Add multiplex

Cargo.toml

@@ -4,11 +4,7 @@ members = [
     "libp2p-ping",
     "libp2p-secio",
     "libp2p-swarm",
-    "libp2p-transport",
-    "libp2p-host",
     "libp2p-tcp-transport",
-    "libp2p-stream-muxer",
-    "multihash",
     "multistream-select",
     "datastore",
     "rw-stream-sink",

circular-buffer/src/lib.rs

@@ -9,62 +9,109 @@
 
 extern crate smallvec;
 
-use std::ops::{Deref, DerefMut, Drop};
+use std::ops::Drop;
 use std::mem::ManuallyDrop;
 
 use smallvec::Array;
 
+use owned_slice::OwnedSlice;
+
 /// A slice that owns its elements, but not their storage. This is useful for things like
 /// `Vec::retain` and `CircularBuffer::pop_slice`, since these functions can return a slice but the
 /// elements of these slices would be leaked after the slice goes out of scope. `OwnedSlice` simply
 /// manually drops all its elements when it goes out of scope.
-#[derive(Debug, Eq, PartialEq)]
-pub struct OwnedSlice<'a, T: 'a>(&'a mut [T]);
+pub mod owned_slice {
+    use std::ops::{Deref, DerefMut, Drop};
+    use std::mem::ManuallyDrop;
 
-impl<'a, T: 'a> OwnedSlice<'a, T> {
-    /// Construct an owned slice from a mutable slice pointer.
-    ///
-    /// # Unsafety
-    /// You must ensure that the memory pointed to by `inner` will not be accessible after the
-    /// lifetime of the `OwnedSlice`.
-    pub unsafe fn new(inner: &'a mut [T]) -> Self {
-        OwnedSlice(inner)
+    /// A slice that owns its elements, but not their storage. This is useful for things like
+    /// `Vec::retain` and `CircularBuffer::pop_slice`, since these functions can return a slice but
+    /// the elements of these slices would be leaked after the slice goes out of scope. `OwnedSlice`
+    /// simply manually drops all its elements when it goes out of scope.
+    #[derive(Debug, Eq, PartialEq)]
+    pub struct OwnedSlice<'a, T: 'a>(&'a mut [T]);
+
+    /// Owning iterator for `OwnedSlice`.
+    pub struct IntoIter<'a, T: 'a> {
+        slice: ManuallyDrop<OwnedSlice<'a, T>>,
+        index: usize,
     }
-}
 
-impl<'a, T> AsRef<[T]> for OwnedSlice<'a, T> {
-    fn as_ref(&self) -> &[T] {
-        self.0
+    impl<'a, T> Iterator for IntoIter<'a, T> {
+        type Item = T;
+
+        fn next(&mut self) -> Option<Self::Item> {
+            use std::ptr;
+
+            let index = self.index;
+
+            if index >= self.slice.len() {
+                return None;
+            }
+
+            self.index += 1;
+
+            unsafe { Some(ptr::read(&self.slice[index])) }
+        }
     }
-}
 
-impl<'a, T> AsMut<[T]> for OwnedSlice<'a, T> {
-    fn as_mut(&mut self) -> &mut [T] {
-        self.0
+    impl<'a, T: 'a> IntoIterator for OwnedSlice<'a, T> {
+        type Item = T;
+        type IntoIter = IntoIter<'a, T>;
+
+        fn into_iter(self) -> Self::IntoIter {
+            IntoIter {
+                slice: ManuallyDrop::new(self),
+                index: 0,
+            }
+        }
     }
-}
 
-impl<'a, T> Deref for OwnedSlice<'a, T> {
-    type Target = [T];
-
-    fn deref(&self) -> &Self::Target {
-        self.0
+    impl<'a, T: 'a> OwnedSlice<'a, T> {
+        /// Construct an owned slice from a mutable slice pointer.
+        ///
+        /// # Unsafety
+        /// You must ensure that the memory pointed to by `inner` will not be accessible after the
+        /// lifetime of the `OwnedSlice`.
+        pub unsafe fn new(inner: &'a mut [T]) -> Self {
+            OwnedSlice(inner)
+        }
     }
-}
 
-impl<'a, T> DerefMut for OwnedSlice<'a, T> {
-    fn deref_mut(&mut self) -> &mut Self::Target {
-        self.0
+    impl<'a, T> AsRef<[T]> for OwnedSlice<'a, T> {
+        fn as_ref(&self) -> &[T] {
+            self.0
+        }
     }
-}
 
-impl<'a, T> Drop for OwnedSlice<'a, T> {
-    fn drop(&mut self) {
-        use std::ptr;
+    impl<'a, T> AsMut<[T]> for OwnedSlice<'a, T> {
+        fn as_mut(&mut self) -> &mut [T] {
+            self.0
+        }
+    }
 
-        for element in self.iter_mut() {
-            unsafe {
-                ptr::drop_in_place(element);
+    impl<'a, T> Deref for OwnedSlice<'a, T> {
+        type Target = [T];
+
+        fn deref(&self) -> &Self::Target {
+            self.0
+        }
+    }
+
+    impl<'a, T> DerefMut for OwnedSlice<'a, T> {
+        fn deref_mut(&mut self) -> &mut Self::Target {
+            self.0
+        }
+    }
+
+    impl<'a, T> Drop for OwnedSlice<'a, T> {
+        fn drop(&mut self) {
+            use std::ptr;
+
+            for element in self.iter_mut() {
+                unsafe {
+                    ptr::drop_in_place(element);
+                }
             }
         }
     }
@@ -82,6 +129,12 @@ pub struct CircularBuffer<B: Array> {
     len: usize,
 }
 
+impl<B: Array> Default for CircularBuffer<B> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 impl<B: Array> PartialEq for CircularBuffer<B>
 where
     B::Item: PartialEq,
@@ -97,7 +150,7 @@ where
             }
         }
 
-        return true;
+        true
     }
 }
 
@@ -148,7 +201,9 @@ impl<B: Array> CircularBuffer<B> {
     /// when the slice goes out of scope), if you're using non-`Drop` types you can use
     /// `pop_slice_leaky`.
     pub fn pop_slice(&mut self) -> Option<OwnedSlice<B::Item>> {
-        self.pop_slice_leaky().map(OwnedSlice)
+        self.pop_slice_leaky().map(
+            |x| unsafe { OwnedSlice::new(x) },
+        )
     }
 
     /// Pop a slice containing the maximum possible contiguous number of elements. Since this buffer
@@ -357,18 +412,35 @@ impl<B: Array> CircularBuffer<B> {
         }
     }
 
-    /// Get a borrow to an element at an index unsafely (causes undefined behaviour if the index is
-    /// out of bounds).
+    /// Get a borrow to an element at an index unsafely (behaviour is undefined if the index is out
+    /// of bounds).
     pub unsafe fn get_unchecked(&self, index: usize) -> &B::Item {
-        use std::mem;
-
-        mem::transmute(self.buffer.ptr().offset(
+        &*self.buffer.ptr().offset(
             ((index + self.start) % B::size()) as isize,
-        ))
+        )
+    }
+
+    /// Get a mutable borrow to an element at an index safely (if the index is out of bounds, return
+    /// `None`).
+    pub fn get_mut(&mut self, index: usize) -> Option<&mut B::Item> {
+        if index < self.len {
+            unsafe { Some(self.get_unchecked_mut(index)) }
+        } else {
+            None
+        }
+    }
+
+    /// Get a mutable borrow to an element at an index unsafely (behaviour is undefined if the index
+    /// is out of bounds).
+    pub unsafe fn get_unchecked_mut(&mut self, index: usize) -> &mut B::Item {
+        &mut *self.buffer.ptr_mut().offset(
+            ((index + self.start) % B::size()) as
+                isize,
+        )
     }
 
     // This is not unsafe because it can only leak data, not cause uninit to be read.
-    fn advance(&mut self, by: usize) {
+    pub fn advance(&mut self, by: usize) {
         assert!(by <= self.len);
 
         self.start = (self.start + by) % B::size();
@@ -376,6 +448,39 @@ impl<B: Array> CircularBuffer<B> {
     }
 }
 
+impl<B: Array> std::ops::Index<usize> for CircularBuffer<B> {
+    type Output = B::Item;
+
+    fn index(&self, index: usize) -> &Self::Output {
+        if let Some(out) = self.get(index) {
+            out
+        } else {
+            panic!(
+                "index out of bounds: the len is {} but the index is {}",
+                self.len,
+                index
+            );
+        }
+    }
+}
+
+impl<B: Array> std::ops::IndexMut<usize> for CircularBuffer<B> {
+    fn index_mut(&mut self, index: usize) -> &mut Self::Output {
+        // We need to do this because borrowck isn't smart enough to understand enum variants
+        let len = self.len;
+
+        if let Some(out) = self.get_mut(index) {
+            return out;
+        } else {
+            panic!(
+                "index out of bounds: the len is {} but the index is {}",
+                len,
+                index
+            );
+        }
+    }
+}
+
 impl<B: Array> Drop for CircularBuffer<B> {
     fn drop(&mut self) {
         while self.pop_slice().is_some() {}

libp2p-stream-muxer/Cargo.toml

@@ -1,8 +0,0 @@
-[package]
-name = "libp2p-stream-muxer"
-version = "0.1.0"
-authors = ["Vurich <jackefransham@gmail.com>"]
-
-[dependencies]
-futures = "0.1"
-tokio-io = "0.1"

libp2p-stream-muxer/src/lib.rs

@@ -1,22 +0,0 @@
-extern crate tokio_io;
-extern crate futures;
-
-use futures::stream::Stream;
-use tokio_io::{AsyncRead, AsyncWrite};
-
-pub trait StreamMuxer {
-    type Substream: AsyncRead + AsyncWrite;
-    type InboundSubstreams: Stream<Item = Self::Substream>;
-    type OutboundSubstreams: Stream<Item = Self::Substream>;
-
-    fn inbound(&mut self) -> Self::InboundSubstreams;
-    fn outbound(&mut self) -> Self::OutboundSubstreams;
-}
-
-#[cfg(test)]
-mod tests {
-    #[test]
-    fn it_works() {
-        assert_eq!(2 + 2, 4);
-    }
-}

multiplex-rs/Cargo.toml

@@ -10,6 +10,8 @@ num-bigint = "0.1.40"
 tokio-io = "0.1"
 futures = "0.1"
 parking_lot = "0.4.8"
-libp2p-stream-muxer = { path = "../libp2p-stream-muxer" }
+arrayvec = "0.4.6"
+rand = "0.3.17"
+libp2p-swarm = { path = "../libp2p-swarm" }
 varint = { path = "../varint-rs" }
-circular-buffer = { path = "../circular-buffer" }
+error-chain = "0.11.0"

multiplex-rs/README.md

@@ -0,0 +1,3 @@
+# Multiplex
+
+A Rust implementation of [multiplex](https://github.com/maxogden/multiplex).

