Much work

Cargo.toml

@@ -8,11 +8,11 @@ futures = "0.1"
 tokio-io = "0.1"
 tokio-timer = { git = "https://github.com/tokio-rs/tokio-timer" }
 bytes = "0.4"
-http = { path = "/Users/carllerche/Code/Oss/Tokio/tower/http" }
+http = { git = "https://github.com/carllerche/http" }
 byteorder = "1.0"
 log = "0.3.8"
-# tower = { path = "/Users/carllerche/Code/Oss/Tokio/tower/tower-http" }
 fnv = "1.0.5"
+ordermap = "0.2.10"
 
 [dev-dependencies]
 hex = "0.2.0"
@@ -21,3 +21,10 @@ serde = "1.0.0"
 serde_json = "1.0.0"
 quickcheck = "0.4.1"
 rand = "0.3.15"
+
+# Akamai example
+tokio-core = "0.1"
+openssl = { version = "0.9.14", "features" = ["v102"] }
+tokio-openssl = "0.1.3"
+env_logger = "0.4.3"
+io-dump = { path = "/Users/carllerche/Code/Oss/Tokio/util/io-dump" }

src/client.rs

@@ -0,0 +1,107 @@
+use {frame, proto, Frame, Peer, ConnectionError, StreamId};
+
+use http;
+
+use futures::{Future, Poll};
+
+use tokio_io::{AsyncRead, AsyncWrite};
+
+/// In progress H2 connection binding
+pub struct Handshake<T> {
+    // TODO: unbox
+    inner: Box<Future<Item = Connection<T>, Error = ConnectionError>>,
+}
+
+/// Marker type indicating a client peer
+pub struct Client;
+
+pub type Connection<T> = super::Connection<T, Client>;
+
+/// Bind an H2 client connection.
+///
+/// Returns a future which resolves to the connection value once the H2
+/// handshake has been completed.
+pub fn bind<T>(io: T) -> Handshake<T>
+    where T: AsyncRead + AsyncWrite + 'static,
+{
+    use tokio_io::io;
+
+    debug!("binding client connection");
+
+    let handshake = io::write_all(io, b"PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n")
+        .map(|(io, _)| {
+            debug!("client connection bound");
+            proto::new_connection(io)
+        })
+        .map_err(ConnectionError::from);
+
+    Handshake { inner: Box::new(handshake) }
+}
+
+impl Peer for Client {
+    type Send = http::request::Head;
+    type Poll = http::response::Head;
+
+    fn check_initiating_id(id: StreamId) -> Result<(), ConnectionError> {
+        if id % 2 == 0 {
+            // Client stream identifiers must be odd
+            unimplemented!();
+        }
+
+        // TODO: Ensure the `id` doesn't overflow u31
+
+        Ok(())
+    }
+
+    fn convert_send_message(
+        id: StreamId,
+        message: Self::Send,
+        body: bool) -> proto::SendMessage
+    {
+        use http::request::Head;
+
+        // Extract the components of the HTTP request
+        let Head { method, uri, headers, .. } = message;
+
+        // Build the set pseudo header set. All requests will include `method`
+        // and `path`.
+        let mut pseudo = frame::Pseudo::request(method, uri.path().into());
+
+        // If the URI includes a scheme component, add it to the pseudo headers
+        if let Some(scheme) = uri.scheme() {
+            pseudo.set_scheme(scheme.into());
+        }
+
+        // If the URI includes an authority component, add it to the pseudo
+        // headers
+        if let Some(authority) = uri.authority() {
+            pseudo.set_authority(authority.into());
+        }
+
+        // Create the HEADERS frame
+        let mut frame = frame::Headers::new(id, pseudo, headers);
+
+        // TODO: Factor in trailers
+        if !body {
+            frame.set_end_stream();
+        } else {
+            unimplemented!();
+        }
+
+        // Return the `SendMessage`
+        proto::SendMessage::new(frame)
+    }
+
+    fn convert_poll_message(message: proto::PollMessage) -> Frame<Self::Poll> {
+        unimplemented!();
+    }
+}
+
+impl<T> Future for Handshake<T> {
+    type Item = Connection<T>;
+    type Error = ConnectionError;
+
+    fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
+        self.inner.poll()
+    }
+}

src/frame/head.rs

@@ -66,7 +66,7 @@ impl Head {
     }
 
     pub fn encode<T: BufMut>(&self, payload_len: usize, dst: &mut T) {
-        debug_assert_eq!(self.encode_len(), dst.remaining_mut());
+        debug_assert!(self.encode_len() <= dst.remaining_mut());
         debug_assert!(self.stream_id & STREAM_ID_MASK == 0);
 
         dst.put_uint::<BigEndian>(payload_len as u64, 3);

src/frame/headers.rs

@@ -34,7 +34,7 @@ pub struct Headers {
     flags: HeadersFlag,
 }
 
-#[derive(Debug, Copy, Clone, Eq, PartialEq, Default)]
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
 pub struct HeadersFlag(u8);
 
