A markdown parser written in Go. Easy to extend, standard compliant, well structured.
goldmark is compliant to CommonMark 0.29.
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.
- 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.
$ go get github.com/yuin/goldmark
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)
}
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)
}
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. |
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. |
extension.Table
extension.Strikethrough
extension.Linkify
extension.TaskList
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
extension.Footnote
extension.Typographer
- This extension substitutes punctuations with typographic entities like smartypants.
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.
## heading ## {#id .className attrName=attrValue class="class1 class2"}
## heading {#id .className attrName=attrValue class="class1 class2"}
heading {#id .className attrName=attrValue}
============
Typographer extension translates plain ASCII punctuation characters into typographic punctuation HTML entities.
Default substitutions are:
Punctuation | Default entitiy |
---|---|
' |
‘ , ’ |
" |
“ , ” |
-- |
– |
--- |
— |
... |
… |
<< |
« |
>> |
» |
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
}),
),
),
)
TODO
See extension
directory for examples of extensions.
Summary:
- Define AST Node as a struct in which
ast.BaseBlock
orast.BaseInline
is embedded. - Write a parser that implements
parser.BlockParser
orparser.InlineParser
. - Write a renderer that implements
renderer.NodeRenderer
. - Define your goldmark extension that implements
goldmark.Extender
.
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.
You can run this benchmark in the _benchmark
directory.
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
----------- 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.
- goldmark-meta : A YAML metadata extension for the goldmark markdown parser.
BTC: 1NEDSyUmo4SMTDP83JJQSWi1MvQUGGNMZB
MIT
Yusuke Inuzuka