From b838a0e3b672eb875047acdf3449e65702f5c0ee Mon Sep 17 00:00:00 2001
From: unniznd <au6695@gmail.com>
Date: Tue, 12 Aug 2025 21:50:10 +0530
Subject: [PATCH] added none type to return value of negotiate and changed
 caller handles to handle none. Added newsfragment.

---
 libp2p/host/basic_host.py                | 3 +++
 libp2p/protocol_muxer/multiselect.py     | 2 +-
 libp2p/security/security_multistream.py  | 7 ++++++-
 libp2p/stream_muxer/muxer_multistream.py | 7 ++++++-
 newsfragments/837.fix.rst                | 1 +
 5 files changed, 17 insertions(+), 3 deletions(-)
 create mode 100644 newsfragments/837.fix.rst

diff --git a/libp2p/host/basic_host.py b/libp2p/host/basic_host.py
index 70e41953..008fe7e5 100644
--- a/libp2p/host/basic_host.py
+++ b/libp2p/host/basic_host.py
@@ -288,6 +288,9 @@ class BasicHost(IHost):
             protocol, handler = await self.multiselect.negotiate(
                 MultiselectCommunicator(net_stream), self.negotiate_timeout
             )
+            if protocol is None:
+                await net_stream.reset()
+                raise StreamFailure("No protocol selected")
         except MultiselectError as error:
             peer_id = net_stream.muxed_conn.peer_id
             logger.debug(
diff --git a/libp2p/protocol_muxer/multiselect.py b/libp2p/protocol_muxer/multiselect.py
index 8d311391..e58c0981 100644
--- a/libp2p/protocol_muxer/multiselect.py
+++ b/libp2p/protocol_muxer/multiselect.py
@@ -53,7 +53,7 @@ class Multiselect(IMultiselectMuxer):
         self,
         communicator: IMultiselectCommunicator,
         negotiate_timeout: int = DEFAULT_NEGOTIATE_TIMEOUT,
-    ) -> tuple[TProtocol, StreamHandlerFn | None]:
+    ) -> tuple[TProtocol | None, StreamHandlerFn | None]:
         """
         Negotiate performs protocol selection.
 
diff --git a/libp2p/security/security_multistream.py b/libp2p/security/security_multistream.py
index 193cc092..d15dbbd9 100644
--- a/libp2p/security/security_multistream.py
+++ b/libp2p/security/security_multistream.py
@@ -26,6 +26,9 @@ from libp2p.protocol_muxer.multiselect_client import (
 from libp2p.protocol_muxer.multiselect_communicator import (
     MultiselectCommunicator,
 )
+from libp2p.transport.exceptions import (
+    SecurityUpgradeFailure,
+)
 
 """
 Represents a secured connection object, which includes a connection and details about
@@ -104,7 +107,7 @@ class SecurityMultistream(ABC):
         :param is_initiator: true if we are the initiator, false otherwise
         :return: selected secure transport
         """
-        protocol: TProtocol
+        protocol: TProtocol | None
         communicator = MultiselectCommunicator(conn)
         if is_initiator:
             # Select protocol if initiator
@@ -114,5 +117,7 @@ class SecurityMultistream(ABC):
         else:
             # Select protocol if non-initiator
             protocol, _ = await self.multiselect.negotiate(communicator)
+            if protocol is None:
+                raise SecurityUpgradeFailure("No protocol selected")
         # Return transport from protocol
         return self.transports[protocol]
diff --git a/libp2p/stream_muxer/muxer_multistream.py b/libp2p/stream_muxer/muxer_multistream.py
index 76699c67..d96820a4 100644
--- a/libp2p/stream_muxer/muxer_multistream.py
+++ b/libp2p/stream_muxer/muxer_multistream.py
@@ -30,6 +30,9 @@ from libp2p.stream_muxer.yamux.yamux import (
     PROTOCOL_ID,
     Yamux,
 )
+from libp2p.transport.exceptions import (
+    MuxerUpgradeFailure,
+)
 
 
 class MuxerMultistream:
@@ -73,7 +76,7 @@ class MuxerMultistream:
         :param conn: conn to choose a transport over
         :return: selected muxer transport
         """
-        protocol: TProtocol
+        protocol: TProtocol | None
         communicator = MultiselectCommunicator(conn)
         if conn.is_initiator:
             protocol = await self.multiselect_client.select_one_of(
@@ -81,6 +84,8 @@ class MuxerMultistream:
             )
         else:
             protocol, _ = await self.multiselect.negotiate(communicator)
+            if protocol is None:
+                raise MuxerUpgradeFailure("No protocol selected")
         return self.transports[protocol]
 
     async def new_conn(self, conn: ISecureConn, peer_id: ID) -> IMuxedConn:
diff --git a/newsfragments/837.fix.rst b/newsfragments/837.fix.rst
new file mode 100644
index 00000000..47919c23
--- /dev/null
+++ b/newsfragments/837.fix.rst
@@ -0,0 +1 @@
+Added multiselect type consistency in negotiate method. Updates all the usages of the method.