# HG changeset patch
# User jbe
# Date 1548098630 -3600
# Node ID fe1a134a92a40b0423ed26b80212410199b794f1
# Parent  9509f1e5e31ac9705f46174a4f7d38bc45ebcea8
Use offsetof macro at compile time to determine maximum length of local socket paths

diff -r 9509f1e5e31a -r fe1a134a92a4 moonbridge_io.c
--- a/moonbridge_io.c	Sat Dec 22 18:42:18 2018 +0100
+++ b/moonbridge_io.c	Mon Jan 21 20:23:50 2019 +0100
@@ -55,6 +55,8 @@
     moonbr_io_return_prepared_errmsg(); \
   } while (0)
 
+#define MOONBR_SUN_PATH_MAXLEN (sizeof(struct sockaddr_un) - offsetof(struct sockaddr_un, sun_path) - 1)
+
 #define MOONBR_IO_MODULE_REGKEY "moonbridge_io_module"
 #define MOONBR_IO_HANDLE_MT_REGKEY "moonbridge_io_handle"
 #define MOONBR_IO_HANDLE_PUBLIC_MT_REGKEY "moonbridge_io_handle_public"
@@ -1143,12 +1145,9 @@
 static int moonbr_io_localconnect_impl(lua_State *L, int nonblocking) {
   const char *path;
   struct sockaddr_un sockaddr = { .sun_family = AF_LOCAL };
-  const int path_maxlen = sizeof(struct sockaddr_un) - (
-    (void *)sockaddr.sun_path - (void *)&sockaddr
-  ) - 1;  /* one byte for termination */
   int sock;
   path = luaL_checkstring(L, 1);
-  if (strlen(path) > path_maxlen) luaL_error(L, "Path too long; only %i characters allowed", path_maxlen);
+  if (strlen(path) > MOONBR_SUN_PATH_MAXLEN) luaL_error(L, "Path too long; only %i characters allowed", MOONBR_SUN_PATH_MAXLEN);
   strcpy(sockaddr.sun_path, path);
   sock = socket(
     PF_LOCAL,