Merge pull request #128 from mjpieters/namespaced_injection

Inject dependencies using a namespace

README.md

@@ -98,9 +98,22 @@ expire | int, states a caching time in seconds
 namespace | str, namespace to use to store certain cache items
 coder | which coder to use, e.g. JsonCoder
 key_builder | which key builder to use, default to builtin
+injected_dependency_namespace | prefix for injected dependency keywords, defaults to `__fastapi_cache`.
 
 You can also use `cache` as decorator like other cache tools to cache common function result.
 
+### Injected Request and Response dependencies
+
+The `cache` decorator adds dependencies for the `Request` and `Response` objects, so that it can
+add cache control headers to the outgoing response, and return a 304 Not Modified response when
+the incoming request has a matching If-Non-Match header. This only happens if the decorated
+endpoint doesn't already list these objects directly.
+
+The keyword arguments for these extra dependencies are named
+`__fastapi_cache_request` and `__fastapi_cache_response` to minimize collisions.
+Use the `injected_dependency_namespace` argument to `@cache()` to change the
+prefix used if those names would clash anyway.
+
 
 ### Supported data types
 

examples/in_memory/main.py

@@ -106,6 +106,17 @@ async def uncached_put():
     return {"value": put_ret}
 
 
+@app.get("/namespaced_injection")
+@cache(namespace="test", expire=5, injected_dependency_namespace="monty_python")
+def namespaced_injection(
+    __fastapi_cache_request: int = 42, __fastapi_cache_response: int = 17
+) -> dict[str, int]:
+    return {
+        "__fastapi_cache_request": __fastapi_cache_request,
+        "__fastapi_cache_response": __fastapi_cache_response,
+    }
+
+
 @app.on_event("startup")
 async def startup():
     FastAPICache.init(InMemoryBackend())

fastapi_cache/decorator.py

@@ -1,7 +1,7 @@
-import inspect
 import logging
 import sys
 from functools import wraps
+from inspect import Parameter, Signature, isawaitable, iscoroutinefunction
 from typing import Awaitable, Callable, Optional, Type, TypeVar
 
 if sys.version_info >= (3, 10):
@@ -10,7 +10,7 @@ else:
     from typing_extensions import ParamSpec
 
 from fastapi.concurrency import run_in_threadpool
-from fastapi.dependencies.utils import get_typed_return_annotation
+from fastapi.dependencies.utils import get_typed_return_annotation, get_typed_signature
 from starlette.requests import Request
 from starlette.responses import Response
 
@@ -24,34 +24,32 @@ P = ParamSpec("P")
 R = TypeVar("R")
 
 
-def _augment_signature(
-    signature: inspect.Signature, add_request: bool, add_response: bool
-) -> inspect.Signature:
-    if not (add_request or add_response):
+def _augment_signature(signature: Signature, *extra: Parameter) -> Signature:
+    if not extra:
         return signature
 
     parameters = list(signature.parameters.values())
     variadic_keyword_params = []
-    while parameters and parameters[-1].kind is inspect.Parameter.VAR_KEYWORD:
+    while parameters and parameters[-1].kind is Parameter.VAR_KEYWORD:
         variadic_keyword_params.append(parameters.pop())
 
-    if add_request:
-        parameters.append(
-            inspect.Parameter(
-                name="request",
-                annotation=Request,
-                kind=inspect.Parameter.KEYWORD_ONLY,
-            ),
-        )
-    if add_response:
-        parameters.append(
-            inspect.Parameter(
-                name="response",
-                annotation=Response,
-                kind=inspect.Parameter.KEYWORD_ONLY,
-            ),
-        )
-    return signature.replace(parameters=[*parameters, *variadic_keyword_params])
+    return signature.replace(parameters=[*parameters, *extra, *variadic_keyword_params])
+
+
+def _locate_param(sig: Signature, dep: Parameter, to_inject: list[Parameter]) -> Parameter:
+    """Locate an existing parameter in the decorated endpoint
+
+    If not found, returns the injectable parameter, and adds it to the to_inject list.
+
+    """
+    param = next(
+        (param for param in sig.parameters.values() if param.annotation is dep.annotation),
+        None,
+    )
+    if param is None:
+        to_inject.append(dep)
+        param = dep
+    return param
 
 
 def cache(
@@ -59,6 +57,7 @@ def cache(
     coder: Optional[Type[Coder]] = None,
     key_builder: Optional[KeyBuilder] = None,
     namespace: Optional[str] = "",
+    injected_dependency_namespace: str = "__fastapi_cache",
 ) -> Callable[[Callable[P, Awaitable[R]]], Callable[P, Awaitable[R]]]:
     """
     cache all function
@@ -70,16 +69,23 @@ def cache(
     :return:
     """
 