 #[derive(Debug)]
@@ -108,6 +108,16 @@ const ALL: u8 = END_STREAM
 // ===== impl Headers =====
 
 impl Headers {
+    pub fn new(stream_id: StreamId, pseudo: Pseudo, fields: HeaderMap<HeaderValue>) -> Self {
+        Headers {
+            stream_id: stream_id,
+            stream_dep: None,
+            fields: fields,
+            pseudo: pseudo,
+            flags: HeadersFlag::default(),
+        }
+    }
+
     pub fn load(head: Head, src: &mut Cursor<Bytes>, decoder: &mut hpack::Decoder)
         -> Result<Self, Error>
     {
@@ -162,6 +172,10 @@ impl Headers {
         })
     }
 
+    pub fn is_end_headers(&self) -> bool {
+        self.flags.is_end_headers()
+    }
+
     pub fn encode(self, encoder: &mut hpack::Encoder, dst: &mut BytesMut)
         -> Option<Continuation>
     {
@@ -210,6 +224,28 @@ impl From<Headers> for Frame {
     }
 }
 
+// ===== impl Pseudo =====
+
+impl Pseudo {
+    pub fn request(method: Method, path: ByteStr) -> Self {
+        Pseudo {
+            method: Some(method),
+            scheme: None,
+            authority: None,
+            path: Some(path),
+            status: None,
+        }
+    }
+
+    pub fn set_scheme(&mut self, scheme: ByteStr) {
+        self.scheme = Some(scheme);
+    }
+
+    pub fn set_authority(&mut self, authority: ByteStr) {
+        self.authority = Some(authority);
+    }
+}
+
 // ===== impl Iter =====
 
 impl Iterator for Iter {
@@ -264,6 +300,10 @@ impl HeadersFlag {
         self.0 & END_STREAM == END_STREAM
     }
 
+    pub fn set_end_stream(&mut self) {
+        self.0 |= END_STREAM
+    }
+
     pub fn is_end_headers(&self) -> bool {
         self.0 & END_HEADERS == END_HEADERS
     }
@@ -277,6 +317,13 @@ impl HeadersFlag {
     }
 }
 
+impl Default for HeadersFlag {
+    /// Returns a `HeadersFlag` value with `END_HEADERS` set.
+    fn default() -> Self {
+        HeadersFlag(END_HEADERS)
+    }
+}
+
 impl From<HeadersFlag> for u8 {
     fn from(src: HeadersFlag) -> u8 {
         src.0

src/frame/mod.rs

@@ -34,7 +34,7 @@ mod util;
 
 pub use self::data::Data;
 pub use self::head::{Head, Kind, StreamId};
-pub use self::headers::{Headers, PushPromise, Continuation};
+pub use self::headers::{Headers, PushPromise, Continuation, Pseudo};
 pub use self::settings::{Settings, SettingSet};
 
 // Re-export some constants

src/frame/settings.rs

@@ -81,6 +81,7 @@ impl Settings {
 
         // Ensure the payload length is correct, each setting is 6 bytes long.
         if payload.len() % 6 != 0 {
+            debug!("invalid settings payload length; len={:?}", payload.len());
             return Err(Error::InvalidPayloadAckSettings);
         }
 

src/lib.rs

@@ -13,14 +13,17 @@ extern crate http;
 // Buffer utilities
 extern crate bytes;
 
-// Hash function used for HPACK encoding
+// Hash function used for HPACK encoding and tracking stream states.
 extern crate fnv;
 
+extern crate ordermap;
+
 extern crate byteorder;
 
 #[macro_use]
 extern crate log;
 
