1//
  2// Blackfriday Markdown Processor
  3// Available at http://github.com/russross/blackfriday
  4//
  5// Copyright © 2011 Russ Ross <russ@russross.com>.
  6// Distributed under the Simplified BSD License.
  7// See README.md for details.
  8//
  9
 10//
 11//
 12// Markdown parsing and processing
 13//
 14//
 15
 16package blackfriday
 17
 18import (
 19	"bytes"
 20	"utf8"
 21)
 22
 23const VERSION = "0.6"
 24
 25// These are the supported markdown parsing extensions.
 26// OR these values together to select multiple extensions.
 27const (
 28	EXTENSION_NO_INTRA_EMPHASIS = 1 << iota
 29	EXTENSION_TABLES
 30	EXTENSION_FENCED_CODE
 31	EXTENSION_AUTOLINK
 32	EXTENSION_STRIKETHROUGH
 33	EXTENSION_LAX_HTML_BLOCKS
 34	EXTENSION_SPACE_HEADERS
 35	EXTENSION_HARD_LINE_BREAK
 36	EXTENSION_TAB_SIZE_EIGHT
 37)
 38
 39// These are the possible flag values for the link renderer.
 40// Only a single one of these values will be used; they are not ORed together.
 41// These are mostly of interest if you are writing a new output format.
 42const (
 43	LINK_TYPE_NOT_AUTOLINK = iota
 44	LINK_TYPE_NORMAL
 45	LINK_TYPE_EMAIL
 46)
 47
 48// These are the possible flag values for the listitem renderer.
 49// Multiple flag values may be ORed together.
 50// These are mostly of interest if you are writing a new output format.
 51const (
 52	LIST_TYPE_ORDERED = 1 << iota
 53	LIST_ITEM_CONTAINS_BLOCK
 54	LIST_ITEM_BEGINNING_OF_LIST
 55	LIST_ITEM_END_OF_LIST
 56)
 57
 58// These are the possible flag values for the table cell renderer.
 59// Only a single one of these values will be used; they are not ORed together.
 60// These are mostly of interest if you are writing a new output format.
 61const (
 62	TABLE_ALIGNMENT_LEFT = 1 << iota
 63	TABLE_ALIGNMENT_RIGHT
 64	TABLE_ALIGNMENT_CENTER = (TABLE_ALIGNMENT_LEFT | TABLE_ALIGNMENT_RIGHT)
 65)
 66
 67// The size of a tab stop.
 68const (
 69	TAB_SIZE_DEFAULT = 4
 70	TAB_SIZE_EIGHT   = 8
 71)
 72
 73// These are the tags that are recognized as HTML block tags.
 74// Any of these can be included in markdown text without special escaping.
 75var blockTags = map[string]bool{
 76	"p":          true,
 77	"dl":         true,
 78	"h1":         true,
 79	"h2":         true,
 80	"h3":         true,
 81	"h4":         true,
 82	"h5":         true,
 83	"h6":         true,
 84	"ol":         true,
 85	"ul":         true,
 86	"del":        true,
 87	"div":        true,
 88	"ins":        true,
 89	"pre":        true,
 90	"form":       true,
 91	"math":       true,
 92	"table":      true,
 93	"iframe":     true,
 94	"script":     true,
 95	"fieldset":   true,
 96	"noscript":   true,
 97	"blockquote": true,
 98}
 99
100// This interface defines the rendering interface.
101// This is mostly of interest if you are implementing a new rendering format.
