src/storage/lib/delivery_blob/src/compression.rs

// Copyright 2023 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

//! Implementation of chunked-compression library in Rust. Archives can be created by making a new
//! [`ChunkedArchive`] and serializing/writing it. An archive's header can be verified and seek
//! table decoded using [`decode_archive`].

use {
    crc::Hasher32,
    itertools::Itertools,
    rayon::prelude::*,
    std::ops::Range,
    thiserror::Error,
    zerocopy::{
        byteorder::{LE, U16, U32, U64},
        AsBytes, FromBytes, FromZeros, NoCell, Ref, Unaligned,
    },
};

#[derive(Debug, Error)]
pub enum ChunkedArchiveError {
    #[error("Invalid or unsupported archive version.")]
    InvalidVersion,

    #[error("Archive header has incorrect magic.")]
    BadMagic,

    #[error("Integrity checks failed (e.g. incorrect CRC, inconsistent header fields).")]
    IntegrityError,

    #[error("Value is out of range or cannot be represented in specified type.")]
    OutOfRange,

    #[error("Error when decompressing chunk: `{0:?}`.")]
    DecompressionError(std::io::Error),
}

/// Validated chunk information from an archive. Compressed ranges are relative to the start of
/// compressed data (i.e. they start after the header and seek table).
#[derive(Clone, Debug)]
pub struct ChunkInfo {
    pub decompressed_range: Range<usize>,
    pub compressed_range: Range<usize>,
}

/// Decode a chunked archive header. Returns validated seek table and start of chunk data. Ranges
/// in resulting chunks are relative to start of returned slice. Returns `Ok(None)` if `data` is not
/// large enough to decode the archive header & seek table.
pub fn decode_archive(
    data: &[u8],
    archive_length: usize,
) -> Result<Option<(Vec<ChunkInfo>, /*archive_data*/ &[u8])>, ChunkedArchiveError> {
    match Ref::<_, ChunkedArchiveHeader>::new_unaligned_from_prefix(data) {
        Some((header, data)) => header.decode_seek_table(data, archive_length as u64),
        None => Ok(None), // Not enough data.
    }
}

impl ChunkInfo {
    fn from_entry(
        entry: &SeekTableEntry,
        header_length: usize,
    ) -> Result<Self, ChunkedArchiveError> {
        let decompressed_start = entry.decompressed_offset.get() as usize;
        let decompressed_size = entry.decompressed_size.get() as usize;
        let decompressed_range = decompressed_start
            ..decompressed_start
                .checked_add(decompressed_size)
                .ok_or(ChunkedArchiveError::OutOfRange)?;

        let compressed_offset = entry.compressed_offset.get() as usize;
        let compressed_start = compressed_offset
            .checked_sub(header_length)
            .ok_or(ChunkedArchiveError::IntegrityError)?;
        let compressed_size = entry.compressed_size.get() as usize;
        let compressed_range = compressed_start
            ..compressed_start
                .checked_add(compressed_size)
                .ok_or(ChunkedArchiveError::OutOfRange)?;

        Ok(Self { decompressed_range, compressed_range })
    }
}

/// Chunked archive header.
#[derive(AsBytes, FromZeros, FromBytes, NoCell, Unaligned, Clone, Copy, Debug)]
#[repr(C)]
struct ChunkedArchiveHeader {
    magic: [u8; 8],
    version: U16<LE>,
    reserved_0: U16<LE>,
    num_entries: U32<LE>,
    checksum: U32<LE>,
    reserved_1: U32<LE>,
    reserved_2: U64<LE>,
}

/// Chunked archive seek table entry.
#[derive(AsBytes, FromZeros, FromBytes, NoCell, Unaligned, Clone, Copy, Debug)]
#[repr(C)]
struct SeekTableEntry {
    decompressed_offset: U64<LE>,
    decompressed_size: U64<LE>,
    compressed_offset: U64<LE>,
    compressed_size: U64<LE>,
}

impl ChunkedArchiveHeader {
    const CHUNKED_ARCHIVE_MAGIC: [u8; 8] = [0x46, 0x9b, 0x78, 0xef, 0x0f, 0xd0, 0xb2, 0x03];
    const CHUNKED_ARCHIVE_VERSION: u16 = 2;
    const CHUNKED_ARCHIVE_MAX_FRAMES: usize = 1023;
    const CHUNKED_ARCHIVE_CHECKSUM_OFFSET: usize = 16;

