Add shared-brotli crate which provides a library for decoding shared …

…brotli patches.

Under the hood it's a small wrapper around brotlic-sys.

Cargo.toml

@@ -12,6 +12,7 @@ members = [
     "fauntlet",
     "klippa",
     "fuzz",
+    "shared-brotli",
 ]
 
 [workspace.package]
@@ -44,6 +45,7 @@ read-fonts = { version = "0.22.2", path = "read-fonts", default-features = false
 # shaping support
 skrifa = { version = "0.22.2", path = "skrifa", default-features = false, features = ["std"] }
 write-fonts = { version = "0.29.0", path = "write-fonts" }
+shared-brotli = { version = "0.1.0", path = "shared-brotli" }
 
 [workspace.metadata.release]
 allow-branch = ["main"]

shared-brotli/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "shared-brotli"
+version = "0.1.0"
+description = "Wrapper around brotli-sys which allows for decoding shared brotli (https://datatracker.ietf.org/doc/draft-vandevenne-shared-brotli-format/) encoded data."
+edition.workspace = true
+license.workspace = true
+repository.workspace = true
+
+[package.metadata.docs.rs]
+# To build locally:
+# RUSTDOCFLAGS="--cfg docsrs" cargo +nightly doc --all-features
+all-features = true
+
+[dependencies]
+brotlic-sys = {version = "0.2.2"}

