README
¶
Blackfriday 
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.
It started as a translation from C of Sundown.
Installation
Blackfriday is compatible with any modern Go release. With Go 1.7 and git installed:
go get gopkg.in/russross/blackfriday.v2
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 "gopkg.in/russross/blackfriday.v2"
and go get without parameters.
Versions
Currently maintained and recommended version of Blackfriday is v2. It's being
developed on its own branch: https://github.com/russross/blackfriday/v2. You
should install and import it via gopkg.in at
gopkg.in/russross/blackfriday.v2.
Version 2 offers a number of improvements over v1:
- Cleaned up API
- A separate call to
Parse, which produces an abstract syntax tree for the document - Latest bug fixes
- Flexibility to easily add your own rendering extensions
Potential drawbacks:
- Our benchmarks show v2 to be slightly slower than v1. Currently in the ballpark of around 15%.
- API breakage. If you can't afford modifying your code to adhere to the new API and don't care too much about the new features, v2 is probably not for you.
- Several bug fixes are trailing behind and still need to be forward-ported to v2. See issue #348 for tracking.
Usage
For the most sensible markdown processing, it is as simple as getting your input into a byte slice and calling:
output := blackfriday.Run(input)
Your input will be parsed and the output rendered with a set of most popular extensions enabled. If you want the most basic feature set, corresponding with the bare Markdown specification, use:
output := blackfriday.Run(input, blackfriday.WithNoExtensions())
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.Run(input)
html := bluemonday.UGCPolicy().SanitizeBytes(unsafe)
Custom options
If you want to customize the set of options, use blackfriday.WithExtensions,
blackfriday.WithRenderer and blackfriday.WithRefOverride.
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
--tidyoption. 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.
-
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.
-
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 catsTerms 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 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,
4/5becomes<sup>4</sup>⁄<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 heading 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.
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
Documentation
¶
Overview ¶
Package blackfriday is a markdown processor.
It translates plain text with simple formatting rules into an AST, which can then be further processed to HTML (provided by Blackfriday itself) or other formats (provided by the community).
The simplest way to invoke Blackfriday is to call the Run function. It will take a text input and produce a text output in HTML (or other format).
A slightly more sophisticated way to use Blackfriday is to create a Markdown processor and to call Parse, which returns a syntax tree for the input document. You can leverage Blackfriday's parsing for content extraction from markdown documents. You can assign a custom renderer and set various options to the Markdown processor.
If you're interested in calling Blackfriday from command line, see https://github.com/russross/blackfriday-tool.
Index ¶
- Constants
- func Run(input []byte, opts ...Option) []byte
- type CellAlignFlags
- type CodeBlockData
- type Extensions
- type HTMLFlags
- type HTMLRenderer
- type HTMLRendererParameters
- type HeadingData
- type LinkData
- type ListData
- type ListType
- type Markdown
- type Node
- type NodeType
- type NodeVisitor
- type Option
- type Reference
- type ReferenceOverrideFunc
- type Renderer
- type SPRenderer
- type TableCellData
- type WalkStatus
Constants ¶
const ( NoExtensions Extensions = 0 NoIntraEmphasis Extensions = 1 << iota // Ignore emphasis markers inside words Tables // Render tables FencedCode // Render fenced code blocks Autolink // Detect embedded URLs that are not explicitly marked Strikethrough // Strikethrough text using ~~test~~ LaxHTMLBlocks // Loosen up HTML block parsing rules SpaceHeadings // Be strict about prefix heading rules HardLineBreak // Translate newlines into line breaks TabSizeEight // Expand tabs to eight spaces instead of four Footnotes // Pandoc-style footnotes NoEmptyLineBeforeBlock // No need to insert an empty line to start a (code, quote, ordered list, unordered list) block HeadingIDs // specify heading IDs with {#id} Titleblock // Titleblock ala pandoc AutoHeadingIDs // Create the heading ID from the text BackslashLineBreak // Translate trailing backslashes into line breaks DefinitionLists // Render definition lists CommonHTMLFlags HTMLFlags = UseXHTML | Smartypants | SmartypantsFractions | SmartypantsDashes | SmartypantsLatexDashes CommonExtensions Extensions = NoIntraEmphasis | Tables | FencedCode | Autolink | Strikethrough | SpaceHeadings | HeadingIDs | BackslashLineBreak | DefinitionLists )
These are the supported markdown parsing extensions. OR these values together to select multiple extensions.
