Permit CORS preflight caching #246
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With this argument, an incrementing query parameter is added to the URL, which prevents a browser from utilising the CORS preflight cache.
The jQuery documentation states:
> If set to false, it will force requested pages not to be cached by the browser. Note: Setting cache to false will only work correctly with HEAD and GET requests. It works by appending "_={timestamp}" to the GET parameters. The parameter is not needed for other types of requests, except in IE8 when a POST is made to a URL that has already been requested by a GET.
The message_bus middleware implementation [sets the correct headers to prevent the browser caching the actual response](https://github.com/discourse/message_bus/blob/master/lib/message_bus/rack/middleware.rb#L115-L118) so it is unnecessary for the JavaScript client to also force a cache miss in a way that doubles request throughput in a use-case which requires CORS.
Fixes #245
SamSaffron
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Apr 27, 2021
benlangfeld
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Apr 27, 2021
#246 intended to prevent this from happening, but we only tested with jQuery, whose default for this value is `true`. Our shim for `$.ajax` defaults to `false`, so in that context the desired change didn't take effect. This shim is supposed to be lightweight to address only MessageBus' requirements, so here we remove support for the now unused `cache` option entirely, rather than flipping the default.
SamSaffron
pushed a commit
that referenced
this pull request
Apr 28, 2021
#246 intended to prevent this from happening, but we only tested with jQuery, whose default for this value is `true`. Our shim for `$.ajax` defaults to `false`, so in that context the desired change didn't take effect. This shim is supposed to be lightweight to address only MessageBus' requirements, so here we remove support for the now unused `cache` option entirely, rather than flipping the default.
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With this argument, an incrementing query parameter is added to the URL, which prevents a browser from utilising the CORS preflight cache.
The jQuery documentation states:
The message_bus middleware implementation sets the correct headers to prevent the browser caching the actual response so it is unnecessary for the JavaScript client to also force a cache miss in a way that doubles request throughput in a use-case which requires CORS.
Fixes #245