html-to-markdown

Convert HTML into Markdown with Go. It is using an HTML Parser to avoid the use of regexp as much as possible. That should prevent some weird cases and allows it to be used for cases where the input is totally unknown.

Installation

go get github.com/JohannesKaufmann/html-to-markdown

Usage

import (
	"fmt"
	"log"

	md "github.com/JohannesKaufmann/html-to-markdown"
)

converter := md.NewConverter("", true, nil)

html := `<strong>Important</strong>`

markdown, err := converter.ConvertString(html)
if err != nil {
  log.Fatal(err)
}
fmt.Println("md ->", markdown)

If you are already using goquery you can pass a selection to Convert.

markdown, err := converter.Convert(selec)

Using it on the command line

If you want to make use of html-to-markdown on the command line without any Go coding, check out html2md, a cli wrapper for html-to-markdown that has all the following options and plugins builtin.

Options

The third parameter to md.NewConverter is *md.Options.

For example you can change the character that is around a bold text ("**") to a different one (for example "__") by changing the value of StrongDelimiter.

opt := &md.Options{
  StrongDelimiter: "__", // default: **
  // ...
}
converter := md.NewConverter("", true, opt)

For all the possible options look at godocs and for a example look at the example.

Adding Rules

converter.AddRules(
  md.Rule{
    Filter: []string{"del", "s", "strike"},
    Replacement: func(content string, selec *goquery.Selection, opt *md.Options) *string {
      // You need to return a pointer to a string (md.String is just a helper function).
      // If you return nil the next function for that html element
      // will be picked. For example you could only convert an element
      // if it has a certain class name and fallback if not.
      content = strings.TrimSpace(content)
      return md.String("~" + content + "~")
    },
  },
  // more rules
)

For more information have a look at the example add_rules.

Using Plugins

If you want plugins (github flavored markdown like striketrough, tables, ...) you can pass it to Use.

import "github.com/JohannesKaufmann/html-to-markdown/plugin"

// Use the `GitHubFlavored` plugin from the `plugin` package.
converter.Use(plugin.GitHubFlavored())

Or if you only want to use the Strikethrough plugin. You can change the character that distinguishes the text that is crossed out by setting the first argument to a different value (for example "~~" instead of "~").

converter.Use(plugin.Strikethrough(""))

For more information have a look at the example github_flavored.

Writing Plugins

Have a look at the plugin folder for a reference implementation. The most basic one is Strikethrough.

Security

This library produces markdown that is readable and can be changed by humans.

Once you convert this markdown back to HTML (e.g. using goldmark or blackfriday) you need to be careful of malicious content.

This library does NOT sanitize untrusted content. Use an HTML sanitizer such as bluemonday before displaying the HTML in the browser.

Other Methods

Godoc

`func (c Converter) Keep(tags ...string) Converter`

Determines which elements are to be kept and rendered as HTML.

`func (c Converter) Remove(tags ...string) Converter`

Determines which elements are to be removed altogether i.e. converted to an empty string.

Escaping

Some characters have a special meaning in markdown. For example, the character "*" can be used for lists, emphasis and dividers. By placing a backlash before that character (e.g. "\*") you can "escape" it. Then the character will render as a raw "*" without the "markdown meaning" applied.

But why is "escaping" even necessary?

Paragraph 1
-
Paragraph 2

The markdown above doesn't seem that problematic. But "Paragraph 1" (with only one hyphen below) will be recognized as a setext heading.

<h2>Paragraph 1</h2>
<p>Paragraph 2</p>

A well-placed backslash character would prevent that...

Paragraph 1
\-
Paragraph 2

How to configure escaping? Depending on the EscapeMode option, the markdown output is going to be different.

opt = &md.Options{
	EscapeMode: "basic", // default
}

Lets try it out with this HTML input:


input	`<p>fake bold and real <strong>bold</strong></p>`

	With EscapeMode "basic"
output	`fake \\bold\\ and real bold`
rendered	fake bold and real bold

	With EscapeMode "disabled"
output	`fake bold and real bold`
rendered	fake bold and real bold

With basic escaping, we get some escape characters (the backlash "\") but it renders correctly.

With escaping disabled, the fake and real bold can't be distinguished in the markdown. That means it is both going to render as bold.

So now you know the purpose of escaping. However, if you encounter some content where the escaping breaks, you can manually disable it. But please also open an issue!

Issues

If you find HTML snippets (or even full websites) that don't produce the expected results, please open an issue!

Contributing & Testing

Please first discuss the change you wish to make, by opening an issue. I'm also happy to guide you to where a change is most likely needed.

Note: The outside API should not change because of backwards compatibility...

You don't have to be afraid of breaking the converter, since there are many "Golden File Tests":

Add your problematic HTML snippet to one of the input.html files in the testdata folder. Then run go test -update and have a look at which .golden files changed in GIT.

You can now change the internal logic and inspect what impact your change has by running go test -update again.

Note: Before submitting your change as a PR, make sure that you run those tests and check the files into GIT...

Related Projects

turndown (js), a very good library written in javascript.
lunny/html2md, which is using regex instead of goquery. I came around a few edge case when using it (leaving some html comments, ...) so I wrote my own.

License

This project is licensed under the terms of the MIT license.

Artnoc1/html-to-markdown