Backport #4312 to v1.4 (#4320)

modules/util/util.go

@@ -4,6 +4,15 @@
 
 package util
 
+import (
+	"net/url"
+	"path"
+	"strings"
+
+	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/setting"
+)
+
 // OptionalBool a boolean that can be "null"
 type OptionalBool byte
 
@@ -47,6 +56,41 @@ func Max(a, b int) int {
 	return a
 }
 
+// URLJoin joins url components, like path.Join, but preserving contents
+func URLJoin(base string, elems ...string) string {
+	if !strings.HasSuffix(base, "/") {
+		base += "/"
+	}
+	baseURL, err := url.Parse(base)
+	if err != nil {
+		log.Error(4, "URLJoin: Invalid base URL %s", base)
+		return ""
+	}
+	joinedPath := path.Join(elems...)
+	argURL, err := url.Parse(joinedPath)
+	if err != nil {
+		log.Error(4, "URLJoin: Invalid arg %s", joinedPath)
+		return ""
+	}
+	joinedURL := baseURL.ResolveReference(argURL).String()
+	if !baseURL.IsAbs() && !strings.HasPrefix(base, "/") {
+		return joinedURL[1:] // Removing leading '/' if needed
+	}
+	return joinedURL
+}
+
+// IsExternalURL checks if rawURL points to an external URL like http://example.com
+func IsExternalURL(rawURL string) bool {
+	parsed, err := url.Parse(rawURL)
+	if err != nil {
+		return true
+	}
+	if len(parsed.Host) != 0 && strings.Replace(parsed.Host, "www.", "", 1) != strings.Replace(setting.Domain, "www.", "", 1) {
+		return true
+	}
+	return false
+}
+
 // Min min of two ints
 func Min(a, b int) int {
 	if a > b {