+pub mod client;
 pub mod error;
 pub mod hpack;
 pub mod proto;
@@ -29,4 +32,42 @@ pub mod frame;
 mod util;
 
 pub use error::{ConnectionError, StreamError, Reason};
+pub use frame::{StreamId};
 pub use proto::Connection;
+
+/// An H2 connection frame
+pub enum Frame<T> {
+    Message {
+        id: StreamId,
+        message: T,
+        body: bool,
+    },
+    Body {
+        id: StreamId,
+        chunk: Option<()>,
+    },
+    Error {
+        id: StreamId,
+        error: (),
+    }
+}
+
+/// Either a Client or a Server
+pub trait Peer {
+    /// Message type sent into the transport
+    type Send;
+
+    /// Message type polled from the transport
+    type Poll;
+
+    fn check_initiating_id(id: StreamId) -> Result<(), ConnectionError>;
+
+    #[doc(hidden)]
+    fn convert_send_message(
+        id: StreamId,
+        message: Self::Send,
+        body: bool) -> proto::SendMessage;
+
+    #[doc(hidden)]
+    fn convert_poll_message(message: proto::PollMessage) -> Frame<Self::Poll>;
+}

src/proto/connection.rs

@@ -1,11 +1,24 @@
-use {frame, proto, ConnectionError};
+use {frame, Frame, ConnectionError, Peer, StreamId};
+use proto::{self, ReadySink, State};
+
 use tokio_io::{AsyncRead, AsyncWrite};
 use tokio_io::codec::length_delimited;
 
+use http;
+
 use futures::*;
 
-pub struct Connection<T> {
+use ordermap::OrderMap;
+use fnv::FnvHasher;
+
+use std::marker::PhantomData;
+use std::hash::BuildHasherDefault;
+
+/// An H2 connection
+pub struct Connection<T, P> {
     inner: Inner<T>,
+    streams: StreamMap<State>,
+    peer: PhantomData<P>,
 }
 
 type Inner<T> =
@@ -15,13 +28,19 @@ type Inner<T> =
                 proto::FramedRead<
                     length_delimited::FramedRead<T>>>>>;
 
-impl<T: AsyncRead + AsyncWrite> Connection<T> {
+type StreamMap<T> = OrderMap<StreamId, T, BuildHasherDefault<FnvHasher>>;
-    pub fn new(io: T) -> Connection<T> {
+
+/// Returns a new `Connection` backed by the given `io`.
+pub fn new<T, P>(io: T) -> Connection<T, P>
+    where T: AsyncRead + AsyncWrite,
+          P: Peer,
+{
+
     // Delimit the frames
     let framed_read = length_delimited::Builder::new()
         .big_endian()
         .length_field_length(3)
-            .length_adjustment(6)
+        .length_adjustment(9)
         .num_skip(0) // Don't skip the header
         .new_read(io);
 
@@ -59,28 +78,104 @@ impl<T: AsyncRead + AsyncWrite> Connection<T> {
 
     Connection {
         inner: connection,
-        }
+        streams: StreamMap::default(),
+        peer: PhantomData,
     }
 }
 
-impl<T: AsyncRead + AsyncWrite> Stream for Connection<T> {
+impl<T, P> Connection<T, P>
-    type Item = frame::Frame;
+    where T: AsyncRead + AsyncWrite,
+          P: Peer,
+{
+    /// Completes when the connection has terminated
+    pub fn poll_shutdown(&mut self) -> Poll<(), ConnectionError> {
+        try_ready!(self.poll_complete());
+        Ok(Async::NotReady)
+    }
+}
+
+impl<T, P> Stream for Connection<T, P>
+    where T: AsyncRead + AsyncWrite,
+          P: Peer,
+{
+    type Item = Frame<P::Poll>;
     type Error = ConnectionError;
 
-    fn poll(&mut self) -> Poll<Option<frame::Frame>, ConnectionError> {
+    fn poll(&mut self) -> Poll<Option<Self::Item>, ConnectionError> {
-        self.inner.poll()
+        use frame::Frame::*;
+
+        match try_ready!(self.inner.poll()) {
+            Some(Headers(v)) => unimplemented!(),
+            Some(frame) => panic!("unexpected frame; frame={:?}", frame),
+            None => return Ok(Async::Ready(None)),
+            _ => unimplemented!(),
+        }
     }
 }
 
