Frontmatter Gen (frontmatter-gen)

A high-performance Rust library for parsing and serialising frontmatter in YAML, TOML, and JSON formats. Engineered for safety, efficiency, and ease of use.

• Website • Documentation • Report Bug • Request Feature • Contributing Guidelines

Overview 🚀

frontmatter-gen is a robust Rust library that provides comprehensive handling of frontmatter in content files. It delivers a type-safe, efficient solution for extracting, parsing, and serialising frontmatter in multiple formats. Whether you're building a static site generator, content management system, or any application requiring structured metadata, frontmatter-gen offers the tools you need with performance and safety at its core.

Key Features 🎯

• Zero-copy parsing: Optimised for memory efficiency
• Multi-format support: Parse and serialise YAML, TOML, and JSON
• Type-safe operations: Comprehensive error handling with Result types
• Secure processing: Input validation and size limits
• Async support: Full asynchronous operations via the ssg feature flag
• Command-line interface: Direct frontmatter manipulation tools
• Memory safety: Guaranteed memory safety through Rust's ownership system
• Comprehensive testing: Extensive test coverage and validation
• Rich documentation: Detailed guides and examples

Available Features 🛠️

This crate provides several feature flags to customise its functionality:

• default: Core frontmatter parsing functionality
• cli: Command-line interface tools for validation and extraction
• ssg: Static Site Generator functionality (includes CLI features)

Configure features in your Cargo.toml:

[dependencies]
# Enable CLI support for validation and extraction
frontmatter-gen = { version = "0.0.5", features = ["cli"] }

# Enable all features (validation, extraction and static site generation)
frontmatter-gen = { version = "0.0.5", features = ["ssg"] }

Installation via Cargo:

# Install with CLI support
cargo install frontmatter-gen --features="cli"

# Install with SSG support
cargo install frontmatter-gen --features="ssg"

Getting Started 📦

Library Usage

Add this to your Cargo.toml:

[dependencies]
# Core library with command-line interface and SSG support
frontmatter-gen = { version = "0.0.5", features = ["cli", "ssg"] }

Basic Usage 🔨

Extract and Parse Frontmatter

use frontmatter_gen::extract;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let content = r#"---
title: My Document
date: 2025-09-09
tags:
  - documentation
  - rust
---
# Content begins here"#;

    let (frontmatter, content) = extract(content)?;

    // Access frontmatter fields safely
    if let Some(title) = frontmatter.get("title").and_then(|v| v.as_str()) {
        println!("Title: {}", title);
    }

    println!("Content: {}", content);
    Ok(())
}

Format Conversion

use frontmatter_gen::{Frontmatter, Format, Value, to_format};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut frontmatter = Frontmatter::new();
    frontmatter.insert(
        "title".to_string(), 
        Value::String("My Document".to_string())
    );

    // Convert to different formats
    let yaml = to_format(&frontmatter, Format::Yaml)?;
    let json = to_format(&frontmatter, Format::Json)?;
    let toml = to_format(&frontmatter, Format::Toml)?;

    println!("YAML output:\n{}", yaml);
    println!("JSON output:\n{}", json);
    println!("TOML output:\n{}", toml);

    Ok(())
}

CLI Tool 🛠️

The fmg command provides comprehensive frontmatter operations:

# Extract frontmatter in various formats
fmg extract input.md --format yaml
fmg extract input.md --format toml
fmg extract input.md --format json

# Save extracted frontmatter
fmg extract input.md --format yaml --output frontmatter.yaml

# Validate frontmatter
fmg validate input.md --required title,date,author

You can also use the CLI directly from the source code:

# Extract frontmatter in various formats
cargo run --features="cli" extract input.md --format yaml
cargo run --features="cli" extract input.md --format toml
cargo run --features="cli" extract input.md --format json

# Save extracted frontmatter
cargo run --features="cli" extract input.md --format yaml --output frontmatter.yaml

# Validate frontmatter
cargo run --features="cli" validate input.md --required title,date,author

Static Site Generation 🌐

Build and serve your static site:

# Generate a static site
fmg build \
    --content-dir content \
    --output-dir public \
    --template-dir templates

# Or using cargo
cargo run --features="ssg" -- build \
    --content-dir content \
    --output-dir public \
    --template-dir templates

Local Development Server

# Change to the output directory
cd public

# Start a local server (using Python for demonstration)
python -m http.server 8000 --bind 127.0.0.1

Visit http://127.0.0.1:8000 in your browser to view the site.

Error Handling 🚨

The library provides comprehensive error handling with context:

use frontmatter_gen::{extract, error::Error};

fn process_content(content: &str) -> Result<(), Error> {
    let (frontmatter, _) = extract(content)?;
    
    // Validate required fields
    for field in ["title", "date", "author"].iter() {
        if !frontmatter.contains_key(*field) {
            return Err(Error::ValidationError(
                format!("Missing required field: {}", field)
            ));
        }
    }
    
    // Validate field types
    if let Some(date) = frontmatter.get("date") {
        if !date.is_string() {
            return Err(Error::ValidationError(
                "Date field must be a string".to_string()
            ));
        }
    }
    
    Ok(())
}

Logging Support 📝

Enable detailed logging with the standard Rust logging facade:

use frontmatter_gen::extract;
use log::{debug, info, Level};
use simple_logger::SimpleLogger;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Initialise logging
    SimpleLogger::new()
        .with_level(Level::Debug.to_level_filter())
        .init()?;

    let content = r#"---
title: My Document
date: 2025-09-09
---
# Content"#;

    info!("Processing frontmatter");
    let (frontmatter, content) = extract(content)?;
    debug!("Extracted frontmatter: {:?}", frontmatter);
    debug!("Content: {:?}", content);

    Ok(())
}

CLI Logging Configuration

Control logging levels via environment variables:

# Set log level for CLI operations
RUST_LOG=debug fmg extract input.md --format yaml

# Configure specific component logging
RUST_LOG=frontmatter_gen=debug,cli=info fmg validate input.md

Documentation 📚

Comprehensive documentation is available at:

• API Documentation
• User Guide and Examples
• Source Code and Examples

Contributing 🤝

We welcome contributions! Please see our Contributing Guidelines for:

• Code of Conduct
• Development Process
• Pull Request Guidelines
• Issue Reporting

Licence 📝

This project is dual-licensed under either:

• Apache License, Version 2.0 (http://www.apache.org/licenses/LICENSE-2.0)
• MIT Licence (http://opensource.org/licenses/MIT)

at your option.

Acknowledgements 🙏

Special thanks to all contributors and the Rust community for their invaluable support and feedback.