diff --git a/src/capnp_runner.rs b/src/capnp_runner.rs
index b9ab505..e71a0bc 100644
--- a/src/capnp_runner.rs
+++ b/src/capnp_runner.rs
@@ -1,19 +1,16 @@
-use std::cmp::{max, min};
-use std::collections::hash_map::{DefaultHasher, HashMap};
-use std::hash::Hasher;
-use std::io::{BufReader, Error, Read};
 use std::str::from_utf8_unchecked;
 
-use capnp::message::ReaderOptions;
-use capnp::serialize::{read_message, write_message};
+use capnp::Error;
+use capnp::message::{Builder, ReaderOptions, ScratchSpace, ScratchSpaceHeapAllocator};
+use capnp::serialize::write_message;
 use capnp::serialize_packed::{read_message as read_message_packed, write_message as write_message_packed};
 use nom::bytes::complete::take_until;
 use nom::IResult;
 
-use crate::iex::{IexMessage, IexParser};
+use crate::{StreamVec, Summarizer};
+use crate::iex::{IexMessage, IexPayload};
 use crate::marketdata_capnp::{multi_message, Side};
 use crate::marketdata_capnp::message;
-use crate::SummaryStats;
 
 fn __take_until<'a>(tag: &'static str, input: &'a [u8]) -> IResult<&'a [u8], &'a [u8]> {
     take_until(tag)(input)
@@ -25,22 +22,44 @@ fn parse_symbol(sym: &[u8; 8]) -> &str {
     unsafe { from_utf8_unchecked(sym_bytes) }
 }
 
-pub fn serialize_capnp(parser: IexParser, size_hint: usize, packed: bool) -> Vec<u8> {
-    let write_fn = if packed { write_message_packed } else { write_message };
+pub struct CapnpWriter<'a> {
+    // We have to be very careful with how messages are built, as running
+    // `init_root` and rebuilding will still accumulate garbage if using
+    // the standard HeapAllocator.
+    // https://github.com/capnproto/capnproto-rust/issues/111
+    words: Vec<capnp::Word>,
+    scratch: ScratchSpace<'a>,
+}
 
-    // Because CapNProto builds messages in heap before serialization,
-    // we'll reserve memory up front and should avoid alloc calls later
-    let mut capnp_message = capnp::message::Builder::new_default();
-    let multimsg = capnp_message.init_root::<multi_message::Builder>();
-    multimsg.init_messages(256);
+impl<'a> CapnpWriter<'a> {
+    pub fn new() -> CapnpWriter<'a> {
+        // Cap'n'Proto words are 8 bytes, MTU is 1500 bytes, theoretically need only 188 words.
+        // In practice, let's just make sure everything fits.
+        let mut words = capnp::Word::allocate_zeroed_vec(1024);
 
-    // Allocate our output buffer
-    let mut output: Vec<u8> = Vec::with_capacity(size_hint);
+        let mut scratch = ScratchSpace::new(unsafe {
+            std::mem::transmute(&mut words[..])
+        });
 
-    // Now to the actual work
-    for iex_msg in parser {
-        // Find the messages we actually care about in this context
-        let num_msgs = iex_msg.messages.iter().map(|m| {
+        CapnpWriter {
+            words,
+            scratch,
+        }
+    }
+
+    fn builder(&mut self) -> capnp::message::Builder<ScratchSpaceHeapAllocator<'a, 'a>> {
+        // Builders are only safe to use for serializing a single message. We can re-use the
+        // backing memory (unsafe because now both `self` and the returned builder have a
+        // mutable reference to `self.scratch), but Bad Things happen if we don't drop
+        // in between serialization.
+        capnp::message::Builder::new(ScratchSpaceHeapAllocator::new(unsafe {
+            std::mem::transmute(&mut self.scratch)
+        }))
+    }
+
+    pub fn serialize(&mut self, payload: &IexPayload, mut output: &mut Vec<u8>, packed: bool) {
+        // First, count the messages we actually care about.
+        let num_msgs = payload.messages.iter().map(|m| {
             match m {
                 IexMessage::TradeReport(_) | IexMessage::PriceLevelUpdate(_) => 1,
                 _ => 0
@@ -48,16 +67,24 @@ pub fn serialize_capnp(parser: IexParser, size_hint: usize, packed: bool) -> Vec
         }).fold(0, |sum, i| sum + i);
 
         if num_msgs == 0 {
-            continue;
+            return;
         }
 
         // And actually serialize the IEX payload to CapNProto format
-        let mut multimsg = capnp_message.init_root::<multi_message::Builder>();
-        multimsg.set_seq_no(iex_msg.first_seq_no);
+
+        // This is the unsafe (but faster) version
+        let mut builder = self.builder();
+        let mut multimsg = builder.init_root::<multi_message::Builder>();
+
+        // And the safe version used for testing
+        //let mut builder = capnp::message::Builder::new_default();
+        //let mut multimsg = builder.init_root::<multi_message::Builder>();
+
+        multimsg.set_seq_no(payload.first_seq_no);
 
         let mut messages = multimsg.init_messages(num_msgs as u32);
         let mut current_msg_no = 0;
-        for iex_msg in iex_msg.messages {
+        for iex_msg in payload.messages.iter() {
             match iex_msg {
                 IexMessage::TradeReport(tr) => {
                     let mut message = messages.reborrow().get(current_msg_no);
@@ -91,76 +118,47 @@ pub fn serialize_capnp(parser: IexParser, size_hint: usize, packed: bool) -> Vec
             }
         }
 