    fn new(seek_table: &[SeekTableEntry]) -> Result<Self, ChunkedArchiveError> {
        let header: ChunkedArchiveHeader = Self {
            magic: Self::CHUNKED_ARCHIVE_MAGIC,
            version: Self::CHUNKED_ARCHIVE_VERSION.into(),
            reserved_0: 0.into(),
            num_entries: TryInto::<u32>::try_into(seek_table.len())
                .or(Err(ChunkedArchiveError::OutOfRange))?
                .into(),
            checksum: 0.into(), // `checksum` is calculated below.
            reserved_1: 0.into(),
            reserved_2: 0.into(),
        };
        Ok(Self { checksum: header.checksum(seek_table).into(), ..header })
    }

    /// Calculate the checksum of the header + all seek table entries.
    fn checksum(&self, entries: &[SeekTableEntry]) -> u32 {
        let mut first_crc = crc::crc32::Digest::new(crc::crc32::IEEE);
        first_crc.write(&self.as_bytes()[..Self::CHUNKED_ARCHIVE_CHECKSUM_OFFSET]);
        let mut crc = crc::crc32::Digest::new_with_initial(crc::crc32::IEEE, first_crc.sum32());
        crc.write(
            &self.as_bytes()
                [Self::CHUNKED_ARCHIVE_CHECKSUM_OFFSET + self.checksum.as_bytes().len()..],
        );
        crc.write(entries.as_bytes());
        crc.sum32()
    }

    /// Calculate the total header length of an archive *including* all seek table entries.
    fn header_length(num_entries: usize) -> usize {
        std::mem::size_of::<ChunkedArchiveHeader>()
            + (std::mem::size_of::<SeekTableEntry>() * num_entries)
    }

    /// Decode seek table for this archive. Returns validated seek table and start of chunk data.
    /// `data` must point to the start of the seek table. Returns `Ok(None)` if `data` is not large
    /// enough to decode all seek table entries.
    fn decode_seek_table(
        self,
        data: &[u8],
        archive_length: u64,
    ) -> Result<Option<(Vec<ChunkInfo>, /*chunk_data*/ &[u8])>, ChunkedArchiveError> {
        // Deserialize seek table.
        let num_entries = self.num_entries.get() as usize;
        let Some((entries, chunk_data)) =
            Ref::<_, [SeekTableEntry]>::new_slice_unaligned_from_prefix(data, num_entries)
        else {
            return Ok(None);
        };
        let entries: &[SeekTableEntry] = entries.into_slice();

        // Validate archive header.
        if self.magic != Self::CHUNKED_ARCHIVE_MAGIC {
            return Err(ChunkedArchiveError::BadMagic);
        }
        if self.version.get() != Self::CHUNKED_ARCHIVE_VERSION {
            return Err(ChunkedArchiveError::InvalidVersion);
        }
        if self.checksum.get() != self.checksum(entries) {
            return Err(ChunkedArchiveError::IntegrityError);
        }
        if entries.len() > Self::CHUNKED_ARCHIVE_MAX_FRAMES {
            return Err(ChunkedArchiveError::IntegrityError);
        }

        // Validate seek table using invariants I0 through I5.

        // I0: The first seek table entry, if any, must have decompressed offset 0.
        if !entries.is_empty() && entries[0].decompressed_offset.get() != 0 {
            return Err(ChunkedArchiveError::IntegrityError);
        }

        // I1: The compressed offsets of all seek table entries must not overlap with the header.
        let header_length = Self::header_length(entries.len());
        if entries.iter().any(|entry| entry.compressed_offset.get() < header_length as u64) {
            return Err(ChunkedArchiveError::IntegrityError);
        }

        // I2: Each entry's decompressed offset must be equal to the end of the previous frame
        //     (i.e. to the previous frame's decompressed offset + length).
        for (prev, curr) in entries.iter().tuple_windows() {
            if (prev.decompressed_offset.get() + prev.decompressed_size.get())
                != curr.decompressed_offset.get()
            {
                return Err(ChunkedArchiveError::IntegrityError);
            }
        }

