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// 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"
"io"
"os"
"strconv"
)
// A TokenType is the type of a Token.
type TokenType int
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
)
// 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"
}
return "Invalid(" + strconv.Itoa(int(t)) + ")"
}
// An Attribute is an attribute key-value pair. 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").
type Attribute struct {
Key, Val string
}
// A Token consists of a TokenType and some Data (tag name for start and end
// tags, content for text). A tag Token may also contain a slice of Attributes.
// Data is unescaped for both tag and text Tokens (it looks like "a<b" rather
// than "a&lt;b").
type Token struct {
Type TokenType
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.NewBuffer(nil)
buf.WriteString(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() + "/>"
}
return "Invalid(" + strconv.Itoa(int(t.Type)) + ")"
}
// 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 most recently read token. If tt == Error
// then err is the error associated with trying to read that token.
tt TokenType
err os.Error
// buf[p0:p1] holds the raw data of the most recent token.
// buf[p1:] is buffered input that will yield future tokens.
p0, p1 int
buf []byte
}
// Error returns the error associated with the most recent ErrorToken token.
// This is typically os.EOF, meaning the end of tokenization.
func (z *Tokenizer) Error() os.Error {
if z.tt != ErrorToken {
return nil
}
return z.err
}
// Raw returns the unmodified text of the current token. Calling Next, Token,
// Text, TagName or TagAttr may change the contents of the returned slice.
func (z *Tokenizer) Raw() []byte {
return z.buf[z.p0:z.p1]
}
// readByte returns the next byte from the input stream, doing a buffered read
// from z.r into z.buf if necessary. z.buf[z.p0:z.p1] remains a contiguous byte
// slice that holds all the bytes read so far for the current token.
func (z *Tokenizer) readByte() (byte, os.Error) {
if z.p1 >= len(z.buf) {
// Our buffer is exhausted and we have to read from z.r.
// We copy z.buf[z.p0:z.p1] to the beginning of z.buf. If the length
// z.p1 - z.p0 is more than half the capacity of z.buf, then we
// allocate a new buffer before the copy.
c := cap(z.buf)
d := z.p1 - z.p0
var buf1 []byte
if 2*d > c {
buf1 = make([]byte, d, 2*c)
} else {
buf1 = z.buf[0:d]
}
copy(buf1, z.buf[z.p0:z.p1])
z.p0, z.p1, z.buf = 0, d, buf1[0:d]
// Now that we have copied the live bytes to the start of the buffer,
// we read from z.r into the remainder.
n, err := z.r.Read(buf1[d:cap(buf1)])
if err != nil {
return 0, err
}
z.buf = buf1[0 : d+n]
}
x := z.buf[z.p1]
z.p1++
return x, nil
}
// readTo keeps reading bytes until x is found.
func (z *Tokenizer) readTo(x uint8) os.Error {
for {
c, err := z.readByte()
if err != nil {
return err
}
switch c {
case x:
return nil
case '\\':
_, err = z.readByte()
if err != nil {
return err
}
}
}
panic("unreachable")
}
// nextTag returns the next TokenType starting from the tag open state.
func (z *Tokenizer) nextTag() (tt TokenType, err os.Error) {
c, err := z.readByte()
if err != nil {
return ErrorToken, err
}
switch {
case c == '/':
tt = EndTagToken
// Lower-cased characters are more common in tag names, so we check for them first.
case 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z':
tt = StartTagToken
case c == '!':
return ErrorToken, os.NewError("html: TODO(nigeltao): implement comments")
case c == '?':
return ErrorToken, os.NewError("html: TODO(nigeltao): implement XML processing instructions")
default:
return ErrorToken, os.NewError("html: TODO(nigeltao): handle malformed tags")
}
for {
c, err := z.readByte()
if err != nil {
return TextToken, err
}
switch c {
case '"':
err = z.readTo('"')
if err != nil {
return TextToken, err
}
case '\'':
err = z.readTo('\'')
if err != nil {
return TextToken, err
}
case '>':
if z.buf[z.p1-2] == '/' && tt == StartTagToken {
return SelfClosingTagToken, nil
}
return tt, nil
}
}
panic("unreachable")
}
// Next scans the next token and returns its type.
