Add minetest.safe_write_file() to script API

doc/lua_api.txt

@@ -2223,6 +2223,10 @@ Helper functions
       * nil: return all entries,
       * true: return only subdirectory names, or
       * false: return only file names.
+* `minetest.safe_file_write(path, content)`: returns boolean indicating success
+    * Replaces contents of file at path with new contents in a safe (atomic) way.
+      Use this instead of below code when writing e.g. database files:
+      `local f = io.open(path, "wb"); f:write(content); f:close()`
 * `minetest.get_version()`: returns a table containing components of the
    engine version.  Components:
     * `project`: Name of the project, eg, "Minetest"

src/script/lua_api/l_util.cpp

@@ -356,6 +356,23 @@ int ModApiUtil::l_get_dir_list(lua_State *L)
 	return 1;
 }
 
+// safe_file_write(path, content)
+int ModApiUtil::l_safe_file_write(lua_State *L)
+{
+	NO_MAP_LOCK_REQUIRED;
+	const char *path = luaL_checkstring(L, 1);
+	size_t size;
+	const char *content = luaL_checklstring(L, 2, &size);
+
+	CHECK_SECURE_PATH(L, path, true);
+
+	bool ret = fs::safeWriteToFile(path, std::string(content, size));
+	lua_pushboolean(L, ret);
+
+	return 1;
+}
+
+// request_insecure_environment()
 int ModApiUtil::l_request_insecure_environment(lua_State *L)
 {
 	NO_MAP_LOCK_REQUIRED;
@@ -475,6 +492,7 @@ void ModApiUtil::Initialize(lua_State *L, int top)
 
 	API_FCT(mkdir);
 	API_FCT(get_dir_list);
+	API_FCT(safe_file_write);
 
 	API_FCT(request_insecure_environment);
 

src/script/lua_api/l_util.h

@@ -81,6 +81,9 @@ private:
 	// get_dir_list(path, is_dir)
 	static int l_get_dir_list(lua_State *L);
 
+	// safe_file_write(path, content)
+	static int l_safe_file_write(lua_State *L);
+
 	// request_insecure_environment()
 	static int l_request_insecure_environment(lua_State *L);