//
// 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
//
//
package blackfriday
import (
"bytes"
"fmt"
"strings"
"unicode/utf8"
)
const VERSION = "1.5"
// 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
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
EXTENSION_JOIN_LINES // delete newline and join lines
commonHtmlFlags = 0 |
HTML_USE_XHTML |
HTML_USE_SMARTYPANTS |
HTML_SMARTYPANTS_FRACTIONS |
HTML_SMARTYPANTS_DASHES |
HTML_SMARTYPANTS_LATEX_DASHES
commonExtensions = 0 |
EXTENSION_NO_INTRA_EMPHASIS |
EXTENSION_TABLES |
EXTENSION_FENCED_CODE |
EXTENSION_AUTOLINK |
EXTENSION_STRIKETHROUGH |
EXTENSION_SPACE_HEADERS |
EXTENSION_HEADER_IDS |
EXTENSION_BACKSLASH_LINE_BREAK |
EXTENSION_DEFINITION_LISTS
)
// 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_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 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
)
// blockTags is a set of tags that are recognized as HTML block tags.
// Any of these can be included in markdown text without special escaping.
var blockTags = map[string]struct{}{
"blockquote": {},
"del": {},
"div": {},
"dl": {},
"fieldset": {},
"form": {},
"h1": {},
"h2": {},
"h3": {},
"h4": {},
"h5": {},
"h6": {},
"iframe": {},
"ins": {},
"math": {},
"noscript": {},
"ol": {},
"pre": {},
"p": {},
"script": {},
"style": {},
"table": {},
"ul": {},
// HTML5
"address": {},
"article": {},
"aside": {},
"canvas": {},
"figcaption": {},
"figure": {},
"footer": {},
"header": {},
"hgroup": {},
"main": {},
"nav": {},
"output": {},
"progress": {},
"section": {},
"video": {},
}
// 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, 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
}
// 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
refOverride ReferenceOverrideFunc
refs map[string]*reference
inlineCallback [256]inlineParser
flags int
nesting int
maxNesting int
insideLink bool
// Footnotes need to be ordered as well as available to quickly check for
// presence. If a ref is also a footnote, it's stored both in refs and here
// in notes. Slice is nil if footnotes not enabled.
notes []*reference
notesRecord map[string]struct{}
}
func (p *parser) getRef(refid string) (ref *reference, found bool) {
if p.refOverride != nil {
r, overridden := p.refOverride(refid)
if overridden {
if r == nil {
return nil, false
}
return &reference{
link: []byte(r.Link),
title: []byte(r.Title),
noteId: 0,
hasBlock: false,
text: []byte(r.Text)}, true
}
}
// refs are case insensitive
ref, found = p.refs[strings.ToLower(refid)]
return ref, found
}
func (p *parser) isFootnote(ref *reference) bool {
_, ok := p.notesRecord[string(ref.link)]
return ok
}
//
//
// Public interface
//
//
// Reference represents the details of a link.
// See the documentation in Options for more details on use-case.
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
}
// 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 ReferenceOverrideFunc func(reference string) (ref *Reference, overridden bool)
// Options represents configurable overrides and callbacks (in addition to the
// extension flag set) for configuring a Markdown parse.
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
}
// 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
return MarkdownOptions(input, renderer, Options{Extensions: 0})
}
// 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 MarkdownCommon(input []byte) []byte {
// set up the HTML renderer
renderer := HtmlRenderer(commonHtmlFlags, "", "")
return MarkdownOptions(input, renderer, Options{
Extensions: commonExtensions})
}
// 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 {
return MarkdownOptions(input, renderer, Options{
Extensions: extensions})
}
// MarkdownOptions is just like Markdown but takes additional options through
// the Options struct.
