Markdown Parser and HTML Renderer for Go

Package github.com/gomarkdown/markdown is a Markdown parser and HTML renderer implemented in Go.

It's fast and supports common extensions.

Installation

To install the library:

go get -u github.com/gomarkdown/markdown

API Docs: https://godoc.org/github.com/gomarkdown/markdown

Usage

To convert markdown text to HTML using reasonable defaults:

md := []byte("## markdown document")
output := markdown.ToHTML(md, nil, nil)

To customize both parser and HTML renderer:

md := []byte("markdown text")
extensions := CommonExtensions | AutoHeadingIDs
parser := NewParserWithExensions(extensions)
htmlParams := CommonHTMLFlags | HrefTargetBlank
renderer := NewHTMLRenderer(htmlParams)
html := ToHTML(md, parser, renderer)

Sanitize untrusted content

We don't protect against malicious content. When dealing with user-provided markdown, run renderer HTML through HTML sanitizer such as Bluemonday.

Here's an example of simple usage with Bluemonday:

import (
    "github.com/microcosm-cc/bluemonday"
    "github.com/gomarkdown/markdown"
)

// ...
maybeUnsafeHTML := markdown.ToHTML(input, nil, nil)
html := bluemonday.UGCPolicy().SanitizeBytes(maybeUnsafeHTML)

Customizing parser and renderer

Ways to customize parser:

• use custom extensions by creating parser with markdown.NewParserWithExtensions(extensions)
• over-ride Parser.ReferenceOverride function

You can also check out cmd/mdhtml for more complete example of how to use it.

You can install it with:

go get -u github.com/gomarkdown/markdown/cmd/mdtohtml

This is a simple command-line tool to convert markdown files to HTML.

Features

• Compatibility. The Markdown v1.0.3 test suite passes with the --tidy option. Without --tidy, the differences are mostly in whitespace and entity escaping, where this package is more consistent and cleaner.

• Common extensions, including table support, fenced code blocks, autolinks, strikethroughs, non-strict emphasis, etc.

• Safety. Markdown is paranoid when parsing, making it safe to feed untrusted user input without fear of bad things happening. The test suite stress tests this and there are no known inputs that make it crash. If you find one, please let me know and send me the input that does it.

  NOTE: "safety" in this context means runtime safety only. In order to protect yourself against JavaScript injection in untrusted content, see this example.

• Fast. It is fast enough to render on-demand in most web applications without having to cache the output.

• Thread safety. You can run multiple parsers in different goroutines without ill effect. There is no dependence on global shared state.

• Minimal dependencies. Only depends on standard library packages in Go.

• Standards compliant. Output successfully validates using the W3C validation tool for HTML 4.01 and XHTML 1.0 Transitional.

Extensions

In addition to the standard markdown syntax, this package implements the following extensions:

• Intra-word emphasis supression. The _ character is commonly used inside words when discussing code, so having markdown interpret it as an emphasis command is usually the wrong thing. We let you treat all emphasis markers as normal characters when they occur inside a word.

• Tables. Tables can be created by drawing them in the input using a simple syntax:

  Name    | Age
  --------|------
  Bob     | 27
  Alice   | 23
  

• Fenced code blocks. In addition to the normal 4-space indentation to mark code blocks, you can explicitly mark them and supply a language (to make syntax highlighting simple). Just mark it like this:

  ```go
  func getTrue() bool {
      return true
  }
  ```
  

  You can use 3 or more backticks to mark the beginning of the block, and the same number to mark the end of the block.

• Definition lists. A simple definition list is made of a single-line term followed by a colon and the definition for that term.

  Cat
  : Fluffy animal everyone likes
  
  Internet
  : Vector of transmission for pictures of cats
  

  Terms must be separated from the previous definition by a blank line.

• Footnotes. A marker in the text that will become a superscript number; a footnote definition that will be placed in a list of footnotes at the end of the document. A footnote looks like this:

  This is a footnote.[^1]
  
  [^1]: the footnote text.
  

• Autolinking. We can find URLs that have not been explicitly marked as links and turn them into links.

• Strikethrough. Use two tildes (~~) to mark text that should be crossed out.

• Hard line breaks. With this extension enabled newlines in the input translate into line breaks in the output. This extension is off by default.

• Smart quotes. Smartypants-style punctuation substitution is supported, turning normal double- and single-quote marks into curly quotes, etc.

• LaTeX-style dash parsing is an additional option, where -- is translated into –, and --- is translated into —. This differs from most smartypants processors, which turn a single hyphen into an ndash and a double hyphen into an mdash.

• Smart fractions, where anything that looks like a fraction is translated into suitable HTML (instead of just a few special cases like most smartypant processors). For example, 4/5 becomes <sup>4</sup>&frasl;<sub>5</sub>, which renders as ⁴⁄₅.

Todo

• port https://github.com/russross/blackfriday/issues/348
• port LaTeX output: renders output as LaTeX.
• port https://github.com/shurcooL/github_flavored_markdown to markdown
• port markdownfmt: like gofmt, but for markdown.
• More unit testing
• Improve unicode support. It does not understand all unicode rules (about what constitutes a letter, a punctuation symbol, etc.), so it may fail to detect word boundaries correctly in some instances. It is safe on all utf-8 input.

History

markdown is a fork of v2 of github.com/russross/blackfriday that is:

• actively maintained (sadly in Feb 2018 blackfriday was inactive for 5 months with many bugs and pull requests accumulated)
• cleaned up API to make it easier to use (IMHO)

Blackfriday itself was based on C implementation sundown which in turn was based on libsoldout.

License

markdown is distributed under the Simplified BSD License