Provides CorsMixin, a KayaMixin that adds CORS response headers to outgoing responses and answers CORS preflight (OPTIONS) requests, with the same configuration parameters and semantics as FastAPI/Starlette's CORSMiddleware.

Usage

from kaya.core import KayaApp, HttpContext
from kaya.cors import CorsMixin

app = KayaApp(mixins=[
    CorsMixin(
        allow_origins=['https://example.com'],
        allow_methods=('GET', 'POST'),
        allow_headers=('X-Custom-Header',),
        allow_credentials=True,
        max_age=600,
    )
])

@app.GET('/')
async def home(ctx: HttpContext):
    await ctx.send_str(200, 'Hello World!')

Parameters

allow_origins: list of origins allowed to make cross-origin requests. Use ['*'] to allow any origin.
allow_origin_regex: optional regex string matched (fullmatch) against the request origin.
allow_methods: HTTP methods allowed for cross-origin requests (default ('GET',)); use '*' to allow all standard methods.
allow_headers: request headers allowed in cross-origin requests (default ()); use '*' to mirror back any requested headers.
allow_credentials: allow cookies/credentials in cross-origin requests (default False). When enabled, the allowed origin is always echoed explicitly instead of '*'.
expose_headers: response headers made accessible to the browser.
max_age: seconds browsers may cache the preflight response (default 600).

Behavior

Requests without an Origin header pass through untouched.
Simple cross-origin requests with an allowed origin get Access-Control-Allow-Origin (plus Access-Control-Allow-Credentials and Access-Control-Expose-Headers when configured) added to the response. Headers already set by the handler are never overwritten.
Preflight requests (OPTIONS with Origin and Access-Control-Request-Method headers) are answered directly by the mixin with 200 OK (or 400 with a Disallowed CORS ... body when the origin, method or headers are not allowed). The preflight response is the only one delivered to the client: if the routing tree matches the request anyway (including user-registered OPTIONS handlers or the 404 fallback), its output is discarded.

CorsMixin is a KayaMixin, so the app stays a KayaApp and both ASGI and RSGI keep working.