FOP — Pure Rust XSL-FO Processor

A high-performance, pure Rust reimplementation of Apache FOP (Formatting Objects Processor), translating XSL-FO documents to PDF, SVG, PostScript, raster images, and plain text.

170 Rust files · 72,872 lines of code · 3,010+ tests · Zero warnings · 10–1200× faster than Java FOP

Project Status

Phase 5–6 Enhanced — Production ready with comprehensive features and testing.

Phase	Status	Description
Phase 1: Foundation	✅ Complete	Core types, property system, FO tree parsing
Phase 2: Basic Layout	✅ Complete	Area tree, block/inline layout, PDF output
Phase 3: Advanced Layout	✅ Complete	Knuth-Plass line breaking, tables, lists, graphics, images
Phase 4: Integration	✅ Complete	Multi-page breaking, engine integration
Phase 5: Advanced Features	✅ Complete	Image rendering, links, bookmarks, font embedding, i18n, encryption
Phase 6: Optimization	🔄 85% Complete	Performance (✅), streaming (✅), testing (✅)

Current stats: 3,010+ tests (all passing), 0 compiler warnings, 0 clippy warnings, 10–1200× faster than Java FOP

Key Features

XSL-FO Processing

294 XSL-FO 1.1 properties with full inheritance and shorthand expansion
29 FO element types — blocks, inlines, tables, lists, graphics, links, page masters
Knuth-Plass optimal line breaking — same algorithm as TeX for publication-quality typography
Multi-page breaking with widow/orphan control and overflow detection

Output Formats

PDF — valid, viewable, text-extractable, with font embedding and subsetting
SVG — scalable vector graphics output
PostScript — for print workflows
PNG / JPEG — raster image output
Plain text — text extraction mode

PDF Advanced Features

PDF encryption — RC4-128 with owner/user passwords and permission control
PDF/A compliance mode — for archival-quality output
Bookmarks and outlines — document navigation
Internal and external links — clickable hyperlinks
Font embedding and subsetting — TrueType/OpenType with CIDFontType2 + Identity-H encoding

Internationalization (i18n)

16+ languages supported — Japanese, Chinese, Korean, Arabic, Thai, Hindi, Hebrew, and more
CJK support — Type 0 composite fonts with proper glyph rendering
Right-to-left (RTL) — Arabic and Hebrew bidirectional text
Emoji and full Unicode — complete Unicode coverage
See docs/I18N_CAPABILITIES.md for the full guide

Streaming & Performance

Streaming mode for large documents (>1000 pages) with bounded memory
Parallel rendering infrastructure for multi-core utilization
10–1200× faster than Java FOP across all benchmarks
<10ms startup vs ~2000ms JVM cold start

Self-verification (Pure Rust)

The fop-pdf-renderer crate parses and rasterizes PDF output with no C dependencies (no poppler, no Ghostscript). Use it programmatically or from the CLI:

use fop_pdf_renderer::PdfRenderer;

let renderer = PdfRenderer::from_bytes(&pdf_bytes)?;
let page = renderer.render_page(0, 150.0)?;  // 150 DPI → RasterPage
let text = renderer.extract_text(0)?;        // user-visible text extraction

CLI equivalents:

# Round-trip self-verification (generates PDF then rasterizes it internally)
fop input.fo output.pdf --render-verify

# Standalone PDF → PNG conversion
fop-render-pdf output.pdf page.png 150

Bindings

CLI — Apache FOP-compatible command-line interface with progress bars and JSON stats
WASM — browser and Node.js bindings via wasm-bindgen
Python — bindings via PyO3 (published as fop2 on PyPI)

Performance

Real benchmark results against Java Apache FOP:

Metric	Java FOP	Rust FOP	Speedup
Simple document render	~50ms	~0.04ms	~1200×
Parse 1000-page doc	~500ms	<50ms	~10×
Memory per page	~50KB	<5KB	~10×
Binary size	15MB+ JAR	<5MB stripped	~3×
Startup time	~2000ms (JVM)	<10ms	~200×

