content_by_lua_file should not return 404 if file permission denied

[jizhuozhi]

There are three situations in opening a file in the Linux file system

1. Open successfully and execute
2. The file exists but has no permissions
3. The file does not exist

In some cases, developers may set wrong permissions when deploying lua scripts. At this time, content_by_lua_file will directly return 404, which is inappropriate. It stands to reason that it should return 403 or other 5xx series exception codes. , which makes it easier for us to use other anomaly detection systems to identify anomalies.

However, in order to be compatible with the old version, the configuration of the status code in both cases of not found and no permission can be provided, and both are set to 404 by default.

[jizhuozhi]

Or more simply, we can check whether the lua script exists and is readable during the configuration file setting stage, otherwise we will report an error and refuse to start

[jizhuozhi]

Here is an example code to fix this issue, but could be more graceful?

    if (rc != 0) {
        /*  Oops! error occurred when loading Lua script */
        switch (rc) {
        case LUA_ERRMEM:
            err = "memory allocation error";
            break;

        case LUA_ERRFILE:
            if (errno == ENOENT)
                errcode = NGX_HTTP_NOT_FOUND;
            else if (errno == EACCES)
                errcode = NGX_HTTP_FORBIDDEN;
            else
                errcode = NGX_HTTP_INTERNAL_SERVER_ERROR;
            /* fall through */

        default:
            if (lua_isstring(L, -1)) {
                err = lua_tostring(L, -1);

            } else {
                err = "unknown error";
            }
        }

        goto error;
    }