        // I3: Each entry's compressed offset must be greater than or equal to the end of the
        //     previous frame (i.e. to the previous frame's compressed offset + length).
        for (prev, curr) in entries.iter().tuple_windows() {
            if (prev.compressed_offset.get() + prev.compressed_size.get())
                > curr.compressed_offset.get()
            {
                return Err(ChunkedArchiveError::IntegrityError);
            }
        }

        // I4: Each entry must have a non-zero decompressed and compressed length.
        for entry in entries.iter() {
            if entry.decompressed_size.get() == 0 || entry.compressed_size.get() == 0 {
                return Err(ChunkedArchiveError::IntegrityError);
            }
        }

        // I5: Data referenced by each entry must fit within the specified file size.
        for entry in entries.iter() {
            let compressed_end = entry.compressed_offset.get() + entry.compressed_size.get();
            if compressed_end > archive_length {
                return Err(ChunkedArchiveError::IntegrityError);
            }
        }

        let seek_table = entries
            .into_iter()
            .map(|entry| ChunkInfo::from_entry(entry, header_length))
            .try_collect()?;
        Ok(Some((seek_table, chunk_data)))
    }
}

/// In-memory representation of a compressed chunk.
pub struct CompressedChunk {
    /// Compressed data for this chunk.
    pub compressed_data: Vec<u8>,
    /// Size of this chunk when decompressed.
    pub decompressed_size: usize,
}

/// In-memory representation of a compressed chunked archive.
pub struct ChunkedArchive {
    /// Chunks this archive contains, in order. Right now we only allow creating archives with
    /// contiguous compressed and decompressed space.
    chunks: Vec<CompressedChunk>,
    /// Size used to chunk input when creating this archive. Last chunk may be smaller than this amount.
    chunk_size: usize,
}

impl ChunkedArchive {
    const MAX_CHUNKS: usize = ChunkedArchiveHeader::CHUNKED_ARCHIVE_MAX_FRAMES;
    const TARGET_CHUNK_SIZE: usize = 32 * 1024;
    const COMPRESSION_LEVEL: i32 = 14;

    /// Create a ChunkedArchive for `data` compressing each chunk in parallel. This function uses
    /// the `rayon` crate for parallelism. By default compression happens in the global thread pool,
    /// but this function can also be executed within a locally scoped pool.
    pub fn new(data: &[u8], chunk_alignment: usize) -> Result<Self, ChunkedArchiveError> {
        let chunk_size = ChunkedArchive::chunk_size_for(data.len(), chunk_alignment);
        let mut chunks: Vec<Result<CompressedChunk, ChunkedArchiveError>> = vec![];
        data.par_chunks(chunk_size)
            .map(|chunk| {
                // Creating and destroying zstd::bulk::Compressor objects is expensive. A single
                // `Compressor` is created for each `rayon` thread and is reused across chunks.
                thread_local! {
                    static COMPRESSOR: std::cell::RefCell<zstd::bulk::Compressor<'static>> =
                        std::cell::RefCell::new({
                            let mut compressor =
                                zstd::bulk::Compressor::new(ChunkedArchive::COMPRESSION_LEVEL)
                                    .unwrap();
                            compressor
                                .set_parameter(zstd::zstd_safe::CParameter::ChecksumFlag(true))
                                .unwrap();
                            compressor
                        });
                }
                let compressed_data = COMPRESSOR.with(|compressor| {
                    let mut compressor = compressor.borrow_mut();
                    compressor.compress(chunk).map_err(ChunkedArchiveError::DecompressionError)
                })?;
                Ok(CompressedChunk { compressed_data, decompressed_size: chunk.len() })
            })
            .collect_into_vec(&mut chunks);
        let chunks: Vec<_> = chunks.into_iter().try_collect()?;
        Ok(ChunkedArchive { chunks, chunk_size })
    }

    /// Accessor for compressed chunk data.
    pub fn chunks(&self) -> &Vec<CompressedChunk> {
        &self.chunks
    }

    /// The chunk size calculated for this archive during compression. Represents how input data
    /// was chunked for compression. Note that the final chunk may be smaller than this amount
    /// when decompressed.
    pub fn chunk_size(&self) -> usize {
        self.chunk_size
    }

