forked from google/webpackager
/
preload_style.go
73 lines (66 loc) · 2.03 KB
/
preload_style.go
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// Copyright 2019 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package htmltask
import (
"strings"
"github.com/layer0-platform/webpackager/processor/htmlproc/htmldoc"
"github.com/layer0-platform/webpackager/resource/preload"
"golang.org/x/net/html"
"golang.org/x/net/html/atom"
)
// PreloadStylesheets detects <link rel="stylesheet"> in the <head> element
// and adds referenced stylesheets to the Preloads field.
//
// PreloadStylesheets does not include stylesheets that have "alternate" in
// the rel attribute. Those stylesheets are unused in the initial rendering.
// They are not used at all on some unsupported browsers.
func PreloadStylesheets() HTMLTask {
return &preloadStylesheets{}
}
type preloadStylesheets struct{}
func isStylesheet(n *html.Node) bool {
if n.Type != html.ElementNode {
return false
}
if n.DataAtom != atom.Link {
return false
}
rel := htmldoc.FindAttr(n, "rel")
if rel == nil {
return false
}
stylesheet := false
for _, linkType := range strings.Fields(rel.Val) {
if strings.EqualFold(linkType, "stylesheet") {
stylesheet = true
}
if strings.EqualFold(linkType, "alternate") {
return false
}
}
return stylesheet
}
func (*preloadStylesheets) Run(resp *htmldoc.HTMLResponse) error {
return htmldoc.Traverse(resp.Doc.Head, func(n *html.Node) error {
if !isStylesheet(n) {
return nil
}
href := resolveURLAttr(htmldoc.FindAttr(n, "href"), resp.Doc)
if href == nil {
return nil
}
resp.AddPreload(preload.NewPreloadForURL(href, preload.AsStyle))
return nil
})
}