102// Currently Html and Latex implementations are provided
103type Renderer interface {
104	// block-level callbacks
105	BlockCode(out *bytes.Buffer, text []byte, lang string)
106	BlockQuote(out *bytes.Buffer, text []byte)
107	BlockHtml(out *bytes.Buffer, text []byte)
108	Header(out *bytes.Buffer, text func() bool, level int)
109	HRule(out *bytes.Buffer)
110	List(out *bytes.Buffer, text func() bool, flags int)
111	ListItem(out *bytes.Buffer, text []byte, flags int)
112	Paragraph(out *bytes.Buffer, text func() bool)
113	Table(out *bytes.Buffer, header []byte, body []byte, columnData []int)
114	TableRow(out *bytes.Buffer, text []byte)
115	TableCell(out *bytes.Buffer, text []byte, flags int)
116
117	// Span-level callbacks
118	AutoLink(out *bytes.Buffer, link []byte, kind int)
119	CodeSpan(out *bytes.Buffer, text []byte)
120	DoubleEmphasis(out *bytes.Buffer, text []byte)
121	Emphasis(out *bytes.Buffer, text []byte)
122	Image(out *bytes.Buffer, link []byte, title []byte, alt []byte)
123	LineBreak(out *bytes.Buffer)
124	Link(out *bytes.Buffer, link []byte, title []byte, content []byte)
125	RawHtmlTag(out *bytes.Buffer, tag []byte)
126	TripleEmphasis(out *bytes.Buffer, text []byte)
127	StrikeThrough(out *bytes.Buffer, text []byte)
128
129	// Low-level callbacks
130	Entity(out *bytes.Buffer, entity []byte)
131	NormalText(out *bytes.Buffer, text []byte)
132
133	// Header and footer
134	DocumentHeader(out *bytes.Buffer)
135	DocumentFooter(out *bytes.Buffer)
136}
137
138// Callback functions for inline parsing. One such function is defined
139// for each character that triggers a response when parsing inline data.
140type inlineParser func(parser *Parser, out *bytes.Buffer, data []byte, offset int) int
141
142// The main parser object.
143// This is constructed by the Markdown function and
144// contains state used during the parsing process.
145type Parser struct {
146	r              Renderer
147	refs           map[string]*reference
148	inlineCallback [256]inlineParser
149	flags          int
150	nesting        int
151	maxNesting     int
152	insideLink     bool
153}
154
155
156//
157//
158// Public interface
159//
160//
161
162// Call Markdown with no extensions
163func MarkdownBasic(input []byte) []byte {
164	// set up the HTML renderer
165	htmlFlags := HTML_USE_XHTML
166	renderer := HtmlRenderer(htmlFlags, "", "")
167
168	// set up the parser
169	extensions := 0
170
171	return Markdown(input, renderer, extensions)
172}
173
174// Call Markdown with most useful extensions enabled
175func MarkdownCommon(input []byte) []byte {
176	// set up the HTML renderer
177	htmlFlags := 0
178	htmlFlags |= HTML_USE_XHTML
179	htmlFlags |= HTML_USE_SMARTYPANTS
180	htmlFlags |= HTML_SMARTYPANTS_FRACTIONS
181	htmlFlags |= HTML_SMARTYPANTS_LATEX_DASHES
182	renderer := HtmlRenderer(htmlFlags, "", "")
183
184	// set up the parser
185	extensions := 0
186	extensions |= EXTENSION_NO_INTRA_EMPHASIS
187	extensions |= EXTENSION_TABLES
188	extensions |= EXTENSION_FENCED_CODE
189	extensions |= EXTENSION_AUTOLINK
190	extensions |= EXTENSION_STRIKETHROUGH
191	extensions |= EXTENSION_SPACE_HEADERS
192
193	return Markdown(input, renderer, extensions)
194}
195
196// Parse and render a block of markdown-encoded text.
197// The renderer is used to format the output, and extensions dictates which
198// non-standard extensions are enabled.
199func Markdown(input []byte, renderer Renderer, extensions int) []byte {
200	// no point in parsing if we can't render
201	if renderer == nil {
202		return nil
203	}
204
205	// fill in the render structure
206	parser := new(Parser)
207	parser.r = renderer
208	parser.flags = extensions
209	parser.refs = make(map[string]*reference)
210	parser.maxNesting = 16
211	parser.insideLink = false
212
213	// register inline parsers
214	parser.inlineCallback['*'] = emphasis
215	parser.inlineCallback['_'] = emphasis
216	if extensions&EXTENSION_STRIKETHROUGH != 0 {
217		parser.inlineCallback['~'] = emphasis
218	}
219	parser.inlineCallback['`'] = codeSpan
220	parser.inlineCallback['\n'] = lineBreak
221	parser.inlineCallback['['] = link
222	parser.inlineCallback['<'] = leftAngle
223	parser.inlineCallback['\\'] = escape
224	parser.inlineCallback['&'] = entity
225
226	if extensions&EXTENSION_AUTOLINK != 0 {
227		parser.inlineCallback[':'] = autoLink
228	}
229
230	first := firstPass(parser, input)
231	second := secondPass(parser, first)
232
233	return second
234}
235
236// first pass:
237// - extract references
238// - expand tabs
239// - normalize newlines
240// - copy everything else
241func firstPass(parser *Parser, input []byte) []byte {
242	var out bytes.Buffer
243	tabSize := TAB_SIZE_DEFAULT
244	if parser.flags&EXTENSION_TAB_SIZE_EIGHT != 0 {
245		tabSize = TAB_SIZE_EIGHT
246	}
247	beg, end := 0, 0
248	for beg < len(input) { // iterate over lines
249		if end = isReference(parser, input[beg:]); end > 0 {
250			beg += end
251		} else { // skip to the next line
252			end = beg
253			for end < len(input) && input[end] != '\n' && input[end] != '\r' {
254				end++
255			}
256
257			// add the line body if present
258			if end > beg {
259				expandTabs(&out, input[beg:end], tabSize)
260			}
261			out.WriteByte('\n')
262
263			if end < len(input) && input[end] == '\r' {
264				end++
265			}
266			if end < len(input) && input[end] == '\n' {
267				end++
268			}
269
270			beg = end
271		}
272	}
273
274	// empty input?
