Remove tokio dependency from serai-coordinator-p2p

Re-implements tokio::mpsc::oneshot with a thin wrapper around async-channel.

Also replaces futures-util with futures-lite.

coordinator/p2p/src/heartbeat.rs

@@ -3,7 +3,7 @@ use std::time::{Duration, SystemTime};
 
 use serai_client::validator_sets::primitives::ValidatorSet;
 
-use futures_util::FutureExt;
+use futures_lite::FutureExt;
 
 use tributary::{ReadWrite, TransactionTrait, Block, Tributary, TributaryReader};
 

coordinator/p2p/src/lib.rs

@@ -8,10 +8,11 @@ use borsh::{BorshSerialize, BorshDeserialize};
 
 use serai_client::{primitives::NetworkId, validator_sets::primitives::ValidatorSet};
 
-use tokio::sync::oneshot;
-
 use serai_cosign::SignedCosign;
 
+/// A oneshot channel.
+pub mod oneshot;
+
 /// The heartbeat task, effecting sync of Tributaries
 pub mod heartbeat;
 

coordinator/p2p/src/oneshot.rs

@@ -0,0 +1,35 @@
+use core::{
+  pin::Pin,
+  task::{Poll, Context},
+  future::Future,
+};
+
+pub use async_channel::{SendError, RecvError};
+
+/// The sender for a oneshot channel.
+pub struct Sender<T: Send>(async_channel::Sender<T>);
+impl<T: Send> Sender<T> {
+  /// Send a value down the channel.
+  ///
+  /// Returns an error if the channel's receiver was dropped.
+  pub fn send(self, msg: T) -> Result<(), SendError<T>> {
+    self.0.send_blocking(msg)
+  }
+}
+
+/// The receiver for a oneshot channel.
+pub struct Receiver<T: Send>(async_channel::Receiver<T>);
+impl<T: Send> Future for Receiver<T> {
+  type Output = Result<T, RecvError>;
+  fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+    let recv = self.0.recv();
+    futures_lite::pin!(recv);
+    recv.poll(cx)
+  }
+}
+
+/// Create a new oneshot channel.
+pub fn channel<T: Send>() -> (Sender<T>, Receiver<T>) {
+  let (send, recv) = async_channel::bounded(1);
+  (Sender(send), Receiver(recv))
+}