gtsocial-umbx

token.go (31496B)

---

 // Copyright 2010 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 package html
 
 import (
 	"bytes"
 	"errors"
 	"io"
 	"strconv"
 	"strings"
 
 	"golang.org/x/net/html/atom"
 )
 
 // A TokenType is the type of a Token.
 type TokenType uint32
 
 const (
 	// ErrorToken means that an error occurred during tokenization.
 	ErrorToken TokenType = iota
 	// TextToken means a text node.
 	TextToken
 	// A StartTagToken looks like <a>.
 	StartTagToken
 	// An EndTagToken looks like </a>.
 	EndTagToken
 	// A SelfClosingTagToken tag looks like <br/>.
 	SelfClosingTagToken
 	// A CommentToken looks like <!--x-->.
 	CommentToken
 	// A DoctypeToken looks like <!DOCTYPE x>
 	DoctypeToken
 )
 
 // ErrBufferExceeded means that the buffering limit was exceeded.
 var ErrBufferExceeded = errors.New("max buffer exceeded")
 
 // String returns a string representation of the TokenType.
 func (t TokenType) String() string {
 	switch t {
 	case ErrorToken:
 		return "Error"
 	case TextToken:
 		return "Text"
 	case StartTagToken:
 		return "StartTag"
 	case EndTagToken:
 		return "EndTag"
 	case SelfClosingTagToken:
 		return "SelfClosingTag"
 	case CommentToken:
 		return "Comment"
 	case DoctypeToken:
 		return "Doctype"
 	}
 	return "Invalid(" + strconv.Itoa(int(t)) + ")"
 }
 
 // An Attribute is an attribute namespace-key-value triple. Namespace is
 // non-empty for foreign attributes like xlink, Key is alphabetic (and hence
 // does not contain escapable characters like '&', '<' or '>'), and Val is
 // unescaped (it looks like "a<b" rather than "a&lt;b").
 //
 // Namespace is only used by the parser, not the tokenizer.
 type Attribute struct {
 	Namespace, Key, Val string
 }
 
 // A Token consists of a TokenType and some Data (tag name for start and end
 // tags, content for text, comments and doctypes). A tag Token may also contain
 // a slice of Attributes. Data is unescaped for all Tokens (it looks like "a<b"
 // rather than "a&lt;b"). For tag Tokens, DataAtom is the atom for Data, or
 // zero if Data is not a known tag name.
 type Token struct {
 	Type     TokenType
 	DataAtom atom.Atom
 	Data     string
 	Attr     []Attribute
 }
 
 // tagString returns a string representation of a tag Token's Data and Attr.
 func (t Token) tagString() string {
 	if len(t.Attr) == 0 {
 		return t.Data
 	}
 	buf := bytes.NewBufferString(t.Data)
 	for _, a := range t.Attr {
 		buf.WriteByte(' ')
 		buf.WriteString(a.Key)
 		buf.WriteString(`="`)
 		escape(buf, a.Val)
 		buf.WriteByte('"')
 	}
 	return buf.String()
 }
 
 // String returns a string representation of the Token.
 func (t Token) String() string {
 	switch t.Type {
 	case ErrorToken:
 		return ""
 	case TextToken:
 		return EscapeString(t.Data)
 	case StartTagToken:
 		return "<" + t.tagString() + ">"
 	case EndTagToken:
 		return "</" + t.tagString() + ">"
 	case SelfClosingTagToken:
 		return "<" + t.tagString() + "/>"
 	case CommentToken:
 		return "<!--" + escapeCommentString(t.Data) + "-->"
 	case DoctypeToken:
 		return "<!DOCTYPE " + EscapeString(t.Data) + ">"
 	}
 	return "Invalid(" + strconv.Itoa(int(t.Type)) + ")"
 }
 
 // span is a range of bytes in a Tokenizer's buffer. The start is inclusive,
 // the end is exclusive.
 type span struct {
 	start, end int
 }
 