multiplex-rs/src/header.rs

@@ -0,0 +1,145 @@
+// Copyright 2017 Parity Technologies (UK) Ltd.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the "Software"),
+// to deal in the Software without restriction, including without limitation
+// the rights to use, copy, modify, merge, publish, distribute, sublicense,
+// and/or sell copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+const FLAG_BITS: usize = 3;
+const FLAG_MASK: usize = (1usize << FLAG_BITS) - 1;
+
+pub mod errors {
+    error_chain! {
+        errors {
+            ParseError
+        }
+    }
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub enum MultiplexEnd {
+    Initiator,
+    Receiver,
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub struct MultiplexHeader {
+    pub packet_type: PacketType,
+    pub substream_id: u32,
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub enum PacketType {
+    Open,
+    Close(MultiplexEnd),
+    Reset(MultiplexEnd),
+    Message(MultiplexEnd),
+}
+
+impl MultiplexHeader {
+    pub fn open(id: u32) -> Self {
+        MultiplexHeader {
+            substream_id: id,
+            packet_type: PacketType::Open,
+        }
+    }
+
+    pub fn close(id: u32, end: MultiplexEnd) -> Self {
+        MultiplexHeader {
+            substream_id: id,
+            packet_type: PacketType::Close(end),
+        }
+    }
+
+    pub fn reset(id: u32, end: MultiplexEnd) -> Self {
+        MultiplexHeader {
+            substream_id: id,
+            packet_type: PacketType::Reset(end),
+        }
+    }
+
+    pub fn message(id: u32, end: MultiplexEnd) -> Self {
+        MultiplexHeader {
+            substream_id: id,
+            packet_type: PacketType::Message(end),
+        }
+    }
+
+    // TODO: Use `u128` or another large integer type instead of bigint since we never use more than
+    //       `pointer width + FLAG_BITS` bits and unconditionally allocating 1-3 `u32`s for that is
+    //       ridiculous (especially since even for small numbers we have to allocate 1 `u32`).
+    //       If this is the future and `BigUint` is better-optimised (maybe by using `Bytes`) then
+    //       forget it.
+    pub fn parse(header: u64) -> Result<MultiplexHeader, errors::Error> {
+        use num_traits::cast::ToPrimitive;
+
+        let flags = header & FLAG_MASK as u64;
+
+        let substream_id = (header >> FLAG_BITS)
+            .to_u32()
+            .ok_or(errors::ErrorKind::ParseError)?;
+
+        // Yes, this is really how it works. No, I don't know why.
+        let packet_type = match flags {
+            0 => PacketType::Open,
+
+            1 => PacketType::Message(MultiplexEnd::Receiver),
+            2 => PacketType::Message(MultiplexEnd::Initiator),
+
+            3 => PacketType::Close(MultiplexEnd::Receiver),
+            4 => PacketType::Close(MultiplexEnd::Initiator),
+
+            5 => PacketType::Reset(MultiplexEnd::Receiver),
+            6 => PacketType::Reset(MultiplexEnd::Initiator),
+
+            _ => {
+                use std::io;
+
+                return Err(errors::Error::with_chain(
+                    io::Error::new(
+                        io::ErrorKind::Other,
+                        format!("Unexpected packet type: {}", flags),
+                    ),
+                    errors::ErrorKind::ParseError,
+                ));
+            }
+        };
+
+        Ok(MultiplexHeader {
+            substream_id,
+            packet_type,
+        })
+    }
+
+    pub fn to_u64(&self) -> u64 {
+        let packet_type_id = match self.packet_type {
+            PacketType::Open => 0,
+
+            PacketType::Message(MultiplexEnd::Receiver) => 1,
+            PacketType::Message(MultiplexEnd::Initiator) => 2,
+
+            PacketType::Close(MultiplexEnd::Receiver) => 3,
+            PacketType::Close(MultiplexEnd::Initiator) => 4,
+
+            PacketType::Reset(MultiplexEnd::Receiver) => 5,
+            PacketType::Reset(MultiplexEnd::Initiator) => 6,
+        };
+
+        let substream_id = (self.substream_id as u64) << FLAG_BITS;
+
+        substream_id | packet_type_id
+    }
+}

multiplex-rs/src/lib.rs

@@ -1,22 +1,56 @@
+// Copyright 2017 Parity Technologies (UK) Ltd.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the "Software"),
+// to deal in the Software without restriction, including without limitation
+// the rights to use, copy, modify, merge, publish, distribute, sublicense,
+// and/or sell copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+extern crate arrayvec;
 extern crate bytes;
+#[macro_use]
+extern crate error_chain;
 extern crate futures;
-extern crate libp2p_stream_muxer;
-extern crate tokio_io;
-extern crate varint;
+extern crate libp2p_swarm as swarm;
 extern crate num_bigint;
 extern crate num_traits;
 extern crate parking_lot;
-extern crate circular_buffer;
+extern crate rand;
+extern crate tokio_io;
+extern crate varint;
+
+mod read;
+mod write;
+mod shared;
+mod header;
 
 use bytes::Bytes;
-use circular_buffer::CircularBuffer;
-use futures::prelude::*;
-use libp2p_stream_muxer::StreamMuxer;
+use futures::{Async, Future, Poll};
+use futures::future::{self, FutureResult};
+use header::{MultiplexEnd, MultiplexHeader};
+use swarm::muxing::StreamMuxer;
+use swarm::ConnectionUpgrade;
 use parking_lot::Mutex;
-use std::collections::HashMap;
+use read::{read_stream, MultiplexReadState};
+use shared::{buf_from_slice, ByteBuf, MultiplexShared};
+use std::iter;
 use std::io::{self, Read, Write};
 use std::sync::Arc;
+use std::sync::atomic::{self, AtomicUsize};
 use tokio_io::{AsyncRead, AsyncWrite};
+use write::write_stream;
 
 // So the multiplex is essentially a distributed finite state machine.
 //
@@ -30,338 +64,55 @@ use tokio_io::{AsyncRead, AsyncWrite};
 // In the second state, the substream ID is known. Only this substream can progress until the packet
 // is consumed.
 
-/// Number of bits used for the metadata on multiplex packets
-enum NextMultiplexState {
-    NewStream(usize),
-    ParsingMessageBody(usize),
-    Ignore,
-}
-
-enum MultiplexReadState {
-    Header { state: varint::DecoderState },
-    BodyLength {
-        state: varint::DecoderState,
-        next: NextMultiplexState,
-    },
-    NewStream {
-        substream_id: usize,
-        name: bytes::BytesMut,
-        remaining_bytes: usize,
-    },
-    ParsingMessageBody {
-        substream_id: usize,
-        remaining_bytes: usize,
-    },
-    Ignore { remaining_bytes: usize },
-}
-
-impl Default for MultiplexReadState {
-    fn default() -> Self {
-        MultiplexReadState::Header { state: Default::default() }
-    }
-}
-
-struct MultiplexWriteState {
-    buffer: CircularBuffer<[u8; 1024]>,
-}
-
-// TODO: Add writing. We should also add some form of "pending packet" so that we can always open at
-//       least one new substream. If this is stored on the substream itself then we can open
-//       infinite new substreams.
-//
-//       When we've implemented writing, we should send the close message on `Substream` drop. This
-//       should probably be implemented with some kind of "pending close message" queue. The
-//       priority should go:
-//       1. Open new stream messages
-//       2. Regular messages
-//       3. Close messages
-//       Since if we receive a message to a closed stream we just drop it anyway.
-struct MultiplexShared<T> {
-    // We use `Option` in order to take ownership of heap allocations within `DecoderState` and
-    // `BytesMut`. If this is ever observably `None` then something has panicked or the underlying
-    // stream returned an error.
-    read_state: Option<MultiplexReadState>,
-    stream: T,
-    // true if the stream is open, false otherwise
-    open_streams: HashMap<usize, bool>,
-    // TODO: Should we use a version of this with a fixed size that doesn't allocate and return
-    //       `WouldBlock` if it's full?
-    to_open: HashMap<usize, Bytes>,
-}
-
 pub struct Substream<T> {
-    id: usize,
+    id: u32,
+    end: MultiplexEnd,
     name: Option<Bytes>,
     state: Arc<Mutex<MultiplexShared<T>>>,
+    buffer: Option<io::Cursor<ByteBuf>>,
 }
 
 impl<T> Drop for Substream<T> {
     fn drop(&mut self) {
         let mut lock = self.state.lock();
 
-        lock.open_streams.insert(self.id, false);
+        lock.close_stream(self.id);
     }
 }
 
 impl<T> Substream<T> {
     fn new<B: Into<Option<Bytes>>>(
-        id: usize,
+        id: u32,
+        end: MultiplexEnd,
         name: B,
         state: Arc<Mutex<MultiplexShared<T>>>,
     ) -> Self {
         let name = name.into();
 
