00mjk / sundown

Standards compliant, fast, secure markdown processing library in C

Sundown

Sundown is a Markdown parser based on the original code of the Upskirt library by Natacha Porté.

Features

• Fully standards compliant

  Sundown passes out of the box the official Markdown v1.0.0 and v1.0.3 test suites, and has been extensively tested with additional corner cases to make sure its output is as sane as possible at all times.

• Massive extension support

  Sundown has optional support for several (unofficial) Markdown extensions, such as non-strict emphasis, fenced code blocks, tables, autolinks, strikethrough and more.

• UTF-8 aware

  Sundown is fully UTF-8 aware, both when parsing the source document and when generating the resulting (X)HTML code.

• Tested & Ready to be used on production

  Sundown has been extensively security audited, and includes protection against all possible DOS attacks (stack overflows, out of memory situations, malformed Markdown syntax...) and against client attacks through malicious embedded HTML.

  We've worked very hard to make Sundown never crash or run out of memory under any input. Sundown renders all the Markdown content in GitHub and so far hasn't crashed a single time.

• Customizable renderers

  Sundown is not stuck with XHTML output: the Markdown parser of the library is decoupled from the renderer, so it's trivial to extend the library with custom renderers. A fully functional (X)HTML renderer is included.

• Optimized for speed

  Sundown is written in C, with a special emphasis on performance. When wrapped on a dynamic language such as Python or Ruby, it has shown to be up to 40 times faster than other native alternatives.

• Zero-dependency

  Sundown is a zero-dependency library composed of 3 .c files and their headers. No dependencies, no bullshit. Only standard C99 that builds everywhere.

Credits

Sundown is based on the original Upskirt parser by Natacha Porté, with many additions by Vicent Marti (@vmg) and contributions from the following authors:

Ben Noordhuis, Bruno Michel, Joseph Koshy, Krzysztof Kowalczyk, Samuel Bronson,
Shuhei Tanuma

Bindings

Sundown is available from other programming languages thanks to these bindings developed by our awesome contributors.

• Redcarpet (Ruby)
• RobotSkirt (Node.js)
• Misaka (Python)
• ffi-sundown (Ruby FFI)
• Sundown HS (Haskell)
• Goskirt (Go)
• Upskirt.go (Go)
• MoonShine (.NET)
• PHP-Sundown (PHP)
• Sundown.net (.NET)

Help us

Sundown is all about security. If you find a (potential) security vulnerability in the library, or a way to make it crash through malicious input, please report it to us, either directly via email or by opening an Issue on GitHub, and help make the web safer for everybody.

Unicode character handling

Given that the Markdown spec makes no provision for Unicode character handling, Sundown takes a conservative approach towards deciding which extended characters trigger Markdown features:

• Punctuation characters outside of the U+007F codepoint are not handled as punctuation. They are considered as normal, in-word characters for word-boundary checks.

• Whitespace characters outside of the U+007F codepoint are not considered as whitespace. They are considered as normal, in-word characters for word-boundary checks.

Install

There is nothing to install. Sundown is composed of 3 .c files (markdown.c, buffer.c and array.c), so just throw them in your project. Zero-dependency means zero-dependency. You might want to include render/html.c if you want to use the included XHTML renderer, or write your own renderer. Either way, it's all fun and joy.

If you are hardcore, you can use the included Makefile to build Sundown into a dynamic library, or to build the sample sundown executable, which is just a commandline Markdown to XHTML parser. (If gcc gives you grief about -fPIC, e.g. with MinGW, try make MFLAGS= instead of just make.)

License

Permission to use, copy, modify, and distribute this software for any purpose with or without fee is hereby granted, provided that the above copyright notice and this permission notice appear in all copies.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.