Quick Start

# Build
cargo build --release

# Run tests (zero warnings policy)
cargo nextest run --all-features
cargo clippy --all-targets -- -D warnings

# Run an example
cargo run --example hello_pdf

Generate a PDF from XSL-FO

use fop_core::FoTreeBuilder;
use fop_layout::LayoutEngine;
use fop_render::PdfRenderer;
use std::io::Cursor;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let xml = r#"<?xml version="1.0"?>
<fo:root xmlns:fo="http://www.w3.org/1999/XSL/Format">
    <fo:layout-master-set>
        <fo:simple-page-master master-name="A4"
            page-width="210mm" page-height="297mm">
            <fo:region-body margin="1in"/>
        </fo:simple-page-master>
    </fo:layout-master-set>
    <fo:page-sequence master-reference="A4">
        <fo:flow flow-name="xsl-region-body">
            <fo:block font-size="14pt">Hello, FOP!</fo:block>
        </fo:flow>
    </fo:page-sequence>
</fo:root>"#;

    // Parse -> Layout -> Render
    let fo_tree = FoTreeBuilder::new().parse(Cursor::new(xml))?;
    let area_tree = LayoutEngine::new().layout(&fo_tree)?;
    let pdf_doc = PdfRenderer::new().render(&area_tree)?;
    let pdf_bytes = pdf_doc.to_bytes()?;

    std::fs::write("output.pdf", &pdf_bytes)?;
    println!("Wrote output.pdf ({} bytes)", pdf_bytes.len());
    Ok(())
}

CLI Usage

# Convert XSL-FO to PDF
fop -fo input.fo -pdf output.pdf

# Convert to SVG
fop -fo input.fo -svg output.svg

# Convert to PostScript
fop -fo input.fo -ps output.ps

# With progress bar and JSON stats
fop -fo input.fo -pdf output.pdf --progress --stats

# See all options
fop --help

See crates/fop-cli/USAGE.md for the full CLI reference.

Python Bindings

The Python package is available on PyPI as fop2.

pip install fop2

import fop

# One-shot conversion
pdf_bytes = fop.convert_to_pdf(fo_xml_string)

# Or use the converter class
converter = fop.FopConverter()
pdf = converter.convert_to_pdf(fo_xml)
svg = converter.convert_to_svg(fo_xml)
text = converter.convert_to_text(fo_xml)

WASM Bindings

The WASM package is available on npm as @cooljapan/fop.

npm install @cooljapan/fop

import init, { FopConverter } from '@cooljapan/fop';

await init();
const converter = new FopConverter();
const pdfBytes = converter.convertToPdf(foXml);
const svgString = converter.convertToSvg(foXml);

Documentation

📚 Comprehensive documentation available in docs/

docs/README.md — Complete documentation index
docs/I18N_CAPABILITIES.md — Internationalization guide (Japanese, CJK, Arabic RTL, etc.)
docs/LIMITATIONS.md — Current limitations and migration guide from Java FOP

Workspace Structure

fop/
├── Cargo.toml                  # Workspace root + top-level fop crate
├── crates/
│   ├── fop-types/              # Core types (Length, Color, Rect, FontMetrics, errors)
│   ├── fop-core/               # FO tree parsing & 294-property system
│   ├── fop-layout/             # Layout engine (block, inline, table, list, page breaking)
│   ├── fop-render/             # Rendering backends (PDF, SVG, PostScript, raster, text)
│   ├── fop-pdf-renderer/       # Pure Rust PDF-to-image renderer (glyph outlines, text extraction, self-verification)
│   ├── fop-cli/                # CLI tool (fop binary)
│   ├── fop-wasm/               # WebAssembly bindings (browser / Node.js)
│   └── fop-python/             # Python bindings via PyO3
├── examples/                   # 23 runnable examples
├── benches/                    # Performance & comparison benchmarks
├── tests/                      # Integration tests
├── fuzz/                       # Fuzz testing targets
└── docs/                       # Documentation

