Drop sender to prevent async client read deadlock.

Fixes #1729.

Co-authored-by: Wesley Norris <repnop@outlook.com>

core/lib/src/local/asynchronous/response.rs

@@ -167,8 +167,8 @@ impl LocalResponse<'_> {
         });
 
         loop {
-            let mut buf = Vec::with_capacity(1024);
             // TODO: Try to fill as much as the buffer before send it off?
+            let mut buf = Vec::with_capacity(1024);
             match self.read_buf(&mut buf).await {
                 Ok(n) if n == 0 => break,
                 Ok(_) => tx.send(Ok(buf)).await.ok()?,
@@ -179,6 +179,9 @@ impl LocalResponse<'_> {
             }
         }
 
+        // NOTE: We _must_ drop tx now to prevent a deadlock!
+        drop(tx);
+
         reader.await.ok()
     }
 

core/lib/tests/local-client-json.rs

@@ -0,0 +1,24 @@
+#![cfg(feature = "json")]
+
+#[macro_use] extern crate rocket;
+
+use rocket::serde::json::Json;
+
+#[get("/int")] fn int() -> Json<i32> { Json(5) }
+#[get("/nil")] fn nil() -> Json<()> { Json(()) }
+
+#[async_test]
+async fn async_json_works() {
+    use rocket::local::asynchronous::Client;
+
+    let client = Client::debug_with(routes![int, nil]).await.unwrap();
+
+    let int0 = client.get("/int").dispatch().await.into_json::<u32>().await;
+    let int1 = client.get("/int").dispatch().await.into_json::<i32>().await;
+
+    assert_eq!(int0, Some(5));
+    assert_eq!(int1, Some(5));
+
+    let nil0 = client.get("/nil").dispatch().await.into_json::<()>().await;
+    assert_eq!(nil0, Some(()));
+}