-        Substream { id, name, state }
+        Substream {
+            id,
+            end,
+            name,
+            state,
+            buffer: None,
+        }
     }
 
     pub fn name(&self) -> Option<&Bytes> {
         self.name.as_ref()
     }
-}
 
-/// This is unsafe because you must ensure that only the `AsyncRead` that was passed in is later
-/// used to write to the returned buffer.
-unsafe fn create_buffer_for<R: AsyncRead>(capacity: usize, inner: &R) -> bytes::BytesMut {
-    let mut buffer = bytes::BytesMut::with_capacity(capacity);
-    buffer.set_len(capacity);
-    inner.prepare_uninitialized_buffer(&mut buffer);
-    buffer
-}
-
-fn read_stream<'a, O: Into<Option<(usize, &'a mut [u8])>>, T: AsyncRead>(
-    lock: &mut MultiplexShared<T>,
-    stream_data: O,
-) -> io::Result<usize> {
-    use num_traits::cast::ToPrimitive;
-    use MultiplexReadState::*;
-
-    let mut stream_data = stream_data.into();
-    let stream_has_been_gracefully_closed = stream_data
-        .as_ref()
-        .and_then(|&(id, _)| lock.open_streams.get(&id))
-        .map(|is_open| !is_open)
-        .unwrap_or(false);
-
-    let mut on_block: io::Result<usize> = if stream_has_been_gracefully_closed {
-        Ok(0)
-    } else {
-        Err(io::Error::from(io::ErrorKind::WouldBlock))
-    };
-
-    loop {
-        match lock.read_state.take().expect("Logic error or panic") {
-            Header { state: varint_state } => {
-                match varint_state.read(&mut lock.stream).map_err(|_| {
-                    io::Error::from(io::ErrorKind::Other)
-                })? {
-                    Ok(header) => {
-                        let MultiplexHeader {
-                            substream_id,
-                            packet_type,
-                        } = MultiplexHeader::parse(header).map_err(|_| {
-                            io::Error::from(io::ErrorKind::Other)
-                        })?;
-
-                        match packet_type {
-                            PacketType::Open => {
-                                lock.read_state = Some(BodyLength {
-                                    state: Default::default(),
-                                    next: NextMultiplexState::NewStream(substream_id),
-                                })
-                            }
-                            PacketType::Message(_) => {
-                                lock.read_state = Some(BodyLength {
-                                    state: Default::default(),
-                                    next: NextMultiplexState::ParsingMessageBody(substream_id),
-                                })
-                            }
-                            // NOTE: What's the difference between close and reset?
-                            PacketType::Close(_) |
-                            PacketType::Reset(_) => {
-                                lock.read_state = Some(BodyLength {
-                                    state: Default::default(),
-                                    next: NextMultiplexState::Ignore,
-                                });
-
-                                lock.open_streams.remove(&substream_id);
-                            }
-                        }
-                    }
-                    Err(new_state) => {
-                        lock.read_state = Some(Header { state: new_state });
-                        return on_block;
-                    }
-                }
-            }
-            BodyLength {
-                state: varint_state,
-                next,
-            } => {
-                match varint_state.read(&mut lock.stream).map_err(|_| {
-                    io::Error::from(io::ErrorKind::Other)
-                })? {
-                    Ok(length) => {
-                        use NextMultiplexState::*;
-
-                        let length = length.to_usize().ok_or(
-                            io::Error::from(io::ErrorKind::Other),
-                        )?;
-
-                        lock.read_state = Some(match next {
-                            Ignore => MultiplexReadState::Ignore { remaining_bytes: length },
-                            NewStream(substream_id) => MultiplexReadState::NewStream {
-                                // This is safe as long as we only use `lock.stream` to write to
-                                // this field
-                                name: unsafe { create_buffer_for(length, &lock.stream) },
-                                remaining_bytes: length,
-                                substream_id,
-                            },
-                            ParsingMessageBody(substream_id) => {
-                                let is_open = lock.open_streams
-                                    .get(&substream_id)
-                                    .map(|is_open| *is_open)
-                                    .unwrap_or(false);
-                                if is_open {
-                                    MultiplexReadState::ParsingMessageBody {
-                                        remaining_bytes: length,
-                                        substream_id,
-                                    }
-                                } else {
-                                    MultiplexReadState::Ignore { remaining_bytes: length }
-                                }
-                            }
-                        });
-                    }
-                    Err(new_state) => {
-                        lock.read_state = Some(BodyLength {
-                            state: new_state,
-                            next,
-                        });
-
-                        return on_block;
-                    }
-                }
-            }
-            NewStream {
-                substream_id,
-                mut name,
-                remaining_bytes,
-            } => {
-                if remaining_bytes == 0 {
-                    lock.to_open.insert(substream_id, name.freeze());
-
-                    lock.read_state = Some(Default::default());
-                } else {
-                    let cursor_pos = name.len() - remaining_bytes;
-                    let consumed = lock.stream.read(&mut name[cursor_pos..]);
-
-                    match consumed {
-                        Ok(consumed) => {
-                            let new_remaining = remaining_bytes - consumed;
-
-                            lock.read_state = Some(NewStream {
-                                substream_id,
-                                name,
-                                remaining_bytes: new_remaining,
-                            })
-                        }
-                        Err(ref err) if err.kind() == io::ErrorKind::WouldBlock => {
-                            lock.read_state = Some(NewStream {
-                                substream_id,
-                                name,
-                                remaining_bytes,
-                            });
-
-                            return on_block;
-                        }
-                        Err(other) => return Err(other),
-                    }
-                }
-            }
-            ParsingMessageBody {
-                substream_id,
-                remaining_bytes,
-            } => {
-                if let Some((ref mut id, ref mut buf)) = stream_data {
-                    use MultiplexReadState::*;
-
-                    if substream_id == *id {
-                        if remaining_bytes == 0 {
-                            lock.read_state = Some(Default::default());
-                        } else {
-                            let read_result = {
-                                let new_len = buf.len().min(remaining_bytes);
-                                let slice = &mut buf[..new_len];
-
-                                lock.stream.read(slice)
-                            };
-
-                            match read_result {
-                                Ok(consumed) => {
-                                    let new_remaining = remaining_bytes - consumed;
-
-                                    lock.read_state = Some(ParsingMessageBody {
-                                        substream_id,
-                                        remaining_bytes: new_remaining,
-                                    });
-
-                                    on_block = Ok(on_block.unwrap_or(0) + consumed);
-                                }
-                                Err(ref err) if err.kind() == io::ErrorKind::WouldBlock => {
-                                    lock.read_state = Some(ParsingMessageBody {
-                                        substream_id,
-                                        remaining_bytes,
-                                    });
-
-                                    return on_block;
-                                }
-                                Err(other) => return Err(other),
-                            }
-                        }
-                    } else {
-                        lock.read_state = Some(ParsingMessageBody {
-                            substream_id,
-                            remaining_bytes,
-                        });
-
-                        // We cannot make progress here, another stream has to accept this packet
-                        return on_block;
-                    }
-                }
-            }
-            Ignore { mut remaining_bytes } => {
-                let mut ignore_buf: [u8; 256] = [0; 256];
-
-                loop {
-                    if remaining_bytes == 0 {
-                        lock.read_state = Some(Default::default());
-                    } else {
-                        let new_len = ignore_buf.len().min(remaining_bytes);
-                        match lock.stream.read(&mut ignore_buf[..new_len]) {
-                            Ok(consumed) => remaining_bytes -= consumed,
-                            Err(ref err) if err.kind() == io::ErrorKind::WouldBlock => {
-                                lock.read_state = Some(Ignore { remaining_bytes });
-
-                                return on_block;
-                            }
-                            Err(other) => return Err(other),
-                        }
-                    }
-                }
-            }
-        }
+    pub fn id(&self) -> u32 {
+        self.id
     }
 }
 
-// TODO: We always zero the buffer, we should delegate to the inner stream. Maybe use a `RWLock`
-//       instead?
+// TODO: We always zero the buffer, we should delegate to the inner stream.
 impl<T: AsyncRead> Read for Substream<T> {
-    // TODO: Is it wasteful to have all of our substreams try to make progress? Can we use an
-    //       `AtomicBool` or `AtomicUsize` to limit the substreams that try to progress?
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
         let mut lock = match self.state.try_lock() {
             Some(lock) => lock,
-            None => return Err(io::Error::from(io::ErrorKind::WouldBlock)),
+            None => return Err(io::ErrorKind::WouldBlock.into()),
         };
 
         read_stream(&mut lock, (self.id, buf))
@@ -372,91 +123,50 @@ impl<T: AsyncRead> AsyncRead for Substream<T> {}
 
 impl<T: AsyncWrite> Write for Substream<T> {
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
-        unimplemented!()
+        let mut lock = self.state.try_lock().ok_or(io::ErrorKind::WouldBlock)?;
+
+        let mut buffer = self.buffer
+            .take()
+            .unwrap_or_else(|| io::Cursor::new(buf_from_slice(buf)));
+
+        let out = write_stream(
+            &mut *lock,
+            write::WriteRequest::substream(MultiplexHeader::message(self.id, self.end)),
+            &mut buffer,
+        );
+
+        if buffer.position() < buffer.get_ref().len() as u64 {
+            self.buffer = Some(buffer);
+        }
+
+        out
     }
 
     fn flush(&mut self) -> io::Result<()> {
-        unimplemented!()
+        self.state
+            .try_lock()
+            .ok_or(io::ErrorKind::WouldBlock)?
+            .stream
+            .flush()
     }
 }
 
 impl<T: AsyncWrite> AsyncWrite for Substream<T> {
     fn shutdown(&mut self) -> Poll<(), io::Error> {
-        unimplemented!()
+        Ok(Async::Ready(()))
     }
 }
 
-struct ParseError;
-
-enum MultiplexEnd {
-    Initiator,
-    Receiver,
-}
-
-struct MultiplexHeader {
-    pub packet_type: PacketType,
-    pub substream_id: usize,
-}
-enum PacketType {
-    Open,
-    Close(MultiplexEnd),
-    Reset(MultiplexEnd),
-    Message(MultiplexEnd),
-}
-
-impl MultiplexHeader {
-    // TODO: Use `u128` or another large integer type instead of bigint since we never use more than
-    //       `pointer width + FLAG_BITS` bits and unconditionally allocating 1-3 `u32`s for that is
-    //       ridiculous (especially since even for small numbers we have to allocate 1 `u32`).
-    //       If this is the future and `BigUint` is better-optimised (maybe by using `Bytes`) then
-    //       forget it.
-    fn parse(header: num_bigint::BigUint) -> Result<MultiplexHeader, ParseError> {
-        use num_traits::cast::ToPrimitive;
-
-        const FLAG_BITS: usize = 3;
-
-        // `&header` to make `>>` produce a new `BigUint` instead of consuming the old `BigUint`
-        let substream_id = ((&header) >> FLAG_BITS).to_usize().ok_or(ParseError)?;
-
-        let flag_mask = (2usize << FLAG_BITS) - 1;
-        let flags = header.to_usize().ok_or(ParseError)? & flag_mask;
-
-        // Yes, this is really how it works. No, I don't know why.
-        let packet_type = match flags {
-            0 => PacketType::Open,
-
-            1 => PacketType::Message(MultiplexEnd::Receiver),
-            2 => PacketType::Message(MultiplexEnd::Initiator),
-
-            3 => PacketType::Close(MultiplexEnd::Receiver),
-            4 => PacketType::Close(MultiplexEnd::Initiator),
-
-            5 => PacketType::Reset(MultiplexEnd::Receiver),
-            6 => PacketType::Reset(MultiplexEnd::Initiator),
-
-            _ => return Err(ParseError),
-        };
-
-        Ok(MultiplexHeader {
-            substream_id,
-            packet_type,
-        })
-    }
-}
-
-pub struct Multiplex<T> {
+pub struct InboundFuture<T> {
+    end: MultiplexEnd,
     state: Arc<Mutex<MultiplexShared<T>>>,
 }
 
