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html: parse misnested formatting tags according to the HTML5 spec.

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This is the "adoption agency" algorithm.

The test case input is "<a><p>X<a>Y</a>Z</p></a>". The correct parse is:
| <html>
|   <head>
|   <body>
|     <a>
|     <p>
|       <a>
|         "X"
|       <a>
|         "Y"
|       "Z"

R=gri
CC=golang-dev
https://golang.org/cl/4771042
This commit is contained in:
Nigel Tao 2011-07-21 11:20:54 +10:00
parent d11c0f1dbb
commit 5a141064ed
5 changed files with 421 additions and 64 deletions
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2
src/pkg/html/Makefile
View File

@ -6,9 +6,11 @@ include ../../Make.inc
TARG=html
GOFILES=\
const.go\
doc.go\
entity.go\
escape.go\
node.go\
parse.go\
token.go\

90
src/pkg/html/const.go Normal file
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@ -0,0 +1,90 @@
// Copyright 2011 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
// Section 11.2.3.2 of the HTML5 specification says "The following elements
// have varying levels of special parsing rules".
// http://www.whatwg.org/specs/web-apps/current-work/multipage/parsing.html#the-stack-of-open-elements
var isSpecialElement = map[string]bool{
"address": true,
"applet": true,
"area": true,
"article": true,
"aside": true,
"base": true,
"basefont": true,
"bgsound": true,
"blockquote": true,
"body": true,
"br": true,
"button": true,
"caption": true,
"center": true,
"col": true,
"colgroup": true,
"command": true,
"dd": true,
"details": true,
"dir": true,
"div": true,
"dl": true,
"dt": true,
"embed": true,
"fieldset": true,
"figcaption": true,
"figure": true,
"footer": true,
"form": true,
"frame": true,
"frameset": true,
"h1": true,
"h2": true,
"h3": true,
"h4": true,
"h5": true,
"h6": true,
"head": true,
"header": true,
"hgroup": true,
"hr": true,
"html": true,
"iframe": true,
"img": true,
"input": true,
"isindex": true,
"li": true,
"link": true,
"listing": true,
"marquee": true,
"menu": true,
"meta": true,
"nav": true,
"noembed": true,
"noframes": true,
"noscript": true,
"object": true,
"ol": true,
"p": true,
"param": true,
"plaintext": true,
"pre": true,
"script": true,
"section": true,
"select": true,
"style": true,
"summary": true,
"table": true,
"tbody": true,
"td": true,
"textarea": true,
"tfoot": true,
"th": true,
"thead": true,
"title": true,
"tr": true,
"ul": true,
"wbr": true,
"xmp": true,
}

146
src/pkg/html/node.go Normal file
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@ -0,0 +1,146 @@
// Copyright 2011 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
// A NodeType is the type of a Node.
type NodeType int
const (
ErrorNode NodeType = iota
TextNode
DocumentNode
ElementNode
CommentNode
scopeMarkerNode
)
// Section 11.2.3.3 says "scope markers are inserted when entering applet
// elements, buttons, object elements, marquees, table cells, and table
// captions, and are used to prevent formatting from 'leaking'".
var scopeMarker = Node{Type: scopeMarkerNode}
// A Node consists of a NodeType and some Data (tag name for element nodes,
// content for text) and are part of a tree of Nodes. Element nodes may also
// contain a slice of Attributes. Data is unescaped, so that it looks like
// "a<b" rather than "a&lt;b".
type Node struct {
Parent *Node
Child []*Node
Type NodeType
Data string
Attr []Attribute
}
// Add adds a node as a child of n.
// It will panic if the child's parent is not nil.
func (n *Node) Add(child *Node) {
if child.Parent != nil {
panic("html: Node.Add called for a child Node that already has a parent")
}
child.Parent = n
n.Child = append(n.Child, child)
}
// Remove removes a node as a child of n.
// It will panic if the child's parent is not n.
func (n *Node) Remove(child *Node) {
if child.Parent == n {
child.Parent = nil
for i, m := range n.Child {
if m == child {
copy(n.Child[i:], n.Child[i+1:])
j := len(n.Child) - 1
n.Child[j] = nil
n.Child = n.Child[:j]
return
}
}
}
panic("html: Node.Remove called for a non-child Node")
}
// reparentChildren reparents all of src's child nodes to dst.
func reparentChildren(dst, src *Node) {
for _, n := range src.Child {
if n.Parent != src {
panic("html: nodes have an inconsistent parent/child relationship")
}
n.Parent = dst
}
dst.Child = append(dst.Child, src.Child...)
src.Child = nil
}
// clone returns a new node with the same type, data and attributes.
// The clone has no parent and no children.
func (n *Node) clone() *Node {
m := &Node{
Type: n.Type,
Data: n.Data,
Attr: make([]Attribute, len(n.Attr)),
}
copy(m.Attr, n.Attr)
return m
}
// nodeStack is a stack of nodes.
type nodeStack []*Node
// pop pops the stack. It will panic if s is empty.
func (s *nodeStack) pop() *Node {
i := len(*s)
n := (*s)[i-1]
*s = (*s)[:i-1]
return n
}
// top returns the most recently pushed node, or nil if s is empty.
func (s *nodeStack) top() *Node {
if i := len(*s); i > 0 {
return (*s)[i-1]
}
return nil
}
// index returns the index of the top-most occurence of n in the stack, or -1
// if n is not present.
func (s *nodeStack) index(n *Node) int {
for i := len(*s) - 1; i >= 0; i-- {
if (*s)[i] == n {
return i
}
}
return -1
}
// insert inserts a node at the given index.
func (s *nodeStack) insert(i int, n *Node) {
(*s) = append(*s, nil)
copy((*s)[i+1:], (*s)[i:])
(*s)[i] = n
}
// remove removes a node from the stack. It is a no-op if n is not present.
func (s *nodeStack) remove(n *Node) {
i := s.index(n)
if i == -1 {
return
}
copy((*s)[i:], (*s)[i+1:])
j := len(*s) - 1
(*s)[j] = nil
*s = (*s)[:j]
}
// forTag returns the top-most element node with the given tag.
func (s *nodeStack) forTag(tag string) *Node {
for i := len(*s) - 1; i >= 0; i-- {
n := (*s)[i]
if n.Type == ElementNode && n.Data == tag {
return n
}
}
return nil
}

