implemented granular cache invalidation based on tags

Author: tworedz

examples/in_memory/main.py

@@ -1,13 +1,15 @@
 # pyright: reportGeneralTypeIssues=false
+from collections import defaultdict
 from contextlib import asynccontextmanager
-from typing import AsyncIterator, Dict, Optional
+from typing import Annotated, AsyncIterator, Dict, List, Optional
 
 import pendulum
 import uvicorn
-from fastapi import FastAPI
+from fastapi import Body, FastAPI, Query
 from fastapi_cache import FastAPICache
 from fastapi_cache.backends.inmemory import InMemoryBackend
-from fastapi_cache.decorator import cache
+from fastapi_cache.decorator import cache, cache_invalidator
+from fastapi_cache.tag_provider import TagProvider
 from pydantic import BaseModel
 from starlette.requests import Request
 from starlette.responses import JSONResponse, Response
@@ -65,7 +67,7 @@ async def get_kwargs(name: str):
 
 
 @app.get("/sync-me")
-@cache(namespace="test") # pyright: ignore[reportArgumentType]
+@cache(namespace="test")  # pyright: ignore[reportArgumentType]
 def sync_me():
     # as per the fastapi docs, this sync function is wrapped in a thread,
     # thereby converted to async. fastapi-cache does the same.
@@ -115,8 +117,10 @@ async def uncached_put():
     put_ret = put_ret + 1
     return {"value": put_ret}
 
+
 put_ret2 = 0
 
+
 @app.get("/cached_put")
 @cache(namespace="test", expire=5)
 async def cached_put():
@@ -126,7 +130,7 @@ async def cached_put():
 
 
 @app.get("/namespaced_injection")
-@cache(namespace="test", expire=5, injected_dependency_namespace="monty_python") # pyright: ignore[reportArgumentType]
+@cache(namespace="test", expire=5, injected_dependency_namespace="monty_python")  # pyright: ignore[reportArgumentType]
 def namespaced_injection(
     __fastapi_cache_request: int = 42, __fastapi_cache_response: int = 17
 ) -> Dict[str, int]:
@@ -136,5 +140,65 @@ def namespaced_injection(
     }
 
 
+# Note: examples with cache invalidation
+files = defaultdict(
+    list,
+    {
+        1: [1, 2, 3],
+        2: [4, 5, 6],
+        3: [100],
+    },
+)
+
+FileTagProvider = TagProvider("file")
+
+
+# Note: providing tags for future granular cache invalidation
+@app.get("/files")
+@cache(expire=10, tag_provider=FileTagProvider)
+async def get_files(file_id_in: Annotated[Optional[List[int]], Query()] = None):
+    return [
+        {"id": k, "value": v}
+        for k, v in files.items()
+        if (True if not file_id_in else k in file_id_in)
+    ]
+
+
+# Note: here we're retrieving keys by file_id, so we also need to invalidate this, when file changes
+@app.get("/files/{file_id:int}")
+@cache(
+    expire=10,
+    tag_provider=FileTagProvider,
+    items_provider=lambda data, method_args, method_kwargs: [
+        {"id": method_kwargs["file_id"]}
+    ],
+)
+async def get_file_keys(file_id: int):
+    if file_id in files:
+        return files[file_id]
+    return Response("file id not found")
+
+
+# Note: here we can use default invalidator, because in response we have :id:
+@app.patch("/files/{file_id:int}")
+@cache_invalidator(tag_provider=FileTagProvider)
+async def edit_file(file_id: int, items: Annotated[List[int], Body(embed=True)]):
+    files[file_id] = items
+    return {
+        "id": file_id,
+        "value": files[file_id]
+    }
+
+
+# Note: here we need to use custom :invalidator: because we don't have access to identifier in response
+@app.delete("/files/{file_id:int}")
+@cache_invalidator(
+    tag_provider=FileTagProvider, invalidator=lambda resp, kwargs: kwargs["file_id"]
+)
+async def delete_file(file_id: int):
+    if file_id in files:
+        del files[file_id]
+
+
 if __name__ == "__main__":
     uvicorn.run("main:app", reload=True)

fastapi_cache/decorator.py

@@ -29,7 +29,8 @@
 
 from fastapi_cache import FastAPICache
 from fastapi_cache.coder import Coder
-from fastapi_cache.types import KeyBuilder
+from fastapi_cache.tag_provider import TagProvider
+from fastapi_cache.types import ItemsProviderProtocol, KeyBuilder
 
 logger: logging.Logger = logging.getLogger(__name__)
 logger.addHandler(logging.NullHandler())
@@ -90,6 +91,8 @@ def cache(
     key_builder: Optional[KeyBuilder] = None,
     namespace: str = "",
     injected_dependency_namespace: str = "__fastapi_cache",
+    tag_provider: Optional[TagProvider] = None,
+    items_provider: Optional[ItemsProviderProtocol] = None,
 ) -> Callable[[Callable[P, Awaitable[R]]], Callable[P, Awaitable[Union[R, Response]]]]:
     """
     cache all function
@@ -98,6 +101,8 @@ def cache(
     :param expire:
     :param coder:
     :param key_builder:
+    :param tag_provider:
+    :param items_provider:
 
