service worker tile prefetch does not work properly if image server proxies are not configured for CORS preflight with OPTIONS enabled
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christopher-johnson commented
noticed that when tiles are fetched by the service worker, it complains about opaque responses. This is a pretty substantial problem as it reduces the caching performance of the viewer significantly.
christopher-johnson commented
As can be observed for all of the major institutions who are supporting IIIF, if OPTIONS is not properly configured on the image server proxy for CORS preflight, these responses are opaque. This is bad and this needs to be addressed globally by the IIIF.
christopher-johnson commented
the workaround for no OPTIONS support is to not cache opaque responses. Implemented with 365cc26