diff --git a/src/lib.rs b/src/lib.rs
index 0ecdfec..dfaf4c5 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -2,6 +2,14 @@ mod rply;
 mod statestream;
 pub use rply::*;
 
+#[derive(Debug, thiserror::Error)]
+pub struct InvalidDeterminant(pub u8);
+impl std::fmt::Display for InvalidDeterminant {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
diff --git a/src/rply.rs b/src/rply.rs
index 72b6e24..027fff6 100644
--- a/src/rply.rs
+++ b/src/rply.rs
@@ -1,14 +1,6 @@
-use crate::statestream;
+use crate::{InvalidDeterminant, statestream};
 use thiserror::Error;
 
-#[derive(Debug, Error)]
-pub struct InvalidDeterminant(pub u8);
-impl std::fmt::Display for InvalidDeterminant {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        write!(f, "{}", self.0)
-    }
-}
-
 // #[repr(usize)]
 // pub enum HeaderV0V1Part {
 //     Magic = 0,
@@ -52,29 +44,6 @@ impl From<u8> for FrameToken {
     }
 }
 
-#[repr(u8)]
-#[non_exhaustive]
-#[derive(Debug)]
-pub enum SSToken {
-    Start = 0,
-    NewBlock = 1,
-    NewSuperblock = 2,
-    SuperblockSeq = 3,
-}
-impl TryFrom<u8> for SSToken {
-    type Error = InvalidDeterminant;
-
-    fn try_from(value: u8) -> std::result::Result<Self, Self::Error> {
-        match value {
-            0 => Ok(SSToken::Start),
-            1 => Ok(SSToken::NewBlock),
-            2 => Ok(SSToken::NewSuperblock),
-            3 => Ok(SSToken::SuperblockSeq),
-            _ => Err(InvalidDeterminant(value)),
-        }
-    }
-}
-
 #[repr(u8)]
 #[non_exhaustive]
 #[derive(Debug, PartialEq, Eq, Clone, Copy)]
@@ -332,8 +301,10 @@ impl<R: std::io::BufRead> ReplayDecoder<'_, R> {
         // read a 4 byte uncompressed unencoded size
         let uc_ue_size = rply.read_u32::<LittleEndian>()? as usize;
         // read a 4 byte uncompressed encoded size
+        #[expect(unused)]
         let uc_enc_size = rply.read_u32::<LittleEndian>()? as usize;
         // read a 4 byte compressed encoded size
+        #[expect(unused)]
         let comp_enc_size = rply.read_u32::<LittleEndian>()? as usize;
         frame.checkpoint_bytes.resize(uc_ue_size, 0);
         // maybe decompress
@@ -342,7 +313,8 @@ impl<R: std::io::BufRead> ReplayDecoder<'_, R> {
                 rply.read_exact(frame.checkpoint_bytes.as_mut_slice())?;
             }
             (Compression::None, Encoding::Statestream) => {
-                let mut ss_decoder = statestream::Decoder::new(rply, &mut self.ss_state);
+                let mut ss_decoder =
+                    statestream::Decoder::new(rply, &mut self.ss_state, uc_ue_size);
                 std::io::copy(
                     &mut ss_decoder,
                     &mut std::io::Cursor::new(frame.checkpoint_bytes.as_mut_slice()),
@@ -359,7 +331,8 @@ impl<R: std::io::BufRead> ReplayDecoder<'_, R> {
             (Compression::Zlib, Encoding::Statestream) => {
                 use flate2::bufread::ZlibDecoder;
                 let mut decoder = ZlibDecoder::new(rply);
-                let mut ss_decoder = statestream::Decoder::new(&mut decoder, &mut self.ss_state);
+                let mut ss_decoder =
+                    statestream::Decoder::new(&mut decoder, &mut self.ss_state, uc_ue_size);
                 std::io::copy(
                     &mut ss_decoder,
                     &mut std::io::Cursor::new(frame.checkpoint_bytes.as_mut_slice()),
@@ -376,7 +349,8 @@ impl<R: std::io::BufRead> ReplayDecoder<'_, R> {
             (Compression::Zstd, Encoding::Statestream) => {
                 use zstd::Decoder;
                 let mut decoder = Decoder::with_buffer(rply)?.single_frame();
-                let mut ss_decoder = statestream::Decoder::new(&mut decoder, &mut self.ss_state);
+                let mut ss_decoder =
+                    statestream::Decoder::new(&mut decoder, &mut self.ss_state, uc_ue_size);
                 std::io::copy(
                     &mut ss_decoder,
                     &mut std::io::Cursor::new(frame.checkpoint_bytes.as_mut_slice()),
diff --git a/src/statestream.rs b/src/statestream.rs
index 53f1349..f515154 100644
--- a/src/statestream.rs
+++ b/src/statestream.rs
@@ -1,5 +1,30 @@
 mod blockindex;
+use crate::InvalidDeterminant;
 use blockindex::BlockIndex;
+use std::io::Write;
+
+#[repr(u8)]
+#[non_exhaustive]
+#[derive(Debug)]
+pub enum SSToken {
+    Start = 0,
+    NewBlock = 1,
+    NewSuperblock = 2,
+    SuperblockSeq = 3,
+}
+impl TryFrom<u8> for SSToken {
+    type Error = InvalidDeterminant;
+
+    fn try_from(value: u8) -> std::result::Result<Self, Self::Error> {
+        match value {
+            0 => Ok(SSToken::Start),
+            1 => Ok(SSToken::NewBlock),
+            2 => Ok(SSToken::NewSuperblock),
+            3 => Ok(SSToken::SuperblockSeq),
+            _ => Err(InvalidDeterminant(value)),
+        }
+    }
+}
 