-impl<T: AsyncRead + AsyncWrite> Sink for Connection<T> {
+impl<T, P> Sink for Connection<T, P>
-    type SinkItem = frame::Frame;
+    where T: AsyncRead + AsyncWrite,
+          P: Peer,
+{
+    type SinkItem = Frame<P::Send>;
     type SinkError = ConnectionError;
 
-    fn start_send(&mut self, item: frame::Frame) -> StartSend<frame::Frame, ConnectionError> {
+    fn start_send(&mut self, item: Self::SinkItem)
-        self.inner.start_send(item)
+        -> StartSend<Self::SinkItem, Self::SinkError>
+    {
+        // First ensure that the upstream can process a new item
+        if !try!(self.poll_ready()).is_ready() {
+            return Ok(AsyncSink::NotReady(item));
+        }
+
+        match item {
+            Frame::Message { id, message, body } => {
+                // Ensure ID is valid
+                try!(P::check_initiating_id(id));
+
+                // TODO: Ensure available capacity for a new stream
+                // This won't be as simple as self.streams.len() as closed
+                // connections should not be factored.
+
+                // Transition the stream state, creating a new entry if needed
+                try!(self.streams.entry(id)
+                     .or_insert(State::default())
+                     .send_headers());
+
+                let message = P::convert_send_message(id, message, body);
+
+                // TODO: Handle trailers and all that jazz
+
+                // We already ensured that the upstream can handle the frame, so
+                // panic if it gets rejected.
+                let res = try!(self.inner.start_send(frame::Frame::Headers(message.frame)));
+
+                // This is a one-way conversion. By checking `poll_ready` first,
+                // it's already been determined that the inner `Sink` can accept
+                // the item. If the item is rejected, then there is a bug.
+                assert!(res.is_ready());
+
+                Ok(AsyncSink::Ready)
+            }
+            Frame::Body { id, chunk } => {
+                unimplemented!();
+            }
+            Frame::Error { id, error } => {
+                unimplemented!();
+            }
+        }
     }
 
     fn poll_complete(&mut self) -> Poll<(), ConnectionError> {
         self.inner.poll_complete()
     }
 }
+
+impl<T, P> ReadySink for Connection<T, P>
+    where T: AsyncRead + AsyncWrite,
+          P: Peer,
+{
+    fn poll_ready(&mut self) -> Poll<(), Self::SinkError> {
+        self.inner.poll_ready()
+    }
+}

src/proto/framed_read.rs

@@ -54,6 +54,13 @@ impl<T> FramedRead<T> {
 
                 // TODO: Change to drain: carllerche/bytes#130
                 let frame = try!(frame::Headers::load(head, &mut buf, &mut self.hpack));
+
+                if !frame.is_end_headers() {
+                    // Wait for continuation frames
+                    self.partial = Some(Partial::Headers(frame));
+                    return Ok(None);
+                }
+
                 frame.into()
             }
             Kind::Priority => unimplemented!(),
@@ -88,6 +95,7 @@ impl<T> Stream for FramedRead<T>
             };
 
             if let Some(frame) = try!(self.decode_frame(bytes)) {
+                debug!("poll; frame={:?}", frame);
                 return Ok(Async::Ready(Some(frame)));
             }
         }

src/proto/framed_write.rs

@@ -1,6 +1,6 @@
-use {ConnectionError, Reason};
+use {hpack, ConnectionError, Reason};
 use frame::{self, Frame, Error};
-use hpack;
+use proto::ReadySink;
 
 use futures::*;
 use tokio_io::AsyncWrite;
@@ -67,7 +67,7 @@ impl<T: AsyncWrite> FramedWrite<T> {
     }
 
     fn is_empty(&self) -> bool {
-        self.next.is_none() && self.buf.has_remaining()
+        self.next.is_none() && !self.buf.has_remaining()
     }
 
     fn frame_len(&self, data: &frame::Data) -> usize {
@@ -80,14 +80,11 @@ impl<T: AsyncWrite> Sink for FramedWrite<T> {
     type SinkError = ConnectionError;
 
     fn start_send(&mut self, item: Frame) -> StartSend<Frame, ConnectionError> {
-        if self.has_capacity() {
+        debug!("start_send; frame={:?}", item);
-            // Try flushing
-            try!(self.poll_complete());
 