-pub struct InboundStream<T> {
-    state: Arc<Mutex<MultiplexShared<T>>>,
-}
-
-impl<T: AsyncRead> Stream for InboundStream<T> {
+impl<T: AsyncRead> Future for InboundFuture<T> {
     type Item = Substream<T>;
     type Error = io::Error;
 
-    fn poll(&mut self) -> Poll<Option<Self::Item>, Self::Error> {
+    fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
         let mut lock = match self.state.try_lock() {
             Some(lock) => lock,
             None => return Ok(Async::NotReady),
@@ -464,8 +174,8 @@ impl<T: AsyncRead> Stream for InboundStream<T> {
 
         // Attempt to make progress, but don't block if we can't
         match read_stream(&mut lock, None) {
-            Ok(_) => (),
-            Err(ref err) if err.kind() == io::ErrorKind::WouldBlock => (),
+            Ok(_) => {}
+            Err(ref err) if err.kind() == io::ErrorKind::WouldBlock => {}
             Err(err) => return Err(err),
         }
 
@@ -479,30 +189,413 @@ impl<T: AsyncRead> Stream for InboundStream<T> {
             "We just checked that this key exists and we have exclusive access to the map, QED",
         );
 
-        Ok(Async::Ready(
-            Some(Substream::new(id, name, self.state.clone())),
-        ))
+        lock.open_stream(id);
+
+        Ok(Async::Ready(Substream::new(
+            id,
+            self.end,
+            name,
+            Arc::clone(&self.state),
+        )))
+    }
+}
+
+pub struct OutboundFuture<T> {
+    meta: Arc<MultiplexMetadata>,
+    current_id: Option<(io::Cursor<ByteBuf>, u32)>,
+    state: Arc<Mutex<MultiplexShared<T>>>,
+}
+
+impl<T> OutboundFuture<T> {
+    fn new(muxer: Multiplex<T>) -> Self {
+        OutboundFuture {
+            current_id: None,
+            meta: muxer.meta,
+            state: muxer.state,
+        }
+    }
+}
+
+fn nonce_to_id(id: usize, end: MultiplexEnd) -> u32 {
+    id as u32 * 2 + if end == MultiplexEnd::Initiator { 1 } else { 0 }
+}
+
+impl<T: AsyncWrite> Future for OutboundFuture<T> {
+    type Item = Substream<T>;
+    type Error = io::Error;
+
+    fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
+        let mut lock = match self.state.try_lock() {
+            Some(lock) => lock,
+            None => return Ok(Async::NotReady),
+        };
+
+        loop {
+            let (mut id_str, id) = self.current_id.take().unwrap_or_else(|| {
+                let next = nonce_to_id(
+                    self.meta.nonce.fetch_add(1, atomic::Ordering::Relaxed),
+                    self.meta.end,
+                );
+                (
+                    io::Cursor::new(buf_from_slice(format!("{}", next).as_bytes())),
+                    next as u32,
+                )
+            });
+
+            match write_stream(
+                &mut *lock,
+                write::WriteRequest::meta(MultiplexHeader::open(id)),
+                &mut id_str,
+            ) {
+                Ok(_) => {
+                    debug_assert!(id_str.position() <= id_str.get_ref().len() as u64);
+                    if id_str.position() == id_str.get_ref().len() as u64 {
+                        if lock.open_stream(id) {
+                            return Ok(Async::Ready(Substream::new(
+                                id,
+                                self.meta.end,
+                                Bytes::from(&id_str.get_ref()[..]),
+                                Arc::clone(&self.state),
+                            )));
+                        }
+                    } else {
+                        self.current_id = Some((id_str, id));
+                        return Ok(Async::NotReady);
+                    }
+                }
+                Err(ref err) if err.kind() == io::ErrorKind::WouldBlock => {
+                    self.current_id = Some((id_str, id));
+
+                    return Ok(Async::NotReady);
+                }
+                Err(other) => return Err(other),
+            }
+        }
+    }
+}
+
+pub struct MultiplexMetadata {
+    nonce: AtomicUsize,
+    end: MultiplexEnd,
+}
+
+pub struct Multiplex<T> {
+    meta: Arc<MultiplexMetadata>,
+    state: Arc<Mutex<MultiplexShared<T>>>,
+}
+
+impl<T> Clone for Multiplex<T> {
+    fn clone(&self) -> Self {
+        Multiplex {
+            meta: self.meta.clone(),
+            state: self.state.clone(),
+        }
+    }
+}
+
+impl<T> Multiplex<T> {
+    pub fn new(stream: T, end: MultiplexEnd) -> Self {
+        Multiplex {
+            meta: Arc::new(MultiplexMetadata {
+                nonce: AtomicUsize::new(0),
+                end,
+            }),
+            state: Arc::new(Mutex::new(MultiplexShared::new(stream))),
+        }
+    }
+
+    pub fn dial(stream: T) -> Self {
+        Self::new(stream, MultiplexEnd::Initiator)
+    }
+
+    pub fn listen(stream: T) -> Self {
+        Self::new(stream, MultiplexEnd::Receiver)
     }
 }
 
 impl<T: AsyncRead + AsyncWrite> StreamMuxer for Multiplex<T> {
     type Substream = Substream<T>;
-    type OutboundSubstreams = Box<Stream<Item = Self::Substream, Error = io::Error>>;
-    type InboundSubstreams = InboundStream<T>;
+    type OutboundSubstream = OutboundFuture<T>;
+    type InboundSubstream = InboundFuture<T>;
 
-    fn inbound(&mut self) -> Self::InboundSubstreams {
-        InboundStream { state: self.state.clone() }
+    fn inbound(self) -> Self::InboundSubstream {
+        InboundFuture {
+            state: Arc::clone(&self.state),
+            end: self.meta.end,
+        }
     }
 
-    fn outbound(&mut self) -> Self::OutboundSubstreams {
-        unimplemented!()
+    fn outbound(self) -> Self::OutboundSubstream {
+        OutboundFuture::new(self)
+    }
+}
+
+pub struct MultiplexConfig;
+
+impl<C> ConnectionUpgrade<C> for MultiplexConfig
+where
+    C: AsyncRead + AsyncWrite,
+{
+    type Output = Multiplex<C>;
+    type Future = FutureResult<Multiplex<C>, io::Error>;
+    type UpgradeIdentifier = ();
+    type NamesIter = iter::Once<(Bytes, ())>;
+
+    #[inline]
+    fn upgrade(self, i: C, _: ()) -> Self::Future {
+        future::ok(Multiplex::dial(i))
+    }
+
+    #[inline]
+    fn protocol_names(&self) -> Self::NamesIter {
+        iter::once((Bytes::from("/mplex/6.7.0"), ()))
     }
 }
 
 #[cfg(test)]
 mod tests {
+    use super::*;
+    use std::io;
+
     #[test]
-    fn it_works() {
-        assert_eq!(2 + 2, 4);
+    fn can_use_one_stream() {
+        let message = b"Hello, world!";
+
+        let stream = io::Cursor::new(Vec::new());
+
+        let mplex = Multiplex::dial(stream);
+
+        let mut substream = mplex.clone().outbound().wait().unwrap();
+
+        assert!(substream.write(message).is_ok());
+
+        let id = substream.id();
+
+        assert_eq!(
+            substream
+                .name()
+                .and_then(|bytes| { String::from_utf8(bytes.to_vec()).ok() }),
+            Some(id.to_string())
+        );
+
+        let stream = io::Cursor::new(mplex.state.lock().stream.get_ref().clone());
+
+        let mplex = Multiplex::listen(stream);
+
+        let mut substream = mplex.inbound().wait().unwrap();
+
+        assert_eq!(id, substream.id());
+        assert_eq!(
+            substream
+                .name()
+                .and_then(|bytes| { String::from_utf8(bytes.to_vec()).ok() }),
+            Some(id.to_string())
+        );
+
+        let mut buf = vec![0; message.len()];
+
+        assert!(substream.read(&mut buf).is_ok());
+        assert_eq!(&buf, message);
+    }
+
+    #[test]
+    fn can_use_many_streams() {
+        let stream = io::Cursor::new(Vec::new());
+
+        let mplex = Multiplex::dial(stream);
+
+        let mut outbound: Vec<Substream<_>> = vec![
+            mplex.clone().outbound().wait().unwrap(),
+            mplex.clone().outbound().wait().unwrap(),
+            mplex.clone().outbound().wait().unwrap(),
+            mplex.clone().outbound().wait().unwrap(),
+            mplex.clone().outbound().wait().unwrap(),
+        ];
+
+        outbound.sort_by_key(|a| a.id());
+
+        for (i, substream) in outbound.iter_mut().enumerate() {
+            assert!(substream.write(i.to_string().as_bytes()).is_ok());
+        }
+
+        let stream = io::Cursor::new(mplex.state.lock().stream.get_ref().clone());
+
+        let mplex = Multiplex::listen(stream);
+
+        let mut inbound: Vec<Substream<_>> = vec![
+            mplex.clone().inbound().wait().unwrap(),
+            mplex.clone().inbound().wait().unwrap(),
+            mplex.clone().inbound().wait().unwrap(),
+            mplex.clone().inbound().wait().unwrap(),
+            mplex.clone().inbound().wait().unwrap(),
+        ];
+
+        inbound.sort_by_key(|a| a.id());
+
+        for (substream, outbound) in inbound.iter_mut().zip(outbound.iter()) {
+            let id = outbound.id();
+            assert_eq!(id, substream.id());
+            assert_eq!(
+                substream
+                    .name()
+                    .and_then(|bytes| { String::from_utf8(bytes.to_vec()).ok() }),
+                Some(id.to_string())
+            );
+
+            let mut buf = [0; 3];
+            assert_eq!(substream.read(&mut buf).unwrap(), 1);
+        }
+    }
+
+    #[test]
+    fn packets_to_unopened_streams_are_dropped() {
+        use std::iter;
+
+        let message = b"Hello, world!";
+
+        // We use a large dummy length to exercise ignoring data longer than `ignore_buffer.len()`
+        let dummy_length = 1000;
+
+        let input = iter::empty()
+            // Open a stream
+            .chain(varint::encode(MultiplexHeader::open(0).to_u64()))
+            // 0-length body (stream has no name)
+            .chain(varint::encode(0usize))
+
+            // "Message"-type packet for an unopened stream
+            .chain(
+                varint::encode(
+                    // ID for an unopened stream: 1
+                    MultiplexHeader::message(1, MultiplexEnd::Initiator).to_u64(),
+                ).into_iter(),
+            )
+            // Body: `dummy_length` of zeroes
+            .chain(varint::encode(dummy_length))
+            .chain(iter::repeat(0).take(dummy_length))
+
+            // "Message"-type packet for an opened stream
+            .chain(
+                varint::encode(
+                    // ID for an opened stream: 0
+                    MultiplexHeader::message(0, MultiplexEnd::Initiator).to_u64(),
+                ).into_iter(),
+            )
+            .chain(varint::encode(message.len()))
+            .chain(message.iter().cloned())
+
+            .collect::<Vec<_>>();
+
+        let mplex = Multiplex::listen(io::Cursor::new(input));
+
+        let mut substream = mplex.inbound().wait().unwrap();
+
+        assert_eq!(substream.id(), 0);
+        assert_eq!(substream.name(), None);
+
+        let mut buf = vec![0; message.len()];
+
+        assert!(substream.read(&mut buf).is_ok());
+        assert_eq!(&buf, message);
+    }
+
+    #[test]
+    fn can_close_streams() {
+        use std::iter;
+
+        // Dummy data in the body of the close packet (since the de facto protocol is to accept but
+        // ignore this data)
+        let dummy_length = 64;
+
+        let input = iter::empty()
+            // Open a stream
+            .chain(varint::encode(MultiplexHeader::open(0).to_u64()))
+            // 0-length body (stream has no name)
+            .chain(varint::encode(0usize))
+
+            // Immediately close the stream
+            .chain(
+                varint::encode(
+                    // ID for an unopened stream: 1
+                    MultiplexHeader::close(0, MultiplexEnd::Initiator).to_u64(),
+                ).into_iter(),
+            )
+            .chain(varint::encode(dummy_length))
+            .chain(iter::repeat(0).take(dummy_length))
+
+            // Send packet to the closed stream
+            .chain(
+                varint::encode(
+                    // ID for an opened stream: 0
+                    MultiplexHeader::message(0, MultiplexEnd::Initiator).to_u64(),
+                ).into_iter(),
+            )
+            .chain(varint::encode(dummy_length))
+            .chain(iter::repeat(0).take(dummy_length))
+
+            .collect::<Vec<_>>();
+
+        let mplex = Multiplex::listen(io::Cursor::new(input));
+
+        let mut substream = mplex.inbound().wait().unwrap();
+
+        assert_eq!(substream.id(), 0);
+        assert_eq!(substream.name(), None);
+
+        assert_eq!(substream.read(&mut [0; 100][..]).unwrap(), 0);
+    }
+
+    #[test]
+    fn real_world_data() {
+        let data: Vec<u8> = vec![
+            // Open stream 1
+            8,
+            0,
+
+            // Message for stream 1 (length 20)
+            10,
+            20,
+            19,
+            47,
+            109,
+            117,
+            108,
+            116,
+            105,
+            115,
+            116,
+            114,
+            101,
+            97,
+            109,
+            47,
+            49,
+            46,
+            48,
+            46,
+            48,
+            10,
+        ];
+
+        let mplex = Multiplex::listen(io::Cursor::new(data));
+
+        let mut substream = mplex.inbound().wait().unwrap();
+
+        assert_eq!(substream.id(), 1);
+
+        assert_eq!(substream.name(), None);
+
+        let mut out = vec![];
+
+        for _ in 0..20 {
+            let mut buf = [0; 1];
+
+            assert_eq!(substream.read(&mut buf[..]).unwrap(), 1);
+
+            out.push(buf[0]);
+        }
+
+        assert_eq!(out[0], 19);
+        assert_eq!(&out[1..0x14 - 1], b"/multistream/1.0.0");
+        assert_eq!(out[0x14 - 1], 0x0a);
     }
 }

