quart-cors 0.3.0

Quart-CORS is an extension for Quart to enable and control Cross Origin Resource Sharing, CORS (also known as access control).

CORS is required to share resources in browsers due to the Same Origin Policy which prevents resources being used from a different origin. An origin in this case is defined as the scheme, host and port combined and a resource corresponds to a path.

In practice the Same Origin Policy means that a browser visiting http://quart.com will prevent the response of GET http://api.com being read. It will also prevent requests such as POST http://api.com. Note that CORS applies to browser initiated requests, non-browser clients such as requests are not subject to CORS restrictions.

CORS allows a server to indicate to a browser that certain resources can be used, contrary to the Same Origin Policy. It does so via access-control headers that inform the browser how the resource can be used. For GET requests these headers are sent in the response. For non-GET requests the browser must ask the server for the access-control headers before sending the actual request, it does so via a preflight OPTIONS request.

The Same Origin Policy does not apply to WebSockets, and hence there is no need for CORS. Instead the server alone is responsible for deciding if the WebSocket is allowed and it should do so by inspecting the WebSocket-request origin header.

Simple (GET) requests should return CORS headers specifying the origins that are allowed to use the resource (response). This can be any origin, * (wildcard), or a list of specific origins. The response should also include a CORS header specifying whether response-credentials e.g. cookies can be used. Note that if credential sharing is allowed the allowed origins must be specific and not a wildcard.

Preflight requests should return CORS headers specifying the origins allowed to use the resource, the methods and headers allowed to be sent in a request to the resource, whether response credentials can be used, and finally which response headers can be used.

Note that certain actions are allowed in the Same Origin Policy such as embedding e.g. <img src="http://api.com/img.gif"> and simple POSTs. For the purposes of this readme though these complications are ignored.

The CORS access control response headers are,

Quart-CORS uses the same naming (without the Access-Control prefix) for it’s arguments and settings when they relate to the same meaning.

app = Quart(__name__)
app = cors(app, **settings)

blueprint = Blueprint(__name__)
blueprint = cors(blueprint, **settings)

@app.route('/')
@route_cors(**settings)
async def handler():
    ...

@app.websocket('/')
@websocket_cors(allow_origin=...)
async def handler():
    ...

app = Quart(__name__)
app = cors(app, allow_origin="*")

@app.route('/')
@route_cors(allow_origin="https://quart.com")
async def handler():
    ...

@app.websocket('/')
@websocket_cors(allow_origin="https://quart.com")
async def handler():
    ...

@app.route('/', methods=["POST"])
@route_cors(
    allow_headers=["content-type"],
    allow_methods=["POST"],
    allow_origin=["https://quart.com"],
)
async def handler():
    data = await request.get_json()
    ...

$ pip install tox
$ tox