Endian-Aware, Seekable File Reader

[stable jungle]

I'm trying to write a library in Zig that reads file formats designed for the Xbox 360, which use both big-endian and little-endian values.
Ideally, I want to be able to seek the reader, change the endianness of the reader, and read byte-by-byte like so:

reader.seekTo(0);
var foo = reader.readByte();
reader.setEndian(Endian.big);
var bar = reader.readInt(u32);
// etc.

References:

• Velocity FileIO class
• Example usage of Velocity FileIO
• Xenia byte order wrapper
• Example of Xenia IO

If there's a better way, it would be nice to see an example that can at least handle two of the three. Doing it in a completely different way might be kind of hard to manage.
Searching the docs, I've found that I can either...

• Use the File type, call seekTo on that, and read all the bytes of the file to a buffer array. This doesn't appear to expose a way to set the endian or read other types, leaving me to do all of that manually.
• Or create a Reader from that File and call readByte or readInt(ReturnType, Endian, usize) on that. But this doesn't appear to expose seekTo.

Related: https://discord.com/channels/605571803288698900/1167211222911942666
I may be wrong but this didn't seem to solve my issue entirely either.

[silent furnace]

readInt takes an endianness parameter :) oops you mentioned this lol

you seek on the file and then read from the associated reader

[stable jungle]

And that doesn't just create an entirely new reader rather than return the one that got seeked? My laptop just died but I could swear I looked for an accessible reader member and only found a factory function.

[silent furnace]

readers are attached to the file, they don't create like a new read head or anything

it's just a wrapper around the file's read function

[stable jungle]

ok cool

So just so I have it for later...

file.seekTo(0);
const reader = File.reader(file);
var foo = reader.readByte();
var bar = reader.readInt(u32, Endian.big, 4);

That should function exactly as I described in the original post?

I could write yet another wrapper around that to reduce the repetition, similar to Velocity's FileIO class. But that might just work.

[silent furnace]

mhm

tho u can just write .big, don't need to write Endian cus the type is already known :)

[stable jungle]

Oh I'm still not sure what needs to be qualified in this lang. :p

[silent furnace]

generally, if there's a known type, it can infer things :)

the only exception is errors i guess? but those are always error.Whatever so yknow

[civic beacon]

the solution i went with for this sort of thing is to take a std.io.StreamSource and then pass around the stream_source.reader() and stream_source.seekable_stream() where needed. For endianness, you'd just specify the endianess in your readInt calls

if you want buffering, you'll need a custom solution to keep the reader and seekable stream synced (here's what i came up with)

[stable jungle]

I still haven't been able to test it, but I think squirl's approach works best

[civic beacon]

it's basically the same approach, StreamSource just makes sources other than File more convenient

[stable jungle]

Neat