blackfriday

package
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 Go to latest Published: Sep 30, 2015 License: BSD-2-Clause, MIT Imports: 7 Imported by: 0

README

Blackfriday Build Status

Blackfriday is a Markdown processor implemented in Go. 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.

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.

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

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:

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.

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 agains JavaScript injection in untrusted content, see this example.

  • 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.

  • 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>&frasl;<sub>5</sub>, which renders as 4⁄5.

Other renderers

Blackfriday is structured to allow alternative rendering engines. Here are a few of note:

  • 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, except the rendering is performed locally.

  • 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.

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

Documentation

Overview

Blackfriday markdown processor.

Translates plain text with simple formatting rules into HTML or LaTeX.

Index

Constants

View Source 
const (
	HTML_SKIP_HTML                 = 1 << iota // skip preformatted HTML blocks
	HTML_SKIP_STYLE                            // skip embedded <style> elements
	HTML_SKIP_IMAGES                           // skip embedded images
	HTML_SKIP_LINKS                            // skip all links
	HTML_SAFELINK                              // only link to trusted protocols
	HTML_NOFOLLOW_LINKS                        // only link with rel="nofollow"
	HTML_NOREFERRER_LINKS                      // only link with rel="noreferrer"
	HTML_HREF_TARGET_BLANK                     // add a blank target
	HTML_TOC                                   // generate a table of contents
	HTML_OMIT_CONTENTS                         // skip the main contents (for a standalone table of contents)
	HTML_COMPLETE_PAGE                         // generate a complete HTML page
	HTML_USE_XHTML                             // generate XHTML output instead of HTML
	HTML_USE_SMARTYPANTS                       // enable smart punctuation substitutions
	HTML_SMARTYPANTS_FRACTIONS                 // enable smart fractions (with HTML_USE_SMARTYPANTS)
	HTML_SMARTYPANTS_LATEX_DASHES              // enable LaTeX-style dashes (with HTML_USE_SMARTYPANTS)
	HTML_SMARTYPANTS_ANGLED_QUOTES             // enable angled double quotes (with HTML_USE_SMARTYPANTS) for double quotes rendering
	HTML_FOOTNOTE_RETURN_LINKS                 // generate a link at the end of a footnote to return to the source
)

Html renderer configuration options.

View Source 
const (
	EXTENSION_NO_INTRA_EMPHASIS          = 1 << iota // ignore emphasis markers inside words
	EXTENSION_TABLES                                 // render tables
	EXTENSION_FENCED_CODE                            // render fenced code blocks
	EXTENSION_AUTOLINK                               // detect embedded URLs that are not explicitly marked
	EXTENSION_STRIKETHROUGH                          // strikethrough text using ~~test~~
	EXTENSION_LAX_HTML_BLOCKS                        // loosen up HTML block parsing rules
	EXTENSION_SPACE_HEADERS                          // be strict about prefix header rules
	EXTENSION_HARD_LINE_BREAK                        // translate newlines into line breaks
	EXTENSION_TAB_SIZE_EIGHT                         // expand tabs to eight spaces instead of four
	EXTENSION_FOOTNOTES                              // Pandoc-style footnotes
	EXTENSION_NO_EMPTY_LINE_BEFORE_BLOCK             // No need to insert an empty line to start a (code, quote, ordered list, unordered list) block
	EXTENSION_HEADER_IDS                             // specify header IDs  with {#id}
	EXTENSION_TITLEBLOCK                             // Titleblock ala pandoc
	EXTENSION_AUTO_HEADER_IDS                        // Create the header ID from the text
	EXTENSION_BACKSLASH_LINE_BREAK                   // translate trailing backslashes into line breaks
	EXTENSION_DEFINITION_LISTS                       // render definition lists

)

These are the supported markdown parsing extensions. OR these values together to select multiple extensions.

