add Consumer::receive_all

Support for batched reads is not uniform among the various backends we
have.

The in-memory and rabbitmq impls differ from the rest as these consumers
are channel/stream based, with no explicit option for consuming messages
in batches.

Using `tokio::time::timeout` for the first item, then looping to
opportunistically try to fill up the batch with any remaining
_already ready_ messages, we can emulate a similar behavior as the other
backends.

In all cases, receive_all should:
- not block longer (+/-) than the specified deadline, even if no items
  are available.
- not linger waiting for _more items_ once it as received _any_.

Additionally, a new bit of config has been exposed for rabbitmq so callers
can specify a prefetch count. This didn't seem to have any impact on the
tests, but seems good to have.

omniqueue/src/backends/gcp_pubsub.rs

@@ -15,6 +15,7 @@ use google_cloud_pubsub::subscription::Subscription;
 use serde::Serialize;
 use std::path::{Path, PathBuf};
 use std::sync::Arc;
+use std::time::Duration;
 use std::{any::TypeId, collections::HashMap};
 
 pub struct GcpPubSubBackend;
@@ -217,31 +218,56 @@ async fn subscription(client: &Client, subscription_id: &str) -> Result<Subscrip
     Ok(subscription)
 }
 
-#[async_trait]
-impl QueueConsumer for GcpPubSubConsumer {
-    type Payload = Payload;
-
-    async fn receive(&mut self) -> Result<Delivery, QueueError> {
-        let subscription = subscription(&self.client, &self.subscription_id).await?;
-        let mut stream = subscription
-            .subscribe(None)
-            .await
-            .map_err(QueueError::generic)?;
-
-        let mut recv_msg = stream.next().await.ok_or_else(|| QueueError::NoData)?;
+impl GcpPubSubConsumer {
+    fn wrap_recv_msg(&self, mut recv_msg: ReceivedMessage) -> Delivery {
         // FIXME: would be nice to avoid having to move the data out here.
         //   While it's possible to ack via a subscription and an ack_id, nack is only
         //   possible via a `ReceiveMessage`. This means we either need to hold 2 copies of
         //   the payload, or move the bytes out so they can be returned _outside of the Acker_.
         let payload = recv_msg.message.data.drain(..).collect();
-        Ok(Delivery {
+
+        Delivery {
             decoders: self.registry.clone(),
             acker: Box::new(GcpPubSubAcker {
                 recv_msg,
                 subscription_id: self.subscription_id.clone(),
             }),
             payload: Some(payload),
-        })
+        }
+    }
+}
+
+#[async_trait]
+impl QueueConsumer for GcpPubSubConsumer {
+    type Payload = Payload;
+
+    async fn receive(&mut self) -> Result<Delivery, QueueError> {
+        let subscription = subscription(&self.client, &self.subscription_id).await?;
+        let mut stream = subscription
+            .subscribe(None)
+            .await
+            .map_err(QueueError::generic)?;
+
+        let recv_msg = stream.next().await.ok_or_else(|| QueueError::NoData)?;
+
+        Ok(self.wrap_recv_msg(recv_msg))
+    }
+
+    async fn receive_all(
+        &mut self,
+        max_messages: usize,
+        deadline: Duration,
+    ) -> Result<Vec<Delivery>, QueueError> {
+        let subscription = subscription(&self.client, &self.subscription_id).await?;
+        match tokio::time::timeout(deadline, subscription.pull(max_messages as _, None)).await {
+            Ok(messages) => Ok(messages
+                .map_err(QueueError::generic)?
+                .into_iter()
+                .map(|m| self.wrap_recv_msg(m))
+                .collect()),
+            // Timeout
+            Err(_) => Ok(vec![]),
+        }
     }
 }
 

omniqueue/src/backends/memory_queue.rs

@@ -1,3 +1,4 @@
+use std::time::{Duration, Instant};
 use std::{any::TypeId, collections::HashMap};
 
 use async_trait::async_trait;
@@ -90,22 +91,53 @@ pub struct MemoryQueueConsumer {
     tx: broadcast::Sender<Vec<u8>>,
 }
 
-#[async_trait]
-impl QueueConsumer for MemoryQueueConsumer {
-    type Payload = Vec<u8>;
-
-    async fn receive(&mut self) -> Result<Delivery, QueueError> {
-        let payload = self.rx.recv().await.map_err(QueueError::generic)?;
-
-        Ok(Delivery {
+impl MemoryQueueConsumer {
+    fn wrap_payload(&self, payload: Vec<u8>) -> Delivery {
+        Delivery {
             payload: Some(payload.clone()),
             decoders: self.registry.clone(),
             acker: Box::new(MemoryQueueAcker {
                 tx: self.tx.clone(),
                 payload_copy: Some(payload),
                 alredy_acked_or_nacked: false,
             }),
-        })
+        }
+    }
+}
+
+#[async_trait]
+impl QueueConsumer for MemoryQueueConsumer {
+    type Payload = Vec<u8>;
+
+    async fn receive(&mut self) -> Result<Delivery, QueueError> {
+        let payload = self.rx.recv().await.map_err(QueueError::generic)?;
+        Ok(self.wrap_payload(payload))
+    }
+
+    async fn receive_all(
+        &mut self,
+        max_messages: usize,
+        deadline: Duration,
+    ) -> Result<Vec<Delivery>, QueueError> {
+        let mut out = Vec::with_capacity(max_messages);
+        let start = Instant::now();
+        match tokio::time::timeout(deadline, self.rx.recv()).await {
+            Ok(Ok(x)) => out.push(self.wrap_payload(x)),
+            // Timeouts and stream termination
+            Err(_) | Ok(Err(_)) => return Ok(out),
+        }
+
+        if max_messages > 1 {
+            // `try_recv` will break the loop if no ready items are already buffered in the channel.
+            // This should allow us to opportunistically fill up the buffer in the remaining time.
+            while let Ok(x) = self.rx.try_recv() {
+                out.push(self.wrap_payload(x));
+                if out.len() >= max_messages || start.elapsed() >= deadline {
+                    break;
+                }
+            }
+        }
+        Ok(out)
     }
 }
 