func MarkdownOptions(input []byte, renderer Renderer, opts Options) []byte {
// no point in parsing if we can't render
if renderer == nil {
return nil
}
extensions := opts.Extensions
// fill in the render structure
p := new(parser)
p.r = renderer
p.flags = extensions
p.refOverride = opts.ReferenceOverride
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
}
if extensions&EXTENSION_FOOTNOTES != 0 {
p.notes = make([]*reference, 0)
p.notesRecord = make(map[string]struct{})
}
first := firstPass(p, input)
second := secondPass(p, first)
return second
}
// first pass:
// - normalize newlines
// - extract references (outside of fenced code blocks)
// - expand tabs (outside of fenced code blocks)
// - 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 := 0
lastFencedCodeBlockEnd := 0
for beg < len(input) {
// Find end of this line, then process the line.
end := beg
for end < len(input) && input[end] != '\n' && input[end] != '\r' {
end++
}
if p.flags&EXTENSION_FENCED_CODE != 0 {
// track fenced code block boundaries to suppress tab expansion
// and reference extraction inside them:
if beg >= lastFencedCodeBlockEnd {
if i := p.fencedCodeBlock(&out, input[beg:], false); i > 0 {
lastFencedCodeBlockEnd = beg + i
}
}
}
// add the line body if present
if end > beg {
if end < lastFencedCodeBlockEnd { // Do not expand tabs while inside fenced code blocks.
out.Write(input[beg:end])
} else if refEnd := isReference(p, input[beg:], tabSize); refEnd > 0 {
beg += refEnd
continue
} else {
expandTabs(&out, input[beg:end], tabSize)
}
}
if end < len(input) && input[end] == '\r' {
end++
}
if end < len(input) && input[end] == '\n' {
end++
}
out.WriteByte('\n')
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)
if p.flags&EXTENSION_FOOTNOTES != 0 && len(p.notes) > 0 {
p.r.Footnotes(&output, func() bool {
flags := LIST_ITEM_BEGINNING_OF_LIST
for i := 0; i < len(p.notes); i += 1 {
ref := p.notes[i]
var buf bytes.Buffer
if ref.hasBlock {
flags |= LIST_ITEM_CONTAINS_BLOCK
p.block(&buf, ref.title)
} else {
p.inline(&buf, ref.title)
}
p.r.FootnoteItem(&output, ref.link, buf.Bytes(), flags)
flags &^= LIST_ITEM_BEGINNING_OF_LIST | LIST_ITEM_CONTAINS_BLOCK
}
return true
})
}
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.
//
// Actual footnotes as specified in Pandoc and supported by some other Markdown
// libraries such as php-markdown are also taken care of. They look like this:
//
// This sentence needs a bit of further explanation.[^note]
//
// [^note]: This is the explanation.
//
// Footnotes should be placed at the end of the document in an ordered list.
// Inline footnotes such as:
//
// Inline footnotes^[Not supported.] also exist.
//
// are not yet supported.
// References are parsed and stored in this struct.
type reference struct {
link []byte
title []byte
noteId int // 0 if not a footnote ref
hasBlock bool
text []byte
}
func (r *reference) String() string {
return fmt.Sprintf("{link: %q, title: %q, text: %q, noteId: %d, hasBlock: %v}",
r.link, r.title, r.text, r.noteId, r.hasBlock)
}
// 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, tabSize int) int {
// up to 3 optional leading spaces
if len(data) < 4 {
return 0
}
i := 0
for i < 3 && data[i] == ' ' {
i++
}
noteId := 0
// id part: anything but a newline between brackets
if data[i] != '[' {
return 0
}
i++
if p.flags&EXTENSION_FOOTNOTES != 0 {
if i < len(data) && data[i] == '^' {
// we can set it to anything here because the proper noteIds will
// be assigned later during the second pass. It just has to be != 0
noteId = 1
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
}
var (
linkOffset, linkEnd int
titleOffset, titleEnd int
lineEnd int
raw []byte
hasBlock bool
)
if p.flags&EXTENSION_FOOTNOTES != 0 && noteId != 0 {
linkOffset, linkEnd, raw, hasBlock = scanFootnote(p, data, i, tabSize)
lineEnd = linkEnd
} else {
linkOffset, linkEnd, titleOffset, titleEnd, lineEnd = scanLinkRef(p, data, i)
