wuff 0.2.7

Pure-rust WOFF and WOFF2 font decoding
Documentation 
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//! Built-in WOFF2 Brotli decompression, backed by `brotli-decompressor`.
//!
//! This module is only compiled when the `brotli` feature is enabled. It plugs the
//! `brotli-decompressor` crate into [`decompress_woff2_with_custom_brotli`](crate::decompress_woff2_with_custom_brotli)
//! using an `alloc`-backed allocator, so it works on `no_std` targets (with a global allocator).

use alloc::{boxed::Box, vec, vec::Vec};
use core::error::Error;

use crate::WuffErr;
use crate::decompress_woff2_with_custom_brotli;

/// A `Box<[T]>` wrapper implementing the allocation traits that `brotli-decompressor`
/// requires, so the decoder can allocate through the global allocator (`alloc`) rather
/// than depending on `std`. This is the no_std equivalent of the crate's built-in
/// `StandardAlloc` (which is only available behind its `std` feature).
struct Rebox<T>(Box<[T]>);

impl<T> Default for Rebox<T> {
    fn default() -> Self {
        Rebox(Vec::new().into_boxed_slice())
    }
}

impl<T> brotli_decompressor::SliceWrapper<T> for Rebox<T> {
    fn slice(&self) -> &[T] {
        &self.0
    }
}

impl<T> brotli_decompressor::SliceWrapperMut<T> for Rebox<T> {
    fn slice_mut(&mut self) -> &mut [T] {
        &mut self.0
    }
}

/// Zero-sized allocator handing out `Rebox` cells backed by the global allocator.
struct HeapAlloc;

impl<T: Clone + Default> brotli_decompressor::Allocator<T> for HeapAlloc {
    type AllocatedMemory = Rebox<T>;
    fn alloc_cell(&mut self, len: usize) -> Rebox<T> {
        Rebox(vec![T::default(); len].into_boxed_slice())
    }
    fn free_cell(&mut self, _data: Rebox<T>) {}
}

fn decompress_brotli(
    compressed_data: &[u8],
    expected_size: usize,
) -> Result<Vec<u8>, Box<dyn Error>> {
    use brotli_decompressor::{BrotliDecompressStream, BrotliResult, BrotliState};

    // Allocate the output buffer once, up front, at exactly the (trusted) expected size and
    // decompress directly into it. `BrotliDecompressStream` never writes past the end of the
    // slice, so `expected_size` is a HARD upper bound on the output: a stream that would expand
    // further stops with `NeedsMoreOutput` rather than driving an unbounded allocation. This
    // mirrors the reference C++ decoder, which decompresses into a fixed-size buffer and rejects
    // the result unless the decoded size matches exactly.
    let mut output = vec![0u8; expected_size];
    let mut available_in = compressed_data.len();
    let mut input_offset = 0usize;
    let mut available_out = output.len();
    let mut output_offset = 0usize;
    let mut total_out = 0usize;
    let mut state = BrotliState::new(HeapAlloc, HeapAlloc, HeapAlloc);

    let result = BrotliDecompressStream(
        &mut available_in,
        &mut input_offset,
        compressed_data,
        &mut available_out,
        &mut output_offset,
        &mut output,
        &mut total_out,
        &mut state,
    );

    // Require a clean end-of-stream producing exactly `expected_size` bytes. Any trailing WOFF2
    // padding bytes (up to 3, counted in `totalCompressedSize`) are harmless: the decoder reports
    // success at end-of-stream and simply leaves them unconsumed in the input.
    if !matches!(result, BrotliResult::ResultSuccess) || output_offset != expected_size {
        return Err(Box::new(WuffErr::GenericError));
    }

    Ok(output)
}

/// Decompress a WOFF2 file using the built-in brotli decompressor
pub fn decompress_woff2(raw_woff_data: &[u8]) -> Result<Vec<u8>, WuffErr> {
    decompress_woff2_with_custom_brotli(raw_woff_data, &mut decompress_brotli)
}