Add xhtml:link support

sitemap.go

@@ -29,24 +29,33 @@ const (
 	Never   ChangeFreq = "never"
 )
 
+// XHTMLLink entry in [URL].
+type XHTMLLink struct {
+	Ref      string `xml:"ref,attr"`
+	HrefLang string `xml:"hreflang,attr"`
+	Href     string `xml:"href,attr"`
+}
+
 // URL entry in [Sitemap] or [SitemapIndex]. LastMod is a pointer
 // to [time.Time] because omitempty does not work otherwise. Loc is the
 // only mandatory item. ChangeFreq and Priority must be left empty when
 // using with a sitemap index.
 type URL struct {
-	Loc        string     `xml:"loc"`
-	LastMod    *time.Time `xml:"lastmod,omitempty"`
-	ChangeFreq ChangeFreq `xml:"changefreq,omitempty"`
-	Priority   float32    `xml:"priority,omitempty"`
+	Loc        string      `xml:"loc"`
+	LastMod    *time.Time  `xml:"lastmod,omitempty"`
+	ChangeFreq ChangeFreq  `xml:"changefreq,omitempty"`
+	Priority   float32     `xml:"priority,omitempty"`
+	XHTMLLinks []XHTMLLink `xml:"xhtml:link"`
 }
 
 // Sitemap represents a complete sitemap which can be marshaled to XML.
 // New instances must be created with [New] in order to set the xmlns
 // attribute correctly. Minify can be set to make the output less human
 // readable.
 type Sitemap struct {
-	XMLName xml.Name `xml:"urlset"`
-	Xmlns   string   `xml:"xmlns,attr"`
+	XMLName    xml.Name `xml:"urlset"`
+	Xmlns      string   `xml:"xmlns,attr"`
+	XmlnsXHTML *string  `xml:"xmlns:xhtml,attr"`
 
 	URLs []*URL `xml:"url"`
 
@@ -61,6 +70,19 @@ func New() *Sitemap {
 	}
 }
 
+// WithXHTML adds the xmlns:xhtml to a [Sitemap].
+func (s *Sitemap) WithXHTML() *Sitemap {
+	xhtml := "http://www.w3.org/1999/xhtml"
+	s.XmlnsXHTML = &xhtml
+	return s
+}
+
+// WithMinify enables minification on a [Sitemap].
+func (s *Sitemap) WithMinify() *Sitemap {
+	s.Minify = true
+	return s
+}
+
 // Add adds an [URL] to a [Sitemap].
 func (s *Sitemap) Add(u *URL) {
 	s.URLs = append(s.URLs, u)
@@ -90,7 +112,8 @@ func (s *Sitemap) WriteTo(w io.Writer) (n int64, err error) {
 var _ io.WriterTo = (*Sitemap)(nil)
 
 // ReadFrom reads and parses an XML encoded sitemap from [io.Reader].
-// Implements [io.ReaderFrom].
+// Implements [io.ReaderFrom]. Due to https://github.com/golang/go/issues/9519,
+// unmarshaling xhtml links doesn't work.
 func (s *Sitemap) ReadFrom(r io.Reader) (n int64, err error) {
 	de := xml.NewDecoder(r)
 	err = de.Decode(s)

sitemap_test.go

@@ -40,31 +40,36 @@ func Example() {
 
 // Sitemap with one URL.
 func ExampleSitemap() {
-	sm := sitemap.New()
+	sm := sitemap.New().WithXHTML()
 	t := time.Date(1984, 1, 1, 0, 0, 0, 0, time.UTC)
 	sm.Add(&sitemap.URL{
 		Loc:        "http://example.com/",
 		LastMod:    &t,
 		ChangeFreq: sitemap.Daily,
 		Priority:   0.5,
+		XHTMLLinks: []sitemap.XHTMLLink{
+			{Ref: "alternate", HrefLang: "en", Href: "http://example.com"},
+			{Ref: "alternate", HrefLang: "fr", Href: "http://example.com?lang=fr"},
+		},
 	})
 	sm.WriteTo(os.Stdout)
 	// Output:
 	// <?xml version="1.0" encoding="UTF-8"?>
-	// <urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
+	// <urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9" xmlns:xhtml="http://www.w3.org/1999/xhtml">
 	//   <url>
 	//     <loc>http://example.com/</loc>
 	//     <lastmod>1984-01-01T00:00:00Z</lastmod>
 	//     <changefreq>daily</changefreq>
 	//     <priority>0.5</priority>
+	//     <xhtml:link ref="alternate" hreflang="en" href="http://example.com"></xhtml:link>
+	//     <xhtml:link ref="alternate" hreflang="fr" href="http://example.com?lang=fr"></xhtml:link>
 	//   </url>
 	// </urlset>
 }
 
-// Setting Minify to true omits indentation and newlines in generated sitemap.
+// WithMinify omits indentation and newlines in generated sitemap.
 func ExampleSitemap_minify() {
-	sm := sitemap.New()
-	sm.Minify = true
+	sm := sitemap.New().WithMinify()
 	t := time.Date(1984, 1, 1, 0, 0, 0, 0, time.UTC)
 	sm.Add(&sitemap.URL{
 		Loc:        "http://example.com/",