diff --git a/libp2p/crypto/secp256k1.py b/libp2p/crypto/secp256k1.py
index 79ffc9d..0e5b9a5 100644
--- a/libp2p/crypto/secp256k1.py
+++ b/libp2p/crypto/secp256k1.py
@@ -1,5 +1,4 @@
 import coincurve
-
 from libp2p.crypto.keys import KeyPair, KeyType, PrivateKey, PublicKey
 
 
diff --git a/libp2p/stream_muxer/abc.py b/libp2p/stream_muxer/abc.py
index 5c11107..7084d7a 100644
--- a/libp2p/stream_muxer/abc.py
+++ b/libp2p/stream_muxer/abc.py
@@ -1,5 +1,5 @@
 from abc import ABC, abstractmethod
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, Optional
 
 from multiaddr import Multiaddr
 
@@ -56,6 +56,12 @@ class IMuxedConn(ABC):
         :return: message read
         """
 
+    @abstractmethod
+    async def read_buffer_nonblocking(self, stream_id: int) -> Optional[bytes]:
+        """
+        Read a message from `stream_id`'s buffer, non-blockingly.
+        """
+
     @abstractmethod
     async def open_stream(
         self, protocol_id: str, multi_addr: Multiaddr