    /// Sum of sizes of all compressed chunks.
    pub fn compressed_data_size(&self) -> usize {
        self.chunks.iter().map(|chunk| chunk.compressed_data.len()).sum()
    }

    /// Total size of the archive in bytes.
    pub fn serialized_size(&self) -> usize {
        ChunkedArchiveHeader::header_length(self.chunks.len()) + self.compressed_data_size()
    }

    /// Write the archive to `writer`.
    pub fn write(self, mut writer: impl std::io::Write) -> Result<(), std::io::Error> {
        let seek_table = self.make_seek_table();
        let header = ChunkedArchiveHeader::new(&seek_table).unwrap();
        writer.write_all(header.as_bytes())?;
        writer.write_all(seek_table.as_slice().as_bytes())?;
        for chunk in self.chunks {
            writer.write_all(&chunk.compressed_data)?;
        }
        Ok(())
    }

    /// Calculate how large chunks must be for a given uncompressed buffer.
    fn chunk_size_for(uncompressed_length: usize, chunk_alignment: usize) -> usize {
        if uncompressed_length <= (Self::MAX_CHUNKS * Self::TARGET_CHUNK_SIZE) {
            return Self::TARGET_CHUNK_SIZE;
        }
        // TODO(https://github.com/rust-lang/rust/issues/88581): Replace with
        // `{integer}::div_ceil()` when `int_roundings` is available.
        let chunk_size =
            round_up(uncompressed_length, ChunkedArchive::MAX_CHUNKS) / ChunkedArchive::MAX_CHUNKS;
        return round_up(chunk_size, chunk_alignment);
    }

    /// Create the seek table for this archive.
    fn make_seek_table(&self) -> Vec<SeekTableEntry> {
        let header_length = ChunkedArchiveHeader::header_length(self.chunks.len());
        let mut seek_table = vec![];
        seek_table.reserve(self.chunks.len());
        let mut compressed_size: usize = 0;
        let mut decompressed_offset: usize = 0;
        for chunk in &self.chunks {
            seek_table.push(SeekTableEntry {
                decompressed_offset: (decompressed_offset as u64).into(),
                decompressed_size: (chunk.decompressed_size as u64).into(),
                compressed_offset: ((header_length + compressed_size) as u64).into(),
                compressed_size: (chunk.compressed_data.len() as u64).into(),
            });
            compressed_size += chunk.compressed_data.len();
            decompressed_offset += chunk.decompressed_size;
        }
        seek_table
    }
}

/// Streaming decompressor for chunked archives. Example:
/// ```
/// // Create a chunked archive:
/// let data: Vec<u8> = vec![3; 1024];
/// let compressed = ChunkedArchive::new(&data, /*block_size*/ 8192).serialize().unwrap();
/// // Verify the header + decode the seek table:
/// let (seek_table, archive_data) = decode_archive(&compressed, compressed.len())?.unwrap();
/// let mut decompressed: Vec<u8> = vec![];
/// let mut on_chunk = |data: &[u8]| { decompressed.extend_from_slice(data); };
/// let mut decompressor = ChunkedDecompressor(seek_table);
/// // `on_chunk` is invoked as each slice is made available. Archive can be provided as chunks.
/// decompressor.update(archive_data, &mut on_chunk);
/// assert_eq!(data.as_slice(), decompressed.as_slice());
/// ```
pub struct ChunkedDecompressor {
    seek_table: Vec<ChunkInfo>,
    buffer: Vec<u8>,
    data_written: usize,
    curr_chunk: usize,
    total_compressed_size: usize,
    decompressor: zstd::bulk::Decompressor<'static>,
    decompressed_buffer: Vec<u8>,
}

impl ChunkedDecompressor {
    /// Create a new decompressor to decode an archive from a validated seek table.
    pub fn new(seek_table: Vec<ChunkInfo>) -> Result<Self, ChunkedArchiveError> {
        let total_compressed_size =
            seek_table.last().map(|last_chunk| last_chunk.compressed_range.end).unwrap_or(0);
        let decompressed_buffer =
            vec![0u8; seek_table.first().map(|c| c.decompressed_range.len()).unwrap_or(0)];
        let decompressor = zstd::bulk::Decompressor::new()
            .map_err(|err| ChunkedArchiveError::DecompressionError(err))?;
        Ok(Self {
            seek_table,
            buffer: vec![],
            data_written: 0,
            curr_chunk: 0,
            total_compressed_size,
            decompressor,
            decompressed_buffer,
        })
    }