 pub(crate) struct Ctx {
     block_size: u32,
@@ -26,31 +51,152 @@ impl Ctx {
 pub(crate) struct Decoder<'r, 'c, R: std::io::Read> {
     reader: &'r mut R,
     ctx: &'c mut Ctx,
+    state_size: usize,
     finished: bool,
+    readout_cursor: usize,
 }
 
 impl<'r, 'c, R: std::io::Read> Decoder<'r, 'c, R> {
-    pub(crate) fn new(reader: &'r mut R, ctx: &'c mut Ctx) -> Self {
+    pub(crate) fn new(reader: &'r mut R, ctx: &'c mut Ctx, state_size: usize) -> Self {
         Self {
             reader,
             ctx,
             finished: false,
+            readout_cursor: 0,
+            state_size,
+        }
+    }
+    fn readout(&mut self, mut buf: &mut [u8]) -> std::io::Result<usize> {
+        match buf.write(&self.ctx.last_state[self.readout_cursor..]) {
+            Err(e) => Err(e),
+            Ok(sz) => {
+                self.readout_cursor += sz;
+                Ok(sz)
+            }
         }
     }
 }
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ParseState {
+    WaitForStart,
+    WaitForSuperblockSeq,
+    Finished,
+}
 
-impl<'r, 'c, R: std::io::Read> std::io::Read for Decoder<'r, 'c, R> {
+#[derive(thiserror::Error, Debug)]
+enum SSError {
+    #[error("Invalid token {0}")]
+    InvalidToken(#[from] InvalidDeterminant),
+    #[error("Too many start tokens in stream")]
+    TooManyStarts(),
+    #[error("Unexpected {1:?} during {0:?}")]
+    ParseError(ParseState, SSToken),
+    #[error("Block {0} is the wrong size")]
+    BlockWrongSize(u32),
+    #[error("Superblock {0} is the wrong size")]
+    SuperblockWrongSize(u32),
+    #[error("Couldn't insert block at {1} on frame {0}")]
+    BadBlockInsert(u64, u32),
+    #[error("Couldn't insert superblock at {1} on frame {0}")]
+    BadSuperblockInsert(u64, u32),
+}
+
+impl<R: std::io::Read> std::io::Read for Decoder<'_, '_, R> {
     /* a slightly degenerate read implementation in that it will keep
      * calling read on the inner reader until a complete checkpoint is
      * read, then return 0 for subsequent reads */
-    fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
+    fn read(&mut self, outbuf: &mut [u8]) -> std::io::Result<usize> {
+        use ParseState as State;
         use rmp::decode as r;
         if self.finished {
-            return Ok(0);
+            if self.readout_cursor == self.state_size {
+                return Ok(0);
+            }
+            return self.readout(outbuf);
         }
-
-        let sz = 0;
-        todo!();
-        Ok(sz)
+        let mut frame = 0;
+        let mut state = State::WaitForStart;
+        let mut buf = vec![0_u8; self.ctx.block_size as usize];
+        let mut superblock = vec![0_u32; self.ctx.superblock_size as usize];
+        loop {
+            let tok: u8 = r::read_int(self.reader).map_err(std::io::Error::other)?;
+            match (
+                state,
+                SSToken::try_from(tok)
+                    .map_err(|e| std::io::Error::other(SSError::InvalidToken(e)))?,
+            ) {
+                (State::WaitForStart, SSToken::Start) => {
+                    frame = r::read_int(self.reader).map_err(std::io::Error::other)?;
+                    state = State::WaitForSuperblockSeq;
+                }
+                (_, SSToken::Start) => return Err(std::io::Error::other(SSError::TooManyStarts())),
+                (State::WaitForSuperblockSeq, SSToken::NewBlock) => {
+                    let idx = r::read_int(self.reader).map_err(std::io::Error::other)?;
+                    let bin_len = r::read_bin_len(self.reader).map_err(std::io::Error::other)?;
+                    if bin_len != self.ctx.block_size {
+                        return Err(std::io::Error::other(SSError::BlockWrongSize(bin_len)));
+                    }
+                    self.reader.read_exact(&mut buf)?;
+                    if !self
+                        .ctx
+                        .block_index
+                        .insert_exact(idx, Box::from(buf.clone()), frame)
+                    {
+                        return Err(std::io::Error::other(SSError::BadBlockInsert(frame, idx)));
+                    }
+                }
+                (State::WaitForSuperblockSeq, SSToken::NewSuperblock) => {
+                    let idx = r::read_int(self.reader).map_err(std::io::Error::other)?;
+                    let arr_len = r::read_array_len(self.reader).map_err(std::io::Error::other)?;
+                    if arr_len != self.ctx.superblock_size {
