kacrab-protocol 0.1.1

//! Zstandard codec (`zstd` crate).
//!
//! The module path `crate::compression::zstd` shadows the external `zstd`
//! crate inside this file — the codec is reached via a fully-qualified
//! `::zstd::...` path.

use super::{Compression, CompressionError, CompressionErrorKind, Result};

const DEFAULT_ZSTD_LEVEL: i32 = 3;

/// Compress `payload` at the given level (`None` -> codec default `3`, range `1..=22`).
pub fn compress_with_level(payload: &[u8], level: Option<i32>) -> Result<Vec<u8>> {
    let lvl = level.unwrap_or(DEFAULT_ZSTD_LEVEL);
    ::zstd::bulk::compress(payload, lvl).map_err(|e| encode_err(e.to_string()))
}

/// Decompress `payload`, bounded by [`super::MAX_DECOMPRESSED_LEN`].
pub fn decompress(payload: &[u8]) -> Result<Vec<u8>> {
    decompress_bounded(payload, super::MAX_DECOMPRESSED_LEN)
}

/// Decompress `payload`, refusing to produce more than `max_len` bytes —
/// zstd frames can claim enormous content sizes, so an unbounded decode is a
/// decompression bomb.
pub fn decompress_bounded(payload: &[u8], max_len: usize) -> Result<Vec<u8>> {
    let decoder =
        ::zstd::stream::read::Decoder::new(payload).map_err(|e| decode_err(e.to_string()))?;
    super::read_to_end_bounded(decoder, max_len, Compression::Zstd)
}

const fn encode_err(message: String) -> CompressionError {
    CompressionError::new(
        Compression::Zstd,
        CompressionErrorKind::EncodeFailed { message },
    )
}

const fn decode_err(message: String) -> CompressionError {
    CompressionError::new(
        Compression::Zstd,
        CompressionErrorKind::DecodeFailed { message },
    )
}

#[cfg(test)]
mod tests {
    use super::{super::CompressionErrorKind, compress_with_level, decompress, decompress_bounded};

    #[test]
    fn decompress_bounded_rejects_a_decompression_bomb() {
        let payload = vec![0u8; 4096];
        let compressed = compress_with_level(&payload, None).unwrap();

        let err = decompress_bounded(&compressed, 64).unwrap_err();
        assert!(
            matches!(
                err.kind,
                CompressionErrorKind::DecompressedTooLarge { limit: 64 }
            ),
            "expected DecompressedTooLarge, got {:?}",
            err.kind
        );
    }

    #[test]
    fn decompress_bounded_allows_output_at_exactly_the_limit() {
        let payload = vec![0u8; 4096];
        let compressed = compress_with_level(&payload, None).unwrap();

        assert_eq!(decompress_bounded(&compressed, 4096).unwrap(), payload);
        assert_eq!(decompress(&compressed).unwrap(), payload);
    }
}