Blackfriday

Blackfriday is a Markdown processor implemented in Go. It is paranoid about its input (so you can safely feed it user-supplied data), it is fast, it supports common extensions (tables, smart punctuation substitutions, etc.), and it is safe for all utf-8 (unicode) input.

HTML output is currently supported, along with Smartypants extensions. An experimental LaTeX output engine is also included.

It started as a translation from C of upskirt.

Installation

Assuming you have recent version of Go installed, along with git:

goinstall github.com/russross/blackfriday

will download, compile, and install the package into $GOROOT/src/pkg/github.com/russross/blackfriday.

For basic usage, it is as simple as getting your input into a byte slice and calling:

output := blackfriday.MarkdownBasic(input)

This renders it with no extensions enabled. To get a more useful feature set, use this instead:

output := blackfriday.MarkdownCommon(input)

If you want to customize the set of options, first get a renderer (currently either the HTML or LaTeX output engines), then use it to call the more general Markdown function. For examples, see the implementations of MarkdownBasic and MarkdownCommon in markdown.go.

You can also check out example/main.go for a more complete example of how to use it. Run gomake in that directory to build a simple command-line markdown tool:

cd $GOROOT/src/pkg/github.com/russross/blackfriday/example
gomake

will build the binary markdown in the example directory.

Features

All features of upskirt are supported, including:

• The Markdown v1.0.3 test suite passes with the --tidy option. Without --tidy, the differences appear to be bugs/dubious features in the original, mostly related to whitespace.

• Common extensions, including table support, fenced code blocks, autolinks, strikethroughs, non-strict emphasis, etc.

• Paranoid parsing, making it safe to feed untrusted used input without fear of bad things happening. There are still some corner cases that are untested, but it is already more strict than upskirt (bounds checking in Go uncovered a few off-by-one errors that were present in upskirt).

• Good performance. I have not done rigorous benchmarking, but informal testing suggests it is around 3--4x slower than upskirt for general input. It blows away most other markdown processors.

• Thread safe. You can run multiple parsers is different goroutines without ill effect. There is no dependence on global shared state.

• Minimal dependencies. Blackfriday only depends on standard library packages in Go. The source code is pretty self-contained, so it is easy to add to any project.

• Output successfully validates using the W3C validation tool for HTML 4.01 and XHTML 1.0 Transitional.

Extensions

In addition to the extensions offered by upskirt, this package implements two additional Smartypants options:

• LaTeX-style dash parsing, where -- is translated into –, and --- is translated into —
• Generic fractions, where anything that looks like a fraction is translated into suitable HTML (instead of just a few special cases). For example, 4/5 becomes <sup>4</sup>&frasl;<sub>5</sub>, which renders as ⁴⁄₅.

LaTeX Output

A rudimentary LaTeX rendering backend is also included. To see an example of its usage, see main.go:

It renders some basic documents, but is only experimental at this point. In particular, it does not do any inline escaping, so input that happens to look like LaTeX code will be passed through without modification.

Todo

• More unit testing
• Code cleanup
• Better code documentation
• Markdown pretty-printer output engine
• Improve unicode support. It does not understand all unicode rules (about what constitutes a letter, a punctuation symbol, etc.), so it may fail to detect word boundaries correctly in some instances. It is safe on all utf-8 input.

License

Blackfriday is distributed under the Simplified BSD License:

Copyright © 2011 Russ Ross. All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

The views and conclusions contained in the software and documentation are those of the authors and should not be interpreted as representing official policies, either expressed or implied, of the copyright holder.