Handle implicit resets at the right time

A stream whose ref count reaches zero while open should
not immediately decrease the number of active streams,
otherwise MAX_CONCURRENT_STREAMS isn't respected anymore.

Author: nox

src/proto/streams/prioritize.rs

@@ -839,6 +839,7 @@ impl Prioritize {
                         }),
                         None => {
                             if let Some(reason) = stream.state.get_scheduled_reset() {
+                                stream.state.did_schedule_reset();
                                 stream.set_reset(reason, Initiator::Library);
 
                                 let frame = frame::Reset::new(stream.id, reason);

src/proto/streams/state.rs

@@ -58,9 +58,20 @@ enum Inner {
     // TODO: these states shouldn't count against concurrency limits:
     ReservedLocal,
     ReservedRemote,
-    Open { local: Peer, remote: Peer },
+    Open {
+        local: Peer,
+        remote: Peer,
+    },
     HalfClosedLocal(Peer), // TODO: explicitly name this value
     HalfClosedRemote(Peer),
+    /// This indicates to the connection that a reset frame must be sent out
+    /// once the send queue has been flushed.
+    ///
+    /// Examples of when this could happen:
+    /// - User drops all references to a stream, so we want to CANCEL the it.
+    /// - Header block size was too large, so we want to REFUSE, possibly
+    ///   after sending a 431 response frame.
+    ScheduledReset(Reason),
     Closed(Cause),
 }
 
@@ -75,15 +86,6 @@ enum Peer {
 enum Cause {
     EndStream,
     Error(Error),
-
-    /// This indicates to the connection that a reset frame must be sent out
-    /// once the send queue has been flushed.
-    ///
-    /// Examples of when this could happen:
-    /// - User drops all references to a stream, so we want to CANCEL the it.
-    /// - Header block size was too large, so we want to REFUSE, possibly
-    ///   after sending a 431 response frame.
-    ScheduledLibraryReset(Reason),
 }
 
 impl State {
@@ -339,24 +341,29 @@ impl State {
     /// Set the stream state to a scheduled reset.
     pub fn set_scheduled_reset(&mut self, reason: Reason) {
         debug_assert!(!self.is_closed());
-        self.inner = Closed(Cause::ScheduledLibraryReset(reason));
+        self.inner = ScheduledReset(reason)
     }
 
     pub fn get_scheduled_reset(&self) -> Option<Reason> {
         match self.inner {
-            Closed(Cause::ScheduledLibraryReset(reason)) => Some(reason),
+            ScheduledReset(reason) => Some(reason),
             _ => None,
         }
     }
 
     pub fn is_scheduled_reset(&self) -> bool {
-        matches!(self.inner, Closed(Cause::ScheduledLibraryReset(..)))
+        matches!(self.inner, ScheduledReset(_))
+    }
+
+    pub fn did_schedule_reset(&mut self) {
+        debug_assert!(self.is_scheduled_reset());
+        self.inner = Closed(Cause::EndStream);
     }
 
     pub fn is_local_error(&self) -> bool {
         match self.inner {
+            ScheduledReset(_) => true,
             Closed(Cause::Error(ref e)) => e.is_local(),
-            Closed(Cause::ScheduledLibraryReset(..)) => true,
             _ => false,
         }
     }
@@ -416,14 +423,14 @@ impl State {
     pub fn is_recv_closed(&self) -> bool {
         matches!(
             self.inner,
-            Closed(..) | HalfClosedRemote(..) | ReservedLocal
+            ScheduledReset(_) | Closed(..) | HalfClosedRemote(..) | ReservedLocal
         )
     }
 
     pub fn is_send_closed(&self) -> bool {
         matches!(
             self.inner,
-            Closed(..) | HalfClosedLocal(..) | ReservedRemote
+            ScheduledReset(_) | Closed(..) | HalfClosedLocal(..) | ReservedRemote
         )
     }
 
@@ -434,10 +441,8 @@ impl State {
     pub fn ensure_recv_open(&self) -> Result<bool, proto::Error> {
         // TODO: Is this correct?
         match self.inner {
+            ScheduledReset(reason) => Err(proto::Error::library_go_away(reason)),
             Closed(Cause::Error(ref e)) => Err(e.clone()),
-            Closed(Cause::ScheduledLibraryReset(reason)) => {
-                Err(proto::Error::library_go_away(reason))
-            }
             Closed(Cause::EndStream) | HalfClosedRemote(..) | ReservedLocal => Ok(false),
             _ => Ok(true),
         }
@@ -446,9 +451,9 @@ impl State {
     /// Returns a reason if the stream has been reset.
     pub(super) fn ensure_reason(&self, mode: PollReset) -> Result<Option<Reason>, crate::Error> {
         match self.inner {
-            Closed(Cause::Error(Error::Reset(_, reason, _)))
-            | Closed(Cause::Error(Error::GoAway(_, reason, _)))
-            | Closed(Cause::ScheduledLibraryReset(reason)) => Ok(Some(reason)),
+            ScheduledReset(reason)
+            | Closed(Cause::Error(Error::Reset(_, reason, _)))
+            | Closed(Cause::Error(Error::GoAway(_, reason, _))) => Ok(Some(reason)),
             Closed(Cause::Error(ref e)) => Err(e.clone().into()),
             Open {
                 local: Streaming, ..