View Source 
const (
	LINK_TYPE_NOT_AUTOLINK = iota
	LINK_TYPE_NORMAL
	LINK_TYPE_EMAIL
)

These are the possible flag values for the link renderer. Only a single one of these values will be used; they are not ORed together. These are mostly of interest if you are writing a new output format.

View Source 
const (
	LIST_TYPE_ORDERED = 1 << iota
	LIST_TYPE_DEFINITION
	LIST_TYPE_TERM
	LIST_ITEM_CONTAINS_BLOCK
	LIST_ITEM_BEGINNING_OF_LIST
	LIST_ITEM_END_OF_LIST
)

These are the possible flag values for the ListItem renderer. Multiple flag values may be ORed together. These are mostly of interest if you are writing a new output format.

View Source 
const (
	TABLE_ALIGNMENT_LEFT = 1 << iota
	TABLE_ALIGNMENT_RIGHT
	TABLE_ALIGNMENT_CENTER = (TABLE_ALIGNMENT_LEFT | TABLE_ALIGNMENT_RIGHT)
)

These are the possible flag values for the table cell renderer. Only a single one of these values will be used; they are not ORed together. These are mostly of interest if you are writing a new output format.

View Source 
const (
	TAB_SIZE_DEFAULT = 4
	TAB_SIZE_EIGHT   = 8
)

The size of a tab stop.

View Source 
const VERSION = "1.1"

Variables

This section is empty.

Functions

func Markdown 

func Markdown(input []byte, renderer Renderer, extensions int) []byte

Markdown is the main rendering function. It parses and renders a block of markdown-encoded text. The supplied Renderer is used to format the output, and extensions dictates which non-standard extensions are enabled.

To use the supplied Html or LaTeX renderers, see HtmlRenderer and LatexRenderer, respectively.

func MarkdownBasic 

func MarkdownBasic(input []byte) []byte

MarkdownBasic is a convenience function for simple rendering. It processes markdown input with no extensions enabled.

func MarkdownCommon 

func MarkdownCommon(input []byte) []byte

Call Markdown with most useful extensions enabled MarkdownCommon is a convenience function for simple rendering. It processes markdown input with common extensions enabled, including:

* Smartypants processing with smart fractions and LaTeX dashes

* Intra-word emphasis suppression

* Tables

* Fenced code blocks

* Autolinking

* Strikethrough support

* Strict header parsing

* Custom Header IDs

func MarkdownOptions 

func MarkdownOptions(input []byte, renderer Renderer, opts Options) []byte

MarkdownOptions is just like Markdown but takes additional options through the Options struct.

Types

type Html 

type Html struct {
	// contains filtered or unexported fields
}

Html is a type that implements the Renderer interface for HTML output.

Do not create this directly, instead use the HtmlRenderer function. 

func (options *Html) AutoLink(out *bytes.Buffer, link []byte, kind int)

func (*Html) BlockCode 

func (options *Html) BlockCode(out *bytes.Buffer, text []byte, lang string)

func (*Html) BlockHtml 

func (options *Html) BlockHtml(out *bytes.Buffer, text []byte)

func (*Html) BlockQuote 

func (options *Html) BlockQuote(out *bytes.Buffer, text []byte)

func (*Html) CodeSpan 

func (options *Html) CodeSpan(out *bytes.Buffer, text []byte)

func (*Html) DocumentFooter 

func (options *Html) DocumentFooter(out *bytes.Buffer)

func (*Html) DocumentHeader 

func (options *Html) DocumentHeader(out *bytes.Buffer)

func (*Html) DoubleEmphasis 

func (options *Html) DoubleEmphasis(out *bytes.Buffer, text []byte)

func (*Html) Emphasis 

func (options *Html) Emphasis(out *bytes.Buffer, text []byte)

func (*Html) Entity 

func (options *Html) Entity(out *bytes.Buffer, entity []byte)

func (*Html) FootnoteItem 

func (options *Html) FootnoteItem(out *bytes.Buffer, name, text []byte, flags int)

func (*Html) FootnoteRef 

func (options *Html) FootnoteRef(out *bytes.Buffer, ref []byte, id int)