Dependency Graph

fop-types              (no internal deps)
    │
    ├── fop-core       (+ quick-xml)
    │       │
    │       ├── fop-layout   (+ image)
    │       │       │
    │       │       ├── fop-render   (+ oxiarc-deflate, ttf-parser, png, aes, sha2, md-5,
    │       │       │                   resvg, usvg, jpeg-encoder, tiny-skia)
    │       │       │
    │       │       ├── fop-cli      (+ clap, anyhow, indicatif, console,
    │       │       │                   humantime, bytesize, serde_json)
    │       │       │
    │       │       ├── fop-wasm     (+ wasm-bindgen, js-sys, serde-wasm-bindgen)
    │       │       │
    │       │       └── fop-python   (+ pyo3)
    │       │
    └───────┘

fop-pdf-renderer       (standalone: thiserror, oxiarc-deflate, ttf-parser, png,
                         jpeg-decoder, tiny-skia)

Supported XSL-FO Elements

Category	Elements
Root & Structure	`fo:root`, `fo:layout-master-set`, `fo:simple-page-master`
Regions	`fo:region-body`, `fo:region-before`, `fo:region-after`, `fo:region-start`, `fo:region-end`
Page Sequences	`fo:page-sequence`, `fo:flow`, `fo:static-content`
Block-level	`fo:block`, `fo:block-container`
Inline-level	`fo:inline`, `fo:character`, `fo:page-number`, `fo:page-number-citation`
Tables	`fo:table`, `fo:table-column`, `fo:table-header`, `fo:table-body`, `fo:table-row`, `fo:table-cell`
Lists	`fo:list-block`, `fo:list-item`, `fo:list-item-label`, `fo:list-item-body`
Graphics & Links	`fo:external-graphic`, `fo:basic-link`
Leaders	`fo:leader`

Examples

All 23 examples can be run with cargo run --example <name>:

Example	Description
`basic_types`	Length, Color, Geometry type usage
`border_background_demo`	Borders and background styling
`cli_production_example`	Production CLI workflow demonstration
`comprehensive_demo`	All Phase 3 features combined
`generate_japanese_pdfs`	Japanese PDF generation with CJK fonts
`hello_pdf`	Minimal PDF generation
`i18n_multi_font`	Multi-font internationalization
`i18n_showcase`	Full i18n showcase (16+ languages)
`layout_demo`	FO tree to area tree transformation
`manual_japanese_font`	Manual Japanese font configuration
`parse_fo_document`	Full XSL-FO document parsing
`pdf_encryption`	PDF encryption with RC4-128
`phase5_complete_demo`	Phase 5 complete feature demonstration
`phase5_features`	Phase 5 individual features
`properties`	Property system and inheritance
`ps_output_demo`	PostScript output generation
`shorthand`	Shorthand property expansion (margin, padding, border)
`streaming_demo`	Streaming mode for large documents
`styled_pdf`	PDF with colors and fonts
`svg_output_demo`	SVG output generation
`tables_lists_demo`	Tables and lists end-to-end
`text_extraction_demo`	Text extraction from PDF
`validation`	Element nesting validation

Dependencies

All dependencies are pure Rust — no C/Fortran/system libraries required.

Production Dependencies

Crate	Version	Purpose
`quick-xml`	0.39	XML parsing (zero-copy)
`thiserror`	2.0	Error type derivation
`log`	0.4	Logging facade
`oxiarc-deflate`	0.2.6	PDF stream compression (deflate) — pure Rust
`ttf-parser`	0.25	TrueType/OpenType font parsing
`png`	0.18	PNG image encoding/decoding
`jpeg-decoder`	0.3	JPEG image decoding
`jpeg-encoder`	0.7	JPEG image encoding
`image`	0.25	Image format detection and loading
`tiny-skia`	0.12	2D raster rendering
`resvg`	0.47	SVG rendering
`usvg`	0.47	SVG tree simplification
`aes`	0.8	AES encryption (PDF security)
`cbc`	0.1	CBC block cipher mode
`sha2`	0.10	SHA-256 hashing (PDF encryption)
`md-5`	0.10	MD5 hashing (PDF encryption)

CLI Dependencies

Crate	Version	Purpose
`clap`	4.5	Command-line argument parsing
`anyhow`	1.0	Error handling
`indicatif`	0.18	Progress bars
`console`	0.16	Terminal formatting
`humantime`	2.3	Human-readable durations
`bytesize`	2.3	Human-readable byte sizes
`serde_json`	1.0	JSON statistics output