-        write_fn(&mut output, &capnp_message).unwrap();
-    }
+        let write_fn = if packed { write_message_packed } else { write_message };
 
-    output
-}
-
-struct AdvancingVec<'a> {
-    pos: usize,
-    inner: &'a Vec<u8>,
-}
-
-impl<'a> Read for AdvancingVec<'a> {
-    fn read(&mut self, buf: &mut [u8]) -> Result<usize, Error> {
-        // TODO: There's *got* to be a better way to handle this
-        let end = self.pos + buf.len();
-        let end = if end > self.inner.len() { self.inner.len() } else { end };
-        let read_size = end - self.pos;
-        buf[..read_size].copy_from_slice(&self.inner[self.pos..end]);
-        self.pos = end;
-
-        Ok(read_size)
+        write_fn(&mut output, &builder).unwrap();
     }
 }
 
-pub fn read_capnp(buffer: &Vec<u8>, packed: bool) -> HashMap<u64, SummaryStats> {
-    let read_fn = if packed { read_message_packed } else { read_message };
-    let unbuffered = AdvancingVec {
-        pos: 0,
-        inner: buffer,
-    };
-    let mut buffered = BufReader::new(unbuffered);
-    let read_opts = ReaderOptions::new();
+pub struct CapnpReader {
+    read_opts: ReaderOptions
+}
 
-    let mut stats = HashMap::new();
-
-    while let Ok(msg) = read_fn(&mut buffered, read_opts) {
-        let multimsg = msg.get_root::<multi_message::Reader>().unwrap();
-
-        for msg in multimsg.get_messages().unwrap().iter() {
-            // Hash the symbol name since we can't return a HashMap containing
-            // string pointers as the keys
-            let sym = msg.get_symbol().unwrap();
-            let mut h = DefaultHasher::new();
-            h.write(sym.as_bytes());
-            let key = h.finish();
-
-            let mut sym_stats = stats.entry(key)
-                .or_insert(SummaryStats::new(sym));
-
-            match msg.which() {
-                Ok(message::Trade(tr)) => {
-                    let tr = tr.unwrap();
-                    sym_stats.trade_volume += tr.get_size() as u64;
-                }
-                Ok(message::Quote(q)) => {
-                    let q = q.unwrap();
-                    if q.get_side().unwrap() == Side::Buy {
-                        sym_stats.bid_high = max(sym_stats.bid_high, q.get_price());
-                        sym_stats.bid_low = min(sym_stats.bid_low, q.get_price());
-                    } else {
-                        sym_stats.ask_high = max(sym_stats.ask_high, q.get_price());
-                        sym_stats.ask_low = min(sym_stats.ask_low, q.get_price());
-                    }
-                }
-                _ => {
-                    panic!("Unrecognized message type")
-                }
-            }
+impl CapnpReader {
+    pub fn new() -> CapnpReader {
+        CapnpReader {
+            read_opts: ReaderOptions::new()
         }
     }
 
-    stats
+    pub fn deserialize_packed<'a>(&self, buf: &'a mut StreamVec, stats: &mut Summarizer) -> Result<(), Error> {
+        // Because `capnp::serialize_packed::PackedRead` is hidden from us, packed reads
+        // *have* to both allocate new segments every read, and copy the buffer into
+        // those same segments. Un-packed reading can use `SliceSegments` for true zero-copy
+        let reader = read_message_packed(buf, self.read_opts)?;
+
+        let multimsg = reader.get_root::<multi_message::Reader>().unwrap();
+        for msg in multimsg.get_messages().unwrap().iter() {
+            match msg.which() {
+                Ok(message::Trade(tr)) => {
+                    let tr = tr.unwrap();
+                    stats.append_trade_volume(msg.get_symbol().unwrap(), tr.get_size() as u64);
+                },
+                Ok(message::Quote(q)) => {
+                    let q = q.unwrap();
+                    let is_bid = match q.get_side().unwrap() {
+                        Side::Buy => true,
+                        _ => false
+                    };
+                    stats.update_quote_prices(msg.get_symbol().unwrap(), q.get_price(), is_bid);
+                },
+                _ => panic!("Unrecognized message type!")
+            }
+        };
+        Ok(())
+    }
 }
diff --git a/src/main.rs b/src/main.rs
index 28d21b3..24cc24f 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,11 +1,15 @@
+use std::cmp::{max, min};
+use std::collections::hash_map::{DefaultHasher, HashMap};
 use std::fs::File;
-use std::io::Read;
+use std::hash::Hasher;
+use std::io::{BufRead, Read};
+use std::io::Error;
 use std::path::Path;
 use std::time::SystemTime;
 
 use clap::{App, Arg};
 
