Internal compression is required and faulty directories cause panic

[tdewolff]

The internal compression seems to be required to be Gzip, but the spec says it's optional?

Besides, this package could use some proper error checking. For faulty directories that point to something that is not Gzip encoded, the Gzip decoder isn't checked for errors and later on causes a nil reference panic. The verify functionality would be very useful if it'd do a lot more checking with helpful messages.

[bdon]

The spec is future-proof relative to this implementation. It hasn't been a priority to implement Brotli or Zstd compression yet, because many use cases of PMTiles are intended to be decoded in the browser, and Gzip has a polyfill for the missing DecompressionStream browser feature.

We may be at the point where the vast majority of browsers have DecompressionStream('br') compared to a few years ago, so it's worth doing some benchmarking to see what the gain is. Or we could just hold out until DecompressionStream('zstd') is everywhere.

CanIUse: https://caniuse.com/?search=DecompressionStream

[tdewolff]

That's OK, but it doesn't support no compression either, and doesn't check. It just blindly decodes with Gzip and doesn't even check the error. In general, I would expect the verify functionality to do more checking to be useful.

[bdon]

Sorry, you're right, that's an oversight on my part - the go program doesn't support the no-compression option right now. It shouldn't be too difficult to add.