243
src/pkg/html/parse.go
View File

@ -9,29 +9,6 @@ import (
"os"
)
// A NodeType is the type of a Node.
type NodeType int
const (
ErrorNode NodeType = iota
TextNode
DocumentNode
ElementNode
CommentNode
)
// A Node consists of a NodeType and some Data (tag name for element nodes,
// content for text) and are part of a tree of Nodes. Element nodes may also
// contain a slice of Attributes. Data is unescaped, so that it looks like
// "a<b" rather than "a&lt;b".
type Node struct {
Parent *Node
Child []*Node
Type NodeType
Data string
Attr []Attribute
}
// A parser implements the HTML5 parsing algorithm:
// http://www.whatwg.org/specs/web-apps/current-work/multipage/tokenization.html#tree-construction
type parser struct {
@ -45,37 +22,22 @@ type parser struct {
hasSelfClosingToken bool
// doc is the document root element.
doc *Node
// The stack of open elements (section 11.2.3.2).
stack []*Node
// The stack of open elements (section 11.2.3.2) and active formatting
// elements (section 11.2.3.3).
oe, afe nodeStack
// Element pointers (section 11.2.3.4).
head, form *Node
// Other parsing state flags (section 11.2.3.5).
scripting, framesetOK bool
}
// push pushes onto the stack of open elements.
func (p *parser) push(n *Node) {
p.stack = append(p.stack, n)
}
// top returns the top of the stack of open elements.
// This is also known as the current node.
func (p *parser) top() *Node {
if n := len(p.stack); n > 0 {
return p.stack[n-1]
if n := p.oe.top(); n != nil {
return n
}
return p.doc
}
// pop pops the top of the stack of open elements.
// It will panic if the stack is empty.
func (p *parser) pop() *Node {
n := len(p.stack)
ret := p.stack[n-1]
p.stack = p.stack[:n-1]
return ret
}
// stopTags for use in popUntil. These come from section 11.2.3.2.
var (
defaultScopeStopTags = []string{"applet", "caption", "html", "table", "td", "th", "marquee", "object"}
@ -102,11 +64,11 @@ var (
// popUntil([]string{"html, "table"}, "table") would return true and leave:
// ["html", "body", "font"]
func (p *parser) popUntil(stopTags []string, matchTags ...string) bool {
for i := len(p.stack) - 1; i >= 0; i-- {
tag := p.stack[i].Data
for i := len(p.oe) - 1; i >= 0; i-- {
tag := p.oe[i].Data
for _, t := range matchTags {
if t == tag {
p.stack = p.stack[:i]
p.oe = p.oe[:i]
return true
}
}
@ -122,10 +84,9 @@ func (p *parser) popUntil(stopTags []string, matchTags ...string) bool {
// addChild adds a child node n to the top element, and pushes n if it is an
// element node (text nodes are not part of the stack of open elements).
func (p *parser) addChild(n *Node) {
m := p.top()
m.Child = append(m.Child, n)
p.top().Add(n)
if n.Type == ElementNode {
p.push(n)
p.oe = append(p.oe, n)
}
}
@ -151,12 +112,47 @@ func (p *parser) addElement(tag string, attr []Attribute) {
// Section 11.2.3.3.
func (p *parser) addFormattingElement(tag string, attr []Attribute) {
p.addElement(tag, attr)
p.afe = append(p.afe, p.top())
// TODO.
}
// Section 11.2.3.3.
func (p *parser) clearActiveFormattingElements() {
for {
n := p.afe.pop()
if len(p.afe) == 0 || n.Type == scopeMarkerNode {
return
}
}
}
// Section 11.2.3.3.
func (p *parser) reconstructActiveFormattingElements() {
// TODO.
n := p.afe.top()
if n == nil {
return
}
if n.Type == scopeMarkerNode || p.oe.index(n) != -1 {
return
}