 // A Tokenizer returns a stream of HTML Tokens.
 type Tokenizer struct {
 	// r is the source of the HTML text.
 	r io.Reader
 	// tt is the TokenType of the current token.
 	tt TokenType
 	// err is the first error encountered during tokenization. It is possible
 	// for tt != Error && err != nil to hold: this means that Next returned a
 	// valid token but the subsequent Next call will return an error token.
 	// For example, if the HTML text input was just "plain", then the first
 	// Next call would set z.err to io.EOF but return a TextToken, and all
 	// subsequent Next calls would return an ErrorToken.
 	// err is never reset. Once it becomes non-nil, it stays non-nil.
 	err error
 	// readErr is the error returned by the io.Reader r. It is separate from
 	// err because it is valid for an io.Reader to return (n int, err1 error)
 	// such that n > 0 && err1 != nil, and callers should always process the
 	// n > 0 bytes before considering the error err1.
 	readErr error
 	// buf[raw.start:raw.end] holds the raw bytes of the current token.
 	// buf[raw.end:] is buffered input that will yield future tokens.
 	raw span
 	buf []byte
 	// maxBuf limits the data buffered in buf. A value of 0 means unlimited.
 	maxBuf int
 	// buf[data.start:data.end] holds the raw bytes of the current token's data:
 	// a text token's text, a tag token's tag name, etc.
 	data span
 	// pendingAttr is the attribute key and value currently being tokenized.
 	// When complete, pendingAttr is pushed onto attr. nAttrReturned is
 	// incremented on each call to TagAttr.
 	pendingAttr   [2]span
 	attr          [][2]span
 	nAttrReturned int
 	// rawTag is the "script" in "</script>" that closes the next token. If
 	// non-empty, the subsequent call to Next will return a raw or RCDATA text
 	// token: one that treats "<p>" as text instead of an element.
 	// rawTag's contents are lower-cased.
 	rawTag string
 	// textIsRaw is whether the current text token's data is not escaped.
 	textIsRaw bool
 	// convertNUL is whether NUL bytes in the current token's data should
 	// be converted into \ufffd replacement characters.
 	convertNUL bool
 	// allowCDATA is whether CDATA sections are allowed in the current context.
 	allowCDATA bool
 }
 
 // AllowCDATA sets whether or not the tokenizer recognizes <![CDATA[foo]]> as
 // the text "foo". The default value is false, which means to recognize it as
 // a bogus comment "<!-- [CDATA[foo]] -->" instead.
 //
 // Strictly speaking, an HTML5 compliant tokenizer should allow CDATA if and
 // only if tokenizing foreign content, such as MathML and SVG. However,
 // tracking foreign-contentness is difficult to do purely in the tokenizer,
 // as opposed to the parser, due to HTML integration points: an <svg> element
 // can contain a <foreignObject> that is foreign-to-SVG but not foreign-to-
 // HTML. For strict compliance with the HTML5 tokenization algorithm, it is the
 // responsibility of the user of a tokenizer to call AllowCDATA as appropriate.
 // In practice, if using the tokenizer without caring whether MathML or SVG
 // CDATA is text or comments, such as tokenizing HTML to find all the anchor
 // text, it is acceptable to ignore this responsibility.
 func (z *Tokenizer) AllowCDATA(allowCDATA bool) {
 	z.allowCDATA = allowCDATA
 }
 
 // NextIsNotRawText instructs the tokenizer that the next token should not be
 // considered as 'raw text'. Some elements, such as script and title elements,
 // normally require the next token after the opening tag to be 'raw text' that
 // has no child elements. For example, tokenizing "<title>a<b>c</b>d</title>"
 // yields a start tag token for "<title>", a text token for "a<b>c</b>d", and
 // an end tag token for "</title>". There are no distinct start tag or end tag
 // tokens for the "<b>" and "</b>".
 //
 // This tokenizer implementation will generally look for raw text at the right
 // times. Strictly speaking, an HTML5 compliant tokenizer should not look for
 // raw text if in foreign content: <title> generally needs raw text, but a
 // <title> inside an <svg> does not. Another example is that a <textarea>
 // generally needs raw text, but a <textarea> is not allowed as an immediate
 // child of a <select>; in normal parsing, a <textarea> implies </select>, but
 // one cannot close the implicit element when parsing a <select>'s InnerHTML.
 // Similarly to AllowCDATA, tracking the correct moment to override raw-text-
 // ness is difficult to do purely in the tokenizer, as opposed to the parser.
 // For strict compliance with the HTML5 tokenization algorithm, it is the
 // responsibility of the user of a tokenizer to call NextIsNotRawText as
 // appropriate. In practice, like AllowCDATA, it is acceptable to ignore this
 // responsibility for basic usage.
 //
 // Note that this 'raw text' concept is different from the one offered by the
 // Tokenizer.Raw method.
 func (z *Tokenizer) NextIsNotRawText() {
 	z.rawTag = ""
 }
 
 // Err returns the error associated with the most recent ErrorToken token.
 // This is typically io.EOF, meaning the end of tokenization.
 func (z *Tokenizer) Err() error {
 	if z.tt != ErrorToken {
 		return nil
 	}
 	return z.err
 }
 