Bindings Dependencies

Crate	Version	Purpose
`pyo3`	0.28	Python bindings (ABI3, Python 3.8+)
`wasm-bindgen`	0.2	WebAssembly bindings
`js-sys`	0.3	JavaScript interop

Architecture

Pipeline

XSL-FO XML ──→ FO Tree ──→ Area Tree ──→ Output (PDF/SVG/PS/PNG/text)
  (parse)       (layout)     (render)

Design Principles

Zero-copy parsing — Cow<'static, str> and arena allocation throughout
Arena allocation — index-based tree nodes (no Rc<RefCell<>> overhead)
Static dispatch — enum dispatch over trait objects where possible
Millipoint arithmetic — 1/1000 pt precision with integer math (no floating-point drift)
Release profile — LTO + single codegen unit + opt-level 3 + stripped binaries

Testing

3,010+ tests — unit, integration, and fuzz targets
Zero warnings — enforced via cargo clippy --all-targets -- -D warnings
Fuzz testing — fuzz_xml_parser, fuzz_property_parser, fuzz_layout
PDF self-verification — fop-pdf-renderer renders generated PDFs back to compare

Continuous Integration

.github/workflows/ci.yml runs fmt, clippy -D warnings, cargo nextest, and doc -D warnings on every push and PR across Linux, macOS, and Windows (stable Rust). No poppler or Ghostscript is installed on any runner — the auto-verify path is exercised end-to-end through the pure-Rust fop-pdf-renderer. Python (PyO3) and WASM bindings are built in a dedicated job that installs the required toolchains.

Development

Zero Warnings Policy

This project enforces zero compiler warnings and zero clippy warnings:

cargo clippy --all-targets -- -D warnings
cargo nextest run --all-features

Build Profiles

# Debug build
cargo build

# Optimized release build (LTO + stripped)
cargo build --release

# Build WASM bindings
cd crates/fop-wasm && wasm-pack build --target web

# Build Python bindings
cd crates/fop-python && maturin develop --release

Benchmarks

cargo bench --bench fop_benchmarks
cargo bench --bench comparison_benchmarks
cargo bench --bench performance_benchmarks

See benches/README.md for benchmark details.

Reference

Based on Apache FOP (Java, 1566+ files across 8 Maven modules)
Implements XSL-FO 1.1 Specification
CHANGELOG.md — Release history

Sponsorship

FOP is developed and maintained by COOLJAPAN OU (Team Kitasan).

If you find FOP useful, please consider sponsoring the project to support continued development of the Pure Rust ecosystem.

https://github.com/sponsors/cool-japan

Your sponsorship helps us:

Maintain and improve the COOLJAPAN ecosystem
Keep the entire ecosystem (OxiBLAS, OxiFFT, SciRS2, etc.) 100% Pure Rust
Provide long-term support and security updates

License

Licensed under the Apache License, Version 2.0. See LICENSE for details.

Name		Name	Last commit message	Last commit date
Latest commit History 2 Commits
.github		.github
benches		benches
crates		crates
docs		docs
examples		examples
fuzz		fuzz
tests		tests
.gitignore		.gitignore
CHANGELOG.md		CHANGELOG.md
Cargo.toml		Cargo.toml
LICENSE		LICENSE
README.md		README.md
TODO.md		TODO.md

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FOP — Pure Rust XSL-FO Processor

Project Status

Key Features

XSL-FO Processing

Output Formats

PDF Advanced Features

Internationalization (i18n)

Streaming & Performance

Self-verification (Pure Rust)

Bindings

Performance

Quick Start

Generate a PDF from XSL-FO

CLI Usage

Python Bindings

WASM Bindings

Documentation

Workspace Structure

Dependency Graph

Supported XSL-FO Elements

Examples

Dependencies

Production Dependencies

CLI Dependencies

Bindings Dependencies

Architecture

Pipeline

Design Principles

Testing

Continuous Integration

Development

Zero Warnings Policy

Build Profiles

Benchmarks

Reference

Sponsorship

License

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