Force external links into new tabs

extlinks.go

@@ -0,0 +1,57 @@
+package main
+
+import (
+	"strings"
+
+	"github.com/yuin/goldmark"
+	"github.com/yuin/goldmark/ast"
+	"github.com/yuin/goldmark/parser"
+	"github.com/yuin/goldmark/text"
+	"github.com/yuin/goldmark/util"
+)
+
+type extLinksTransformer struct{}
+
+func (extLinksTransformer) Transform(doc *ast.Document, reader text.Reader, pc parser.Context) {
+	ast.Walk(doc, func(n ast.Node, entering bool) (ast.WalkStatus, error) {
+		if !entering {
+			return ast.WalkContinue, nil
+		}
+		link, ok := n.(*ast.Link)
+		if !ok {
+			return ast.WalkContinue, nil
+		}
+		if isExternalURL(string(link.Destination)) {
+			link.SetAttribute([]byte("target"), []byte("_blank"))
+			link.SetAttribute([]byte("rel"), []byte("noopener noreferrer"))
+		}
+		return ast.WalkContinue, nil
+	})
+}
+
+func isExternalURL(dest string) bool {
+	if strings.HasPrefix(dest, "//") {
+		return true
+	}
+	i := strings.Index(dest, ":")
+	if i <= 0 {
+		return false
+	}
+	for _, c := range dest[:i] {
+		if !(c >= 'a' && c <= 'z') && !(c >= 'A' && c <= 'Z') &&
+			!(c >= '0' && c <= '9') && c != '+' && c != '-' && c != '.' {
+			return false
+		}
+	}
+	return true
+}
+
+type extLinksExt struct{}
+
+func newExtLinksExt() goldmark.Extender { return &extLinksExt{} }
+
+func (e *extLinksExt) Extend(m goldmark.Markdown) {
+	m.Parser().AddOptions(parser.WithASTTransformers(
+		util.Prioritized(extLinksTransformer{}, 999),
+	))
+}

render.go

@@ -22,7 +22,7 @@ var md goldmark.Markdown
 // targets against the filesystem.
 func initMarkdown(root string) {
 	md = goldmark.New(
-		goldmark.WithExtensions(extension.GFM, extension.Table, newWikiLinkExt(root)),
+		goldmark.WithExtensions(extension.GFM, extension.Table, newWikiLinkExt(root), newExtLinksExt()),
 		goldmark.WithParserOptions(parser.WithAutoHeadingID()),
 		goldmark.WithRendererOptions(html.WithUnsafe()),
 	)