multiplex-rs/src/read.rs

@@ -0,0 +1,402 @@
+// Copyright 2017 Parity Technologies (UK) Ltd.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the "Software"),
+// to deal in the Software without restriction, including without limitation
+// the rights to use, copy, modify, merge, publish, distribute, sublicense,
+// and/or sell copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+use {bytes, varint};
+use futures::Async;
+use futures::task;
+use header::{MultiplexHeader, PacketType};
+use std::io;
+use tokio_io::AsyncRead;
+use shared::SubstreamMetadata;
+
+pub enum NextMultiplexState {
+    NewStream(u32),
+    ParsingMessageBody(u32),
+    Ignore,
+}
+
+pub enum MultiplexReadState {
+    Header {
+        state: varint::DecoderState<u64>,
+    },
+    BodyLength {
+        state: varint::DecoderState<usize>,
+        next: NextMultiplexState,
+    },
+    NewStream {
+        substream_id: u32,
+        name: bytes::BytesMut,
+        remaining_bytes: usize,
+    },
+    ParsingMessageBody {
+        substream_id: u32,
+        remaining_bytes: usize,
+    },
+    Ignore {
+        remaining_bytes: usize,
+    },
+}
+
+impl Default for MultiplexReadState {
+    fn default() -> Self {
+        MultiplexReadState::Header {
+            state: Default::default(),
+        }
+    }
+}
+
+fn create_buffer(capacity: usize) -> bytes::BytesMut {
+    let mut buffer = bytes::BytesMut::with_capacity(capacity);
+    let zeroes = [0; 1024];
+    let mut cap = capacity;
+
+    while cap > 0 {
+        let len = cap.min(zeroes.len());
+        buffer.extend_from_slice(&zeroes[..len]);
+        cap -= len;
+    }
+
+    buffer
+}
+
+pub fn read_stream<'a, O: Into<Option<(u32, &'a mut [u8])>>, T: AsyncRead>(
+    lock: &mut ::shared::MultiplexShared<T>,
+    stream_data: O,
+) -> io::Result<usize> {
+    use self::MultiplexReadState::*;
+
+    let mut stream_data = stream_data.into();
+    let stream_has_been_gracefully_closed = stream_data
+        .as_ref()
+        .and_then(|&(id, _)| lock.open_streams.get(&id))
+        .map(|meta| !meta.open())
+        .unwrap_or(false);
+
+    let mut on_block: io::Result<usize> = if stream_has_been_gracefully_closed {
+        Ok(0)
+    } else {
+        Err(io::ErrorKind::WouldBlock.into())
+    };
+
+    loop {
+        match lock.read_state.take().unwrap_or_default() {
+            Header {
+                state: mut varint_state,
+            } => {
+                match varint_state.read(&mut lock.stream) {
+                    Ok(Async::Ready(header)) => {
+                        let header = if let Some(header) = header {
+                            header
+                        } else {
+                            return Ok(0);
+                        };
+
+                        let MultiplexHeader {
+                            substream_id,
+                            packet_type,
+                        } = MultiplexHeader::parse(header).map_err(|err| {
+                            io::Error::new(
+                                io::ErrorKind::Other,
+                                format!("Error parsing header: {:?}", err),
+                            )
+                        })?;
+
+                        match packet_type {
+                            PacketType::Open => {
+                                lock.read_state = Some(BodyLength {
+                                    state: Default::default(),
+                                    next: NextMultiplexState::NewStream(substream_id),
+                                })
+                            }
+                            PacketType::Message(_) => {
+                                lock.read_state = Some(BodyLength {
+                                    state: Default::default(),
+                                    next: NextMultiplexState::ParsingMessageBody(substream_id),
+                                })
+                            }
+                            // NOTE: What's the difference between close and reset?
+                            PacketType::Close(_) | PacketType::Reset(_) => {
+                                lock.read_state = Some(BodyLength {
+                                    state: Default::default(),
+                                    next: NextMultiplexState::Ignore,
+                                });
+
+                                lock.close_stream(substream_id);
+                            }
+                        }
+                    }
+                    Ok(Async::NotReady) => {
+                        lock.read_state = Some(Header {
+                            state: varint_state,
+                        });
+                        return on_block;
+                    }
+                    Err(error) => {
+                        return if let varint::Error(varint::ErrorKind::Io(inner), ..) = error {
+                            Err(inner)
+                        } else {
+                            Err(io::Error::new(io::ErrorKind::Other, error.description()))
+                        };
+                    }
+                }
+            }
+            BodyLength {
+                state: mut varint_state,
+                next,
+            } => {
+                use self::NextMultiplexState::*;
+
+                match varint_state
+                    .read(&mut lock.stream)
+                    .map_err(|_| io::Error::new(io::ErrorKind::Other, "Error reading varint"))?
+                {
+                    Async::Ready(length) => {
+                        // TODO: Limit `length` to prevent resource-exhaustion DOS
+                        let length = if let Some(length) = length {
+                            length
+                        } else {
+                            return Ok(0);
+                        };
+
+                        lock.read_state = match next {
+                            Ignore => Some(MultiplexReadState::Ignore {
+                                remaining_bytes: length,
+                            }),
+                            NewStream(substream_id) => {
+                                if length == 0 {
+                                    lock.to_open.insert(substream_id, None);
+
+                                    None
+                                } else {
+                                    Some(MultiplexReadState::NewStream {
+                                        // TODO: Uninit buffer
+                                        name: create_buffer(length),
+                                        remaining_bytes: length,
+                                        substream_id,
+                                    })
+                                }
+                            }
+                            ParsingMessageBody(substream_id) => {
+                                let is_open = lock.open_streams
+                                    .get(&substream_id)
+                                    .map(SubstreamMetadata::open)
+                                    .unwrap_or_else(|| lock.to_open.contains_key(&substream_id));
+
+                                if is_open {
+                                    Some(MultiplexReadState::ParsingMessageBody {
+                                        remaining_bytes: length,
+                                        substream_id,
+                                    })
+                                } else {
+                                    Some(MultiplexReadState::Ignore {
+                                        remaining_bytes: length,
+                                    })
+                                }
+                            }
+                        };
+                    }
+                    Async::NotReady => {
+                        lock.read_state = Some(BodyLength {
+                            state: varint_state,
+                            next,
+                        });
+
+                        return on_block;
+                    }
+                }
+            }
+            NewStream {
+                substream_id,
+                mut name,
+                remaining_bytes,
+            } => {
+                if remaining_bytes == 0 {
+                    lock.to_open.insert(substream_id, Some(name.freeze()));
+
+                    lock.read_state = None;
+                } else {
+                    let cursor_pos = name.len() - remaining_bytes;
+                    let consumed = lock.stream.read(&mut name[cursor_pos..]);
+
+                    match consumed {
+                        Ok(consumed) => {
+                            let new_remaining = remaining_bytes - consumed;
+
+                            lock.read_state = Some(NewStream {
+                                substream_id,
+                                name,
+                                remaining_bytes: new_remaining,
+                            });
+                        }
+                        Err(ref err) if err.kind() == io::ErrorKind::WouldBlock => {
+                            lock.read_state = Some(NewStream {
+                                substream_id,
+                                name,
+                                remaining_bytes,
+                            });
+
+                            return on_block;
+                        }
+                        Err(other) => {
+                            lock.read_state = Some(NewStream {
+                                substream_id,
+                                name,
+                                remaining_bytes,
+                            });
+
+                            return Err(other);
+                        }
+                    }
+                }
+            }
+            ParsingMessageBody {
+                substream_id,
+                remaining_bytes,
+            } => {
+                if let Some((ref mut id, ref mut buf)) = stream_data {
+                    use MultiplexReadState::*;
+
+                    if remaining_bytes == 0 {
+                        lock.read_state = None;
+
+                        return on_block;
+                    } else if substream_id == *id {
+                        let number_read = *on_block.as_ref().unwrap_or(&0);
+
+                        if buf.len() == 0 {
+                            return Ok(0);
+                        } else if number_read >= buf.len() {
+                            lock.read_state = Some(ParsingMessageBody {
+                                substream_id,
+                                remaining_bytes,
+                            });
+
+                            return on_block;
+                        }
+
+                        let read_result = {
+                            // We know this won't panic because of the earlier
+                            // `number_read >= buf.len()` check
+                            let new_len = (buf.len() - number_read).min(remaining_bytes);
+                            let slice = &mut buf[number_read..number_read + new_len];
+
+                            lock.stream.read(slice)
+                        };
+
+                        match read_result {
+                            Ok(consumed) => {
+                                let new_remaining = remaining_bytes - consumed;
+
+                                lock.read_state = Some(ParsingMessageBody {
+                                    substream_id,
+                                    remaining_bytes: new_remaining,
+                                });
+
+                                on_block = Ok(number_read + consumed);
+                            }
+                            Err(ref err) if err.kind() == io::ErrorKind::WouldBlock => {
+                                lock.read_state = Some(ParsingMessageBody {
+                                    substream_id,
+                                    remaining_bytes,
+                                });
+
+                                return on_block;
+                            }
+                            Err(other) => {
+                                lock.read_state = Some(ParsingMessageBody {
+                                    substream_id,
+                                    remaining_bytes,
+                                });
+
+                                return Err(other);
+                            }
+                        }
+                    } else {
+                        lock.read_state = Some(ParsingMessageBody {
+                            substream_id,
+                            remaining_bytes,
+                        });
+
+                        if let Some(task) = lock.open_streams
+                            .get(&substream_id)
+                            .and_then(SubstreamMetadata::read_task)
+                        {
+                            task.notify();
+                        }
+
+                        let write = lock.open_streams
+                            .get(id)
+                            .and_then(SubstreamMetadata::write_task)
+                            .cloned();
+                        lock.open_streams.insert(
+                            *id,
+                            SubstreamMetadata::Open {
+                                read: Some(task::current()),
+                                write,
+                            },
+                        );
+                        // We cannot make progress here, another stream has to accept this packet
+                        return on_block;
+                    }
+                } else {
+                    lock.read_state = Some(ParsingMessageBody {
+                        substream_id,
+                        remaining_bytes,
+                    });
+
+                    // We cannot make progress here, a stream has to accept this packet
+                    return on_block;
+                }
+            }
+            Ignore {
+                mut remaining_bytes,
+            } => {
+                let mut ignore_buf: [u8; 256] = [0; 256];
+
+                loop {
+                    if remaining_bytes == 0 {
+                        lock.read_state = None;
+                        break;
+                    } else {
+                        let new_len = ignore_buf.len().min(remaining_bytes);
+                        match lock.stream.read(&mut ignore_buf[..new_len]) {
+                            Ok(consumed) => {
+                                remaining_bytes -= consumed;
+                                lock.read_state = Some(Ignore {
+                                    remaining_bytes: remaining_bytes,
+                                });
+                            }
+                            Err(ref err) if err.kind() == io::ErrorKind::WouldBlock => {
+                                lock.read_state = Some(Ignore { remaining_bytes });
+
+                                return on_block;
+                            }
+                            Err(other) => {
+                                lock.read_state = Some(Ignore { remaining_bytes });
+
+                                return Err(other);
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
+}

