Improve channel forward compatibility (#103)

Unknown messages are now filtered through Python's warning
machinery rather than always raising an immediate exception.

Author: ncoghlan

src/lmstudio/json_api.py

@@ -4,6 +4,7 @@
 import copy
 import json
 import uuid
+import warnings
 
 from abc import ABC, abstractmethod
 from contextlib import contextmanager
@@ -152,7 +153,7 @@
     "LMStudioPredictionError",
     "LMStudioPresetNotFoundError",
     "LMStudioServerError",
-    "LMStudioUnknownMessageError",
+    "LMStudioUnknownMessageWarning",
     "LMStudioWebsocketError",
     "ModelInfo",
     "ModelInstanceInfo",
@@ -414,7 +415,7 @@ class LMStudioClientError(LMStudioError):
 
 
 @sdk_public_type
-class LMStudioUnknownMessageError(LMStudioClientError):
+class LMStudioUnknownMessageWarning(LMStudioClientError, UserWarning):
     """Client has received a message in a format it wasn't expecting."""
 
 
@@ -699,11 +700,19 @@ def result(self) -> T:
         assert self._result is not None
         return self._result
 
-    def raise_unknown_message_error(self, unknown_message: Any) -> NoReturn:
-        # TODO: improve forward compatibility by switching this to use warnings.warn
-        # instead of failing immediately for all unknown messages
-        raise LMStudioUnknownMessageError(
-            f"{self._NOTICE_PREFIX} unexpected message contents: {unknown_message!r}"
+    def report_unknown_message(self, unknown_message: Any) -> None:
+        # By default, each unique unknown message will be reported once per
+        # calling code location, NOT per channel instance. This is reasonable,
+        # since it generally indicates an SDK/server version compatibility issue,
+        # not a problem with any specific instance
+        # Potentially useful warnings filters:
+        # * Always show: "always:LMStudioUnknownMessageWarning"
+        # * Never show: "ignore:LMStudioUnknownMessageWarning"
+        # * Client exception: "error:LMStudioUnknownMessageWarning"
+        warnings.warn(
+            f"{self._NOTICE_PREFIX} unexpected message contents: {unknown_message!r}",
+            LMStudioUnknownMessageWarning,
+            stacklevel=2,  # Handle based on caller's code location
         )
 
     # See ChannelHandler below for more details on the routing of received messages
@@ -797,7 +806,7 @@ def iter_message_events(
             case {"type": "success", "defaultIdentifier": str(default_identifier)}:
                 yield self._set_result(default_identifier)
             case unmatched:
-                self.raise_unknown_message_error(unmatched)
+                self.report_unknown_message(unmatched)
 
     def handle_rx_event(self, event: ModelDownloadRxEvent) -> None:
         match event:
@@ -921,7 +930,7 @@ def iter_message_events(
                 )
                 yield self._set_result(result)
             case unmatched:
-                self.raise_unknown_message_error(unmatched)
+                self.report_unknown_message(unmatched)
 
     def handle_rx_event(self, event: ModelLoadingRxEvent) -> None:
         match event:
@@ -1290,7 +1299,7 @@ def iter_message_events(
                     )
                 )
             case unmatched:
-                self.raise_unknown_message_error(unmatched)
+                self.report_unknown_message(unmatched)
 
     def handle_rx_event(self, event: PredictionRxEvent) -> None:
         match event: