[Webkit-unassigned] [Bug 199492] New: XHR CORS requests logged twice in the server

Thu Jul 4 00:31:56 PDT 2019

https://bugs.webkit.org/show_bug.cgi?id=199492

            Bug ID: 199492
           Summary: XHR CORS requests logged twice in the server
           Product: WebKit
           Version: Safari 12
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: karl at sutt.ee

Overview:
A simple XHR CORS request after a page refresh â€” either with in `onload` handler on <body> or an `onclick` on a <button> â€” gets processed twice by the server.
This does not seem to happen 100% of the time, sometimes it's only processed once, but after a page refresh it's processed twice.
I initially opened a StackOverflow question with a bit more context: https://stackoverflow.com/questions/56877116/flask-logs-duplicate-xhr-cors-requests-from-safari
A screen recording of the behaviour: https://d.pr/v/1h7iRZ

Steps to reproduce:
Clone https://github.com/karls/flask-safari-troubleshoot and follow the instructions in the README.

Actual results:
After refreshing the page and triggering the XHR request, the server logs (and processes) the request twice, but not 100% of the time.

Expected results:
After refreshing the page and triggering the XHR request, the server should only process the request once.

Software and hardware:
MacBook Pro (13-inch, 2018, Four Thunderbolt 3 Ports)
OSX 10.14.5 (18F132)
Safari 12.1.1 (14607.2.6.1.1) (but also happens on Technology Preview Release 86 (Safari 13.0, WebKit 14608.1.30.2))
Server software is Flask 1.0.3 (Python)
Using vanilla XMLHttpRequest to perform the HTTP CORS request.

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