rss-tools/vendor/golang.org/x/net/html/render.go (view raw)
| 1 | // Copyright 2011 The Go Authors. All rights reserved. |
| 2 | // Use of this source code is governed by a BSD-style |
| 3 | // license that can be found in the LICENSE file. |
| 4 | |
| 5 | package html |
| 6 | |
| 7 | import ( |
| 8 | "bufio" |
| 9 | "errors" |
| 10 | "fmt" |
| 11 | "io" |
| 12 | "strings" |
| 13 | ) |
| 14 | |
| 15 | type writer interface { |
| 16 | io.Writer |
| 17 | io.ByteWriter |
| 18 | WriteString(string) (int, error) |
| 19 | } |
| 20 | |
| 21 | // Render renders the parse tree n to the given writer. |
| 22 | // |
| 23 | // Rendering is done on a 'best effort' basis: calling Parse on the output of |
| 24 | // Render will always result in something similar to the original tree, but it |
| 25 | // is not necessarily an exact clone unless the original tree was 'well-formed'. |
| 26 | // 'Well-formed' is not easily specified; the HTML5 specification is |
| 27 | // complicated. |
| 28 | // |
| 29 | // Calling Parse on arbitrary input typically results in a 'well-formed' parse |
| 30 | // tree. However, it is possible for Parse to yield a 'badly-formed' parse tree. |
| 31 | // For example, in a 'well-formed' parse tree, no <a> element is a child of |
| 32 | // another <a> element: parsing "<a><a>" results in two sibling elements. |
| 33 | // Similarly, in a 'well-formed' parse tree, no <a> element is a child of a |
| 34 | // <table> element: parsing "<p><table><a>" results in a <p> with two sibling |
| 35 | // children; the <a> is reparented to the <table>'s parent. However, calling |
| 36 | // Parse on "<a><table><a>" does not return an error, but the result has an <a> |
| 37 | // element with an <a> child, and is therefore not 'well-formed'. |
| 38 | // |
| 39 | // Programmatically constructed trees are typically also 'well-formed', but it |
| 40 | // is possible to construct a tree that looks innocuous but, when rendered and |
| 41 | // re-parsed, results in a different tree. A simple example is that a solitary |
| 42 | // text node would become a tree containing <html>, <head> and <body> elements. |
| 43 | // Another example is that the programmatic equivalent of "a<head>b</head>c" |
| 44 | // becomes "<html><head><head/><body>abc</body></html>". |
| 45 | func Render(w io.Writer, n *Node) error { |
| 46 | if x, ok := w.(writer); ok { |
| 47 | return render(x, n) |
| 48 | } |
| 49 | buf := bufio.NewWriter(w) |
| 50 | if err := render(buf, n); err != nil { |
| 51 | return err |
| 52 | } |
| 53 | return buf.Flush() |
| 54 | } |
| 55 | |
| 56 | // plaintextAbort is returned from render1 when a <plaintext> element |
| 57 | // has been rendered. No more end tags should be rendered after that. |
| 58 | var plaintextAbort = errors.New("html: internal error (plaintext abort)") |
| 59 | |
| 60 | func render(w writer, n *Node) error { |
| 61 | err := render1(w, n) |
| 62 | if err == plaintextAbort { |
| 63 | err = nil |
| 64 | } |
| 65 | return err |
| 66 | } |
| 67 | |
| 68 | func render1(w writer, n *Node) error { |
| 69 | // Render non-element nodes; these are the easy cases. |
| 70 | switch n.Type { |
| 71 | case ErrorNode: |
| 72 | return errors.New("html: cannot render an ErrorNode node") |
| 73 | case TextNode: |
| 74 | return escape(w, n.Data) |
| 75 | case DocumentNode: |
| 76 | for c := n.FirstChild; c != nil; c = c.NextSibling { |
| 77 | if err := render1(w, c); err != nil { |