 // readByte returns the next byte from the input stream, doing a buffered read
 // from z.r into z.buf if necessary. z.buf[z.raw.start:z.raw.end] remains a contiguous byte
 // slice that holds all the bytes read so far for the current token.
 // It sets z.err if the underlying reader returns an error.
 // Pre-condition: z.err == nil.
 func (z *Tokenizer) readByte() byte {
 	if z.raw.end >= len(z.buf) {
 		// Our buffer is exhausted and we have to read from z.r. Check if the
 		// previous read resulted in an error.
 		if z.readErr != nil {
 			z.err = z.readErr
 			return 0
 		}
 		// We copy z.buf[z.raw.start:z.raw.end] to the beginning of z.buf. If the length
 		// z.raw.end - z.raw.start is more than half the capacity of z.buf, then we
 		// allocate a new buffer before the copy.
 		c := cap(z.buf)
 		d := z.raw.end - z.raw.start
 		var buf1 []byte
 		if 2*d > c {
 			buf1 = make([]byte, d, 2*c)
 		} else {
 			buf1 = z.buf[:d]
 		}
 		copy(buf1, z.buf[z.raw.start:z.raw.end])
 		if x := z.raw.start; x != 0 {
 			// Adjust the data/attr spans to refer to the same contents after the copy.
 			z.data.start -= x
 			z.data.end -= x
 			z.pendingAttr[0].start -= x
 			z.pendingAttr[0].end -= x
 			z.pendingAttr[1].start -= x
 			z.pendingAttr[1].end -= x
 			for i := range z.attr {
 				z.attr[i][0].start -= x
 				z.attr[i][0].end -= x
 				z.attr[i][1].start -= x
 				z.attr[i][1].end -= x
 			}
 		}
 		z.raw.start, z.raw.end, z.buf = 0, d, buf1[:d]
 		// Now that we have copied the live bytes to the start of the buffer,
 		// we read from z.r into the remainder.
 		var n int
 		n, z.readErr = readAtLeastOneByte(z.r, buf1[d:cap(buf1)])
 		if n == 0 {
 			z.err = z.readErr
 			return 0
 		}
 		z.buf = buf1[:d+n]
 	}
 	x := z.buf[z.raw.end]
 	z.raw.end++
 	if z.maxBuf > 0 && z.raw.end-z.raw.start >= z.maxBuf {
 		z.err = ErrBufferExceeded
 		return 0
 	}
 	return x
 }
 
 // Buffered returns a slice containing data buffered but not yet tokenized.
 func (z *Tokenizer) Buffered() []byte {
 	return z.buf[z.raw.end:]
 }
 
 // readAtLeastOneByte wraps an io.Reader so that reading cannot return (0, nil).
 // It returns io.ErrNoProgress if the underlying r.Read method returns (0, nil)
 // too many times in succession.
 func readAtLeastOneByte(r io.Reader, b []byte) (int, error) {
 	for i := 0; i < 100; i++ {
 		if n, err := r.Read(b); n != 0 || err != nil {
 			return n, err
 		}
 	}
 	return 0, io.ErrNoProgress
 }
 
 // skipWhiteSpace skips past any white space.
 func (z *Tokenizer) skipWhiteSpace() {
 	if z.err != nil {
 		return
 	}
 	for {
 		c := z.readByte()
 		if z.err != nil {
 			return
 		}
 		switch c {
 		case ' ', '\n', '\r', '\t', '\f':
 			// No-op.
 		default:
 			z.raw.end--
 			return
 		}
 	}
 }
 
 // readRawOrRCDATA reads until the next "</foo>", where "foo" is z.rawTag and
 // is typically something like "script" or "textarea".
 func (z *Tokenizer) readRawOrRCDATA() {
 	if z.rawTag == "script" {
 		z.readScript()
 		z.textIsRaw = true
 		z.rawTag = ""
 		return
 	}
 loop:
 	for {
 		c := z.readByte()
 		if z.err != nil {
 			break loop
 		}
 		if c != '<' {
 			continue loop
 		}
 		c = z.readByte()
 		if z.err != nil {
 			break loop
 		}
 		if c != '/' {
 			z.raw.end--
 			continue loop
 		}
 		if z.readRawEndTag() || z.err != nil {
 			break loop
 		}
 	}
 	z.data.end = z.raw.end
 	// A textarea's or title's RCDATA can contain escaped entities.
 	z.textIsRaw = z.rawTag != "textarea" && z.rawTag != "title"
 	z.rawTag = ""
 }
 
 // readRawEndTag attempts to read a tag like "</foo>", where "foo" is z.rawTag.
 // If it succeeds, it backs up the input position to reconsume the tag and
 // returns true. Otherwise it returns false. The opening "</" has already been
 // consumed.
 func (z *Tokenizer) readRawEndTag() bool {
 	for i := 0; i < len(z.rawTag); i++ {
 		c := z.readByte()
 		if z.err != nil {
 			return false
 		}
 		if c != z.rawTag[i] && c != z.rawTag[i]-('a'-'A') {
 			z.raw.end--
 			return false
 		}
 	}
 	c := z.readByte()
 	if z.err != nil {
 		return false
 	}
 	switch c {
 	case ' ', '\n', '\r', '\t', '\f', '/', '>':
 		// The 3 is 2 for the leading "</" plus 1 for the trailing character c.
 		z.raw.end -= 3 + len(z.rawTag)
 		return true
 	}
 	z.raw.end--
 	return false
 }
 
 // readScript reads until the next </script> tag, following the byzantine
 // rules for escaping/hiding the closing tag.
 func (z *Tokenizer) readScript() {
 	defer func() {
 		z.data.end = z.raw.end
 	}()
 	var c byte
 
 scriptData:
 	c = z.readByte()
 	if z.err != nil {
 		return
 	}
 	if c == '<' {
 		goto scriptDataLessThanSign
 	}
 	goto scriptData
 
 scriptDataLessThanSign:
 	c = z.readByte()
 	if z.err != nil {
 		return
 	}
 	switch c {
 	case '/':
 		goto scriptDataEndTagOpen
 	case '!':
 		goto scriptDataEscapeStart
 	}
 	z.raw.end--
 	goto scriptData
 
 scriptDataEndTagOpen:
 	if z.readRawEndTag() || z.err != nil {
 		return
 	}
 	goto scriptData
 
 scriptDataEscapeStart:
 	c = z.readByte()
 	if z.err != nil {
 		return
 	}
 	if c == '-' {
 		goto scriptDataEscapeStartDash
 	}
 	z.raw.end--
 	goto scriptData
 
 scriptDataEscapeStartDash:
 	c = z.readByte()
 	if z.err != nil {
 		return
 	}
 	if c == '-' {
 		goto scriptDataEscapedDashDash
 	}
 	z.raw.end--
 	goto scriptData
 
 scriptDataEscaped:
 	c = z.readByte()
 	if z.err != nil {
 		return
 	}
 	switch c {
 	case '-':
 		goto scriptDataEscapedDash
 	case '<':
 		goto scriptDataEscapedLessThanSign
 	}
 	goto scriptDataEscaped
 
 scriptDataEscapedDash:
 	c = z.readByte()
 	if z.err != nil {
 		return
 	}
 	switch c {
 	case '-':
 		goto scriptDataEscapedDashDash
 	case '<':
 		goto scriptDataEscapedLessThanSign
 	}
 	goto scriptDataEscaped
 
 scriptDataEscapedDashDash:
 	c = z.readByte()
 	if z.err != nil {
 		return
 	}
 	switch c {
 	case '-':
 		goto scriptDataEscapedDashDash
 	case '<':
 		goto scriptDataEscapedLessThanSign
 	case '>':
 		goto scriptData
 	}
 	goto scriptDataEscaped
 
 scriptDataEscapedLessThanSign:
 	c = z.readByte()
 	if z.err != nil {
 		return
 	}
 	if c == '/' {
 		goto scriptDataEscapedEndTagOpen
 	}
 	if 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z' {
 		goto scriptDataDoubleEscapeStart
 	}
 	z.raw.end--
 	goto scriptData
 
 scriptDataEscapedEndTagOpen:
 	if z.readRawEndTag() || z.err != nil {
 		return
 	}
 	goto scriptDataEscaped
 
 scriptDataDoubleEscapeStart:
 	z.raw.end--
 	for i := 0; i < len("script"); i++ {
 		c = z.readByte()
 		if z.err != nil {
 			return
 		}
 		if c != "script"[i] && c != "SCRIPT"[i] {
 			z.raw.end--
 			goto scriptDataEscaped
 		}
 	}
 	c = z.readByte()
 	if z.err != nil {
 		return
 	}
 	switch c {
 	case ' ', '\n', '\r', '\t', '\f', '/', '>':
 		goto scriptDataDoubleEscaped
 	}
 	z.raw.end--
 	goto scriptDataEscaped
 
 scriptDataDoubleEscaped:
 	c = z.readByte()
 	if z.err != nil {
 		return
 	}
 	switch c {
 	case '-':
 		goto scriptDataDoubleEscapedDash
 	case '<':
 		goto scriptDataDoubleEscapedLessThanSign
 	}
 	goto scriptDataDoubleEscaped
 
 scriptDataDoubleEscapedDash:
 	c = z.readByte()
 	if z.err != nil {
 		return
 	}
 	switch c {
 	case '-':
 		goto scriptDataDoubleEscapedDashDash
 	case '<':
 		goto scriptDataDoubleEscapedLessThanSign
 	}
 	goto scriptDataDoubleEscaped
 
 scriptDataDoubleEscapedDashDash:
 	c = z.readByte()
 	if z.err != nil {
 		return
 	}
 	switch c {
 	case '-':
 		goto scriptDataDoubleEscapedDashDash
 	case '<':
 		goto scriptDataDoubleEscapedLessThanSign
 	case '>':
 		goto scriptData
 	}
 	goto scriptDataDoubleEscaped
 
 scriptDataDoubleEscapedLessThanSign:
 	c = z.readByte()
 	if z.err != nil {
 		return
 	}
 	if c == '/' {
 		goto scriptDataDoubleEscapeEnd
 	}
 	z.raw.end--
 	goto scriptDataDoubleEscaped
 
 scriptDataDoubleEscapeEnd:
 	if z.readRawEndTag() {
 		z.raw.end += len("</script>")
 		goto scriptDataEscaped
 	}
 	if z.err != nil {
 		return
 	}
 	goto scriptDataDoubleEscaped
 }
 
 // readComment reads the next comment token starting with "<!--". The opening
 // "<!--" has already been consumed.
 func (z *Tokenizer) readComment() {
 	// When modifying this function, consider manually increasing the
 	// maxSuffixLen constant in func TestComments, from 6 to e.g. 9 or more.
 	// That increase should only be temporary, not committed, as it
 	// exponentially affects the test running time.
 
