blackfriday.v2: Index | Files

package blackfriday

import ""

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


Package Files

block.go doc.go esc.go html.go inline.go markdown.go node.go smartypants.go


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.

func Run Uses

func Run(input []byte, opts ...Option) []byte

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),

type CellAlignFlags Uses

type CellAlignFlags int

CellAlignFlags holds a type of alignment in a table cell.

const (
    TableAlignmentLeft CellAlignFlags = 1 << iota
    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 Uses

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 Uses

type Extensions int

Extensions is a bitwise or'ed collection of enabled Blackfriday's extensions.

type HTMLFlags Uses

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"
    NoopenerLinks                                 // Only link with rel="noopener"
    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 Uses

type HTMLRenderer struct {
    // 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 Uses

func NewHTMLRenderer(params HTMLRendererParameters) *HTMLRenderer

NewHTMLRenderer creates and configures an HTMLRenderer object, which satisfies the Renderer interface.

func (*HTMLRenderer) RenderFooter Uses

func (r *HTMLRenderer) RenderFooter(w io.Writer, ast *Node)

RenderFooter writes HTML document footer.

func (*HTMLRenderer) RenderHeader Uses

func (r *HTMLRenderer) RenderHeader(w io.Writer, ast *Node)

RenderHeader writes HTML document preamble and TOC if requested.

func (*HTMLRenderer) RenderNode Uses

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 Uses

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
    // Increase heading levels: if the offset is 1, <h1> becomes <h2> etc.
    // Negative offset is also valid.
    // Resulting levels are clipped between 1 and 6.
    HeadingLevelOffset int

    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 Uses

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 Uses

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 Uses

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 Uses

type ListType int

ListType contains bitwise or'ed flags for list and list item objects.

const (
    ListTypeOrdered ListType = 1 << iota

    ListItemBeginningOfList // TODO: figure out if this is of any use now

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 Uses

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 Uses

func New(opts ...Option) *Markdown

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 Uses

func (p *Markdown) Parse(input []byte) *Node

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 Uses

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 NewNode Uses

func NewNode(typ NodeType) *Node

NewNode allocates a node of a specified type.

func (*Node) AppendChild Uses

func (n *Node) AppendChild(child *Node)

AppendChild adds a node 'child' as a child of 'n'. It panics if either node is nil.

func (*Node) InsertBefore Uses

func (n *Node) InsertBefore(sibling *Node)

InsertBefore inserts 'sibling' immediately before 'n'. It panics if either node is nil.

func (*Node) String Uses

func (n *Node) String() string
func (n *Node) Unlink()

Unlink removes node 'n' from the tree. It panics if the node is nil.

func (*Node) Walk Uses

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 Uses

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.

const (
    Document NodeType = iota

Constants for identifying different types of nodes. See NodeType.

func (NodeType) String Uses

func (t NodeType) String() string

type NodeVisitor Uses

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 Uses

type Option func(*Markdown)

Option customizes the Markdown processor's default behavior.

func WithExtensions Uses

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 Uses

func WithNoExtensions() Option

WithNoExtensions turns off all extensions and custom behavior.

func WithRefOverride Uses

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 Uses

func WithRenderer(r Renderer) Option

WithRenderer allows you to override the default renderer.

type Reference Uses

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 Uses

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 Uses

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 is a symmetric counterpart of RenderHeader.
    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 Uses

type SPRenderer struct {
    // contains filtered or unexported fields

SPRenderer is a struct containing state of a Smartypants renderer.

func NewSmartypantsRenderer Uses

func NewSmartypantsRenderer(flags HTMLFlags) *SPRenderer

NewSmartypantsRenderer constructs a Smartypants renderer object.

func (*SPRenderer) Process Uses

func (r *SPRenderer) Process(w io.Writer, text []byte)

Process is the entry point of the Smartypants renderer.

type TableCellData Uses

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 Uses

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.
    // Terminate tells walker to terminate the traversal.

Package blackfriday imports 9 packages (graph) and is imported by 119 packages. Updated 2019-05-03. Refresh now. Tools for package owners.