[Feature] Local images not accessible from WKWebView

[brunnobraga]

Please help prevent duplicate issues before submitting a new one:

• I've searched other open/closed issues for duplicates before opening up this new issue.
  I've looked into Can not load local image and link to local .md file #40 , but it covers only local images bundled with the app.

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What did you do?

I'm using DownView(frame: .zero, markdownString: markdown, templateBundle: bundle) and in this case bundle points to a folder in my app's documents directory. The markdown files and associated images are downloaded to this location during runtime, could be refreshed and must be kept for offline use (the template assets might be dynamic in the future too, but its not at the moment).

What did you expect to happen?

DownView renders using the template and following referenced style, JS and images.

What happened instead?

It renders the content of template file with inserted markdown content, but any content linked on index.html with local references does not load (eg. css, js, images).

Using Safari's web inspector to check on WKWebView I can see this on console:
Failed to load resource: The operation couldn’t be completed. (kCFErrorDomainCFNetwork error 1.)
Which after some research I found to be a permission issue.

I searched deeper and I think this traces down to use of loadHTMLString(_:baseURL:). baseURL points to the correct place, but in this case WKWebView doesn't have access to it by default. The alternative would be to use loadFileURL(_:allowingReadAccessTo:) which can provide read access to a path.

I wasn't sure if I should file this under feature request or a bug.

[iwasrobbed-ks]

Feel free to open a pull request as long as it's backwards compatible with the existing API

[brunnobga]

Created #200 for this.