Service worker in Isolated Web Application (IWA)

[Sez Ibraim]

I am trying to build IWA with custom service worker file. In custom service worker file I am using CacheAPI to cache resources. But when I built my application there were errors that "failed to execute .add method or .put method and request scheme isolated-app is unsupported. I asked gpt and it says that CacheAPI does not support isolated:app protocol and it recommends to use indexeddb for caching resources instead of czcheAPI. Is it true because I cannot find any other source about this topic?

[Reilly Grant]

I don't think there's any reason why we couldn't add support for caching resources on an isolated-app:// origin but why are you caching sources at all? All of your IWA's resources come from the Web Bundle which is already stored locally (essentially pre-cached).

Reilly Grant | Software Engineer | rei...@chromium.org | Google Chrome

On Wed, Feb 5, 2025 at 7:57 AM Sez Ibraim <sezi...@gmail.com> wrote:

I am trying to build IWA with custom service worker file. In custom service worker file I am using CacheAPI to cache resources. But when I built my application there were errors that "failed to execute .add method or .put method and request scheme isolated-app is unsupported. I asked gpt and it says that CacheAPI does not support isolated:app protocol and it recommends to use indexeddb for caching resources instead of czcheAPI. Is it true because I cannot find any other source about this topic?

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[Sez Ibraim]

I am trying to cache media items which I get them from API request. Then I am displaying them in html file. For example I get url link for a media like https://domain.com/Image/item1.png and I cache that media. So if there is no internet connection the cached media will still continue to display. This is my purpose why I want to use service worker and caching. In PWA it is working.

[guest271314]

One option is to use navigator.storage.getDirectory() then write to the Origin Private File System, which writes created directories and files to the Chromium configuration folder - without prompting user for permissions. Technically it is possible to read that data with user defined means outside of Chromium. Or, use WICG File System Access and write the directories and files to the user file system with prompting the user.

[Claudio Klemp]

A unusual solution for you : 

Cache it in the DOM. Instead of indexDB, session storage, etc , the resources you have from the APIs.

Create a domStorage ( chatGPT can help you in this ) for put , get, delete, list ... less than 100 lines of javascript. Store the items, whatever it is in a DIV or different DIV's , retrieve and / or cancel the content of the DIV.

under http://egittoturismo.com you can find such a usage under "const domStorage = {...}" so you have a better idea.

Hope it can be useful to you.

Claudio.

[Robbie McElrath]

It's failing due to the check here, and we should fix that. I filed a bug to track this, but in the meantime alternative storage APIs like OPFS or indexedDB are probably your best option.

[Matthew Hunt]

Hi,

Are you able to share the link to the bug/issue that was raised for this for tracking purposes? We have run into the same issue and could really do with support for the CacheAPI in an IWA.

Thanks

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[Robbie McElrath]

Unfortunately the bug is internal, but doesn't have anything interesting in it at the moment. There was a CL to implement this, but it was abandoned with the argument that caching IWA content doesn't make sense as the resources are all local anyway.

Out of curiosity, what is your use case for the Cache API?