275	if out.Len() == 0 {
276		out.WriteByte('\n')
277	}
278
279	return out.Bytes()
280}
281
282// second pass: actual rendering
283func secondPass(parser *Parser, input []byte) []byte {
284	var output bytes.Buffer
285
286	parser.r.DocumentHeader(&output)
287	parser.block(&output, input)
288	parser.r.DocumentFooter(&output)
289
290	if parser.nesting != 0 {
291		panic("Nesting level did not end at zero")
292	}
293
294	return output.Bytes()
295}
296
297
298//
299// Link references
300//
301// This section implements support for references that (usually) appear
302// as footnotes in a document, and can be referenced anywhere in the document.
303// The basic format is:
304//
305//    [1]: http://www.google.com/ "Google"
306//    [2]: http://www.github.com/ "Github"
307//
308// Anywhere in the document, the reference can be linked by referring to its
309// label, i.e., 1 and 2 in this example, as in:
310//
311//    This library is hosted on [Github][2], a git hosting site.
312
313// References are parsed and stored in this struct.
314type reference struct {
315	link  []byte
316	title []byte
317}
318
319// Check whether or not data starts with a reference link.
320// If so, it is parsed and stored in the list of references
321// (in the render struct).
322// Returns the number of bytes to skip to move past it,
323// or zero if the first line is not a reference.
324func isReference(parser *Parser, data []byte) int {
325	// up to 3 optional leading spaces
326	if len(data) < 4 {
327		return 0
328	}
329	i := 0
330	for i < 3 && data[i] == ' ' {
331		i++
332	}
333
334	// id part: anything but a newline between brackets
335	if data[i] != '[' {
336		return 0
337	}
338	i++
339	idOffset := i
340	for i < len(data) && data[i] != '\n' && data[i] != '\r' && data[i] != ']' {
341		i++
342	}
343	if i >= len(data) || data[i] != ']' {
344		return 0
345	}
346	idEnd := i
347
348	// spacer: colon (space | tab)* newline? (space | tab)*
349	i++
350	if i >= len(data) || data[i] != ':' {
351		return 0
352	}
353	i++
354	for i < len(data) && (data[i] == ' ' || data[i] == '\t') {
355		i++
356	}
357	if i < len(data) && (data[i] == '\n' || data[i] == '\r') {
358		i++
359		if i < len(data) && data[i] == '\n' && data[i-1] == '\r' {
360			i++
361		}
362	}
363	for i < len(data) && (data[i] == ' ' || data[i] == '\t') {
364		i++
365	}
366	if i >= len(data) {
367		return 0
368	}
369
370	// link: whitespace-free sequence, optionally between angle brackets
371	if data[i] == '<' {
372		i++
373	}
374	linkOffset := i
375	for i < len(data) && data[i] != ' ' && data[i] != '\t' && data[i] != '\n' && data[i] != '\r' {
376		i++
377	}
378	linkEnd := i
379	if data[linkOffset] == '<' && data[linkEnd-1] == '>' {
380		linkOffset++
381		linkEnd--
382	}
383
384	// optional spacer: (space | tab)* (newline | '\'' | '"' | '(' )
385	for i < len(data) && (data[i] == ' ' || data[i] == '\t') {
386		i++
387	}
388	if i < len(data) && data[i] != '\n' && data[i] != '\r' && data[i] != '\'' && data[i] != '"' && data[i] != '(' {
389		return 0
390	}
391
392	// compute end-of-line
393	lineEnd := 0
394	if i >= len(data) || data[i] == '\r' || data[i] == '\n' {
395		lineEnd = i
396	}
397	if i+1 < len(data) && data[i] == '\r' && data[i+1] == '\n' {
398		lineEnd++
399	}
400
401	// optional (space|tab)* spacer after a newline
