Preflight for Google Cloud Storage signed URL not returning CORS response headers

Question

I'm trying to perform a signed resumable upload to GCS. Our frontend is running up against CORS restrictions on the initial request: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.

The response headers show no CORS headers:

alt-svc: quic=":443"; ma=2592000; v="44,43,39,35" cache-control: private, max-age=0 content-length: 0 content-type: text/html; charset=UTF-8 date: Tue, 13 Nov 2018 20:28:32 GMT expires: Tue, 13 Nov 2018 20:28:32 GMT server: UploadServer status: 200 x-guploader-uploadid: AEnB2Ups1tKbTbhPmsjrPXbIuIUyQt135AlSJ1n7-7XTwMrtQ2vUvn1WwpX3a_iusfmsXHaufdf5B3H2PzmDONs2wW7tKkLarYoxrVyWalhaX6FzGQPoRW0

Debugging, I sent a curl request mimicking our frontend's request:

curl -H "Access-Control-Request-Headers: content-type,x-goog-resumable" \ -H "Access-Control-Request-Method: POST" \ -H "Origin: https://www.example.com" \ -X OPTIONS -I https://storage.googleapis.com/bucket/...

Again, the response contains no CORS response headers:

HTTP/2 200 x-guploader-uploadid: AEnB2UqwKiRSJjHjF9mzsZRMODdQmF6xhUAhdeEenuD0_WXmxpVA6n0i_HWY2NOJxvXS2t_I4IoFW_yvz6lssMz_HVmvlswL5NilGC3wE2YT0-L9aD7Pf1Q date: Tue, 13 Nov 2018 21:39:53 GMT expires: Tue, 13 Nov 2018 21:39:53 GMT cache-control: private, max-age=0 content-length: 0 server: UploadServer content-type: text/html; charset=UTF-8 alt-svc: quic=":443"; ma=2592000; v="44,43,39,35"

I've set my bucket CORS settings with gsutil cors set cors.json gs://bucket where cors.json contains [{"maxAgeSeconds": 3600, "method": ["GET", "POST", "PUT", "OPTIONS"], "origin": ["*"]}]

Am I missing something here?

Answer 1

I have found a solution. I had to add x-goog-resumable to the list of response headers.

My CORS file is

[
    {
      "origin": ["*"],
      "responseHeader": [
        "Content-Type",
        "Access-Control-Allow-Origin",
        "x-goog-resumable"],
      "method": ["GET", "HEAD", "DELETE", "POST", "OPTIONS"],
      "maxAgeSeconds": 3600
    }
]

At least preflight started to work