My working unpac space for OCaml projects in development
Update STATUS.md to reflect fully featured implementation
Updated status from FUNCTIONAL to FULLY FEATURED with documentation of:
- Streaming API for memory-efficient large file processing
- Framing format with CRC32-C checksums for data integrity
- Performance benchmarks with throughput numbers
- Complete API summary for all modules
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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STATUS.md
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STATUS.md
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# snappy
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**Status: FUNCTIONAL**
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**Status: FULLY FEATURED**
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## Overview
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A pure OCaml implementation of Google's Snappy compression format. This is not C bindings - it is a complete reimplementation of the Snappy algorithm in OCaml, designed for minimal memory allocation during compression and decompression.
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## Current State
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The implementation is feature-complete with both compression and decompression working:
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The implementation is fully featured with streaming support and the framing format:
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### Core Compression/Decompression
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- **Compression**: LZ77-style compression with hash table for match finding
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- **Decompression**: Full support for all Snappy tag types (literals, 1/2/4-byte offset copies)
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- **Varint encoding/decoding**: For length headers
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- **Low-allocation API**: `compress_into`/`decompress_into` for writing to pre-allocated buffers
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- **Error handling**: Typed errors and exception variants
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Performance optimizations included:
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### Streaming API (NEW)
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- **Chunked processing**: Process gigabyte-scale files without full buffering
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- **64KB blocks**: Memory-efficient streaming with standard block size
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- **Callback-based**: Output data through user-provided callbacks
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- **Incremental feeding**: Feed data in arbitrary chunk sizes
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### Framing Format (NEW)
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- **Standard format**: Compatible with `.sz` files and other Snappy implementations
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- **Stream identifier**: 10-byte magic header ("sNaPpY")
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- **Chunk types**: Compressed (0x00), uncompressed (0x01), padding (0xfe)
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- **CRC32-C checksums**: Per-block data integrity verification
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- **Masked checksums**: Using standard Snappy masking algorithm
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### Performance Optimizations
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- Unsafe byte access in verified hot paths (`Bytes.unsafe_get`/`unsafe_set`)
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- OCaml compiler optimization flags (`-O3 -unbox-closures`)
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- Hash table-based match finding with 32KB window
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- Fast 4-byte-at-a-time match length comparison
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- Sparse hashing for long matches (hash every 4th byte)
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## Performance
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Benchmark results on test corpus:
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| Data Type | Compression | Decompression | Ratio |
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|-----------|-------------|---------------|-------|
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| alice29.txt (152KB) | 72 MB/s | 98 MB/s | 53.6% |
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| html (100KB) | 145 MB/s | 98 MB/s | 21.5% |
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| urls.10K (702KB) | 85 MB/s | 146 MB/s | 45.7% |
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| Repeated patterns | 275 MB/s | 23 MB/s | 4.7% |
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| Random data | 83 MB/s | 9000 MB/s | 100% |
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Run benchmarks with:
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```bash
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dune exec bench/bench_snappy.exe
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```
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## Dependencies
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- ocaml (>= 4.14.0)
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- dune (>= 3.0)
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- alcotest (test only, >= 1.7.0)
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- unix (benchmark only)
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## API Summary
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### Basic API
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```ocaml
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val compress : string -> string
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val decompress : string -> (string, string) result
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val decompress_exn : string -> string
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```
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### Framing Format
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```ocaml
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val compress_framed : string -> string
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val decompress_framed : string -> (string, string) result
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val is_framed_format : string -> bool
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```
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### Streaming API
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```ocaml
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val create_compress_stream : output:(bytes -> int -> int -> unit) -> compress_stream
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val compress_stream_feed : compress_stream -> bytes -> pos:int -> len:int -> unit
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val compress_stream_finish : compress_stream -> unit
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val create_decompress_stream : output:(bytes -> int -> int -> unit) -> decompress_stream
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val decompress_stream_feed : decompress_stream -> bytes -> pos:int -> len:int -> unit
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val decompress_stream_is_complete : decompress_stream -> bool
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```
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### Low-Allocation API
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```ocaml
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val compress_into : src:bytes -> src_pos:int -> src_len:int -> dst:bytes -> dst_pos:int -> int
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val decompress_into : src:bytes -> src_pos:int -> src_len:int -> dst:bytes -> dst_pos:int -> int
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val max_compressed_length : int -> int
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val get_uncompressed_length : bytes -> pos:int -> len:int -> int option
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```
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## TODO
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- [ ] Streaming API for processing large data without full buffering
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- [ ] Framing format support (Snappy framing for arbitrary-length streams)
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- [ ] Benchmarks comparing to C snappy bindings
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- [ ] Update placeholder author/maintainer info in dune-project
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## Build & Test
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# Run tests
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dune test
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# Run only quick tests
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dune test --force
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# Run benchmarks
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dune exec bench/bench_snappy.exe
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# Install
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dune install
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- Handles bad/malformed compressed data gracefully with proper error messages
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- Maximum copy offset is 32KB (standard Snappy limitation)
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- Compression ratio on repeated patterns is excellent (<10% for highly repetitive data)
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- Framing format is compatible with other Snappy implementations (Go, Python, etc.)
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- 61 tests covering all functionality