    pub fn seek_table(&self) -> &Vec<ChunkInfo> {
        &self.seek_table
    }

    fn finish_chunk(
        &mut self,
        data: &[u8],
        chunk_callback: &mut impl FnMut(&[u8]) -> (),
    ) -> Result<(), ChunkedArchiveError> {
        debug_assert_eq!(data.len(), self.seek_table[self.curr_chunk].compressed_range.len());
        let chunk = &self.seek_table[self.curr_chunk];
        let decompressed_size = self
            .decompressor
            .decompress_to_buffer(data, self.decompressed_buffer.as_mut_slice())
            .map_err(|err| ChunkedArchiveError::DecompressionError(err))?;
        if decompressed_size != chunk.decompressed_range.len() {
            return Err(ChunkedArchiveError::IntegrityError);
        }
        chunk_callback(&self.decompressed_buffer[..decompressed_size]);
        self.curr_chunk += 1;
        Ok(())
    }

    pub fn update(
        &mut self,
        mut data: &[u8],
        chunk_callback: &mut impl FnMut(&[u8]) -> (),
    ) -> Result<(), ChunkedArchiveError> {
        // Caller must not provide too much data.
        if self.data_written + data.len() > self.total_compressed_size {
            return Err(ChunkedArchiveError::OutOfRange);
        }
        self.data_written += data.len();

        // If we had leftover data from a previous read, append until we've filled a chunk.
        if !self.buffer.is_empty() {
            let to_read = std::cmp::min(
                data.len(),
                self.seek_table[self.curr_chunk]
                    .compressed_range
                    .len()
                    .checked_sub(self.buffer.len())
                    .unwrap(),
            );
            self.buffer.extend_from_slice(&data[..to_read]);
            if self.buffer.len() == self.seek_table[self.curr_chunk].compressed_range.len() {
                // Take self.buffer temporarily (so we don't have to split borrows).
                // That way we don't have to re-commit the pages we've already used in the buffer
                // for next time.
                let full_chunk = std::mem::take(&mut self.buffer);
                self.finish_chunk(&full_chunk[..], chunk_callback)?;
                self.buffer = full_chunk;
                // Draining the buffer will set the length to 0 but keep the capacity the same.
                self.buffer.drain(..);
            }
            data = &data[to_read..];
        }

        // Decode as many full chunks as we can.
        while !data.is_empty()
            && self.curr_chunk < self.seek_table.len()
            && self.seek_table[self.curr_chunk].compressed_range.len() <= data.len()
        {
            let len = self.seek_table[self.curr_chunk].compressed_range.len();
            self.finish_chunk(&data[..len], chunk_callback)?;
            data = &data[len..];
        }

        // Buffer the rest for the next call.
        if !data.is_empty() {
            debug_assert!(self.curr_chunk < self.seek_table.len());
            debug_assert!(self.data_written < self.total_compressed_size);
            self.buffer.extend_from_slice(data);
        }

        debug_assert!(
            self.data_written < self.total_compressed_size
                || self.curr_chunk == self.seek_table.len()
        );

        Ok(())
    }
}

/// TODO(https://github.com/rust-lang/rust/issues/88581): Replace with
/// `{integer}::checked_next_multiple_of()` when `int_roundings` is available.
fn round_up(value: usize, multiple: usize) -> usize {
    let remainder = value % multiple;
    if remainder > 0 {
        value.checked_add(multiple - remainder).unwrap()
    } else {
        value
    }
}

#[cfg(test)]
mod tests {

    use {super::*, rand::Rng, std::matches};

    const BLOCK_SIZE: usize = 8192;

    /// Create a compressed archive and ensure we can decode it as a valid archive that passes all
    /// required integrity checks.
    #[test]
    fn compress_simple() {
        let data: Vec<u8> = vec![0; 32 * 1024 * 16];
        let archive = ChunkedArchive::new(&data, BLOCK_SIZE).unwrap();
        // This data is highly compressible, so the result should be smaller than the original.
        let mut compressed: Vec<u8> = vec![];
        archive.write(&mut compressed).unwrap();
        assert!(compressed.len() <= data.len());
        // We should be able to decode and verify the archive's integrity in-place.
        assert!(decode_archive(&compressed, compressed.len()).unwrap().is_some());
    }

