Chrome cancels CORS XHR upon HTTP 302 redirect

Question

It looks like according to the CORS Spec, GET and POST requests should transparently follow 302 redirects. But Chrome is canceling my request.

Here's the JS that does the request:

var r = new XMLHttpRequest(); r.open('GET', 'https://dev.mysite.com/rest', true); r.send(); 

Here's what should happen:

1. Client: XHR POST request to /rest
2. Server: responds with HTTP 302 redirect to /rest/
3. Client: Follow that redirect

But after step 2, Chrome cancels the request. If there was no HTTP 302, the request would work perfectly. I've confirmed this.

When the request runs, I can see in Chrome's Network panel only one XHR -- a canceled POST request with no response headers or response body.

Debugging with Chrome's net-internals tool, I see that there was a response sent from the server, and after that, the request was cancelled. Here is the output of the request:

79295: URL_REQUEST https://dev.mysite.com/rest Start Time: 2013-08-30 12:41:11.637  t=1377880871637 [st=    0] +REQUEST_ALIVE  [dt=13455] t=1377880871638 [st=    1]    URL_REQUEST_BLOCKED_ON_DELEGATE  [dt=1]                               --> delegate = "extension Adblock Plus" t=1377880871639 [st=    2]   +URL_REQUEST_START_JOB  [dt=13453]                               --> load_flags = 143540480 (DO_NOT_SAVE_COOKIES | DO_NOT_SEND_AUTH_DATA | DO_NOT_SEND_COOKIES | ENABLE_LOAD_TIMING | MAYBE_USER_GESTURE | REPORT_RAW_HEADERS | VERIFY_EV_CERT)                               --> method = "POST"                               --> priority = 2                               --> upload_id = "0"                               --> url = "https://dev.mysite.com/rest" t=1377880871639 [st=    2]      HTTP_CACHE_GET_BACKEND  [dt=0] t=1377880871639 [st=    2]     +HTTP_STREAM_REQUEST  [dt=7] t=1377880871646 [st=    9]        HTTP_STREAM_REQUEST_BOUND_TO_JOB                                   --> source_dependency = 79296 (HTTP_STREAM_JOB) t=1377880871646 [st=    9]     -HTTP_STREAM_REQUEST t=1377880871646 [st=    9]     +HTTP_TRANSACTION_SEND_REQUEST  [dt=0] t=1377880871646 [st=    9]        HTTP_TRANSACTION_SEND_REQUEST_HEADERS                                   --> GET /facultyportfolio-rest HTTP/1.1                                       Host: dev.liberty.edu                                       Connection: keep-alive                                       Content-Length: 46                                       Origin: http://localhost:8080                                       User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/29.0.1547.62 Safari/537.36                                       Content-Type: application/json; charset=UTF-8                                       Accept: */*                                       Referer: http://localhost:8080/ajaxtest.html                                       Accept-Encoding: gzip,deflate,sdch                                       Accept-Language: en-US,en;q=0.8 t=1377880871646 [st=    9]        HTTP_TRANSACTION_SEND_REQUEST_BODY                                   --> did_merge = true                                   --> is_chunked = false                                   --> length = 46 t=1377880871646 [st=    9]     -HTTP_TRANSACTION_SEND_REQUEST t=1377880871646 [st=    9]     +HTTP_TRANSACTION_READ_HEADERS  [dt=1001] t=1377880871646 [st=    9]        HTTP_STREAM_PARSER_READ_HEADERS  [dt=1000] t=1377880872646 [st= 1009]        HTTP_TRANSACTION_READ_RESPONSE_HEADERS                                   --> HTTP/1.1 302 Found                                       Date: Fri, 30 Aug 2013 16:41:11 GMT                                       Server: Apache/2                                       Access-Control-Allow-Origin: http://localhost:8080                                       Access-Control-Allow-Credentials: true                                       Location: https://dev.mysite.com/rest/                                       Content-Language: en-US                                       Vary: Accept-Encoding,User-Agent                                       Content-Encoding: gzip                                       Content-Length: 20                                       Connection: close                                       Content-Type: text/plain; charset=UTF-8 t=1377880872647 [st= 1010]     -HTTP_TRANSACTION_READ_HEADERS t=1377880872647 [st= 1010]     +URL_REQUEST_BLOCKED_ON_DELEGATE  [dt=12445] t=1377880885091 [st=13454]        CANCELLED t=1377880885092 [st=13455]   -URL_REQUEST_START_JOB                               --> net_error = -3 (ERR_ABORTED) t=1377880885092 [st=13455] -REQUEST_ALIVE 

At the end, you can see "Cancelled" because of "URL_REQUEST_BLOCKED_ON_DELEGATE". I don't know what that means. But again, if there was no HTTP 302 redirect, the error would not occur.

Does anyone know what is causing Chrome to cancel this request?

Answer 1

The answers in here are mixed, hinting on certain settings in code etc. which may solve the redirect problem with CORS, but the CORS spec clearly specifies when such CORS redirects will fail/pass : As per the spec, browsers should

1. Allows 3XX redirect , if the request to the redirected resource doesn't require pre-flight check (simple CORS requests without custom header for example). See https://www.w3.org/TR/cors/#simple-cross-origin-request-0

If the manual redirect flag is unset and the response has an HTTP status code of 301, 302, 303, 307, or 308 Apply the redirect steps

2. Don't allow 3XX redirect, if the request to redirected resource requires pre-flight check. See https://www.w3.org/TR/cors/#cross-origin-request-with-preflight-0

If the response has an HTTP status code of 301, 302, 303, 307, or 308 Apply the cache and network error steps.

I have explored various CORS scenarios in github repo: https://github.com/monmohan/cors-experiment.

This specific issue with failed redirect can also be easily reproduced in isolation by the bundle here: https://github.com/monmohan/cors-experiment/tree/master/issue

Answer 2

I found this post about setting the correct Access-Control-Allow-Origin CORS header on your 302 response to be helpful, at least in my similar-sounding case.

Investigation of the problem showed that his XHR was not landing on the CORS-enabled URL directly, but was being redirected to it through an HTTP 302 (redirect) response.

So bear in mind that the redirecting URL must also include an Access-Control-Allow-Origin header, else the browser will stop right there with its attempted cross-domain request.

I've also found that setting additional CORS headers above and beyond Access-Control-Allow-Origin will often result in a cancelled transaction.