util/UriExtract: add uri_is_relative_path()

src/util/UriExtract.cxx

@@ -95,6 +95,12 @@ uri_get_scheme(const char *uri) noexcept
 	return {uri, end};
 }
 
+bool
+uri_is_relative_path(const char *uri) noexcept
+{
+	return !uri_has_scheme(uri) && *uri != '/';
+}
+
 const char *
 uri_get_path(const char *uri) noexcept
 {

src/util/UriExtract.hxx

@@ -49,6 +49,10 @@ gcc_pure
 StringView
 uri_get_scheme(const char *uri) noexcept;
 
+gcc_pure
+bool
+uri_is_relative_path(const char *uri) noexcept;
+
 /**
  * Returns the URI path (including the query string) or nullptr if the
  * given URI has no path.