402	if lineEnd > 0 {
403		i = lineEnd + 1
404		for i < len(data) && (data[i] == ' ' || data[i] == '\t') {
405			i++
406		}
407	}
408
409	// optional title: any non-newline sequence enclosed in '"() alone on its line
410	titleOffset, titleEnd := 0, 0
411	if i+1 < len(data) && (data[i] == '\'' || data[i] == '"' || data[i] == '(') {
412		i++
413		titleOffset = i
414
415		// look for EOL
416		for i < len(data) && data[i] != '\n' && data[i] != '\r' {
417			i++
418		}
419		if i+1 < len(data) && data[i] == '\n' && data[i+1] == '\r' {
420			titleEnd = i + 1
421		} else {
422			titleEnd = i
423		}
424
425		// step back
426		i--
427		for i > titleOffset && (data[i] == ' ' || data[i] == '\t') {
428			i--
429		}
430		if i > titleOffset && (data[i] == '\'' || data[i] == '"' || data[i] == ')') {
431			lineEnd = titleEnd
432			titleEnd = i
433		}
434	}
435	if lineEnd == 0 { // garbage after the link
436		return 0
437	}
438
439	// a valid ref has been found
440	if parser == nil {
441		return lineEnd
442	}
443
444	// id matches are case-insensitive
445	id := string(bytes.ToLower(data[idOffset:idEnd]))
446	parser.refs[id] = &reference{
447		link:  data[linkOffset:linkEnd],
448		title: data[titleOffset:titleEnd],
449	}
450
451	return lineEnd
452}
453
454
455//
456//
457// Miscellaneous helper functions
458//
459//
460
461
462// Test if a character is a punctuation symbol.
463// Taken from a private function in regexp in the stdlib.
464func ispunct(c byte) bool {
465	for _, r := range []byte("!\"#$%&'()*+,-./:;<=>?@[\\]^_`{|}~") {
466		if c == r {
467			return true
468		}
469	}
470	return false
471}
472
473// Test if a character is a whitespace character.
474func isspace(c byte) bool {
475	return c == ' ' || c == '\t' || c == '\n' || c == '\r' || c == '\f' || c == '\v'
476}
477
478// Test if a character is a letter or a digit.
479// TODO: check when this is looking for ASCII alnum and when it should use unicode
480func isalnum(c byte) bool {
481	return (c >= '0' && c <= '9') || (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z')
482}
483
484// Replace tab characters with spaces, aligning to the next TAB_SIZE column.
485// always ends output with a newline
486func expandTabs(out *bytes.Buffer, line []byte, tabSize int) {
487	// first, check for common cases: no tabs, or only tabs at beginning of line
488	i, prefix := 0, 0
489	slowcase := false
490	for i = 0; i < len(line); i++ {
491		if line[i] == '\t' {
492			if prefix == i {
493				prefix++
494			} else {
495				slowcase = true
496				break
497			}
498		}
499	}
500
501	// no need to decode runes if all tabs are at the beginning of the line
502	if !slowcase {
503		for i = 0; i < prefix*tabSize; i++ {
504			out.WriteByte(' ')
505		}
506		out.Write(line[prefix:])
507		return
508	}
509
510	// the slow case: we need to count runes to figure out how
511	// many spaces to insert for each tab
512	column := 0
513	i = 0
514	for i < len(line) {
515		start := i
516		for i < len(line) && line[i] != '\t' {
517			_, size := utf8.DecodeRune(line[i:])
518			i += size
519			column++
520		}
521
522		if i > start {
523			out.Write(line[start:i])
524		}
525
526		if i >= len(line) {
527			break
528		}
529
530		for {
531			out.WriteByte(' ')
532			column++
533			if column%tabSize == 0 {
534				break
535			}
536		}
537
538		i++
539	}
540}