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aklomp
Base64url support?
Hi, aklomp i was searching for a nice base64 library and ended here but my low level C is a bit rusty, so i would like to ask you if this library could be used to handle base64URL variant? or at least some tips on how to add it?(i would post patches back if i made it)
Thanks you very much for your time
Hi! Currently this library only supports the standard Base64 alphabet.
It would probably be feasible, but difficult, to add support for additional alphabets. It could be non-trivial to add that support to the SIMD codecs, because they do arithmetic on the raw character values. Here's an encoder example and here's a decoder.
My intuition is that it would probably be possible to find an arithmetic-based solution that works with the alternative alphabet since the differences are small. However, it would require duplicating a lot of code, and adding some sort of user-visible flag to the API to indicate which alphabet to use. Maybe it could be a compile-time flag to not incur runtime penalties or complexities.
since the differences are small. However, it would require duplicating a lot of code
Yeah, it's possible. I've done this for C#, but as @aklomp says there's a lot of duplication and the nice tricks applied to standard base64 don't work so nice with base64Url. Especially on the decoding side for input-validation.
Thank you very much for your time.
Yeah, i see your point and probably will be easier to handle base64url to base64 translation externally in the c++17 side of thing since the chunk are small and this library already give me a nice speed up so i have some wiggle room.
There's an example of translation in https://github.com/mayeut/pybase64/blob/1e2f3ec63549085f06b3118671818edb969c1e3d/pybase64/_pybase64.c#L71
The translation is done in-place for encoding. The translation is done out-of-place for decoding (warning, the translation is not safe here to mimic python behavior, c.f. inline comment)
well for now a very simple std implementation seems to do the job with very small assembly output
https://godbolt.org/z/8J2zKG
What is being asked is to just accept base64url format when decoding. Replacing characters 62 and 63 is best done at https://github.com/aklomp/base64/blob/master/lib/tables/tables.c Supporting encoding would require more work...
