Have a clear error for when the I/O closes and when some protocol is violated. this should help find the rootcause of a bug.

If its Closed it looks like the TCP connection got dropped/cut off (e.g. OS, Wifi).
If its Violated we for sure know the cause is the messages send/recv in a wrong way

network/protocol/src/error.rs

@@ -11,13 +11,21 @@ pub enum InitProtocolError {
 /// When you return closed you must stay closed!
 #[derive(Debug, PartialEq)]
 pub enum ProtocolError {
+    /// Closed indicates the underlying I/O got closed
+    /// e.g. the TCP, UDP or MPSC connection is dropped by the OS
     Closed,
+    /// Violated indicates the veloren_network_protocol was violated
+    /// the underlying I/O connection is still valid, but the remote side
+    /// send WRONG (e.g. Invalid, or wrong order) data on the protocol layer.
+    Violated,
 }
 
 impl From<ProtocolError> for InitProtocolError {
     fn from(err: ProtocolError) -> Self {
         match err {
             ProtocolError::Closed => InitProtocolError::Closed,
+            // not possible as the Init has raw access to the I/O
+            ProtocolError::Violated => InitProtocolError::Closed,
         }
     }
 }
@@ -46,6 +54,7 @@ impl core::fmt::Display for ProtocolError {
     fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
         match self {
             ProtocolError::Closed => write!(f, "Channel closed"),
+            ProtocolError::Violated => write!(f, "Channel protocol violated"),
         }
     }
 }

network/protocol/src/mpsc.rs

@@ -142,7 +142,7 @@ where
                 }
                 Ok(e)
             },
-            MpscMsg::InitFrame(_) => Err(ProtocolError::Closed),
+            MpscMsg::InitFrame(_) => Err(ProtocolError::Violated),
         }
     }
 }
@@ -164,7 +164,7 @@ where
 {
     async fn recv(&mut self) -> Result<InitFrame, ProtocolError> {
         match self.sink.recv().await? {
-            MpscMsg::Event(_) => Err(ProtocolError::Closed),
+            MpscMsg::Event(_) => Err(ProtocolError::Violated),
             MpscMsg::InitFrame(f) => Ok(f),
         }
     }

network/protocol/src/tcp.rs

@@ -266,7 +266,7 @@ where
                                     ?mid,
                                     "protocol violation by remote side: send Data before Header"
                                 );
-                                break 'outer Err(ProtocolError::Closed);
+                                break 'outer Err(ProtocolError::Violated);
                             },
                         };
                         m.data.extend_from_slice(&data);
@@ -321,7 +321,7 @@ where
                 return Ok(frame);
             }
         }
-        Err(ProtocolError::Closed)
+        Err(ProtocolError::Violated)
     }
 }