refactor!: Apply command_scope as a Middleware

cq/_core/cq.py

@@ -10,7 +10,6 @@
     SingleHandlerRegistry,
 )
 from cq._core.message import Command, Event, Query
-from cq._core.middlewares.scope import CommandDispatchScopeMiddleware
 
 
 class CQ:
@@ -57,8 +56,7 @@ def query_types(self) -> KeysView[type[Query]]:
 
     def new_command_bus(self) -> Bus[Command, Any]:
         bus = SimpleBus(self.__command_registry)
-        command_middleware = CommandDispatchScopeMiddleware(self.__di)
-        bus.add_middlewares(command_middleware)
+        bus.add_middlewares(self.__di.command_scope())
         return bus
 
     def new_event_bus(self) -> Bus[Event, None]:

cq/_core/di.py

@@ -3,10 +3,12 @@
 from abc import abstractmethod
 from collections.abc import Awaitable, Callable
 from contextlib import nullcontext
-from typing import TYPE_CHECKING, Any, AsyncContextManager, Protocol, runtime_checkable
+from typing import TYPE_CHECKING, Any, Protocol, runtime_checkable
+
+from cq.middlewares.contextlib import AsyncContextManagerMiddleware
 
 if TYPE_CHECKING:  # pragma: no cover
-    from cq import CommandBus, EventBus, QueryBus
+    from cq import Command, CommandBus, EventBus, Middleware, QueryBus
 
 
 @runtime_checkable
@@ -22,30 +24,19 @@ class DIAdapter(Protocol):
     __slots__ = ()
 
     @abstractmethod
-    def command_scope(self) -> AsyncContextManager[None]:
+    def command_scope(self) -> Middleware[[Command], Any]:
         """
-        Return an async context manager that delimits the lifetime of a
-        command dispatch.
+        Return a middleware that wraps each command dispatch.
 
         **Responsibilities**
 
-        The scope must at minimum manage the lifecycle of a ``RelatedEvents``
-        instance and register it so that it is resolvable via injection for
-        the duration of the scope.
-
-        **Nested calls**
-
-        ``command_scope`` is entered in two distinct situations:
-
-        1. Around a standard command dispatch (via
-           ``CommandDispatchScopeMiddleware``).
-        2. Around each step of a ``ContextCommandPipeline``, which itself
-           wraps a command dispatch.
+        The middleware must at minimum manage the lifecycle of a
+        ``RelatedEvents`` instance and register it so that it is resolvable
+        via injection for the duration of the dispatch.
 
-        This means two nested calls can occur for a single logical command.
-        Implementations must detect re-entrant activation (e.g. a scope
-        already active on the current task) and silently ignore the inner
-        call instead of opening a second, conflicting scope.
+        If you already have an async context manager for the scope, wrap it
+        with ``cq.middlewares.contextlib.AsyncContextManagerMiddleware``
+        instead of writing the middleware by hand.
         """
 
         raise NotImplementedError
@@ -97,8 +88,8 @@ def wire[T](self, tp: type[T]) -> Callable[..., Awaitable[T]]:
 class NoDI(DIAdapter):
     __slots__ = ()
 
-    def command_scope(self) -> AsyncContextManager[None]:
-        return nullcontext()
+    def command_scope(self) -> Middleware[[Command], Any]:
+        return AsyncContextManagerMiddleware(nullcontext())
 
     def lazy[T](self, tp: type[T], /) -> Callable[[], Awaitable[T]]:
         tp_str = getattr(tp, "__name__", str(tp))

cq/_core/pipetools.py

@@ -11,7 +11,6 @@
     ConvertMethodSync,
 )
 from cq._core.message import Command, CommandBus, Query, QueryBus
-from cq._core.middlewares.scope import CommandDispatchScopeMiddleware
 
 
 class ContextCommandPipeline[C: Command](ContextPipeline[C]):
@@ -22,8 +21,6 @@ class ContextCommandPipeline[C: Command](ContextPipeline[C]):
     def __init__(self, di: DIAdapter) -> None:
         super().__init__(LazyDispatcher(CommandBus, di))
         self.__query_dispatcher = LazyDispatcher(QueryBus, di)
-        command_middleware = CommandDispatchScopeMiddleware(di)
-        self.add_middlewares(command_middleware)
 