| 78 | return err |
| 79 | } |
| 80 | } |
| 81 | return nil |
| 82 | case ElementNode: |
| 83 | // No-op. |
| 84 | case CommentNode: |
| 85 | if _, err := w.WriteString("<!--"); err != nil { |
| 86 | return err |
| 87 | } |
| 88 | if err := escapeComment(w, n.Data); err != nil { |
| 89 | return err |
| 90 | } |
| 91 | if _, err := w.WriteString("-->"); err != nil { |
| 92 | return err |
| 93 | } |
| 94 | return nil |
| 95 | case DoctypeNode: |
| 96 | if _, err := w.WriteString("<!DOCTYPE "); err != nil { |
| 97 | return err |
| 98 | } |
| 99 | if err := escape(w, n.Data); err != nil { |
| 100 | return err |
| 101 | } |
| 102 | if n.Attr != nil { |
| 103 | var p, s string |
| 104 | for _, a := range n.Attr { |
| 105 | switch a.Key { |
| 106 | case "public": |
| 107 | p = a.Val |
| 108 | case "system": |
| 109 | s = a.Val |
| 110 | } |
| 111 | } |
| 112 | if p != "" { |
| 113 | if _, err := w.WriteString(" PUBLIC "); err != nil { |
| 114 | return err |
| 115 | } |
| 116 | if err := writeQuoted(w, p); err != nil { |
| 117 | return err |
| 118 | } |
| 119 | if s != "" { |
| 120 | if err := w.WriteByte(' '); err != nil { |
| 121 | return err |
| 122 | } |
| 123 | if err := writeQuoted(w, s); err != nil { |
| 124 | return err |
| 125 | } |
| 126 | } |
| 127 | } else if s != "" { |
| 128 | if _, err := w.WriteString(" SYSTEM "); err != nil { |
| 129 | return err |
| 130 | } |
| 131 | if err := writeQuoted(w, s); err != nil { |
| 132 | return err |
| 133 | } |
| 134 | } |
| 135 | } |
| 136 | return w.WriteByte('>') |
| 137 | case RawNode: |
| 138 | _, err := w.WriteString(n.Data) |
| 139 | return err |
| 140 | default: |
| 141 | return errors.New("html: unknown node type") |
| 142 | } |
| 143 | |
| 144 | // Render the <xxx> opening tag. |
| 145 | if err := w.WriteByte('<'); err != nil { |
| 146 | return err |
| 147 | } |
| 148 | if _, err := w.WriteString(n.Data); err != nil { |
| 149 | return err |
| 150 | } |
| 151 | for _, a := range n.Attr { |
| 152 | if err := w.WriteByte(' '); err != nil { |
| 153 | return err |
| 154 | } |
| 155 | if a.Namespace != "" { |
| 156 | if _, err := w.WriteString(a.Namespace); err != nil { |
| 157 | return err |
| 158 | } |
| 159 | if err := w.WriteByte(':'); err != nil { |
| 160 | return err |
| 161 | } |
| 162 | } |
| 163 | if _, err := w.WriteString(a.Key); err != nil { |
| 164 | return err |
| 165 | } |
| 166 | if _, err := w.WriteString(`="`); err != nil { |
| 167 | return err |
| 168 | } |
| 169 | if err := escape(w, a.Val); err != nil { |
| 170 | return err |
| 171 | } |
| 172 | if err := w.WriteByte('"'); err != nil { |
| 173 | return err |
| 174 | } |
| 175 | } |
| 176 | if voidElements[n.Data] { |
| 177 | if n.FirstChild != nil { |
| 178 | return fmt.Errorf("html: void element <%s> has child nodes", n.Data) |
| 179 | } |
| 180 | _, err := w.WriteString("/>") |
| 181 | return err |
| 182 | } |
| 183 | if err := w.WriteByte('>'); err != nil { |
| 184 | return err |
| 185 | } |
| 186 | |
| 187 | // Add initial newline where there is danger of a newline being ignored. |
| 188 | if c := n.FirstChild; c != nil && c.Type == TextNode && strings.HasPrefix(c.Data, "\n") { |
| 189 | switch n.Data { |
| 190 | case "pre", "listing", "textarea": |
| 191 | if err := w.WriteByte('\n'); err != nil { |
| 192 | return err |
| 193 | } |
| 194 | } |
| 195 | } |
| 196 | |
| 197 | // Render any child nodes |
| 198 | if childTextNodesAreLiteral(n) { |
