107 lines
3.3 KiB
Go
107 lines
3.3 KiB
Go
// 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 implements an HTML5-compliant tokenizer and parser.
|
|
|
|
Tokenization is done by creating a Tokenizer for an io.Reader r. It is the
|
|
caller's responsibility to ensure that r provides UTF-8 encoded HTML.
|
|
|
|
z := html.NewTokenizer(r)
|
|
|
|
Given a Tokenizer z, the HTML is tokenized by repeatedly calling z.Next(),
|
|
which parses the next token and returns its type, or an error:
|
|
|
|
for {
|
|
tt := z.Next()
|
|
if tt == html.ErrorToken {
|
|
// ...
|
|
return ...
|
|
}
|
|
// Process the current token.
|
|
}
|
|
|
|
There are two APIs for retrieving the current token. The high-level API is to
|
|
call Token; the low-level API is to call Text or TagName / TagAttr. Both APIs
|
|
allow optionally calling Raw after Next but before Token, Text, TagName, or
|
|
TagAttr. In EBNF notation, the valid call sequence per token is:
|
|
|
|
Next {Raw} [ Token | Text | TagName {TagAttr} ]
|
|
|
|
Token returns an independent data structure that completely describes a token.
|
|
Entities (such as "<") are unescaped, tag names and attribute keys are
|
|
lower-cased, and attributes are collected into a []Attribute. For example:
|
|
|
|
for {
|
|
if z.Next() == html.ErrorToken {
|
|
// Returning io.EOF indicates success.
|
|
return z.Err()
|
|
}
|
|
emitToken(z.Token())
|
|
}
|
|
|
|
The low-level API performs fewer allocations and copies, but the contents of
|
|
the []byte values returned by Text, TagName and TagAttr may change on the next
|
|
call to Next. For example, to extract an HTML page's anchor text:
|
|
|
|
depth := 0
|
|
for {
|
|
tt := z.Next()
|
|
switch tt {
|
|
case html.ErrorToken:
|
|
return z.Err()
|
|
case html.TextToken:
|
|
if depth > 0 {
|
|
// emitBytes should copy the []byte it receives,
|
|
// if it doesn't process it immediately.
|
|
emitBytes(z.Text())
|
|
}
|
|
case html.StartTagToken, html.EndTagToken:
|
|
tn, _ := z.TagName()
|
|
if len(tn) == 1 && tn[0] == 'a' {
|
|
if tt == html.StartTagToken {
|
|
depth++
|
|
} else {
|
|
depth--
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
Parsing is done by calling Parse with an io.Reader, which returns the root of
|
|
the parse tree (the document element) as a *Node. It is the caller's
|
|
responsibility to ensure that the Reader provides UTF-8 encoded HTML. For
|
|
example, to process each anchor node in depth-first order:
|
|
|
|
doc, err := html.Parse(r)
|
|
if err != nil {
|
|
// ...
|
|
}
|
|
var f func(*html.Node)
|
|
f = func(n *html.Node) {
|
|
if n.Type == html.ElementNode && n.Data == "a" {
|
|
// Do something with n...
|
|
}
|
|
for c := n.FirstChild; c != nil; c = c.NextSibling {
|
|
f(c)
|
|
}
|
|
}
|
|
f(doc)
|
|
|
|
The relevant specifications include:
|
|
https://html.spec.whatwg.org/multipage/syntax.html and
|
|
https://html.spec.whatwg.org/multipage/syntax.html#tokenization
|
|
*/
|
|
package html // import "golang.org/x/net/html"
|
|
|
|
// The tokenization algorithm implemented by this package is not a line-by-line
|
|
// transliteration of the relatively verbose state-machine in the WHATWG
|
|
// specification. A more direct approach is used instead, where the program
|
|
// counter implies the state, such as whether it is tokenizing a tag or a text
|
|
// node. Specification compliance is verified by checking expected and actual
|
|
// outputs over a test suite rather than aiming for algorithmic fidelity.
|
|
|
|
// TODO(nigeltao): Does a DOM API belong in this package or a separate one?
|
|
// TODO(nigeltao): How does parsing interact with a JavaScript engine?
|