From 3ed8e43aeda2d9a2436165bb661a5d6626b63b6c Mon Sep 17 00:00:00 2001
From: Matthias Seitz <matthias.seitz@outlook.de>
Date: Tue, 31 Oct 2023 18:14:10 +0100
Subject: [PATCH] feat: add NoopPayloadBuilderService (#5205)

Co-authored-by: joshieDo <93316087+joshieDo@users.noreply.github.com>
---
 crates/payload/builder/src/lib.rs     |  2 ++
 crates/payload/builder/src/noop.rs    | 49 +++++++++++++++++++++++++++
 crates/payload/builder/src/service.rs | 21 ++++++++----
 3 files changed, 66 insertions(+), 6 deletions(-)
 create mode 100644 crates/payload/builder/src/noop.rs

diff --git a/crates/payload/builder/src/lib.rs b/crates/payload/builder/src/lib.rs
index a743553b9..0d5bdec9d 100644
--- a/crates/payload/builder/src/lib.rs
+++ b/crates/payload/builder/src/lib.rs
@@ -108,6 +108,8 @@ mod payload;
 mod service;
 mod traits;
 
+pub mod noop;
+
 #[cfg(any(test, feature = "test-utils"))]
 pub mod test_utils;
 
diff --git a/crates/payload/builder/src/noop.rs b/crates/payload/builder/src/noop.rs
new file mode 100644
index 000000000..805244f2f
--- /dev/null
+++ b/crates/payload/builder/src/noop.rs
@@ -0,0 +1,49 @@
+//! A payload builder service task that does nothing.
+
+use crate::{service::PayloadServiceCommand, PayloadBuilderHandle};
+use futures_util::{ready, StreamExt};
+use std::{
+    future::Future,
+    pin::Pin,
+    task::{Context, Poll},
+};
+use tokio::sync::mpsc;
+use tokio_stream::wrappers::UnboundedReceiverStream;
+
+/// A service task that does not build any payloads.
+#[derive(Debug)]
+pub struct NoopPayloadBuilderService {
+    /// Receiver half of the command channel.
+    command_rx: UnboundedReceiverStream<PayloadServiceCommand>,
+}
+
+impl NoopPayloadBuilderService {
+    /// Creates a new [NoopPayloadBuilderService].
+    pub fn new() -> (Self, PayloadBuilderHandle) {
+        let (service_tx, command_rx) = mpsc::unbounded_channel();
+        let handle = PayloadBuilderHandle::new(service_tx);
+        (Self { command_rx: UnboundedReceiverStream::new(command_rx) }, handle)
+    }
+}
+
+impl Future for NoopPayloadBuilderService {
+    type Output = ();
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let this = self.get_mut();
+        loop {
+            let Some(cmd) = ready!(this.command_rx.poll_next_unpin(cx)) else {
+                return Poll::Ready(())
+            };
+            match cmd {
+                PayloadServiceCommand::BuildNewPayload(attr, tx) => {
+                    let id = attr.payload_id();
+                    tx.send(Ok(id)).ok()
+                }
+                PayloadServiceCommand::BestPayload(_, tx) => tx.send(None).ok(),
+                PayloadServiceCommand::PayloadAttributes(_, tx) => tx.send(None).ok(),
+                PayloadServiceCommand::Resolve(_, tx) => tx.send(None).ok(),
+            };
+        }
+    }
+}
diff --git a/crates/payload/builder/src/service.rs b/crates/payload/builder/src/service.rs
index 9d4a2b8ef..0750fc009 100644
--- a/crates/payload/builder/src/service.rs
+++ b/crates/payload/builder/src/service.rs
@@ -75,10 +75,13 @@ pub struct PayloadBuilderHandle {
     /// Sender half of the message channel to the [PayloadBuilderService].
     to_service: mpsc::UnboundedSender<PayloadServiceCommand>,
 }
-
 // === impl PayloadBuilderHandle ===
 
 impl PayloadBuilderHandle {
+    pub(crate) fn new(to_service: mpsc::UnboundedSender<PayloadServiceCommand>) -> Self {
+        Self { to_service }
+    }
+
     /// Resolves the payload job and returns the best payload that has been built so far.
     ///
     /// Note: depending on the installed [PayloadJobGenerator], this may or may not terminate the
@@ -162,7 +165,7 @@ where
     /// All active payload jobs.
     payload_jobs: Vec<(Gen::Job, PayloadId)>,
     /// Copy of the sender half, so new [`PayloadBuilderHandle`] can be created on demand.
-    _service_tx: mpsc::UnboundedSender<PayloadServiceCommand>,
+    service_tx: mpsc::UnboundedSender<PayloadServiceCommand>,
     /// Receiver half of the command channel.
     command_rx: UnboundedReceiverStream<PayloadServiceCommand>,
     /// Metrics for the payload builder service
@@ -175,20 +178,26 @@ impl<Gen> PayloadBuilderService<Gen>
 where
     Gen: PayloadJobGenerator,
 {
-    /// Creates a new payload builder service.
+    /// Creates a new payload builder service and returns the [PayloadBuilderHandle] to interact
+    /// with it.
     pub fn new(generator: Gen) -> (Self, PayloadBuilderHandle) {
         let (service_tx, command_rx) = mpsc::unbounded_channel();
         let service = Self {
             generator,
             payload_jobs: Vec::new(),
-            _service_tx: service_tx.clone(),
+            service_tx,
             command_rx: UnboundedReceiverStream::new(command_rx),
             metrics: Default::default(),
         };
-        let handle = PayloadBuilderHandle { to_service: service_tx };
+        let handle = service.handle();
         (service, handle)
     }
 
+    /// Returns a handle to the service.
+    pub fn handle(&self) -> PayloadBuilderHandle {
+        PayloadBuilderHandle::new(self.service_tx.clone())
+    }
+
     /// Returns true if the given payload is currently being built.
     fn contains_payload(&self, id: PayloadId) -> bool {
         self.payload_jobs.iter().any(|(_, job_id)| *job_id == id)
@@ -319,7 +328,7 @@ type PayloadFuture =
     Pin<Box<dyn Future<Output = Result<Arc<BuiltPayload>, PayloadBuilderError>> + Send + Sync>>;
 
 /// Message type for the [PayloadBuilderService].
-enum PayloadServiceCommand {
+pub(crate) enum PayloadServiceCommand {
     /// Start building a new payload.
     BuildNewPayload(
         PayloadBuilderAttributes,