From 65877cb4b173e9ded7cc905030a49436e4f6c9c7 Mon Sep 17 00:00:00 2001
From: Henry de Valence <hdevalence@hdevalence.ca>
Date: Fri, 18 Sep 2020 14:11:29 -0700
Subject: [PATCH] zebrad: make Inbound propagate backpressure

---
 zebrad/src/components/inbound.rs | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/zebrad/src/components/inbound.rs b/zebrad/src/components/inbound.rs
index 40503a50..a811b4d8 100644
--- a/zebrad/src/components/inbound.rs
+++ b/zebrad/src/components/inbound.rs
@@ -50,10 +50,11 @@ impl Service<zn::Request> for Inbound {
     type Future =
         Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>> + Send + 'static>>;
 
-    #[instrument(skip(self, _cx))]
-    fn poll_ready(&mut self, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+    #[instrument(skip(self, cx))]
+    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
         use oneshot::error::TryRecvError;
         match self.network_setup.take() {
+            // If we're waiting for setup, check if we became ready
             Some(mut rx) => match rx.try_recv() {
                 Ok((outbound, address_book)) => {
                     self.outbound = Some(outbound);
@@ -73,7 +74,17 @@ impl Service<zn::Request> for Inbound {
                     Poll::Pending
                 }
             },
-            None => Poll::Ready(Ok(())),
+            // Otherwise, check readiness of services we might call to propagate backpressure.
+            None => {
+                match (
+                    self.state.poll_ready(cx),
+                    self.outbound.as_mut().unwrap().poll_ready(cx),
+                ) {
+                    (Poll::Ready(Err(e)), _) | (_, Poll::Ready(Err(e))) => Poll::Ready(Err(e)),
+                    (Poll::Pending, _) | (_, Poll::Pending) => Poll::Pending,
+                    (Poll::Ready(Ok(())), Poll::Ready(Ok(()))) => Poll::Ready(Ok(())),
+                }
+            }
         }
     }