+ if (!stateless_rpc) {
+ /* returned nonce MUST match what we gave out earlier */
+ retval = NONCE_BAD;
+ goto leave;
+ }
+
+ /*
+ * In stateless mode, we may be receiving a nonce issued by
+ * another instance of the server that serving the same
+ * repository, and the timestamps may not match, but the
+ * nonce-seed and dir should match, so we can recompute and
+ * report the time slop.
+ *
+ * In addition, when a nonce issued by another instance has
+ * timestamp within receive.certnonceslop seconds, we pretend
+ * as if we issued that nonce when reporting to the hook.
+ */
+
+ /* nonce is concat(<seconds-since-epoch>, "-", <hmac>) */
+ if (*nonce <= '0' || '9' < *nonce) {
+ retval = NONCE_BAD;
+ goto leave;
+ }
+ stamp = strtoul(nonce, &bohmac, 10);
+ if (bohmac == nonce || bohmac[0] != '-') {
+ retval = NONCE_BAD;
+ goto leave;
+ }
+
+ expect = prepare_push_cert_nonce(service_dir, stamp);
+ if (strcmp(expect, nonce)) {
+ /* Not what we would have signed earlier */
+ retval = NONCE_BAD;
+ goto leave;
+ }
+
+ /*
+ * By how many seconds is this nonce stale? Negative value
+ * would mean it was issued by another server with its clock
+ * skewed in the future.
+ */
+ ostamp = strtoul(push_cert_nonce, NULL, 10);
+ nonce_stamp_slop = (long)ostamp - (long)stamp;
+
+ if (nonce_stamp_slop_limit &&
+ abs(nonce_stamp_slop) <= nonce_stamp_slop_limit) {
+ /*
+ * Pretend as if the received nonce (which passes the
+ * HMAC check, so it is not a forged by third-party)
+ * is what we issued.
+ */
+ free((void *)push_cert_nonce);
+ push_cert_nonce = xstrdup(nonce);
+ retval = NONCE_OK;
+ } else {
+ retval = NONCE_SLOP;
+ }