fix(client): retry when checking out a closed connection

nox · nox · commit 814179340f7e · 2021-06-24T16:54:08.000+02:00
When http2_only is true, we never try to open a new connection if there
is one open already, which means that if the existing connection that
gets checked out of the pool is closed, then the request won't happen.
diff --git a/src/client/client.rs b/src/client/client.rs
@@ -11,7 +11,9 @@ use http::{Method, Request, Response, Uri, Version};
 
 use super::conn;
 use super::connect::{self, sealed::Connect, Alpn, Connected, Connection};
-use super::pool::{self, Key as PoolKey, Pool, Poolable, Pooled, Reservation};
+use super::pool::{
+    self, CheckoutIsClosedError, Key as PoolKey, Pool, Poolable, Pooled, Reservation,
+};
 #[cfg(feature = "tcp")]
 use super::HttpConnector;
 use crate::body::{Body, HttpBody};
@@ -223,7 +225,17 @@ where
         mut req: Request<B>,
         pool_key: PoolKey,
     ) -> Result<Response<Body>, ClientError<B>> {
-        let mut pooled = self.connection_for(pool_key).await?;
+        let mut pooled = match self.connection_for(pool_key).await {
+            Ok(pooled) => pooled,
+            Err(ClientConnectError::Normal(err)) => return Err(ClientError::Normal(err)),
+            Err(ClientConnectError::H2CheckoutIsClosed(reason)) => {
+                return Err(ClientError::Canceled {
+                    connection_reused: true,
+                    req,
+                    reason,
+                })
+            }
+        };
 
         if pooled.is_http1() {
             if req.version() == Version::HTTP_2 {
@@ -321,7 +333,7 @@ where
     async fn connection_for(
         &self,
         pool_key: PoolKey,
-    ) -> Result<Pooled<PoolClient<B>>, ClientError<B>> {
+    ) -> Result<Pooled<PoolClient<B>>, ClientConnectError> {
         // This actually races 2 different futures to try to get a ready
         // connection the fastest, and to reduce connection churn.
         //
@@ -337,6 +349,7 @@ where
         //   and then be inserted into the pool as an idle connection.
         let checkout = self.pool.checkout(pool_key.clone());
         let connect = self.connect_to(pool_key);
+        let is_ver_h2 = self.config.ver == Ver::Http2;
 
         // The order of the `select` is depended on below...
 
@@ -380,16 +393,25 @@ where
             // In both cases, we should just wait for the other future.
             Either::Left((Err(err), connecting)) => {
                 if err.is_canceled() {
-                    connecting.await.map_err(ClientError::Normal)
+                    connecting.await.map_err(ClientConnectError::Normal)
                 } else {
-                    Err(ClientError::Normal(err))
+                    Err(ClientConnectError::Normal(err))
                 }
             }
             Either::Right((Err(err), checkout)) => {
                 if err.is_canceled() {
-                    checkout.await.map_err(ClientError::Normal)
+                    checkout.await.map_err(move |err| {
+                        if is_ver_h2
+                            && err.is_canceled()
+                            && err.find_source::<CheckoutIsClosedError>().is_some()
+                        {
+                            ClientConnectError::H2CheckoutIsClosed(err)
+                        } else {
+                            ClientConnectError::Normal(err)
+                        }
+                    })
                 } else {
-                    Err(ClientError::Normal(err))
+                    Err(ClientConnectError::Normal(err))
                 }
             }
         }
@@ -722,6 +744,11 @@ impl<B> ClientError<B> {
     }
 }
 
+enum ClientConnectError {
+    Normal(crate::Error),
+    H2CheckoutIsClosed(crate::Error),
+}
+
 /// A marker to identify what version a pooled connection is.
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
 pub(super) enum Ver {
diff --git a/src/client/pool.rs b/src/client/pool.rs
@@ -1,4 +1,5 @@
 use std::collections::{HashMap, HashSet, VecDeque};
+use std::error::Error as StdError;
 use std::fmt;
 use std::ops::{Deref, DerefMut};
 use std::sync::{Arc, Mutex, Weak};
@@ -560,28 +561,40 @@ pub(super) struct Checkout<T> {
     waiter: Option<oneshot::Receiver<T>>,
 }
 
+#[derive(Debug)]
+pub(super) struct CheckoutIsClosedError;
+
+impl StdError for CheckoutIsClosedError {}
+
+impl fmt::Display for CheckoutIsClosedError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str("checked out connection was closed")
+    }
+}
+
 impl<T: Poolable> Checkout<T> {
     fn poll_waiter(
         &mut self,
         cx: &mut task::Context<'_>,
     ) -> Poll<Option<crate::Result<Pooled<T>>>> {
-        static CANCELED: &str = "pool checkout failed";
         if let Some(mut rx) = self.waiter.take() {
             match Pin::new(&mut rx).poll(cx) {
                 Poll::Ready(Ok(value)) => {
                     if value.is_open() {
                         Poll::Ready(Some(Ok(self.pool.reuse(&self.key, value))))
                     } else {
-                        Poll::Ready(Some(Err(crate::Error::new_canceled().with(CANCELED))))
+                        Poll::Ready(Some(Err(
+                            crate::Error::new_canceled().with(CheckoutIsClosedError)
+                        )))
                     }
                 }
                 Poll::Pending => {
                     self.waiter = Some(rx);
                     Poll::Pending
                 }
-                Poll::Ready(Err(_canceled)) => {
-                    Poll::Ready(Some(Err(crate::Error::new_canceled().with(CANCELED))))
-                }
+                Poll::Ready(Err(_canceled)) => Poll::Ready(Some(Err(
+                    crate::Error::new_canceled().with("request has been canceled")
+                ))),
             }
         } else {
             Poll::Ready(None)
diff --git a/src/error.rs b/src/error.rs
@@ -214,7 +214,7 @@ impl Error {
         &self.inner.kind
     }
 
-    fn find_source<E: StdError + 'static>(&self) -> Option<&E> {
+    pub(crate) fn find_source<E: StdError + 'static>(&self) -> Option<&E> {
         let mut cause = self.source();
         while let Some(err) = cause {
             if let Some(ref typed) = err.downcast_ref() {

Original file line number	Diff line number	Diff line change
`@@ -214,7 +214,7 @@ impl Error {`
`214`	`214`	`&self.inner.kind`
`215`	`215`	`}`
`216`	`216`
`217`		`- fn find_source<E: StdError + 'static>(&self) -> Option<&E> {`
	`217`	`+ pub(crate) fn find_source<E: StdError + 'static>(&self) -> Option<&E> {`
`218`	`218`	`let mut cause = self.source();`
`219`	`219`	`while let Some(err) = cause {`
`220`	`220`	`if let Some(ref typed) = err.downcast_ref() {`