implement snappy and tests

.github/workflows/ci.yml

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+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
+  cancel-in-progress: true
+
+jobs:
+  lint:
+    name: Lint and format checks - Python ${{ matrix.python-version }}
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        python-version: ["3.12", "3.13", "3.14"]
+    steps:
+      - name: Checkout py-snappy
+        uses: actions/checkout@v4
+
+      - name: Install uv and Python ${{ matrix.python-version }}
+        uses: astral-sh/setup-uv@v4
+        with:
+          enable-cache: true
+          cache-dependency-glob: "pyproject.toml"
+          python-version: ${{ matrix.python-version }}
+
+      - name: Run all quality checks via tox
+        run: uvx tox -e all-checks
+
+  test:
+    name: Tests - Python ${{ matrix.python-version }} on ${{ matrix.os }}
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macos-latest]
+        python-version: ["3.12", "3.13", "3.14"]
+    steps:
+      - name: Checkout py-snappy
+        uses: actions/checkout@v4
+
+      - name: Install uv and Python ${{ matrix.python-version }}
+        uses: astral-sh/setup-uv@v4
+        with:
+          enable-cache: true
+          cache-dependency-glob: "pyproject.toml"
+          python-version: ${{ matrix.python-version }}
+
+      - name: Run tests via tox
+        run: uvx tox -e pytest

.gitignore

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+# Byte-compiled / optimized / DLL files
+__pycache__/
+*.py[cod]
+*$py.class
+
+# C extensions
+*.so
+
+# Distribution / packaging
+.Python
+build/
+develop-eggs/
+dist/
+downloads/
+eggs/
+.eggs/
+lib/
+lib64/
+parts/
+sdist/
+var/
+wheels/
+share/python-wheels/
+*.egg-info/
+.installed.cfg
+*.egg
+MANIFEST
+
+# PyInstaller
+*.manifest
+*.spec
+
+# Installer logs
+pip-log.txt
+pip-delete-this-directory.txt
+
+# Unit test / coverage reports
+htmlcov/
+.tox/
+.nox/
+.coverage
+.coverage.*
+.cache
+nosetests.xml
+coverage.xml
+*.cover
+*.py,cover
+.hypothesis/
+.pytest_cache/
+cover/
+
+# Translations
+*.mo
+*.pot
+
+# Django stuff:
+*.log
+local_settings.py
+db.sqlite3
+db.sqlite3-journal
+
+# Flask stuff:
+instance/
+.webassets-cache
+
+# Scrapy stuff:
+.scrapy
+
+# Sphinx documentation
+docs/_build/
+
+# PyBuilder
+.pybuilder/
+target/
+
+# Jupyter Notebook
+.ipynb_checkpoints
+
+# IPython
+profile_default/
+ipython_config.py
+
+# pyenv
+.python-version
+
+# pipenv
+Pipfile.lock
+
+# poetry
+poetry.lock
+
+# pdm
+.pdm.toml
+.pdm-python
+.pdm-build/
+
+# PEP 582
+__pypackages__/
+
+# Celery stuff
+celerybeat-schedule
+celerybeat.pid
+
+# SageMath parsed files
+*.sage.py
+
+# Environments
+.env
+.venv
+env/
+venv/
+ENV/
+env.bak/
+venv.bak/
+
+# Spyder project settings
+.spyderproject
+.spyproject
+
+# Rope project settings
+.ropeproject
+
+# mkdocs documentation
+/site
+
+# mypy
+.mypy_cache/
+.dmypy.json
+dmypy.json
+
+# Pyre type checker
+.pyre/
+
+# pytype static type analyzer
+.pytype/
+
+# Cython debug symbols
+cython_debug/
+
+# IDEs
+.idea/
+.vscode/
+*.swp
+*.swo
+*~
+.DS_Store
+
+# UV
+.uv/
+
+# Ruff
+.ruff_cache/

README.md

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+# py-snappy
+
+Pure Python implementation of Google's Snappy compression algorithm.
+
+## Features
+
+- **Pure Python**: No external dependencies or C extensions required
+- **Full compatibility**: Produces output compatible with Google's Snappy format
+- **Well documented**: Extensive inline documentation explaining the algorithm
+- **Thoroughly tested**: Comprehensive test suite using C++ Snappy test data
+
+## Installation
+
+```bash
+uv sync
+```
+
+## Usage
+
+```python
+from src import compress, decompress
+
+# Compress data
+data = b"Hello, World!" * 100
+compressed = compress(data)
+
+# Decompress data
+original = decompress(compressed)
+assert original == data
+```
+
+## API
+
+### Core Functions
+
+- `compress(data: bytes) -> bytes`: Compress data using Snappy
+- `decompress(data: bytes) -> bytes`: Decompress Snappy-compressed data
+
+### Utilities
+
+- `max_compressed_length(size: int) -> int`: Maximum possible compressed size
+- `get_uncompressed_length(data: bytes) -> int`: Read uncompressed length from header
+- `is_valid_compressed_data(data: bytes) -> bool`: Quick validation check
+
+### Exceptions
+
+- `SnappyDecompressionError`: Raised when decompression fails
+
+## Development
+
+```bash
+# Install dependencies
+uv sync
+
+# Run tests
+uv run pytest
+
+# Run linter
+uv run ruff check src/ tests/
+
+# Format code
+uv run ruff format src/ tests/
+```
+
+## Algorithm
+
+Snappy is an LZ77-variant compression algorithm that prioritizes speed over compression ratio. Key characteristics:
+
+- **Block-based**: Data is processed in 64KB blocks
+- **Hash table**: O(1) match lookup using a simple hash function
+- **Greedy matching**: No optimal parsing or lazy evaluation
+- **Wire format**: Varint length prefix followed by literals and copy references
+
+## References
+
+- [Google Snappy](https://github.com/google/snappy)
+- [Format Description](https://github.com/google/snappy/blob/main/format_description.txt)
+
+## License
+
+MIT License