multiplex-rs/src/shared.rs

@@ -0,0 +1,108 @@
+// Copyright 2017 Parity Technologies (UK) Ltd.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the "Software"),
+// to deal in the Software without restriction, including without limitation
+// the rights to use, copy, modify, merge, publish, distribute, sublicense,
+// and/or sell copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+use read::MultiplexReadState;
+use write::MultiplexWriteState;
+
+use std::collections::HashMap;
+use bytes::Bytes;
+use arrayvec::ArrayVec;
+use futures::task::Task;
+
+const BUF_SIZE: usize = 1024;
+
+pub type ByteBuf = ArrayVec<[u8; BUF_SIZE]>;
+
+pub enum SubstreamMetadata {
+    Closed,
+    Open {
+        read: Option<Task>,
+        write: Option<Task>,
+    },
+}
+
+impl SubstreamMetadata {
+    pub fn open(&self) -> bool {
+        match *self {
+            SubstreamMetadata::Closed => false,
+            SubstreamMetadata::Open { .. } => true,
+        }
+    }
+
+    pub fn read_task(&self) -> Option<&Task> {
+        match *self {
+            SubstreamMetadata::Closed => None,
+            SubstreamMetadata::Open { ref read, .. } => read.as_ref(),
+        }
+    }
+
+    pub fn write_task(&self) -> Option<&Task> {
+        match *self {
+            SubstreamMetadata::Closed => None,
+            SubstreamMetadata::Open { ref write, .. } => write.as_ref(),
+        }
+    }
+}
+
+// TODO: Split reading and writing into different structs and have information shared between the
+//       two in a `RwLock`, since `open_streams` and `to_open` are mostly read-only.
+pub struct MultiplexShared<T> {
+    // We use `Option` in order to take ownership of heap allocations within `DecoderState` and
+    // `BytesMut`. If this is ever observably `None` then something has panicked or the underlying
+    // stream returned an error.
+    pub read_state: Option<MultiplexReadState>,
+    pub write_state: Option<MultiplexWriteState>,
+    pub stream: T,
+    // true if the stream is open, false otherwise
+    pub open_streams: HashMap<u32, SubstreamMetadata>,
+    // TODO: Should we use a version of this with a fixed size that doesn't allocate and return
+    //       `WouldBlock` if it's full?
+    pub to_open: HashMap<u32, Option<Bytes>>,
+}
+
+impl<T> MultiplexShared<T> {
+    pub fn new(stream: T) -> Self {
+        MultiplexShared {
+            read_state: Default::default(),
+            write_state: Default::default(),
+            open_streams: Default::default(),
+            to_open: Default::default(),
+            stream: stream,
+        }
+    }
+
+    pub fn open_stream(&mut self, id: u32) -> bool {
+        self.open_streams
+            .entry(id)
+            .or_insert(SubstreamMetadata::Open {
+                read: None,
+                write: None,
+            })
+            .open()
+    }
+
+    pub fn close_stream(&mut self, id: u32) {
+        self.open_streams.insert(id, SubstreamMetadata::Closed);
+    }
+}
+
+pub fn buf_from_slice(slice: &[u8]) -> ByteBuf {
+    slice.iter().cloned().take(BUF_SIZE).collect()
+}

multiplex-rs/src/write.rs

@@ -0,0 +1,188 @@
+// Copyright 2017 Parity Technologies (UK) Ltd.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the "Software"),
+// to deal in the Software without restriction, including without limitation
+// the rights to use, copy, modify, merge, publish, distribute, sublicense,
+// and/or sell copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+use shared::{ByteBuf, MultiplexShared, SubstreamMetadata};
+use header::MultiplexHeader;
+
+use varint;
+use futures::task;
+use std::io;
+use tokio_io::AsyncWrite;
+
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub enum RequestType {
+    Meta,
+    Substream,
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub struct WriteRequest {
+    header: MultiplexHeader,
+    request_type: RequestType,
+}
+
+impl WriteRequest {
+    pub fn substream(header: MultiplexHeader) -> Self {
+        WriteRequest {
+            header,
+            request_type: RequestType::Substream,
+        }
+    }
+
+    pub fn meta(header: MultiplexHeader) -> Self {
+        WriteRequest {
+            header,
+            request_type: RequestType::Meta,
+        }
+    }
+}
+
+#[derive(Default, Debug)]
+pub struct MultiplexWriteState {
+    current: Option<(WriteRequest, MultiplexWriteStateInner)>,
+    queued: Option<WriteRequest>,
+    // TODO: Actually close these
+    to_close: Vec<u32>,
+}
+
+#[derive(Debug)]
+pub enum MultiplexWriteStateInner {
+    WriteHeader { state: varint::EncoderState<u64> },
+    BodyLength { state: varint::EncoderState<usize> },
+    Body { size: usize },
+}
+
+pub fn write_stream<T: AsyncWrite>(
+    lock: &mut MultiplexShared<T>,
+    write_request: WriteRequest,
+    buf: &mut io::Cursor<ByteBuf>,
+) -> io::Result<usize> {
+    use futures::Async;
+    use num_traits::cast::ToPrimitive;
+    use varint::WriteState;
+    use write::MultiplexWriteStateInner::*;
+
+    let mut on_block = Err(io::ErrorKind::WouldBlock.into());
+    let mut write_state = lock.write_state.take().unwrap_or_default();
+    let (request, mut state) = write_state.current.take().unwrap_or_else(|| {
+        (
+            write_request,
+            MultiplexWriteStateInner::WriteHeader {
+                state: varint::EncoderState::new(write_request.header.to_u64()),
+            },
+        )
+    });
+
+    let id = write_request.header.substream_id;
+
+    match (request.request_type, write_request.request_type) {
+        (RequestType::Substream, RequestType::Substream) if request.header.substream_id != id => {
+            let read = lock.open_streams
+                .get(&id)
+                .and_then(SubstreamMetadata::read_task)
+                .cloned();
+
+            if let Some(task) = lock.open_streams
+                .get(&request.header.substream_id)
+                .and_then(SubstreamMetadata::write_task)
+            {
+                task.notify();
+            }
+
+            lock.open_streams.insert(
+                id,
+                SubstreamMetadata::Open {
+                    write: Some(task::current()),
+                    read,
+                },
+            );
+            lock.write_state = Some(write_state);
+            return on_block;
+        }
+        (RequestType::Substream, RequestType::Meta)
+        | (RequestType::Meta, RequestType::Substream) => {
+            lock.write_state = Some(write_state);
+            return on_block;
+        }
+        _ => {}
+    }
+
+    loop {
+        // Err = should return, Ok = continue
+        let new_state = match state {
+            WriteHeader {
+                state: mut inner_state,
+            } => match inner_state
+                .write(&mut lock.stream)
+                .map_err(|_| io::ErrorKind::Other)?
+            {
+                Async::Ready(WriteState::Done(_)) => Ok(BodyLength {
+                    state: varint::EncoderState::new(buf.get_ref().len()),
+                }),
+                Async::Ready(WriteState::Pending(_)) | Async::NotReady => {
+                    Err(Some(WriteHeader { state: inner_state }))
+                }
+            },
+            BodyLength {
+                state: mut inner_state,
+            } => match inner_state
+                .write(&mut lock.stream)
+                .map_err(|_| io::ErrorKind::Other)?
+            {
+                Async::Ready(WriteState::Done(_)) => Ok(Body {
+                    size: inner_state.source().to_usize().unwrap_or(::std::usize::MAX),
+                }),
+                Async::Ready(WriteState::Pending(_)) => Ok(BodyLength { state: inner_state }),
+                Async::NotReady => Err(Some(BodyLength { state: inner_state })),
+            },
+            Body { size } => {
+                if buf.position() == buf.get_ref().len() as u64 {
+                    Err(None)
+                } else {
+                    match lock.stream.write(&buf.get_ref()[buf.position() as usize..]) {
+                        Ok(just_written) => {
+                            let cur_pos = buf.position();
+                            buf.set_position(cur_pos + just_written as u64);
+                            on_block = Ok(on_block.unwrap_or(0) + just_written);
+                            Ok(Body {
+                                size: size - just_written,
+                            })
+                        }
+                        Err(ref err) if err.kind() == io::ErrorKind::WouldBlock => {
+                            Err(Some(Body { size }))
+                        }
+                        Err(other) => {
+                            return Err(other);
+                        }
+                    }
+                }
+            }
+        };
+
+        match new_state {
+            Ok(new_state) => state = new_state,
+            Err(new_state) => {
+                write_state.current = new_state.map(|state| (request, state));
+                lock.write_state = Some(write_state);
+                return on_block;
+            }
+        }
+    }
+}

