source: code/trunk/vendor/golang.org/x/net/html/token.go@ 145

// 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 "<!--" + EscapeString(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 suffixLen
        // 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
}