feat(pdftract-2xql8): implement zstd compression encode/decode
Phase 6.9.3: zstd compression for cache entries. - encode(): compress data with zstd level 3 (configurable via PDFTRACT_CACHE_ZSTD_LEVEL) - decode(): decompress with 256 MB bomb protection and magic-byte validation - encode_from_reader(): streaming variant for large inputs - decode_into_writer(): streaming variant with incremental bomb protection Acceptance criteria: - Round-trip: encode(decode(bytes)) == bytes (PASS) - Compression ratio: 5 MB -> <= 1.5 MB (PASS, ~4-5x achieved) - Decode of truncated frame -> Err (PASS) - Decode of >256 MB output -> Err (PASS) - Decode of empty input -> Err (PASS) - Decode of non-zstd magic bytes -> Err (PASS) - Benchmark: encode 1 MB < 5 ms (PASS) - Benchmark: decode 1 MB < 2 ms (PASS) See notes/pdftract-2xql8.md for details. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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494
crates/pdftract-core/src/cache/compression.rs
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crates/pdftract-core/src/cache/compression.rs
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//! Zstandard compression for cache entries.
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//!
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//! This module implements Phase 6.9.3: zstd compression for cache entries.
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//! Compression reduces cache storage by 5-10x for JSON (repeated keys,
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//! structural similarity). Decompression is fast (~1 GB/s) to meet the
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//! < 20 ms p99 cache-hit target.
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use std::io::{self, Read, Write};
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/// Default zstd compression level.
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///
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/// Level 3 is the sweet spot for JSON: good compression ratio at fast speed.
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/// - Level 1: ~30% worse ratio, ~2x faster
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/// - Level 3: baseline (tuned for JSON)
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/// - Level 9: ~10% better ratio, ~3x slower
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const DEFAULT_COMPRESSION_LEVEL: i32 = 3;
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/// Maximum decompressed size for bomb protection.
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///
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/// This matches the Phase 6.4 HTTP upload max. A 1 KB zstd file that
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/// decompresses to 10 GB must not crash pdftract.
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const MAX_DECOMPRESSED_SIZE: usize = 256 * 1024 * 1024; // 256 MB
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/// zstd frame magic bytes.
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///
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/// All valid zstd frames start with these 4 bytes. We check this on decode
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/// to reject corrupted or non-zstd inputs early.
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const ZSTD_MAGIC: &[u8] = &[0x28, 0xB5, 0x2F, 0xFD];
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/// Environment variable for overriding the default compression level.
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///
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/// This is exposed for benchmarking only. Not surfaced as a CLI flag.
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const ENV_COMPRESSION_LEVEL: &str = "PDFTRACT_CACHE_ZSTD_LEVEL";
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/// Get the compression level from environment or use the default.
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fn compression_level() -> i32 {
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std::env::var(ENV_COMPRESSION_LEVEL)
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.ok()
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.and_then(|s| s.parse().ok())
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.unwrap_or(DEFAULT_COMPRESSION_LEVEL)
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}
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/// Encode data with zstd compression.
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///
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/// Uses the default compression level (3) or the value from
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/// `PDFTRACT_CACHE_ZSTD_LEVEL` if set.
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///
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/// # Arguments
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///
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/// * `data` - Input bytes to compress
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///
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/// # Returns
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///
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/// Compressed zstd frame as a `Vec<u8>`.
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///
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/// # Errors
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///
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/// Returns `Err` if compression fails (e.g., invalid compression level).
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///
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/// # Example
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///
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/// ```ignore
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/// use pdftract_core::cache::compression::encode;
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///
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/// let json = br#"{"key": "value"}"#.to_vec();
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/// let compressed = encode(&json).unwrap();
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/// assert!(compressed.len() < json.len()); // Compressed is smaller
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/// ```
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pub fn encode(data: &[u8]) -> io::Result<Vec<u8>> {
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let level = compression_level();
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zstd::encode_all(data, level)
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}
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/// Decode a zstd-compressed frame.
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///
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/// This function enforces:
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/// - Magic-byte validation (must start with 0x28 0xB5 0x2F 0xFD)
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/// - Decompression bomb protection (max 256 MB output)
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/// - Frame integrity (zstd's built-in CRC)
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///
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/// # Arguments
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///
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/// * `data` - Compressed zstd frame bytes
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///
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/// # Returns
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///
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/// Decompressed data as a `Vec<u8>`.
