Create isValidURN and isValidURI and use isValidURI everywhere where it is needed

atom.go

@@ -3,6 +3,7 @@ package atomfeed
 import (
 	"mime"
 	"net/url"
+	"regexp"
 	"strings"
 )
 
@@ -13,11 +14,20 @@ type (
 	URI          string
 )
 
-func isValidURL(testURL URI) bool {
-	_, err := url.ParseRequestURI(string(testURL))
+func isValidURL(uri URI) bool {
+	_, err := url.ParseRequestURI(string(uri))
 	return err == nil
 }
 
+func isValidURN(uri URI) bool {
+	pattern := `\A(?i:urn:(?!urn:)(?<nid>[a-z0-9][a-z0-9-]{1,31}):(?<nss>(?:[-a-z0-9()+,.:=@;$_!*'&~\/]|%[0-9a-f]{2})+)(?:\?\+(?<rcomponent>.*?))?(?:\?=(?<qcomponent>.*?))?(?:#(?<fcomponent>.*?))?)\z`
+	return regexp.MustCompile(pattern).MatchString(string(uri))
+}
+
+func isValidURI(uri URI) bool {
+	return isValidURL(uri) || isValidURN(uri)
+}
+
 func isCompositeMediaType(mediaType string) bool {
 	mediaType, _, err := mime.ParseMediaType(mediaType)
 	if err != nil {