271 lines
6.9 KiB
Go
271 lines
6.9 KiB
Go
// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package html
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import (
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"bufio"
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"errors"
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"fmt"
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"io"
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"strings"
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)
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type writer interface {
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io.Writer
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io.ByteWriter
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WriteString(string) (int, error)
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}
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// Render renders the parse tree n to the given writer.
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//
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// Rendering is done on a 'best effort' basis: calling Parse on the output of
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// Render will always result in something similar to the original tree, but it
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// is not necessarily an exact clone unless the original tree was 'well-formed'.
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// 'Well-formed' is not easily specified; the HTML5 specification is
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// complicated.
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//
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// Calling Parse on arbitrary input typically results in a 'well-formed' parse
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// tree. However, it is possible for Parse to yield a 'badly-formed' parse tree.
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// For example, in a 'well-formed' parse tree, no <a> element is a child of
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// another <a> element: parsing "<a><a>" results in two sibling elements.
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// Similarly, in a 'well-formed' parse tree, no <a> element is a child of a
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// <table> element: parsing "<p><table><a>" results in a <p> with two sibling
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// children; the <a> is reparented to the <table>'s parent. However, calling
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// Parse on "<a><table><a>" does not return an error, but the result has an <a>
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// element with an <a> child, and is therefore not 'well-formed'.
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//
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// Programmatically constructed trees are typically also 'well-formed', but it
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// is possible to construct a tree that looks innocuous but, when rendered and
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// re-parsed, results in a different tree. A simple example is that a solitary
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// text node would become a tree containing <html>, <head> and <body> elements.
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// Another example is that the programmatic equivalent of "a<head>b</head>c"
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// becomes "<html><head><head/><body>abc</body></html>".
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func Render(w io.Writer, n *Node) error {
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if x, ok := w.(writer); ok {
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return render(x, n)
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}
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buf := bufio.NewWriter(w)
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if err := render(buf, n); err != nil {
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return err
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}
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return buf.Flush()
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}
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// plaintextAbort is returned from render1 when a <plaintext> element
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// has been rendered. No more end tags should be rendered after that.
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var plaintextAbort = errors.New("html: internal error (plaintext abort)")
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func render(w writer, n *Node) error {
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err := render1(w, n)
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if err == plaintextAbort {
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err = nil
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}
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return err
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}
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func render1(w writer, n *Node) error {
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// Render non-element nodes; these are the easy cases.
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switch n.Type {
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case ErrorNode:
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return errors.New("html: cannot render an ErrorNode node")
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case TextNode:
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return escape(w, n.Data)
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case DocumentNode:
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for c := n.FirstChild; c != nil; c = c.NextSibling {
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if err := render1(w, c); err != nil {
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return err
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}
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}
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return nil
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case ElementNode:
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// No-op.
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case CommentNode:
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if _, err := w.WriteString("<!--"); err != nil {
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return err
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}
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if _, err := w.WriteString(n.Data); err != nil {
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return err
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}
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if _, err := w.WriteString("-->"); err != nil {
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return err
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}
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return nil
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case DoctypeNode:
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if _, err := w.WriteString("<!DOCTYPE "); err != nil {
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return err
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}
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if _, err := w.WriteString(n.Data); err != nil {
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return err
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}
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if n.Attr != nil {
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var p, s string
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for _, a := range n.Attr {
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switch a.Key {
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case "public":
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p = a.Val
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case "system":
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s = a.Val
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}
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}
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if p != "" {
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if _, err := w.WriteString(" PUBLIC "); err != nil {
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return err
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}
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if err := writeQuoted(w, p); err != nil {
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return err
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}
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if s != "" {
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if err := w.WriteByte(' '); err != nil {
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return err
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}
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if err := writeQuoted(w, s); err != nil {
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return err
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}
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}
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} else if s != "" {
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if _, err := w.WriteString(" SYSTEM "); err != nil {
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return err
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}
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if err := writeQuoted(w, s); err != nil {
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return err
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}
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}
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}
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return w.WriteByte('>')
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default:
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return errors.New("html: unknown node type")
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}
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// Render the <xxx> opening tag.
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if err := w.WriteByte('<'); err != nil {
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return err
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}
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if _, err := w.WriteString(n.Data); err != nil {
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return err
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}
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for _, a := range n.Attr {
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if err := w.WriteByte(' '); err != nil {
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return err
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}
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if a.Namespace != "" {
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if _, err := w.WriteString(a.Namespace); err != nil {
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return err
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}
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if err := w.WriteByte(':'); err != nil {
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return err
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}
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}
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if _, err := w.WriteString(a.Key); err != nil {
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return err
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}
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if _, err := w.WriteString(`="`); err != nil {
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return err
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}
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if err := escape(w, a.Val); err != nil {
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return err
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}
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if err := w.WriteByte('"'); err != nil {
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return err
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}
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}
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if voidElements[n.Data] {
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if n.FirstChild != nil {
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return fmt.Errorf("html: void element <%s> has child nodes", n.Data)
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}
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_, err := w.WriteString("/>")
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return err
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}
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if err := w.WriteByte('>'); err != nil {
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return err
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}
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// Add initial newline where there is danger of a newline beging ignored.
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if c := n.FirstChild; c != nil && c.Type == TextNode && strings.HasPrefix(c.Data, "\n") {
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switch n.Data {
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case "pre", "listing", "textarea":
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if err := w.WriteByte('\n'); err != nil {
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return err
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}
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}
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}
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// Render any child nodes.
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switch n.Data {
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case "iframe", "noembed", "noframes", "noscript", "plaintext", "script", "style", "xmp":
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for c := n.FirstChild; c != nil; c = c.NextSibling {
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if c.Type == TextNode {
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if _, err := w.WriteString(c.Data); err != nil {
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return err
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}
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} else {
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if err := render1(w, c); err != nil {
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return err
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}
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}
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}
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if n.Data == "plaintext" {
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// Don't render anything else. <plaintext> must be the
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// last element in the file, with no closing tag.
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return plaintextAbort
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}
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default:
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for c := n.FirstChild; c != nil; c = c.NextSibling {
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if err := render1(w, c); err != nil {
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return err
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}
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}
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}
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// Render the </xxx> closing tag.
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if _, err := w.WriteString("</"); err != nil {
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return err
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}
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if _, err := w.WriteString(n.Data); err != nil {
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return err
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}
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return w.WriteByte('>')
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}
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// writeQuoted writes s to w surrounded by quotes. Normally it will use double
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// quotes, but if s contains a double quote, it will use single quotes.
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// It is used for writing the identifiers in a doctype declaration.
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// In valid HTML, they can't contain both types of quotes.
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func writeQuoted(w writer, s string) error {
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var q byte = '"'
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if strings.Contains(s, `"`) {
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q = '\''
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}
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if err := w.WriteByte(q); err != nil {
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return err
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}
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if _, err := w.WriteString(s); err != nil {
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return err
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}
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if err := w.WriteByte(q); err != nil {
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return err
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}
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return nil
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}
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// Section 12.1.2, "Elements", gives this list of void elements. Void elements
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// are those that can't have any contents.
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var voidElements = map[string]bool{
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"area": true,
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"base": true,
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"br": true,
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"col": true,
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"command": true,
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"embed": true,
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"hr": true,
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"img": true,
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"input": true,
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"keygen": true,
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"link": true,
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"meta": true,
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"param": true,
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"source": true,
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"track": true,
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"wbr": true,
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}
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