diff --git a/hptp-send/src/main.rs b/hptp-send/src/main.rs
index 81d8754..475e3dd 100644
--- a/hptp-send/src/main.rs
+++ b/hptp-send/src/main.rs
@@ -7,6 +7,8 @@ extern crate thiserror;
 use hptp::logger::Logger;
 use hptp::msg::UpMsg;
 use hptp::peer::{self, Peer, UpPeer};
+use hptp::seg::SegIdx;
+use std::collections::HashMap;
 use std::net::SocketAddr;
 use tokio::io::AsyncRead;
 // use tokio::net::UdpSocket;
@@ -87,6 +89,64 @@ async fn send(peer: &mut UpPeer, m: UpMsg) -> Result<(), Error> {
     }
 }
 
+struct SegmentStore<'i, IN> {
+    inp: &'i mut IN,
+    unacked_segs: HashMap<SegIdx, UnAcked>,
+    unacked_upper_bound: u32,
+}
+
+struct UnAcked {
+    payload: Vec<u8>,
+    nacks: usize,
+}
+
+impl<'i, IN> SegmentStore<'i, IN>
+where
+    IN: AsyncRead + Unpin,
+{
+    fn new(inp: &'i mut IN) -> Self {
+        SegmentStore {
+            inp,
+            unacked_segs: HashMap::new(),
+            unacked_upper_bound: 0,
+        }
+    }
+
+    async fn read_segment(&mut self) -> Option<(SegIdx, &[u8])> {
+        use tokio::io::AsyncReadExt;
+        let mut buf = [0u8; hptp::seg::MAX_SEG_SIZE];
+        let len = self.inp.read(&mut buf).await.unwrap_or(0);
+        if len > 0 {
+            let seg_idx = self.unacked_upper_bound;
+            self.unacked_upper_bound += 1;
+            let unack = self.unacked_segs.entry(seg_idx);
+            let unack = unack.or_insert(UnAcked {
+                payload: buf[..len].into(),
+                nacks: 0,
+            });
+            Some((seg_idx, unack.payload.as_ref()))
+        } else {
+            None
+        }
+    }
+
+    async fn get_segment(&mut self) -> Option<(SegIdx, &[u8])> {
+        if self.unacked_segs.is_empty() {
+            self.read_segment().await
+        } else {
+            self.unacked_segs
+                .iter()
+                .next() // get any entry, no ordering guarunteed or needed
+                .map(|(seg_idx, unack)| (*seg_idx, unack.payload.as_ref()))
+        }
+    }
+
+    fn ack(&mut self, seg_idx: SegIdx) {
+        self.unacked_segs.remove(&seg_idx);
+        // TODO: update bounds
+    }
+}
+
 async fn upload<IN>(log: &mut Logger, peer: &mut UpPeer, inp: &mut IN) -> Result<(), Error>
 where
     IN: AsyncRead + Unpin,