-use crate::iex::{IexMessage, IexParser};
+use crate::iex::IexParser;
 
 // Cap'n'Proto and Flatbuffers typically ask that you generate code on the fly to match
 // the schemas. For purposes of auto-complete and easy browsing in the repository,
@@ -39,19 +43,28 @@ fn main() {
     file.read_to_end(&mut buf)
         .expect(&format!("Unable to read file={}", path.display()));
 
-    let start = SystemTime::now();
+    let _start = SystemTime::now();
+    let mut summarizer = Summarizer::default();
+    let mut parser = IexParser::new(&buf[..]);
 
-    // Try with Capnproto for now
-    let parser = IexParser::new(&buf[..]);
-    let capnp_buf = capnp_runner::serialize_capnp(parser, buf.len(), true);
-    let stats = capnp_runner::read_capnp(&capnp_buf, true);
+    let mut capnp_writer = capnp_runner::CapnpWriter::new();
+    let capnp_reader = capnp_runner::CapnpReader::new();
+    let mut output_buf = Vec::new();
 
-    dbg!(stats);
+    for iex_payload in parser {
+        //let iex_payload = parser.next().unwrap();
+        capnp_writer.serialize(&iex_payload, &mut output_buf, true);
+    }
 
-    println!(
-        "Parse time seconds={}",
-        SystemTime::now().duration_since(start).unwrap().as_secs()
-    )
+    let mut read_buf = StreamVec::new(output_buf);
+    let mut parsed_msgs: u64 = 0;
+    while let Ok(_) = capnp_reader.deserialize_packed(&mut read_buf, &mut summarizer) {
+        parsed_msgs += 1;
+    }
+
+    assert_eq!(read_buf.pos, read_buf.inner.len());
+    dbg!(parsed_msgs);
+    dbg!(summarizer);
 }
 
 #[derive(Debug)]
@@ -64,15 +77,75 @@ pub struct SummaryStats {
     ask_low: u64,
 }
 
-impl SummaryStats {
-    fn new(sym: &str) -> SummaryStats {
-        SummaryStats {
-            symbol: sym.to_string(),
-            trade_volume: 0,
-            bid_high: 0,
-            bid_low: u64::max_value(),
-            ask_high: 0,
-            ask_low: u64::max_value(),
+#[derive(Default, Debug)]
+pub struct Summarizer {
+    data: HashMap<u64, SummaryStats>
+}
+
+impl Summarizer {
+    fn entry(&mut self, sym: &str) -> &mut SummaryStats {
+        let mut hasher = DefaultHasher::new();
+        hasher.write(sym.as_bytes());
+        self.data.entry(hasher.finish())
+            .or_insert(SummaryStats {
+                symbol: sym.to_string(),
+                trade_volume: 0,
+                bid_high: 0,
+                bid_low: u64::max_value(),
+                ask_high: 0,
+                ask_low: u64::max_value(),
+            })
+    }
+
+    pub fn append_trade_volume(&mut self, sym: &str, volume: u64) {
+        self.entry(sym).trade_volume += volume;
+    }
+
+    pub fn update_quote_prices(&mut self, sym: &str, price: u64, is_buy: bool) {
+        let entry = self.entry(sym);
+        if is_buy {
+            entry.bid_low = min(entry.bid_low, price);
+            entry.bid_high = max(entry.bid_high, price);
+        } else {
+            entry.ask_low = min(entry.ask_low, price);
+            entry.ask_high = max(entry.ask_high, price);
         }
     }
 }
+
+pub struct StreamVec {
+    pos: usize,
+    inner: Vec<u8>,
+}
+
+impl StreamVec {
+    pub fn new(buf: Vec<u8>) -> StreamVec {
+        StreamVec {
+            pos: 0,
+            inner: buf,
+        }
+    }
+}
+
+impl Read for StreamVec {
+    fn read(&mut self, buf: &mut [u8]) -> Result<usize, Error> {
+        // TODO: There's *got* to be a better way to handle this
+        let end = self.pos + buf.len();
+        let end = if end > self.inner.len() { self.inner.len() } else { end };
+        let read_size = end - self.pos;
+        buf[..read_size].copy_from_slice(&self.inner[self.pos..end]);
+        self.pos = end;
+
+        Ok(read_size)
+    }
+}
+
+impl BufRead for StreamVec {
+    fn fill_buf(&mut self) -> Result<&[u8], Error> {
+        Ok(&self.inner[self.pos..])
+    }
+
+    fn consume(&mut self, amt: usize) {
+        self.pos += amt;
+    }
+}