@@ -146,6 +178,7 @@ impl Acker for MemoryQueueAcker {
 #[cfg(test)]
 mod tests {
     use serde::{Deserialize, Serialize};
+    use std::time::{Duration, Instant};
 
     use crate::{
         queue::{consumer::QueueConsumer, producer::QueueProducer, QueueBuilder},
@@ -233,4 +266,133 @@ mod tests {
             TypeA { a: 12 }
         );
     }
+
+    #[derive(Debug, Deserialize, Serialize, PartialEq)]
+    pub struct ExType {
+        a: u8,
+    }
+
+    /// Consumer will return immediately if there are fewer than max messages to start with.
+    #[tokio::test]
+    async fn test_send_recv_all_partial() {
+        let payload = ExType { a: 2 };
+
+        let (p, mut c) = QueueBuilder::<MemoryQueueBackend, _>::new(16)
+            .build_pair()
+            .await
+            .unwrap();
+
+        p.send_serde_json(&payload).await.unwrap();
+        let deadline = Duration::from_secs(1);
+
+        let now = Instant::now();
+        let mut xs = c.receive_all(2, deadline).await.unwrap();
+        assert_eq!(xs.len(), 1);
+        let d = xs.remove(0);
+        assert_eq!(d.payload_serde_json::<ExType>().unwrap().unwrap(), payload);
+        d.ack().await.unwrap();
+        assert!(now.elapsed() <= deadline);
+    }
+
+    /// Consumer should yield items immediately if there's a full batch ready on the first poll.
+    #[tokio::test]
+    async fn test_send_recv_all_full() {
+        let payload1 = ExType { a: 1 };
+        let payload2 = ExType { a: 2 };
+
+        let (p, mut c) = QueueBuilder::<MemoryQueueBackend, _>::new(16)
+            .build_pair()
+            .await
+            .unwrap();
+
+        p.send_serde_json(&payload1).await.unwrap();
+        p.send_serde_json(&payload2).await.unwrap();
+        let deadline = Duration::from_secs(1);
+
+        let now = Instant::now();
+        let mut xs = c.receive_all(2, deadline).await.unwrap();
+        assert_eq!(xs.len(), 2);
+        let d1 = xs.remove(0);
+        assert_eq!(
+            d1.payload_serde_json::<ExType>().unwrap().unwrap(),
+            payload1
+        );
+        d1.ack().await.unwrap();
+
+        let d2 = xs.remove(0);
+        assert_eq!(
+            d2.payload_serde_json::<ExType>().unwrap().unwrap(),
+            payload2
+        );
+        d2.ack().await.unwrap();
+        // N.b. it's still possible this could turn up false if the test runs too slow.
+        assert!(now.elapsed() < deadline);
+    }
+
+    /// Consumer will return the full batch immediately, but also return immediately if a partial batch is ready.
+    #[tokio::test]
+    async fn test_send_recv_all_full_then_partial() {
+        let payload1 = ExType { a: 1 };
+        let payload2 = ExType { a: 2 };
+        let payload3 = ExType { a: 3 };
+
+        let (p, mut c) = QueueBuilder::<MemoryQueueBackend, _>::new(16)
+            .build_pair()
+            .await
+            .unwrap();
+
+        p.send_serde_json(&payload1).await.unwrap();
+        p.send_serde_json(&payload2).await.unwrap();
+        p.send_serde_json(&payload3).await.unwrap();
+
+        let deadline = Duration::from_secs(1);
+        let now1 = Instant::now();
+        let mut xs = c.receive_all(2, deadline).await.unwrap();
+        assert_eq!(xs.len(), 2);
+        let d1 = xs.remove(0);
+        assert_eq!(
+            d1.payload_serde_json::<ExType>().unwrap().unwrap(),
+            payload1
+        );
+        d1.ack().await.unwrap();
+
+        let d2 = xs.remove(0);
+        assert_eq!(
+            d2.payload_serde_json::<ExType>().unwrap().unwrap(),
+            payload2
+        );
+        d2.ack().await.unwrap();
+        assert!(now1.elapsed() < deadline);
+
+        // 2nd call
+        let now2 = Instant::now();
+        let mut ys = c.receive_all(2, deadline).await.unwrap();
+        assert_eq!(ys.len(), 1);
+        let d3 = ys.remove(0);
+        assert_eq!(
+            d3.payload_serde_json::<ExType>().unwrap().unwrap(),
+            payload3
+        );
+        d3.ack().await.unwrap();
+        assert!(now2.elapsed() <= deadline);
+    }
+
+    /// Consumer will NOT wait indefinitely for at least one item.
+    #[tokio::test]
+    async fn test_send_recv_all_late_arriving_items() {
+        let (_p, mut c) = QueueBuilder::<MemoryQueueBackend, _>::new(16)
+            .build_pair()
+            .await
+            .unwrap();
+
+        let deadline = Duration::from_secs(1);
+        let now = Instant::now();
+        let xs = c.receive_all(2, deadline).await.unwrap();
+        let elapsed = now.elapsed();
+
+        assert_eq!(xs.len(), 0);
+        // Elapsed should be around the deadline, ballpark
+        assert!(elapsed >= deadline);
+        assert!(elapsed <= deadline + Duration::from_millis(200));
+    }
 }