Change Sans-I/O constructors to keyword-only.

docs/project/changelog.rst

@@ -45,6 +45,13 @@ Backwards-incompatible changes
       ``client.ClientConnection`` classes were renamed to ``protocol.Protocol``,
       ``server.ServerProtocol``, and ``client.ClientProtocol``.
 
+.. admonition:: Sans-I/O protocol constructors now use keyword-only arguments.
+    :class: caution
+
+    If you instantiate :class:`~server.ServerProtocol` or
+    :class:`~client.ClientProtocol` directly, make sure you are using keyword
+    arguments.
+
 .. admonition:: Closing a connection without an empty close frame is OK.
     :class: note
 

src/websockets/client.py

@@ -70,6 +70,7 @@ class ClientProtocol(Protocol):
     def __init__(
         self,
         wsuri: WebSocketURI,
+        *,
         origin: Optional[Origin] = None,
         extensions: Optional[Sequence[ClientExtensionFactory]] = None,
         subprotocols: Optional[Sequence[Subprotocol]] = None,

src/websockets/protocol.py

@@ -86,6 +86,7 @@ class Protocol:
     def __init__(
         self,
         side: Side,
+        *,
         state: State = OPEN,
         max_size: Optional[int] = 2**20,
         logger: Optional[LoggerLike] = None,

src/websockets/server.py

@@ -69,6 +69,7 @@ class ServerProtocol(Protocol):
 
     def __init__(
         self,
+        *,
         origins: Optional[Sequence[Optional[Origin]]] = None,
         extensions: Optional[Sequence[ServerExtensionFactory]] = None,
         subprotocols: Optional[Sequence[Subprotocol]] = None,

tests/test_server.py

@@ -621,6 +621,6 @@ def test_server_connection_class(self):
         ):
             from websockets.server import ServerConnection
 
-            server = ServerConnection("ws://localhost/")
+            server = ServerConnection()
 
         self.assertIsInstance(server, ServerProtocol)