Add v1 only detection

protocol/src/lib.rs

@@ -976,7 +976,11 @@ impl<'a> Handshake<'a> {
 #[cfg(feature = "std")]
 #[derive(Debug)]
 pub enum ProtocolError {
+    /// Wrap an IO errors.
     Io(std::io::Error),
+    /// Remote party likely only supports V1 protocol.
+    IncompatibleProtocol,
+    /// Internal protocol specific errors.
     Internal(Error),
 }
 
@@ -1001,8 +1005,11 @@ 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) => write!(f, "IO error: {:?}.", e),
+            ProtocolError::Internal(e) => write!(f, "Internal error: {:?}.", e),
+            ProtocolError::IncompatibleProtocol => {
+                write!(f, "Remote likely only supports V1 protocol.")
+            }
         }
     }
 }
@@ -1061,7 +1068,16 @@ where
 
         // Read remote's initial key.
         let mut remote_ellswift_buffer = [0u8; 64];
-        reader.read_exact(&mut remote_ellswift_buffer).await?;
+        // Try to detect errors which likely mean the remote doesn't understand
+        // the V2 protocol and the caller should re-attempt on V1 if they want.
+        if let Err(e) = reader.read_exact(&mut remote_ellswift_buffer).await {
+            return match e.kind() {
+                std::io::ErrorKind::UnexpectedEof
+                | std::io::ErrorKind::ConnectionReset
+                | std::io::ErrorKind::TimedOut => Err(ProtocolError::IncompatibleProtocol),
+                _ => Err(ProtocolError::Io(e)),
+            };
+        }
 
         let num_version_packet_bytes = PacketWriter::required_packet_allocation(&VERSION_CONTENT);
         let num_decoy_packets_bytes: usize = match decoys {