Make legacy fileOpen API accept configurable cleanup and rejection

[jmrog]

Here is a rough idea/proposal for handling the later discussion in #41.

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Thanks for your pull request. It looks like this may be your first contribution to a Google open source project (if not, look below for help). Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

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[jmrog]

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[tomayac]

Thanks for opening this PR. I have to admit I'm not a fan of the way this complicates the API. Let me think a bit more if there is a different way.

I had more something in mind like the following:

import { fileOpen, supported } from 'browser-fs-access';

// … before
let file;
if (supported) {
  try {
    file = await fileOpen();
  } catch (err) {
    console.error(err);
  }
} else {
  file = await fileOpen();
}
// … after

I admit this looks not very elegant, but it makes clear that there is no magic. What do you think of this?

[jmrog]

Thanks for opening this PR. I have to admit I'm not a fan of the way this complicates the API. Let me think a bit more if there is a different way.

Yeah, it does complicate the API a bit. I'm inclined to think it doesn't complicate things too much, though, especially given the payoff: the only change surfaced to the library user is that you can, if you wish, provide an optional callback that can be used to set up the conditions under which a cancel/rejection is triggered in the legacy API. The callback just sets the rejectionHandler and then returns a method that will be called on "cleanup" (i.e., when success occurs, or when the rejection condition is hit). This is a bit analogous to React's useEffect hook or React Router's history.listen API, so there's something like "prior art" for it that people may be familiar with. The payoff is that you can, if you wish, completely configure how rejection is both triggered and handled for the legacy API; fewer need-to-fix bug reports on browser-fs-access and more control for the developer (but it's opt-in; you don't need to deal with this part of the API at all).

I should've included the example of how it would work here, rather than just in the issue comments for #41, so I'm dropping the example here just for reference (note that I've removed the comments this time, in case that made it look more complicated than it is):

const file = await fileOpen({
  setupLegacyCleanupAndRejection: (rejectionHandler) => {
    const timeoutId = setTimeout(rejectionHandler, 10000);
    return (reject) => {
      clearTimeout(timeoutId);
      if (reject) {
        reject('My error message here.');
      }
    };
  },
});

If you don't want to use the option to configure this stuff, you can still of course just do:

const file = await fileOpen();

I had more something in mind like the following:

import { fileOpen, supported } from 'browser-fs-access';

// … before
let file;
if (supported) {
  try {
    file = await fileOpen();
  } catch (err) {
    console.error(err);
  }
} else {
  file = await fileOpen();
}
// … after

I admit this looks not very elegant, but it makes clear that there is no magic. What do you think of this?

I don't think I understand this part. Wasn't the goal to make rejection behavior configurable, so that the user could control how/when rejection occurs (that's what I took from the last line of this comment)? The example above doesn't seem to do that anywhere, but I could be missing it. Is the example supposed to show that the library itself would handle rejection if and only if supported is true, but would otherwise not handle the rejection and instead leave the handling up to the developer? That wouldn't be enough for us (i.e., not enough to fix #41 for us), because the library would still do the rejecting immediately in Chrome over HTTP (at least with the current implementation), even if it were to then be left up to us how to handle the rejection. We need some control over when a "rejection" is triggered in the first place (or else we need the library just not to reject at all -- which is why we've temporarily reverted back to v0.13.1 of the library). EDIT: Ah, now that I look more closely, I'm wondering if perhaps the example is showing that the library will just not reject in the case where supported is false?

[tomayac]

LGTM, approval

Thank you! You have convinced me. Let's give it a try…