const ( TabSizeDefault = 4 TabSizeDouble = 8 )
The size of a tab stop.
const Version = "2.0"
Version string of the package. Appears in the rendered document when CompletePage flag is on.
Variables ¶
This section is empty.
Functions ¶
func Run ¶
Run is the main entry point to Blackfriday. It parses and renders a block of markdown-encoded text.
The simplest invocation of Run takes one argument, input:
output := Run(input)
This will parse the input with CommonExtensions enabled and render it with the default HTMLRenderer (with CommonHTMLFlags).
Variadic arguments opts can customize the default behavior. Since Markdown type does not contain exported fields, you can not use it directly. Instead, use the With* functions. For example, this will call the most basic functionality, with no extensions:
output := Run(input, WithNoExtensions())
You can use any number of With* arguments, even contradicting ones. They will be applied in order of appearance and the latter will override the former:
output := Run(input, WithNoExtensions(), WithExtensions(exts),
WithRenderer(yourRenderer))
Types ¶
type CellAlignFlags ¶
type CellAlignFlags int
CellAlignFlags holds a type of alignment in a table cell.
const ( TableAlignmentLeft CellAlignFlags = 1 << iota TableAlignmentRight TableAlignmentCenter = (TableAlignmentLeft | TableAlignmentRight) )
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.
type CodeBlockData ¶
type CodeBlockData struct {
IsFenced bool // Specifies whether it's a fenced code block or an indented one
Info []byte // This holds the info string
FenceChar byte
FenceLength int
FenceOffset int
}
CodeBlockData contains fields relevant to a CodeBlock node type.
type Extensions ¶
type Extensions int
Extensions is a bitwise or'ed collection of enabled Blackfriday's extensions.
type HTMLFlags ¶
type HTMLFlags int
HTMLFlags control optional behavior of HTML renderer.
const ( HTMLFlagsNone HTMLFlags = 0 SkipHTML HTMLFlags = 1 << iota // Skip preformatted HTML blocks SkipImages // Skip embedded images SkipLinks // Skip all links Safelink // Only link to trusted protocols NofollowLinks // Only link with rel="nofollow" NoreferrerLinks // Only link with rel="noreferrer" HrefTargetBlank // Add a blank target CompletePage // Generate a complete HTML page UseXHTML // Generate XHTML output instead of HTML FootnoteReturnLinks // Generate a link at the end of a footnote to return to the source Smartypants // Enable smart punctuation substitutions SmartypantsFractions // Enable smart fractions (with Smartypants) SmartypantsDashes // Enable smart dashes (with Smartypants) SmartypantsLatexDashes // Enable LaTeX-style dashes (with Smartypants) SmartypantsAngledQuotes // Enable angled double quotes (with Smartypants) for double quotes rendering SmartypantsQuotesNBSP // Enable « French guillemets » (with Smartypants) TOC // Generate a table of contents )
HTML renderer configuration options.
type HTMLRenderer ¶
type HTMLRenderer struct {
HTMLRendererParameters
// contains filtered or unexported fields
}
HTMLRenderer is a type that implements the Renderer interface for HTML output.