func (z *Tokenizer) Next() TokenType {
if z.err != nil {
z.tt = ErrorToken
return z.tt
}
z.p0 = z.p1
c, err := z.readByte()
if err != nil {
z.tt, z.err = ErrorToken, err
return z.tt
}
if c == '<' {
z.tt, z.err = z.nextTag()
return z.tt
}
for {
c, err := z.readByte()
if err != nil {
z.tt, z.err = ErrorToken, err
if err == os.EOF {
z.tt = TextToken
}
return z.tt
}
if c == '<' {
z.p1--
z.tt = TextToken
return z.tt
}
}
panic("unreachable")
}
// trim returns the largest j such that z.buf[i:j] contains only white space,
// or only white space plus the final ">" or "/>" of the raw data.
func (z *Tokenizer) trim(i int) int {
k := z.p1
for ; i < k; i++ {
switch z.buf[i] {
case ' ', '\n', '\t', '\f':
continue
case '>':
if i == k-1 {
return k
}
case '/':
if i == k-2 {
return k
}
}
return i
}
return k
}
// lower finds the largest alphabetic [0-9A-Za-z]* word at the start of z.buf[i:]
// and returns that word lower-cased, as well as the trimmed cursor location
// after that word.
func (z *Tokenizer) lower(i int) ([]byte, int) {
i0 := i
loop:
for ; i < z.p1; i++ {
c := z.buf[i]
switch {
case '0' <= c && c <= '9':
// No-op.
case 'A' <= c && c <= 'Z':
z.buf[i] = c + 'a' - 'A'
case 'a' <= c && c <= 'z':
// No-op.
default:
break loop
}
}
return z.buf[i0:i], z.trim(i)
}
// Text returns the raw data after unescaping.
// The contents of the returned slice may change on the next call to Next.
func (z *Tokenizer) Text() []byte {
s := unescape(z.Raw())
z.p0 = z.p1
return s
}
// 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, remaining bool) {
i := z.p0 + 1
if i >= z.p1 {
z.p0 = z.p1
return nil, false
}
if z.buf[i] == '/' {
i++
}
name, z.p0 = z.lower(i)
remaining = z.p0 != z.p1
return
}
// 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, remaining bool) {
key, i := z.lower(z.p0)
// Get past the "=\"".
if i == z.p1 || z.buf[i] != '=' {
return
}
i = z.trim(i + 1)
if i == z.p1 || z.buf[i] != '"' {
return
}
i = z.trim(i + 1)
// Copy and unescape everything up to the closing '"'.
dst, src := i, i
loop:
for src < z.p1 {
c := z.buf[src]
switch c {
case '"':
src++
break loop
case '&':
dst, src = unescapeEntity(z.buf, dst, src)
case '\\':
if src == z.p1 {
z.buf[dst] = '\\'
dst++
} else {
z.buf[dst] = z.buf[src+1]
dst, src = dst+1, src+2
}
default:
z.buf[dst] = c
dst, src = dst+1, src+1
}
}
val, z.p0 = z.buf[i:dst], z.trim(src)
remaining = z.p0 != z.p1
return
}
// Token returns the next 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:
t.Data = string(z.Text())
case StartTagToken, EndTagToken, SelfClosingTagToken:
var attr []Attribute
name, remaining := z.TagName()
for remaining {
var key, val []byte
key, val, remaining = z.TagAttr()
attr = append(attr, Attribute{string(key), string(val)})
}
t.Data = string(name)
t.Attr = attr
}
return t
}
// 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 &Tokenizer{
r: r,
buf: make([]byte, 0, 4096),
}
}