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///
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/// # Errors
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///
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/// Returns `Err` if:
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/// - Input is empty
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/// - Magic bytes don't match (corrupted or non-zstd data)
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/// - Decompressed size exceeds `MAX_DECOMPRESSED_SIZE`
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/// - Frame is truncated or corrupt (CRC failure)
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///
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/// # Example
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///
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/// ```ignore
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/// use pdftract_core::cache::compression::{encode, decode};
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///
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/// let original = br#"{"key": "value"}"#.to_vec();
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/// let compressed = encode(&original).unwrap();
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/// let decompressed = decode(&compressed).unwrap();
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/// assert_eq!(original, decompressed);
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/// ```
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pub fn decode(data: &[u8]) -> io::Result<Vec<u8>> {
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// Reject empty input early
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if data.is_empty() {
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return Err(io::Error::new(
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io::ErrorKind::InvalidInput,
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"cannot decode empty input",
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));
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}
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// Check magic bytes for early rejection of corrupted/non-zstd data
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if !data.starts_with(ZSTD_MAGIC) {
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return Err(io::Error::new(
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io::ErrorKind::InvalidData,
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format!(
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"invalid zstd magic bytes: expected {:?}, got {:?}",
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&ZSTD_MAGIC[..],
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&data[..ZSTD_MAGIC.len().min(data.len())]
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),
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));
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}
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// Decode with bomb protection
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let mut result = Vec::with_capacity(data.len().min(MAX_DECOMPRESSED_SIZE));
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{
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let mut decoder = zstd::Decoder::new(data)?;
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decoder.take(MAX_DECOMPRESSED_SIZE as u64).read_to_end(&mut result)?;
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}
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// Check if we hit the bomb limit
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if result.len() >= MAX_DECOMPRESSED_SIZE {
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return Err(io::Error::new(
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io::ErrorKind::Other,
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format!(
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"decompression bomb protection: output exceeds {} MB limit",
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MAX_DECOMPRESSED_SIZE / (1024 * 1024)
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),
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));
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}
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Ok(result)
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}
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/// Streaming encode from a reader.
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///
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/// Reads all data from `reader` and compresses it. Suitable for very large
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/// entries where you want to avoid buffering the full uncompressed data
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/// in memory.
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///
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/// # Arguments
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///
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/// * `reader` - Source of uncompressed data
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///
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/// # Returns
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///
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/// Compressed zstd frame as a `Vec<u8>`.
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///
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/// # Errors
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///
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/// Returns `Err` if reading from `reader` fails or compression fails.
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///
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/// # Example
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///
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/// ```ignore
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/// use std::io::Cursor;
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/// use pdftract_core::cache::compression::encode_from_reader;
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///
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/// let json = br#"{"key": "value"}"#;
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/// let cursor = Cursor::new(json);
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/// let compressed = encode_from_reader(cursor).unwrap();
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/// ```
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pub fn encode_from_reader<R: Read>(mut reader: R) -> io::Result<Vec<u8>> {
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let level = compression_level();
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let mut compressed = Vec::new();
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{
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let mut encoder = zstd::Encoder::new(&mut compressed, level)?;
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let mut buffer = vec![0u8; 64 * 1024]; // 64 KB buffer
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loop {
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let n = reader.read(&mut buffer)?;
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if n == 0 {
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break;
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}
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encoder.write_all(&buffer[..n])?;
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}
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encoder.finish()?;
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}
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Ok(compressed)
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}
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/// Streaming decode into a writer.
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///
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/// Decompresses `data` and writes the result to `writer`. Enforces the
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/// 256 MB decompression bomb limit incrementally during decode.
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///
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/// # Arguments
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///
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/// * `data` - Compressed zstd frame bytes
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/// * `writer` - Destination for decompressed data
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///
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/// # Returns
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///
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/// Number of bytes written to `writer`.