Do not create this directly, instead use the NewHTMLRenderer function.
func NewHTMLRenderer ¶
func NewHTMLRenderer(params HTMLRendererParameters) *HTMLRenderer
NewHTMLRenderer creates and configures an HTMLRenderer object, which satisfies the Renderer interface.
func (*HTMLRenderer) RenderFooter ¶
func (r *HTMLRenderer) RenderFooter(w io.Writer, ast *Node)
RenderFooter writes HTML document footer.
func (*HTMLRenderer) RenderHeader ¶
func (r *HTMLRenderer) RenderHeader(w io.Writer, ast *Node)
RenderHeader writes HTML document preamble and TOC if requested.
func (*HTMLRenderer) RenderNode ¶
func (r *HTMLRenderer) RenderNode(w io.Writer, node *Node, entering bool) WalkStatus
RenderNode is a default renderer of a single node of a syntax tree. For block nodes it will be called twice: first time with entering=true, second time with entering=false, so that it could know when it's working on an open tag and when on close. It writes the result to w.
The return value is a way to tell the calling walker to adjust its walk pattern: e.g. it can terminate the traversal by returning Terminate. Or it can ask the walker to skip a subtree of this node by returning SkipChildren. The typical behavior is to return GoToNext, which asks for the usual traversal to the next node.
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 Heading ID, to ensure
// uniqueness.
HeadingIDPrefix string
// If set, add this text to the back of each Heading ID, to ensure uniqueness.
HeadingIDSuffix string
Title string // Document title (used if CompletePage is set)
CSS string // Optional CSS file URL (used if CompletePage is set)
Icon string // Optional icon file URL (used if CompletePage is set)
Flags HTMLFlags // Flags allow customizing this renderer's behavior
}
HTMLRendererParameters is a collection of supplementary parameters tweaking the behavior of various parts of HTML renderer.
type HeadingData ¶
type HeadingData struct {
Level int // This holds the heading level number
HeadingID string // This might hold heading ID, if present
IsTitleblock bool // Specifies whether it's a title block
}
HeadingData contains fields relevant to a Heading node type.
type LinkData ¶
type LinkData struct {
Destination []byte // Destination is what goes into a href
Title []byte // Title is the tooltip thing that goes in a title attribute
NoteID int // NoteID contains a serial number of a footnote, zero if it's not a footnote
Footnote *Node // If it's a footnote, this is a direct link to the footnote Node. Otherwise nil.
}
LinkData contains fields relevant to a Link node type.
type ListData ¶
type ListData struct {
ListFlags ListType
Tight bool // Skip <p>s around list item data if true
BulletChar byte // '*', '+' or '-' in bullet lists
Delimiter byte // '.' or ')' after the number in ordered lists
RefLink []byte // If not nil, turns this list item into a footnote item and triggers different rendering
IsFootnotesList bool // This is a list of footnotes
}
ListData contains fields relevant to a List and Item node type.
type ListType ¶
type ListType int
ListType contains bitwise or'ed flags for list and list item objects.
const ( ListTypeOrdered ListType = 1 << iota ListTypeDefinition ListTypeTerm ListItemContainsBlock ListItemBeginningOfList // TODO: figure out if this is of any use now ListItemEndOfList )
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.
type Markdown ¶
type Markdown struct {
// contains filtered or unexported fields
}
Markdown is a type that holds extensions and the runtime state used by Parse, and the renderer. You can not use it directly, construct it with New.
func New ¶
New constructs a Markdown processor. You can use the same With* functions as for Run() to customize parser's behavior and the renderer.
func (*Markdown) Parse ¶
Parse is an entry point to the parsing part of Blackfriday. It takes an input markdown document and produces a syntax tree for its contents. This tree can then be rendered with a default or custom renderer, or analyzed/transformed by the caller to whatever non-standard needs they have. The return value is the root node of the syntax tree.
type Node ¶
type Node struct {
Type NodeType // Determines the type of the node
Parent *Node // Points to the parent
FirstChild *Node // Points to the first child, if any
LastChild *Node // Points to the last child, if any
Prev *Node // Previous sibling; nil if it's the first child
Next *Node // Next sibling; nil if it's the last child
Literal []byte // Text contents of the leaf nodes
HeadingData // Populated if Type is Heading
ListData // Populated if Type is List
CodeBlockData // Populated if Type is CodeBlock
LinkData // Populated if Type is Link
TableCellData // Populated if Type is TableCell
// contains filtered or unexported fields
}
Node is a single element in the abstract syntax tree of the parsed document. It holds connections to the structurally neighboring nodes and, for certain types of nodes, additional information that might be needed when rendering.
