fix(p2p): disable sending message when not ready to prevent busy loop (…

…#5032)

Signed-off-by: Shanin Roman <[email protected]>

p2p/src/peer.rs

@@ -261,7 +261,12 @@ mod run {
                         idle_interval.reset();
                         ping_interval.reset();
                     }
-                    result = message_sender.send() => {
+                    // `message_sender.send()` is safe to be cancelled, it won't advance the queue or write anything if another branch completes first.
+                    // 
+                    // We need to conditionally disable it in case there is no data is to be sent, otherwise `message_sender.send()` will complete immediately
+                    //
+                    // The only source of data to be sent is other branches of this loop, so we do not need any async waiting mechanism for waiting for readiness.
+                    result = message_sender.send(), if message_sender.ready() => {
                         if let Err(error) = result {
                             iroha_logger::error!(%error, "Failed to send message to peer.");
                             break;
@@ -427,6 +432,11 @@ mod run {
             }
             Ok(())
         }
+
+        /// Check if message sender has data ready to be sent.
+        fn ready(&self) -> bool {
+            !self.queue.is_empty()
+        }
     }
 
     /// Either message or ping