    /// Generate a header + seek table for verifying invariants/integrity checks.
    fn generate_archive(
        num_entries: usize,
    ) -> (ChunkedArchiveHeader, Vec<SeekTableEntry>, /*archive_length*/ u64) {
        let mut seek_table = vec![];
        seek_table.reserve(num_entries);
        let header_length = ChunkedArchiveHeader::header_length(num_entries) as u64;
        const COMPRESSED_CHUNK_SIZE: u64 = 1024;
        const DECOMPRESSED_CHUNK_SIZE: u64 = 2048;
        for n in 0..(num_entries as u64) {
            seek_table.push(SeekTableEntry {
                compressed_offset: (header_length + (n * COMPRESSED_CHUNK_SIZE)).into(),
                compressed_size: COMPRESSED_CHUNK_SIZE.into(),
                decompressed_offset: (n * DECOMPRESSED_CHUNK_SIZE).into(),
                decompressed_size: DECOMPRESSED_CHUNK_SIZE.into(),
            });
        }
        let header = ChunkedArchiveHeader::new(&seek_table).unwrap();
        let archive_length: u64 = header_length + (num_entries as u64 * COMPRESSED_CHUNK_SIZE);
        (header, seek_table, archive_length)
    }

    #[test]
    fn should_validate_self() {
        let (header, seek_table, archive_length) = generate_archive(4);
        let serialized_table = seek_table.as_slice().as_bytes();
        assert!(header.decode_seek_table(serialized_table, archive_length).unwrap().is_some());
    }

    #[test]
    fn should_validate_empty() {
        let (header, _, archive_length) = generate_archive(0);
        assert!(header.decode_seek_table(&[], archive_length).unwrap().is_some());
    }

    #[test]
    fn should_detect_bad_magic() {
        let (header, seek_table, archive_length) = generate_archive(4);
        let mut corrupt_magic = ChunkedArchiveHeader::CHUNKED_ARCHIVE_MAGIC;
        corrupt_magic[0] = !corrupt_magic[0];
        let bad_magic = ChunkedArchiveHeader { magic: corrupt_magic, ..header };
        let serialized_table = seek_table.as_slice().as_bytes();
        assert!(matches!(
            bad_magic.decode_seek_table(serialized_table, archive_length).unwrap_err(),
            ChunkedArchiveError::BadMagic
        ));
    }
    #[test]
    fn should_detect_wrong_version() {
        let (header, seek_table, archive_length) = generate_archive(4);
        let wrong_version = ChunkedArchiveHeader {
            version: (ChunkedArchiveHeader::CHUNKED_ARCHIVE_VERSION + 1).into(),
            ..header
        };
        let serialized_table = seek_table.as_slice().as_bytes();
        assert!(matches!(
            wrong_version.decode_seek_table(serialized_table, archive_length).unwrap_err(),
            ChunkedArchiveError::InvalidVersion
        ));
    }

    #[test]
    fn should_detect_corrupt_checksum() {
        let (header, seek_table, archive_length) = generate_archive(4);
        let corrupt_checksum =
            ChunkedArchiveHeader { checksum: (!header.checksum.get()).into(), ..header };
        let serialized_table = seek_table.as_slice().as_bytes();
        assert!(matches!(
            corrupt_checksum.decode_seek_table(serialized_table, archive_length).unwrap_err(),
            ChunkedArchiveError::IntegrityError
        ));
    }

    #[test]
    fn should_reject_too_many_entries() {
        let (too_many_entries, seek_table, archive_length) =
            generate_archive(ChunkedArchiveHeader::CHUNKED_ARCHIVE_MAX_FRAMES + 1);

        let serialized_table = seek_table.as_slice().as_bytes();
        assert!(matches!(
            too_many_entries.decode_seek_table(serialized_table, archive_length).unwrap_err(),
            ChunkedArchiveError::IntegrityError
        ));
    }