 	z.data.start = z.raw.end
 	defer func() {
 		if z.data.end < z.data.start {
 			// It's a comment with no data, like <!-->.
 			z.data.end = z.data.start
 		}
 	}()
 
 	var dashCount int
 	beginning := true
 	for {
 		c := z.readByte()
 		if z.err != nil {
 			z.data.end = z.calculateAbruptCommentDataEnd()
 			return
 		}
 		switch c {
 		case '-':
 			dashCount++
 			continue
 		case '>':
 			if dashCount >= 2 || beginning {
 				z.data.end = z.raw.end - len("-->")
 				return
 			}
 		case '!':
 			if dashCount >= 2 {
 				c = z.readByte()
 				if z.err != nil {
 					z.data.end = z.calculateAbruptCommentDataEnd()
 					return
 				} else if c == '>' {
 					z.data.end = z.raw.end - len("--!>")
 					return
 				} else if c == '-' {
 					dashCount = 1
 					beginning = false
 					continue
 				}
 			}
 		}
 		dashCount = 0
 		beginning = false
 	}
 }
 
 func (z *Tokenizer) calculateAbruptCommentDataEnd() int {
 	raw := z.Raw()
 	const prefixLen = len("<!--")
 	if len(raw) >= prefixLen {
 		raw = raw[prefixLen:]
 		if hasSuffix(raw, "--!") {
 			return z.raw.end - 3
 		} else if hasSuffix(raw, "--") {
 			return z.raw.end - 2
 		} else if hasSuffix(raw, "-") {
 			return z.raw.end - 1
 		}
 	}
 	return z.raw.end
 }
 
 func hasSuffix(b []byte, suffix string) bool {
 	if len(b) < len(suffix) {
 		return false
 	}
 	b = b[len(b)-len(suffix):]
 	for i := range b {
 		if b[i] != suffix[i] {
 			return false
 		}
 	}
 	return true
 }
 
 // readUntilCloseAngle reads until the next ">".
 func (z *Tokenizer) readUntilCloseAngle() {
 	z.data.start = z.raw.end
 	for {
 		c := z.readByte()
 		if z.err != nil {
 			z.data.end = z.raw.end
 			return
 		}
 		if c == '>' {
 			z.data.end = z.raw.end - len(">")
 			return
 		}
 	}
 }
 
 // readMarkupDeclaration reads the next token starting with "<!". It might be
 // a "<!--comment-->", a "<!DOCTYPE foo>", a "<![CDATA[section]]>" or
 // "<!a bogus comment". The opening "<!" has already been consumed.
 func (z *Tokenizer) readMarkupDeclaration() TokenType {
 	z.data.start = z.raw.end
 	var c [2]byte
 	for i := 0; i < 2; i++ {
 		c[i] = z.readByte()
 		if z.err != nil {
 			z.data.end = z.raw.end
 			return CommentToken
 		}
 	}
 	if c[0] == '-' && c[1] == '-' {
 		z.readComment()
 		return CommentToken
 	}
 	z.raw.end -= 2
 	if z.readDoctype() {
 		return DoctypeToken
 	}
 	if z.allowCDATA && z.readCDATA() {
 		z.convertNUL = true
 		return TextToken
 	}
 	// It's a bogus comment.
 	z.readUntilCloseAngle()
 	return CommentToken
 }
 
 // readDoctype attempts to read a doctype declaration and returns true if
 // successful. The opening "<!" has already been consumed.
 func (z *Tokenizer) readDoctype() bool {
 	const s = "DOCTYPE"
 	for i := 0; i < len(s); i++ {
 		c := z.readByte()
 		if z.err != nil {
 			z.data.end = z.raw.end
 			return false
 		}
 		if c != s[i] && c != s[i]+('a'-'A') {
 			// Back up to read the fragment of "DOCTYPE" again.
 			z.raw.end = z.data.start
 			return false
 		}
 	}
 	if z.skipWhiteSpace(); z.err != nil {
 		z.data.start = z.raw.end
 		z.data.end = z.raw.end
 		return true
 	}
 	z.readUntilCloseAngle()
 	return true
 }
 
 // readCDATA attempts to read a CDATA section and returns true if
 // successful. The opening "<!" has already been consumed.
 func (z *Tokenizer) readCDATA() bool {
 	const s = "[CDATA["
 	for i := 0; i < len(s); i++ {
 		c := z.readByte()
 		if z.err != nil {
 			z.data.end = z.raw.end
 			return false
 		}
 		if c != s[i] {
 			// Back up to read the fragment of "[CDATA[" again.
 			z.raw.end = z.data.start
 			return false
 		}
 	}
 	z.data.start = z.raw.end
 	brackets := 0
 	for {
 		c := z.readByte()
 		if z.err != nil {
 			z.data.end = z.raw.end
 			return true
 		}
 		switch c {
 		case ']':
 			brackets++
 		case '>':
 			if brackets >= 2 {
 				z.data.end = z.raw.end - len("]]>")
 				return true
 			}
 			brackets = 0
 		default:
 			brackets = 0
 		}
 	}
 }
 