func (*Html) Footnotes 

func (options *Html) Footnotes(out *bytes.Buffer, text func() bool)

func (*Html) GetFlags 

func (options *Html) GetFlags() int

func (*Html) HRule 

func (options *Html) HRule(out *bytes.Buffer)

func (*Html) Header 

func (options *Html) Header(out *bytes.Buffer, text func() bool, level int, id string)

func (*Html) Image 

func (options *Html) Image(out *bytes.Buffer, link []byte, title []byte, alt []byte)

func (*Html) LineBreak 

func (options *Html) LineBreak(out *bytes.Buffer)
func (options *Html) Link(out *bytes.Buffer, link []byte, title []byte, content []byte)

func (*Html) List 

func (options *Html) List(out *bytes.Buffer, text func() bool, flags int)

func (*Html) ListItem 

func (options *Html) ListItem(out *bytes.Buffer, text []byte, flags int)

func (*Html) NormalText 

func (options *Html) NormalText(out *bytes.Buffer, text []byte)

func (*Html) Paragraph 

func (options *Html) Paragraph(out *bytes.Buffer, text func() bool)

func (*Html) RawHtmlTag 

func (options *Html) RawHtmlTag(out *bytes.Buffer, text []byte)

func (*Html) Smartypants 

func (options *Html) Smartypants(out *bytes.Buffer, text []byte)

func (*Html) StrikeThrough 

func (options *Html) StrikeThrough(out *bytes.Buffer, text []byte)

func (*Html) Table 

func (options *Html) Table(out *bytes.Buffer, header []byte, body []byte, columnData []int)

func (*Html) TableCell 

func (options *Html) TableCell(out *bytes.Buffer, text []byte, align int)

func (*Html) TableHeaderCell 

func (options *Html) TableHeaderCell(out *bytes.Buffer, text []byte, align int)

func (*Html) TableRow 

func (options *Html) TableRow(out *bytes.Buffer, text []byte)

func (*Html) TitleBlock 

func (options *Html) TitleBlock(out *bytes.Buffer, text []byte)

func (*Html) TocFinalize 

func (options *Html) TocFinalize()

func (*Html) TocHeader 

func (options *Html) TocHeader(text []byte, level int)

func (*Html) TocHeaderWithAnchor 

func (options *Html) TocHeaderWithAnchor(text []byte, level int, anchor string)

func (*Html) TripleEmphasis 

func (options *Html) TripleEmphasis(out *bytes.Buffer, text []byte)

type HtmlRendererParameters 

type HtmlRendererParameters struct {
	// Prepend this text to each relative URL.
	AbsolutePrefix string
	// Add this text to each footnote anchor, to ensure uniqueness.
	FootnoteAnchorPrefix string
	// Show this text inside the <a> tag for a footnote return link, if the
	// HTML_FOOTNOTE_RETURN_LINKS flag is enabled. If blank, the string
	// <sup>[return]</sup> is used.
	FootnoteReturnLinkContents string
	// If set, add this text to the front of each Header ID, to ensure
	// uniqueness.
	HeaderIDPrefix string
	// If set, add this text to the back of each Header ID, to ensure uniqueness.
	HeaderIDSuffix string
}

type Latex 

type Latex struct {
}

Latex is a type that implements the Renderer interface for LaTeX output.

Do not create this directly, instead use the LatexRenderer function. 

