req-resp: Fix panic on connection closed for substream open failure (#291)

When a new connection is reported to the request-response protocol, the
protocol tracks the state of the connection if and only if it could open
a substream with the remote peer.

We do not track the state of the connection in cases where the substream
cannot be opened because the connection is closed.

A further `ConnectionClosed` event triggered a debug_assert assumption
for this case. The assumption is wrong since opening substreams can fail
which informs us that the connection is closed.


Connection details not tracked:

https://github.com/paritytech/litep2p/blob/eed0f755d591eb49e1b715a78aceb5a653ddf529/src/protocol/request_response/mod.rs#L267-L284

Which later leads to panics:

https://github.com/paritytech/litep2p/blob/d6fae559fbe2aaf8cb3fff021fb5608ca7b43766/src/protocol/request_response/mod.rs#L295-L301



Related to: #290

---------

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

Author: lexnv

src/protocol/request_response/mod.rs

@@ -296,9 +296,8 @@ impl RequestResponseProtocol {
             tracing::error!(
                 target: LOG_TARGET,
                 ?peer,
-                "state mismatch: peer doesn't exist",
+                "Peer does not exist or substream open failed during connection establishment",
             );
-            debug_assert!(false);
             return;
         };
 

src/protocol/request_response/tests.rs

@@ -92,7 +92,6 @@ async fn connection_closed_twice() {
 
 #[tokio::test]
 #[cfg(debug_assertions)]
-#[should_panic]
 async fn connection_established_twice() {
     let (mut protocol, _handle, _manager, _tx) = protocol();