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markdown.go
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markdown.go
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//
// Blackfriday Markdown Processor
// Available at http://github.com/russross/blackfriday
//
// Copyright © 2011 Russ Ross <russ@russross.com>.
// Distributed under the Simplified BSD License.
// See README.md for details.
//
//
//
// Markdown parsing and processing
//
//
// Blackfriday markdown processor.
//
// Translates plain text with simple formatting rules into HTML or LaTeX.
package blackfriday
import (
"bytes"
"unicode/utf8"
)
const VERSION = "1.1"
// These are the supported markdown parsing extensions.
// OR these values together to select multiple extensions.
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
)
// 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.
const (
LINK_TYPE_NOT_AUTOLINK = iota
LINK_TYPE_NORMAL
LINK_TYPE_EMAIL
)
// 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.
const (
LIST_TYPE_ORDERED = 1 << iota
LIST_ITEM_CONTAINS_BLOCK
LIST_ITEM_BEGINNING_OF_LIST
LIST_ITEM_END_OF_LIST
)
// 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.
const (
TABLE_ALIGNMENT_LEFT = 1 << iota
TABLE_ALIGNMENT_RIGHT
TABLE_ALIGNMENT_CENTER = (TABLE_ALIGNMENT_LEFT | TABLE_ALIGNMENT_RIGHT)
)
// The size of a tab stop.
const (
TAB_SIZE_DEFAULT = 4
TAB_SIZE_EIGHT = 8
)
// These are the tags that are recognized as HTML block tags.
// Any of these can be included in markdown text without special escaping.
var blockTags = map[string]bool{
"p": true,
"dl": true,
"h1": true,
"h2": true,
"h3": true,
"h4": true,
"h5": true,
"h6": true,
"ol": true,
"ul": true,
"del": true,
"div": true,
"ins": true,
"pre": true,
"form": true,
"math": true,
"table": true,
"iframe": true,
"script": true,
"fieldset": true,
"noscript": true,
"blockquote": true,
// HTML5
"video": true,
"aside": true,
"canvas": true,
"figure": true,
"footer": true,
"header": true,
"hgroup": true,
"output": true,
"article": true,
"section": true,
"progress": true,
"figcaption": true,
}
// 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
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)
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)
TableCell(out *bytes.Buffer, text []byte, flags int)
// 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)
// 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)
}
// Callback functions for inline parsing. One such function is defined
// for each character that triggers a response when parsing inline data.
type inlineParser func(p *parser, out *bytes.Buffer, data []byte, offset int) int
// Parser holds runtime state used by the parser.
// This is constructed by the Markdown function.
type parser struct {
r Renderer
refs map[string]*reference
inlineCallback [256]inlineParser
flags int
nesting int
maxNesting int
insideLink bool
}
//
//
// Public interface
//
//
// MarkdownBasic is a convenience function for simple rendering.
// It processes markdown input with no extensions enabled.
