GitHub - commonmark/cmark: CommonMark parsing and rendering library and program in C (original) (raw)
cmark
cmark
is the C reference implementation of CommonMark, a rationalized version of Markdown syntax with a spec. (For the JavaScript reference implementation, seecommonmark.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 usingcmark
. - Robust. The library has been extensively fuzz-tested usingamerican 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
forGo,Haskell,Ruby,Lua,Perl,Python,R,Scala andPHP.
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
fromscanners.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:
cmake -S . -B build # optionally: -DCMAKE_INSTALL_PREFIX=path
cmake --build build # executable will be created as build/src/cmark
ctest --test-dir build
cmake --install build
Or, to create Xcode project files on OSX:
cmake -S . -B build -G Xcode
open build/cmark.xcodeproj
The GNU Makefile also provides a few other targets for developers. To run a benchmark:
For more detailed benchmarks:
To run a test for memory leaks using valgrind
:
To reformat source code using clang-format
:
To run a "fuzz test" against ten long randomly generated inputs:
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:
To make a release tarball and zip archive:
Installing (Windows)
To compile with MSVC and NMAKE:
You can cross-compile a Windows binary and dll on linux if you have themingw32
compiler:
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.
Contributing
There is a forum for discussing CommonMark; you should use it instead of github issues for questions and possibly open-ended discussions. Use the github issue trackeronly 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.