Fix creation of gRPC sessions (#949)

Check outgoing channels

iris-mpc-cpu/src/network/grpc.rs

@@ -98,6 +98,10 @@ impl OutgoingStreams {
             ))
             .map(|s| s.value().clone())
     }
+
+    fn contains_session(&self, session_id: SessionId) -> bool {
+        self.streams.iter().any(|v| v.key().0 == session_id)
+    }
 }
 
 #[derive(Default, Clone)]
@@ -139,7 +143,7 @@ impl GrpcNetworking {
     }
 
     pub async fn create_session(&self, session_id: SessionId) -> eyre::Result<()> {
-        if self.message_queues.contains_key(&session_id) {
+        if self.outgoing_streams.contains_session(session_id) {
             return Err(eyre!(
                 "Player {:?} has already created session {session_id:?}",
                 self.party_id
@@ -403,6 +407,7 @@ mod tests {
 
         // Each party sending and receiving messages to each other
         {
+            let players = players.clone();
             jobs.spawn(async move {
                 let session_id = SessionId::from(1);
 
@@ -455,6 +460,18 @@ mod tests {
             });
         }
 
+        // Parties create a session consecutively
+        {
+            let players = players.clone();
+            jobs.spawn(async move {
+                let session_id = SessionId::from(2);
+
+                for player in players.iter() {
+                    player.create_session(session_id).await.unwrap();
+                }
+            });
+        }
+
         jobs.join_all().await;
 
         Ok(())