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cmark
=====
[![Build Status]](https://travis-ci.org/commonmark/cmark)
[![Windows Build Status]](https://ci.appveyor.com/project/jgm/cmark)
`cmark` is the C reference implementation of [CommonMark], a
rationalized version of Markdown syntax with a [spec][the spec].
(For the JavaScript reference implementation, see
[commonmark.js].)
It provides a shared library (`libcmark`) with functions for parsing
CommonMark documents to an abstract syntax tree (AST), manipulating
the AST, and rendering the document to HTML, groff man, LaTeX,
CommonMark, or an XML representation of the AST. It also provides a
command-line program (`cmark`) for parsing and rendering CommonMark
documents.
Advantages of this library:
- **Portable.** The library and program are written in standard
C99 and have no external dependencies. They have been tested with
MSVC, gcc, tcc, and clang.
- **Fast.** cmark can render a Markdown version of *War and Peace* in
the blink of an eye (127 milliseconds on a ten year old laptop,
vs. 100-400 milliseconds for an eye blink). In our [benchmarks],
cmark is 10,000 times faster than the original `Markdown.pl`, and
on par with the very fastest available Markdown processors.
- **Accurate.** The library passes all CommonMark conformance tests.
- **Standardized.** The library can be expected to parse CommonMark
the same way as any other conforming parser. So, for example,
you can use `commonmark.js` on the client to preview content that
will be rendered on the server using `cmark`.
- **Robust.** The library has been extensively fuzz-tested using
[american fuzzy lop]. The test suite includes pathological cases
that bring many other Markdown parsers to a crawl (for example,
thousands-deep nested bracketed text or block quotes).
- **Flexible.** CommonMark input is parsed to an AST which can be
manipulated programmatically prior to rendering.
- **Multiple renderers.** Output in HTML, groff man, LaTeX, CommonMark,
and a custom XML format is supported. And it is easy to write new
renderers to support other formats.
- **Free.** BSD2-licensed.
It is easy to use `libcmark` in python, lua, ruby, and other dynamic
languages: see the `wrappers/` subdirectory for some simple examples.
There are also libraries that wrap `libcmark` for
[Go](https://github.com/rhinoman/go-commonmark),
[Haskell](https://hackage.haskell.org/package/cmark),
[Ruby](https://github.com/gjtorikian/commonmarker),
[Lua](https://github.com/jgm/cmark-lua),
[Perl](https://metacpan.org/release/CommonMark),
[Python](https://pypi.python.org/pypi/paka.cmark),
[R](https://cran.r-project.org/package=commonmark) and
[Scala](https://github.com/sparsetech/cmark-scala).
Installing
----------
Building the C program (`cmark`) and shared library (`libcmark`)
requires [cmake]. If you modify `scanners.re`, then you will also
need [re2c] \(>= 0.14.2\), which is used to generate `scanners.c` from
`scanners.re`. We have included a pre-generated `scanners.c` in
the repository to reduce build dependencies.
If you have GNU make, you can simply `make`, `make test`, and `make
install`. This calls [cmake] to create a `Makefile` in the `build`
directory, then uses that `Makefile` to create the executable and
library. The binaries can be found in `build/src`. The default
installation prefix is `/usr/local`. To change the installation
prefix, pass the `INSTALL_PREFIX` variable if you run `make` for the
first time: `make INSTALL_PREFIX=path`.
For a more portable method, you can use [cmake] manually. [cmake] knows
how to create build environments for many build systems. For example,
on FreeBSD:
mkdir build
cd build
cmake .. # optionally: -DCMAKE_INSTALL_PREFIX=path
make # executable will be created as build/src/cmark
make test
make install
Or, to create Xcode project files on OSX:
mkdir build
cd build
cmake -G Xcode ..
open cmark.xcodeproj
The GNU Makefile also provides a few other targets for developers.
To run a benchmark:
make bench
For more detailed benchmarks:
make newbench
To run a test for memory leaks using `valgrind`:
make leakcheck
To reformat source code using `clang-format`:
make format
To run a "fuzz test" against ten long randomly generated inputs:
make fuzztest
To do a more systematic fuzz test with [american fuzzy lop]:
AFL_PATH=/path/to/afl_directory make afl
Fuzzing with [libFuzzer] is also supported but, because libFuzzer is still
under active development, may not work with your system-installed version of
clang. Assuming LLVM has been built in `$HOME/src/llvm/build` the fuzzer can be
run with:
CC="$HOME/src/llvm/build/bin/clang" LIB_FUZZER_PATH="$HOME/src/llvm/lib/Fuzzer/libFuzzer.a" make libFuzzer
To make a release tarball and zip archive:
make archive
Installing (Windows)
--------------------
To compile with MSVC and NMAKE:
nmake
You can cross-compile a Windows binary and dll on linux if you have the
`mingw32` compiler:
make mingw
The binaries will be in `build-mingw/windows/bin`.
Usage
-----
Instructions for the use of the command line program and library can
be found in the man pages in the `man` subdirectory.
Security
--------
By default, the library will pass through raw HTML and potentially
dangerous links (`javascript:`, `vbscript:`, `data:`, `file:`).
It is recommended that users either disable this potentially unsafe
feature by using the option `CMARK_OPT_SAFE` (or `--safe` with the
command-line program), or run the output through an HTML sanitizer
to protect against
[XSS attacks](http://en.wikipedia.org/wiki/Cross-site_scripting).
Contributing
------------
There is a [forum for discussing
CommonMark](http://talk.commonmark.org); you should use it instead of
github issues for questions and possibly open-ended discussions.
Use the [github issue tracker](http://github.com/commonmark/CommonMark/issues)
only for simple, clear, actionable issues.
Authors
-------
John MacFarlane wrote the original library and program.
The block parsing algorithm was worked out together with David
Greenspan. Vicent Marti optimized the C implementation for
performance, increasing its speed tenfold. Kārlis Gaņģis helped
work out a better parsing algorithm for links and emphasis,
eliminating several worst-case performance issues.
Nick Wellnhofer contributed many improvements, including
most of the C library's API and its test harness.
[benchmarks]: benchmarks.md
[the spec]: http://spec.commonmark.org
[CommonMark]: http://commonmark.org
[cmake]: http://www.cmake.org/download/
[re2c]: http://re2c.org
[commonmark.js]: https://github.com/commonmark/commonmark.js
[Build Status]: https://img.shields.io/travis/commonmark/cmark/master.svg?style=flat
[Windows Build Status]: https://ci.appveyor.com/api/projects/status/32r7s2skrgm9ubva?svg=true
[american fuzzy lop]: http://lcamtuf.coredump.cx/afl/
[libFuzzer]: http://llvm.org/docs/LibFuzzer.html
|
