Factor out criterion for sending stream-level flow control

quinn-proto/src/connection/streams/recv.rs

@@ -107,8 +107,7 @@ impl Recv {
         // smaller than `stream_receive_window` in order to make sure the stream
         // does not get stuck.
         let diff = max_stream_data - self.sent_max_stream_data;
-        let transmit =
-            self.final_offset_unknown() && !self.stopped && diff >= (stream_receive_window / 8);
+        let transmit = self.can_send_flow_control() && diff >= (stream_receive_window / 8);
         (max_stream_data, ShouldTransmit(transmit))
     }
 
@@ -134,6 +133,13 @@ impl Recv {
         matches!(self.state, RecvState::Recv { size: None })
     }
 
+    /// Whether stream-level flow control updates should be sent for this stream
+    pub(super) fn can_send_flow_control(&self) -> bool {
+        // Stream-level flow control is redundant if the sender has already sent the whole stream,
+        // and moot if we no longer want data on this stream.
+        self.final_offset_unknown() && !self.stopped
+    }
+
     /// Whether data is still being accepted from the peer
     pub(super) fn is_receiving(&self) -> bool {
         matches!(self.state, RecvState::Recv { .. })

quinn-proto/src/connection/streams/state.rs

@@ -358,7 +358,7 @@ impl StreamsState {
         self.recv
             .get(&id)
             .and_then(|s| s.as_ref())
-            .map_or(false, |s| s.final_offset_unknown() && !s.stopped)
+            .map_or(false, |s| s.can_send_flow_control())
     }
 
     pub(in crate::connection) fn write_control_frames(
@@ -446,7 +446,7 @@ impl StreamsState {
                 Some(x) => x,
                 None => continue,
             };
-            if !rs.final_offset_unknown() || rs.stopped {
+            if !rs.can_send_flow_control() {
                 continue;
             }
             retransmits.get_or_create().max_stream_data.insert(id);