 // startTagIn returns whether the start tag in z.buf[z.data.start:z.data.end]
 // case-insensitively matches any element of ss.
 func (z *Tokenizer) startTagIn(ss ...string) bool {
 loop:
 	for _, s := range ss {
 		if z.data.end-z.data.start != len(s) {
 			continue loop
 		}
 		for i := 0; i < len(s); i++ {
 			c := z.buf[z.data.start+i]
 			if 'A' <= c && c <= 'Z' {
 				c += 'a' - 'A'
 			}
 			if c != s[i] {
 				continue loop
 			}
 		}
 		return true
 	}
 	return false
 }
 
 // readStartTag reads the next start tag token. The opening "<a" has already
 // been consumed, where 'a' means anything in [A-Za-z].
 func (z *Tokenizer) readStartTag() TokenType {
 	z.readTag(true)
 	if z.err != nil {
 		return ErrorToken
 	}
 	// Several tags flag the tokenizer's next token as raw.
 	c, raw := z.buf[z.data.start], false
 	if 'A' <= c && c <= 'Z' {
 		c += 'a' - 'A'
 	}
 	switch c {
 	case 'i':
 		raw = z.startTagIn("iframe")
 	case 'n':
 		raw = z.startTagIn("noembed", "noframes", "noscript")
 	case 'p':
 		raw = z.startTagIn("plaintext")
 	case 's':
 		raw = z.startTagIn("script", "style")
 	case 't':
 		raw = z.startTagIn("textarea", "title")
 	case 'x':
 		raw = z.startTagIn("xmp")
 	}
 	if raw {
 		z.rawTag = strings.ToLower(string(z.buf[z.data.start:z.data.end]))
 	}
 	// Look for a self-closing token like "<br/>".
 	if z.err == nil && z.buf[z.raw.end-2] == '/' {
 		return SelfClosingTagToken
 	}
 	return StartTagToken
 }
 
 // readTag reads the next tag token and its attributes. If saveAttr, those
 // attributes are saved in z.attr, otherwise z.attr is set to an empty slice.
 // The opening "<a" or "</a" has already been consumed, where 'a' means anything
 // in [A-Za-z].
 func (z *Tokenizer) readTag(saveAttr bool) {
 	z.attr = z.attr[:0]
 	z.nAttrReturned = 0
 	// Read the tag name and attribute key/value pairs.
 	z.readTagName()
 	if z.skipWhiteSpace(); z.err != nil {
 		return
 	}
 	for {
 		c := z.readByte()
 		if z.err != nil || c == '>' {
 			break
 		}
 		z.raw.end--
 		z.readTagAttrKey()
 		z.readTagAttrVal()
 		// Save pendingAttr if saveAttr and that attribute has a non-empty key.
 		if saveAttr && z.pendingAttr[0].start != z.pendingAttr[0].end {
 			z.attr = append(z.attr, z.pendingAttr)
 		}
 		if z.skipWhiteSpace(); z.err != nil {
 			break
 		}
 	}
 }
 
 // readTagName sets z.data to the "div" in "<div k=v>". The reader (z.raw.end)
 // is positioned such that the first byte of the tag name (the "d" in "<div")
 // has already been consumed.
 func (z *Tokenizer) readTagName() {
 	z.data.start = z.raw.end - 1
 	for {
 		c := z.readByte()
 		if z.err != nil {
 			z.data.end = z.raw.end
 			return
 		}
 		switch c {
 		case ' ', '\n', '\r', '\t', '\f':
 			z.data.end = z.raw.end - 1
 			return
 		case '/', '>':
 			z.raw.end--
 			z.data.end = z.raw.end
 			return
 		}
 	}
 }
 
 // readTagAttrKey sets z.pendingAttr[0] to the "k" in "<div k=v>".
 // Precondition: z.err == nil.
 func (z *Tokenizer) readTagAttrKey() {
 	z.pendingAttr[0].start = z.raw.end
 	for {
 		c := z.readByte()
 		if z.err != nil {
 			z.pendingAttr[0].end = z.raw.end
 			return
 		}
 		switch c {
 		case ' ', '\n', '\r', '\t', '\f', '/':
 			z.pendingAttr[0].end = z.raw.end - 1
 			return
 		case '=', '>':
 			z.raw.end--
 			z.pendingAttr[0].end = z.raw.end
 			return
 		}
 	}
 }
 