| 199 | for c := n.FirstChild; c != nil; c = c.NextSibling { |
| 200 | if c.Type == TextNode { |
| 201 | if _, err := w.WriteString(c.Data); err != nil { |
| 202 | return err |
| 203 | } |
| 204 | } else { |
| 205 | if err := render1(w, c); err != nil { |
| 206 | return err |
| 207 | } |
| 208 | } |
| 209 | } |
| 210 | if n.Data == "plaintext" { |
| 211 | // Don't render anything else. <plaintext> must be the |
| 212 | // last element in the file, with no closing tag. |
| 213 | return plaintextAbort |
| 214 | } |
| 215 | } else { |
| 216 | for c := n.FirstChild; c != nil; c = c.NextSibling { |
| 217 | if err := render1(w, c); err != nil { |
| 218 | return err |
| 219 | } |
| 220 | } |
| 221 | } |
| 222 | |
| 223 | // Render the </xxx> closing tag. |
| 224 | if _, err := w.WriteString("</"); err != nil { |
| 225 | return err |
| 226 | } |
| 227 | if _, err := w.WriteString(n.Data); err != nil { |
| 228 | return err |
| 229 | } |
| 230 | return w.WriteByte('>') |
| 231 | } |
| 232 | |
| 233 | func childTextNodesAreLiteral(n *Node) bool { |
| 234 | // Per WHATWG HTML 13.3, if the parent of the current node is a style, |
| 235 | // script, xmp, iframe, noembed, noframes, or plaintext element, and the |
| 236 | // current node is a text node, append the value of the node's data |
| 237 | // literally. The specification is not explicit about it, but we only |
| 238 | // enforce this if we are in the HTML namespace (i.e. when the namespace is |
| 239 | // ""). |
| 240 | // NOTE: we also always include noscript elements, although the |
| 241 | // specification states that they should only be rendered as such if |
| 242 | // scripting is enabled for the node (which is not something we track). |
| 243 | if n.Namespace != "" { |
| 244 | return false |
| 245 | } |
| 246 | switch n.Data { |
| 247 | case "iframe", "noembed", "noframes", "noscript", "plaintext", "script", "style", "xmp": |
| 248 | return true |
| 249 | default: |
| 250 | return false |
| 251 | } |
| 252 | } |
| 253 | |
| 254 | // writeQuoted writes s to w surrounded by quotes. Normally it will use double |
| 255 | // quotes, but if s contains a double quote, it will use single quotes. |
| 256 | // It is used for writing the identifiers in a doctype declaration. |
| 257 | // In valid HTML, they can't contain both types of quotes. |
| 258 | func writeQuoted(w writer, s string) error { |
| 259 | var q byte = '"' |
| 260 | if strings.Contains(s, `"`) { |
| 261 | q = '\'' |
| 262 | } |
| 263 | if err := w.WriteByte(q); err != nil { |
| 264 | return err |
| 265 | } |
| 266 | if _, err := w.WriteString(s); err != nil { |
| 267 | return err |
| 268 | } |
| 269 | if err := w.WriteByte(q); err != nil { |
| 270 | return err |
| 271 | } |
| 272 | return nil |
| 273 | } |
| 274 | |
| 275 | // Section 12.1.2, "Elements", gives this list of void elements. Void elements |
| 276 | // are those that can't have any contents. |
| 277 | var voidElements = map[string]bool{ |
| 278 | "area": true, |
| 279 | "base": true, |
| 280 | "br": true, |
| 281 | "col": true, |
| 282 | "embed": true, |
| 283 | "hr": true, |
| 284 | "img": true, |
| 285 | "input": true, |
| 286 | "keygen": true, // "keygen" has been removed from the spec, but are kept here for backwards compatibility. |
| 287 | "link": true, |
| 288 | "meta": true, |
| 289 | "param": true, |
| 290 | "source": true, |
| 291 | "track": true, |
| 292 | "wbr": true, |
| 293 | } |