Restore request-response code to the coordinator

coordinator/src/main.rs

@@ -1,4 +1,5 @@
 mod tributary;
+mod p2p;
 
 fn main() {
   todo!("TODO")

coordinator/src/p2p/reqres.rs

@@ -0,0 +1,126 @@
+use core::time::Duration;
+use std::io::{self, Read};
+
+use async_trait::async_trait;
+
+use borsh::{BorshSerialize, BorshDeserialize};
+use serai_client::validator_sets::primitives::ValidatorSet;
+
+use futures_util::{AsyncRead, AsyncReadExt, AsyncWrite, AsyncWriteExt};
+
+use libp2p::request_response::{Codec as CodecTrait, Config, Behaviour, ProtocolSupport};
+
+use serai_cosign::SignedCosign;
+
+/// The maximum message size for the request-response protocol
+// This is derived from the heartbeat message size as it's our largest message
+const MAX_LIBP2P_REQRES_MESSAGE_SIZE: usize =
+  (tributary::BLOCK_SIZE_LIMIT * crate::p2p::heartbeat::BLOCKS_PER_BATCH) + 1024;
+
+const PROTOCOL: &str = "/serai/coordinator";
+
+/// Requests which can be made via the request-response protocol.
+#[derive(Clone, Copy, Debug, BorshSerialize, BorshDeserialize)]
+pub(crate) enum Request {
+  /// A keep-alive to prevent our connections from being dropped.
+  KeepAlive,
+  /// A heartbeat informing our peers of our latest block, for the specified blockchain, on regular
+  /// intervals.
+  ///
+  /// If our peers have more blocks than us, they're expected to respond with those blocks.
+  Heartbeat { set: ValidatorSet, latest_block_hash: [u8; 32] },
+  /// A request for the notable cosigns for a global session.
+  NotableCosigns { global_session: [u8; 32] },
+}
+
+/// A tributary block and its commit.
+#[derive(Clone, BorshSerialize, BorshDeserialize)]
+pub(crate) struct TributaryBlockWithCommit {
+  pub(crate) block: Vec<u8>,
+  pub(crate) commit: Vec<u8>,
+}
+
+/// Responses which can be received via the request-response protocol.
+#[derive(Clone, BorshSerialize, BorshDeserialize)]
+pub(crate) enum Response {
+  Blocks(Vec<TributaryBlockWithCommit>),
+  NotableCosigns(Vec<SignedCosign>),
+}
+
+/// The codec used for the request-response protocol.
+///
+/// We don't use CBOR or JSON, but use borsh to create `Vec<u8>`s we then length-prefix. While
+/// ideally, we'd use borsh directly with the `io` traits defined here, they're async and there
+/// isn't an amenable API within borsh for incremental deserialization.
+#[derive(Default, Clone, Copy, Debug)]
+struct Codec;
+impl Codec {
+  async fn read<M: BorshDeserialize>(io: &mut (impl Unpin + AsyncRead)) -> io::Result<M> {
+    let mut len = [0; 4];
+    io.read_exact(&mut len).await?;
+    let len = usize::try_from(u32::from_le_bytes(len)).expect("not at least a 32-bit platform?");
+    if len > MAX_LIBP2P_REQRES_MESSAGE_SIZE {
+      Err(io::Error::other("request length exceeded MAX_LIBP2P_REQRES_MESSAGE_SIZE"))?;
+    }
+    // This may be a non-trivial allocation easily causable
+    // While we could chunk the read, meaning we only perform the allocation as bandwidth is used,
+    // the max message size should be sufficiently sane
+    let mut buf = vec![0; len];
+    io.read_exact(&mut buf).await?;
+    let mut buf = buf.as_slice();
+    let res = M::deserialize(&mut buf)?;
+    if !buf.is_empty() {
+      Err(io::Error::other("p2p message had extra data appended to it"))?;
+    }
+    Ok(res)
+  }
+  async fn write(io: &mut (impl Unpin + AsyncWrite), msg: &impl BorshSerialize) -> io::Result<()> {
+    let msg = borsh::to_vec(msg).unwrap();
+    io.write_all(&u32::try_from(msg.len()).unwrap().to_le_bytes()).await?;
+    io.write_all(&msg).await
+  }
+}
+#[async_trait]
+impl CodecTrait for Codec {
+  type Protocol = &'static str;
+  type Request = Request;
+  type Response = Response;
+
+  async fn read_request<R: Send + Unpin + AsyncRead>(
+    &mut self,
+    _: &Self::Protocol,
+    io: &mut R,
+  ) -> io::Result<Request> {
+    Self::read(io).await
+  }
+  async fn read_response<R: Send + Unpin + AsyncRead>(
+    &mut self,
+    proto: &Self::Protocol,
+    io: &mut R,
+  ) -> io::Result<Response> {
+    Self::read(io).await
+  }
+  async fn write_request<W: Send + Unpin + AsyncWrite>(
+    &mut self,
+    _: &Self::Protocol,
+    io: &mut W,
+    req: Request,
+  ) -> io::Result<()> {
+    Self::write(io, &req).await
+  }
+  async fn write_response<W: Send + Unpin + AsyncWrite>(
+    &mut self,
+    proto: &Self::Protocol,
+    io: &mut W,
+    res: Response,
+  ) -> io::Result<()> {
+    Self::write(io, &res).await
+  }
+}
+
+pub(crate) type Behavior = Behaviour<Codec>;
+pub(crate) fn new_behavior() -> Behavior {
+  let mut config = Config::default();
+  config.set_request_timeout(Duration::from_secs(5));
+  Behavior::new([(PROTOCOL, ProtocolSupport::Full)], config)
+}

coordinator/src/tributary/transaction.rs

@@ -43,12 +43,14 @@ impl SigningProtocolRound {
   }
 }
 
-/// `tributary::Signed` without the nonce.
+/// `tributary::Signed` but without the nonce.
 ///
 /// All of our nonces are deterministic to the type of transaction and fields within.
 #[derive(Clone, Copy, PartialEq, Eq, Debug)]
 pub struct Signed {
+  /// The signer.
   pub signer: <Ristretto as Ciphersuite>::G,
+  /// The signature.
   pub signature: SchnorrSignature<Ristretto>,
 }