+                        return Err(std::io::Error::other(SSError::SuperblockWrongSize(arr_len)));
+                    }
+                    for superblock_elt in &mut superblock {
+                        *superblock_elt =
+                            r::read_int(self.reader).map_err(std::io::Error::other)?;
+                    }
+                    if !self.ctx.superblock_index.insert_exact(
+                        idx,
+                        Box::from(superblock.clone()),
+                        frame,
+                    ) {
+                        return Err(std::io::Error::other(SSError::BadSuperblockInsert(
+                            frame, idx,
+                        )));
+                    }
+                }
+                (State::WaitForSuperblockSeq, SSToken::SuperblockSeq) => {
+                    let arr_len =
+                        r::read_array_len(self.reader).map_err(std::io::Error::other)? as usize;
+                    let block_byte_size = self.ctx.block_size as usize;
+                    let superblock_byte_size = self.ctx.superblock_size as usize * block_byte_size;
+                    self.ctx.last_state.resize(self.state_size, 0);
+                    for superblock_i in 0..arr_len {
+                        let superblock_idx =
+                            r::read_int(self.reader).map_err(std::io::Error::other)?;
+                        self.ctx.last_superseq[superblock_i] = superblock_idx;
+                        let superblock_data = self.ctx.superblock_index.get(superblock_idx);
+                        for (block_i, block_id) in superblock_data.iter().copied().enumerate() {
+                            let block_start = (superblock_i * superblock_byte_size
+                                + block_i * block_byte_size)
+                                .min(self.state_size);
+                            let block_end = (block_start + block_byte_size).min(self.state_size);
+                            let block_bytes = self.ctx.block_index.get(block_id);
+                            if block_end <= block_start {
+                                // This can happen in the last superblock if it was padded with extra blocks
+                                break;
+                            }
+                            self.ctx.last_state[block_start..block_end]
+                                .copy_from_slice(&block_bytes[0..(block_end - block_start)]);
+                        }
+                    }
+                    state = State::Finished;
+                    break;
+                }
+                (s, tok) => return Err(std::io::Error::other(SSError::ParseError(s, tok))),
+            }
+        }
+        assert_eq!(state, State::Finished);
+        self.readout(outbuf)
     }
 }
diff --git a/src/statestream/blockindex.rs b/src/statestream/blockindex.rs
index 1a61125..1b7ab52 100644
--- a/src/statestream/blockindex.rs
+++ b/src/statestream/blockindex.rs
@@ -18,6 +18,7 @@ pub(crate) struct BlockIndex<
     object_size: usize,
 }
 
+#[expect(unused)]
 pub(crate) struct Insertion {
     index: u32,
     is_new: bool,
@@ -42,7 +43,9 @@ impl<T: bytemuck::Zeroable + bytemuck::AnyBitPattern + bytemuck::NoUninit + Part
             hashes: vec![zero_hash],
         }
     }
+    #[expect(unused)]
     pub fn insert(&mut self, obj: &[T], _frame: u64) -> Insertion {
+        assert_eq!(obj.len(), self.object_size);
         let hash = hash(obj);
         match self.index.entry(hash) {
             std::collections::hash_map::Entry::Occupied(mut e) => {
@@ -81,6 +84,7 @@ impl<T: bytemuck::Zeroable + bytemuck::AnyBitPattern + bytemuck::NoUninit + Part
         }
     }
     pub fn insert_exact(&mut self, idx: u32, obj: Box<[T]>, _frame: u64) -> bool {
+        assert_eq!(obj.len(), self.object_size);
         if self.objects.len() != idx as usize {
             return false;
         }
@@ -88,17 +92,19 @@ impl<T: bytemuck::Zeroable + bytemuck::AnyBitPattern + bytemuck::NoUninit + Part
         self.index.entry(hash).or_default().push(idx);
         self.objects.push(obj);
         self.hashes.push(hash);
-        return true;
+        true
     }
     pub fn get(&self, which: u32) -> &[T] {
         &self.objects[which as usize]
     }
+    #[expect(unused)]
     pub fn clear(&mut self) {
         self.index.clear();
         self.objects.truncate(1);
         self.hashes.truncate(1);
         self.index.insert(self.hashes[0], smallvec![0]);
     }
+    #[expect(unused)]
     pub fn len(&self) -> usize {
         self.objects.len()
     }