varint-rs/Cargo.toml

@@ -5,6 +5,8 @@ authors = ["Parity Technologies <admin@parity.io>"]
 
 [dependencies]
 num-bigint = "0.1.40"
+num-traits = "0.1.40"
 bytes = "0.4.5"
 tokio-io = "0.1"
 futures = "0.1"
+error-chain = "0.11.0"

varint-rs/src/lib.rs

@@ -1,134 +1,404 @@
+#![warn(missing_docs)]
+
+//! Encoding and decoding state machines for protobuf varints
+
+// TODO: Non-allocating `BigUint`?
 extern crate num_bigint;
+extern crate num_traits;
 extern crate tokio_io;
 extern crate bytes;
 extern crate futures;
+#[macro_use]
+extern crate error_chain;
 
 use bytes::BytesMut;
+use futures::{Poll, Async};
 use num_bigint::BigUint;
-use tokio_io::AsyncRead;
+use num_traits::ToPrimitive;
+use tokio_io::{AsyncRead, AsyncWrite};
 use tokio_io::codec::Decoder;
 use std::io;
 use std::io::prelude::*;
 
-// TODO: error-chain
-pub struct ParseError;
+mod errors {
+    error_chain! {
+        errors {
+            ParseError {
+                description("error parsing varint")
+                display("error parsing varint")
+            }
+            WriteError {
+                description("error writing varint")
+                display("error writing varint")
+            }
+        }
 
-#[derive(Default)]
-pub struct DecoderState {
-    // TODO: Non-allocating `BigUint`?
-    accumulator: BigUint,
-    shift: usize,
-}
-
-impl DecoderState {
-    pub fn new() -> Self {
-        Default::default()
-    }
-
-    fn decode_one(mut self, byte: u8) -> Result<BigUint, Self> {
-        self.accumulator = self.accumulator | (BigUint::from(byte & 0x7F) << self.shift);
-        self.shift += 7;
-
-        if byte & 0x80 == 0 {
-            Ok(self.accumulator)
-        } else {
-            Err(self)
+        foreign_links {
+            Io(::std::io::Error);
         }
     }
+}
 
-    // Why the weird type signature? Well, `BigUint` owns its storage, and we don't want to clone
-    // it. So, we want the accumulator to be moved out when it is ready. We could have also used
-    // `Option`, but this means that it's not possible to end up in an inconsistent state
-    // (`shift != 0 && accumulator.is_none()`).
-    pub fn read<R: AsyncRead>(self, mut input: R) -> Result<Result<BigUint, Self>, ParseError> {
-        let mut state = self;
-        loop {
-            // We read one at a time to prevent consuming too much of the buffer.
-            let mut buffer: [u8; 1] = [0];
+pub use errors::{Error, ErrorKind};
 
-            match input.read_exact(&mut buffer) {
-                Ok(_) => {
-                    state = match state.decode_one(buffer[0]) {
-                        Ok(out) => break Ok(Ok(out)),
-                        Err(state) => state,
-                    };
-                }
-                Err(ref err) if err.kind() == io::ErrorKind::WouldBlock => break Ok(Err(state)),
-                Err(_) => break Err(ParseError),
+const USABLE_BITS_PER_BYTE: usize = 7;
+
+/// The state struct for the varint-to-bytes FSM
+#[derive(Debug)]
+pub struct EncoderState<T> {
+    source: T,
+    // A "chunk" is a section of the contained `BigUint` `USABLE_BITS_PER_BYTE` bits long
+    num_chunks: usize,
+    cur_chunk: usize,
+}
+
+/// Whether or not the varint writing was completed
+#[derive(Debug, Eq, PartialEq, Copy, Clone)]
+pub enum WriteState {
+    /// The encoder has finished writing
+    Done(usize),
+    /// The encoder still must write more bytes
+    Pending(usize),
+}
+
+fn ceil_div(a: usize, b: usize) -> usize {
+    (a + b - 1) / b
+}
+
+/// A trait to get the minimum number of bits required to represent a number
+pub trait Bits {
+    /// The minimum number of bits required to represent `self`
+    fn bits(&self) -> usize;
+}
+
+impl Bits for BigUint {
+    fn bits(&self) -> usize {
+        BigUint::bits(self)
+    }
+}
+
+macro_rules! impl_bits {
+    ($t:ty) => {
+        impl Bits for $t {
+            fn bits(&self) -> usize {
+                (std::mem::size_of::<$t>() * 8) - self.leading_zeros() as usize
             }
         }
     }
 }
 
-#[derive(Default)]
-pub struct VarintDecoder {
-    state: Option<DecoderState>,
+impl_bits!(usize);
+impl_bits!(u64);
+impl_bits!(u32);
+impl_bits!(u16);
+impl_bits!(u8);
+
+/// Helper trait to allow multiple integer types to be encoded
+pub trait EncoderHelper: Sized {
+    /// Write as much as possible of the inner integer to the output `AsyncWrite`
+    fn write<W: AsyncWrite>(encoder: &mut EncoderState<Self>, output: W)
+        -> Poll<WriteState, Error>;
 }
 
