feat(network): implement chain sync server side (#277)

pallas-network/src/miniprotocols/chainsync/client.rs

@@ -6,7 +6,7 @@ use tracing::debug;
 use crate::miniprotocols::Point;
 use crate::multiplexer;
 
-use super::{BlockContent, HeaderContent, Message, State, Tip};
+use super::{BlockContent, HeaderContent, IntersectResponse, Message, State, Tip};
 
 #[derive(Error, Debug)]
 pub enum Error {
@@ -29,8 +29,6 @@ pub enum Error {
     Plexer(multiplexer::Error),
 }
 
-pub type IntersectResponse = (Option<Point>, Tip);
-
 #[derive(Debug)]
 pub enum NextResponse<CONTENT> {
     RollForward(CONTENT, Tip),

pallas-network/src/miniprotocols/chainsync/codec.rs

@@ -1,4 +1,5 @@
 use pallas_codec::minicbor;
+use pallas_codec::minicbor::encode::Error;
 use pallas_codec::minicbor::{decode, encode, Decode, Decoder, Encode, Encoder};
 
 use super::{BlockContent, HeaderContent, Message, SkippedContent, Tip};
@@ -167,10 +168,32 @@ impl<'b> Decode<'b, ()> for HeaderContent {
 impl Encode<()> for HeaderContent {
     fn encode<W: encode::Write>(
         &self,
-        _e: &mut Encoder<W>,
+        e: &mut Encoder<W>,
         _ctx: &mut (),
     ) -> Result<(), encode::Error<W::Error>> {
-        todo!()
+        e.array(2)?;
+        e.u8(self.variant)?;
+
+        // variant 0 is byron
+        if self.variant == 0 {
+            e.array(2)?;
+
+            if let Some((a, b)) = self.byron_prefix {
+                e.array(2)?;
+                e.u8(a)?;
+                e.u64(b)?;
+            } else {
+                return Err(Error::message("header variant 0 but no byron prefix"));
+            }
+
+            e.tag(minicbor::data::Tag::Cbor)?;
+            e.bytes(&self.cbor)?;
+        } else {
+            e.tag(minicbor::data::Tag::Cbor)?;
+            e.bytes(&self.cbor)?;
+        }
+
+        Ok(())
     }
 }
 
@@ -185,10 +208,13 @@ impl<'b> Decode<'b, ()> for BlockContent {
 impl Encode<()> for BlockContent {
     fn encode<W: encode::Write>(
         &self,
-        _e: &mut Encoder<W>,
+        e: &mut Encoder<W>,
         _ctx: &mut (),
     ) -> Result<(), encode::Error<W::Error>> {
-        todo!()
+        e.tag(minicbor::data::Tag::Cbor)?;
+        e.bytes(&self.0)?;
+
+        Ok(())
     }
 }
 
@@ -202,9 +228,11 @@ impl<'b> Decode<'b, ()> for SkippedContent {
 impl Encode<()> for SkippedContent {
     fn encode<W: encode::Write>(
         &self,
-        _e: &mut Encoder<W>,
+        e: &mut Encoder<W>,
         _ctx: &mut (),
     ) -> Result<(), encode::Error<W::Error>> {
-        todo!()
+        e.null()?;
+
+        Ok(())
     }
 }

pallas-network/src/miniprotocols/chainsync/mod.rs

@@ -2,8 +2,10 @@ mod buffer;
 mod client;
 mod codec;
 mod protocol;
+mod server;
 
 pub use buffer::*;
 pub use client::*;
 pub use codec::*;
 pub use protocol::*;
+pub use server::*;

pallas-network/src/miniprotocols/chainsync/protocol.rs

@@ -5,6 +5,8 @@ use crate::miniprotocols::Point;
 #[derive(Debug, Clone)]
 pub struct Tip(pub Point, pub u64);
 
