fix: Added multiselect type consistency in negotiate method

libp2p/host/basic_host.py

@@ -297,6 +297,11 @@ async def _swarm_stream_handler(self, net_stream: INetStream) -> None:
             protocol, handler = await self.multiselect.negotiate(
                 MultiselectCommunicator(net_stream), self.negotiate_timeout
             )
+            if protocol is None:
+                await net_stream.reset()
+                raise StreamFailure(
+                    "Failed to negotiate protocol: no protocol selected"
+                )
         except MultiselectError as error:
             peer_id = net_stream.muxed_conn.peer_id
             logger.debug(

libp2p/security/security_multistream.py

@@ -118,6 +118,8 @@ async def select_transport(
             # Select protocol if non-initiator
             protocol, _ = await self.multiselect.negotiate(communicator)
         if protocol is None:
-            raise MultiselectError("fail to negotiate a security protocol")
+            raise MultiselectError(
+                "Failed to negotiate a security protocol: no protocol selected"
+            )
         # Return transport from protocol
         return self.transports[protocol]

libp2p/stream_muxer/muxer_multistream.py

@@ -85,7 +85,9 @@ async def select_transport(self, conn: IRawConnection) -> TMuxerClass:
         else:
             protocol, _ = await self.multiselect.negotiate(communicator)
         if protocol is None:
-            raise MultiselectError("fail to negotiate a stream muxer protocol")
+            raise MultiselectError(
+                "Fail to negotiate a stream muxer protocol: no protocol selected"
+            )
         return self.transports[protocol]
 
     async def new_conn(self, conn: ISecureConn, peer_id: ID) -> IMuxedConn:

newsfragments/837.bugfix.rst

@@ -0,0 +1 @@
+Added multiselect type consistency in negotiate method. Updates all the usages of the method.

tests/core/host/test_basic_host.py

@@ -1,3 +1,10 @@
+from unittest.mock import (
+    AsyncMock,
+    MagicMock,
+)
+
+import pytest
+
 from libp2p import (
     new_swarm,
 )
@@ -10,6 +17,9 @@
 from libp2p.host.defaults import (
     get_default_protocols,
 )
+from libp2p.host.exceptions import (
+    StreamFailure,
+)
 
 
 def test_default_protocols():
@@ -22,3 +32,30 @@ def test_default_protocols():
     # NOTE: comparing keys for equality as handlers may be closures that do not compare
     # in the way this test is concerned with
     assert handlers.keys() == get_default_protocols(host).keys()
+
+
+@pytest.mark.trio
+async def test_swarm_stream_handler_no_protocol_selected(monkeypatch):
+    key_pair = create_new_key_pair()
+    swarm = new_swarm(key_pair)
+    host = BasicHost(swarm)
+
+    # Create a mock net_stream
+    net_stream = MagicMock()
+    net_stream.reset = AsyncMock()
+    net_stream.muxed_conn.peer_id = "peer-test"
+
+    # Monkeypatch negotiate to simulate "no protocol selected"
+    async def fake_negotiate(comm, timeout):
+        return None, None
+
+    monkeypatch.setattr(host.multiselect, "negotiate", fake_negotiate)
+
+    # Now run the handler and expect StreamFailure
+    with pytest.raises(
+        StreamFailure, match="Failed to negotiate protocol: no protocol selected"
+    ):
+        await host._swarm_stream_handler(net_stream)
+
+    # Ensure reset was called since negotiation failed
+    net_stream.reset.assert_awaited()