fix: Do not save messages from failed fits

Do not save any messages from failed sampling runs.
For example, if sampling starts but cannot continue because attempts
to find appropriate initial values are rejected, there will be some
(logger) messages saved to disk. The presence of these messages
confuses the cache machinery, which assumes the presence of messages
on disk indicates a successful fit. Deleting them avoids the problem.

There remains the problem of retrieving the logger messages associated
with the failed fit. It's possible that this is something someone might
want to do. Future work might address this. Such a user is also free to
use CmdStan.

Closes #452

httpstan/views.py

@@ -389,6 +389,9 @@ def _services_call_done(operation: dict, future: asyncio.Future) -> None:
             )
             logger.critical(message)
             operation["result"] = _make_error(message, status=status)
+            # Delete messages associated with the fit. If initialization
+            # fails, for example, messages will exist on disk. Remove them.
+            httpstan.cache.delete_fit(operation["metadata"]["fit"]["name"])
         else:
             logger.info(f"Operation `{operation['name']}` finished.")
             operation["result"] = schemas.Fit().load(operation["metadata"]["fit"])

tests/test_sampling_exceptions.py

@@ -32,27 +32,12 @@ async def test_sampling_initialization_failed(api_url: str) -> None:
     assert operation["result"].get("code") == 400
     assert "Initialization failed." in operation["result"]["message"]
 
-    # recover the error messages sent to `logger`
-    # note that the fit name is retrieved from metadata. If sampling had
-    # completed without error, it would be available under `result`.
+    # verify the partial fit has been deleted.
     fit_name = operation["metadata"]["fit"]["name"]
-
-    # verify operation finished and that fit is available
     async with aiohttp.ClientSession() as session:
         fit_url = f"{api_url}/{fit_name}"
         async with session.get(fit_url) as resp:
-            assert resp.status == 200
-
-    # verify (error) messages are available
-    fit_bytes_ = await helpers.fit_bytes(api_url, fit_name)
-    assert isinstance(fit_bytes_, bytes)
-    messages = helpers.decode_messages(fit_bytes_)
-
-    assert len(messages) > 100
-
-    # first message should be an "Rejecting initial value" message.
-    error_message = messages[0]["values"].pop()
-    assert "Rejecting initial value" in error_message
+            assert resp.status == 404
 
 
 @pytest.mark.asyncio