Hacker News Reader

I hear you there. I'm more thinking someone probably hard coded txt file extension somewhere so something is likely to fall apart in simply handling that file.

Is it? Seems superior to arbitrary magic numbers or headers, and God forbid full naive parsing, in most ways.

I doubt there is any solution that is both robust and simple. In a sense, it is the same problem as that which ad blockers are attempting to solve.

Whats wrong with storing and delivering the intended content type as metadata, whether thats headers or filesystem metadata like in Mac OS X?

Transmitting in-band (headers) seems ripe for arbitrary complexity. Someone out there would write a Turing-complete header DSL. And then someone else would write an incompatible alternative implementation.

At least file extension is limited and externally visible (and thus accountable) to third party behavior, which should limit the worst complexity excesses.

Is filesystem metadata actually different (theoretically) from extension? Or just data in a different format?

Extension seems a nice balance between simplicity / brevity and utility, albeit as a hint, not a commandment.

Fun stuff like embedding data into jpgs or pngs.