@@ -0,0 +1,5 @@
+module git.icyphox.sh/rel2abs
+
+go 1.16
+
+require golang.org/x/net v0.0.0-20210924151903-3ad01bbaa167

@@ -0,0 +1,7 @@
+golang.org/x/net v0.0.0-20210924151903-3ad01bbaa167 h1:eDd+TJqbgfXruGQ5sJRU7tEtp/58OAx4+Ayjxg4SM+4=
+golang.org/x/net v0.0.0-20210924151903-3ad01bbaa167/go.mod h1:9nx3DQGgdP8bBQD5qxJ1jj9UTztislL4KSBs9R2vV5Y=
+golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20210423082822-04245dca01da/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
+golang.org/x/text v0.3.6/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
+golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=

@@ -0,0 +1,50 @@
+package rel2abs
+
+import (
+	"bytes"
+	"fmt"
+	"net/url"
+
+	"golang.org/x/net/html"
+)
+
+func rel2abs(n *html.Node, nurl *url.URL) error {
+	if n.Type == html.ElementNode && n.Data == "a" {
+		for _, a := range n.Attr {
+			if a.Key == "href" {
+				rel, err := url.Parse(a.Val)
+				if err != nil {
+					return fmt.Errorf("relative url: %w\n", err)
+				}
+
+				a.Val = nurl.ResolveReference(rel).String()
+			}
+		}
+		for c := n.FirstChild; c != nil; c = c.NextSibling {
+			rel2abs(c, nurl)
+		}
+	}
+	return nil
+}
+
+// Converts all relative URLs in htmlContent to absolute URLs,
+// resolved against a base URL.
+// Example, with base as http://example.com/foo:
+//    <a href="#fn-1">
+// becomes
+//    <a href="http://example.com/foo#fn-1">
+func Rel2Abs(htmlContent []byte, base string) ([]byte, error) {
+	doc, err := html.Parse(bytes.NewReader(htmlContent))
+	if err != nil {
+		return nil, fmt.Errorf("html parse: %w\n", err)
+	}
+
+	nurl, err := url.Parse(base)
+	if err != nil {
+		return nil, fmt.Errorf("url parse: %w\n", err)
+	}
+	rel2abs(doc, nurl)
+	buf := bytes.Buffer{}
+	html.Render(&buf, doc)
+	return buf.Bytes(), nil
+}