fix(transport): Fix lazily reconnecting (#187)

Closes #167

tonic/src/transport/service/reconnect.rs

@@ -1,5 +1,5 @@
 use crate::Error;
-use pin_project::pin_project;
+use pin_project::{pin_project, project};
 use std::fmt;
 use std::{
     future::Future,
@@ -17,6 +17,7 @@ where
     mk_service: M,
     state: State<M::Future, M::Response>,
     target: Target,
+    error: Option<M::Error>,
 }
 
 #[derive(Debug)]
@@ -41,6 +42,7 @@ where
             mk_service,
             state: State::Connected(initial_connection),
             target,
+            error: None,
         }
     }
 }
@@ -55,10 +57,9 @@ where
 {
     type Response = S::Response;
     type Error = Error;
-    type Future = ResponseFuture<S::Future>;
+    type Future = ResponseFuture<S::Future, M::Error>;
 
     fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
-        let ret;
         let mut state;
 
         loop {
@@ -90,7 +91,7 @@ where
                         Poll::Ready(Err(e)) => {
                             trace!("poll_ready; error");
                             state = State::Idle;
-                            ret = Err(e.into());
+                            self.error = Some(e.into());
                             break;
                         }
                     }
@@ -118,10 +119,14 @@ where
         }
 
         self.state = state;
-        Poll::Ready(ret)
+        Poll::Ready(Ok(()))
     }
 
     fn call(&mut self, request: Request) -> Self::Future {
+        if let Some(error) = self.error.take() {
+            return ResponseFuture::error(error);
+        }
+
         let service = match self.state {
             State::Connected(ref mut service) => service,
             _ => panic!("service not ready; poll_ready must be called first"),
@@ -148,27 +153,54 @@ where
     }
 }
 
+/// Future that resolves to the response or failure to connect.
 #[pin_project]
 #[derive(Debug)]
-pub(crate) struct ResponseFuture<F> {
+pub(crate) struct ResponseFuture<F, E> {
     #[pin]
-    inner: F,
+    inner: Inner<F, E>,
 }
 
-impl<F> ResponseFuture<F> {
+#[pin_project]
+#[derive(Debug)]
+enum Inner<F, E> {
+    Future(#[pin] F),
+    Error(Option<E>),
+}
+
+impl<F, E> ResponseFuture<F, E> {
     pub(crate) fn new(inner: F) -> Self {
-        ResponseFuture { inner }
+        ResponseFuture {
+            inner: Inner::Future(inner),
+        }
+    }
+
+    pub(crate) fn error(error: E) -> Self {
+        ResponseFuture {
+            inner: Inner::Error(Some(error)),
+        }
     }
 }
 
-impl<F, T, E> Future for ResponseFuture<F>
+impl<F, T, E, ME> Future for ResponseFuture<F, ME>
 where
     F: Future<Output = Result<T, E>>,
     E: Into<Error>,
+    ME: Into<Error>,
 {
     type Output = Result<T, Error>;
 
+    #[project]
     fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
-        self.project().inner.poll(cx).map_err(Into::into)
+        //self.project().inner.poll(cx).map_err(Into::into)
+        let me = self.project();
+        #[project]
+        match me.inner.project() {
+            Inner::Future(fut) => fut.poll(cx).map_err(Into::into),
+            Inner::Error(e) => {
+                let e = e.take().expect("Polled after ready.").into();
+                Poll::Ready(Err(e))
+            }
+        }
     }
 }