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===========

Blackfriday is a [Markdown][1] processor implemented in [Go][2]. It

is paranoid about its input (so you can safely feed it user-supplied

data), it is fast, it supports common extensions (tables, smart

punctuation substitutions, etc.), and it is safe for all utf-8

(unicode) input.

HTML output is currently supported, along with Smartypants

extensions. An experimental LaTeX output engine is also included.

It started as a translation from C of [Sundown][3].

Installation

------------

Blackfriday is compatible with Go 1. If you are using an older

release of Go, consider using v1.1 of blackfriday, which was based

on the last stable release of Go prior to Go 1. You can find it as a

tagged commit on github.

With Go 1 and git installed:

    go get github.com/russross/blackfriday

will download, compile, and install the package into your `$GOPATH`

directory hierarchy. Alternatively, you can achieve the same if you

import it into a project:

    import "github.com/russross/blackfriday"

and `go get` without parameters.

Usage

-----

For basic usage, it is as simple as getting your input into a byte

slice and calling:

    output := blackfriday.MarkdownBasic(input)

This renders it with no extensions enabled. To get a more useful

feature set, use this instead:

    output := blackfriday.MarkdownCommon(input)

### Sanitize untrusted content

Blackfriday itself does nothing to protect against malicious content. If you are

dealing with user-supplied markdown, we recommend running blackfriday's output

through HTML sanitizer such as

[Bluemonday](https://github.com/microcosm-cc/bluemonday).

Here's an example of simple usage of blackfriday together with bluemonday:

``` go

import (

    "github.com/microcosm-cc/bluemonday"

    "github.com/russross/blackfriday"

)

// ...

unsafe := blackfriday.MarkdownCommon(input)

html := bluemonday.UGCPolicy().SanitizeBytes(unsafe)

```

### Custom options

If you want to customize the set of options, first get a renderer

(currently either the HTML or LaTeX output engines), then use it to

call the more general `Markdown` function. For examples, see the

implementations of `MarkdownBasic` and `MarkdownCommon` in

`markdown.go`.

You can also check out `blackfriday-tool` for a more complete example

of how to use it. Download and install it using:

    go get github.com/russross/blackfriday-tool

This is a simple command-line tool that allows you to process a

markdown file using a standalone program.  You can also browse the

source directly on github if you are just looking for some example

code:

* <http://github.com/russross/blackfriday-tool>

Note that if you have not already done so, installing

`blackfriday-tool` will be sufficient to download and install

blackfriday in addition to the tool itself. The tool binary will be

installed in `$GOPATH/bin`.  This is a statically-linked binary that

can be copied to wherever you need it without worrying about

dependencies and library versions.

### Sanitized anchor names

Blackfriday includes an algorithm for creating sanitized anchor names

corresponding to a given input text. This algorithm is used to create

anchors for headings when `EXTENSION_AUTO_HEADER_IDS` is enabled. The

algorithm has a specification, so that other packages can create

compatible anchor names and links to those anchors.

The specification is located at https://godoc.org/github.com/russross/blackfriday#hdr-Sanitized_Anchor_Names.

[`SanitizedAnchorName`](https://godoc.org/github.com/russross/blackfriday#SanitizedAnchorName) exposes this functionality, and can be used to

create compatible links to the anchor names generated by blackfriday.

This algorithm is also implemented in a small standalone package at

[`github.com/shurcooL/sanitized_anchor_name`](https://godoc.org/github.com/shurcooL/sanitized_anchor_name). It can be useful for clients

that want a small package and don't need full functionality of blackfriday.

Features

--------

All features of Sundown are supported, including:

*   **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 blackfriday is

    more consistent and cleaner.

*   **Common extensions**, including table support, fenced code

    blocks, autolinks, strikethroughs, non-strict emphasis, etc.

*   **Safety**. Blackfriday 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](https://github.com/russross/blackfriday#sanitize-untrusted-content).

*   **Fast processing**. 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**. Blackfriday only depends on standard

    library packages in Go. The source code is pretty

    self-contained, so it is easy to add to any project, including

    Google App Engine projects.

*   **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. Blackfriday lets 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.

    To preserve classes of fenced code blocks while using the bluemonday

    HTML sanitizer, use the following policy:

    ``` go

    p := bluemonday.UGCPolicy()

    p.AllowAttrs("class").Matching(regexp.MustCompile("^language-[a-zA-Z0-9]+$")).OnElements("code")

    html := p.SanitizeBytes(unsafe)

    ```

*   **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**. Blackfriday 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 (it is off by

    default in the `MarkdownBasic` and `MarkdownCommon` convenience

    functions), newlines in the input translate into line breaks in

    the output.

*   **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>⁄<sub>5</sub>`, which renders as

    <sup>4</sup>⁄<sub>5</sub>.

Other renderers

---------------

Blackfriday is structured to allow alternative rendering engines. Here

are a few of note:

*   [github_flavored_markdown](https://godoc.org/github.com/shurcooL/github_flavored_markdown):

    provides a GitHub Flavored Markdown renderer with fenced code block

    highlighting, clickable header anchor links.

    It's not customizable, and its goal is to produce HTML output

    equivalent to the [GitHub Markdown API endpoint](https://developer.github.com/v3/markdown/#render-a-markdown-document-in-raw-mode),

    except the rendering is performed locally.

*   [markdownfmt](https://github.com/shurcooL/markdownfmt): like gofmt,

    but for markdown.

*   LaTeX output: renders output as LaTeX. This is currently part of the

    main Blackfriday repository, but may be split into its own project

    in the future. If you are interested in owning and maintaining the

    LaTeX output component, please be in touch.

    It renders some basic documents, but is only experimental at this

    point. In particular, it does not do any inline escaping, so input

    that happens to look like LaTeX code will be passed through without

    modification.

*   [Md2Vim](https://github.com/FooSoft/md2vim): transforms markdown files into vimdoc format.

Todo

----

*   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.

License

-------

[Blackfriday is distributed under the Simplified BSD License](LICENSE.txt)

   [1]: http://daringfireball.net/projects/markdown/ "Markdown"

   [2]: http://golang.org/ "Go Language"

   [3]: https://github.com/vmg/sundown "Sundown"