fix: panic in when there is connection window available, but not stream (#657)

We met the panic in our production environment, so handle this panic
    condition before panic. The stack backtrace:

Co-authored-by: winters.zc <[email protected]>

Author: aftersnow

src/proto/streams/flow_control.rs

@@ -173,12 +173,15 @@ impl FlowControl {
             self.available
         );
 
-        // Ensure that the argument is correct
-        assert!(self.window_size >= sz as usize);
-
-        // Update values
-        self.window_size -= sz;
-        self.available -= sz;
+        // If send size is zero it's meaningless to update flow control window
+        if sz > 0 {
+            // Ensure that the argument is correct
+            assert!(self.window_size >= sz as usize);
+
+            // Update values
+            self.window_size -= sz;
+            self.available -= sz;
+        }
     }
 }
 

src/proto/streams/prioritize.rs

@@ -744,6 +744,14 @@ impl Prioritize {
                             // capacity at this point.
                             debug_assert!(len <= self.flow.window_size());
 
+                            // Check if the stream level window the peer knows is available. In some
+                            // scenarios, maybe the window we know is available but the window which
+                            // peer knows is not.
+                            if len > 0 && len > stream.send_flow.window_size() {
+                                stream.pending_send.push_front(buffer, frame.into());
+                                continue;
+                            }
+
                             tracing::trace!(len, "sending data frame");
 
                             // Update the flow control