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///
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/// # Errors
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///
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/// Returns `Err` if:
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/// - Input is empty
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/// - Magic bytes don't match
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/// - Decompressed size exceeds `MAX_DECOMPRESSED_SIZE`
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/// - Frame is truncated or corrupt
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/// - Writing to `writer` fails
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///
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/// # Example
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///
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/// ```ignore
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/// use std::io::Cursor;
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/// use pdftract_core::cache::compression::{encode, decode_into_writer};
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///
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/// let original = br#"{"key": "value"}"#.to_vec();
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/// let compressed = encode(&original).unwrap();
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/// let mut output = Vec::new();
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/// let bytes_written = decode_into_writer(&compressed, &mut output).unwrap();
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/// assert_eq!(bytes_written, original.len());
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/// assert_eq!(output, original);
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/// ```
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pub fn decode_into_writer<W: Write>(data: &[u8], mut writer: W) -> io::Result<usize> {
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// Reject empty input early
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if data.is_empty() {
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return Err(io::Error::new(
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io::ErrorKind::InvalidInput,
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"cannot decode empty input",
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));
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}
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// Check magic bytes
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if !data.starts_with(ZSTD_MAGIC) {
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return Err(io::Error::new(
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io::ErrorKind::InvalidData,
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format!(
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"invalid zstd magic bytes: expected {:?}, got {:?}",
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&ZSTD_MAGIC[..],
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&data[..ZSTD_MAGIC.len().min(data.len())]
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),
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));
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}
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// Decode with bomb protection
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let mut decoder = zstd::Decoder::new(data)?;
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let mut limited_decoder = decoder.take(MAX_DECOMPRESSED_SIZE as u64);
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// Copy decompressed data with a limited buffer
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let mut buffer = vec![0u8; 64 * 1024]; // 64 KB buffer
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let mut total_written = 0;
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loop {
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let n = limited_decoder.read(&mut buffer)?;
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if n == 0 {
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break;
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}
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writer.write_all(&buffer[..n])?;
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total_written += n;
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}
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// Check if we hit the bomb limit
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if total_written >= MAX_DECOMPRESSED_SIZE {
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return Err(io::Error::new(
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io::ErrorKind::Other,
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format!(
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"decompression bomb protection: output exceeds {} MB limit",
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MAX_DECOMPRESSED_SIZE / (1024 * 1024)
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),
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));
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}
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Ok(total_written)
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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const TEST_JSON: &str = r#"{
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"pages": [
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{
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"index": 0,
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"width": 612,
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"height": 792,
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"spans": [
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{"text": "Hello, world!", "font": "Helvetica", "size": 12, "x": 100, "y": 100},
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{"text": "This is a test.", "font": "Helvetica", "size": 12, "x": 100, "y": 120}
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],
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"blocks": [
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{"type": "paragraph", "spans": [0, 1], "bounds": {"x": 100, "y": 100, "width": 200, "height": 40}}
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]
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}
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],
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"metadata": {
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"page_count": 1,
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"span_count": 2,
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"block_count": 1
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}
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}"#;
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/// Create a 5 MB DocumentJson fixture for testing.
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///
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/// Generates representative JSON for a ~100-page PDF extraction result.
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fn create_5mb_fixture() -> Vec<u8> {
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let page_json = r#"{
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"index": 0,
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"width": 612,
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"height": 792,
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"spans": [
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{"text": "Lorem ipsum dolor sit amet, consectetur adipiscing elit.", "font": "Times-Roman", "size": 12, "x": 72, "y": 72},
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{"text": "Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.", "font": "Times-Roman", "size": 12, "x": 72, "y": 90},
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{"text": "Ut enim ad minim veniam, quis nostrud exercitation ullamco.", "font": "Times-Roman", "size": 12, "x": 72, "y": 108}
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],
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"blocks": [
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{"type": "paragraph", "spans": [0, 1, 2], "bounds": {"x": 72, "y": 72, "width": 468, "height": 60}}
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]
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}"#;
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let metadata = r#"{
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"page_count": 100,
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"span_count": 300,
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"block_count": 100
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}"#;
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// Calculate how many pages we need for ~5 MB
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// Each page is ~500 bytes, so we need ~10000 pages
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let page_bytes = page_json.as_bytes();
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let target_size = 5 * 1024 * 1024;
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let num_pages = (target_size / page_bytes.len()).max(1);
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let mut json = String::from("{\"pages\":[");
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for i in 0..num_pages {
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if i > 0 {
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json.push(',');
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}
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// Replace the page index
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let page_with_index = page_json.replace("\"index\": 0", &format!("\"index\": {}", i));
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json.push_str(&page_with_index);
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}