func (options *Latex) AutoLink(out *bytes.Buffer, link []byte, kind int)

func (*Latex) BlockCode 

func (options *Latex) BlockCode(out *bytes.Buffer, text []byte, lang string)

render code chunks using verbatim, or listings if we have a language

func (*Latex) BlockHtml 

func (options *Latex) BlockHtml(out *bytes.Buffer, text []byte)

func (*Latex) BlockQuote 

func (options *Latex) BlockQuote(out *bytes.Buffer, text []byte)

func (*Latex) CodeSpan 

func (options *Latex) CodeSpan(out *bytes.Buffer, text []byte)

func (*Latex) DocumentFooter 

func (options *Latex) DocumentFooter(out *bytes.Buffer)

func (*Latex) DocumentHeader 

func (options *Latex) DocumentHeader(out *bytes.Buffer)

header and footer

func (*Latex) DoubleEmphasis 

func (options *Latex) DoubleEmphasis(out *bytes.Buffer, text []byte)

func (*Latex) Emphasis 

func (options *Latex) Emphasis(out *bytes.Buffer, text []byte)

func (*Latex) Entity 

func (options *Latex) Entity(out *bytes.Buffer, entity []byte)

func (*Latex) FootnoteItem 

func (options *Latex) FootnoteItem(out *bytes.Buffer, name, text []byte, flags int)

func (*Latex) FootnoteRef 

func (options *Latex) FootnoteRef(out *bytes.Buffer, ref []byte, id int)

TODO: this

func (*Latex) Footnotes 

func (options *Latex) Footnotes(out *bytes.Buffer, text func() bool)

TODO: this

func (*Latex) GetFlags 

func (options *Latex) GetFlags() int

func (*Latex) HRule 

func (options *Latex) HRule(out *bytes.Buffer)

func (*Latex) Header 

func (options *Latex) Header(out *bytes.Buffer, text func() bool, level int, id string)

func (*Latex) Image 

func (options *Latex) Image(out *bytes.Buffer, link []byte, title []byte, alt []byte)

func (*Latex) LineBreak 

func (options *Latex) LineBreak(out *bytes.Buffer)
func (options *Latex) Link(out *bytes.Buffer, link []byte, title []byte, content []byte)

func (*Latex) List 

func (options *Latex) List(out *bytes.Buffer, text func() bool, flags int)

func (*Latex) ListItem 

func (options *Latex) ListItem(out *bytes.Buffer, text []byte, flags int)

func (*Latex) NormalText 

func (options *Latex) NormalText(out *bytes.Buffer, text []byte)

func (*Latex) Paragraph 

func (options *Latex) Paragraph(out *bytes.Buffer, text func() bool)

func (*Latex) RawHtmlTag 

func (options *Latex) RawHtmlTag(out *bytes.Buffer, tag []byte)

func (*Latex) StrikeThrough 

func (options *Latex) StrikeThrough(out *bytes.Buffer, text []byte)

func (*Latex) Table 

func (options *Latex) Table(out *bytes.Buffer, header []byte, body []byte, columnData []int)

func (*Latex) TableCell 

func (options *Latex) TableCell(out *bytes.Buffer, text []byte, align int)

func (*Latex) TableHeaderCell 

func (options *Latex) TableHeaderCell(out *bytes.Buffer, text []byte, align int)

func (*Latex) TableRow 

func (options *Latex) TableRow(out *bytes.Buffer, text []byte)

func (*Latex) TitleBlock 

func (options *Latex) TitleBlock(out *bytes.Buffer, text []byte)

func (*Latex) TripleEmphasis 

func (options *Latex) TripleEmphasis(out *bytes.Buffer, text []byte)

type Options 

type Options struct {
	// Extensions is a flag set of bit-wise ORed extension bits. See the
	// EXTENSION_* flags defined in this package.
	Extensions int

	// ReferenceOverride is an optional function callback that is called every
	// time a reference is resolved.
	//
	// In Markdown, the link reference syntax can be made to resolve a link to
	// a reference instead of an inline URL, in one of the following ways:
	//
	//  * [link text][refid]
	//  * [refid][]
	//
	// Usually, the refid is defined at the bottom of the Markdown document. If
	// this override function is provided, the refid is passed to the override
	// function first, before consulting the defined refids at the bottom. If
	// the override function indicates an override did not occur, the refids at
	// the bottom will be used to fill in the link details.
	ReferenceOverride ReferenceOverrideFunc
}

