1package rel2abs
 2
 3import (
 4	"bytes"
 5	"fmt"
 6	"net/url"
 7
 8	"golang.org/x/net/html"
 9)
10
11func rel2abs(n *html.Node, nurl *url.URL) error {
12	if n.Type == html.ElementNode && n.Data == "a" {
13		for _, a := range n.Attr {
14			if a.Key == "href" {
15				rel, err := url.Parse(a.Val)
16				if err != nil {
17					return fmt.Errorf("relative url: %w\n", err)
18				}
19
20				a.Val = nurl.ResolveReference(rel).String()
21			}
22		}
23		for c := n.FirstChild; c != nil; c = c.NextSibling {
24			rel2abs(c, nurl)
25		}
26	}
27	return nil
28}
29
30// Converts all relative URLs in htmlContent to absolute URLs,
31// resolved against a base URL.
32// Example, with base as http://example.com/foo:
33//    <a href="#fn-1">
34// becomes
35//    <a href="http://example.com/foo#fn-1">
36func Rel2Abs(htmlContent []byte, base string) ([]byte, error) {
37	doc, err := html.Parse(bytes.NewReader(htmlContent))
38	if err != nil {
39		return nil, fmt.Errorf("html parse: %w\n", err)
40	}
41
42	nurl, err := url.Parse(base)
43	if err != nil {
44		return nil, fmt.Errorf("url parse: %w\n", err)
45	}
46	rel2abs(doc, nurl)
47	buf := bytes.Buffer{}
48	html.Render(&buf, doc)
49	return buf.Bytes(), nil
50}