shared-brotli/src/lib.rs

@@ -0,0 +1,241 @@
+use brotlic_sys::{
+    BrotliDecoderAttachDictionary, BrotliDecoderCreateInstance, BrotliDecoderDecompressStream,
+    BrotliDecoderDestroyInstance, BrotliDecoderResult_BROTLI_DECODER_RESULT_ERROR,
+    BrotliDecoderResult_BROTLI_DECODER_RESULT_NEEDS_MORE_INPUT,
+    BrotliDecoderResult_BROTLI_DECODER_RESULT_NEEDS_MORE_OUTPUT,
+    BrotliDecoderResult_BROTLI_DECODER_RESULT_SUCCESS,
+    BrotliSharedDictionaryType_BROTLI_SHARED_DICTIONARY_RAW, BROTLI_FALSE,
+};
+use core::ptr;
+
+#[derive(Debug, Clone, PartialEq)]
+pub enum DecodeError {
+    InitFailure,
+    InvalidStream,
+    InvalidDictionary,
+    MaxSizeExceeded,
+    ExcessInputData,
+}
+
+impl std::fmt::Display for DecodeError {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        match self {
+            DecodeError::InitFailure => write!(f, "Failed to initialize the brotli decoder."),
+            DecodeError::InvalidStream => {
+                write!(f, "Brotli compressed stream is invalid, decoding failed.")
+            }
+            DecodeError::InvalidDictionary => write!(f, "Shared dictionary format is invalid."),
+            DecodeError::MaxSizeExceeded => write!(f, "Decompressed size greater than maximum."),
+            DecodeError::ExcessInputData => write!(
+                f,
+                "There is unconsumed data in the input stream after decoding."
+            ),
+        }
+    }
+}
+
+impl std::error::Error for DecodeError {}
+
+/// Decodes shared brotli encoded data using the optional shared dictionary.
+///
+/// The shared dictionary is a raw LZ77 style dictionary, see:
+/// https://datatracker.ietf.org/doc/html/draft-vandevenne-shared-brotli-format-11#section-3.2
+///
+/// Will fail if the decoded result will be greater then max_uncompressed_length. Any excess data
+/// in encoded after the encoded stream finishes is also considered an error.
+pub fn shared_brotli_decode(
+    encoded: &[u8],
+    shared_dictionary: Option<&[u8]>,
+    max_uncompressed_length: u32,
+) -> Result<Vec<u8>, DecodeError> {
+    let decoder = unsafe { BrotliDecoderCreateInstance(None, None, ptr::null_mut()) };
+    if decoder.is_null() {
+        return Err(DecodeError::InitFailure);
+    }
+
+    if let Some(shared_dictionary) = shared_dictionary {
+        if unsafe {
+            BrotliDecoderAttachDictionary(
+                decoder,
+                BrotliSharedDictionaryType_BROTLI_SHARED_DICTIONARY_RAW,
+                shared_dictionary.len(),
+                shared_dictionary.as_ptr(),
+            )
+        } == BROTLI_FALSE
+        {
+            unsafe {
+                BrotliDecoderDestroyInstance(decoder);
+            }
+            return Err(DecodeError::InvalidDictionary);
+        }
+    }
+
+    let mut sink = vec![0u8; max_uncompressed_length as usize];
+
+    let mut next_in = encoded.as_ptr();
+    let mut available_in = encoded.len();
+    let mut next_out = sink.as_mut_ptr();
+    let mut available_out = sink.len();
+    let mut total_out = 0;
+
+    let mut error: Option<DecodeError> = None;
+    loop {
+        let result = unsafe {
+            BrotliDecoderDecompressStream(
+                decoder,
+                &mut available_in,
+                &mut next_in,
+                &mut available_out,
+                &mut next_out,
+                &mut total_out,
+            )
+        };
+
+        #[allow(non_upper_case_globals)]
+        match result {
+            BrotliDecoderResult_BROTLI_DECODER_RESULT_SUCCESS => break,
+            BrotliDecoderResult_BROTLI_DECODER_RESULT_ERROR => {
+                error = Some(DecodeError::InvalidStream);
+                break;
+            }
+            BrotliDecoderResult_BROTLI_DECODER_RESULT_NEEDS_MORE_INPUT if available_in == 0 => {
+                // Needs more input and none is available.
+                error = Some(DecodeError::InvalidStream);
+                break;
+            }
+            BrotliDecoderResult_BROTLI_DECODER_RESULT_NEEDS_MORE_OUTPUT if available_out == 0 => {
+                // Needs more output space, but none is available.
+                error = Some(DecodeError::MaxSizeExceeded);
+                break;
+            }
+            _ => continue,
+        }
+    }
+
+    unsafe {
+        BrotliDecoderDestroyInstance(decoder);
+    }
+    if let Some(error) = error {
+        return Err(error);
+    }
+
+    if available_in > 0 {
+        // There's is data left in the input stream, which is not allowed
+        return Err(DecodeError::ExcessInputData);
+    }
+
+    if total_out > sink.len() {
+        return Err(DecodeError::MaxSizeExceeded);
+    }
+
+    sink.resize(total_out, 0);
+
+    Ok(sink)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const TARGET: &[u8] = "hijkabcdeflmnohijkabcdeflmno\n".as_bytes();
+    const BASE: &str = "abcdef\n";
+
+    // This patch was manually generated with a brotli encoder (https://github.com/google/brotli)
+    // uncompressed = TARGET
+    // dict = BASE
+    const SHARED_DICT_PATCH: [u8; 23] = [
+        0xa1, 0xe0, 0x00, 0xc0, 0x2f, 0x3a, 0x38, 0xf4, 0x01, 0xd1, 0xaf, 0x54, 0x84, 0x14, 0x71,
+        0x2a, 0x80, 0x04, 0xa2, 0x1c, 0xd3, 0xdd, 0x07,
+    ];
+
+    // This patch was manually generated with a brotli encoder (https://github.com/google/brotli)
+    // uncompressed = TARGET
+    const NO_DICT_PATCH: [u8; 26] = [
+        0xa1, 0xe0, 0x00, 0xc0, 0x2f, 0x96, 0x1c, 0xf3, 0x03, 0xb1, 0xcf, 0x45, 0x95, 0x22, 0x4a,
+        0xc5, 0x03, 0x21, 0xb2, 0x9a, 0x58, 0xd4, 0x7c, 0xf6, 0x1e, 0x00u8,
+    ];
+
+    // TODO move input streams to constants.
+
+    #[test]
+    fn brotli_decode_with_shared_dict() {
+        assert_eq!(
+            Ok(TARGET.to_vec()),
+            shared_brotli_decode(
+                &SHARED_DICT_PATCH,
+                Some(BASE.as_bytes()),
+                TARGET.len() as u32,
+            )
+        );
+    }
+
+    #[test]
+    fn brotli_decode_without_shared_dict() {
+        let base = "".as_bytes();
+
+        assert_eq!(
+            Ok(TARGET.to_vec()),
+            shared_brotli_decode(&NO_DICT_PATCH, None, TARGET.len() as u32)
+        );
+
+        // Check that empty base is handled the same as no base.
+        assert_eq!(
+            Ok(TARGET.to_vec()),
+            shared_brotli_decode(&NO_DICT_PATCH, Some(base), TARGET.len() as u32)
+        );
+    }
+
+    #[test]
+    fn brotli_decode_too_little_output() {
+        assert_eq!(
+            Err(DecodeError::MaxSizeExceeded),
+            shared_brotli_decode(
+                &SHARED_DICT_PATCH,
+                Some(BASE.as_bytes()),
+                (TARGET.len() - 1) as u32
+            )
+        );
+    }
+
+    #[test]
+    fn brotli_decode_excess_output() {
+        assert_eq!(
+            Ok(TARGET.to_vec()),
+            shared_brotli_decode(
+                &SHARED_DICT_PATCH,
+                Some(BASE.as_bytes()),
+                (TARGET.len() + 1) as u32,
+            )
+        );
+    }
+
+    #[test]
+    fn brotli_decode_too_much_input() {
+        let mut patch: Vec<u8> = NO_DICT_PATCH.to_vec();
+        patch.push(0u8);
+
+        assert_eq!(
+            Err(DecodeError::ExcessInputData),
+            shared_brotli_decode(&patch, None, TARGET.len() as u32)
+        );
+    }
+
+    #[test]
+    fn brotli_decode_input_missing() {
+        // Check what happens if input stream is missing some trailing bytes
+        let patch: Vec<u8> = NO_DICT_PATCH[..NO_DICT_PATCH.len() - 1].to_vec();
+        assert_eq!(
+            Err(DecodeError::InvalidStream),
+            shared_brotli_decode(&patch, None, TARGET.len() as u32)
+        );
+    }
+
+    #[test]
+    fn brotli_decode_invalid() {
+        let patch = [0xFF, 0xFF, 0xFFu8];
+        assert_eq!(
+            Err(DecodeError::InvalidStream),
+            shared_brotli_decode(&patch, None, 10)
+        );
+    }
+}