Add v1 only detection

protocol/src/lib.rs

@@ -996,14 +996,31 @@ impl<'a> Handshake<'a> {
 #[cfg(feature = "std")]
 #[derive(Debug)]
 pub enum ProtocolError {
-    Io(std::io::Error),
+    /// Wrap all IO errors with a flag which indicates if the error
+    /// possibly means the remote does not support the V2 protocol
+    /// and could be retried with the V1 protocol as a fallback.
+    Io(std::io::Error, bool),
+    /// Internal protocol specific errors.
     Internal(Error),
 }
 
 #[cfg(feature = "std")]
 impl From<std::io::Error> for ProtocolError {
     fn from(error: std::io::Error) -> Self {
-        ProtocolError::Io(error)
+        // Detect IO errors which possibly mean the remote doesn't understand
+        // the V2 protocol and immediatly closed the connection.
+        let retry_with_v1 = matches!(
+            error.kind(),
+            // The remote force closed the connection.
+            std::io::ErrorKind::ConnectionReset
+                // A more general error than ConnectionReset, but could be caused
+                // by the remote closing the connection.
+                | std::io::ErrorKind::ConnectionAborted
+                // End of file read errors can occur if the remote closes the connection,
+                // but the local system reads due to timing issues.
+                | std::io::ErrorKind::UnexpectedEof
+        );
+        ProtocolError::Io(error, retry_with_v1)
     }
 }
 
@@ -1021,8 +1038,13 @@ impl std::error::Error for ProtocolError {}
 impl fmt::Display for ProtocolError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
-            ProtocolError::Io(e) => write!(f, "IO error: {:?}", e),
-            ProtocolError::Internal(e) => write!(f, "Internal error: {:?}", e),
+            ProtocolError::Io(e, retry_with_v1) => write!(
+                f,
+                "IO error: {:?}. Possibly retry on V1 protocol: {}.",
+                e,
+                if *retry_with_v1 { "Yes" } else { "No" }
+            ),
+            ProtocolError::Internal(e) => write!(f, "Internal error: {:?}.", e),
         }
     }
 }
@@ -1060,6 +1082,10 @@ where
     /// A `Result` containing:
     ///   * `Ok(AsyncProtocol)`: An initialized protocol handler.
     ///   * `Err(ProtocolError)`: An error that occurred during the handshake.
+    ///
+    /// # Errors
+    ///
+    /// * `Io` - Includes a flag for if the remote probably only understands the V1 protocol.
     pub async fn new<'a>(
         network: Network,
         role: Role,
@@ -1135,7 +1161,7 @@ where
                     std::io::ErrorKind::WouldBlock | std::io::ErrorKind::Interrupted => {
                         continue;
                     }
-                    _ => return Err(ProtocolError::Io(e)),
+                    _ => return Err(ProtocolError::Io(e, false)),
                 },
             }
         }