+    injected_request = Parameter(
+        name=f"{injected_dependency_namespace}_request",
+        annotation=Request,
+        kind=Parameter.KEYWORD_ONLY,
+    )
+    injected_response = Parameter(
+        name=f"{injected_dependency_namespace}_response",
+        annotation=Response,
+        kind=Parameter.KEYWORD_ONLY,
+    )
+
     def wrapper(func: Callable[P, Awaitable[R]]) -> Callable[P, Awaitable[R]]:
-        signature = inspect.signature(func)
-        request_param = next(
-            (param for param in signature.parameters.values() if param.annotation is Request),
-            None,
-        )
-        response_param = next(
-            (param for param in signature.parameters.values() if param.annotation is Response),
-            None,
-        )
+        # get_typed_signature ensures that any forward references are resolved first
+        wrapped_signature = get_typed_signature(func)
+        to_inject: list[Parameter] = []
+        request_param = _locate_param(wrapped_signature, injected_request, to_inject)
+        response_param = _locate_param(wrapped_signature, injected_response, to_inject)
         return_type = get_typed_return_annotation(func)
 
         @wraps(func)
@@ -90,14 +96,13 @@ def cache(
 
             async def ensure_async_func(*args: P.args, **kwargs: P.kwargs) -> R:
                 """Run cached sync functions in thread pool just like FastAPI."""
-                # if the wrapped function does NOT have request or response in its function signature,
-                # make sure we don't pass them in as keyword arguments
-                if not request_param:
-                    kwargs.pop("request", None)
-                if not response_param:
-                    kwargs.pop("response", None)
+                # if the wrapped function does NOT have request or response in
+                # its function signature, make sure we don't pass them in as
+                # keyword arguments
+                kwargs.pop(injected_request.name, None)
+                kwargs.pop(injected_response.name, None)
 
-                if inspect.iscoroutinefunction(func):
+                if iscoroutinefunction(func):
                     # async, return as is.
                     # unintuitively, we have to await once here, so that caller
                     # does not have to await twice. See
@@ -109,8 +114,8 @@ def cache(
                     return await run_in_threadpool(func, *args, **kwargs)
 
             copy_kwargs = kwargs.copy()
-            request: Optional[Request] = copy_kwargs.pop("request", None)
-            response: Optional[Response] = copy_kwargs.pop("response", None)
+            request: Optional[Request] = copy_kwargs.pop(request_param.name, None)
+            response: Optional[Response] = copy_kwargs.pop(response_param.name, None)
             if (
                 request and request.headers.get("Cache-Control") in ("no-store", "no-cache")
             ) or not FastAPICache.get_enable():
@@ -129,7 +134,7 @@ def cache(
                 args=args,
                 kwargs=copy_kwargs,
             )
-            if inspect.isawaitable(cache_key):
+            if isawaitable(cache_key):
                 cache_key = await cache_key
 
             try:
@@ -178,9 +183,7 @@ def cache(
             response.headers["ETag"] = etag
             return ret
 
-        inner.__signature__ = _augment_signature(
-            signature, request_param is None, response_param is None
-        )
+        inner.__signature__ = _augment_signature(wrapped_signature, *to_inject)
         return inner
 
     return wrapper

tests/test_decorator.py

@@ -94,3 +94,9 @@ def test_non_get() -> None:
         assert response.json() == {"value": 1}
         response = client.put("/uncached_put")
         assert response.json() == {"value": 2}
+
+
+def test_alternate_injected_namespace() -> None:
+    with TestClient(app) as client:
+        response = client.get("/namespaced_injection")
+        assert response.json() == {"__fastapi_cache_request": 42, "__fastapi_cache_response": 17}