tests/h2-tests/tests/stream_states.rs

@@ -1218,3 +1218,140 @@ async fn reset_new_stream_before_send() {
 
     join(srv, client).await;
 }
+
+#[tokio::test]
+async fn explicit_reset_with_max_concurrent_stream() {
+    h2_support::trace_init!();
+
+    let (io, mut srv) = mock::new();
+
+    let mock = async move {
+        let settings = srv
+            .assert_client_handshake_with_settings(frames::settings().max_concurrent_streams(1))
+            .await;
+        assert_default_settings!(settings);
+
+        srv.recv_frame(frames::headers(1).request("POST", "https://www.example.com/"))
+            .await;
+        srv.send_frame(frames::headers(1).response(200)).await;
+
+        srv.recv_frame(frames::reset(1).cancel()).await;
+
+        srv.recv_frame(
+            frames::headers(3)
+                .request("POST", "https://www.example.com/")
+                .eos(),
+        )
+        .await;
+        srv.send_frame(frames::headers(3).response(200)).await;
+    };
+
+    let h2 = async move {
+        let (mut client, mut h2) = client::handshake(io).await.unwrap();
+
+        {
+            let request = Request::builder()
+                .method(Method::POST)
+                .uri("https://www.example.com/")
+                .body(())
+                .unwrap();
+
+            let (resp, mut stream) = client.send_request(request, false).unwrap();
+
+            {
+                let resp = h2.drive(resp).await.unwrap();
+                assert_eq!(resp.status(), StatusCode::OK);
+            }
+
+            stream.send_reset(Reason::CANCEL);
+        };
+
+        {
+            let request = Request::builder()
+                .method(Method::POST)
+                .uri("https://www.example.com/")
+                .body(())
+                .unwrap();
+
+            let (resp, _) = client.send_request(request, true).unwrap();
+
+            {
+                let resp = h2.drive(resp).await.unwrap();
+                assert_eq!(resp.status(), StatusCode::OK);
+            }
+        };
+
+        h2.await.unwrap();
+    };
+
+    join(mock, h2).await;
+}
+
+#[tokio::test]
+async fn implicit_cancel_with_max_concurrent_stream() {
+    h2_support::trace_init!();
+
+    let (io, mut srv) = mock::new();
+
+    let mock = async move {
+        let settings = srv
+            .assert_client_handshake_with_settings(frames::settings().max_concurrent_streams(1))
+            .await;
+        assert_default_settings!(settings);
+
+        srv.recv_frame(frames::headers(1).request("POST", "https://www.example.com/"))
+            .await;
+        srv.send_frame(frames::headers(1).response(200)).await;
+
+        srv.recv_frame(frames::reset(1).cancel()).await;
+
+        srv.recv_frame(
+            frames::headers(3)
+                .request("POST", "https://www.example.com/")
+                .eos(),
+        )
+        .await;
+        srv.send_frame(frames::headers(3).response(200)).await;
+    };
+
+    let h2 = async move {
+        let (mut client, mut h2) = client::handshake(io).await.unwrap();
+
+        {
+            let request = Request::builder()
+                .method(Method::POST)
+                .uri("https://www.example.com/")
+                .body(())
+                .unwrap();
+
+            let (resp, stream) = client.send_request(request, false).unwrap();
+
+            {
+                let resp = h2.drive(resp).await.unwrap();
+                assert_eq!(resp.status(), StatusCode::OK);
+            }
+
+            // This implicitly resets the stream with CANCEL.
+            drop(stream);
+        };
+
+        {
+            let request = Request::builder()
+                .method(Method::POST)
+                .uri("https://www.example.com/")
+                .body(())
+                .unwrap();
+
+            let (resp, _) = client.send_request(request, true).unwrap();
+
+            {
+                let resp = h2.drive(resp).await.unwrap();
+                assert_eq!(resp.status(), StatusCode::OK);
+            }
+        };
+
+        h2.await.unwrap();
+    };
+
+    join(mock, h2).await;
+}