+pub type IntersectResponse = (Option<Point>, Tip);
+
 #[derive(Debug, PartialEq, Eq, Clone)]
 pub enum State {
     Idle,

pallas-network/src/miniprotocols/chainsync/server.rs

@@ -0,0 +1,285 @@
+use pallas_codec::Fragment;
+use std::marker::PhantomData;
+use thiserror::Error;
+use tracing::debug;
+
+use crate::miniprotocols::Point;
+use crate::multiplexer;
+
+use super::{BlockContent, HeaderContent, Message, State, Tip};
+
+#[derive(Error, Debug)]
+pub enum Error {
+    #[error("attempted to receive message while agency is ours")]
+    AgencyIsOurs,
+
+    #[error("attempted to send message while agency is theirs")]
+    AgencyIsTheirs,
+
+    #[error("inbound message is not valid for current state")]
+    InvalidInbound,
+
+    #[error("outbound message is not valid for current state")]
+    InvalidOutbound,
+
+    #[error("error while sending or receiving data through the channel")]
+    Plexer(multiplexer::Error),
+}
+
+#[derive(Debug)]
+pub enum ClientRequest {
+    Intersect(Vec<Point>),
+    RequestNext,
+}
+
+pub struct Server<O>(State, multiplexer::ChannelBuffer, PhantomData<O>)
+where
+    Message<O>: Fragment;
+
+impl<O> Server<O>
+where
+    Message<O>: Fragment,
+{
+    /// Constructs a new ChainSync `Server` instance.
+    ///
+    /// # Arguments
+    ///
+    /// * `channel` - An instance of `multiplexer::AgentChannel` to be used for
+    ///   communication.
+    pub fn new(channel: multiplexer::AgentChannel) -> Self {
+        Self(
+            State::Idle,
+            multiplexer::ChannelBuffer::new(channel),
+            PhantomData {},
+        )
+    }
+
+    /// Returns the current state of the server.
+    pub fn state(&self) -> &State {
+        &self.0
+    }
+
+    /// Checks if the server state is done.
+    pub fn is_done(&self) -> bool {
+        self.0 == State::Done
+    }
+
+    /// Checks if the server has agency.
+    pub fn has_agency(&self) -> bool {
+        match self.state() {
+            State::Idle => false,
+            State::CanAwait => true,
+            State::MustReply => true,
+            State::Intersect => true,
+            State::Done => false,
+        }
+    }
+
+    fn assert_agency_is_ours(&self) -> Result<(), Error> {
+        if !self.has_agency() {
+            Err(Error::AgencyIsTheirs)
+        } else {
+            Ok(())
+        }
+    }
+
+    fn assert_agency_is_theirs(&self) -> Result<(), Error> {
+        if self.has_agency() {
+            Err(Error::AgencyIsOurs)
+        } else {
+            Ok(())
+        }
+    }
+
+    fn assert_outbound_state(&self, msg: &Message<O>) -> Result<(), Error> {
+        match (&self.0, msg) {
+            (State::CanAwait, Message::RollForward(_, _)) => Ok(()),
+            (State::CanAwait, Message::RollBackward(_, _)) => Ok(()),
+            (State::CanAwait, Message::AwaitReply) => Ok(()),
+            (State::MustReply, Message::RollForward(_, _)) => Ok(()),
+            (State::MustReply, Message::RollBackward(_, _)) => Ok(()),
+            (State::Intersect, Message::IntersectFound(_, _)) => Ok(()),
+            (State::Intersect, Message::IntersectNotFound(_)) => Ok(()),
+            _ => Err(Error::InvalidOutbound),
+        }
+    }
+
+    fn assert_inbound_state(&self, msg: &Message<O>) -> Result<(), Error> {
+        match (&self.0, msg) {
+            (State::Idle, Message::RequestNext) => Ok(()),
+            (State::Idle, Message::FindIntersect(_)) => Ok(()),
+            (State::Idle, Message::Done) => Ok(()),
+            _ => Err(Error::InvalidInbound),
+        }
+    }
+
+    /// Sends a message to the client
+    ///
+    /// # Arguments
+    ///
+    /// * `msg` - A reference to the `Message` to be sent.
+    ///
+    /// # Errors
+    ///
+    /// Returns an error if the agency is not ours or if the outbound state is
+    /// invalid.
+    pub async fn send_message(&mut self, msg: &Message<O>) -> Result<(), Error> {
+        self.assert_agency_is_ours()?;
+        self.assert_outbound_state(msg)?;
+
+        self.1.send_msg_chunks(msg).await.map_err(Error::Plexer)?;
+
+        Ok(())
+    }
+
+    /// Receives the next message from the client.
+    ///
+    /// # Errors
+    ///
+    /// Returns an error if the agency is not theirs or if the inbound state is
+    /// invalid.
+    async fn recv_message(&mut self) -> Result<Message<O>, Error> {
+        self.assert_agency_is_theirs()?;
+
+        let msg = self.1.recv_full_msg().await.map_err(Error::Plexer)?;