     :return:
     """
@@ -194,6 +199,22 @@ async def ensure_async_func(*args: P.args, **kwargs: P.kwargs) -> R:
                         f"Error setting cache key '{cache_key}' in backend:",
                         exc_info=True,
                     )
+                else:
+                    if tag_provider:
+                        decoded = coder.decode(to_cache)
+                        try:
+                            await tag_provider.provide(
+                                data=decoded,
+                                parent_key=cache_key,
+                                expire=expire,
+                                items_provider=items_provider,
+                                method_args=args,
+                                method_kwargs=kwargs,
+                            )
+                        except Exception:
+                            logger.warning(
+                                f"Error while providing tags: {cache_key}", exc_info=True
+                            )
 
                 if response:
                     response.headers.update(
@@ -229,3 +250,36 @@ async def ensure_async_func(*args: P.args, **kwargs: P.kwargs) -> R:
         return inner
 
     return wrapper
+
+
+def default_invalidator(response: dict, kwargs: dict) -> str:
+    return f"{response['id']}"
+
+
+def cache_invalidator(
+    tag_provider: TagProvider,
+    invalidator: Callable[[dict, dict], str] = default_invalidator,
+):
+    def wrapper(func: Callable[P, Awaitable[R]]) -> Callable[P, Awaitable[Union[R, Response]]]:
+        @wraps(func)
+        async def inner(*args: P.args, **kwargs: P.kwargs) -> Union[R, Response]:
+            coder = FastAPICache.get_coder()
+
+            response = await func(*args, **kwargs)
+
+            data = coder.decode(coder.encode(response))
+
+            try:
+                object_id = invalidator(data, kwargs)
+                await tag_provider.invalidate(object_id)
+            except Exception as e:
+                logger.warning(
+                    f"Exception occurred while invalidating cache: {e}",
+                    exc_info=True,
+                )
+
+            return response
+
+        return inner
+
+    return wrapper

fastapi_cache/tag_provider.py

@@ -0,0 +1,93 @@
+import asyncio
+from typing import Callable, List, Optional, Union
+
+from fastapi_cache import FastAPICache
+from fastapi_cache.types import ItemsProviderProtocol
+
+
+class TagProvider:
+    def __init__(
+        self,
+        object_type: str,
+        object_id_provider: Optional[Callable[[dict], str]] = None,
+    ) -> None:
+        self.object_type = object_type
+        self.object_id_provider = object_id_provider or self.default_object_id_provider
+
+    @staticmethod
+    def default_object_id_provider(item: dict) -> str:
+        return f"{item['id']}"
+
+    @staticmethod
+    def default_items_provider(
+        data: Union[dict, list],
+        method_args: Optional[tuple] = None,
+        method_kwargs: Optional[dict] = None,
+    ) -> list[dict]:
+        return data
+
+    def get_tag(self, item: Optional[dict] = None, object_id: Optional[str] = None) -> str:
+        prefix = FastAPICache.get_prefix()
+        object_id = object_id or self.object_id_provider(item)
+        return f"{prefix}:invalidation:{self.object_type}:{object_id}"
+
+    @staticmethod
+    async def _append_value(key: str, parent_key: str, expire: int):
+        backend = FastAPICache.get_backend()
+        coder = FastAPICache.get_coder()
+        value = await backend.get(key)
+        if value:
+            value = coder.decode(value)
+            value.append(parent_key)
+        else:
+            value = [parent_key]
+        await backend.set(key=key, value=coder.encode(value), expire=expire)
+
+    async def provide(
+        self,
+        data: Union[dict, list],
+        parent_key: str,
+        expire: Optional[int] = None,
+        items_provider: Optional[ItemsProviderProtocol] = None,
+        method_args: Optional[tuple] = None,
+        method_kwargs: Optional[dict] = None,
+    ) -> None:
+        """
+        Provides tags for endpoint.
+
+        :param data:
+        :param parent_key:
+        :param expire:
+        :param items_provider:
+        :param method_args:
+        :param method_kwargs:
+        """
+        provider = items_provider or self.default_items_provider
+        tasks = [
+            self._append_value(
+                key=self.get_tag(item),
+                parent_key=parent_key,
+                expire=expire or FastAPICache.get_expire(),
+            )
+            for item in provider(data, method_args, method_kwargs)
+        ]
+        await asyncio.gather(*tasks)
+
+    async def invalidate(self, object_id: str) -> None:
+        """
+        Invalidate tags with given object_id
+
+        :param object_id: object_id to invalidate
+        """
+        backend = FastAPICache.get_backend()
+        coder = FastAPICache.get_coder()
+        tag = self.get_tag(object_id=object_id)
+
+        value = await backend.get(tag)
+        if not value:
+            return
+
+        keys: List[str] = coder.decode(value)
+        tasks = [backend.clear(key=key) for key in keys]
+        tasks.append(backend.clear(key=tag))
+        await asyncio.gather(*tasks)

fastapi_cache/types.py

@@ -1,5 +1,5 @@
 import abc
-from typing import Any, Awaitable, Callable, Dict, Optional, Tuple, Union
+from typing import Any, Awaitable, Callable, Dict, Optional, Tuple, TypeAlias, Union
 
 from starlette.requests import Request
 from starlette.responses import Response
@@ -38,3 +38,23 @@ async def set(self, key: str, value: bytes, expire: Optional[int] = None) -> Non
     @abc.abstractmethod
     async def clear(self, namespace: Optional[str] = None, key: Optional[str] = None) -> int:
         raise NotImplementedError
+
+
+class _ItemsProviderProtocol(Protocol):
+    def __call__(self, data: Union[dict, list]):
+        pass
+
+
+class _ItemsProviderProtocolWithParams(Protocol):
+    def __call__(
+        self,
+        data: Union[dict, list],
+        method_args: Optional[tuple] = None,
+        method_kwargs: Optional[dict] = None,
+    ) -> list[dict]:
+        pass
+
+
+ItemsProviderProtocol: TypeAlias = (
+    _ItemsProviderProtocol | _ItemsProviderProtocolWithParams
+)