ferropdf 0.2.6

Fast HTML to PDF — Rust-powered, 10x faster than WeasyPrint

ferropdf

Fast HTML-to-PDF for Python — Rust-powered, up to 13x faster than WeasyPrint.

---

Why ferropdf?

Most Python HTML-to-PDF libraries are slow. ferropdf is a native Rust engine exposed as a Python package via PyO3 — it renders complex invoices, reports, and dashboards in milliseconds, not seconds.

Feature	ferropdf	WeasyPrint
Speed (invoice)	~25ms	~330ms
GIL	Released during render	Held
Async-safe	Yes (FastAPI, Django)	No
Font subsetting	Automatic	Manual
Install	pip install ferropdf	System deps required

Benchmarks on Linux x86_64, median of 20 runs, reusable engine with font cache.

---

Install

pip install ferropdf

Pre-built wheels for Linux (x86_64, aarch64), macOS (x86_64, ARM), and Windows (x86_64).
Python 3.8 – 3.13 supported.

---

Quick start

One-shot rendering

import ferropdf

# HTML string → PDF bytes
pdf = ferropdf.from_html("<h1>Hello, World!</h1>")

# With options
pdf = ferropdf.from_html(
    "<h1>Invoice</h1><p>Total: $1,234</p>",
    options=ferropdf.Options(page_size="Letter", margin="25mm"),
)

# Write directly to disk
ferropdf.write_pdf("<h1>Report</h1>", "report.pdf")

# From an HTML file
pdf = ferropdf.from_file("templates/invoice.html")

Reusable engine (recommended for servers)

from ferropdf import Engine, Options

engine = Engine(Options(page_size="A4", margin="20mm"))

# Font database is cached — subsequent renders are faster
pdf1 = engine.render("<h1>Invoice #1</h1>")
pdf2 = engine.render("<h1>Invoice #2</h1>")

---

API reference

Options

ferropdf.Options(
    page_size="A4",         # A4, Letter, Legal, A3, Tabloid, ...
    margin="20mm",          # CSS margin (mm, pt, px)
    base_url=None,          # Resolve relative paths in CSS
    title=None,             # PDF metadata
    author=None,            # PDF metadata
)

Engine

engine = ferropdf.Engine(options=None)
engine.render(html: str) -> bytes         # Render HTML to PDF bytes
engine.render_file(path: str) -> bytes    # Render from file

The engine caches fonts internally — create once, render many times.

Functions

Function	Description
from_html(html, base_url=None, options=None) -> bytes	Render HTML string to PDF
from_file(path, options=None) -> bytes	Render HTML file to PDF
write_pdf(html, output_path, base_url=None, options=None)	Render and write to disk

Exceptions

All exceptions inherit from ferropdf.FerroError (itself a RuntimeError):

• ParseError — HTML/CSS parsing failure
• LayoutError — Layout computation failure
• FontError — Font loading/resolution failure
• RenderError — PDF generation failure

---

Framework integration

Django

# views.py
from ferropdf.contrib.django import PdfResponse

def invoice(request, pk):
    context = {"invoice_id": pk, "items": get_items(pk)}
    return PdfResponse("invoice.html", context, request=request)

PdfResponse renders a Django template to PDF. Pass inline=False to force download instead of browser preview.

FastAPI

# main.py
from ferropdf.contrib.fastapi import pdf_response

@app.get("/invoice/{id}/pdf")
async def invoice_pdf(id: int):
    html = templates.get_template("invoice.html").render(invoice_id=id)
    return await pdf_response(html, filename=f"invoice-{id}.pdf")

pdf_response is async — rendering runs in a thread executor with the GIL released, so it won't block your event loop.

---

CSS support

ferropdf uses industry-standard libraries for parsing and layout — not a hand-rolled engine.

Layout

Feature	Status
Block layout	Supported
Flexbox (flex-direction, flex-wrap, gap, justify-content, align-items)	Supported
Tables (<table>, <thead>, <tbody>, <tr>, <td>)	Supported
width, height (px, %, em)	Supported
margin, padding (px, mm, em, auto)	Supported
box-sizing: border-box	Supported
CSS Grid	Not yet
float	Not yet

Typography

Feature	Status
font-family (system fonts, fallbacks)	Supported
font-size (px, pt, mm, em, rem)	Supported
font-weight (normal, bold, 100–900)	Supported
font-style (normal, italic)	Supported
line-height	Supported
text-align (left, center, right)	Supported
@font-face	Not yet

Visual

Feature	Status
color, background-color (hex, rgb, rgba)	Supported
border (width, style, color)	Supported
border-radius	Supported
opacity	Not yet
box-shadow	Not yet

Page

Feature	Status
Multi-page documents	Supported
Page sizes (A0–A10, Letter, Legal, Tabloid, B-series)	Supported
Configurable margins	Supported
PDF metadata (title, author)	Supported
@page rules	Planned

---

Architecture

ferropdf is built as a modular Rust workspace with 6 crates:

HTML string
  ↓  ferropdf-parse      (html5ever + cssparser)
DOM tree + Stylesheets
  ↓  ferropdf-style       (Mozilla's selectors crate — cascade, specificity, inheritance)
Style tree
  ↓  ferropdf-layout      (Taffy flexbox engine + cosmic-text shaping)
Layout tree
  ↓  ferropdf-page        (pagination into discrete pages)
Pages
  ↓  ferropdf-render      (pdf-writer — font subsetting, compression, embedding)
PDF bytes

Crate	Role	Key dependency
ferropdf-core	Shared types: DOM, styles, geometry, errors	—
ferropdf-parse	HTML & CSS parsing	html5ever, cssparser
ferropdf-style	CSS cascade, specificity, inheritance	selectors (Mozilla)
ferropdf-layout	Box layout + text shaping	taffy, cosmic-text
ferropdf-page	Pagination across pages	—
ferropdf-render	PDF generation, font embedding	pdf-writer, subsetter

Python bindings are via PyO3 + maturin.

---

Performance

Font subsetting + caching means:

• First render: loads system fonts + builds cache (~100ms)
• Subsequent renders: 15–30ms for typical documents
• PDF sizes: small, because only used glyphs are embedded

The Engine class keeps the font cache alive — ideal for web servers handling many requests.

---

Examples

The examples/ directory includes:

• basic.py — Hello world, styled report card, invoice
• FastAPI app — Invoice, report, receipt, dashboard, letter endpoints
• Django app — Same templates with Django views

Run the FastAPI example:

cd examples/fastapi_app
pip install fastapi uvicorn jinja2
uvicorn main:app --reload
# Visit http://localhost:8000/invoice/42/pdf

---

Development

# Clone and setup
git clone https://github.com/MoncefMak/ferropdf.git
cd ferropdf
python -m venv .venv && source .venv/bin/activate
pip install maturin pytest

# Build and install locally
maturin develop --release

# Run tests
cargo test --no-default-features   # Rust tests
pytest tests/ -v                   # Python tests

# Lint
cargo fmt --all --check
cargo clippy --workspace -- -D warnings
cargo audit

---

License

MIT