Remove all FairPlay formatting

It seems that different FairPlay license servers communicate differently. We initially implemented a superset of the format used in Apple’s sample docs, but this turns out to be a poor intermediate format for others to build request/response filters for arbitrary formats.

We should remove the formatting of requests and responses, which unfortunately will require applications to use request/response filters for FairPlay in (probably) all cases.

To close this issue, we should:

• Remove specific FairPlay formatting from DrmEngine
  • Unfortunately, this will be a breaking change, which makes it difficult to justify cherry-picking to v2.5.x. On the other hand, applications may not be able to use what we shipped in v2.5.0, so it may be better to break it quickly and get it over with.
• Write a tutorial document on special requirements of FairPlay usage, including:
  • Server certificate
  • Request/response filters
  • Sample request/response filters for common formats we encounter
• Add functionality to the demo app to allow request/response filters to be specified for custom assets, to facilitate FairPlay testing
  • This will involve eval, which is regrettable, and will need to be whitelisted in build/conformance.textproto

See also https://github.com/google/shaka-player/issues/1915#issuecomment-493374738, #1923.

[TheModMaker]

I wonder if we should just remove all formatting from FairPlay requests. So all we’d do is pass the init data we get from the browser. The app would then have to create a request filter that appends their cert. We could provide a helper to aid in this. This would allow the app to have their own content ID calculations. We also would no longer require a server certificate for FairPlay since the app will be adding it in the request filter. So every app would need to do something like:

player.getNetworkingEngine().registerRequestFilter((type, request) => {
  if (type != shaka.net.NetworkingEngine.RequestType.LICENSE) {
    return;
  }

  const initData = new Uint8Array(request.body);
  const contentId = shaka.util.FairPlayUtils.defaultGetContentId(initData);

  request.body = shaka.util.FairPlayUtils.defaultCreatePostData(
      initData, contentId, myCert);
});

We could even have a default filter generator, something like this:

player.getNetworkingEngine().registerRequestFilter(
    shaka.util.FairPlayUtils.createRequestFilter(myCert));
player.getNetworkingEngine().registerRequestFilter(
    shaka.util.FairPlayUtils.createRequestFilter(myCert, getContentId));
// Or alternatively
shaka.util.FairPlayUtils.addRequestFilter(player, myCert, getContentId));

[TheModMaker]

These will be cherry-picked to appear in v2.5.5. But, to avoid breaking anyone depending on it, we will still provide the old filters by default. For v2.5.x, you can disable this by setting the drm.fairPlayTransform configuration to false. This will be the default in v2.6.