    #[test]
    fn invariant_i0_first_entry_zero() {
        let (header, mut seek_table, archive_length) = generate_archive(4);
        assert_eq!(seek_table[0].decompressed_offset.get(), 0);
        seek_table[0].decompressed_offset = 1.into();

        let serialized_table = seek_table.as_slice().as_bytes();
        assert!(matches!(
            header.decode_seek_table(serialized_table, archive_length).unwrap_err(),
            ChunkedArchiveError::IntegrityError
        ));
    }

    #[test]
    fn invariant_i1_no_header_overlap() {
        let (header, mut seek_table, archive_length) = generate_archive(4);
        let header_end = ChunkedArchiveHeader::header_length(seek_table.len()) as u64;
        assert!(seek_table[0].compressed_offset.get() >= header_end);
        seek_table[0].compressed_offset = (header_end - 1).into();
        let serialized_table = seek_table.as_slice().as_bytes();
        assert!(matches!(
            header.decode_seek_table(serialized_table, archive_length).unwrap_err(),
            ChunkedArchiveError::IntegrityError
        ));
    }

    #[test]
    fn invariant_i2_decompressed_monotonic() {
        let (header, mut seek_table, archive_length) = generate_archive(4);
        assert_eq!(
            seek_table[0].decompressed_offset.get() + seek_table[0].decompressed_size.get(),
            seek_table[1].decompressed_offset.get()
        );
        seek_table[1].decompressed_offset = (seek_table[1].decompressed_offset.get() - 1).into();
        let serialized_table = seek_table.as_slice().as_bytes();
        assert!(matches!(
            header.decode_seek_table(serialized_table, archive_length).unwrap_err(),
            ChunkedArchiveError::IntegrityError
        ));
    }

    #[test]
    fn invariant_i3_compressed_monotonic() {
        let (header, mut seek_table, archive_length) = generate_archive(4);
        assert!(
            (seek_table[0].compressed_offset.get() + seek_table[0].compressed_size.get())
                <= seek_table[1].compressed_offset.get()
        );
        seek_table[1].compressed_offset = (seek_table[1].compressed_offset.get() - 1).into();
        let serialized_table = seek_table.as_slice().as_bytes();
        assert!(matches!(
            header.decode_seek_table(serialized_table, archive_length).unwrap_err(),
            ChunkedArchiveError::IntegrityError
        ));
    }

    #[test]
    fn invariant_i4_nonzero_compressed_size() {
        let (header, mut seek_table, archive_length) = generate_archive(4);
        assert!(seek_table[0].compressed_size.get() > 0);
        seek_table[0].compressed_size = 0.into();
        let serialized_table = seek_table.as_slice().as_bytes();
        assert!(matches!(
            header.decode_seek_table(serialized_table, archive_length).unwrap_err(),
            ChunkedArchiveError::IntegrityError
        ));
    }

    #[test]
    fn invariant_i4_nonzero_decompressed_size() {
        let (header, mut seek_table, archive_length) = generate_archive(4);
        assert!(seek_table[0].decompressed_size.get() > 0);
        seek_table[0].decompressed_size = 0.into();
        let serialized_table = seek_table.as_slice().as_bytes();
        assert!(matches!(
            header.decode_seek_table(serialized_table, archive_length).unwrap_err(),
            ChunkedArchiveError::IntegrityError
        ));
    }

    #[test]
    fn invariant_i5_within_archive() {
        let (header, mut seek_table, archive_length) = generate_archive(4);
        let last_entry = seek_table.last_mut().unwrap();
        assert!(
            (last_entry.compressed_offset.get() + last_entry.compressed_size.get())
                <= archive_length
        );
        last_entry.compressed_offset = (archive_length + 1).into();
        let serialized_table = seek_table.as_slice().as_bytes();
        assert!(matches!(
            header.decode_seek_table(serialized_table, archive_length).unwrap_err(),
            ChunkedArchiveError::IntegrityError
        ));
    }

    #[test]
    fn max_chunks() {
        assert_eq!(
            ChunkedArchive::chunk_size_for(
                ChunkedArchive::MAX_CHUNKS * ChunkedArchive::TARGET_CHUNK_SIZE,
                BLOCK_SIZE,
            ),
            ChunkedArchive::TARGET_CHUNK_SIZE
        );
        assert_eq!(
            ChunkedArchive::chunk_size_for(
                ChunkedArchive::MAX_CHUNKS * ChunkedArchive::TARGET_CHUNK_SIZE + 1,
                BLOCK_SIZE,
            ),
            ChunkedArchive::TARGET_CHUNK_SIZE + BLOCK_SIZE
        );
    }

