Introduce base Backend

src/py/flwr/server/superlink/fleet/vce/backend/__init__.py

@@ -0,0 +1,22 @@
+# Copyright 2024 Flower Labs GmbH. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ==============================================================================
+"""Simulation Engine Backends."""
+
+from .backend import Backend, BackendConfig
+
+__all__ = [
+    "Backend",
+    "BackendConfig",
+]

src/py/flwr/server/superlink/fleet/vce/backend/backend.py

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+# Copyright 2024 Flower Labs GmbH. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ==============================================================================
+"""Generic Backend class for Fleet API using the Simulation Engine."""
+
+
+from abc import ABC, abstractmethod
+from typing import Callable, Dict, Tuple
+
+from flwr.client.clientapp import ClientApp
+from flwr.common.context import Context
+from flwr.common.message import Message
+from flwr.common.typing import ConfigsRecordValues
+
+BackendConfig = Dict[str, Dict[str, ConfigsRecordValues]]
+
+
+class Backend(ABC):
+    """Abstract base class for a Simulation Engine Backend."""
+
+    @abstractmethod
+    async def build(self) -> None:
+        """Build backend asynchronously.
+
+        Different components need to be in place before workers in a backend are ready
+        to accept jobs. When this method finishes executing, the backend should be fully
+        ready to run jobs.
+        """
+
+    @property
+    def num_workers(self) -> int:
+        """Return number of workers in the backend.
+
+        This is the number of TaskIns that can be processed concurrently.
+        """
+        return 0
+
+    @abstractmethod
+    def is_worker_idle(self) -> bool:
+        """Report whether a backend worker is idle and can therefore run a ClientApp."""
+
+    @abstractmethod
+    async def process_message(
+        self,
+        app: Callable[[], ClientApp],
+        message: Message,
+        context: Context,
+    ) -> Tuple[Message, Context]:
+        """Submit a job to the backend."""