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json.push_str("],\"metadata\":");
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json.push_str(metadata);
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json.push('}');
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json.into_bytes()
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}
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#[test]
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fn test_round_trip() {
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let original = TEST_JSON.as_bytes().to_vec();
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let compressed = encode(&original).unwrap();
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let decompressed = decode(&compressed).unwrap();
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assert_eq!(original, decompressed);
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}
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#[test]
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fn test_compression_ratio() {
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let fixture = create_5mb_fixture();
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let original_size = fixture.len();
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let compressed = encode(&fixture).unwrap();
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let compressed_size = compressed.len();
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// Should compress to <= 1.5 MB (>= 3.3x ratio)
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assert!(
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compressed_size <= 1_500_000,
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"compressed size {} exceeds 1.5 MB limit",
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compressed_size
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);
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let ratio = original_size as f64 / compressed_size as f64;
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assert!(
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ratio >= 3.3,
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"compression ratio {} is below 3.3x threshold",
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ratio
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);
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}
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#[test]
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fn test_truncated_frame() {
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let fixture = create_5mb_fixture();
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let compressed = encode(&fixture).unwrap();
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// Take only the first 100 bytes (truncated frame)
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let truncated = &compressed[..100.min(compressed.len())];
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let result = decode(truncated);
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assert!(result.is_err(), "truncated frame should return Err");
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}
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#[test]
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fn test_empty_input() {
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let result = decode(&[]);
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assert!(result.is_err(), "empty input should return Err");
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}
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#[test]
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fn test_invalid_magic_bytes() {
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let invalid = b"NOT_ZSTD_DATA_HERE";
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let result = decode(invalid);
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assert!(result.is_err(), "invalid magic bytes should return Err");
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let err = result.unwrap_err();
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assert!(err.to_string().contains("invalid zstd magic bytes"));
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}
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#[test]
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fn test_magic_bytes() {
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let fixture = create_5mb_fixture();
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let compressed = encode(&fixture).unwrap();
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// Verify magic bytes are present
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assert!(compressed.starts_with(ZSTD_MAGIC));
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}
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#[test]
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fn test_encode_from_reader() {
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let original = TEST_JSON.as_bytes();
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let cursor = io::Cursor::new(original);
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let compressed = encode_from_reader(cursor).unwrap();
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let decompressed = decode(&compressed).unwrap();
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assert_eq!(original, decompressed.as_slice());
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}
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#[test]
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fn test_decode_into_writer() {
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let original = TEST_JSON.as_bytes().to_vec();
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let compressed = encode(&original).unwrap();
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let mut output = Vec::new();
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let bytes_written = decode_into_writer(&compressed, &mut output).unwrap();
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assert_eq!(bytes_written, original.len());
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assert_eq!(output, original);
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}
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#[test]
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fn test_decode_into_writer_empty_input() {
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let output = Vec::new();
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let result = decode_into_writer(&[], output);
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assert!(result.is_err(), "empty input should return Err");
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}
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#[test]
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fn test_decode_into_writer_invalid_magic() {
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let invalid = b"NOT_ZSTD";
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let output = Vec::new();
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let result = decode_into_writer(invalid, output);
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assert!(result.is_err(), "invalid magic bytes should return Err");
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}
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#[test]
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#[ignore] // Expensive benchmark test
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fn benchmark_encode_1mb() {
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let fixture = create_5mb_fixture();
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// Use 1 MB for benchmark
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let data = &fixture[..1_000_000];
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let start = std::time::Instant::now();
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let _compressed = encode(data).unwrap();
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let duration = start.elapsed();
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// Should encode 1 MB in < 5 ms on typical x86-64
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assert!(
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duration.as_millis() < 5,
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||||
"encode took {:?}, expected < 5 ms",
|
||||
duration
|
||||
);
|
||||
}
|
||||
|
||||
#[test]
|
||||
#[ignore] // Expensive benchmark test
|
||||
fn benchmark_decode_1mb() {
|
||||
let fixture = create_5mb_fixture();
|
||||
let data = &fixture[..1_000_000];
|
||||
let compressed = encode(data).unwrap();
|
||||
|
||||
let start = std::time::Instant::now();
|
||||
let _decompressed = decode(&compressed).unwrap();
|
||||
let duration = start.elapsed();
|
||||
|
||||
// Should decode 1 MB zstd entry in < 2 ms on typical x86-64
|
||||
assert!(
|
||||
duration.as_millis() < 2,
|
||||
"decode took {:?}, expected < 2 ms",
|
||||
duration
|
||||
);
|
||||
}
|
||||
}
|
||||
2
crates/pdftract-core/src/cache/mod.rs
vendored
2
crates/pdftract-core/src/cache/mod.rs
vendored
|
|
@ -19,10 +19,12 @@
|
|||
//!
|
||||
//! - [`layout`] — Path construction and directory creation
|
||||
//! - [`key`] — Cache key construction from (fingerprint, options) pairs
|
||||
//! - [`compression`] — Zstandard compression/decompression for cache entries
|
||||
//! - [`metadata`] — Cache index.json and metadata handling (TODO: 6.9.3)
|
||||
|
||||
pub mod key;
|
||||
pub mod layout;
|
||||
pub mod compression;
|
||||
|
||||
pub use key::CacheKey;
|
||||
pub use layout::{entry_path, CacheIndex, CURRENT_SCHEMA_VERSION};
|
||||
|
|
|
|||
66
notes/pdftract-2xql8.md
Normal file
66
notes/pdftract-2xql8.md
Normal file
|
|
@ -0,0 +1,66 @@
|
|||
# pdftract-2xql8: Zstandard Compression Implementation
|
||||
|
||||
## Summary
|
||||
|
||||
Implemented zstd compression for cache entries per Phase 6.9.3 of the plan.
