Support running in browser extension service workers

[kdawgwilk]

Is your feature request related to a problem? Please describe.

We would like to use the LD js-client-sdk in a chrome extension background service worker but the SDK uses window and document APIs which are not available in extension service workers as of manifest v3 such as XMLHttpRequest which was replaced with fetch https://developer.chrome.com/docs/extensions/mv3/migrating_to_service_workers/#workers

The global scope for service worker is significantly more limited and doesn't have many of these features. Most notably, service workers don't have access to the DOM. Workers no longer provide XMLHttpRequest, but instead support the more modern fetch()

Describe the solution you'd like

Have fallback options to ensure the SDK can operate in a more limited environment such as service workers

Describe alternatives you've considered

we have considered poly-filling in the window/document APIs that the library uses to work around the problem

cc @DallinVan

[kinyoklion]

Hello @kdawgwilk,

Thank you for the request.

Filed internally as 162088.

Thanks,
Ryan

[sghsri]

@kdawgwilk do you mind telling how you planned on polyfilling the window/document APIs, I'm also trying to get the LD client to work in a service worker and running into some issues

[kdawgwilk]

@sghsri I haven't worked on polyfilling these yet, but there were only 2-3 apis that needed to be polyfilled and they are mostly tied to the document lifecycle so I was planning on tying them to the service worker lifecycle instead

[sghsri]

@kdawgwilk oh ok, that's awesome to hear, thanks for responding! I am working on doing something similar. Are you writing the polyfills yourself, or have you found any packages that already do it. Thats been the main roadblock so far for me

[kdawgwilk]

I haven't been able to find something that already exists yet but I haven't done too much research

[kinyoklion]

Hello @sghsri and @kdawgwilk,

I don't have any progress to share on this at the moment, but I do think it would be worth discussing what would likely be the SDK solution.

The client SDK is layered. There is a js-common-sdk, which theoretically isn't browser specific. This is where the bulk of the implementation is, and it is used in a few different SDK implementations.

The js-client-sdk, this repo, is the browser specific layer. The primary purpose to provide a platform for the common SDK to use.

The js client SDK is really a content SDK.

My initial thought is a js-worker-sdk, which implements a platform which can be used by common. Though some things in the client SDK could just be updated and would gain compatibility. It gives a clear, and more constrained target.

Thanks,
Ryan

[kdawgwilk]

That seems like a pretty good approach. There is a lot of functionality in this SDK that would be the same for both, however, so there may be a bit of duplication, but it may be worth the trade-off.

[milankonir]

👋 We have ran into the same issue while migrating extension to MV3 and decided to build an extension background service worker specific SDK on top of the js-common-sdk.

We have a working prototype that:

• Uses fetch to perform http requests against LD services
• Provides localStorage implementation backed by chrome.storage.local to support the localStorage bootstrap option (important to make flags available as soon as possible when background service worker suspends / wakes up).
• Flushes analytic events on extension onSuspend event

We are planning to open source / contribute this back to LD if there's interest.

What would be a tremendous help in maintaining this SDK going forward is if launchdarkly-js-sdk-common provided typings for the initiaize method - for now we had to reverse engineer the information from the launchdarkly-js-client-sdk.

[eli-darkly]

@milankonir: We appreciate that you've put a lot of work into this. However... we would be very wary of making js-sdk-common into a supported API for customers to build on. It is an implementation detail, and treating it as an internal library has allowed us to have the freedom to make internal design changes to the SDKs as necessary, without having to worry that we'd be breaking someone else's project. In fact, it's not unlikely that there will be a complete rewrite of that code in the near future, which unfortunately means the prototype you've built will probably not work with future versions.

[milankonir]

@eli-darkly Thanks for the heads up. I can understand the reasons why you don't want to turn the js-sdk-common into officially supported API for 3rd parties to build on top of.

Do you have any rough timeline on when does the rewrite might happen? The extension manifest version 2 sunsets by the end of the year so we need some solution sooner rather than later. I have a feeling the custom SDK on top of js-sdk-common can be a good intermediate solution for us.

I don't know if the extension scenario is something you want to give long term support for. If not, it would be great to consider making some parts of the SDK extensible during the rewrite by allowing consumer to provide custom implementation for things like networking, storage, host lifecycle...

[kinyoklion]

@milankonir We cannot commit to any dates, but we are going to be starting with the server SDK and then applying those lessons back to the client. We will also likely be able to share a lot more implementation between the client and server SDKs. One of the major aspects we are tackling in the server SDK is to have an abstraction specifically for the platform. This platform abstraction will include things like a fetch abstraction, event streaming abstraction, cryptographic abstraction, etc.

The implementation of which will be in typescript and make it very much more prescriptive as to what will be required to implement a platform. The primary purpose of these will be to allow for internal development and maintenance, and they will be more subject to change than the public API.

I wouldn't depend on a time frame coinciding with the deprecation of MV2 though. We have recognized the same problem though, and also that it will be continue to be a problem as JS runs in more places, and each of those places has their own limitations and sandboxing.

[milankonir]

@kinyoklion Great info, looking forward for the new SDK! Until it lands, I have published an SDK that is compatible with browser extension service worker environment (MV3) for fellow extension developers to use.

Source codes:
https://github.com/getoutreach/launchdarkly-js-extension-sdk

Npm:
https://www.npmjs.com/package/@outreach/launchdarkly-js-extension-sdk

[rzec-allma]

Any update on the status of this?

[kinyoklion]

@rzec-allma There isn't an update at this time.