Use ResolveReference instead of path.Join (#4073)

Signed-off-by: Jonas Franz <info@jonasfranz.software>

modules/markup/html.go

@@ -114,16 +114,25 @@ func cutoutVerbosePrefix(prefix string) string {
 
 // URLJoin joins url components, like path.Join, but preserving contents
 func URLJoin(base string, elems ...string) string {
-	u, err := url.Parse(base)
+	if !strings.HasSuffix(base, "/") {
+		base += "/"
+	}
+	baseURL, err := url.Parse(base)
 	if err != nil {
 		log.Error(4, "URLJoin: Invalid base URL %s", base)
 		return ""
 	}
-	joinArgs := make([]string, 0, len(elems)+1)
-	joinArgs = append(joinArgs, u.Path)
-	joinArgs = append(joinArgs, elems...)
-	u.Path = path.Join(joinArgs...)
-	return u.String()
+	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() {
+		return joinedURL[1:] // Removing leading '/'
+	}
+	return joinedURL
 }
 
 // RenderIssueIndexPatternOptions options for RenderIssueIndexPattern function

modules/markup/html_test.go

@@ -83,6 +83,8 @@ func TestURLJoin(t *testing.T) {
 			"a", "b/c/"),
 		newTest("a/b/d",
 			"a/", "b/c/", "/../d/"),
+		newTest("https://try.gitea.io/a/b/c#d",
+			"https://try.gitea.io", "a/b", "c#d"),
 	} {
 		assert.Equal(t, test.Expected, URLJoin(test.Base, test.Elements...))
 	}