From f59a82e4c627cd0fa93b40321f29b7f98799ae92 Mon Sep 17 00:00:00 2001
From: Shane K Moore <41407272+shane-moore@users.noreply.github.com>
Date: Thu, 19 Jun 2025 11:46:34 -0700
Subject: [PATCH] chore: add node synced helper (#16928)

---
 crates/rpc/rpc/src/eth/helpers/mod.rs         |   3 +
 .../rpc/rpc/src/eth/helpers/sync_listener.rs  | 133 ++++++++++++++++++
 crates/rpc/rpc/src/eth/mod.rs                 |   2 +-
 crates/rpc/rpc/src/lib.rs                     |   2 +-
 4 files changed, 138 insertions(+), 2 deletions(-)
 create mode 100644 crates/rpc/rpc/src/eth/helpers/sync_listener.rs

diff --git a/crates/rpc/rpc/src/eth/helpers/mod.rs b/crates/rpc/rpc/src/eth/helpers/mod.rs
index 03e0443a15..15fcf612d9 100644
--- a/crates/rpc/rpc/src/eth/helpers/mod.rs
+++ b/crates/rpc/rpc/src/eth/helpers/mod.rs
@@ -2,6 +2,7 @@
 //! files.
 
 pub mod signer;
+pub mod sync_listener;
 pub mod types;
 
 mod block;
@@ -13,3 +14,5 @@ mod spec;
 mod state;
 mod trace;
 mod transaction;
+
+pub use sync_listener::SyncListener;
diff --git a/crates/rpc/rpc/src/eth/helpers/sync_listener.rs b/crates/rpc/rpc/src/eth/helpers/sync_listener.rs
new file mode 100644
index 0000000000..13c8de19b0
--- /dev/null
+++ b/crates/rpc/rpc/src/eth/helpers/sync_listener.rs
@@ -0,0 +1,133 @@
+//! A utility Future to asynchronously wait until a node has finished syncing.
+
+use futures::Stream;
+use pin_project::pin_project;
+use reth_network_api::NetworkInfo;
+use std::{
+    future::Future,
+    pin::Pin,
+    task::{ready, Context, Poll},
+};
+
+/// This future resolves once the node is no longer syncing: [`NetworkInfo::is_syncing`].
+#[must_use = "futures do nothing unless polled"]
+#[pin_project]
+#[derive(Debug)]
+pub struct SyncListener<N, St> {
+    #[pin]
+    tick: St,
+    network_info: N,
+}
+
+impl<N, St> SyncListener<N, St> {
+    /// Create a new [`SyncListener`] using the given tick stream.
+    pub const fn new(network_info: N, tick: St) -> Self {
+        Self { tick, network_info }
+    }
+}
+
+impl<N, St, Out> Future for SyncListener<N, St>
+where
+    N: NetworkInfo,
+    St: Stream<Item = Out> + Unpin,
+{
+    type Output = ();
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let mut this = self.project();
+
+        if !this.network_info.is_syncing() {
+            return Poll::Ready(());
+        }
+
+        loop {
+            let tick_event = ready!(this.tick.as_mut().poll_next(cx));
+
+            match tick_event {
+                Some(_) => {
+                    if !this.network_info.is_syncing() {
+                        return Poll::Ready(());
+                    }
+                }
+                None => return Poll::Ready(()),
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use alloy_rpc_types_admin::EthProtocolInfo;
+    use futures::stream;
+    use reth_network_api::{NetworkError, NetworkStatus};
+    use std::{
+        net::{IpAddr, SocketAddr},
+        sync::{
+            atomic::{AtomicBool, Ordering},
+            Arc,
+        },
+    };
+
+    #[derive(Clone)]
+    struct TestNetwork {
+        syncing: Arc<AtomicBool>,
+    }
+
+    impl NetworkInfo for TestNetwork {
+        fn local_addr(&self) -> SocketAddr {
+            (IpAddr::from([0, 0, 0, 0]), 0).into()
+        }
+
+        async fn network_status(&self) -> Result<NetworkStatus, NetworkError> {
+            #[allow(deprecated)]
+            Ok(NetworkStatus {
+                client_version: "test".to_string(),
+                protocol_version: 5,
+                eth_protocol_info: EthProtocolInfo {
+                    network: 1,
+                    difficulty: None,
+                    genesis: Default::default(),
+                    config: Default::default(),
+                    head: Default::default(),
+                },
+            })
+        }
+
+        fn chain_id(&self) -> u64 {
+            1
+        }
+
+        fn is_syncing(&self) -> bool {
+            self.syncing.load(Ordering::SeqCst)
+        }
+
+        fn is_initially_syncing(&self) -> bool {
+            self.is_syncing()
+        }
+    }
+
+    #[tokio::test]
+    async fn completes_immediately_if_not_syncing() {
+        let network = TestNetwork { syncing: Arc::new(AtomicBool::new(false)) };
+        let fut = SyncListener::new(network, stream::pending::<()>());
+        fut.await;
+    }
+
+    #[tokio::test]
+    async fn resolves_when_syncing_stops() {
+        use tokio::sync::mpsc::unbounded_channel;
+        use tokio_stream::wrappers::UnboundedReceiverStream;
+
+        let syncing = Arc::new(AtomicBool::new(true));
+        let network = TestNetwork { syncing: syncing.clone() };
+        let (tx, rx) = unbounded_channel();
+        let listener = SyncListener::new(network, UnboundedReceiverStream::new(rx));
+        let handle = tokio::spawn(listener);
+
+        syncing.store(false, Ordering::Relaxed);
+        let _ = tx.send(());
+
+        handle.await.unwrap();
+    }
+}
diff --git a/crates/rpc/rpc/src/eth/mod.rs b/crates/rpc/rpc/src/eth/mod.rs
index b4dca3b9f2..af8619de86 100644
--- a/crates/rpc/rpc/src/eth/mod.rs
+++ b/crates/rpc/rpc/src/eth/mod.rs
@@ -15,6 +15,6 @@ pub use core::{EthApi, EthApiFor};
 pub use filter::EthFilter;
 pub use pubsub::EthPubSub;
 
-pub use helpers::signer::DevSigner;
+pub use helpers::{signer::DevSigner, sync_listener::SyncListener};
 
 pub use reth_rpc_eth_api::{EthApiServer, EthApiTypes, FullEthApiServer, RpcNodeCore};
diff --git a/crates/rpc/rpc/src/lib.rs b/crates/rpc/rpc/src/lib.rs
index bac57b6303..690fb33e87 100644
--- a/crates/rpc/rpc/src/lib.rs
+++ b/crates/rpc/rpc/src/lib.rs
@@ -49,7 +49,7 @@ mod web3;
 pub use admin::AdminApi;
 pub use debug::DebugApi;
 pub use engine::{EngineApi, EngineEthApi};
-pub use eth::{EthApi, EthApiBuilder, EthBundle, EthFilter, EthPubSub};
+pub use eth::{helpers::SyncListener, EthApi, EthApiBuilder, EthBundle, EthFilter, EthPubSub};
 pub use miner::MinerApi;
 pub use net::NetApi;
 pub use otterscan::OtterscanApi;