Imagery stops being requested.

[jfrancis537]

After updating to the latest version of cesium I noticed that imagery will stop loading, http requests for the imagery are no longer going out.

I did notice that my event handler on my imageryProvider.errorEvent is no longer being called in 1.56.1+ vs 1.55 "throwing" a tile not found error.

Environment Details:
Our imagery is incomplete, we are missing various sections.
Our environment is offline.

Works Correctly in: Cesium 1.55
Version: Cesium 1.57 and 1.56.1

[hpinkos]

@kring any ideas here?

[hpinkos]

@jfrancis537 Do you also see this issue in Sandcastle? https://cesiumjs.org/Cesium/Build/Apps/Sandcastle/
If not, can you please put together a code sample to reproduce this? Thanks!

[jfrancis537]

I can't find a way to reproduce it in Sandcastle because I don't have an imagery set located outside of our closed network, but I think I found the source of the issue / a workaround.

We use a UrlTemplateImageryProvider which makes a call to the server which would look up the image on the filesystem and return it as Content-Type jpeg.
it looks somewhat like this:

let imageryProvider = new Cesium.UrlTemplateImageryProvider({
 url: Cesium.buildModuleUrl("/endpoint/{somecustomtag}"),
 customTags: {
     someCustomTag: function() {
       ...doSomething
    }
 }
});

Given that our imagery is incomplete, if the image doesn't exist, we return an HttpResponse with a status code of 204 No content. Once one of those is received in the browser, the imagery stops loading.

However If the status code is changed to 404, the imagery continues to load as expected.

[jfrancis537]

It doesn't appear as though the actual content matters. Returning a 200 with a text/plain, still works as expected.

After further testing it only appears to do this with the 204 response.

[kring]

That's very odd, I can't think of why a 204 would be different from an invalid-image 200. Is there a proper Access-Control-Allow-Origin: * header in the response in both cases?

[jfrancis537]

Neither has that header.

[OmarShehata]

@jfrancis537 just to rule out ImageBitmap as the culprit, can you add the snippet in #7735 at the top of your code before requesting any imagery and see if the issue still happens?

[jfrancis537]

Adding that snippet does make the issue go away.

[OmarShehata]

@jfrancis537 can you check if this issue is still present with the latest CesiumJS? I made a fix here #7914 that might have resolved this.

[jfrancis537]

Yep, it fixed it.