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[etc/vim.git] / src / blackd / middlewares.py
1 from typing import TYPE_CHECKING, Any, Awaitable, Callable, Iterable, TypeVar
2
3 from aiohttp.web_request import Request
4 from aiohttp.web_response import StreamResponse
5
6 if TYPE_CHECKING:
7     F = TypeVar("F", bound=Callable[..., Any])
8     middleware: Callable[[F], F]
9 else:
10     try:
11         from aiohttp.web_middlewares import middleware
12     except ImportError:
13         # @middleware is deprecated and its behaviour is the default since aiohttp 4.0
14         # so if it doesn't exist anymore, define a no-op for forward compatibility.
15         middleware = lambda x: x  # noqa: E731
16
17 Handler = Callable[[Request], Awaitable[StreamResponse]]
18 Middleware = Callable[[Request, Handler], Awaitable[StreamResponse]]
19
20
21 def cors(allow_headers: Iterable[str]) -> Middleware:
22     @middleware
23     async def impl(request: Request, handler: Handler) -> StreamResponse:
24         is_options = request.method == "OPTIONS"
25         is_preflight = is_options and "Access-Control-Request-Method" in request.headers
26         if is_preflight:
27             resp = StreamResponse()
28         else:
29             resp = await handler(request)
30
31         origin = request.headers.get("Origin")
32         if not origin:
33             return resp
34
35         resp.headers["Access-Control-Allow-Origin"] = "*"
36         resp.headers["Access-Control-Expose-Headers"] = "*"
37         if is_options:
38             resp.headers["Access-Control-Allow-Headers"] = ", ".join(allow_headers)
39             resp.headers["Access-Control-Allow-Methods"] = ", ".join(
40                 ("OPTIONS", "POST")
41             )
42
43         return resp
44
45     return impl