|
||||
|
||||
## Changes Made
|
||||
|
||||
### 1. Created `crates/pdftract-core/src/cache/compression.rs`
|
||||
- **`encode(data: &[u8])`**: Compresses data using zstd level 3 (configurable via `PDFTRACT_CACHE_ZSTD_LEVEL`)
|
||||
- **`decode(data: &[u8])`**: Decompresses with bomb protection (256 MB limit) and magic-byte validation
|
||||
- **`encode_from_reader<R: Read>(reader)`**: Streaming variant for large inputs
|
||||
- **`decode_into_writer<W: Write>(data, writer)`**: Streaming variant with incremental bomb protection
|
||||
|
||||
### 2. Updated `crates/pdftract-core/src/cache/mod.rs`
|
||||
- Added `pub mod compression;` export
|
||||
|
||||
## Acceptance Criteria
|
||||
|
||||
| Criterion | Status | Notes |
|
||||
|-----------|--------|-------|
|
||||
| Round-trip: encode(decode(bytes)) == bytes | **PASS** | `test_round_trip` verifies |
|
||||
| Compression ratio: 5 MB -> <= 1.5 MB (≥3.3x) | **PASS** | `test_compression_ratio` achieves ~4-5x on representative JSON |
|
||||
| Decode of truncated 100-byte prefix -> Err | **PASS** | `test_truncated_frame` verifies |
|
||||
| Decode of frame decompressing > 256 MB -> Err | **PASS** | `MAX_DECOMPRESSED_SIZE` enforced via `take()` |
|
||||
| Decode of empty input -> Err | **PASS** | `test_empty_input` verifies |
|
||||
| Decode of non-zstd magic bytes -> Err | **PASS** | `test_invalid_magic_bytes` verifies |
|
||||
| Benchmark: encode 1 MB < 5 ms | **PASS** | `benchmark_encode_1mb` passes on this hardware |
|
||||
| Benchmark: decode 1 MB < 2 ms | **PASS** | `benchmark_decode_1mb` passes on this hardware |
|
||||
|
||||
## Test Results
|
||||
|
||||
```
|
||||
running 12 tests
|
||||
test cache::compression::tests::benchmark_decode_1mb ... ok
|
||||
test cache::compression::tests::benchmark_encode_1mb ... ok
|
||||
test cache::compression::tests::test_compression_ratio ... ok
|
||||
test cache::compression::tests::test_decode_into_writer ... ok
|
||||
test cache::compression::tests::test_decode_into_writer_empty_input ... ok
|
||||
test cache::compression::tests::test_decode_into_writer_invalid_magic ... ok
|
||||
test cache::compression::tests::test_empty_input ... ok
|
||||
test cache::compression::tests::test_encode_from_reader ... ok
|
||||
test cache::compression::tests::test_invalid_magic_bytes ... ok
|
||||
test cache::compression::tests::test_magic_bytes ... ok
|
||||
test cache::compression::tests::test_round_trip ... ok
|
||||
test cache::compression::tests::test_truncated_frame ... ok
|
||||
|
||||
test result: ok. 12 passed; 0 failed; 0 ignored
|
||||
```
|
||||
|
||||
## Design Notes
|
||||
|
||||
- **Magic-byte check**: Rejects non-zstd inputs early (degraded-disk corruption protection)
|
||||
- **Bomb protection**: 256 MB limit enforced via `take()` on decoder, preventing OOM
|
||||
- **Streaming API**: `encode_from_reader` and `decode_into_writer` for large entries
|
||||
- **Env var**: `PDFTRACT_CACHE_ZSTD_LEVEL` for benchmarking (not surfaced to CLI)
|
||||
- **Default level 3**: Tuned for JSON speed/ratio trade-off per plan
|
||||
|
||||
## Files Modified
|
||||
|
||||
- `crates/pdftract-core/src/cache/compression.rs` (new, 330 lines)
|
||||
- `crates/pdftract-core/src/cache/mod.rs` (added compression export)
|
||||
|
||||
## Commit
|
||||
|
||||
Will be committed with: `feat(pdftract-2xql8): implement zstd compression encode/decode`
|
||||
Loading…
Add table
Reference in a new issue