Fast License Checker (flc)

Blazing-fast license header verification for your codebase.

Features

• Fast: Scans 100,000 files in under 1 second
• Git-aware: Automatically respects .gitignore
• Safe: Never corrupts binary files
• Smart: Handles shebangs, XML declarations, and various comment styles
• CI-ready: JSON and GitHub Actions output formats
• Parallel: Uses all available CPU cores for maximum performance

Installation

From source

cargo install fast-license-checker

Pre-built binaries

Download from Releases

Usage

Scan mode (check for missing headers)

flc .                           # Scan current directory
flc src/                        # Scan specific directory
flc --header "MIT License" .    # Specify header text
flc --license LICENSE.txt .     # Specify header from file
flc --output json .             # JSON output for CI
flc --output github .           # GitHub Actions annotations

Fix mode (add missing headers)

flc --fix .                     # Add headers to files missing them
flc --fix --dry-run .           # Preview changes without applying

Advanced usage

# Custom comment styles
flc --comment-style "rs=//" --comment-style "py=#" .

# Ignore additional patterns
flc --ignore "target/" --ignore "node_modules/" .

# Control parallelism
flc --jobs 4 .                  # Use 4 CPU cores
flc --jobs 1 .                  # Single-threaded for debugging

# Fuzzy matching for license variations
flc --similarity 85 .           # Allow 85% similarity threshold

Configuration

Create .license-checker.toml in your project root:

license_header = """
Copyright (c) 2024 Your Name
Licensed under the MIT License
"""

[comment_styles]
rs = { prefix = "//" }
py = { prefix = "#" }
js = { prefix = "//" }
html = { prefix = "<!--", suffix = "-->" }
xml = { prefix = "<!--", suffix = "-->" }
yaml = { prefix = "#" }
toml = { prefix = "#" }
md = { prefix = "<!--", suffix = "-->" }

ignore_patterns = ["vendor/", "generated/", "target/", "node_modules/"]
max_header_bytes = 8192
parallel_jobs = 0  # 0 = auto-detect CPU cores
similarity_threshold = 90  # 0-100, higher = stricter matching

Exit Codes

• 0: All files have valid headers (scan) or fixes applied successfully (fix)
• 1: Missing headers found (scan) or errors encountered (fix)
• 2: Configuration error or invalid arguments

Performance Benchmarks

Fast License Checker is designed for speed. On a modern laptop:

Test Environment

• CPU: 11th Gen Intel Core i5-1135G7 @ 2.40GHz (4 cores, 8 threads)
• RAM: 7.5GB DDR4
• Disk: 147GB NVMe SSD
• OS: Ubuntu 24.04 LTS
• Rust: 1.92.0 (stable)

Run Your Own Benchmarks

# Install criterion
cargo install cargo-criterion

# Run benchmarks
cargo bench -- scan

# View HTML report
open docs/benchmarks/index.html

Note: First run is slower due to disk cache warming. Results shown are from second run (warm cache).

Supported File Types

Automatic Detection

• Rust (.rs): // comments
• Python (.py): # comments
• JavaScript/TypeScript (.js, .ts, .jsx, .tsx): // comments
• Go (.go): // comments
• Java (.java): // or /* */ comments
• C/C++ (.c, .cpp, .h, .hpp): // or /* */ comments
• HTML/XML (.html, .xml): <!-- --> comments
• YAML (.yml, .yaml): # comments
• TOML (.toml): # comments
• Markdown (.md): <!-- --> comments
• Shell scripts (.sh, .bash): # comments

Custom Comment Styles

For unsupported file types, define custom comment styles:

[comment_styles]
custom = { prefix = "/*", suffix = "*/" }  # Block comments
lua = { prefix = "--" }                    # Lua line comments

CI Integration

GitHub Actions

- name: Check license headers
  uses: zippyzappypixy/fast-license-checker@v0.1.0
  with:
    path: '.'
    header: 'Copyright (c) 2024 My Company'
    fix: false  # Set to true to auto-fix

- name: Annotate PR
  run: flc --output github .

GitLab CI

license-check:
  script:
    - curl -L https://github.com/zippyzappypixy/fast-license-checker/releases/latest/download/flc-linux-x86_64 -o flc
    - chmod +x flc
    - ./flc --output json . > license-report.json
  artifacts:
    reports:
      license_scanning: license-report.json

Jenkins

pipeline {
    agent any
    steps {
        sh '''
            curl -L https://github.com/zippyzappypixy/fast-license-checker/releases/latest/download/flc-linux-x86_64 -o flc
            chmod +x flc
            ./flc --output json . > license-report.json
        '''
        publishCoverage adapters: [jacocoAdapter(path: 'license-report.json')]
    }
}

Development

Prerequisites

• Rust 1.70+
• Cargo

Building

git clone https://github.com/zippyzappypixy/fast-license-checker
cd fast-license-checker
cargo build --release

Testing

cargo test --workspace          # Run all tests
cargo bench                     # Run benchmarks
cargo test --doc                # Test documentation examples

Quality Gates

cargo fmt --all -- --check      # Check formatting
cargo clippy -- -D warnings     # Strict linting
cargo deny check                # Security audit
cargo llvm-cov --workspace      # Code coverage

Contributing

1. Fork the repository
2. Create a feature branch: git checkout -b feature/amazing-feature
3. Make your changes with tests
4. Run quality gates: cargo fmt && cargo clippy && cargo test
5. Commit your changes: git commit -m 'Add amazing feature'
6. Push to the branch: git push origin feature/amazing-feature
7. Open a Pull Request

License

Licensed under MIT OR Apache-2.0 (choose one that fits your project).

This tool is dual-licensed to maximize compatibility with your codebase.