    #[test]
    fn test_decompressor_empty_archive() {
        let mut compressed: Vec<u8> = vec![];
        ChunkedArchive::new(&[], BLOCK_SIZE)
            .expect("compress")
            .write(&mut compressed)
            .expect("write archive");
        let (seek_table, chunk_data) =
            decode_archive(&compressed, compressed.len()).unwrap().unwrap();
        assert!(seek_table.is_empty());
        let mut decompressor = ChunkedDecompressor::new(seek_table).unwrap();
        let mut chunk_callback = |_chunk: &[u8]| panic!("Archive doesn't have any chunks.");
        // Stream data into the decompressor in small chunks to exhaust more edge cases.
        chunk_data
            .chunks(4)
            .for_each(|data| decompressor.update(data, &mut chunk_callback).unwrap());
    }

    #[test]
    fn test_decompressor() {
        const UNCOMPRESSED_LENGTH: usize = 3_000_000;
        let data: Vec<u8> = {
            let range = rand::distributions::Uniform::<u8>::new_inclusive(0, 255);
            rand::thread_rng().sample_iter(&range).take(UNCOMPRESSED_LENGTH).collect()
        };
        let mut compressed: Vec<u8> = vec![];
        ChunkedArchive::new(&data, BLOCK_SIZE)
            .expect("compress")
            .write(&mut compressed)
            .expect("write archive");
        let (seek_table, chunk_data) =
            decode_archive(&compressed, compressed.len()).unwrap().unwrap();

        // Make sure we have multiple chunks for this test.
        let num_chunks = seek_table.len();
        assert!(num_chunks > 1);

        let mut decompressor = ChunkedDecompressor::new(seek_table).unwrap();

        let mut decoded_chunks: usize = 0;
        let mut decompressed_offset: usize = 0;
        let mut chunk_callback = |decompressed_chunk: &[u8]| {
            assert!(
                decompressed_chunk
                    == &data[decompressed_offset..decompressed_offset + decompressed_chunk.len()]
            );
            decompressed_offset += decompressed_chunk.len();
            decoded_chunks += 1;
        };

        // Stream data into the decompressor in small chunks to exhaust more edge cases.
        chunk_data
            .chunks(4)
            .for_each(|data| decompressor.update(data, &mut chunk_callback).unwrap());
        assert_eq!(decoded_chunks, num_chunks);
    }

    #[test]
    fn test_decompressor_corrupt_decompressed_size() {
        let data = vec![0; 3_000_000];
        let mut compressed: Vec<u8> = vec![];
        ChunkedArchive::new(&data, BLOCK_SIZE)
            .expect("compress")
            .write(&mut compressed)
            .expect("write archive");
        let (mut seek_table, chunk_data) =
            decode_archive(&compressed, compressed.len()).unwrap().unwrap();

        // Corrupt the decompressed size of the chunk.
        seek_table[0].decompressed_range =
            seek_table[0].decompressed_range.start..seek_table[0].decompressed_range.end + 1;

        let mut decompressor = ChunkedDecompressor::new(seek_table).unwrap();
        assert!(matches!(
            decompressor.update(&chunk_data, &mut |_chunk| {}),
            Err(ChunkedArchiveError::IntegrityError)
        ));
    }

    #[test]
    fn test_decompressor_corrupt_compressed_size() {
        let data = vec![0; 3_000_000];
        let mut compressed: Vec<u8> = vec![];
        ChunkedArchive::new(&data, BLOCK_SIZE)
            .expect("compress")
            .write(&mut compressed)
            .expect("write archive");
        let (mut seek_table, chunk_data) =
            decode_archive(&compressed, compressed.len()).unwrap().unwrap();

        // Corrupt the compressed size of the chunk.
        seek_table[0].compressed_range =
            seek_table[0].compressed_range.start..seek_table[0].compressed_range.end - 1;

        let mut decompressor = ChunkedDecompressor::new(seek_table).unwrap();
        assert!(matches!(
            decompressor.update(&chunk_data, &mut |_chunk| {}),
            Err(ChunkedArchiveError::DecompressionError(_))
        ));
    }
}