i := len(p.afe) - 1
for n.Type != scopeMarkerNode && p.oe.index(n) == -1 {
if i == 0 {
i = -1
break
}
i--
n = p.afe[i]
}
for {
i++
n = p.afe[i]
p.addChild(n.clone())
p.afe[i] = n
if i == len(p.afe)-1 {
break
}
}
}
// read reads the next token. This is usually from the tokenizer, but it may
@ -305,7 +301,7 @@ func inHeadIM(p *parser) (insertionMode, bool) {
// TODO.
}
if pop || implied {
n := p.pop()
n := p.oe.pop()
if n.Data != "head" {
panic("html: bad parser state")
}
@ -359,6 +355,7 @@ func inBodyIM(p *parser) (insertionMode, bool) {
var endP bool
switch p.tok.Type {
case TextToken:
p.reconstructActiveFormattingElements()
p.addText(p.tok.Data)
p.framesetOK = false
case StartTagToken:
@ -375,16 +372,24 @@ func inBodyIM(p *parser) (insertionMode, bool) {
// TODO: auto-insert </p> if necessary.
switch n := p.top(); n.Data {
case "h1", "h2", "h3", "h4", "h5", "h6":
p.pop()
p.oe.pop()
}
p.addElement(p.tok.Data, p.tok.Attr)
case "a":
if n := p.afe.forTag("a"); n != nil {
p.inBodyEndTagFormatting("a")
p.oe.remove(n)
p.afe.remove(n)
}
p.reconstructActiveFormattingElements()
p.addFormattingElement(p.tok.Data, p.tok.Attr)
case "b", "big", "code", "em", "font", "i", "s", "small", "strike", "strong", "tt", "u":
p.reconstructActiveFormattingElements()
p.addFormattingElement(p.tok.Data, p.tok.Attr)
case "area", "br", "embed", "img", "input", "keygen", "wbr":
p.reconstructActiveFormattingElements()
p.addElement(p.tok.Data, p.tok.Attr)
p.pop()
p.oe.pop()
p.acknowledgeSelfClosingTag()
p.framesetOK = false
case "table":
@ -395,7 +400,7 @@ func inBodyIM(p *parser) (insertionMode, bool) {
case "hr":
// TODO: auto-insert </p> if necessary.
p.addElement(p.tok.Data, p.tok.Attr)
p.pop()
p.oe.pop()
p.acknowledgeSelfClosingTag()
p.framesetOK = false
default:
@ -408,21 +413,17 @@ func inBodyIM(p *parser) (insertionMode, bool) {
// TODO: autoclose the stack of open elements.
return afterBodyIM, true
case "a", "b", "big", "code", "em", "font", "i", "nobr", "s", "small", "strike", "strong", "tt", "u":
// TODO: implement the "adoption agency" algorithm:
// http://www.whatwg.org/specs/web-apps/current-work/multipage/tokenization.html#adoptionAgency
if p.tok.Data == p.top().Data {
p.pop()
}
p.inBodyEndTagFormatting(p.tok.Data)
default:
// TODO: any other end tag
if p.tok.Data == p.top().Data {
p.pop()
p.oe.pop()
}
}
}
if endP {
// TODO: do the proper algorithm.
n := p.pop()
n := p.oe.pop()
if n.Type != ElementNode || n.Data != "p" {
panic("unreachable")
}
@ -430,6 +431,122 @@ func inBodyIM(p *parser) (insertionMode, bool) {
return inBodyIM, !endP
}
func (p *parser) inBodyEndTagFormatting(tag string) {
// This is the "adoption agency" algorithm, described at
// http://www.whatwg.org/specs/web-apps/current-work/multipage/tokenization.html#adoptionAgency
// TODO: this is a fairly literal line-by-line translation of that algorithm.
// Once the code successfully parses the comprehensive test suite, we should
// refactor this code to be more idiomatic.
// Steps 1-3. The outer loop.
for i := 0; i < 8; i++ {
// Step 4. Find the formatting element.
var formattingElement *Node
for j := len(p.afe) - 1; j >= 0; j-- {
if p.afe[j].Type == scopeMarkerNode {
break
}
if p.afe[j].Data == tag {
formattingElement = p.afe[j]
break
}
}
if formattingElement == nil {
return
}
feIndex := p.oe.index(formattingElement)