-            if self.has_capacity() {
+        if !try!(self.poll_ready()).is_ready() {
             return Ok(AsyncSink::NotReady(item));
         }
-        }
 
         match item {
             Frame::Data(v) => {
@@ -117,6 +114,7 @@ impl<T: AsyncWrite> Sink for FramedWrite<T> {
             }
             Frame::Settings(v) => {
                 v.encode(self.buf.get_mut());
+                trace!("encoded settings; rem={:?}", self.buf.remaining());
             }
         }
 
@@ -124,6 +122,8 @@ impl<T: AsyncWrite> Sink for FramedWrite<T> {
     }
 
     fn poll_complete(&mut self) -> Poll<(), ConnectionError> {
+        trace!("FramedWrite::poll_complete");
+
         // TODO: implement
         match self.next {
             Some(Next::Data { .. }) => unimplemented!(),
@@ -132,9 +132,14 @@ impl<T: AsyncWrite> Sink for FramedWrite<T> {
 
         // As long as there is data to write, try to write it!
         while !self.is_empty() {
+            trace!("writing buffer; next={:?}; rem={:?}", self.next, self.buf.remaining());
             try_ready!(self.inner.write_buf(&mut self.buf));
         }
 
+        trace!("flushing buffer");
+        // Flush the upstream
+        try_nb!(self.inner.flush());
+
         // Clear internal buffer
         self.buf.set_position(0);
         self.buf.get_mut().clear();
@@ -148,6 +153,21 @@ impl<T: AsyncWrite> Sink for FramedWrite<T> {
     }
 }
 
+impl<T: AsyncWrite> ReadySink for FramedWrite<T> {
+    fn poll_ready(&mut self) -> Poll<(), Self::SinkError> {
+        if !self.has_capacity() {
+            // Try flushing
+            try!(self.poll_complete());
+
+            if !self.has_capacity() {
+                return Ok(Async::NotReady);
+            }
+        }
+
+        Ok(Async::Ready(()))
+    }
+}
+
 impl<T: Stream> Stream for FramedWrite<T> {
     type Item = T::Item;
     type Error = T::Error;

src/proto/mod.rs

@@ -2,10 +2,34 @@ mod connection;
 mod framed_read;
 mod framed_write;
 mod ping_pong;
+mod ready;
 mod settings;
+mod state;
 
-pub use self::connection::Connection;
+pub use self::connection::{Connection, new as new_connection};
 pub use self::framed_read::FramedRead;
 pub use self::framed_write::FramedWrite;
 pub use self::ping_pong::PingPong;
+pub use self::ready::ReadySink;
 pub use self::settings::Settings;
+pub use self::state::State;
+
+use frame;
+
+/// A request or response issued by the current process.
+pub struct SendMessage {
+    frame: frame::Headers,
+}
+
+/// A request or response received by the current process.
+pub struct PollMessage {
+    frame: frame::Headers,
+}
+
+impl SendMessage {
+    pub fn new(frame: frame::Headers) -> Self {
+        SendMessage {
+            frame: frame,
+        }
+    }
+}

src/proto/ping_pong.rs

@@ -1,5 +1,6 @@
 use ConnectionError;
 use frame::Frame;
+use proto::ReadySink;
 
 use futures::*;
 
@@ -45,3 +46,13 @@ impl<T> Sink for PingPong<T>
         self.inner.poll_complete()
     }
 }
+
+impl<T> ReadySink for PingPong<T>
+    where T: Stream<Item = Frame, Error = ConnectionError>,
+          T: Sink<SinkItem = Frame, SinkError = ConnectionError>,
+          T: ReadySink,
+{
+    fn poll_ready(&mut self) -> Poll<(), ConnectionError> {
+        self.inner.poll_ready()
+    }
+}

src/proto/ready.rs

@@ -0,0 +1,5 @@
+use futures::{Sink, Poll};
+
+pub trait ReadySink: Sink {
+    fn poll_ready(&mut self) -> Poll<(), Self::SinkError>;
+}

src/proto/settings.rs

@@ -1,16 +1,22 @@
 use ConnectionError;
 use frame::{self, Frame};
+use proto::ReadySink;
 
 use futures::*;
 
 pub struct Settings<T> {
+    // Upstream transport
     inner: T,
+
     // Our settings
     local: frame::SettingSet,
+
     // Peer settings
     remote: frame::SettingSet,
+
     // Number of acks remaining to send to the peer
     remaining_acks: usize,
+
     // True when the local settings must be flushed to the remote
     is_dirty: bool,
 }
@@ -30,17 +36,13 @@ impl<T> Settings<T>
             local: local,
             remote: frame::SettingSet::default(),
             remaining_acks: 0,
-            is_dirty: false,
+            is_dirty: true,
         }
     }
 