func MarkdownBasic(input []byte) []byte {
// set up the HTML renderer
htmlFlags := HTML_USE_XHTML
renderer := HtmlRenderer(htmlFlags, "", "")
// set up the parser
extensions := 0
return Markdown(input, renderer, extensions)
}
// 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 supression
//
// * Tables
//
// * Fenced code blocks
//
// * Autolinking
//
// * Strikethrough support
//
// * Strict header parsing
func MarkdownCommon(input []byte) []byte {
// set up the HTML renderer
htmlFlags := 0
htmlFlags |= HTML_USE_XHTML
htmlFlags |= HTML_USE_SMARTYPANTS
htmlFlags |= HTML_SMARTYPANTS_FRACTIONS
htmlFlags |= HTML_SMARTYPANTS_LATEX_DASHES
renderer := HtmlRenderer(htmlFlags, "", "")
// set up the parser
extensions := 0
extensions |= EXTENSION_NO_INTRA_EMPHASIS
extensions |= EXTENSION_TABLES
extensions |= EXTENSION_FENCED_CODE
extensions |= EXTENSION_AUTOLINK
extensions |= EXTENSION_STRIKETHROUGH
extensions |= EXTENSION_SPACE_HEADERS
return Markdown(input, renderer, extensions)
}
// 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 Markdown(input []byte, renderer Renderer, extensions int) []byte {
// no point in parsing if we can't render
if renderer == nil {
return nil
}
// fill in the render structure
p := new(parser)
p.r = renderer
p.flags = extensions
p.refs = make(map[string]*reference)
p.maxNesting = 16
p.insideLink = false
// register inline parsers
p.inlineCallback['*'] = emphasis
p.inlineCallback['_'] = emphasis
if extensions&EXTENSION_STRIKETHROUGH != 0 {
p.inlineCallback['~'] = emphasis
}
p.inlineCallback['`'] = codeSpan
p.inlineCallback['\n'] = lineBreak
p.inlineCallback['['] = link
p.inlineCallback['<'] = leftAngle
p.inlineCallback['\\'] = escape
p.inlineCallback['&'] = entity
if extensions&EXTENSION_AUTOLINK != 0 {
p.inlineCallback[':'] = autoLink
}
first := firstPass(p, input)
second := secondPass(p, first)
return second
}
// first pass:
// - extract references
// - expand tabs
// - normalize newlines
// - copy everything else
func firstPass(p *parser, input []byte) []byte {
var out bytes.Buffer
tabSize := TAB_SIZE_DEFAULT
if p.flags&EXTENSION_TAB_SIZE_EIGHT != 0 {
tabSize = TAB_SIZE_EIGHT
}
beg, end := 0, 0
for beg < len(input) { // iterate over lines
if end = isReference(p, input[beg:]); end > 0 {
beg += end
} else { // skip to the next line
end = beg
for end < len(input) && input[end] != '\n' && input[end] != '\r' {
end++
}
// add the line body if present
if end > beg {
expandTabs(&out, input[beg:end], tabSize)
}
out.WriteByte('\n')
if end < len(input) && input[end] == '\r' {
end++
}
if end < len(input) && input[end] == '\n' {
end++
}
beg = end
}
}
// empty input?
if out.Len() == 0 {
out.WriteByte('\n')
}
return out.Bytes()
}
// second pass: actual rendering
func secondPass(p *parser, input []byte) []byte {
var output bytes.Buffer
p.r.DocumentHeader(&output)
p.block(&output, input)
p.r.DocumentFooter(&output)
if p.nesting != 0 {
panic("Nesting level did not end at zero")
}
return output.Bytes()
}
//
// Link references
//
// This section implements support for references that (usually) appear
// as footnotes in a document, and can be referenced anywhere in the document.
// The basic format is:
//
// [1]: http://www.google.com/ "Google"
// [2]: http://www.github.com/ "Github"
//
// Anywhere in the document, the reference can be linked by referring to its
// label, i.e., 1 and 2 in this example, as in:
//
// This library is hosted on [Github][2], a git hosting site.
// References are parsed and stored in this struct.
type reference struct {
link []byte
title []byte
}
// Check whether or not data starts with a reference link.
// If so, it is parsed and stored in the list of references
// (in the render struct).
// Returns the number of bytes to skip to move past it,
// or zero if the first line is not a reference.