     def add_static_query_step[Q: Query](self, query: Q, /) -> Self:
         return self.add_static_step(query, dispatcher=self.__query_dispatcher)

cq/ext/injection.py

@@ -1,15 +1,15 @@
 from collections.abc import AsyncIterator
-from contextlib import AsyncExitStack, asynccontextmanager
+from contextlib import AsyncExitStack
 from dataclasses import dataclass, field
 from enum import StrEnum
-from typing import Any, AsyncContextManager, Awaitable, Callable
+from typing import Any, Awaitable, Callable
 
 from injection import Module, adefine_scope, mod
 from injection.exceptions import ScopeAlreadyDefinedError
 
 from cq._core.di import DIAdapter
-from cq._core.message import CommandBus, EventBus, QueryBus
-from cq._core.middleware import MiddlewareResult
+from cq._core.message import Command, CommandBus, EventBus, QueryBus
+from cq._core.middleware import Middleware, MiddlewareResult
 from cq._core.related_events import AnyIORelatedEvents, RelatedEvents
 
 __all__ = ("CQScope", "InjectionAdapter", "InjectionScopeMiddleware")
@@ -24,12 +24,11 @@ class InjectionAdapter(DIAdapter):
     module: Module = field(default_factory=mod)
     threadsafe: bool | None = field(default=None)
 
-    def command_scope(self) -> AsyncContextManager[None]:
-        return InjectionScopeMiddleware(  # type: ignore[return-value]
+    def command_scope(self) -> Middleware[[Command], Any]:
+        return InjectionScopeMiddleware(
             CQScope.COMMAND_DISPATCH,
-            exist_ok=True,
             threadsafe=self.threadsafe,
-        )._cm
+        )
 
     def lazy[T](self, tp: type[T], /) -> Callable[[], Awaitable[T]]:
         awaitable = self.module.aget_lazy_instance(tp, threadsafe=self.threadsafe)
@@ -83,12 +82,6 @@ class InjectionScopeMiddleware:
     threadsafe: bool | None = field(default=None, kw_only=True)
 
     async def __call__(self, /, *args: Any, **kwargs: Any) -> MiddlewareResult[Any]:
-        async with self._cm:  # type: ignore[attr-defined]
-            yield
-
-    @property
-    @asynccontextmanager
-    async def _cm(self) -> AsyncIterator[None]:
         async with AsyncExitStack() as stack:
             try:
                 await stack.enter_async_context(

cq/middlewares/contextlib.py

@@ -0,0 +1,27 @@
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import TYPE_CHECKING, Any, AsyncContextManager, ContextManager
+
+if TYPE_CHECKING:  # pragma: no cover
+    from cq import MiddlewareResult
+
+__all__ = ("AsyncContextManagerMiddleware", "ContextManagerMiddleware")
+
+
+@dataclass(repr=False, eq=False, frozen=True, slots=True)
+class AsyncContextManagerMiddleware:
+    context: AsyncContextManager[Any]
+
+    async def __call__(self, /, *args: Any, **kwargs: Any) -> MiddlewareResult[Any]:
+        async with self.context:
+            yield
+
+
+@dataclass(repr=False, eq=False, frozen=True, slots=True)
+class ContextManagerMiddleware:
+    context: ContextManager[Any]
+
+    async def __call__(self, /, *args: Any, **kwargs: Any) -> MiddlewareResult[Any]:
+        with self.context:
+            yield