}
if lineEnd == 0 {
return 0
}
// a valid ref has been found
ref := &reference{
noteId: noteId,
hasBlock: hasBlock,
}
if noteId > 0 {
// reusing the link field for the id since footnotes don't have links
ref.link = data[idOffset:idEnd]
// if footnote, it's not really a title, it's the contained text
ref.title = raw
} else {
ref.link = data[linkOffset:linkEnd]
ref.title = data[titleOffset:titleEnd]
}
// id matches are case-insensitive
id := string(bytes.ToLower(data[idOffset:idEnd]))
p.refs[id] = ref
return lineEnd
}
func scanLinkRef(p *parser, data []byte, i int) (linkOffset, linkEnd, titleOffset, titleEnd, lineEnd int) {
// link: whitespace-free sequence, optionally between angle brackets
if data[i] == '<' {
i++
}
linkOffset = i
if i == len(data) {
return
}
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
}
// compute end-of-line
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
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
}
}
return
}
// The first bit of this logic is the same as (*parser).listItem, but the rest
// is much simpler. This function simply finds the entire block and shifts it
// over by one tab if it is indeed a block (just returns the line if it's not).
// blockEnd is the end of the section in the input buffer, and contents is the
// extracted text that was shifted over one tab. It will need to be rendered at
// the end of the document.
func scanFootnote(p *parser, data []byte, i, indentSize int) (blockStart, blockEnd int, contents []byte, hasBlock bool) {
if i == 0 || len(data) == 0 {
return
}
// skip leading whitespace on first line
for i < len(data) && data[i] == ' ' {
i++
}
blockStart = i
// find the end of the line
blockEnd = i
for i < len(data) && data[i-1] != '\n' {
i++
}
// get working buffer
var raw bytes.Buffer
// put the first line into the working buffer
raw.Write(data[blockEnd:i])
blockEnd = i
// process the following lines
containsBlankLine := false
gatherLines:
for blockEnd < len(data) {
i++
// find the end of this line
for i < len(data) && data[i-1] != '\n' {
i++
}
// if it is an empty line, guess that it is part of this item
// and move on to the next line
if p.isEmpty(data[blockEnd:i]) > 0 {
containsBlankLine = true
blockEnd = i
continue
}
n := 0
if n = isIndented(data[blockEnd:i], indentSize); n == 0 {
// this is the end of the block.
// we don't want to include this last line in the index.
break gatherLines
}
// if there were blank lines before this one, insert a new one now
if containsBlankLine {
raw.WriteByte('\n')
containsBlankLine = false
}
// get rid of that first tab, write to buffer
raw.Write(data[blockEnd+n : i])
hasBlock = true
blockEnd = i
}
if data[blockEnd-1] != '\n' {
raw.WriteByte('\n')
}
contents = raw.Bytes()
return
}
//
//
// 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 letter.
func isletter(c byte) bool {
return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z')
}
// 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') || isletter(c)
}
// 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++
}
}
// Find if a line counts as indented or not.
// Returns number of characters the indent is (0 = not indented).
func isIndented(data []byte, indentSize int) int {
if len(data) == 0 {
return 0
}
if data[0] == '\t' {
return 1
}
if len(data) < indentSize {
return 0
}
for i := 0; i < indentSize; i++ {
if data[i] != ' ' {
return 0
}
}
return indentSize
}
// Create a url-safe slug for fragments
func slugify(in []byte) []byte {
if len(in) == 0 {
return in
}
out := make([]byte, 0, len(in))
sym := false
for _, ch := range in {
if isalnum(ch) {
sym = false
out = append(out, ch)
} else if sym {
continue
} else {
out = append(out, '-')
sym = true
}
}
var a, b int
var ch byte
for a, ch = range out {
if ch != '-' {
break
}
}
for b = len(out) - 1; b > 0; b-- {
if out[b] != '-' {
break
}
}
return out[a : b+1]
}