 // readTagAttrVal sets z.pendingAttr[1] to the "v" in "<div k=v>".
 func (z *Tokenizer) readTagAttrVal() {
 	z.pendingAttr[1].start = z.raw.end
 	z.pendingAttr[1].end = z.raw.end
 	if z.skipWhiteSpace(); z.err != nil {
 		return
 	}
 	c := z.readByte()
 	if z.err != nil {
 		return
 	}
 	if c != '=' {
 		z.raw.end--
 		return
 	}
 	if z.skipWhiteSpace(); z.err != nil {
 		return
 	}
 	quote := z.readByte()
 	if z.err != nil {
 		return
 	}
 	switch quote {
 	case '>':
 		z.raw.end--
 		return
 
 	case '\'', '"':
 		z.pendingAttr[1].start = z.raw.end
 		for {
 			c := z.readByte()
 			if z.err != nil {
 				z.pendingAttr[1].end = z.raw.end
 				return
 			}
 			if c == quote {
 				z.pendingAttr[1].end = z.raw.end - 1
 				return
 			}
 		}
 
 	default:
 		z.pendingAttr[1].start = z.raw.end - 1
 		for {
 			c := z.readByte()
 			if z.err != nil {
 				z.pendingAttr[1].end = z.raw.end
 				return
 			}
 			switch c {
 			case ' ', '\n', '\r', '\t', '\f':
 				z.pendingAttr[1].end = z.raw.end - 1
 				return
 			case '>':
 				z.raw.end--
 				z.pendingAttr[1].end = z.raw.end
 				return
 			}
 		}
 	}
 }
 
 // Next scans the next token and returns its type.
 func (z *Tokenizer) Next() TokenType {
 	z.raw.start = z.raw.end
 	z.data.start = z.raw.end
 	z.data.end = z.raw.end
 	if z.err != nil {
 		z.tt = ErrorToken
 		return z.tt
 	}
 	if z.rawTag != "" {
 		if z.rawTag == "plaintext" {
 			// Read everything up to EOF.
 			for z.err == nil {
 				z.readByte()
 			}
 			z.data.end = z.raw.end
 			z.textIsRaw = true
 		} else {
 			z.readRawOrRCDATA()
 		}
 		if z.data.end > z.data.start {
 			z.tt = TextToken
 			z.convertNUL = true
 			return z.tt
 		}
 	}
 	z.textIsRaw = false
 	z.convertNUL = false
 
 loop:
 	for {
 		c := z.readByte()
 		if z.err != nil {
 			break loop
 		}
 		if c != '<' {
 			continue loop
 		}
 
 		// Check if the '<' we have just read is part of a tag, comment
 		// or doctype. If not, it's part of the accumulated text token.
 		c = z.readByte()
 		if z.err != nil {
 			break loop
 		}
 		var tokenType TokenType
 		switch {
 		case 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z':
 			tokenType = StartTagToken
 		case c == '/':
 			tokenType = EndTagToken
 		case c == '!' || c == '?':
 			// We use CommentToken to mean any of "<!--actual comments-->",
 			// "<!DOCTYPE declarations>" and "<?xml processing instructions?>".
 			tokenType = CommentToken
 		default:
 			// Reconsume the current character.
 			z.raw.end--
 			continue
 		}
 
 		// We have a non-text token, but we might have accumulated some text
 		// before that. If so, we return the text first, and return the non-
 		// text token on the subsequent call to Next.
 		if x := z.raw.end - len("<a"); z.raw.start < x {
 			z.raw.end = x
 			z.data.end = x
 			z.tt = TextToken
 			return z.tt
 		}
 		switch tokenType {
 		case StartTagToken:
 			z.tt = z.readStartTag()
 			return z.tt
 		case EndTagToken:
 			c = z.readByte()
 			if z.err != nil {
 				break loop
 			}
 			if c == '>' {
 				// "</>" does not generate a token at all. Generate an empty comment
 				// to allow passthrough clients to pick up the data using Raw.
 				// Reset the tokenizer state and start again.
 				z.tt = CommentToken
 				return z.tt
 			}
 			if 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z' {
 				z.readTag(false)
 				if z.err != nil {
 					z.tt = ErrorToken
 				} else {
 					z.tt = EndTagToken
 				}
 				return z.tt
 			}
 			z.raw.end--
 			z.readUntilCloseAngle()
 			z.tt = CommentToken
 			return z.tt
 		case CommentToken:
 			if c == '!' {
 				z.tt = z.readMarkupDeclaration()
 				return z.tt
 			}
 			z.raw.end--
 			z.readUntilCloseAngle()
 			z.tt = CommentToken
 			return z.tt
 		}
 	}
 	if z.raw.start < z.raw.end {
 		z.data.end = z.raw.end
 		z.tt = TextToken
 		return z.tt
 	}
 	z.tt = ErrorToken
 	return z.tt
 }
 
 // Raw returns the unmodified text of the current token. Calling Next, Token,
 // Text, TagName or TagAttr may change the contents of the returned slice.
 //
 // The token stream's raw bytes partition the byte stream (up until an
 // ErrorToken). There are no overlaps or gaps between two consecutive token's
 // raw bytes. One implication is that the byte offset of the current token is
 // the sum of the lengths of all previous tokens' raw bytes.
 func (z *Tokenizer) Raw() []byte {
 	return z.buf[z.raw.start:z.raw.end]
 }
 