func isReference(p *parser, data []byte) int {
// up to 3 optional leading spaces
if len(data) < 4 {
return 0
}
i := 0
for i < 3 && data[i] == ' ' {
i++
}
// id part: anything but a newline between brackets
if data[i] != '[' {
return 0
}
i++
idOffset := i
for i < len(data) && data[i] != '\n' && data[i] != '\r' && data[i] != ']' {
i++
}
if i >= len(data) || data[i] != ']' {
return 0
}
idEnd := i
// spacer: colon (space | tab)* newline? (space | tab)*
i++
if i >= len(data) || data[i] != ':' {
return 0
}
i++
for i < len(data) && (data[i] == ' ' || data[i] == '\t') {
i++
}
if i < len(data) && (data[i] == '\n' || data[i] == '\r') {
i++
if i < len(data) && data[i] == '\n' && data[i-1] == '\r' {
i++
}
}
for i < len(data) && (data[i] == ' ' || data[i] == '\t') {
i++
}
if i >= len(data) {
return 0
}
// link: whitespace-free sequence, optionally between angle brackets
if data[i] == '<' {
i++
}
linkOffset := i
for i < len(data) && data[i] != ' ' && data[i] != '\t' && data[i] != '\n' && data[i] != '\r' {
i++
}
linkEnd := i
if data[linkOffset] == '<' && data[linkEnd-1] == '>' {
linkOffset++
linkEnd--
}
// optional spacer: (space | tab)* (newline | '\'' | '"' | '(' )
for i < len(data) && (data[i] == ' ' || data[i] == '\t') {
i++
}
if i < len(data) && data[i] != '\n' && data[i] != '\r' && data[i] != '\'' && data[i] != '"' && data[i] != '(' {
return 0
}
// compute end-of-line
lineEnd := 0
if i >= len(data) || data[i] == '\r' || data[i] == '\n' {
lineEnd = i
}
if i+1 < len(data) && data[i] == '\r' && data[i+1] == '\n' {
lineEnd++
}
// optional (space|tab)* spacer after a newline
if lineEnd > 0 {
i = lineEnd + 1
for i < len(data) && (data[i] == ' ' || data[i] == '\t') {
i++
}
}
// optional title: any non-newline sequence enclosed in '"() alone on its line
titleOffset, titleEnd := 0, 0
if i+1 < len(data) && (data[i] == '\'' || data[i] == '"' || data[i] == '(') {
i++
titleOffset = i
// look for EOL
for i < len(data) && data[i] != '\n' && data[i] != '\r' {
i++
}
if i+1 < len(data) && data[i] == '\n' && data[i+1] == '\r' {
titleEnd = i + 1
} else {
titleEnd = i
}
// step back
i--
for i > titleOffset && (data[i] == ' ' || data[i] == '\t') {
i--
}
if i > titleOffset && (data[i] == '\'' || data[i] == '"' || data[i] == ')') {
lineEnd = titleEnd
titleEnd = i
}
}
if lineEnd == 0 { // garbage after the link
return 0
}
// a valid ref has been found
// id matches are case-insensitive
id := string(bytes.ToLower(data[idOffset:idEnd]))
p.refs[id] = &reference{
link: data[linkOffset:linkEnd],
title: data[titleOffset:titleEnd],
}
return lineEnd
}
//
//
// Miscellaneous helper functions
//
//
// Test if a character is a punctuation symbol.
// Taken from a private function in regexp in the stdlib.
func ispunct(c byte) bool {
for _, r := range []byte("!\"#$%&'()*+,-./:;<=>?@[\\]^_`{|}~") {
if c == r {
return true
}
}
return false
}
// Test if a character is a whitespace character.
func isspace(c byte) bool {
return c == ' ' || c == '\t' || c == '\n' || c == '\r' || c == '\f' || c == '\v'
}
// Test if a character is a letter or a digit.
// TODO: check when this is looking for ASCII alnum and when it should use unicode
func isalnum(c byte) bool {
return (c >= '0' && c <= '9') || (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z')
}
// Replace tab characters with spaces, aligning to the next TAB_SIZE column.
// always ends output with a newline
func expandTabs(out *bytes.Buffer, line []byte, tabSize int) {
// first, check for common cases: no tabs, or only tabs at beginning of line
i, prefix := 0, 0
slowcase := false
for i = 0; i < len(line); i++ {
if line[i] == '\t' {
if prefix == i {
prefix++
} else {
slowcase = true
break
}
}
}
// no need to decode runes if all tabs are at the beginning of the line
if !slowcase {
for i = 0; i < prefix*tabSize; i++ {
out.WriteByte(' ')
}
out.Write(line[prefix:])
return
}
// the slow case: we need to count runes to figure out how
// many spaces to insert for each tab
column := 0
i = 0
for i < len(line) {
start := i
for i < len(line) && line[i] != '\t' {
_, size := utf8.DecodeRune(line[i:])
i += size
column++
}
if i > start {
out.Write(line[start:i])
}
if i >= len(line) {
break
}
for {
out.WriteByte(' ')
column++
if column%tabSize == 0 {
break
}
}
i++
}
}