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https://github.com/commonmark/cmark

CommonMark parsing and rendering library and program in C
https://github.com/commonmark/cmark

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CommonMark parsing and rendering library and program in C

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README 

        
cmark

=====



[![CI

tests](https://github.com/commonmark/cmark/workflows/CI%20tests/badge.svg)](https://github.com/commonmark/cmark/actions)



`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),

[Scala](https://github.com/sparsetech/cmark-scala) and

[PHP](https://www.php.net/manual/en/book.cmark.php).



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. The fuzzer can be run with:



    make libFuzzer



To make a release tarball and zip archive:



    make archive



Installing (Windows)

--------------------



To compile with MSVC and NMAKE:



    nmake /f Makefile.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 scrub raw HTML and potentially

dangerous links (`javascript:`, `vbscript:`, `data:`, `file:`).



To allow these, use the option `CMARK_OPT_UNSAFE` (or

`--unsafe`) with the command line program. If doing so, we

recommend you use a HTML sanitizer specific to your needs 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

[american fuzzy lop]: http://lcamtuf.coredump.cx/afl/

[libFuzzer]: http://llvm.org/docs/LibFuzzer.html