rss-tools @ master

// 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<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 (e.g. <br/>).

	//

	// Originally, we did this by just checking that the last character of the

	// tag (ignoring the closing bracket) was a solidus (/) character, but this

	// is not always accurate.

	//

	// We need to be careful that we don't misinterpret a non-self-closing tag

	// as self-closing, as can happen if the tag contains unquoted attribute

	// values (i.e. <p a=/>).

	//

	// To avoid this, we check that the last non-bracket character of the tag

	// (z.raw.end-2) isn't the same character as the last non-quote character of

	// the last attribute of the tag (z.pendingAttr[1].end-1), if the tag has

	// attributes.

	nAttrs := len(z.attr)

	if z.err == nil && z.buf[z.raw.end-2] == '/' && (nAttrs == 0 || z.raw.end-2 != z.attr[nAttrs-1][1].end-1) {

		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 '=':

			if z.pendingAttr[0].start+1 == z.raw.end {

				// WHATWG 13.2.5.32, if we see an equals sign before the attribute name

				// begins, we treat it as a character in the attribute name and continue.

				continue

			}

			fallthrough

		case ' ', '\n', '\r', '\t', '\f', '/', '>':

			// WHATWG 13.2.5.33 Attribute name state

			// We need to reconsume the char in the after attribute name state to support the / character

			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 == '/' {

		// WHATWG 13.2.5.34 After attribute name state

		// U+002F SOLIDUS (/) - Switch to the self-closing start tag state.

		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

}