goldmark

A markdown parser written in Go. Easy to extend, standard compliant, well structured.

goldmark is compliant to CommonMark 0.29.

Motivation

I need a markdown parser for Go that meets following conditions:

• Easy to extend.
  • Markdown is poor in document expressions compared with other light markup languages like restructuredText.
  • We have extended a markdown syntax. i.e. : PHPMarkdownExtra, Github Flavored Markdown.
• Standard compliant.
  • Markdown has many dialects.
  • Github Flavored Markdown is widely used and it is based on CommonMark aside from whether CommonMark is good specification or not.
    • CommonMark is too complicated and hard to implement.
• Well structured.
  • AST based, and preserves source position of nodes.
• Written in pure Go.

golang-commonmark may be a good choice, but it seems copy of the markdown-it .

blackfriday.v2 is a fast and widely used implementation, but it is not CommonMark compliant and can not be extended from outside of the package since it's AST is not interfaces but structs.

Furthermore, its behavior differs with other implementations in some cases especially of lists. (Deep nested lists don't output correctly #329, List block cannot have a second line #244, etc).

This behavior sometimes causes problems. If you migrate your markdown text to blackfriday based wikis from Github, many lists will immediately be broken.

As mentioned above, CommonMark is too complicated and hard to implement, So Markdown parsers based on CommonMark barely exist.

Features

• Standard compliant. : goldmark get full compliance with latest CommonMark spec.
• Extensible. : Do you want to add a @username mention syntax to the markdown? You can easily do it in goldmark. You can add your AST nodes, parsers for block level elements, parsers for inline level elements, transformers for paragraphs, transformers for whole AST structure, and renderers.
• Preformance. : goldmark performs pretty much equally to the cmark (CommonMark reference implementation written in c).
• Builtin extensions. : goldmark ships with common extensions like tables, strikethrough, task lists, and definition lists.
• Depends only on standard libraries.

Installation

$ go get github.com/yuin/goldmark

Usage

Import packages:

import (
	"bytes"
	"github.com/yuin/goldmark"
)

Convert Markdown documents with the CommonMark compliant mode:

var buf bytes.Buffer
if err := goldmark.Convert(source, &buf); err != nil {
  panic(err)
}

Custom parser and renderer

import (
	"bytes"
	"github.com/yuin/goldmark"
	"github.com/yuin/goldmark/extension"
	"github.com/yuin/goldmark/parser"
	"github.com/yuin/goldmark/renderer/html"
)

md := goldmark.New(
          goldmark.WithExtensions(extension.GFM),
          goldmark.WithParserOptions(
              parser.WithAutoHeadingID(),
          ),
          goldmark.WithRendererOptions(
              html.WithHardWraps(),
              html.WithXHTML(),
          ),
      )
var buf bytes.Buffer
if err := md.Convert(source, &buf); err != nil {
    panic(err)
}

Parser and Renderer options

Parser options

Functional option	Type	Description
parser.WithBlockParsers	A util.PrioritizedSlice whose elements are parser.BlockParser	Parsers for parsing block level elements.
parser.WithInlineParsers	A util.PrioritizedSlice whose elements are parser.InlineParser	Parsers for parsing inline level elements.
parser.WithParagraphTransformers	A util.PrioritizedSlice whose elements are parser.ParagraphTransformer	Transformers for transforming paragraph nodes.
parser.WithAutoHeadingID	-	Enables auto heading ids.
parser.WithAttribute	-	Enables custom attributes. Currently only headings supports attributes.

HTML Renderer options

Functional option	Type	Description
html.WithWriter	html.Writer	html.Writer for writing contents to an io.Writer.
html.WithHardWraps	-	Render new lines as <br>.
html.WithXHTML	-	Render as XHTML.
html.WithUnsafe	-	By default, goldmark does not render raw HTMLs and potentially dangerous links. With this option, goldmark renders these contents as it is.

Built-in extensions

• extension.Table
  • Github Flavored Markdown: Tables
• extension.Strikethrough
  • Github Flavored Markdown: Strikethrough
• extension.Linkify
  • Github Flavored Markdown: Autolinks
• extension.TaskList
  • Github Flavored Markdown: Task list items
• extension.GFM
  • This extension enables Table, Strikethrough, Linkify and TaskList.
  • This extension does not filter tags defined in 6.11Disallowed Raw HTML (extension). If you need to filter HTML tags, see Security
• extension.DefinitionList
  • PHP Markdown Extra: Definition lists
• extension.Footnote
  • PHP Markdown Extra: Footnotes
• extension.Typographer
  • This extension substitutes punctuations with typographic entities like smartypants.

Attributes

parser.WithAttribute option allows you to define attributes on some elements.

Currently only headings support attributes.

Attributes are being discussed in the CommonMark forum. This syntax possibly changes in the future.

Headings

## heading ## {#id .className attrName=attrValue class="class1 class2"}

## heading {#id .className attrName=attrValue class="class1 class2"}

heading {#id .className attrName=attrValue}
============

Typographer extension

Typographer extension translates plain ASCII punctuation characters into typographic punctuation HTML entities.

Default substitutions are:

Punctuation	Default entitiy
'	‘, ’
"	“, ”
--	–
---	—
...	…
<<	&laquo;
>>	&raquo;

You can overwrite the substitutions by extensions.WithTypographicSubstitutions.

markdown := goldmark.New(
	goldmark.WithExtensions(
		extension.NewTypographer(
			extension.WithTypographicSubstitutions(extension.TypographicSubstitutions{
				extension.LeftSingleQuote:  []byte("‚"),
				extension.RightSingleQuote: nil, // nil disables a substitution
			}),
		),
	),
)

Create extensions

TODO

See extension directory for examples of extensions.

Summary:

1. Define AST Node as a struct in which ast.BaseBlock or ast.BaseInline is embedded.
2. Write a parser that implements parser.BlockParser or parser.InlineParser.
3. Write a renderer that implements renderer.NodeRenderer.
4. Define your goldmark extension that implements goldmark.Extender.

Security

By default, goldmark does not render raw HTMLs and potentially dangerous urls. If you need to gain more control over untrusted contents, it is recommended to use HTML sanitizer such as bluemonday.

Benchmark

You can run this benchmark in the _benchmark directory.

against other golang libraries

blackfriday v2 seems fastest, but it is not CommonMark compiliant so performance of the blackfriday v2 can not simply be compared with other Commonmark compliant libraries.

Though goldmark builds clean extensible AST structure and get full compliance with Commonmark, it is resonably fast and less memory consumption.

BenchmarkGoldMark-4                  200           6388385 ns/op         2085552 B/op      13856 allocs/op
BenchmarkGolangCommonMark-4          200           7056577 ns/op         2974119 B/op      18828 allocs/op
BenchmarkBlackFriday-4               300           5635122 ns/op         3341668 B/op      20057 allocs/op

against cmark(A CommonMark reference implementation written in c)

----------- cmark -----------
file: _data.md
iteration: 50
average: 0.0050112160 sec
go run ./goldmark_benchmark.go
------- goldmark -------
file: _data.md
iteration: 50
average: 0.0064833820 sec

As you can see, goldmark performs pretty much equally to the cmark.

Extensions

• goldmark-meta : A YAML metadata extension for the goldmark markdown parser.
• goldmark-highlighting : A Syntax highlighting extension for the goldmark markdown parser.
• goldmark-mathjax : Mathjax support for goldmark markdown parser

Donation

BTC: 1NEDSyUmo4SMTDP83JJQSWi1MvQUGGNMZB

License

MIT

Author

Yusuke Inuzuka