First pass at srcset handling

guile/broken-link-checker.scm

@@ -42,14 +42,33 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
                           (// audio @ src)
                           (// audio source @ src))))
 
+(define srcset-paths (map sxpath
+                          '((// picture source @ srcset)
+                            (// img @ srcset))))
+
+;; Special handling for srcset
+(define (parse-srcset s)
+  "Parse out the list of URLs from an image srcset, discarding whitespace and the
+width/density descriptor."
+  (map (compose first (cut string-split <> #\space))
+       (map string-trim-both (string-split s #\,))))
+
+(define (extract-srcset x)
+  (concatenate
+   (map (compose parse-srcset cadr)
+        (concatenate
+         (map (lambda (f) (f x)) srcset-paths)))))
+
 (define (extract-links body)
   "Extract links from an HTML document, discarding any tel: or mailto: links."
   (let ((x (html->sxml body)))
     (remove (lambda (s) (or (string-prefix? "tel:" s) (string-prefix? "mailto:" s)))
             (delete-duplicates
-             (map cadr
-                  (concatenate
-                   (map (lambda (f) (f x)) link-paths)))))))
+             (append
+              (map cadr
+                   (concatenate
+                    (map (lambda (f) (f x)) link-paths)))
+              (extract-srcset x))))))
 
 (define (uri-without-fragment uri)
   "If uri has a fragment, return a new URI without the fragment."