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