+
+        self.assert_inbound_state(&msg)?;
+
+        Ok(msg)
+    }
+
+    /// Receive a message from the client when the protocol state is Idle.
+    ///
+    /// # Errors
+    ///
+    /// Returns an error if the agency is not theirs or if the inbound message
+    /// is invalid for Idle protocol state.
+    pub async fn recv_while_idle(&mut self) -> Result<Option<ClientRequest>, Error> {
+        match self.recv_message().await? {
+            Message::FindIntersect(points) => {
+                self.0 = State::Intersect;
+                Ok(Some(ClientRequest::Intersect(points)))
+            }
+            Message::RequestNext => {
+                self.0 = State::CanAwait;
+                Ok(Some(ClientRequest::RequestNext))
+            }
+            Message::Done => {
+                self.0 = State::Done;
+
+                Ok(None)
+            }
+            _ => Err(Error::InvalidInbound),
+        }
+    }
+
+    /// Sends an IntersectNotFound message to the client.
+    ///
+    /// # Arguments
+    ///
+    /// * `tip` - the most recent point of the server's chain.
+    ///
+    /// # Errors
+    ///
+    /// Returns an error if the message cannot be sent or if it's not valid for
+    /// the current state of the server.
+    pub async fn send_intersect_not_found(&mut self, tip: Tip) -> Result<(), Error> {
+        debug!("send intersect not found");
+
+        let msg = Message::IntersectNotFound(tip);
+        self.send_message(&msg).await?;
+        self.0 = State::Idle;
+
+        Ok(())
+    }
+
+    /// Sends an IntersectFound message to the client.
+    ///
+    /// # Arguments
+    ///
+    /// * `point` - the first point in the client's provided list of intersect
+    ///   points that was found in the servers's current chain.
+    /// * `tip` - the most recent point of the server's chain.
+    ///
+    /// # Errors
+    ///
+    /// Returns an error if the message cannot be sent or if it's not valid for
+    /// the current state of the server.
+    pub async fn send_intersect_found(&mut self, point: Point, tip: Tip) -> Result<(), Error> {
+        debug!("send intersect found ({point:?}");
+
+        let msg = Message::IntersectFound(point, tip);
+        self.send_message(&msg).await?;
+        self.0 = State::Idle;
+
+        Ok(())
+    }
+
+    /// Sends a RollForward message to the client.
+    ///
+    /// # Arguments
+    ///
+    /// * `content` - the data to send to the client: for example block headers
+    ///   for N2N or full blocks for N2C.
+    /// * `tip` - the most recent point of the server's chain.
+    ///
+    /// # Errors
+    ///
+    /// Returns an error if the message cannot be sent or if it's not valid for
+    /// the current state of the server.
+    pub async fn send_roll_forward(&mut self, content: O, tip: Tip) -> Result<(), Error> {
+        debug!("send roll forward");
+
+        let msg = Message::RollForward(content, tip);
+        self.send_message(&msg).await?;
+        self.0 = State::Idle;
+
+        Ok(())
+    }
+
+    /// Sends a RollBackward message to the client.
+    ///
+    /// # Arguments
+    ///
+    /// * `point` - point at which the client should rollback their chain to.
+    /// * `tip` - the most recent point of the server's chain.
+    ///
+    /// # Errors
+    ///
+    /// Returns an error if the message cannot be sent or if it's not valid for
+    /// the current state of the server.
+    pub async fn send_roll_backward(&mut self, point: Point, tip: Tip) -> Result<(), Error> {
+        debug!("send roll backward {point:?}");
+
+        let msg = Message::RollBackward(point, tip);
+        self.send_message(&msg).await?;
+        self.0 = State::Idle;
+
+        Ok(())
+    }
+
+    /// Sends an AwaitReply message to the client.
+    ///
+    /// # Arguments
+    ///
+    /// * `point` - point at which the client should rollback their chain to.
+    /// * `tip` - the most recent point of the server's chain.
+    ///
+    /// # Errors
+    ///
+    /// Returns an error if the message cannot be sent or if it's not valid for
+    /// the current state of the server.
+    pub async fn send_await_reply(&mut self) -> Result<(), Error> {
+        debug!("send await reply");
+
+        let msg = Message::AwaitReply;
+        self.send_message(&msg).await?;
+        self.0 = State::MustReply;
+
+        Ok(())
+    }
+}
+
+pub type N2NServer = Server<HeaderContent>;
+
+pub type N2CServer = Server<BlockContent>;