A lightweight, pure-Rust file compression and archiving utility.

📖 Overview

PressRs is a custom data compression tool built from scratch in Rust. It combines a TAR-like packager with an LZW (Lempel–Ziv–Welch) compressor to reduce file sizes while preserving directory structures.

It is designed as an educational project to demonstrate low-level bit manipulation, dictionary-based compression algorithms, and file stream handling in Rust.

✨ Features

• Custom LZW Implementation: Uses variable-width codes (9 to 12 bits) with dynamic dictionary resetting.
• Archive Capability: Bundles multiple files and directories into a single .pressrs file.
• Memory Efficient: Streams data using buffered readers/writers to handle large files.
• Web Compatibility: Designed for both native and WASM environments.
• No external Dependencies: Built from scratch without any libs/frameworks.
• CLI: Simple text-based interface for selecting modes.

📈Performance Benchmarks

Operation	Input Size	Throughput	Time
Compression	1 KB	81 MiB/s	12 µs
Compression	100 KB	103 MiB/s	945 µs
Compression	1 MB	102 MiB/s	9.8 ms
Decompression	1 KB	152 MiB/s	6.4 µs
Decompression	100 KB	171 MiB/s	570 µs
Pack (small)	3 entries	-	475 ns
Unpack (small)	5 KB archive	-	328 ns
Full Pipeline	Pack + Compress 100 KB	101 MiB/s	965 µs
Full Pipeline	Decompress + Unpack 100 KB	175 MiB/s	576 µs

Benchmarks run on intel i5-11400H wsl ubuntu. LZW compression algorithm.

Performance Characteristics

• Linear scaling: 2x data = 2x time (stable ~100 MiB/s)
• Decompression faster: 1.7x faster than compression
• Low overhead: Small files (<1KB) see ~20% overhead
• Predictable: 1MB ≈ 10ms, 100MB ≈ 1

🛠️ Technical Details

Compression Algorithm (LZW)

The core of PressRs is the LZW algorithm.

1. Dictionary: Starts with a default ASCII set (0-255).
2. Dynamic Growth: As patterns are found, new codes are added to the dictionary.
3. Variable Bit Width: The output code size starts at 9 bits and grows up to 12 bits as the dictionary fills up.
4. Reset Mechanism: Once the dictionary reaches its limit (4096 entries), it sends a Clear Code and resets, preventing memory overflow and adapting to new data patterns.

Packaging Format

PressRs uses a custom binary format similar to TAR:

• It traverses the target directory recursively.
• Each file is preceded by a metadata header (containing relative path and size).
• The continuous stream of file data is then passed to the LZW compressor.

🚀 Usage

Installation

Ensure you have Rust installed, then clone and build:

git clone https://github.com/TeseySTD/press.rs.git
cd press.rs 
cargo build --release

Executable will be at ./target/release/press_rs