if feIndex == -1 {
p.afe.remove(formattingElement)
return
}
// Steps 5-6. Find the furthest block.
var furthestBlock *Node
for _, e := range p.oe[feIndex:] {
if isSpecialElement[e.Data] {
furthestBlock = e
break
}
}
if furthestBlock == nil {
e := p.oe.pop()
for e != formattingElement {
e = p.oe.pop()
}
p.afe.remove(e)
return
}
// Steps 7-8. Find the common ancestor and bookmark node.
commonAncestor := p.oe[feIndex-1]
bookmark := p.afe.index(formattingElement)
// Step 9. The inner loop. Find the lastNode to reparent.
lastNode := furthestBlock
node := furthestBlock
x := p.oe.index(node)
// Steps 9.1-9.3.
for j := 0; j < 3; j++ {
// Step 9.4.
x--
node = p.oe[x]
// Step 9.5.
if p.afe.index(node) == -1 {
p.oe.remove(node)
continue
}
// Step 9.6.
if node == formattingElement {
break
}
// Step 9.7.
clone := node.clone()
p.afe[p.afe.index(node)] = clone
p.oe[p.oe.index(node)] = clone
node = clone
// Step 9.8.
if lastNode == furthestBlock {
bookmark = p.afe.index(node) + 1
}
// Step 9.9.
if lastNode.Parent != nil {
lastNode.Parent.Remove(lastNode)
}
node.Add(lastNode)
// Step 9.10.
lastNode = node
}
// Step 10. Reparent lastNode to the common ancestor,
// or for misnested table nodes, to the foster parent.
if lastNode.Parent != nil {
lastNode.Parent.Remove(lastNode)
}
switch commonAncestor.Data {
case "table", "tbody", "tfoot", "thead", "tr":
// TODO: fix up misnested table nodes; find the foster parent.
fallthrough
default:
commonAncestor.Add(lastNode)
}
// Steps 11-13. Reparent nodes from the furthest block's children
// to a clone of the formatting element.
clone := formattingElement.clone()
reparentChildren(clone, furthestBlock)
furthestBlock.Add(clone)
// Step 14. Fix up the list of active formatting elements.
p.afe.remove(formattingElement)
p.afe.insert(bookmark, clone)
// Step 15. Fix up the stack of open elements.
p.oe.remove(formattingElement)
p.oe.insert(p.oe.index(furthestBlock)+1, clone)
}
}
// Section 11.2.5.4.9.
func inTableIM(p *parser) (insertionMode, bool) {
var (
@ -540,7 +657,7 @@ func inRowIM(p *parser) (insertionMode, bool) {
case "td", "th":
// TODO: clear the stack back to a table row context.
p.addElement(p.tok.Data, p.tok.Attr)
// TODO: insert a marker at the end of the list of active formatting elements.
p.afe = append(p.afe, &scopeMarker)
return inCellIM, true
default:
// TODO.
@ -592,7 +709,7 @@ func inCellIM(p *parser) (insertionMode, bool) {
}
if closeTheCellAndReprocess {
if p.popUntil(tableScopeStopTags, "td") || p.popUntil(tableScopeStopTags, "th") {
// TODO: clear the list of active formatting elements up to the last marker.
p.clearActiveFormattingElements()
return inRowIM, false
}
}

4
src/pkg/html/parse_test.go
View File

@ -85,6 +85,8 @@ func dumpLevel(w io.Writer, n *Node, level int) os.Error {
fmt.Fprintf(w, "%q", EscapeString(n.Data))
case CommentNode:
return os.NewError("COMMENT")
case scopeMarkerNode:
return os.NewError("unexpected scopeMarkerNode")
default:
return os.NewError("unknown node type")
}
@ -119,7 +121,7 @@ func TestParser(t *testing.T) {
rc := make(chan io.Reader)
go readDat(filename, rc)
// TODO(nigeltao): Process all test cases, not just a subset.
for i := 0; i < 22; i++ {
for i := 0; i < 23; i++ {
// Parse the #data section.
b, err := ioutil.ReadAll(<-rc)
if err != nil {