Options represents configurable overrides and callbacks (in addition to the extension flag set) for configuring a Markdown parse.

type Reference 

type Reference struct {
	// Link is usually the URL the reference points to.
	Link string
	// Title is the alternate text describing the link in more detail.
	Title string
	// Text is the optional text to override the ref with if the syntax used was
	// [refid][]
	Text string
}

Reference represents the details of a link. See the documentation in Options for more details on use-case.

type ReferenceOverrideFunc 

type ReferenceOverrideFunc func(reference string) (ref *Reference, overridden bool)

ReferenceOverrideFunc is expected to be called with a reference string and return either a valid Reference type that the reference string maps to or nil. If overridden is false, the default reference logic will be executed. See the documentation in Options for more details on use-case.

type Renderer 

type Renderer interface {
	// block-level callbacks
	BlockCode(out *bytes.Buffer, text []byte, lang string)
	BlockQuote(out *bytes.Buffer, text []byte)
	BlockHtml(out *bytes.Buffer, text []byte)
	Header(out *bytes.Buffer, text func() bool, level int, id string)
	HRule(out *bytes.Buffer)
	List(out *bytes.Buffer, text func() bool, flags int)
	ListItem(out *bytes.Buffer, text []byte, flags int)
	Paragraph(out *bytes.Buffer, text func() bool)
	Table(out *bytes.Buffer, header []byte, body []byte, columnData []int)
	TableRow(out *bytes.Buffer, text []byte)
	TableHeaderCell(out *bytes.Buffer, text []byte, flags int)
	TableCell(out *bytes.Buffer, text []byte, flags int)
	Footnotes(out *bytes.Buffer, text func() bool)
	FootnoteItem(out *bytes.Buffer, name, text []byte, flags int)
	TitleBlock(out *bytes.Buffer, text []byte)

	// Span-level callbacks
	AutoLink(out *bytes.Buffer, link []byte, kind int)
	CodeSpan(out *bytes.Buffer, text []byte)
	DoubleEmphasis(out *bytes.Buffer, text []byte)
	Emphasis(out *bytes.Buffer, text []byte)
	Image(out *bytes.Buffer, link []byte, title []byte, alt []byte)
	LineBreak(out *bytes.Buffer)
	Link(out *bytes.Buffer, link []byte, title []byte, content []byte)
	RawHtmlTag(out *bytes.Buffer, tag []byte)
	TripleEmphasis(out *bytes.Buffer, text []byte)
	StrikeThrough(out *bytes.Buffer, text []byte)
	FootnoteRef(out *bytes.Buffer, ref []byte, id int)

	// Low-level callbacks
	Entity(out *bytes.Buffer, entity []byte)
	NormalText(out *bytes.Buffer, text []byte)

	// Header and footer
	DocumentHeader(out *bytes.Buffer)
	DocumentFooter(out *bytes.Buffer)

	GetFlags() int
}

Renderer is the rendering interface. This is mostly of interest if you are implementing a new rendering format.

When a byte slice is provided, it contains the (rendered) contents of the element.

When a callback is provided instead, it will write the contents of the respective element directly to the output buffer and return true on success. If the callback returns false, the rendering function should reset the output buffer as though it had never been called.

Currently Html and Latex implementations are provided

func HtmlRenderer 

func HtmlRenderer(flags int, title string, css string) Renderer

HtmlRenderer creates and configures an Html object, which satisfies the Renderer interface.

flags is a set of HTML_* options ORed together. title is the title of the document, and css is a URL for the document's stylesheet. title and css are only used when HTML_COMPLETE_PAGE is selected.

func HtmlRendererWithParameters 

func HtmlRendererWithParameters(flags int, title string,
	css string, renderParameters HtmlRendererParameters) Renderer

func LatexRenderer 

func LatexRenderer(flags int) Renderer

LatexRenderer creates and configures a Latex object, which satisfies the Renderer interface.

flags is a set of LATEX_* options ORed together (currently no such options are defined).

Source Files

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