-    fn has_pending_sends(&self) -> bool {
-        self.is_dirty || self.remaining_acks > 0
-    }
-
     fn try_send_pending(&mut self) -> Poll<(), ConnectionError> {
         if self.is_dirty {
-            let frame = frame::Settings::new(self.local.clone()).into();
+            let frame = frame::Settings::new(self.local.clone());
             try_ready!(self.try_send(frame));
 
             self.is_dirty = false;
@@ -56,8 +58,8 @@ impl<T> Settings<T>
         Ok(Async::Ready(()))
     }
 
-    fn try_send(&mut self, item: frame::Frame) -> Poll<(), ConnectionError> {
+    fn try_send(&mut self, item: frame::Settings) -> Poll<(), ConnectionError> {
-        if let AsyncSink::NotReady(_) = try!(self.inner.start_send(item)) {
+        if let AsyncSink::NotReady(_) = try!(self.inner.start_send(item.into())) {
             // Ensure that call to `poll_complete` guarantee is called to satisfied
             try!(self.inner.poll_complete());
 
@@ -110,3 +112,17 @@ impl<T> Sink for Settings<T>
         self.inner.close()
     }
 }
+
+impl<T> ReadySink for Settings<T>
+    where T: Stream<Item = Frame, Error = ConnectionError>,
+          T: Sink<SinkItem = Frame, SinkError = ConnectionError>,
+          T: ReadySink,
+{
+    fn poll_ready(&mut self) -> Poll<(), ConnectionError> {
+        if try!(self.try_send_pending()).is_ready() {
+            return self.inner.poll_ready();
+        }
+
+        Ok(Async::NotReady)
+    }
+}

src/proto/state.rs

@@ -0,0 +1,72 @@
+use ConnectionError;
+
+/// Represents the state of an H2 stream
+///
+/// ```not_rust
+///                              +--------+
+///                      send PP |        | recv PP
+///                     ,--------|  idle  |--------.
+///                    /         |        |         \
+///                   v          +--------+          v
+///            +----------+          |           +----------+
+///            |          |          | send H /  |          |
+///     ,------| reserved |          | recv H    | reserved |------.
+///     |      | (local)  |          |           | (remote) |      |
+///     |      +----------+          v           +----------+      |
+///     |          |             +--------+             |          |
+///     |          |     recv ES |        | send ES     |          |
+///     |   send H |     ,-------|  open  |-------.     | recv H   |
+///     |          |    /        |        |        \    |          |
+///     |          v   v         +--------+         v   v          |
+///     |      +----------+          |           +----------+      |
+///     |      |   half   |          |           |   half   |      |
+///     |      |  closed  |          | send R /  |  closed  |      |
+///     |      | (remote) |          | recv R    | (local)  |      |
+///     |      +----------+          |           +----------+      |
+///     |           |                |                 |           |
+///     |           | send ES /      |       recv ES / |           |
+///     |           | send R /       v        send R / |           |
+///     |           | recv R     +--------+   recv R   |           |
+///     | send R /  `----------->|        |<-----------'  send R / |
+///     | recv R                 | closed |               recv R   |
+///     `----------------------->|        |<----------------------'
+///                              +--------+
+///
+///        send:   endpoint sends this frame
+///        recv:   endpoint receives this frame
+///
+///        H:  HEADERS frame (with implied CONTINUATIONs)
+///        PP: PUSH_PROMISE frame (with implied CONTINUATIONs)
+///        ES: END_STREAM flag
+///        R:  RST_STREAM frame
+/// ```
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
+pub enum State {
+    Idle,
+    ReservedLocal,
+    ReservedRemote,
+    Open,
+    HalfClosedLocal,
+    HalfClosedRemote,
+    Closed,
+}
+
+impl State {
+    /// Transition the state to represent headers being sent.
+    ///
+    /// Returns an error if this is an invalid state transition.
+    pub fn send_headers(&mut self) -> Result<(), ConnectionError> {
+        if *self != State::Idle {
+            unimplemented!();
+        }
+
+        *self = State::Open;
+        Ok(())
+    }
+}
+
+impl Default for State {
+    fn default() -> State {
+        State::Idle
+    }
+}