func (*Node) AppendChild ¶
AppendChild adds a node 'child' as a child of 'n'. It panics if either node is nil.
func (*Node) InsertBefore ¶
InsertBefore inserts 'sibling' immediately before 'n'. It panics if either node is nil.
func (*Node) Unlink ¶
func (n *Node) Unlink()
Unlink removes node 'n' from the tree. It panics if the node is nil.
func (*Node) Walk ¶
func (n *Node) Walk(visitor NodeVisitor)
Walk is a convenience method that instantiates a walker and starts a traversal of subtree rooted at n.
type NodeType ¶
type NodeType int
NodeType specifies a type of a single node of a syntax tree. Usually one node (and its type) corresponds to a single markdown feature, e.g. emphasis or code block.
type NodeVisitor ¶
type NodeVisitor func(node *Node, entering bool) WalkStatus
NodeVisitor is a callback to be called when traversing the syntax tree. Called twice for every node: once with entering=true when the branch is first visited, then with entering=false after all the children are done.
type Option ¶
type Option func(*Markdown)
Option customizes the Markdown processor's default behavior.
func WithExtensions ¶
func WithExtensions(e Extensions) Option
WithExtensions allows you to pick some of the many extensions provided by Blackfriday. You can bitwise OR them.
func WithNoExtensions ¶
func WithNoExtensions() Option
WithNoExtensions turns off all extensions and custom behavior.
func WithRefOverride ¶
func WithRefOverride(o ReferenceOverrideFunc) Option
WithRefOverride sets 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.
func WithRenderer ¶
WithRenderer allows you to override the default renderer.
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 ¶
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 {
// RenderNode is the main rendering method. It will be called once for
// every leaf node and twice for every non-leaf node (first with
// entering=true, then with entering=false). The method should write its
// rendition of the node to the supplied writer w.
RenderNode(w io.Writer, node *Node, entering bool) WalkStatus
// RenderHeader is a method that allows the renderer to produce some
// content preceding the main body of the output document. The header is
// understood in the broad sense here. For example, the default HTML
// renderer will write not only the HTML document preamble, but also the
// table of contents if it was requested.
//
// The method will be passed an entire document tree, in case a particular
// implementation needs to inspect it to produce output.
//
// The output should be written to the supplied writer w. If your
// implementation has no header to write, supply an empty implementation.
RenderHeader(w io.Writer, ast *Node)
RenderFooter(w io.Writer, ast *Node)
}
Renderer is the rendering interface. This is mostly of interest if you are implementing a new rendering format.
Only an HTML implementation is provided in this repository, see the README for external implementations.
type SPRenderer ¶
type SPRenderer struct {
// contains filtered or unexported fields
}
SPRenderer is a struct containing state of a Smartypants renderer.
func NewSmartypantsRenderer ¶
func NewSmartypantsRenderer(flags HTMLFlags) *SPRenderer
NewSmartypantsRenderer constructs a Smartypants renderer object.
type TableCellData ¶
type TableCellData struct {
IsHeader bool // This tells if it's under the header row
Align CellAlignFlags // This holds the value for align attribute
}
TableCellData contains fields relevant to a TableCell node type.
type WalkStatus ¶
type WalkStatus int
WalkStatus allows NodeVisitor to have some control over the tree traversal. It is returned from NodeVisitor and different values allow Node.Walk to decide which node to go to next.
const ( // GoToNext is the default traversal of every node. GoToNext WalkStatus = iota // SkipChildren tells walker to skip all children of current node. SkipChildren // Terminate tells walker to terminate the traversal. Terminate )
Source Files