Add the cache_key parameter to the cache decorator

[danerlt]

The cache decorator is generated using the key-builder method. Can a cache_key parameter be added? If the cache_key parameter is added, the key-builder will not be used for construction.

[danerlt]

The code is as follows

def cache(
        expire: Optional[int] = None,
        coder: Optional[Type[Coder]] = None,
        key_builder: Optional[KeyBuilder] = None,
        cache_key: Optional[str] = None,
        namespace: str = "",
        injected_dependency_namespace: str = "__fastapi_cache",
) -> Callable[[Callable[P, Awaitable[R]]], Callable[P, Awaitable[Union[R, Response]]]]:
    """
    cache all function
    :param injected_dependency_namespace:
    :param namespace:
    :param expire:
    :param coder:
    :param cache_key:
    :param key_builder:

    :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[Union[R, Response]]]:
        # 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)
        async def inner(*args: P.args, **kwargs: P.kwargs) -> Union[R, Response]:
            nonlocal coder
            nonlocal expire
            nonlocal key_builder
            nonlocal cache_key

            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
                kwargs.pop(injected_request.name, None)
                kwargs.pop(injected_response.name, None)

                if iscoroutinefunction(func):
                    # async, return as is.
                    # unintuitively, we have to await once here, so that caller
                    # does not have to await twice. See
                    # https://stackoverflow.com/a/59268198/532513
                    return await func(*args, **kwargs)
                else:
                    # sync, wrap in thread and return async
                    # see above why we have to await even although caller also awaits.
                    return await run_in_threadpool(func, *args, **kwargs)  # type: ignore[arg-type]

            copy_kwargs = kwargs.copy()
            request: Optional[Request] = copy_kwargs.pop(request_param.name, None)  # type: ignore[assignment]
            response: Optional[Response] = copy_kwargs.pop(response_param.name, None)  # type: ignore[assignment]

            if _uncacheable(request):
                return await ensure_async_func(*args, **kwargs)

            prefix = FastAPICache.get_prefix()
            coder = coder or FastAPICache.get_coder()
            expire = expire or FastAPICache.get_expire()
            key_builder = key_builder or FastAPICache.get_key_builder()
            backend = FastAPICache.get_backend()
            cache_status_header = FastAPICache.get_cache_status_header()
            
            if cache_key is None:
                cache_key = key_builder(
                    func,
                    f"{prefix}:{namespace}",
                    request=request,
                    response=response,
                    args=args,
                    kwargs=copy_kwargs,
                )
                if isawaitable(cache_key):
                    cache_key = await cache_key
            assert isinstance(cache_key, str)  # noqa: S101  # assertion is a type guard

            try:
                ttl, cached = await backend.get_with_ttl(cache_key)
            except Exception:
                logger.warning(
                    f"Error retrieving cache key '{cache_key}' from backend:",
                    exc_info=True,
                )
                ttl, cached = 0, None

            if cached is None or (request is not None and request.headers.get("Cache-Control") == "no-cache"):  # cache miss
                result = await ensure_async_func(*args, **kwargs)
                to_cache = coder.encode(result)

                try:
                    await backend.set(cache_key, to_cache, expire)
                except Exception:
                    logger.warning(
                        f"Error setting cache key '{cache_key}' in backend:",
                        exc_info=True,
                    )

                if response:
                    response.headers.update(
                        {
                            "Cache-Control": f"max-age={expire}",
                            "ETag": f"W/{hash(to_cache)}",
                            cache_status_header: "MISS",
                        }
                    )

            else:  # cache hit
                if response:
                    etag = f"W/{hash(cached)}"
                    response.headers.update(
                        {
                            "Cache-Control": f"max-age={ttl}",
                            "ETag": etag,
                            cache_status_header: "HIT",
                        }
                    )

                    if_none_match = request and request.headers.get("if-none-match")
                    if if_none_match == etag:
                        response.status_code = HTTP_304_NOT_MODIFIED
                        return response

                result = cast(R, coder.decode_as_type(cached, type_=return_type))

            return result

        inner.__signature__ = _augment_signature(wrapped_signature, *to_inject)  # type: ignore[attr-defined]

        return inner

    return wrapper