docs/di.md

@@ -39,24 +39,22 @@ If you use the default `CQ`, `ContextCommandPipeline()` (with no argument) is en
 
 ```python
 from collections.abc import Awaitable, Callable
-from cq import CQ, DIAdapter, CommandBus, EventBus, QueryBus
-from typing import Any, AsyncContextManager
+from cq import CQ, Command, DIAdapter, CommandBus, EventBus, Middleware, QueryBus
+from typing import Any
 
 class MyDIAdapter(DIAdapter):
-    def command_scope(self) -> AsyncContextManager[None]:
+    def command_scope(self) -> Middleware[[Command], Any]:
         """
-        Return an async context manager that delimits a command dispatch.
+        Return a middleware that wraps each command dispatch.
 
         Responsibilities:
           1. Open a DI scope for the duration of the command.
           2. Build a `RelatedEvents` instance inside that scope and make it
              resolvable, so command handlers can inject it.
-          3. Silently ignore nested re-entrant activations (see below).
 
-        Re-entrancy: `command_scope` is opened twice for a single logical
-        command when a `ContextCommandPipeline` wraps a command dispatch.
-        Implementations must detect that case (for example, by checking a
-        contextvar) and skip opening a second scope.
+        If you already have an async context manager for the scope, wrap it
+        with `cq.middlewares.contextlib.AsyncContextManagerMiddleware` instead
+        of writing the middleware by hand.
         """
         ...
 

tests/middlewares/test_contextlib.py

@@ -0,0 +1,125 @@
+from collections.abc import AsyncIterator, Iterator
+from contextlib import asynccontextmanager, contextmanager
+from typing import Any, Self
+
+import pytest
+
+from cq import Bus
+from cq.middlewares.contextlib import (
+    AsyncContextManagerMiddleware,
+    ContextManagerMiddleware,
+)
+
+
+class TestAsyncContextManagerMiddleware:
+    async def test_call_with_success(self, bus: Bus[Any, Any]) -> None:
+        events: list[str] = []
+
+        @asynccontextmanager
+        async def context() -> AsyncIterator[None]:
+            events.append("enter")
+            try:
+                yield
+            finally:
+                events.append("exit")
+
+        class Handler:
+            async def handle(self, message: str) -> None:
+                events.append("handle")
+
+            @classmethod
+            async def async_factory(cls) -> Self:
+                return cls()
+
+        bus.add_middlewares(AsyncContextManagerMiddleware(context()))
+        bus.subscribe(str, Handler.async_factory)
+
+        await bus.dispatch("Hello world!")
+        assert events == ["enter", "handle", "exit"]
+
+    async def test_call_with_handler_error_raise_value_error(
+        self,
+        bus: Bus[Any, Any],
+    ) -> None:
+        events: list[str] = []
+
+        @asynccontextmanager
+        async def context() -> AsyncIterator[None]:
+            events.append("enter")
+            try:
+                yield
+            finally:
+                events.append("exit")
+
+        class Handler:
+            async def handle(self, message: str) -> None:
+                raise ValueError(message)
+
+            @classmethod
+            async def async_factory(cls) -> Self:
+                return cls()
+
+        bus.add_middlewares(AsyncContextManagerMiddleware(context()))
+        bus.subscribe(str, Handler.async_factory)
+
+        with pytest.raises(ValueError):
+            await bus.dispatch("Hello world!")
+
+        assert events == ["enter", "exit"]
+
+
+class TestContextManagerMiddleware:
+    async def test_call_with_success(self, bus: Bus[Any, Any]) -> None:
+        events: list[str] = []
+
+        @contextmanager
+        def context() -> Iterator[None]:
+            events.append("enter")
+            try:
+                yield
+            finally:
+                events.append("exit")
+
+        class Handler:
+            async def handle(self, message: str) -> None:
+                events.append("handle")
+
+            @classmethod
+            async def async_factory(cls) -> Self:
+                return cls()
+
+        bus.add_middlewares(ContextManagerMiddleware(context()))
+        bus.subscribe(str, Handler.async_factory)
+
+        await bus.dispatch("Hello world!")
+        assert events == ["enter", "handle", "exit"]
+
+    async def test_call_with_handler_error_raise_value_error(
+        self,
+        bus: Bus[Any, Any],
+    ) -> None:
+        events: list[str] = []
+
+        @contextmanager
+        def context() -> Iterator[None]:
+            events.append("enter")
+            try:
+                yield
+            finally:
+                events.append("exit")
+
+        class Handler:
+            async def handle(self, message: str) -> None:
+                raise ValueError(message)
+
+            @classmethod
+            async def async_factory(cls) -> Self:
+                return cls()
+
+        bus.add_middlewares(ContextManagerMiddleware(context()))
+        bus.subscribe(str, Handler.async_factory)
+
+        with pytest.raises(ValueError):
+            await bus.dispatch("Hello world!")
+
+        assert events == ["enter", "exit"]