 // convertNewlines converts "\r" and "\r\n" in s to "\n".
 // The conversion happens in place, but the resulting slice may be shorter.
 func convertNewlines(s []byte) []byte {
 	for i, c := range s {
 		if c != '\r' {
 			continue
 		}
 
 		src := i + 1
 		if src >= len(s) || s[src] != '\n' {
 			s[i] = '\n'
 			continue
 		}
 
 		dst := i
 		for src < len(s) {
 			if s[src] == '\r' {
 				if src+1 < len(s) && s[src+1] == '\n' {
 					src++
 				}
 				s[dst] = '\n'
 			} else {
 				s[dst] = s[src]
 			}
 			src++
 			dst++
 		}
 		return s[:dst]
 	}
 	return s
 }
 
 var (
 	nul         = []byte("\x00")
 	replacement = []byte("\ufffd")
 )
 
 // Text returns the unescaped text of a text, comment or doctype token. The
 // contents of the returned slice may change on the next call to Next.
 func (z *Tokenizer) Text() []byte {
 	switch z.tt {
 	case TextToken, CommentToken, DoctypeToken:
 		s := z.buf[z.data.start:z.data.end]
 		z.data.start = z.raw.end
 		z.data.end = z.raw.end
 		s = convertNewlines(s)
 		if (z.convertNUL || z.tt == CommentToken) && bytes.Contains(s, nul) {
 			s = bytes.Replace(s, nul, replacement, -1)
 		}
 		if !z.textIsRaw {
 			s = unescape(s, false)
 		}
 		return s
 	}
 	return nil
 }
 
 // TagName returns the lower-cased name of a tag token (the `img` out of
 // `<IMG SRC="foo">`) and whether the tag has attributes.
 // The contents of the returned slice may change on the next call to Next.
 func (z *Tokenizer) TagName() (name []byte, hasAttr bool) {
 	if z.data.start < z.data.end {
 		switch z.tt {
 		case StartTagToken, EndTagToken, SelfClosingTagToken:
 			s := z.buf[z.data.start:z.data.end]
 			z.data.start = z.raw.end
 			z.data.end = z.raw.end
 			return lower(s), z.nAttrReturned < len(z.attr)
 		}
 	}
 	return nil, false
 }
 
 // TagAttr returns the lower-cased key and unescaped value of the next unparsed
 // attribute for the current tag token and whether there are more attributes.
 // The contents of the returned slices may change on the next call to Next.
 func (z *Tokenizer) TagAttr() (key, val []byte, moreAttr bool) {
 	if z.nAttrReturned < len(z.attr) {
 		switch z.tt {
 		case StartTagToken, SelfClosingTagToken:
 			x := z.attr[z.nAttrReturned]
 			z.nAttrReturned++
 			key = z.buf[x[0].start:x[0].end]
 			val = z.buf[x[1].start:x[1].end]
 			return lower(key), unescape(convertNewlines(val), true), z.nAttrReturned < len(z.attr)
 		}
 	}
 	return nil, nil, false
 }
 
 // Token returns the current Token. The result's Data and Attr values remain
 // valid after subsequent Next calls.
 func (z *Tokenizer) Token() Token {
 	t := Token{Type: z.tt}
 	switch z.tt {
 	case TextToken, CommentToken, DoctypeToken:
 		t.Data = string(z.Text())
 	case StartTagToken, SelfClosingTagToken, EndTagToken:
 		name, moreAttr := z.TagName()
 		for moreAttr {
 			var key, val []byte
 			key, val, moreAttr = z.TagAttr()
 			t.Attr = append(t.Attr, Attribute{"", atom.String(key), string(val)})
 		}
 		if a := atom.Lookup(name); a != 0 {
 			t.DataAtom, t.Data = a, a.String()
 		} else {
 			t.DataAtom, t.Data = 0, string(name)
 		}
 	}
 	return t
 }
 
 // SetMaxBuf sets a limit on the amount of data buffered during tokenization.
 // A value of 0 means unlimited.
 func (z *Tokenizer) SetMaxBuf(n int) {
 	z.maxBuf = n
 }
 
 // NewTokenizer returns a new HTML Tokenizer for the given Reader.
 // The input is assumed to be UTF-8 encoded.
 func NewTokenizer(r io.Reader) *Tokenizer {
 	return NewTokenizerFragment(r, "")
 }
 
 // NewTokenizerFragment returns a new HTML Tokenizer for the given Reader, for
 // tokenizing an existing element's InnerHTML fragment. contextTag is that
 // element's tag, such as "div" or "iframe".
 //
 // For example, how the InnerHTML "a<b" is tokenized depends on whether it is
 // for a <p> tag or a <script> tag.
 //
 // The input is assumed to be UTF-8 encoded.
 func NewTokenizerFragment(r io.Reader, contextTag string) *Tokenizer {
 	z := &Tokenizer{
 		r:   r,
 		buf: make([]byte, 0, 4096),
 	}
 	if contextTag != "" {
 		switch s := strings.ToLower(contextTag); s {
 		case "iframe", "noembed", "noframes", "noscript", "plaintext", "script", "style", "title", "textarea", "xmp":
 			z.rawTag = s
 		}
 	}
 	return z
 }