diff --git a/hptp-recv/src/main.rs b/hptp-recv/src/main.rs
index b29a5a0..d45dbda 100644
--- a/hptp-recv/src/main.rs
+++ b/hptp-recv/src/main.rs
@@ -7,6 +7,7 @@ extern crate thiserror;
 use hptp::logger::Logger;
 use hptp::msg::{DownMsg, UpMsg};
 use hptp::peer::{self, DownPeer, Peer};
+use hptp::seg::SegIdx;
 use std::collections::HashMap;
 use tokio::io::AsyncWrite;
 
@@ -44,11 +45,55 @@ async fn start(log: &mut Logger) -> Result<(), Error> {
     download(log, &mut peer, &mut out).await
 }
 
-async fn send(peer: &mut DownPeer, m: DownMsg) -> Result<(), Error> {
-    match peer.send(m).await {
-        Ok(()) => Ok(()),
-        Err(peer::SendError::Io { source }) => Err(source.into()),
-        Err(peer::SendError::NoTarget) => unreachable!(),
+struct SegmentSink<'o, OUT> {
+    out: &'o mut OUT,
+    segs: HashMap<SegIdx, Option<Vec<u8>>>,
+    n_flushed: u32,
+}
+
+#[derive(Copy, Clone, Eq, PartialEq, Debug)]
+enum Put {
+    Duplicate,
+    Fresh,
+}
+
+impl<'o, OUT> SegmentSink<'o, OUT>
+where
+    OUT: AsyncWrite + Unpin,
+{
+    fn new(out: &'o mut OUT) -> Self {
+        SegmentSink {
+            out,
+            segs: HashMap::new(),
+            n_flushed: 0,
+        }
+    }
+
+    async fn flush(&mut self) {
+        use tokio::io::AsyncWriteExt;
+        while let Some(cache) = self.segs.get_mut(&self.n_flushed) {
+            if let Some(data) = cache.take() {
+                self.out.write_all(&data).await.expect("god help us");
+                self.out.flush().await.expect("god help us");
+            }
+            self.n_flushed += 1;
+        }
+    }
+
+    async fn put(&mut self, seg_idx: SegIdx, data: Vec<u8>) -> Put {
+        if seg_idx < self.n_flushed || self.segs.contains_key(&seg_idx) {
+            Put::Duplicate
+        } else {
+            self.segs.insert(seg_idx, Some(data));
+            self.flush().await;
+            Put::Fresh
+        }
+    }
+
+    fn ack_msg(&self) -> DownMsg {
+        DownMsg::Ack {
+            idxs: self.segs.keys().cloned().collect(),
+        }
     }
 }
 
@@ -56,45 +101,50 @@ async fn download<OUT>(log: &mut Logger, peer: &mut DownPeer, out: &mut OUT) ->
 where
     OUT: AsyncWrite + Unpin,
 {
-    let mut segs = HashMap::new();
-    let mut flush_seg_idx = 0;
+    let mut sink = SegmentSink::new(out);
+    let mut to_send = vec![];
+
     loop {
-        match peer.recv().await {
-            Ok(UpMsg::Data { payload, seg_idx }) => {
-                if segs.contains_key(&seg_idx) {
-                    log.recv_data_ignored(seg_idx as usize, payload.len()).await;
-                } else {
-                    log.recv_data_accepted(
-                        seg_idx as usize,
-                        payload.len(),
-                        hptp::logger::OutOfOrder,
-                    )
-                    .await;
-                    segs.insert(seg_idx, Some(payload));
-                    let ack = DownMsg::Ack {
-                        idxs: segs.keys().cloned().collect(),
-                    };
-                    log.debug_msg(format!("sent ack: {:?}", {
-                        let mut idxs = segs.keys().collect::<Vec<_>>();
-                        idxs.sort_unstable();
-                        idxs
-                    }))
-                    .await;
-                    send(peer, ack).await?;
+        let msg = match peer.recv().await {
+            Ok(m) => m,
+            Err(peer::RecvError::InvalidMessage { .. }) => {
+                log.recv_corrupt().await;
+                continue;
+            }
+            Err(peer::RecvError::Io { source }) => {
+                return Err(source.into());
+            }
+        };
+
+        match msg {
+            UpMsg::Data { payload, seg_idx } => {
+                let len = payload.len();
+                match sink.put(seg_idx, payload).await {
+                    Put::Duplicate => {
+                        log.recv_data_ignored(seg_idx as usize, len).await;
+                    }
+
+                    Put::Fresh => {
+                        log.recv_data_accepted(seg_idx as usize, len, hptp::logger::OutOfOrder)
+                            .await;
+                        log.debug_msg(format!("sending acks: {:?}", {
+                            let mut idxs = sink.segs.keys().cloned().collect::<Vec<_>>();
+                            idxs.sort();
+                            idxs
+                        }))
+                        .await;
+                        to_send.push(sink.ack_msg());
+                    }
                 }
             }
-
-            Err(peer::RecvError::InvalidMessage { .. }) => log.recv_corrupt().await,
-            Err(peer::RecvError::Io { source }) => return Err(source.into()),
         }
 
-        while let Some(v) = segs.get_mut(&flush_seg_idx) {
-            if let Some(payload) = v.take() {
-                use tokio::io::AsyncWriteExt;
-                out.write_all(&payload).await?;
-                out.flush().await?;
+        for m in to_send.drain(..) {
+            match peer.send(m).await {
+                Ok(()) => (),
+                Err(hptp::peer::SendError::NoTarget) => log.debug_msg("no target").await,
+                Err(hptp::peer::SendError::Io { source }) => return Err(source.into()),
             }
-            flush_seg_idx += 1;
         }
     }
 }