+static int submodule_url_is_relative(const char *url)
+{
+ return starts_with_dot_slash(url) || starts_with_dot_dot_slash(url);
+}
+
+/*
+ * Count directory components that a relative submodule URL should chop
+ * from the remote_url it is to be resolved against.
+ *
+ * In other words, this counts "../" components at the start of a
+ * submodule URL.
+ *
+ * Returns the number of directory components to chop and writes a
+ * pointer to the next character of url after all leading "./" and
+ * "../" components to out.
+ */
+static int count_leading_dotdots(const char *url, const char **out)
+{
+ int result = 0;
+ while (1) {
+ if (starts_with_dot_dot_slash(url)) {
+ result++;
+ url += strlen("../");
+ continue;
+ }
+ if (starts_with_dot_slash(url)) {
+ url += strlen("./");
+ continue;
+ }
+ *out = url;
+ return result;
+ }
+}
+/*
+ * Check whether a transport is implemented by git-remote-curl.
+ *
+ * If it is, returns 1 and writes the URL that would be passed to
+ * git-remote-curl to the "out" parameter.
+ *
+ * Otherwise, returns 0 and leaves "out" untouched.
+ *
+ * Examples:
+ * http::https://example.com/repo.git -> 1, https://example.com/repo.git
+ * https://example.com/repo.git -> 1, https://example.com/repo.git
+ * git://example.com/repo.git -> 0
+ *
+ * This is for use in checking for previously exploitable bugs that
+ * required a submodule URL to be passed to git-remote-curl.
+ */
+static int url_to_curl_url(const char *url, const char **out)
+{
+ /*
+ * We don't need to check for case-aliases, "http.exe", and so
+ * on because in the default configuration, is_transport_allowed
+ * prevents URLs with those schemes from being cloned
+ * automatically.
+ */
+ if (skip_prefix(url, "http::", out) ||
+ skip_prefix(url, "https::", out) ||
+ skip_prefix(url, "ftp::", out) ||
+ skip_prefix(url, "ftps::", out))
+ return 1;
+ if (starts_with(url, "http://") ||
+ starts_with(url, "https://") ||
+ starts_with(url, "ftp://") ||
+ starts_with(url, "ftps://")) {
+ *out = url;
+ return 1;
+ }
+ return 0;