return strbuf_detach(&buf, NULL);
 }
 
-static int handle_curl_result(struct slot_results *results)
+void normalize_curl_result(CURLcode *result, long http_code,
+                          char *errorstr, size_t errorlen)
 {
        /*
         * If we see a failing http code with CURLE_OK, we have turned off
         * Likewise, if we see a redirect (30x code), that means we turned off
         * redirect-following, and we should treat the result as an error.
         */
-       if (results->curl_result == CURLE_OK &&
-           results->http_code >= 300) {
-               results->curl_result = CURLE_HTTP_RETURNED_ERROR;
+       if (*result == CURLE_OK && http_code >= 300) {
+               *result = CURLE_HTTP_RETURNED_ERROR;
                /*
                 * Normally curl will already have put the "reason phrase"
                 * from the server into curl_errorstr; unfortunately without
                 * FAILONERROR it is lost, so we can give only the numeric
                 * status code.
                 */
-               xsnprintf(curl_errorstr, sizeof(curl_errorstr),
+               xsnprintf(errorstr, errorlen,
                          "The requested URL returned error: %ld",
-                         results->http_code);
+                         http_code);
        }
+}
+
+static int handle_curl_result(struct slot_results *results)
+{
+       normalize_curl_result(&results->curl_result, results->http_code,
+                             curl_errorstr, sizeof(curl_errorstr));
 
        if (results->curl_result == CURLE_OK) {
                credential_approve(&http_auth);
 
 
 #define missing_target(a) missing__target((a)->http_code, (a)->curl_result)
 
+/*
+ * Normalize curl results to handle CURL_FAILONERROR (or lack thereof). Failing
+ * http codes have their "result" converted to CURLE_HTTP_RETURNED_ERROR, and
+ * an appropriate string placed in the errorstr buffer (pass curl_errorstr if
+ * you don't have a custom buffer).
+ */
+void normalize_curl_result(CURLcode *result, long http_code, char *errorstr,
+                          size_t errorlen);
+
 /* Helpers for modifying and creating URLs */
 extern void append_remote_object_url(struct strbuf *buf, const char *url,
                                     const char *hex,