summaryrefslogtreecommitdiff
path: root/README.md
blob: 5c43c1a84a13ff33d325778e23a8c364da5e76b2 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
cmark
=====

[![Build Status]](https://travis-ci.org/jgm/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](http://hackage.haskell.org/package/cmark),
[ruby](https://github.com/gjtorikian/commonmarker),
[lua](https://github.com/jgm/cmark-lua),
[Perl](https://metacpan.org/release/CommonMark), and
[R](http://cran.r-project.org/package=commonmark).

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

To run a test for memory leaks using `valgrind`:

    make leakcheck

To reformat source code using `astyle`:

    make astyle

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

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/jgm/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/jgm/commonmark.js
[Build Status]: https://img.shields.io/travis/jgm/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/