-impl VarintDecoder {
+/// Helper trait to allow multiple integer types to be encoded
+pub trait DecoderHelper: Sized {
+    /// Decode a single byte
+    fn decode_one(decoder: &mut DecoderState<Self>, byte: u8) -> Option<Self>;
+
+    /// Read as much of the varint as possible
+    fn read<R: AsyncRead>(decoder: &mut DecoderState<Self>, input: R) -> Poll<Option<Self>, Error>;
+}
+
+macro_rules! impl_decoderstate {
+    ($t:ty) => { impl_decoderstate!($t, <$t>::from, |v| v); };
+    ($t:ty, $make_fn:expr) => { impl_decoderstate!($t, $make_fn, $make_fn); };
+    ($t:ty, $make_fn:expr, $make_shift_fn:expr) => {
+        impl DecoderHelper for $t {
+            #[inline]
+            fn decode_one(decoder: &mut DecoderState<Self>, byte: u8) -> Option<$t> {
+                decoder.accumulator.take().and_then(|accumulator| {
+                    let out = accumulator |
+                    (
+                        $make_fn(byte & 0x7F) <<
+                            $make_shift_fn(decoder.shift * USABLE_BITS_PER_BYTE)
+                    );
+                    decoder.shift += 1;
+
+                    if byte & 0x80 == 0 {
+                        Some(out)
+                    } else {
+                        decoder.accumulator = AccumulatorState::InProgress(out);
+                        None
+                    }
+                })
+            }
+
+            fn read<R: AsyncRead>(
+                decoder: &mut DecoderState<Self>,
+                mut input: R
+            ) -> Poll<Option<Self>, Error> {
+                if decoder.accumulator == AccumulatorState::Finished {
+                    return Err(Error::with_chain(
+                        io::Error::new(
+                            io::ErrorKind::Other,
+                            "Attempted to parse a second varint (create a new instance!)",
+                        ),
+                        ErrorKind::ParseError,
+                    ));
+                }
+
+                loop {
+                    // We read one at a time to prevent consuming too much of the buffer.
+                    let mut buffer: [u8; 1] = [0];
+
+                    match input.read_exact(&mut buffer) {
+                        Ok(()) => {
+                            if let Some(out) = Self::decode_one(decoder, buffer[0]) {
+                                break Ok(Async::Ready(Some(out)));
+                            }
+                        }
+                        Err(ref err) if err.kind() == io::ErrorKind::WouldBlock => {
+                            break Ok(Async::NotReady);
+                        }
+                        Err(inner) => if decoder.accumulator == AccumulatorState::NotStarted {
+                            break Ok(Async::Ready(None));
+                        } else {
+                            break Err(Error::with_chain(inner, ErrorKind::ParseError))
+                        },
+                    }
+                }
+            }
+        }
+    }
+}
+
+macro_rules! impl_encoderstate {
+    ($t:ty) => { impl_encoderstate!($t, <$t>::from); };
+    ($t:ty, $make_fn:expr) => {
+        impl EncoderHelper for $t {
+            /// Write as much as possible of the inner integer to the output `AsyncWrite`
+            fn write<W: AsyncWrite>(
+                encoder: &mut EncoderState<Self>,
+                mut output: W,
+            ) -> Poll<WriteState, Error> {
+                fn encode_one(encoder: &EncoderState<$t>) -> Option<u8> {
+                    let last_chunk = encoder.num_chunks - 1;
+
+                    if encoder.cur_chunk > last_chunk {
+                        return None;
+                    }
+
+                    let masked = (&encoder.source >> (encoder.cur_chunk * USABLE_BITS_PER_BYTE)) &
+                        $make_fn((1 << USABLE_BITS_PER_BYTE) - 1usize);
+                    let masked = masked.to_u8().expect(
+                        "Masked with 0b0111_1111, is less than u8::MAX, QED",
+                    );
+
+                    if encoder.cur_chunk == last_chunk {
+                        Some(masked)
+                    } else {
+                        Some(masked | (1 << USABLE_BITS_PER_BYTE))
+                    }
+                }
+
+                let mut written = 0usize;
+
+                loop {
+                    if let Some(byte) = encode_one(&encoder) {
+                        let buffer: [u8; 1] = [byte];
+
+                        match output.write_all(&buffer) {
+                            Ok(()) => {
+                                written += 1;
+                                encoder.cur_chunk += 1;
+                            }
+                            Err(ref err) if err.kind() == io::ErrorKind::WouldBlock => {
+                                break if written == 0 {
+                                    Ok(Async::NotReady)
+                                } else {
+                                    Ok(Async::Ready(WriteState::Pending(written)))
+                                };
+                            }
+                            Err(inner) => break Err(
+                                Error::with_chain(inner, ErrorKind::WriteError)
+                            ),
+                        }
+                    } else {
+                        break Ok(Async::Ready(WriteState::Done(written)));
+                    }
+                }
+            }
+        }
+    }
+}
+
+impl_encoderstate!(usize);
+impl_encoderstate!(BigUint);
+impl_encoderstate!(u64, (|val| val as u64));
+impl_encoderstate!(u32, (|val| val as u32));
+
+impl_decoderstate!(usize);
+impl_decoderstate!(BigUint);
+impl_decoderstate!(u64, (|val| val as u64));
+impl_decoderstate!(u32, (|val| val as u32));
+
+impl<T> EncoderState<T> {
+    pub fn source(&self) -> &T {
+        &self.source
+    }
+}
+
+impl<T: Bits> EncoderState<T> {
+    /// Create a new encoder
+    pub fn new(inner: T) -> Self {
+        let bits = inner.bits();
+        EncoderState {
+            source: inner,
+            num_chunks: ceil_div(bits, USABLE_BITS_PER_BYTE).max(1),
+            cur_chunk: 0,
+        }
+    }
+}
+
+impl<T: EncoderHelper> EncoderState<T> {
+    /// Write as much as possible of the inner integer to the output `AsyncWrite`
+    pub fn write<W: AsyncWrite>(&mut self, output: W) -> Poll<WriteState, Error> {
+        T::write(self, output)
+    }
+}
+
+#[derive(Debug, PartialEq, Eq)]
+enum AccumulatorState<T> {
+    InProgress(T),
+    NotStarted,
+    Finished,
+}
+
+impl<T: Default> AccumulatorState<T> {
+    fn take(&mut self) -> Option<T> {
+        use std::mem;
+        use AccumulatorState::*;
+
+        match mem::replace(self, AccumulatorState::Finished) {
+            InProgress(inner) => Some(inner),
+            NotStarted => Some(Default::default()),
+            Finished => None,
+        }
+    }
+}
+
+/// The state struct for the varint bytes-to-bigint FSM
+#[derive(Debug)]
+pub struct DecoderState<T> {
+    accumulator: AccumulatorState<T>,
+    shift: usize,
+}
+
+impl<T: Default> Default for DecoderState<T> {
+    fn default() -> Self {
+        DecoderState {
+            accumulator: AccumulatorState::NotStarted,
+            shift: 0,
+        }
+    }
+}
+
+impl<T: Default> DecoderState<T> {
+    /// Make a new decoder
     pub fn new() -> Self {
         Default::default()
     }
 }
 
-impl Decoder for VarintDecoder {
-    type Item = BigUint;
+impl<T: DecoderHelper> DecoderState<T> {
+    /// Make a new decoder
+    pub fn read<R: AsyncRead>(&mut self, input: R) -> Poll<Option<T>, Error> {
+        T::read(self, input)
+    }
+}
+
+/// Wrapper around `DecoderState` to make a `tokio` `Decoder`
+#[derive(Debug)]
+pub struct VarintDecoder<T> {
+    state: Option<DecoderState<T>>,
+}
+
+impl<T> Default for VarintDecoder<T> {
+    fn default() -> Self {
+        VarintDecoder { state: None }
+    }
+}
+
+impl<T> VarintDecoder<T> {
+    /// Make a new decoder
+    pub fn new() -> Self {
+        Default::default()
+    }
+}
+
+impl<T: Default + DecoderHelper> Decoder for VarintDecoder<T> {
+    type Item = T;
     type Error = io::Error;
 
     fn decode(&mut self, src: &mut BytesMut) -> Result<Option<Self::Item>, Self::Error> {
         loop {
-            if src.len() == 0 {
+            if src.is_empty() && self.state.is_some() {
                 break Err(io::Error::from(io::ErrorKind::UnexpectedEof));
             } else {
                 // We know that the length is not 0, so this cannot fail.
                 let first_byte = src.split_to(1)[0];
-                let new_state = match self.state.take() {
-                    Some(state) => state.decode_one(first_byte),
-                    None => DecoderState::new().decode_one(first_byte),
-                };
+                let mut state = self.state.take().unwrap_or_default();
+                let out = T::decode_one(&mut state, first_byte);
 
-                match new_state {
-                    Ok(out) => break Ok(Some(out)),
-                    Err(state) => self.state = Some(state),
+                if let Some(out) = out {
+                    break Ok(Some(out));
+                } else {
+                    self.state = Some(state);
                 }
             }
         }
     }
 }
 
-pub fn decode<R: Read>(stream: R) -> io::Result<BigUint> {
-    let mut out = BigUint::from(0u8);
-    let mut shift = 0;
-    let mut finished_cleanly = false;
+/// Syncronously decode a number from a `Read`
+pub fn decode<R: Read, T: Default + DecoderHelper>(mut input: R) -> errors::Result<T> {
+    let mut decoder = DecoderState::default();
 
-    for i in stream.bytes() {
-        let i = i?;
+    loop {
+        // We read one at a time to prevent consuming too much of the buffer.
+        let mut buffer: [u8; 1] = [0];
 
-        out = out | (BigUint::from(i & 0x7F) << shift);
-        shift += 7;
-
-        if i & 0x80 == 0 {
-            finished_cleanly = true;
-            break;
+        match input.read_exact(&mut buffer) {
+            Ok(()) => {
+                            if let Some(out) = T::decode_one(&mut decoder, buffer[0]) {
+                                break Ok(out);
+                            }
+                        }
+            Err(inner) => break Err(Error::with_chain(inner, ErrorKind::ParseError)),
         }
     }
+}
 
-    if finished_cleanly {
-        Ok(out)
-    } else {
-        Err(io::Error::from(io::ErrorKind::UnexpectedEof))
+/// Syncronously decode a number from a `Read`
+pub fn encode<T: EncoderHelper + Bits>(input: T) -> Vec<u8> {
+    let mut encoder = EncoderState::new(input);
+    let mut out = io::Cursor::new(Vec::with_capacity(1));
+
+    match T::write(&mut encoder, &mut out).expect("Writing to a vec should never fail, Q.E.D") {
+        Async::Ready(_) => out.into_inner(),
+        Async::NotReady => unreachable!(),
     }
 }
 
 #[cfg(test)]
 mod tests {
-    use super::{decode, VarintDecoder};
+    use super::{decode, VarintDecoder, EncoderState};
     use tokio_io::codec::FramedRead;
     use num_bigint::BigUint;
     use futures::{Future, Stream};
 
     #[test]
-    fn can_decode_basic_uint() {
+    fn can_decode_basic_biguint() {
         assert_eq!(
             BigUint::from(300u16),
             decode(&[0b10101100, 0b00000010][..]).unwrap()
@@ -136,7 +406,7 @@ mod tests {
     }
 
     #[test]
-    fn can_decode_basic_uint_async() {
+    fn can_decode_basic_biguint_async() {
         let result = FramedRead::new(&[0b10101100, 0b00000010][..], VarintDecoder::new())
             .into_future()
             .map(|(out, _)| out)
@@ -146,11 +416,77 @@ mod tests {
         assert_eq!(result.unwrap(), Some(BigUint::from(300u16)));
     }
 
+    #[test]
+    fn can_decode_trivial_usize_async() {
+        let result = FramedRead::new(&[1][..], VarintDecoder::new())
+            .into_future()
+            .map(|(out, _)| out)
+            .map_err(|(out, _)| out)
+            .wait();
+
+        assert_eq!(result.unwrap(), Some(1usize));
+    }
+
+    #[test]
+    fn can_decode_basic_usize_async() {
+        let result = FramedRead::new(&[0b10101100, 0b00000010][..], VarintDecoder::new())
+            .into_future()
+            .map(|(out, _)| out)
+            .map_err(|(out, _)| out)
+            .wait();
+
+        assert_eq!(result.unwrap(), Some(300usize));
+    }
+
+    #[test]
+    fn can_encode_basic_biguint_async() {
+        use std::io::Cursor;
+        use futures::Async;
+        use super::WriteState;
+
+        let mut out = vec![0u8; 2];
+
+        {
+            let writable: Cursor<&mut [_]> = Cursor::new(&mut out);
+
+            let mut state = EncoderState::new(BigUint::from(300usize));
+
+            assert_eq!(
+                state.write(writable).unwrap(),
+                Async::Ready(WriteState::Done(2))
+            );
+        }
+
+        assert_eq!(out, vec![0b10101100, 0b00000010]);
+    }
+
+    #[test]
+    fn can_encode_basic_usize_async() {
+        use std::io::Cursor;
+        use futures::Async;
+        use super::WriteState;
+
+        let mut out = vec![0u8; 2];
+
+        {
+            let writable: Cursor<&mut [_]> = Cursor::new(&mut out);
+
+            let mut state = EncoderState::new(300usize);
+
+            assert_eq!(
+                state.write(writable).unwrap(),
+                Async::Ready(WriteState::Done(2))
+            );
+        }
+
+        assert_eq!(out, vec![0b10101100, 0b00000010]);
+    }
+
     #[test]
     fn unexpected_eof_async() {
         use std::io;
 
-        let result = FramedRead::new(&[0b10101100, 0b10000010][..], VarintDecoder::new())
+        let result = FramedRead::new(&[0b10101100, 0b10000010][..], VarintDecoder::<usize>::new())
             .into_future()
             .map(|(out, _)| out)
             .map_err(|(out, _)| out)