
+impl std::fmt::Display for RateLimitQueueError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::RateLimited => write!(f, "rate limited: capacity exhausted"),
+            Self::Other(e) => write!(f, "queue error: {e}"),
+        }
+    }
+}
+
+impl std::error::Error for RateLimitQueueError {}
+
+impl From<QueueError> for RateLimitQueueError {
+    fn from(e: QueueError) -> Self {
+        Self::Other(e)
+    }
+}
+
+impl From<RateLimitQueueError> for QueueError {
+    fn from(e: RateLimitQueueError) -> Self {
+        match e {
+            RateLimitQueueError::RateLimited => Self::RateLimit("capacity exhausted".into()),
+            RateLimitQueueError::Other(e) => e,
+        }
+    }
+}
+
+/// Token-bucket rate limiter (no extra deps beyond tokio).
+struct TokenBucket {
+    /// Maximum burst capacity.
+    capacity: u32,
+    /// Current tokens (float for fractional refill).
+    tokens: f64,
+    /// Refill rate (tokens per second).
+    rate: f64,
+    /// Last refill timestamp.
+    last: Instant,
+}
+
+impl TokenBucket {
+    fn new(rate_per_sec: f64, burst: u32) -> Self {
+        Self {
+            capacity: burst.max(1),
+            tokens: burst as f64,
+            rate: rate_per_sec.max(0.0),
+            last: Instant::now(),
+        }
+    }
+
+    /// Attempts to consume one token. Returns true on success.
+    fn try_consume(&mut self) -> bool {
+        let now = Instant::now();
+        let elapsed = now.saturating_duration_since(self.last).as_secs_f64();
+        self.tokens = (self.tokens + elapsed * self.rate).min(self.capacity as f64);
+        self.last = now;
+        if self.tokens >= 1.0 {
+            self.tokens -= 1.0;
+            true
+        } else {
+            false
+        }
+    }
+}
+
+/// A queue decorator that enforces a rate limit on enqueue.
+pub struct RateLimitedQueue<Q: ?Sized> {
+    inner: Arc<Q>,
+    bucket: Arc<Mutex<TokenBucket>>,
+}
+
+impl<Q: Queue + 'static> RateLimitedQueue<Q> {
+    /// Creates a new rate-limited wrapper around `inner`.
+    pub fn new(inner: Q, rate_per_sec: f64, burst: u32) -> Self {
+        Self {
+            inner: Arc::new(inner),
+            bucket: Arc::new(Mutex::new(TokenBucket::new(rate_per_sec, burst))),
+        }
+    }
+}
+
+#[async_trait]
+impl<Q: Queue + ?Sized> Queue for RateLimitedQueue<Q> {
+    async fn enqueue(&self, topic: &str, payload: Vec<u8>) -> Result<(), QueueError> {
+        let mut b = self.bucket.lock().await;
+        if !b.try_consume() {
+            return Err(RateLimitQueueError::RateLimited.into());
+        }
+        self.inner.enqueue(topic, payload).await
+    }
+
+    async fn dequeue(&self, topic: &str, timeout: Duration) -> Result<Option<crate::job::Job>, QueueError> {
+        self.inner.dequeue(topic, timeout).await
+    }
+
+    async fn ack(&self, job: &crate::job::Job) -> Result<(), crate::error::JobError> {
+        self.inner.ack(job).await
+    }
+
+    async fn nack(&self, job: &crate::job::Job, requeue: bool) -> Result<(), crate::error::JobError> {
+        self.inner.nack(job, requeue).await
+    }
+
+    async fn dlq_move(&self, topic: &str, job: crate::job::Job) -> Result<(), QueueError> {
+        self.inner.dlq_move(topic, job).await
+    }
+
+    async fn len(&self, topic: &str) -> Result<u64, QueueError> {
+        self.inner.len(topic).await
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::in_memory::InMemoryQueue;
+
+    #[tokio::test]
+    async fn allows_enqueue_within_rate() {
+        let inner = InMemoryQueue::new();
+        let rl = RateLimitedQueue::new(inner, 100.0, 10);
+        assert!(rl.enqueue("t", b"x".to_vec()).await.is_ok());
+    }
+
+    #[tokio::test]
+    async fn rejects_when_bucket_empty() {
+        let inner = InMemoryQueue::new();
+        let rl = RateLimitedQueue::new(inner, 0.0, 1); // 0 tokens/sec, 1 burst
+        // consume the single burst token
+        let _ = rl.enqueue("t", b"x".to_vec()).await;
+        // next should be rate limited (no refill)
+        let result = rl.enqueue("t", b"y".to_vec()).await;
+        assert!(matches!(result, Err(QueueError::RateLimit(_))));
+    }
+}