One of the frequent emails that I get about Infinite Mac is “I’ve been copying over these files to every mac I’ve owned for the past 20 (or 30 or 40) years, how can I load them into your site?” While there’s been a “The Outside World” drive from the very beginning, all it can do is a best-effort import/export using available browser APIs. Classic Mac OS used resource forks for structured data and stored additional metadata in the file system (where it belongs). Modern macOS still supports all of this, but unfortunately none of that data is visible to web apps – all they can read is the “data fork” of the file (i.e. its raw contents).

This is a long-standing issue – once Macintosh files started to be distributed over the Internet in the mid-90s, they were usually in a container format like MacBinary or StuffIt to preserve this extra data. While StuffIt is still around, having to download a separate program goes against the ethos of Infinite Mac being as easy to use as possible. After some investigation, I remembered that .zip archives created by modern macOS preserve resource forks ("modern" in this case being relative – this feature dates back to 10.3). Specifically they create a parallel __MACOSX directory structure that has metadata and resource forks in an AppleDouble file.

A while back I added detection of such .zip files, which helped with getting data in. More recently, I also switched the .zip files that Infinite Mac generates when exporting to also use this convention, allowing the Finder to expand and reconstruct the full contents. I also wanted to make this feature somewhat discoverable, and I chanced upon an exemption to the “browsers can’t see resource forks” limitation that I mentioned above – when dragging a whole folder into the window it’s possible to read a file’s resource fork via a magic file/..namedfork/rsrc path (sadly there’s no equivalent for the metadata). I used this to show a notification to remind users of the .zip capabilities.

This video shows these features working together – an old app of mine starts out on the modern macOS host – it can be imported, its vers resource edited, and then exported back out (miraculously today’s Finder still displays information based on it).

Odds and Ends

Using the same notification mechanism, I also made the need to click into the window for emulators that use relative mouse movements (DingsuPPC, PearPC, Previous) more discoverable. Thanks to this tip I figured out how to (ab)use GitHub releases to store large files, letting me finally share the Mac OS X disk images I’ve been using. Finally I fixed some longstanding issues with audio playback in some browsers and stuck modifier keys.